As filed with the Securities and Exchange Commission on April 4, 2023

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 20-F

OR

For the fiscal year ended December 31, 2022

OR

OR

For the transition period from _______________________ to ______________________________

Commission File Number 001-38215

NUCANA PLC

(Exact name of Registrant as specified in its charter)

England and Wales

(Jurisdiction of incorporation or organization)

NuCana plc

3 Lochside Way

Edinburgh EH12 9DT

United Kingdom

Telephone: +44 (0)131 357 1111

(Address of principal executive offices)

Hugh S. Griffith, Chief Executive Officer

NuCana plc

3 Lochside Way

Edinburgh EH12 9DT

United Kingdom

Telephone: +44 (0)131 357 1111

Email: info@nucana.com

(Name, Telephone, E-mail and/or Facsimile number and Address of Company Contact Person)

Securities registered or to be registered pursuant to Section 12(b) of the Act:

Securities registered or to be registered pursuant to Section 12(g) of the Act: None

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act: None

Indicate the number of outstanding shares of each of the issuer’s classes of capital or common stock as of the close of the period covered by the annual report: 52,372,887 ordinary shares, par value £0.04 per share.

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒

If this report is an annual or transition report, indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. Yes ☐ No ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or an emerging growth company. See definition of “large accelerated filer,” “accelerated filer” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company that prepares its financial statements in accordance with U.S. GAAP, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards† provided pursuant to Section 13(a) of the Exchange Act. ☐

† The term “new or revised financial accounting standard” refers to any update issued by the Financial Accounting Standards Board to its Accounting Standards Codification after April 5, 2012.

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. ☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ☐

Indicate by check mark which basis of accounting the registrant has used to prepare the financial statements included in this filing:

If “Other” has been checked in response to the previous question, indicate by check mark which financial statement item the registrant has elected to follow. Item 17 ☐ Item 18 ☐

If this is an annual report, indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

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TABLE OF CONTENTS

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TABLE OF CONTENTS

(continued)

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GENERAL INFORMATION

In this annual report on Form 20-F (“Annual Report”), “NuCana,” “NuCana plc,” the “Group,” the “Company,” “we,” “us” and “our” refer to NuCana plc and its consolidated subsidiaries, except where the context otherwise requires.

NuCana® and Acelarin® are our registered trademarks and ProTidesTM is our trademark.

PRESENTATION OF FINANCIAL AND OTHER DATA

The consolidated financial statement data as at December 31, 2022, 2021, 2020, 2019, and 2018 and for the years ended December 31, 2022, 2021, 2020, 2019, and 2018 have been derived from our consolidated financial statements, which have been prepared in accordance with International Financial Reporting Standards, or IFRS, as issued by the International Accounting Standards Board, or IASB and audited in accordance with the standards of the Public Company Accounting Oversight Board (United States). The financial statement data as at December 31, 2020, 2019 and 2018 and for the years ended December 31, 2019 and 2018 have been derived from our consolidated financial statements, which are not presented herein, which have also been prepared in accordance with IFRS as issued by IASB.

All references in this Annual Report to “$” are to U.S. dollars and all references to “£” are to pounds sterling.

INFORMATION REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report contains estimates and forward-looking statements, principally in the sections titled “Risk Factors,” “Operating and Financial Review and Prospects” and “Business.” Some of the matters discussed concerning our operations and financial performance include forward-looking statements and estimates within the meaning of the Securities Act of 1933, as amended, and the Securities Exchange Act of 1934, as amended. The words “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect” and similar words are intended to identify forward-looking statements and estimates. Forward-looking statements include, but are not limited to, statements about:

These forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors that could cause our actual results of operations, financial condition, liquidity, performance, prospects, opportunities, achievements or industry results, as well as those of the markets we serve or intend to serve, to differ materially from those expressed in, or suggested by, these forward-looking statements. Factors that could cause actual results, financial condition, liquidity, performance, prospects, opportunities, achievements or industry results to differ materially include, but are not limited to, those discussed under “Risk Factors” in this Annual Report. Additional risks that we may currently deem immaterial or that are not presently known to us could also cause the forward-looking events discussed in this Annual Report not to occur. These forward-looking statements are based on assumptions regarding our present and future business strategies and the environment in which we expect to operate in the future.

Forward-looking statements and estimates speak only at the date they were made, and we undertake no obligation to update or to review any forward-looking statement or estimate because of new information, future events or other factors. Forward-looking statements and estimates involve risks and uncertainties and are not guarantees of future performance. Our future results may differ materially from those expressed in these forward-looking statements and estimates.

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The words “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect” and similar words are intended to identify estimates and forward-looking statements. Estimates and forward-looking statements speak only at the date they were made, and we undertake no obligation to update or to review any estimate and/or forward-looking statement because of new information, future events or other factors. Estimates and forward-looking statements involve risks and uncertainties and are not guarantees of future performance. Our future results may differ materially from those expressed in these estimates and forward-looking statements. In light of the risks and uncertainties described above, the estimates and forward-looking statements discussed in this Annual Report might not occur, and our future results and our performance may differ materially from those expressed in these forward-looking statements due to, inclusive of, but not limited to, the factors mentioned above. Because of these uncertainties, you should not make any investment decision based on these estimates and forward-looking statements.

WEBSITE DISCLOSURE

We maintain a public website at https://www.nucana.com and use our website as a routine channel of distribution of company information, including press releases, analyst presentations, and supplemental financial information, as a means of disclosing material non-public information and for complying with our disclosure obligations under Regulation FD. Our website includes an Investors section through which we make available, free of charge, our Annual Reports on Form 20-F, Reports on Form 6-K, as well as any amendments to those reports filed or furnished pursuant to the Exchange Act as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. Accordingly, investors should monitor our website in addition to following press releases, filings with the SEC, and public conference calls and webcasts.

None of the information provided on our website, in our press releases or public conference calls and webcasts or through social media is incorporated into, or deemed to be a part of, this Annual Report or in any other report or document we file with the SEC, and any references to such website is intended to be inactive textual references only.

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PART I

Item 1. Identity of Directors, Senior Management and Advisers

Not Applicable.

Item 2. Offer Statistics and Expected Timetable

Not Applicable.

Item 3. Key Information

The following tables summarize our consolidated financial data as of the dates and for the periods indicated. The consolidated financial data as of and for the years ended December 31, 2022, 2021, 2020, 2019 and 2018 have been derived from our consolidated financial statements, which have been prepared in accordance with International Financial Reporting Standards, or IFRS, as issued by the International Accounting Standard Board, or IASB, and audited in accordance with the standards of the Public Company Accounting Oversight Board (United States).

Our historical results are not necessarily indicative of the results that may be expected in the future. The following selected consolidated financial data should be read in conjunction with Item 5, “Operating and Financial Review and Prospects” and our consolidated financial statements included elsewhere in this Annual Report.

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B. Capitalization and Indebtedness

Not Applicable.

C. Reasons for the Offer and Use of Proceeds

Not Applicable.

D. Risk Factors

Our business has significant risks. You should carefully consider the following risk factors and all other information contained in our Annual Report on Form 20-F for the year ended December 31, 2022 (our “Annual Report”) and in subsequent reports filed on Form 6-K, including our consolidated financial statements and the related notes. The risks and uncertainties described below are those significant risk factors, currently known and specific to us, that we believe are relevant to our business, results of operations and financial condition. If any of these risks materialize, our business, results of operations or financial condition could suffer and the price of the ADSs could decline. Additional risks and uncertainties not currently known to us or that we now deem immaterial may also harm us and adversely affect our business, results of operations and financial condition.

Summary of Risk Factors

An investment in our ADSs is subject to a number of risks, including risks related to our business and industry, risks related to development of our product candidates, and risks related to our ADSs. The following summarizes some, but not all, of these risks. Please carefully consider all of the information discussed in our Annual Report and in subsequent reports filed on Form 6-K for a more thorough description of these and other risks.

