Quarterly Report for Quarter Ending September 30, 2025 (Form 10-Q)

Management's Discussion and Analysis of Financial Condition and Results of Operations.

You should read this discussion and analysis of our financial condition and consolidated results of operations together with our unaudited condensed consolidated financial statements and the related notes appearing elsewhere in this Quarterly Report and our audited financial statements and related notes for the year ended December 31, 2024, included in our Annual Report on Form 10-K for the year ended December 31, 2024, or the 2024 Annual Report, which was filed with the Securities and Exchange Commission, or SEC, on February 25, 2025. Some of the information contained in this discussion and analysis or set forth elsewhere in this report, including statements of our plans, objectives, expectations and intentions, contain forward-looking statements that involve risks and uncertainties. As a result of many factors, including those factors set forth in the "Risk Factors" section of this report, our actual results could differ materially from the results described in or implied by the forward-looking statements contained in the following discussion and analysis. Please also see the section titled "Forward-Looking Statements."

Overview

We are a clinical-stage pharmaceutical company developing a novel class of medicines, which we refer to as Bicycle^®molecules, for diseases that are underserved by existing therapeutics. Bicycle molecules are fully synthetic short peptides constrained to form two loops which stabilize their structural geometry. This constraint facilitates target binding with high affinity and selectivity, making Bicycle molecules attractive candidates for drug development. Bicycle molecules are a unique therapeutic modality combining the pharmacology usually associated with a biologic with the manufacturing and pharmacokinetic, or PK, properties of a small molecule. The relatively large surface area presented by Bicycle molecules allows targets to be drugged that have historically been intractable to non-biological approaches. Bicycle molecules are excreted by the kidney rather than the liver and have shown no significant signs of immunogenicity to date, qualities which we believe explain the molecules' favorable toxicological profile.

We have a novel and proprietary phage display screening platform which we use to identify Bicycle molecules in an efficient manner. The platform initially displays linear peptides on the surface of engineered bacteriophages, or phages, before "on-phage" cyclization with a range of small molecule scaffolds which can confer differentiated physicochemical and structural properties. Our platform encodes quadrillions of potential Bicycle molecules which can be screened to identify molecules for optimization to potential product candidates. We have used this powerful screening technology to identify our current portfolio of candidates in oncology and intend to use it in conjunction with our collaborators to seek to develop additional future candidates across a range of other disease areas.

Our product candidates zelenectide pevedotin, formerly BT8009, and BT5528 are each a Bicycle Drug Conjugate, or BDC^® molecule. These Bicycle molecules are chemically attached to a toxin that when administered is cleaved from the Bicycle molecule and kills the tumor cells. We are evaluating zelenectide pevedotin, a BDC molecule targeting Nectin-4, in an ongoing company-sponsored Phase I/II clinical trial to assess the safety, pharmacokinetics and clinical activity in patients with Nectin-4 expressing advanced malignancies and an ongoing Phase II/III registrational trial called Duravelo-2, designed to allow for potential accelerated approval in untreated and previously treated metastatic urothelial cancer. We are also evaluating zelenectide pevedotin in ongoing company-sponsored Phase I/II clinical trials to assess the efficacy and safety of zelenectide pevedotin in patients with NECTIN4 amplified advanced breast cancer and NECTIN4 amplified advanced or metastatic non-small cell lung cancer, which commenced recruiting patients in the first and third quarters of 2025, respectively.Enrollment in these trials is ongoing. In addition, we are evaluating BT5528, a BDC molecule targeting Ephrin type A receptor 2, or EphA2, in an ongoing company-sponsored Phase I/II clinical trial. Additionally, our other product candidate, BT7480, is a Bicycle Tumor-Targeted Immune Cell Agonist^®, or Bicycle TICA^® molecule. A Bicycle TICA molecule links immune cell receptor binding Bicycle molecules to tumor antigen binding Bicycle molecules. We are evaluating BT7480, a Bicycle TICA molecule targeting Nectin-4 and agonizing CD137, in a company-sponsored Phase I/II clinical trial. Our discovery pipeline in oncology includes next-generation BDC molecules and Bicycle Radioconjugates, or BRC^® molecules.