Risks Related to Our Business and Industry

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Risks Related to Development of Our Product Candidates

Risks Related to Marketing Approval of Our Product Candidates

Risks Related to Our Dependence on Third Parties

Risks Related to the Commercialization of Our Product Candidates

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Risks Related to Our Intellectual Property

Risks Related to Employee Matters, Managing Growth and Other Risks Related to Our Business

Risks Related to the ADSs

Risks Related to Our Business and Industry

We have incurred significant operating losses since our inception. We expect to incur losses for the foreseeable future and may never achieve or maintain profitability.

We have incurred significant operating losses since our inception. We incurred net losses of £13.8 million for the year ended December 31, 2018, £21.4 million for the year ended December 31, 2019, £30.7 million for the year ended December 31, 2020, £40.5 million for the year ended December 31, 2021, and £32.0 million for the year ended December 31, 2022. As of December 31, 2022, we had an accumulated deficit of £180.6 million. Our product candidate, NUC-3373, is currently in a Phase 1b/2 clinical trial, in combination with other agents, in patients with advanced colorectal cancer. We have also initiated a randomized Phase 2 clinical trial of NUC-3373, in combination with other agents, for the second-line treatment of patients with advanced colorectal cancer. In addition, we have initiated a Phase 1b/2 modular clinical trial of NUC-3373 in combination with the PD-1 inhibitor pembrolizumab in patients with advanced solid tumors and in combination with docetaxel in patients with lung cancer. Our product candidate NUC-7738 is currently in the Phase 2 part of a Phase 1/2 clinical trial for patients with advanced solid tumors which is evaluating NUC-7738 as a monotherapy and in combination

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with pembrolizumab. It may be several years, if ever, before we have a product candidate ready for commercialization. To date, we have financed our operations primarily through public and private placements of our equity securities. We expect to continue to incur significant expenses and increasing operating losses for the foreseeable future. The net losses we incur may fluctuate significantly from quarter to quarter. We anticipate that our expenses will increase substantially if and as we:

In addition, protecting our intellectual property may result in litigation aimed at enforcing or defending our patents. Intellectual property litigation is expensive and, in the event that we lose any such litigation, we may be subject to additional significant legal expense, including the potential requirement to pay the legal expenses of opposing parties.

Because of the numerous risks and uncertainties associated with developing new pharmaceutical drugs, we are unable to predict the extent of any future losses or when we will become profitable, if at all. In addition, our expenses could increase beyond expectations if we are required by the Food and Drug Administration, or FDA, the European Medicines Agency, or EMA, or other foreign regulatory agencies, to perform studies and clinical trials in addition to those that we currently anticipate, or if there are any delays in the completion of planned clinical trials or the development of any of our ProTides.

To become and remain profitable, we must develop and eventually commercialize products with significant market potential. This will require us to be successful in a range of challenging activities, including the following:

We may never succeed in these activities and, even if we do, may never generate revenues that are significant or large enough to achieve profitability. If we do achieve profitability, we may not be able to sustain or increase profitability on a quarterly or annual basis. Our failure to become and remain profitable would decrease the value of the company and could impair our ability to raise capital, maintain our discovery and preclinical development efforts, expand our business or continue our operations and may require us to raise additional capital that may dilute your ownership interest. A decline in the value of the company could also cause you to lose all or part of your investment.

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We depend heavily on the success of our product candidates, NUC-3373 and NUC-7738. We cannot give any assurance that these product candidates will receive regulatory approval for any indication, which is necessary before any of them can be commercialized. If we, and any collaborators with whom we may enter into agreements for the development and commercialization of any of these product candidates, are unable to commercialize them, or experience significant delays in doing so, our ability to generate revenue and our financial condition will be adversely affected.

We do not currently generate any revenues from sales of any products, and we may never be able to develop or commercialize a marketable product. We have invested substantially all of our efforts and financial resources to date in the development of NUC-3373 and NUC-7738, as well as Acelarin, for which we discontinued the NuTide:121 clinical trial in March 2022. Our ability to generate product revenues, which we do not expect will occur for at least the next several years, if ever, will depend heavily on the successful development and eventual commercialization of these product candidates, if approved, which may never occur. Each of NUC-3373 and NUC-7738 will require additional clinical development, management of clinical, preclinical and manufacturing activities, regulatory approval in multiple jurisdictions, procurement of manufacturing supply, commercialization, substantial additional investment and significant marketing efforts before we generate any revenues from product sales, if at all. We are not permitted to market or promote any product candidates in the United States, Europe or other countries before we receive regulatory approval from the FDA, the EMA or comparable foreign regulatory authorities, and we may never receive such regulatory approval for NUC-3373, NUC-7738 or any future product candidate. We have not submitted a New Drug Application, or NDA, to the FDA, a Marketing Authorization Application, or MAA, to the EMA or comparable applications to other regulatory authorities for any of our product candidates and do not expect to be in a position to do so in the foreseeable future. The success of our product candidates will depend on many factors, including the following:

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With respect to each of NUC-3373 and NUC-7738, if we or our suppliers, as applicable, do not overcome one or more of these factors in a timely manner or at all, we could experience significant delays or an inability to successfully commercialize that product candidate.

We cannot be certain that NUC-3373 or NUC-7738 or any future product candidates will be successful in clinical trials or receive regulatory approval. Further, NUC-3373 or NUC-7738 or any future product candidates may not receive regulatory approval even if they are successful in clinical trials. If we do not receive regulatory approvals for NUC-3373 or NUC-7738 or any future product candidates, we may not be able to continue our operations. Even if we successfully obtain regulatory approvals to manufacture and market NUC-3373 or NUC-7738 or any future product candidates, our revenues will be dependent, in part, upon the size of the markets in the territories for which we gain regulatory approval and have commercial rights. If the markets for patient groups that we are targeting are not as significant as we estimate, we may not generate significant revenues from sales of such products, if approved.

We plan to seek regulatory approval to commercialize NUC-3373 and NUC-7738 in the United States and the European Union, and potentially in additional foreign countries. While the scope of regulatory approval is similar in many countries, to obtain separate regulatory approval in multiple countries requires us to comply with the numerous and varying regulatory requirements of such countries regarding safety and efficacy and governing, among other things, clinical trials, commercial sales, pricing and distribution of NUC-3373 and NUC-7738, and we cannot predict success in these jurisdictions.

Products studied for their safety and effectiveness in treating serious or life-threatening illnesses and that provide meaningful therapeutic benefit over existing treatments may receive accelerated approval from the FDA and may be approved on the basis of adequate and well-controlled clinical trials establishing that the drug product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit or an effect on an intermediate clinical endpoint that can be measured earlier than an effect on irreversible morbidity or mortality. Discussions with the FDA about the feasibility of an accelerated approval typically begin early in the development of a new drug or biological product in order to identify, among other things, an appropriate surrogate or intermediate clinical endpoint.

However, even if we were to generate clinical data sufficient to support an NDA submission seeking accelerated approval for any of our product candidates, there can be no assurance that such marketing application will be accepted by the FDA for substantive review or that approval will be granted on a timely basis, or at all. In addition, if another company receives full approval from the FDA to market a product for treatment of a similar indication to our product candidate, our ability to seek and obtain accelerated approval for our product candidate in the same or similar indication may be materially adversely affected. The FDA or foreign regulatory authorities also could require us to conduct further studies or trials prior to

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considering our application or granting a marketing approval of any type. We might not be able to fulfill the FDA’s requirements in a timely manner, which would cause delays, or approval might not be granted because our submission is deemed incomplete by the FDA. A failure to obtain accelerated approval for any of our product candidates would result in a longer time period to obtain approval for and commercialize such product candidate, could increase the cost of development of such product candidates and could harm our competitive position in the marketplace.

Even if we were to receive accelerated approval from the FDA for any of our other product candidates, we will be subject to rigorous post-marketing requirements, including the submission of confirmatory clinical data verifying the clinical benefit of the product. Drug products marketed under an accelerated approval NDA also are subject to a requirement that all promotional materials must be submitted to the FDA at least 30 days prior to their dissemination. The FDA could seek to withdraw accelerated approval for multiple reasons, including if we fail to conduct the required post-marketing study with due diligence, the post-marketing study fails to verify the product’s clinical benefit, other evidence shows that the product is not safe or effective under the conditions of use, or we disseminate promotional materials that are found by the FDA to be false and misleading.

Our lack of any approved products may make it difficult for you to evaluate the success of our business to date and to assess our future viability.

Biopharmaceutical drug development is a highly speculative undertaking and involves a substantial degree of risk. Our operations to date have been limited to organizing and staffing our company, business planning, raising capital, developing our technology, identifying potential product candidates, undertaking preclinical studies, and conducting clinical trials of our product candidates. We have not yet demonstrated our ability to successfully complete large-scale, randomized, pivotal clinical trials compared to standards of care, obtain marketing approvals, manufacture a commercial scale product, or arrange for a third party to do so on our behalf, or conduct sales and marketing activities necessary for successful product commercialization. Typically, it takes several years to develop one new drug from the time it is discovered to when it is available for treating patients. In addition, we may encounter unforeseen expenses, difficulties, complications, delays and other known and unknown factors. We will need to transition from a company with a research and development focus to a company capable of supporting commercial activities. We may not be successful in such a transition.

We will require substantial additional funding which may not be available to us on acceptable terms, or at all. If we fail to obtain additional financing, we may be unable to complete the development and commercialization of our product candidates or continue our development programs.

The development of pharmaceutical drugs is capital-intensive. We expect our expenses to increase with our ongoing activities, particularly as we conduct larger-scale clinical trials of, and seek marketing approval for, our product candidates. In addition, if we obtain marketing approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution. We may also need to raise additional funds sooner if we choose to pursue additional indications or geographies for our product candidates or otherwise expand more rapidly than we presently anticipate. Furthermore, we will continue to incur costs associated with operating as a public company. Accordingly, we will need to obtain substantial additional funding in connection with our continuing operations.

As of December 31, 2022, we had £41.9 million in cash and cash equivalents. We believe, based upon our current operating plan, that, our cash and cash equivalents on hand will be sufficient to fund our anticipated operations for at least the next twelve months. Our future capital requirements and the period for which we expect our existing resources to support our operations may vary significantly from what we expect. Our monthly spending levels vary based on new and ongoing research and development and other corporate activities. Because the length of time and activities associated with successful research and development of our product candidates is highly uncertain, we are unable to estimate the actual funds we will require for development and any approved marketing and commercialization activities. In addition, our future capital requirements will depend on many factors, and could increase significantly as a result of many factors, including:

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Conducting preclinical studies and clinical trials is a time-consuming, expensive and uncertain process that can take years to complete, and we may never generate the necessary data or results required to obtain marketing approval and achieve product sales. In addition, our product candidates, if approved, may not achieve commercial success. Our commercial revenues, if any, will be derived from sales of products that may not be commercially available for several years, if ever. Accordingly, we will need to continue to rely on additional financing to achieve our business objectives.

Any additional fundraising efforts may divert our management from their day-to-day activities, which may adversely affect our ability to develop and commercialize our product candidates. Volatility in the financial markets has generally made equity and debt financing more difficult to obtain and may compromise our ability to meet our fundraising needs. We cannot guarantee that future financing will be available in sufficient amounts or on terms acceptable to us, if at all.

If we are unable to obtain funding on a timely basis, we may be required to significantly curtail, delay or discontinue one or more of our research or development programs or the commercialization of any product candidate or be unable to expand our operations or otherwise capitalize on our business opportunities.

Raising additional capital may cause dilution to our shareholders, restrict our operations or require us to relinquish rights to our technologies or product candidates.

Until such time, if ever, as we can generate substantial product revenues, we expect to finance our cash needs through a combination of equity and debt financings. The sale of additional equity or convertible debt securities would dilute all of our shareholders. The incurrence of indebtedness could result in increased fixed payment obligations, and we may be required to agree to certain restrictive covenants, such as limitations on our ability to incur additional debt, limitations on our ability to acquire, sell or license intellectual property rights, limitations on declaring dividends and other operating restrictions that could adversely impact our ability to conduct our business. Moreover, the terms of any financing may adversely affect the holdings or the rights of our shareholders and the issuance of additional securities, whether equity or debt, by us, or the possibility of such issuance, may cause the market price of our ADSs to decline.

We could decide to seek funds through collaborations, strategic alliances or licensing arrangements with third parties, and we could be required to do so at an earlier stage than otherwise would be desirable. In connection with any such collaborations, strategic alliances or licensing arrangements, we may be required to relinquish valuable rights to our intellectual property, future revenue streams, research programs or product candidates, grant rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves, or otherwise agree to terms unfavorable to us.

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Inadequate funding for the FDA, the SEC and other, government agencies could hinder such agencies’ ability to hire and retain key leadership and other personnel, prevent new products and services from being developed or commercialized in a timely manner or otherwise prevent those agencies from performing normal business functions on which the operation of our business may rely, which could negatively impact our business.

The ability of the FDA to review and approve new products can be affected by a variety of factors, including government budget and funding levels, ability to hire and retain key personnel and accept the payment of user fees, and statutory, regulatory, and policy changes. Average review times at the agency have fluctuated in recent years as a result. In addition, government funding of the SEC and other government agencies on which our operations may rely, including those that fund research and development activities is subject to the political process, which is inherently fluid and unpredictable.

Disruptions at the FDA and other agencies may also slow the time necessary for new drugs to be reviewed and/or approved by necessary government agencies, which would adversely affect our business. For example, over the last several years, the U.S. government has shut down several times and certain regulatory agencies, such as the FDA and the SEC, have had to furlough critical FDA, SEC and other government employees and stop critical activities. Moreover, recent shutdowns or slowdowns in normal agency work caused by the federal response to the COVID-19 public health emergency can increase the time needed for the agency to complete its review or make final approval or other administrative decisions. If a prolonged government shutdown or slowdown occurs, it could significantly impact the ability of the FDA to timely review and process our regulatory submissions, which could have a material adverse effect on our business. Further, in our operations as a public company, future government shutdowns could impact our ability to access the public market and obtain necessary capital in order to properly capitalize and continue our operations.

We may be unable to use net operating loss and tax credit carryforwards and certain built-in losses to reduce future tax payments or benefit from favorable United Kingdom tax legislation.

As a United Kingdom resident company, we are subject to U.K. corporate taxation. We have generated losses since inception. As of December 31, 2022, we had cumulative carry forward tax losses of £84.6 million. Subject to any relevant restrictions, including the Corporate Income Loss Restriction and the Corporate Capital Loss Restriction that, broadly, restrict the amount of carried forward losses that can be utilized to 50% of group profits or gains arising above £5.0 million per tax year, we expect these to be available to carry forward and offset against future operating profits.