Zelenectide pevedotin has been granted Fast Track Designation, or FTD, by the FDA as a monotherapy for the treatment of adult patients with previously treated locally advanced or metastatic urothelial cancer as well as for the treatment of adult patients with previously treated, NECTIN4 gene-amplified, advanced or metastatic triple-negative breast cancer and non-small cell lung cancer. BT5528 has been granted FTD for the treatment of adult patients with

previously treated, locally advanced or metastatic urothelial cancer. Zelenectide pevedotin has also been selected to participate in the Chemistry, Manufacturing and Controls, or CMC, Development and Readiness Pilot Program launched by the FDA to facilitate CMC development for therapies with expedited clinical development timeframes based on the anticipated clinical benefits of earlier patient access to the therapy.

In September 2024, we announced updated Phase I/II clinical results for zelenectide pevedotin used as a monotherapy in metastatic urothelial cancer at the European Society for Medical Oncology, or ESMO, Congress 2024, and in January 2025, we also announced updated topline results from the ongoing Phase I trial evaluating 5 mg/m²weekly of zelenectide pevedotin plus 200 mg of pembrolizumab once every three weeks. In addition, in December 2024, we announced data showing the enhanced anti-tumor activity of zelenectide pevedotin monotherapy in breast cancer patients with NECTIN4 gene amplification at the 2024 San Antonio Breast Cancer Symposium and shared topline monotherapy data for zelenectide pevedotin in non-small cell lung cancer patients with NECTIN4 gene amplification. We plan to advance development of zelenectide pevedotin in broader indications outside of metastatic urothelial cancer utilizing a NECTIN4 gene amplification strategy to target patients who have the potential for significantly deeper responses.

In addition, at the ESMO Congress 2024, we announced updated Phase I/II clinical results for BT5528 in advanced solid tumors, including metastatic urothelial cancer and ovarian cancer, and updated Phase I/II clinical results for BT7480 in advanced solid tumors. In October 2024, first human imaging data for a BRC molecule targeting MT1-MMP was presented by the German Cancer Consortium, or DKTK, and we presented preclinical data about BRC molecules for radioisotope delivery to solid tumors at the European Association of Nuclear Medicine, or EANM, 2024 Congress. In April 2025, DKTK presented additional human imaging data for a BRC molecule targeting MT1-MMP at the American Association for Cancer Research, or AACR, Annual Meeting 2025. In October 2025, at the EANM 2025 Congress, we presented data outlining the first clinical experience with an early BRC molecule targeting MT1-MMP and DKTK presented preclinical data about BRC molecules demonstrating high specificity and tunability supporting their potential for radiotheranostic use.

Beyond our wholly owned oncology portfolio, we are collaborating with biopharmaceutical companies and organizations in additional therapeutic areas in which we believe our proprietary Bicycle screening platform can identify therapies to treat diseases with significant unmet medical need.

In August 2025, we announced cost reduction initiatives that are expected to reduce planned operating costs by approximately 30% over the course of our expected financial runway period, primarily through a workforce reduction that is expected to result in a reduction of approximately 25% of our current and planned workforce. We expect the workforce reduction to be substantially completed by the fourth quarter of 2025. As a result, we anticipate that we will incur aggregate charges, representing cash expenditure for severance and other employee termination benefits, of approximately $5.3 million, $4.1 million of which was recognized during the three months ended September 30, 2025.

Financial Overview

Since our inception, we have devoted substantially all of our resources to developing our Bicycle platform and our product candidates, conducting research and development of our product candidates and preclinical programs, raising capital and providing general and administrative support for our operations. To date, we have financed our operations primarily with proceeds from the sale of our equity securities; proceeds received from upfront payments, research and development payments, and development milestone payments from our collaboration agreements; and borrowings pursuant to a loan and security agreement, or the Loan Agreement, with Hercules Capital, Inc., or Hercules. From our inception in 2009 through September 30, 2025, we have received gross proceeds of $1.4 billion from the sale of our equity securities; and $239.3 million of cash payments under our collaboration arrangements, including $45.9 million from Bayer, $53.0 million from Novartis, $49.7 million from Ionis, and $56.0 million from Genentech. We do not have any products approved for sale and have not generated any revenue from product sales.

Since our inception, we have incurred significant operating losses. Our ability to generate product revenue sufficient to achieve profitability will depend on the successful development and eventual commercialization of one or more of our product candidates. Our net losses were $59.1 million and $198.8 million for the three and nine months

ended September 30, 2025, respectively. As of September 30, 2025, we had an accumulated deficit of $879.6 million. These losses have resulted primarily from costs incurred in connection with research and development activities and general and administrative costs associated with our operations. We expect to continue to incur significant expenses and increasing operating losses for the foreseeable future.