As a company that carries out extensive research and development activities, we benefit from the United Kingdom research and development tax credit regime for small and medium-sized companies, whereby we are able to surrender the trading losses that arise from our qualifying research and development activities for a payable tax credit of up to 33.35% in respect of eligible research and development expenditures incurred prior to April 1, 2023. This rate generally reduces to a general rate of 18.6% in respect of expenditure incurred on or after April 1, 2023. However, at the Spring Budget 2023, the U.K. Government announced a new tax credit rate under this scheme for R&D intensive companies, which will amount to a payable tax credit of up to 26.97% of eligible research and development expenditures incurred on or after April 1, 2023. R&D intensive companies will be those that spend 40% or more of their total expenditure on qualifying R&D in a given period, although detailed guidance and draft legislation on this new rate is yet to be published. Based on the amount of our qualifying R&D expenditure in the fiscal year ended December 31, 2022 and our expectations as to the amount of our qualifying R&D expenditure in the current fiscal year, we believe that we qualified as an R&D intensive company for 2022 and we currently expect to qualify for 2023. Our qualifying expenditures largely comprise employment costs for research staff, consumables and subcontract costs incurred as part of research projects. Certain subcontracted qualifying research expenditures are eligible for a cash rebate of up to 21.68% in respect of eligible research and development expenditures incurred prior to April 1, 2023 (reducing to a general rate of 12.09%, or, on the assumption that the new R&D intensive companies rules will also apply to subcontracted R&D, an enhanced rate of 17.53% for R&D intensive companies, in respect of expenditure incurred on or after April 1, 2023). The majority of our pipeline research, clinical trials management and manufacturing development activities are currently eligible for inclusion within these tax credit cash rebate claims. In relation to accounting periods beginning on or after April 1, 2021 there is a cap on payable credit claims in excess of £20,000 by reference to, broadly, three times the total Pay As You Earn, or PAYE, and national insurance contributions, or NICs, liability of the company. Unless an exemption applies, this could restrict the amount of payable credit that we can claim. In addition to the rate reductions referred to above, there are further changes to the U.K.’s research and development tax regime which will apply in respect of expenditure incurred on or after April 1, 2024. These include the introduction of a territoriality restriction to refocus the relief on activity carried out in the U.K.. This is subject to an exemption where it would be wholly unreasonable for the claimant to replicate the conditions necessary for the research and development activity within the U.K.. This new requirement may have an impact on our ability to claim relief in respect of certain costs in the future. The U.K. Government is considering and has consulted on further reforms to the United Kingdom’s research and development tax

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relief system, including the introduction of a new single research and development tax relief regime in place of the two regimes currently in place and these reforms may also affect our ability to claim such relief in the future. Also, we may not be able to continue to claim payable research and development tax credits in the future because we may no longer qualify as a small or medium-sized company.

We may benefit in the future from the United Kingdom’s “patent box” regime, which allows certain profits attributable to revenues from patented products to be taxed at an effective rate of 10%. As we have many different patents covering our products, future upfront fees, milestone fees, product revenues and royalties could be taxed at this favorably low tax rate. When taken in combination with the enhanced relief available on our research and development expenditures, we expect a long-term lower rate of corporation tax to apply to us. If, however, there are unexpected adverse changes to the United Kingdom research and development tax credit regime (whether as a result of the potential reform of the U.K. research and development tax regime outlined above, or otherwise) or the “patent box” regime, or for any reason we are unable to qualify for such advantageous tax legislation, or we are unable to use net operating loss and tax credit carryforwards and certain built-in losses to reduce future tax payments then our business, results of operations and financial condition may be adversely affected.

Tax authorities may disagree with our positions and conclusions regarding certain tax positions, or may apply existing rules in an arbitrary or unforeseen manner, resulting in unanticipated costs, taxes or non-realization of expected benefits.

A tax authority may disagree with tax positions that we have taken, which could result in increased tax liabilities. For example, His Majesty’s Revenue & Customs, or HMRC, the U.S. Internal Revenue Service or another tax authority could challenge our allocation of income by tax jurisdiction and the amounts paid between our affiliated companies pursuant to our intercompany arrangements and transfer pricing policies, including methodologies for valuing developed technology and amounts paid with respect to our intellectual property development. Similarly, a tax authority could assert that we are subject to tax in a jurisdiction where we believe we have not established a taxable connection, often referred to as a “permanent establishment” under international tax treaties, and such an assertion, if successful, could increase our expected tax liability in one or more jurisdictions.

A tax authority may take the position that material income tax liabilities, interest and penalties are payable by us, for example where there has been a technical violation of contradictory laws and regulations that are relatively new and have not been subject to extensive review or interpretation, in which case we expect that we might contest such assessment. Contesting such an assessment may be lengthy and costly and if we were unsuccessful in disputing the assessment, the implications could increase our anticipated effective tax rate, where applicable.

Changes and uncertainties in the tax system in the countries in which we have operations, could materially adversely affect our financial condition and results of operations, and reduce net returns to our shareholders.

We are unable to predict what tax reform may be proposed or enacted in the future or what effect such changes would have on our business, but such changes, to the extent they are brought into tax legislation, regulations, policies or practices in jurisdictions in which we operate or in the future into which we sell our products, could increase the estimated tax liability that we have expensed to date and paid or accrued on our balance sheets, and otherwise affect our financial position, future results of operations, cash flows in a particular period and overall or effective tax rates in the future in countries where we have operations or may sell our products, reduce post-tax returns to our shareholders and increase the complexity, burden and cost of tax compliance.

Our business may become subject to economic, political, regulatory and other risks associated with international operations.

As a company based in the United Kingdom, our business is subject to risks associated with conducting business internationally. Many of our suppliers and collaborative and clinical trial relationships are located outside of the United States. Accordingly, our future results could be harmed by a variety of factors, including:

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We may be adversely affected by the effects of inflation.

Inflation has the potential to adversely affect our liquidity, business, financial condition and results of operations by increasing our overall cost structure. The existence of inflation in the economy has resulted in, and may continue to result in, higher interest rates and capital costs, shipping costs, supply shortages, increased costs of labor, weakening exchange rates and other similar effects. As a result of inflation, we have experienced and may continue to experience, cost increases. Although we may take measures to mitigate the impact of this inflation, if these measures are not effective our business, financial condition, results of operations and liquidity could be materially adversely affected. Even if such measures are effective, there could be a difference between the timing of when these beneficial actions impact our results of operations and when the cost inflation is incurred.

Adverse developments affecting the financial services industry, such as actual events or concerns involving liquidity, defaults or non-performance by financial institutions or transactional counterparties, could adversely affect our current and projected business operations and its financial condition and results of operations.

Actual events involving limited liquidity, defaults, non-performance or other adverse developments that affect financial institutions, transactional counterparties or other companies in the financial services industry or the financial services industry generally, or concerns or rumors about any events of these kinds or other similar risks, have in the past and may in the future lead to market-wide liquidity problems. For example, on March 10, 2023, Silicon Valley Bank, or SVB, was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation, or the FDIC, as receiver. Similarly, on March 12, 2023, Signature Bank and Silvergate Capital Corp. were each swept into receivership. A statement issued on March 12, 2023, by the Department of the Treasury, the Federal Reserve and the FDIC stated that all depositors of SVB would have access to all of their money, including funds held in uninsured deposit accounts, borrowers under credit agreements, letters of credit and certain other financial instruments with SVB, Signature Bank or any other financial institution that is placed into receivership by the FDIC. In the United Kingdom, on March 13, 2023, the Bank of England, or BoE, issued a press release stating that the BoE, in consultation with the Prudential Regulation Authority, or PRA, HM Treasury, or HMT, and the Financial Conduct Authority, or FCA, had taken the decision (using the resolution powers for stabilizing failing banks under the Banking Act 2009) to sell Silicon Valley Bank UK Limited, or SVBUK, the U.K. affiliate of SVB, to HSBC UK Bank Plc. According to the press release, the BoE and HMT confirmed

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that depositors would have access to all of their money with SVBUK as a result of this transaction. However, if any of our other counterparties to instruments such as uninsured deposit accounts, credit agreements, letters of credit and certain other financial instruments were to be placed into receivership, we may be unable to access such funds. In addition, if any parties with whom we conduct business are unable to access funds pursuant to such instruments or lending arrangements with such a financial institution, such parties’ ability to pay their obligations to us or to enter into new commercial arrangements requiring additional payments to us could be adversely affected. In this regard, counterparties to SVB credit agreements and arrangements, and third parties such as beneficiaries of letters of credit (among others), may experience direct impacts from the closure of SVB and uncertainty remains over liquidity concerns in the broader financial services industry. Similar impacts have occurred in the past, such as during the 2008-2010 financial crisis.

Inflation and rapid increases in interest rates have led to a decline in the trading value of previously issued government securities with interest rates below current market interest rates. Although the U.S. Department of Treasury, FDIC and Federal Reserve Board have announced a program to provide up to $25 billion of loans to financial institutions secured by certain of such government securities held by financial institutions to mitigate the risk of potential losses on the sale of such instruments, widespread demands for customer withdrawals or other liquidity needs of financial institutions for immediate liquidity may exceed the capacity of such program. There is no guarantee that the U.S. Department of Treasury, FDIC and Federal Reserve Board will provide access to uninsured funds in the future in the event of the closure of other banks or financial institutions, or that they would do so in a timely fashion.

Although we assess our banking relationships as we believe necessary or appropriate, our access to funding sources and other credit arrangements in amounts adequate to finance or capitalize our current and projected future business operations could be significantly impaired by factors that affect us, the financial institutions with which we have arrangements directly, or the financial services industry or economy in general. These factors could include, among others, events such as liquidity constraints or failures, the ability to perform obligations under various types of financial, credit or liquidity agreements or arrangements, disruptions or instability in the financial services industry or financial markets, or concerns or negative expectations about the prospects for companies in the financial services industry. These factors could involve financial institutions or financial services industry companies with which we have financial or business relationships, but could also include factors involving financial markets or the financial services industry generally.

The results of events or concerns that involve one or more of these factors could include a variety of material and adverse impacts on our current and projected business operations and our financial condition and results of operations. These could include, but may not be limited to, the following:

In addition, investor concerns regarding the U.S., U.K. or international financial systems could result in less favorable commercial financing terms, including higher interest rates or costs and tighter financial and operating covenants, or systemic limitations on access to credit and liquidity sources, thereby making it more difficult for us to acquire financing on acceptable terms or at all. Any decline in available funding or access to our cash and liquidity resources could, among other risks, adversely impact our ability to meet our operating expenses, financial obligations or fulfill our other obligations, result in breaches of our financial and/or contractual obligations or result in violations of federal or state wage and hour laws. Any of these impacts, or any other impacts resulting from the factors described above or other related or similar factors not described above, could have material adverse impacts on our liquidity and our current and/or projected business operations and financial condition and results of operations.

In addition, any further deterioration in the macroeconomic economy or financial services industry could lead to losses or defaults by parties with whom we conduct business, which in turn, could have a material adverse effect on our current and/or projected business operations and results of operations and financial condition. For example, a party with whom we conduct business may fail to make payments when due, default under their agreements with us, become insolvent or declare

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bankruptcy. Any bankruptcy or insolvency, or the failure to make payments when due, of any counterparty of ours, or the loss of any significant relationships, could result in material losses to us and may material adverse impacts on our business.

The COVID-19 pandemic or future pandemics or public health crises could adversely impact our business, including our preclinical studies and clinical trials.

Public health crises such as pandemics or similar outbreaks could adversely impact our business. The coronavirus, SARS-CoV-2, which causes COVID-19, and its variants have spread to every country in the world and throughout the United States and the United Kingdom. Many countries, as well as most states of the United States, reacted by instituting quarantines, “lockdowns” and other public health restrictions on leisure activities, work and travel. Although pandemic-related restrictions have been eased or removed in most geographies, our business remains subject to pandemic-related controls, which may become more restrictive at any time. We rely on third-party manufacturers, distributors, information technology and software service providers, law and accounting firms, CROs, and consultants who are subject to, or may become subject to, pandemic-related controls. COVID-19 may also affect employees of third-party CROs located in affected geographies that we rely upon to carry out clinical trials. If these third parties cannot perform the services we require in a timely way and we cannot successfully implement replacements or workarounds, our business, results of operations, and financial condition could be harmed. As a result of the COVID-19 pandemic, or potential future pandemics, we have experienced and may in the future experience disruptions that could severely impact our business, preclinical studies and clinical trials, including:

These and other factors arising from the COVID-19 pandemic could worsen in countries that are already afflicted with COVID-19, could continue to spread to additional countries, or could return to countries where the pandemic has been partially contained, each of which could further adversely impact our ability to conduct clinical trials and our business generally, and could have a material adverse impact on our operations and financial condition and results.

In addition, the trading prices for our ADSs and for the securities of other biopharmaceutical companies have been highly volatile during certain periods as a result of the COVID-19 pandemic. As a result, we may face difficulties raising capital through sales of our ADSs or such sales may be on unfavorable terms. The COVID-19 pandemic continues to evolve. The extent to which this pandemic may impact our business, preclinical studies and clinical trials will depend on future developments, which are highly uncertain and cannot be predicted with confidence, such as the emergence, severity and spread of new variants of the disease, the duration of the pandemic and any outbreak of future variants, the potential

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imposition of travel restrictions and actions to contain the pandemic and any future outbreaks, such as social distancing and quarantines or lock-downs in the United Kingdom, the United States and other countries, business closures or business disruptions and the effectiveness of actions taken in the United Kingdom, the United States and other countries to contain and treat the disease.

The ongoing conflict in Ukraine could adversely impact our business, in particular with respect to enrollment and data collection in any clinical trials of our product candidates conducted in Ukraine, Russia or Belarus.

The ongoing military conflict in Ukraine could disrupt our clinical trials and increase our costs in this region. Although the length and impacts of any military action are highly unpredictable, clinical trial sites in Ukraine, Russia and Belarus and neighboring countries could suspend or terminate their participation in trials, and patients and physicians could be forced to evacuate or voluntarily choose to relocate far from clinical trial sites, making them unavailable and potentially making data collection more difficult or not possible. Any such difficulties at clinical trial sites, or the unavailability of such clinical trial sites, could result in delays in enrolling or completing clinical trials, the need to identify alternative clinical trial sites, and increased overall development costs. Furthermore, the United States and its European allies have imposed significant sanctions against Russia and Belarus, including embargoes, sanctions and other restrictions targeting major Russian financial institutions. Our ability to conduct future clinical trials or purchases from suppliers located in Russia, Belarus and parts of Ukraine and elsewhere in the region has become restricted under applicable sanctions laws. All of the foregoing could impede the execution of our clinical development plans, which could materially harm our business.

Exchange rate fluctuations may adversely affect our results of operations and financial condition.

Owing to the international scope of our operations, fluctuations in exchange rates, particularly between the pound sterling and the U.S. dollar, may adversely affect us. Although we are based in the United Kingdom, we source our active pharmaceutical ingredient, or API, and other raw materials and our research and development, manufacturing, consulting and other services worldwide, including from the United States, the European Union and India. Any weakening of the pound sterling against the currencies of such other jurisdictions makes the purchase of such goods and services more expensive for us. Further, potential future revenue may be derived from abroad, particularly from the United States. As a result, our business and the price of our ADSs may be affected by fluctuations in foreign exchange rates not only between the pound sterling and the U.S. dollar, but also the currencies of other countries, which may have a significant impact on our results of operations and cash flows from period to period. Currently, we do not have any exchange rate hedging arrangements in place.

Our business may be negatively impacted by future changes in applicable regulatory regimes.

We may face new regulatory costs and challenges that could have an adverse effect on our operations. The regulatory frameworks applicable to our operations and the development of our product candidates, including those with respect to the FDA and the EMA, can change at any time as a result of political decisions. Any changes to the applicable regulatory frameworks could have a material impact on our plans and development strategy, including our supply of investigational medicinal products. Furthermore, the implications of the withdrawal of the United Kingdom from the European Union and any other significant European political changes could result in disruption that could in turn delay the approval of new medicines at the EMA.

Risks Related to Development of Our Product Candidates

Initial success in the completed and ongoing early-stage clinical trials may not be indicative of results obtained when these trials are completed or in later stage trials.