We anticipate that our expenses and capital requirements will increase substantially in connection with our ongoing activities, particularly as we advance our product candidates into later-stage clinical trials and continue preclinical activities and clinical trials for our pipeline programs and, if any product candidates are approved, pursue the commercialization of such product candidates by building internal sales and marketing capabilities. We expect that our expenses and capital requirements will increase substantially if and as we:

We do not expect to generate revenue from product sales unless and until we successfully complete development and obtain marketing approval for one or more of our product candidates, which we expect will take many years and is subject to significant uncertainty. We have no commercial-scale manufacturing facilities of our own, and all of our manufacturing activities have been and are planned to be contracted out to third parties. Additionally, we currently utilize third-party contract research organizations, or CROs, to carry out our clinical development activities. If we seek to obtain marketing approval for any of our product candidates from which we obtain encouraging results in clinical development, we expect to incur significant commercialization expenses as we prepare for product sales, marketing, manufacturing, and distribution.

As a result, we will need substantial additional funding to support our continuing operations and pursue our growth strategy. Until such time as we can generate significant revenue from product sales, if ever, we expect to finance our operations through a combination of equity offerings, debt financings, collaborations, strategic alliances, charitable and governmental grants, monetization transactions or licensing arrangements. We may be unable to raise additional funds or enter into such other agreements or arrangements when needed on favorable terms, or at all. If we fail to raise capital or enter into such agreements as, and when, needed, we may have to significantly delay, scale back, or discontinue the development and commercialization of one or more of our product candidates. Because of the numerous risks and uncertainties associated with product development, we are unable to predict the timing or amount of increased

expenses or when or if we will be able to achieve or maintain profitability. Even if we are able to generate product sales, we may not become profitable. If we fail to become profitable or are unable to sustain profitability on a continuing basis, we may be unable to continue our operations at planned levels and be forced to reduce or terminate our operations.

As of September 30, 2025, we had cash and cash equivalents of $648.3 million. In October 2025, we received $38.2 million of research and development incentives related to relevant expenditures incurred in the year ended December 31, 2024. We believe that our existing cash and cash equivalents will enable us to fund our operating expenses and capital expenditure requirements for at least 12 months from the date of filing of this Quarterly Report. We have based this estimate on assumptions that may prove to be wrong, and we could deplete our available capital resources sooner than we expect. See "-Liquidity and Capital Resources" and "-Capital Resources and Funding Requirements."

Components of Our Results of Operations

Collaboration Revenue

To date, we have not generated any revenue from product sales and we do not expect to generate any revenue from product sales for the foreseeable future. Our revenue primarily consists of collaboration revenue under our arrangements with our collaboration partners, including amounts that are recognized related to upfront payments, milestone payments and option exercise payments, and amounts due to us for research and development services. In the future, revenue may include additional milestone payments and option exercise payments, and royalties on any net product sales under our collaborations. We expect that any revenue we generate will fluctuate from period to period as a result of the timing and amount of license, research and development services, milestone and other payments, as well as the exercise or expiration of options.

Expenses

Research and Development Expenses

Research and development expenses consist primarily of costs incurred for our research and development activities, including our discovery efforts, and the development of our product candidates, which include:

Research and development costs are expensed as incurred. Costs for certain activities are recognized based on an evaluation of the progress to completion of specific tasks. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected in our condensed consolidated financial statements as a prepaid expense or accrued research and development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Our direct external research and development expenses are tracked on a program-by-program basis and consist of costs, such as fees paid to consultants, CROs and contract manufacturing organizations, or CMOs, in connection with our preclinical and clinical development activities. Costs incurred after a product candidate has been designated and that are directly related to the product candidate are included in direct research and development expenses for that program. Costs incurred prior to designating a product candidate are included in discovery, platform and other expenses. We do not allocate employee costs, costs associated with our discovery efforts, laboratory supplies, and facilities, including depreciation or other indirect costs, to specific product development programs because these costs are deployed across multiple product development programs and, as such, are not separately classified.