NUC-3373 is currently being evaluated, in combination with other agents, in a Phase 1b/2 clinical trial in patients with advanced colorectal cancer. We have also initiated a randomized Phase 2 clinical trial of NUC-3373, in combination with other agents, for the second-line treatment of patients with advanced colorectal cancer. In addition, we have initiated a Phase 1b/2 modular clinical trial of NUC-3373 in combination with the PD-1 inhibitor pembrolizumab in patients with advanced solid tumors and in combination with docetaxel in patients with lung cancer. Favorable results obtained from our Phase 1 clinical trial of NUC-3373 in patients with advanced solid tumors and our ongoing Phase 1b/2 clinical trial of NUC-3373 in patients with advanced colorectal cancer may not be replicated in any future clinical trials. Similarly, while NUC-7738 is currently being evaluated in the Phase 2 part of a Phase 1/2 clinical trial in patients with advanced solid tumors which is evaluating NUC-7738 as a monotherapy and in combination with the PD-1 inhibitor pembrolizumab, favorable results obtained to date may not be replicated in any future clinical trials. In addition, data generated in these early-stage trials in particular are not the basis on which marketing approval by the FDA or a comparable foreign regulatory authority would be

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sought. Furthermore, the results of our clinical trials may not meet the level of statistical significance required by the FDA or comparable foreign regulatory authorities for marketing approval. Statistical significance means that an effect is unlikely to have occurred by chance. Clinical trial results are considered statistically significant when the probability of the results occurring by chance, rather than from the efficacy of the product candidate, is sufficiently low. There can be no assurance that any of our clinical trials will ultimately be successful or support further clinical development of any of our product candidates. There is a high failure rate for drugs proceeding through clinical trials. A number of companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in clinical development even after achieving promising results in earlier studies.

Preliminary and interim data from our clinical trials that we may announce or publish from time to time may change as patient enrollment continues, patient data are further examined and more patient data become available.

From time to time, we may announce or publish preliminary or interim data from our clinical studies, which include preliminary or interim data from our clinical trials, including those from the Phase 1b/2 clinical trial in patients with advanced colorectal cancer, Phase 2 clinical trial of NUC-3373 for the second-line treatment of patients with advanced colorectal cancer, or the Phase 1b/2 modular clinical trial of NUC-3373 in patients with advanced solid tumors, the Phase 2 part of the Phase 1/2 trial of NUC-7738 for patients with advanced solid tumors, and any future clinical trials of any of product candidates. Preliminary and interim data from a clinical trial are not always entirely representative of final data. Preliminary and interim data are subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues, patient data are further examined, more patient data become available, and we prepare and issue our final clinical trial report. As a result, preliminary and interim data should be viewed with caution until the final data are available. Material adverse changes in the final data compared to the preliminary or interim data could significantly harm our business prospects.

We are relatively early in our development efforts. If we are unable to successfully develop and commercialize our product candidates or experience significant delays in doing so, our business will be harmed.

We currently do not have any products that have gained marketing approval. We have invested substantially all of our efforts and financial resources identifying and developing our ProTides, such as NUC-3373 and NUC-7738, as well as Acelarin for which we discontinued the NuTide:121 clinical trial in March 2022. Our ability to generate product revenues, which may not occur for several years, if ever, will depend on the successful development and eventual commercialization of our product candidates: NUC-3373, for which a Phase 1b/2 clinical trial in patients with advanced colorectal cancer, Phase 2 clinical trial of NUC-3373 for the second-line treatment of patients with advanced colorectal cancer and Phase 1b/2 modular clinical trial of NUC-3373 in combination with the PD-1 inhibitor pembrolizumab, in patients with advanced solid tumors or in combination with docetaxel in patients with lung cancer are ongoing; and NUC-7738, for which the Phase 2 part of the Phase 1/2 trial is ongoing which is evaluating NUC-7738 as a monotherapy and in combination with the PD-1 inhibitor pembrolizumab for patients with advanced solid tumors. We currently do not generate any revenues from sales of any products, and we may never be able to develop or commercialize a marketable drug. Each of our product candidates will require development, management of development and manufacturing activities, marketing approval in multiple jurisdictions, obtaining manufacturing supply, building of a commercial organization, substantial investment and significant marketing efforts before we generate any revenues from drug sales.

We have not yet demonstrated an ability to successfully overcome many of the risks and uncertainties frequently encountered by companies in new and rapidly evolving fields, particularly in the biopharmaceutical area. For example, to execute our business plan, we will need to successfully:

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If we do not achieve one or more of these factors in a timely manner or at all, we could experience significant delays or an inability to successfully commercialize our product candidates, which would harm our business. If we do not receive marketing approvals for our product candidates, we may not be able to continue our operations.

If we experience delays or difficulties in the enrollment of patients in clinical trials, development of our product candidates may be delayed or prevented.

Identifying and qualifying patients to participate in clinical trials for our product candidates is critical to our success. We may not be able to initiate or continue clinical trials for our product candidates if we are unable to locate and enroll a sufficient number of eligible patients to participate in these trials. Patient enrollment may be affected by many factors including:

If we experience delays or difficulties in the enrollment of patients in clinical trials, including those that may be caused by the ongoing COVID-19 pandemic, our clinical trials may be delayed or terminated. Any delays in completing our clinical trials will increase our costs, delay or prevent our product candidate development and approval process, and jeopardize our ability to commence product sales and generate revenue.

Clinical drug development involves a lengthy and expensive process, with an uncertain outcome. We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and may experience delays in obtaining, or ultimately be unable to obtain, the approval of our product candidates.

The risk of failure in drug development is high. NUC-3373 is currently being studied in two Phase 1b/2 trials and a Phase 2 trial, and NUC-7738 is in the Phase 2 part of a Phase 1/2 trial. Before obtaining marketing approval from regulatory authorities for the sale of any product candidate, we must complete preclinical development and conduct extensive clinical trials to demonstrate the safety and efficacy of our product candidates in patients. Clinical trials are expensive, difficult to design and implement and can take several years to complete, and their outcome is inherently uncertain. Failure can occur at any time during the clinical trial process. Further, the results of preclinical studies and early clinical trials of our product candidates may not be predictive of the results of later-stage clinical trials, and interim results of a clinical trial do not necessarily predict final results. Moreover, preclinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that have believed their product candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failed to obtain marketing approval of their products. It is impossible to predict when or if any of our product candidates will prove effective or safe in humans or will receive marketing approval.

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We may experience numerous unforeseen events during, or as a result of, clinical trials that could delay or prevent our ability to receive marketing approval or commercialize our product candidates. Clinical trials may be delayed, suspended or prematurely terminated because costs are greater than we anticipate or for a variety of reasons, such as:

Many of the factors that cause, or lead to, a delay in the commencement or completion of clinical trials may also ultimately lead to the denial of marketing approval for our product candidates. The FDA may disagree with our clinical trial design and our interpretation of data from clinical trials, or may change the requirements for approval even after it has reviewed and commented on the design for our clinical trials. For example, the FDA published guidance in 2022 on “Project Optimus”, an initiative to reform dose selection in oncology drug development. If the FDA does not believe we have sufficiently demonstrated that the selected doses for our investigational products maximize not only the efficacy of the investigational product, but the safety and tolerability as well, our ability to initiate new studies may be delayed. Even if we

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conducted the additional studies or generated the additional information requested, the FDA could disagree that we have satisfied their requirements, all of which will cause significant delays and expense to our programs.

In addition, even though NUC-3373 is a transformation of a chemotherapeutic agent that has been widely used for many years and there is a clear unmet medical need in each of the indications that we are currently pursuing in the clinic, there can be no assurance that the FDA will permit us to move more quickly to the initiation of pivotal clinical trials in large patient populations. Furthermore, NUC-7738 is a transformation of 3’-deoxyadenosine, a nucleoside analog that has never been successfully developed or approved as a chemotherapy, which may result in the need for more preclinical studies or clinical trials than would be the case for transformations of approved chemotherapeutic agents.

If we are required to conduct additional clinical trials or other studies of our product candidates beyond those that we currently contemplate, if we are unable to successfully complete clinical trials of our product candidates or other studies, if the results of these trials or tests are not positive or are only modestly positive or if there are safety concerns, we may:

Our product development costs will also increase if we experience delays in preclinical and clinical development or receiving the requisite marketing approvals. We do not know whether any of our preclinical studies or clinical trials will need to be restructured or will be completed on schedule, or at all. Significant preclinical or clinical trial delays also could shorten any periods during which we may have the exclusive right to commercialize our product candidates or allow our competitors to bring products to market before we do and impair our ability to successfully commercialize our product candidates and may harm our business and results of operations.

We face regulation and potential liability related to the privacy of health information we obtain from clinical trials sponsored by us or our collaborators.

The regulatory environment surrounding information security and privacy is increasingly demanding, and these laws and regulations are increasing in complexity and number, and may change frequently and sometimes conflict. We are subject to numerous regulations governing the protection of personal and confidential information of our clinical trial subjects, clinical investigators, and employees, including in relation to medical records, credit card data and financial information, which encompass state privacy and confidentiality laws (including state laws requiring disclosure of breaches), federal and state consumer protection and employment laws, the Health Insurance Portability and Accountability Act, or HIPAA, and European and other foreign data protection laws. For example, the European Union General Data Protection Regulation, or GDPR, is applicable in all E.U. member states and member states of the European Economic Area, or E.E.A. Following the United Kingdom’s withdrawal from the European Union, the data protection obligations of the GDPR continue to apply to U.K.-related processing of personal data in substantially unvaried form and fashion (retained in U.K. law as the “U.K. GDPR”).

We are subject to the GDPR and/or U.K. GDPR when conducting clinical trials involving U.K.- or E.E.A.-based data subjects (whether the trials are conducted directly by us or through a clinical vendor or collaborator) or offering approved products (or any other products or services) to U.K. or E.E.A. based data subjects (regardless of whether involving a U.K. or E.E.A. based subsidiary or operation), when monitoring of their behavior of data subjects in the United Kingdom or E.E.A. and/or when acting through a U.K.- or E.E.A.-based subsidiary, operation or other establishment.

The GDPR (and U.K. GDPR) sets out a number of requirements that must be complied with when handling personal data (i.e. data relating to an identified or identifiable living individual) in these circumstances, including: the obligation to appoint data protection officers in certain circumstances; accountability and record-keeping obligations; transparency obligations for data controllers; the obligation to carry out ‘data protection impact assessments’ in certain circumstances; rights for data subjects (such as rights for individuals to be “forgotten”, rights to data portability, rights to object etc.); a stringent standard of data subject consent; and the obligation to notify certain significant personal data breaches to the relevant Supervisory Authority(ies) and affected individuals. In addition, the GDPR provides a very broad definition of what

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constitutes personal data (for example, the GDPR expressly clarifies that it applies to ‘pseudonymized’ (i.e., key-coded) data). A number of opinions from Supervisory Authorities has further supported a very wide interpretation of the concept of personal data and, thus, the application of the GDPR.

The GDPR and U.K. GDPR also impose strict rules on the transfer of personal data out of the E.E.A. and U.K. to U.S. and other Third Countries. Recent legal developments in the European Union have created further complexity and uncertainty regarding transfers of personal data from the E.E.A. and United Kingdom to the United States, e.g. on July 16, 2020, the Court of Justice of the European Union, or CJEU, made it clear that reliance on any of the specific safeguards for data transfers provided for in the GDPR (the most common of which is the standard contractual clauses, a standard form contract approved by the European Commission) alone may not necessarily be sufficient in all circumstances. Use of the standard contractual clauses must now be assessed on a case-by-case basis taking into account the legal regime applicable in the destination country, in particular applicable surveillance laws and rights of individuals and additional measures and/or contractual provisions may need to be put in place, however, the nature of these additional measures is currently uncertain. Guidance from the European Data Protection Board on what is required by way of additional measures further emphasized the challenges of transferring personal data, in particular unencrypted data, from the E.E.A. A small number of enforcement decisions have also been issued. As supervisory authorities issue further guidance on personal data export mechanisms, including circumstances where the standard contractual clauses can/cannot be used, and/or increase their enforcement activities, we could suffer additional costs, complaints, and/or regulatory scrutiny, investigations or fines, and/or if we are otherwise unable to transfer personal data between and among countries and regions in which we operate, it could affect the manner in which we provide our services, the geographical location or segregation of our relevant systems and operations, and could adversely affect our financial results and generally increase compliance risk.

On June 28, 2021, the European Commission adopted an ‘adequacy decision’ in respect of the United Kingdom, allowing the unrestricted transfer of personal data from the E.E.A. to the United Kingdom. The adequacy decision is intended to apply for a period of four years; however, the Commission is also tasked with monitoring developments in the United Kingdom on an ongoing basis; if it considers that the United Kingdom no longer ensures an essentially equivalent level of data protection, the decision could be suspended or repealed. Were the adequacy decision to be invalidated or withdrawn, this would likely necessitate additional compliance costs and increase our overall risk.

On December 13, 2022, the European Commission launched the process to adopt a new adequacy decision for the ‘E.U. - U.S. Data Privacy Framework’, which would allow personal data to be transferred from the E.E.A to U.S. entities who self-certify under the Data Privacy Framework. Although there is no specified timeframe for the adequacy decision, it is expected to be approved at some point in the Summer of 2023. While the Data Privacy Framework adequacy decision (if issued) will, in principle, make it easier to transfer personal data from the E.E.A. to the U.S., prominent European privacy campaigners have already indicated their intention to bring a legal challenge against any such decision. Consequently, it is expected that the uncertainty surrounding data transfers will continue in 2023 and beyond.

The GDPR also provides that E.E.A. member states may make their own further laws and regulations to introduce specific requirements related to the processing of: “special categories of personal data”, including personal data related to health, biometric data used for unique identification purposes and genetic information; as well as personal data related to criminal offences or convictions — for example, in the United Kingdom, the Data Protection Act 2018 complements the GDPR in this regard in the United Kingdom. This fact may lead to greater divergence on the law that applies to the processing of such data types across the E.E.A. and U.K., compliance with which as and where applicable may increase our costs and could increase our overall risk.

Now that the United Kingdom is no longer a member of the European Union, there is increasing scope for divergence in application, interpretation and enforcement of the data protection law between the United Kingdom and European Union. On March 8, 2023, the U.K. Government presented the ‘Data Protection and Digital Information Bill’ to Parliament, seeking to amend various aspects of the United Kingdom’s data protection regime. As currently drafted, the Bill will result in only minor changes to the substance of the U.K. GDPR, and so the United Kingdom will remain very closely aligned with the European Union in this regard. However, any changes relating to the U.K. and E.U. position regarding aspects of data protection law may lead to additional compliance costs and could increase our overall risk. There are also concerns that changes to the U.K. regime, in particular changes to the data transfer rules, could increase the risk of the European Commission’s adequacy decision in respect of the U.K. being invalidated or withdrawn.

Alongside the GDPR, the European Union has a number of new laws currently going through the legislative process, including the European Health Data Space (EHDS) Regulation. The EHDS Regulation may, for example, require us to make health data available to other organizations in this sector (in an anonymized form) and to the patients themselves. Although

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this law is still only in the initial stages and so unlikely to be applicable for several years, we may have to devote substantial resources to understanding and preparing for it.

These laws and regulations are increasing in complexity and number, and new regulatory guidance and case law means the regulatory landscape changes frequently. Complying with these numerous, complex and often changing regulations is expensive and difficult. Failure by us, any partners, our service providers, or our employees or contractors to comply with the GDPR could result in regulatory investigations, enforcement notices and/or fines of up to the higher of €20 million or up to 4% of our total worldwide annual turnover. Further, following the withdrawal of the United Kingdom from the European Union, we now have to comply with the GDPR and U.K. GDPR separately, each regime separately having the ability to fine up to the higher of €20 million / £17.5 million or 4% of global turnover. Numerous multi-million € / £ fines have been issued by supervisory authorities across the E.E.A. and by the U.K. Information Commissioner’s Office. In addition to administrative fines, a wide variety of other potential enforcement powers are available to competent authorities in respect of potential and suspected violations of the GDPR, including extensive audit and inspection rights, and powers to order temporary or permanent bans on all or some processing of personal data carried out by non-compliant actors.