Through our subsidiaries in the U.K., we receive reimbursements of certain research and development expenditures as part of a U.K. government research and development tax reliefs program. For 2024, we benefitted from the Small and Medium-sized Enterprises, or SME, R&D Tax Relief program, under which we were able to surrender trading losses that arose from qualifying research and development expenses incurred by our subsidiaries in the U.K. for a cash rebate of up to 26.97% of qualifying expenditure incurred as long as we qualified as "R&D intensive" (broadly, a loss-making SME whose relevant R&D expenditure represents, for 2024, 40% of its total expenditure for the accounting period). Such rebate percentage was increased from 18.6% of qualifying expenditure, retroactively applied to expenditures incurred after April 1, 2023, upon the enactment of the Finance Act 2024 in February 2024. For accounting periods beginning on or after April 1, 2024, the Finance Act 2024 replaced the legacy research and development expenditure credit and the SME R&D Tax Relief program with a merged research and development expenditure credit scheme, or RDEC, and an enhanced research and development intensive support scheme, or ERIS. Therefore, for 2025 we qualify for the ERIS scheme, and are therefore eligible for a cash rebate up to 26.97% of qualifying expenditures, as we remain R&D intensive (for 2025, a loss-making SME whose relevant R&D expenditure represents 30% of its total expenditure for the accounting period). Going forward, if we no longer qualify as an R&D intensive SME during an accounting period, we will be subject to a single 20% gross rebate rate applying to all claims under the RDEC scheme.

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For 2025 and beyond, the Finance Act 2024 also introduces restrictions (unless limited exceptions apply) on the tax relief that can be claimed for expenditures incurred on sub-contracted R&D activities or externally provided workers, where such sub-contracted activities are not carried out in the U.K. or such workers are not subject to U.K. payroll taxes. These restrictions may limit our ability to claim R&D tax credits for sub-contracted R&D in the future.

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The U.K. research and development tax credit is fully refundable to us after surrendering tax losses and is not dependent on current or future taxable income. As a result, we have recorded the entire benefit from the U.K. research and development tax credit as a reduction to research and development expenses and is not reflected as part of the income tax provision.

Research and development activities are central to our business model. Product candidates in later stages of clinical development generally have higher development costs than those in earlier stages of clinical development, primarily due to the increased size and duration of later-stage clinical trials. We expect that our research and development expenses will continue to increase for the foreseeable future as a result of our expanded portfolio of product candidates and as we: (i) continue the clinical development and seek to obtain marketing approval for our product candidates; (ii) initiate clinical trials for our product candidates; and (iii) build our in-house process development and analytical capabilities and continue to discover and develop additional product candidates.

The successful development of our product candidates is highly uncertain. As such, at this time, we cannot reasonably estimate or know the nature, timing and estimated costs of the efforts that will be necessary to complete the remainder of the development of these product candidates. We are also unable to predict when, if ever, material net cash inflows will commence from our product candidates. This is due to the numerous risks and uncertainties associated with developing products, including the uncertainty of:

A change in the outcome of any of these variables with respect to the development of a product candidate could mean a significant change in the costs and timing associated with the development of that product candidate. For example, the FDA, the European Medicines Agency, or EMA, or another regulatory authority may require us to conduct clinical trials beyond those that we anticipate will be required for the completion of clinical development of a product candidate, or we may experience significant trial delays due to patient enrollment or other reasons in which case we would be required to expend significant additional financial resources and time on the completion of clinical development. In addition, we may obtain unexpected results from our clinical trials and we may elect to discontinue, delay or modify clinical trials of some product candidates or focus on others. Identifying potential product candidates and conducting preclinical testing and clinical trials is a time-consuming, expensive and uncertain process that takes 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. In addition, on April 26, 2023, the European Commission adopted a proposal for a new Directive and Regulation to revise the current EU pharmaceutical legislation. The proposed revisions remain to be agreed and adopted by the European Council. Moreover, on December 1, 2024, a new European Commission took office. The proposal could, therefore, still be subject to revisions. If adopted in the form proposed, the European Commission proposals may result in a decrease in data and market exclusivity opportunities for our product candidates in the EU and make them open to generic or biosimilar competition earlier than is currently the case with a related reduction in reimbursement status.

General and Administrative Expenses

General and administrative expenses consist primarily of salaries and other related costs, including share-based compensation, for personnel in our executive, finance, corporate and business development, commercial and

administrative functions. General and administrative expenses also include professional fees for legal, patent, accounting, auditing, tax and consulting services, insurance, travel expenses and facility-related expenses, which include direct depreciation costs and allocated expenses for rent and maintenance of facilities and other operating costs.

Foreign currency transactions in currencies different from the applicable functional currency are translated into the functional currency using the exchange rates prevailing at the dates of the transactions. Foreign exchange differences resulting from the settlement of such transactions and from the remeasurement at period-end exchange rates in foreign currencies are recorded in general and administrative expenses in the condensed consolidated statements of operations and comprehensive loss. As such, our operating expenses may be impacted by future changes in exchange rates. See "Quantitative and Qualitative Disclosure About Market Risks" for further discussion.

We expect that our general and administrative expenses will increase in the future as we increase our general and administrative headcount to support our continued research and development and potential commercialization of our portfolio of product candidates. We also expect to continue to incur increased expenses associated with being a public company including costs of accounting, audit, information systems, legal, intellectual property, regulatory and tax compliance services, director and officer insurance and investor and public relations.

Other Income (Expense)

Interest and Other Income

Interest and other income consists primarily of interest earned on our cash held in operating accounts and our cash equivalents.

Interest Expense

Interest expense consists primarily of interest expense for financing arrangements.

Loss on Extinguishment of Debt

Loss on extinguishment of debt is related to the loss recognized from the repayment and voluntary termination of the Loan Agreement on July 9, 2024.

Provision for (Benefit from) Income Taxes

We are subject to corporate taxation in the United States and the U.K. We have generated losses since inception and have therefore not paid U.K. corporation tax. The provision for (benefit from) income taxes included in the condensed consolidated statements of operations and comprehensive loss represents the tax impact from operating activities in the United States, which has generated taxable income based on intercompany service arrangements.

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After consideration of our history of cumulative net losses in the U.K., we have concluded that it is more likely than not that we will not realize the benefits of our U.K. deferred tax assets and accordingly we have provided a valuation allowance for the full amount of the net deferred tax assets in the U.K. We intend to continue to maintain a full valuation allowance on our U.K. deferred tax assets until there is sufficient evidence to support the reversal of all or some portion of these allowances. The release of the valuation allowance would result in the recognition of certain deferred tax assets and an increase to the benefit from income taxes for the period the release is recorded. However, the exact timing and amount of the valuation allowance release are subject to change on the basis of the level of profitability that we are able to actually achieve.

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Unsurrendered U.K. losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of U.K. taxable profits.

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Results of Operations

Comparison of the Three Months Ended September 30, 2025 and 2024

The following table summarizes our results of operations for the periods presented:

Collaboration Revenue

Collaboration revenue increased by $9.1 million in the three months ended September 30, 2025, compared to the three months ended September 30, 2024, due to increases of $6.0 million from our collaboration with Genentech primarily due to the recognition of remaining deferred revenue under the arrangement of $6.5 million upon the termination of our Discovery Collaboration and License Agreement with Genentech during the third quarter of 2025, $2.0 million for a milestone achieved from our collaboration with Ionis, and $0.9 million from our collaboration with Novartis.

Research and Development Expenses

The table below summarizes our research and development expenses for the periods presented:

Research and development expenses increased by $10.2 million in the three months ended September 30, 2025 compared to the three months ended September 30, 2024, due to increases of $5.5 million in clinical program expenses for zelenectide pevedotin primarily due to the ongoing Phase II/III Duravelo-2 registrational trial as well as the ongoing

Phase I/II clinical trials assessing zelenectide pevedotin in patients with NECTIN4 amplified advanced breast cancer and NECTIN4 amplified advanced or metastatic non-small cell lung cancer, which commenced recruiting patients in the first and third quarters of 2025, respectively; $3.9 million in discovery, platform and other expense due to continued development of our pipeline programs, including advancing our BRC molecule pipeline; $3.0 million in employee and contractor related expenses primarily attributable to increased headcount as well as incremental severance-related costs of $1.4 million period over period; and $0.9 million resulting from lower research and development incentives primarily due to restrictions, effective in 2025, on the tax relief that can be claimed on expenditures for certain activities that are not carried out in the U.K. These increases were primarily offset by decreases of $1.0 million in Bicycle TICA program development expenses due to the timing of clinical program activities and $0.8 million in share-based compensation expense due to the Company's workforce reduction in August 2025.

We begin to separately track program expenses at candidate nomination, at which point we accumulate all direct external program costs to support that program to date. Through September 30, 2025, we have incurred approximately $260.8 million and $55.4 million of direct external expenses for the development of zelenectide pevedotin and BT5528, respectively, since their candidate nominations, and an aggregate of $50.9 million of direct external expenses for the development of two named Bicycle TICA candidates since their nominations.

General and Administrative Expenses

The table below summarizes our general and administrative expenses for the periods presented:

General and administrative expenses increased by $0.6 million in the three months ended September 30, 2025 compared to the three months ended September 30, 2024. This increase is primarily due to an increase of $1.5 million in personnel-related costs as a result of increased headcount as well as incremental severance-related costs of $0.8 million period over period, offset by a decrease of $0.7 million in professional and consulting fees due to ongoing cost reduction initiatives.

Other Income, net

Other income, net decreased by $2.9 million in the three months ended September 30, 2025 compared to the three months ended September 30, 2024, which was primarily due to a decrease in interest income of $3.9 million related to lower interest rates as well as lower average interest-bearing cash and cash equivalents balances period over period offset by the loss on extinguishment of debt of $1.0 million recognized in the third quarter of 2024.

Provision For (Benefit From) Income Taxes

The provision for income taxes of $0.2 million for the three months ended September 30, 2025 was primarily due to the impact of the August 2025 workforce reduction on our estimated effective tax rate. The benefit of income taxes of $3.4 million for the three months ended September 30, 2024 was mainly the result of incremental income tax benefits of approximately $3.5 million recognized during the third quarter of 2024 related to the completion of a U.S. research and development tax credit study.

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Comparison of the Nine Months Ended September 30, 2025 and 2024

The following table summarizes our results of operations for the periods presented:

Collaboration Revenue

Collaboration revenue decreased by $6.9 million in the nine months ended September 30, 2025, compared to the nine months ended September 30, 2024, due to decreases of $6.9 million from our collaboration with Ionis primarily due to the completion of the combined licenses and research and discovery performance obligation in the second quarter of 2024, and $1.2 million from our collaboration with Novartis due to the recognition of revenue related to the expiration of Novartis' material rights for limited substitution rights for the first and second targets in the second quarter of 2024. These decreases were offset by an increase of $0.8 million from our collaboration with Genentech.

Research and Development Expenses

The table below summarizes our research and development expenses for the periods presented:

Research and development expenses increased by $65.3 million in the nine months ended September 30, 2025 compared to the nine months ended September 30, 2024, due to increases of $48.9 million in clinical program expenses for zelenectide pevedotin primarily related to the ongoing Phase II/III Duravelo-2 registrational trial as well as the ongoing Phase I/II clinical trials assessing zelenectide pevedotin in patients with NECTIN4 amplified advanced breast cancer and NECTIN4 amplified advanced or metastatic non-small cell lung cancer, which commenced recruiting

patients in the first and third quarters of 2025; $10.9 million in employee and contractor related expenses primarily attributable to increased headcount; $10.1 million in discovery, platform and other expense due to continued development of our pipeline programs, including advancing our BRC molecule pipeline; and $2.7 million resulting from a decrease in research and development incentives due to the retroactive impact of U.K. R&D tax credit reimbursement rate changes that were enacted and effective in the first quarter of 2024, retroactively applied to April 1, 2023. These increases were primarily offset by decreases of $4.6 million in Bicycle TICA program development expenses due to the timing of clinical program activities, and $1.4 million in share-based compensation expense due to our workforce reduction in August 2025.

General and Administrative Expenses

The table below summarizes our general and administrative expenses for the periods presented:

General and administrative expenses increased by $7.9 million in the nine months ended September 30, 2025 compared to the nine months ended September 30, 2024. This increase is primarily due to increases of $4.3 million in personnel-related costs as a result of increased headcount, $2.4 million in professional and consulting fees primarily associated with increased legal and consulting fees to support our growth, and $1.5 million of incremental share-based compensation expense primarily associated with equity grants issued since the same period in the prior year.

Other Income, net

Other income, net increased by $1.1 million in the nine months ended September 30, 2025 compared to the nine months ended September 30, 2024, which was primarily due to a decrease in interest expense of $1.5 million due to the repayment and termination of the Loan Agreement in July 2024 as well as the loss on extinguishment of debt of $1.0 million recognized in the third quarter of 2024, offset by a decrease in interest income of $1.4 million primarily related to lower average interest rates period over period as well as higher cash and cash equivalents balances during the second half of 2024.

Benefit from Income Taxes

The benefit from income taxes of $1.1 million and $3.7 million for the nine months ended September 30, 2025 and 2024, respectively, is mainly the result of deferred tax assets in the United States that do not have a valuation allowance against them because of profits that will be generated by an intercompany service agreement. The benefit from income taxes for the nine months ended September 30, 2024 includes incremental income tax benefits of approximately $3.5 million recognized during the third quarter of 2024 related to the completion of a U.S. research and development tax credit study.

Liquidity and Capital Resources

Liquidity

From our inception through September 30, 2025, we have not generated any revenue from product sales and have incurred significant operating losses and negative cash flows from our operations. We do not expect to generate significant revenue from sales of any products for several years, if at all.

To date, we have financed our operations primarily with proceeds from the sale of our equity securities; proceeds received from upfront payments, payments for research and development services, and development milestone payments pursuant to collaboration agreements; and borrowings pursuant to our Loan Agreement with Hercules.

On May 23, 2024, we entered into a securities purchase agreement, or the Purchase Agreement, with purchasers named therein. Pursuant to the Purchase Agreement, we sold 6,764,705 ADSs, representing the same number of ordinary shares, nominal value £0.01 per share, and 19,169,001 non-voting ordinary shares, nominal value £0.01, each at a purchase price equal to $21.42 per share, or the Private Placement. We completed the Private Placement on May 28, 2024. The transaction resulted in gross proceeds to us of $555.5 million, and after deducting commissions and offering expenses of $11.4 million, net proceeds to us of $544.1 million.

Cash Flows

The following table summarizes our cash flows for each of the periods presented:

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Operating Activities

Net cash used in operating activities for the nine months ended September 30, 2025 was $230.3 million as compared to $155.3 million for the nine months ended September 30, 2024. The increase in cash used in operations of $75.0 million is primarily due to an increase in cash payments for clinical program activities, primarily related to the multiple ongoing clinical trials for zelenectide pevedotin, including for the ongoing Phase II/III registrational trial for zelenectide pevedotin in patients with untreated and previously treated metastatic urothelial cancer and the initiation of the Phase I/II clinical trials for zelenectide pevedotin in patients with NECTIN4 amplified advanced breast cancer and NECTIN4 amplified advanced or metastatic non-small cell lung cancer.

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Investing Activities

During the nine months ended September 30, 2025 and 2024, we used $1.8 million and $0.9 million, respectively, of cash in investing activities for purchases of property and equipment, consisting primarily of laboratory equipment.

Financing Activities

During the nine months ended September 30, 2025, net cash used in financing activities was $0.1 million, primarily consisting of payments of finance lease obligations.

During the nine months ended September 30, 2024, net cash provided by financing activities was $519.5 million, primarily consisting of net proceeds of $544.1 million from the Private Placement and $7.3 million from the exercise of share options, offset by payments on debt of $31.9 million associated with the repayment and voluntary termination of the Loan Agreement.

Loan Agreement with Hercules

On July 9, 2024, we repaid all amounts outstanding, including $30.0 million in outstanding borrowings, $0.1 million in accrued and unpaid interest, an end-of-term charge of $1.5 million and a prepayment charge of $0.3 million, for a total aggregate payment of $31.9 million, and terminated the Loan Agreement. Upon the termination of the Loan Agreement, all security interests granted to the secured parties thereunder were terminated and released. For additional information on the Loan Agreement, see Note 6. "Debt" of our condensed consolidated financial statements included elsewhere in this Quarterly Report.

Capital Resources and Funding Requirements

Our material cash requirements include expenses associated with our ongoing activities, particularly as we advance the preclinical activities and clinical trials of our product candidates and as we:

If we obtain marketing approval for any product candidate that we identify and develop, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing, and distribution to the extent that such sales, marketing, and distribution are not the responsibility of our collaboration partners.

The following table summarizes our contractual obligations as of September 30, 2025, and the effects that such obligations are expected to have on our liquidity and cash flows in future periods. For additional information, see Note 11 to our condensed consolidated financial statements included in this Quarterly Report.

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In the ordinary course of business, we enter into various agreements with contract research organizations to provide clinical trial services, with contract manufacturing organizations to provide clinical trial materials, and with vendors for preclinical research studies, synthetic chemistry and other services for operating purposes. These payments are not included in the table above since the contracts are generally cancelable with advanced written notice, generally with a notice period of 90 days or less. From the time of notice until termination, we are contractually obligated to make certain minimum payments to the vendors, based on the timing of the notification and the exact terms of the agreement.

We havealso entered into separate agreements with third parties which provide for various future milestone payments upon the achievement of specified development, regulatory, commercial and sales-based milestones with an aggregate total value of $105.8 million, as well as potential future royalty and other payments at percentages ranging from very low to low single digits.These additional milestone payments are contingent upon future events that are not considered probable of achievement as of September 30, 2025. As of September 30, 2025, we were unable to estimate the timing or likelihood of achieving these milestones.

As of September 30, 2025, we had cash and cash equivalents of $648.3 million. In October 2025, we received $38.2 million of research and development incentives related to relevant expenditures incurred in the year ended December 31, 2024. We expect that our existing cash and cash equivalents will enable us to fund our operating expenses and capital expenditure requirements for at least 12 months from the date of filing of this Quarterly Report.

We have based our estimates on assumptions that may prove to be wrong, and we may use our available capital resources sooner than we currently expect. Because of the numerous risks and uncertainties associated with the development of product candidates and programs, and because the extent to which we may enter into collaborations with third parties for development of our product candidates is unknown, we are unable to estimate the timing and amounts of increased capital outlays and operating expenses associated with completing the research and development of our product candidates. Our future capital requirements will depend on many factors, including:

Until such time, if ever, that we can generate product revenue sufficient to achieve profitability, we expect to finance our cash needs through a combination of equity offerings, debt financings, collaborations, monetization transactions, government contracts or other strategic transactions. To the extent that we raise additional capital through the sale of equity, ownership interests of existing holders of our ADSs and ordinary shares will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of holders of our ADSs or ordinary shares. If we raise additional funds through collaboration agreements, strategic alliances, licensing arrangements, monetization transactions, or marketing and distribution arrangements, we may have to relinquish valuable rights to our technologies, future revenue streams, research programs or product candidates or grant licenses on terms that may not be favorable to us or grant rights to develop and market products or product candidates that we would otherwise prefer to develop and market ourselves. Future debt financing, if available, may involve covenants restricting our operations or our ability to incur additional debt. Any debt or equity financing that we raise may contain terms that are not favorable to us or our shareholders.

Recent global trade disruption, volatility in the capital markets and continued uncertainty may contribute to a general global economic slowdown or recession. The resulting high inflation rates may materially affect our business and corresponding financial position and cash flows. Inflationary factors, such as increases in the cost of our clinical trial materials and supplies, interest rates and overhead costs may adversely affect our operating results. High interest rates also present a recent challenge impacting the U.S. economy and could make it more difficult for us to obtain traditional financing on acceptable terms, if at all, in the future. Additionally, the general consensus among economists suggests that we should expect a higher recession risk to continue over the next year, which, together with the foregoing, could result in further economic uncertainty and volatility in the capital markets in the near term, and could negatively affect our operations. Furthermore, such economic conditions have produced downward pressure on share prices. Although we do not believe that inflation has had a material impact on our financial position or results of operations to date, we may experience increases in the near future (especially if inflation rates remain high or begin to rise again) on our operating costs, including our labor costs and research and development costs, due to supply chain constraints, consequences associated with geopolitical conflicts such as those involving Ukraine and Israel, worsening global macroeconomic conditions, including those resulting from changes in global trade policies, which may result in additional stress on our working capital resources. If we are unable to raise capital when needed or on attractive terms, we would be forced to delay, reduce, or eliminate our research and development programs or future commercialization efforts.

Critical Accounting Estimates

Our management's discussion and analysis of financial condition and results of operations is based on our condensed consolidated financial statements, which have been prepared in accordance with U.S. GAAP. The preparation

of our condensed consolidated financial statements and related disclosures requires us to make estimates, assumptions and judgments that affect the reported amount of assets, liabilities, revenue, costs and expenses, and related disclosures. We base our estimates on historical experience, known trends and events and various other factors that we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. We evaluate our estimates and assumptions on an ongoing basis. Our actual results may differ from these estimates under different assumptions or conditions.

Our critical accounting policies are described under the heading "Management's Discussion and Analysis of Financial Condition and Results of Operations-Critical Accounting Estimates" in our 2024 Annual Report, which was filed with the SEC on February 25, 2025. If actual results or events differ materially from the estimates, judgments and assumptions used by us in applying these policies, our reported financial condition and results of operations could be materially affected. Other than as disclosed in Note 2 to the condensed consolidated financial statements included in this Quarterly Report, there have been no significant changes to our critical accounting estimates from those described in our 2024 Annual Report.