In addition to the foregoing, a breach of privacy laws or data security laws, particularly those resulting in a significant security incident or breach involving the misappropriation, loss or other unauthorized use or disclosure of sensitive or confidential patient or consumer information, could have a material adverse effect on our business, reputation and financial condition. In addition, widely publicized security breaches are increasingly being followed in the European Union by large ‘class action’ style claims. Although these have yet to succeed in any significant compensation orders, defending these claims is costly and could still result in substantial liability for compensation and legal fees. As a data controller, we are accountable for any third-party service providers we engage to process personal data on our behalf, including our CROs. We attempt to mitigate the associated risks by performing security assessments and due diligence of our vendors and requiring all such third-party providers with data access to sign agreements, and obligating them to only process data according to our instructions and to take sufficient security measures to protect such data. There is no assurance that these contractual measures and our own privacy and security-related safeguards will protect us from the risks associated with the third-party processing, storage and transmission of such information. Any violation of data or security laws by our third-party processors could have a material adverse effect on our business and result in the fines, penalties and/or other enforcement actions outlined above.

We strive to comply with all applicable laws, but they may conflict with each other, and by complying with the laws or regulations of one jurisdiction, we may find that we are violating the laws or regulations of another jurisdiction. Despite our efforts, we may not have fully complied in the past and may not in the future. If we become liable under laws or regulations applicable to us, we could be required to pay significant fines and penalties (including those described above), our reputation may be harmed and we may be forced to change the way we operate. That could require us to incur significant expenses or to discontinue certain services, which could negatively affect our business.

Due to our limited resources and access to capital, we must, and have in the past decided to, prioritize development of certain ProTide candidates over other potential candidates. These decisions may prove to have been wrong and may adversely affect our performance.

Because we have limited resources and access to capital to fund our operations, we must decide which ProTides to pursue and the resources to allocate to each. Our decisions concerning the allocation of research, collaboration, management and financial resources toward particular ProTides or therapeutic areas may not lead to the development of viable commercial products and may divert resources away from better opportunities. Similarly, our decisions to delay, terminate or collaborate with third parties in respect of product development programs may also prove not to be optimal and could cause us to miss valuable opportunities. If we make incorrect determinations regarding the market potential of our ProTides or misread trends in the biopharmaceutical industry, in particular for our lead ProTides, then our business may be adversely affected.

We may not be successful in our efforts to use and expand our technology platform to build a pipeline of additional ProTide candidates.

A key element of our strategy is to use and expand our proprietary ProTide technology to build a pipeline of additional ProTide candidates and progress these ProTide candidates through clinical development for the treatment of cancer. Although our research and development efforts to date have resulted in a pipeline of ProTide candidates directed at the treatment of many solid tumors and hematological malignancies, we may not be able to develop ProTide candidates that are safe and effective. Even if we are successful in continuing to build our pipeline, the potential product candidates that we identify may not be suitable for clinical development, including as a result of being shown to have harmful side effects or other

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characteristics that indicate that they are unlikely to be products that will receive marketing approval and achieve market acceptance.

Risks Related to Marketing Approval of Our Product Candidates

If we are not able to obtain, or if there are delays in obtaining, required marketing approvals, we will not be able to commercialize our product candidates and our ability to generate revenue will be impaired.

Our product candidates and the activities associated with their development and commercialization, including their design, testing, manufacture, safety, efficacy, recordkeeping, labeling, storage, approval, advertising, promotion, sale, distribution, import and export are subject to comprehensive regulation by the FDA and other regulatory agencies in the United States and by comparable authorities in other countries.

These requirements include submissions of safety and other post-marketing information and reports, registration and listing requirements, current good manufacturing practice, or cGMP, requirements relating to manufacturing, quality control, quality assurance and corresponding maintenance of records and documents, including periodic inspections by FDA and other regulatory authorities, requirements regarding the distribution of samples to physicians and recordkeeping. Before we can commercialize any of our product candidates, each such product candidate must be approved by the FDA pursuant to an NDA in the United States, by the EMA pursuant to an MAA in the European Union, and by similar regulatory authorities outside the United States prior to commercialization.

The process of obtaining marketing approvals, both in the United States and abroad, is expensive and takes several years, if approval is obtained at all, and can vary substantially based upon a variety of factors, including the type, complexity and novelty of the product candidates involved. Failure to obtain marketing approval for a product candidate will prevent us from commercializing the product candidate. We have not received approval to market any of our product candidates from regulatory authorities in any jurisdiction. We have limited experience in planning and conducting the clinical trials required for marketing approvals, and we expect to rely on third-party contract research organizations, or CROs, to assist us in this process. Obtaining marketing approval requires the submission of extensive preclinical and clinical data and supporting information to regulatory authorities for each therapeutic indication to establish the product candidate’s safety and efficacy. Securing marketing approval also requires the submission of information about the product manufacturing process, and in many cases the inspection of manufacturing facilities by the regulatory authorities. Our product candidates may not be effective, may be only moderately effective or may prove to have undesirable or unintended side effects, toxicities or other characteristics that may preclude our obtaining marketing approval or prevent or limit commercial use. Because a number of our clinical trials will be in combination with other approved therapies, there may also be undesirable or unintended side effects, toxicities or other characteristics resulting from the other therapy or from its combination with our product candidate.

In addition, because our product candidates are transformations of nucleoside analogs, including those that are approved chemotherapeutic agents and those that have never been approved as chemotherapeutic agents, our product candidates could be negatively impacted by the identification of any new undesirable or unintended side effects, toxicities or other characteristics in such existing nucleoside analogs, in particular in those that have never been approved as chemotherapeutic agents.

Regulatory authorities have substantial discretion in the new drug approval process and may refuse to accept any application or may decide that our data are insufficient for approval and require additional preclinical studies or clinical trials. Our product candidates could be delayed in receiving, or fail to receive, marketing approval for many reasons, including the following:

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In addition, even if we were to obtain approval, regulatory authorities may approve our product candidates for fewer or more limited indications than we request, may grant approval contingent on the performance of costly post-marketing clinical trials, may approve a product candidate with restrictions on distribution or other REMS elements, or may approve a product candidate with a label that does not include the labeling claims necessary or desirable for the successful commercialization of that product candidate. Any of the foregoing scenarios could harm the commercial prospects for our product candidates.

If we experience delays in obtaining approval or if we fail to obtain approval of our product candidates, the commercial prospects for our product candidates may be harmed and our ability to generate revenues will be impaired.

Our product candidates may cause undesirable side effects that could delay or prevent their marketing approval, limit the commercial profile of an approved label, or result in significant negative consequences following marketing approval, if any.

Undesirable side effects caused by our product candidates could cause us or the FDA or other regulatory authorities to interrupt, delay or halt our clinical trials and could result in more restrictive labels or the delay or denial of marketing approval by the FDA or other regulatory authorities of our product candidates. Results of our clinical trials could reveal a high and unacceptable severity and prevalence of these or other side effects. In such an event, our trials could be suspended or terminated and the FDA or comparable foreign regulatory authorities could order us to cease further development of or deny approval of our product candidates for any or all targeted indications. The drug-related side effects could also affect patient recruitment or the ability of enrolled patients to complete the trial or result in potential product liability claims.

Further, clinical trials by their nature utilize a sample of the potential patient population. With a limited number of patients, rare and severe side effects of our product candidates may only be uncovered with a significantly larger number of patients exposed to the product candidate. If our product candidates receive marketing approval and we or others identify undesirable side effects caused by such product candidates or any other similar drugs after such approval, a number of potentially significant negative consequences could result, including: