Boundless Bio, Inc.: Form 10-Q for the period ended Jun 30, 2026

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with our unaudited condensed financial statements and notes thereto included elsewhere in this Quarterly Report on Form 10-Q and with our audited financial statements and notes thereto and management’s discussion and analysis of financial condition and results of operations for the year ended December 31, 2025, included in our 2025 10-K. This discussion and analysis contains forward-looking statements that involve risks and uncertainties, including those described in the section titled “Special Note Regarding Forward Looking Statements and Market and Industry Data.” As a result of many factors, including those factors set forth in the “Risk Factors” section of this Quarterly Report and our 2025 10-K, our actual results and the timing of events could differ materially from the results and timing described in or implied by the forward-looking statements contained in the following discussion and analysis. Unless the context requires otherwise, references in this report to “Boundless Bio,” the “Company,” “we,” “us,” and “our” refer to Boundless Bio, Inc. prior to consummation of the Merger. In addition, in this report we refer to our extrachromosomal DNA directed therapeutic candidates as “ecDTx,” which until recently were under clinical or preclinical investigation and which have not yet been approved for marketing by the FDA or any other regulatory authority.

Overview

We are a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics that addresses the significant unmet need in patients with oncogene amplified tumors by interrogating extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14 to 17% of cancer patients.

ecDNA are large circular units of nuclear DNA that are a primary mechanism of gene amplification and are detected only in cancer cells, not in healthy cells. Despite tremendous advancements in treating cancer broadly, patients with oncogene amplified cancers generally derive little benefit from existing therapies, such as molecular targeted therapies or immunotherapies, and have worse survival rates than patients without oncogene amplification. Using our proprietary Spyglass platform, we were focused on identifying targets essential for ecDNA functionality in oncogene amplified cancer cells, then designing and developing small molecule drugs called ecDNA-directed therapeutic candidates (ecDTx) to inhibit those targets, with the aim to prevent cancer cells from using chromosomal instability and ecDNA amplification biology to grow, adapt, and become resistant to existing therapies. Instead of directly targeting the proteins produced by amplified oncogenes, which is the approach of traditional targeted therapies, our ecDTx are intended to be synthetic lethal in tumor cells reliant on ecDNA amplification biology. In the context of drug development, synthetic lethality is a therapeutic approach wherein using a drug to inhibit one target is lethal to cancer cells harboring a specific genetic alteration to a second target, but not lethal to healthy cells that lack the genetic alteration to the second target. Accordingly, our ecDTx were designed to preferentially kill ecDNA-enabled cancer cells, but not healthy cells. They were engineered to disrupt the underlying cellular machinery that enables ecDNA or functional amplification.

Our lead ecDTx, BBI-940, is a novel, oral, selective degrader that targets a previously undrugged kinesin involved in DNA segregation, including ecDNA segregation during mitosis. In February 2026, we initiated the KOMODO-1 trial, a Phase 1, open-label, multicenter, first-in-human clinical trial of BBI-940 in patients with estrogen receptor positive and human epidermal growth factor receptor 2 negative, or ER+/HER2-, breast cancer who have progressed following treatment with a cyclin-dependent kinase 4/6 inhibitor (CDK4/6 inhibitor) plus endocrine therapy, as well as patients with triple-negative breast cancer luminal androgen receptor subtype (TNBC-LAR). In June 2026, we announced that based on preliminary exposure data obtained in the early dose escalation cohorts of the KOMODO-1 clinical trial, we believed that the observed pharmacokinetic exposure data, indicating that human oral bioavailability of BBI-940 was significantly lower than what had been predicted based on preclinical studies, did not support continued clinical development of BBI-940.

We had been investigating BBI-355, a novel, oral, selective inhibitor of checkpoint kinase 1 designed to target replication stress in oncogene amplified cancers, and BBI-825, a novel, oral, selective inhibitor of ribonucleotide reductase, in the clinic in the POTENTIATE trial and the STARMAP trial. As previously reported, we made decisions to cease enrollment in each of these trials, and, accordingly, we also do not plan to invest further in the development of ECHO, which is an ecDNA diagnostic clinical trial assay used in the POTENTIATE trial. We completed winding down the STARMAP trial of BBI-825 in 2025, while the wind down of the POTENTIATE trial is ongoing. For additional information, see “Other Programs” in Part I, Item 1., “Business,” of our 2025 10-K.

Spyglass is our internal proprietary platform used to identify new targets. We utilized Spyglass to identify targets that exploit cellular vulnerabilities of oncogene amplified cancers. Our target identification efforts revealed multiple distinct nodes of vulnerability within the lifecycle of ecDNA. In addition to the program described above, we have preclinically validated multiple additional targets and have historically initiated ecDTx drug discovery efforts to identify potential candidates against such targets.

Business Overview

Since we commenced operations in 2018, we have devoted substantially all of our efforts and resources to organizing and staffing our company, business planning, raising capital, building our proprietary Spyglass platform, discovering our ecDTx, developing our diagnostic, establishing our intellectual property portfolio, conducting research, preclinical studies, and clinical trials, establishing arrangements with third parties for the manufacture of our ecDTx and related raw materials, and providing general and administrative support for these operations. During this time, we have incurred significant operating losses and, as of June 30, 2026, we had an accumulated deficit of $296.9 million. We expect to continue to incur losses for the foreseeable future, and, in general, we anticipate these losses will increase substantially in the future if we continue our development of, seek regulatory approval for, and potentially commercialize our current or any future ecDTx, conduct any clinical trials and preclinical studies, utilize third parties to manufacture our ecDTx and related raw materials, leverage Spyglass to potentially identify additional development opportunities for our ecDTx and expand our therapeutic pipeline, seek to expand and protect our intellectual property, as well as incur additional costs associated with being a public company. If we obtain regulatory approval for our ecDTx, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing, and distribution. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our clinical trials, preclinical studies, and our other research and development activities and capital expenditures.

Through June 30, 2026, we have raised a total of $353.9 million to fund our operations primarily from the gross proceeds from the sale and issuance of our convertible preferred and common stock. In April 2024, we completed our IPO, in which we sold and issued 6,250,000 shares of our common stock for gross proceeds of $100.0 million. In April 2025, we commenced an “at the market” (ATM) offering as defined in Rule 415(a)(4) under the Securities Act, under which we may offer and sell shares of our common stock having an aggregate offering price of up to $14.5 million from time to time through or to our sales agent, as described further under “Liquidity and Capital Resources” below. As of June 30, 2026, we had cash, cash equivalents, and short-term investments of $72.6 million.

In response to clinical data and other market considerations, we have made a series of portfolio prioritization decisions and taken steps to streamline operations in connection with those decisions. In January 2026, we focused our research and development activities on BBI-940. In April 2026, we further streamlined our operations by restructuring our facilities footprint, terminating our long-term lease (the 2024 Lease) for approximately 80,168 rentable square feet of laboratory and office space in San Diego effective May 31, 2026, and entering into a new, shorter-term lease for approximately 10,822 rentable square feet at a nearby location commencing June 1, 2026. The 2024 Lease termination involved a cash payment of $10.0 million by us to the landlord, and the landlord’s retention of our security deposit of approximately $0.5 million.

We do not have any products approved for sale and have not generated any revenue to date. We do not expect to generate any revenue from product sales unless we decide to continue to develop and successfully complete development and obtain regulatory approval for one or more of our ecDTx, which we expect would take several years and may never occur. If the Merger is not completed, we will need substantial additional funding to support our continuing operations and pursue any long-term business plan, including to complete the development and commercialization of any ecDTx, if approved. Accordingly, until such time as we can generate significant revenue from sales of our ecDTx, if ever, we expect to finance our cash needs through equity offerings, debt financings, or other capital sources, including potential collaborations, licenses, and other similar arrangements. However, we may be unable to raise additional funds or enter such other arrangements when needed on favorable terms or at all. Our failure to raise capital or enter such other arrangements when needed would have a negative impact on our financial condition and could force us to delay, limit, reduce, or terminate our research and development programs or other operations, or grant rights to develop and market ecDTx that we would otherwise prefer to develop and market ourselves.

We do not own or operate, and currently have no plans to establish, any manufacturing facilities. If the Merger is not completed, we expect to continue to rely, on third parties for the manufacture of our ecDTx, for preclinical and clinical testing, as well as for commercial manufacture if we develop any ecDTx and any such ecDTx were to obtain marketing approval.

The Proposed Merger

On June 22, 2026, Boundless Bio entered into an Agreement and Plan of Merger (the Merger Agreement) with Serapha Bio, Inc. (Serapha), a privately held biotechnology company advancing SERP-01, an investigational in vivo base editing therapy for Alpha-1 Antitrypsin Deficiency (AATD), and Boulder Merger Sub Corp., a wholly owned subsidiary of Boundless Bio (Merger Sub). Pursuant to the Merger Agreement, among other matters and subject to the satisfaction or waiver of the conditions set forth therein, Merger Sub will merge with and into Serapha, with Serapha continuing as a wholly owned subsidiary of Boundless Bio and the surviving corporation of the merger (the Merger). The Merger is intended to qualify for federal income tax purposes as (1) a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended (the Code), and/or (2) an exchange of shares of Serapha capital stock for Boundless Bio common stock under Section 351(a) of the Code.

Upon closing, Serapha's existing stockholders are expected to own approximately 96.31% of the combined company, and Boundless Bio's existing stockholders are expected to own approximately 3.69%, in each case on a fully diluted basis. Prior to closing, Boundless Bio may declare a special cash dividend to its current stockholders to the extent its net cash is estimated, based on a reasonable, good faith approximation, to exceed zero at closing (as further discussed below).

The transaction requires approval from stockholders of both companies, as well as continued Nasdaq listing of Boundless Bio’s common stock, effectiveness of a Form S-4 registration statement, the receipt of at least $200 million in gross proceeds from related financings by Serapha (as described below), among other closing conditions. In connection with the Merger, Boundless Bio stockholders will also be asked to approve a reverse stock split and an increase in authorized shares. Either party may terminate the agreement under certain circumstances, in which case a termination fee of $1.0 million may be payable by the terminating party.

In connection with the signing of the Merger Agreement, on June 23, 2026, we announced a reduction in workforce of approximately 75%. We recognized a charge of approximately $2.8 million during the three and six months ended June 30, 2026 and estimate aggregate one-time charges of approximately $3.0 million to $5.0 million, with the remainder to be recognized in the second half of 2026. See Note 1 to our unaudited condensed financial statements included elsewhere in this Quarterly Report on Form 10-Q for further information.

The transaction is expected to close in the fourth quarter of 2026, subject to the satisfaction of certain closing conditions, along with the concurrent Serapha Pre-Closing Financing (as defined below). Following completion of the Merger, the combined company plans to focus on advancing SERP-01 and does not intend to continue development of any of Boundless Bio’s legacy ecDTx. Boundless Bio may continue to evaluate opportunities for its ecDTx, which may include a sale, license, transfer, disposition, divestiture or other monetization transaction to a third party or to a related party so long as the transaction would not result in material post-closing obligations to the combined company without Serapha’s consent. If the Merger is not completed, Boundless Bio may continue to explore development opportunities for its ecDTx and pursue other strategic alternatives, including collaborations, financing opportunities or a transaction similar to the proposed Merger, or liquidation.

Serapha Series A Preferred Stock Financing

In connection with the execution of the Merger Agreement, certain institutional and accredited investors (the Series A Investors, led by affiliates of RTW Investments, LP and RA Capital Management, L.P.) and Serapha entered into a Series A Preferred Stock Purchase Agreement, pursuant to which such persons invested in and purchased an aggregate of 30,668,708 shares of Serapha Series A Preferred Stock at a purchase price of $4.4997 per share for aggregate gross proceeds to Serapha of approximately $138.0 million.

Serapha Pre‑Closing Financing

Concurrently with the execution and delivery of the Merger Agreement, the Series A Investors also entered into the Securities Purchase Agreement with Serapha, pursuant to which such investors have agreed to purchase, immediately prior to the Merger, shares of Serapha common stock or, in lieu thereof, Serapha pre‑funded warrants, representing an aggregate commitment of approximately $92.0 million (the Serapha Pre‑Closing Financing). The shares of Serapha common stock and Serapha pre‑funded warrants that are issued in the Serapha Pre‑Closing Financing will be or will have the right to be, respectively, converted into shares of Boundless Bio common stock in the Merger.

The Securities Purchase Agreement also contemplates Serapha and the investors participating in the Serapha Pre‑Closing Financing entering into a registration rights agreement at the closing of the Serapha Pre‑Closing Financing, pursuant to which, among other things, the combined company will agree to provide for the registration and resale of certain shares of Boundless Bio common stock that are held by the investors participating in the Serapha Pre‑Closing Financing from time to time pursuant to Rule 415.

Pre‑Closing Dividend

Further, prior to the closing of the Merger (the Closing), Boundless Bio expects to declare and set aside the aggregate cash amount to be paid in accordance with a special cash dividend (the Pre-Closing Dividend) to holders of record of outstanding shares of its common stock as of a record date prior to the effective time of the Merger, to be determined by its board of directors. The ex‑dividend date in respect of the Pre-Closing Dividend will be determined by Nasdaq. Boundless Bio’s stockholders of record prior to the ex‑dividend date will be entitled to receive the Pre-Closing Dividend, regardless of whether they beneficially own such shares as of the dividend date. The amount of the Pre-Closing Dividend is expected to be approximately $44 to $48 million in the aggregate.

Macroeconomic, Political, and Regulatory Environment Considerations

Uncertainty in the United States and global macroeconomic, political, and regulatory environments present significant risks to our business. Our operating costs, ability to raise additional capital, and stock price could be materially and adversely affected by macroeconomic and geopolitical events and conditions outside of our control, including market volatility, high interest rates, inflation, tariffs and other trade barriers, retaliatory measures taken by foreign countries, slowed economic growth or recession, uncertainty with respect to the federal budget and debt ceiling, potential or prolonged government shutdowns related thereto, liquidity concerns at financial institutions, supply chain disruptions, military conflicts, and other geopolitical events and instability. Further, one or more of our current service providers or vendors, manufacturers, clinical investigative sites, financial institutions, and other partners may be adversely affected by the foregoing risks, which could directly affect our ability to attain our operating goals on schedule and on budget.

In addition, FDA-regulated industries, such as ours, face uncertainty with regard to the regulatory environment we will face if the Merger is not completed and we proceed with research and development and possibly in the future commercialization. The FDA has recently experienced significant leadership changes, voluntary and involuntary staff departures, shifts in scientific and regulatory priorities, and political pressure to increase scrutiny of certain products. These and other factors increase uncertainties associated with interpreting the FDA’s guidance and predicting its areas of focus and responses to various issues. Changes and disruptions at the FDA, including due to federal government shutdowns, could impact the FDA’s ability to retain key personnel and hire additional personnel and may result in delays or limitations on our ability to obtain guidance from agency staff and slow review times for applications we may submit to obtain the requisite regulatory approvals in the future. Moreover, actions that the federal government recently has taken and may take in the future to freeze or reduce federal funding for medical research, has and could further decrease the ability of facilities that rely on such funding to conduct clinical trials or increase the costs to us of conducting clinical trials at those facilities. There remains general uncertainty regarding future activities. New executive orders, regulations, policies, or guidance could be issued or promulgated that adversely affect us or create a more challenging or costly environment to pursue the development and commercialization of our ecDTx, including in areas relating to regulatory framework and oversight, research and development funding, drug pricing reform, intellectual property rights, global trade policy, and tariffs.

Although, to date, our business has not been materially impacted, the ultimate impact of global economic and market conditions and changes in government agencies, regulations and policies remains highly uncertain and will depend on future developments and factors that continue to evolve. We closely monitor these ongoing developments and the potential impact of these factors on our business, operating expenses, and cash position and, if circumstances warrant, we may make adjustments to our operating plan. For more information regarding these risks and uncertainties, see Item 1A, “Risk Factors,” in Part I of our 2025 10-K.

Components of Our Results of Operations

Revenue

To date, we have not generated any revenue from the sale of products. We do not expect to generate any such revenue unless and until such time that our ecDTx have advanced through clinical development and regulatory approval, if ever. If we fail to complete preclinical and clinical development of our ecDTx or obtain regulatory approval for them, our ability to generate future revenues, and our results of operations and financial position would be adversely affected.

Operating Expenses

Our operating expenses consist of research and development expenses and general and administrative expenses.

Research and Development

Our research and development (R&D) expenses have related primarily to building our Spyglass platform, our ecDTx discovery efforts, our preclinical and clinical development activities, and the development of a diagnostic test. R&D expenses are recognized as incurred, and payments made prior to the receipt of goods or services to be used in R&D are capitalized until the goods or services are received. We use internal resources primarily to conduct our research and discovery activities, as well as for managing our preclinical development, process development, manufacturing, and clinical development activities. We track direct costs on a development program specific basis. Indirect costs are not included in program costs, as these costs are general in nature and benefit all our discovery efforts and development programs.

Our direct, or development program specific, R&D costs consist of:

• costs incurred under agreements with our contract research organizations (CROs), investigative sites, and consultants to conduct our clinical trials and preclinical studies, as well as third party costs related to the development of a diagnostic test; and
• expenses related to manufacturing our ecDTx for clinical trials and preclinical studies, including fees paid to third-party manufacturers.

Our indirect R&D costs include:

• personnel-related costs, including salaries, severance, bonuses, benefits, travel, and stock-based compensation expenses for employees engaged in R&D functions,
• the costs of outside services from third parties, including consultants,
• the costs of lab and pharmacology supplies,
• facilities-related costs, including rent and maintenance costs, and other costs including insurance, depreciation, supplies, and miscellaneous expenses, and
• other costs, including costs related to travel, repairs and maintenance, service contracts, computer supplies, software, and publications and subscription services.

The successful development of our ecDTx is highly uncertain. There are numerous factors associated with the successful development of our ecDTx, including future trial design and various regulatory requirements, many of which cannot be determined with accuracy at this time based on our stage of development. In addition, future regulatory factors beyond our control may impact our clinical development programs. Product candidates in later stages of development generally have higher development costs than those in earlier stages of development.

If we resume development of any ecDTx, our future R&D expenses may vary significantly based on a wide variety of factors such as:

• the number, scope, rate of progress, expense, and results of our clinical trials and preclinical activities;
• per patient trial costs;
• the number of trials required for approval;
• the number of sites included in the trials;
• the countries in which the trials are conducted;
• the length of time required to enroll eligible patients;
• the number of patients that participate in the trials;
• the number of doses that patients receive;
• the drop-out or discontinuation rates of patients;
• the potential additional safety monitoring requested by regulatory agencies;
• the duration of patient participation in the trials and follow-up;
• the cost and timing of manufacturing our ecDTx;
• the phase of development of our ecDTx;
• a decision not to advance the clinical development of an ecDTx;
• the necessity and cost of developing a diagnostic for our ecDTx;
• the costs of laboratory supplies and equipment and pharmacology supplies for our preclinical activities and clinical trials;
• the extent of changes in government regulation and regulatory guidance;
• disruptions at the FDA that hinder its ability to perform routine activities or function in the normal course;
• the efficacy and safety profile of our ecDTx;
• the timing, receipt, and terms of any approvals from applicable regulatory authorities; and
• the extent to which we establish collaboration, license, or other arrangements.

A change in the outcome of any of these variables with respect to development of our ecDTx could significantly change the costs and timing associated with any development of our ecDTx.

The process of conducting the necessary preclinical and clinical research to obtain regulatory approval is costly and time-consuming. The actual probability of success for our ecDTx or any future ecDTx may be affected by a variety of factors. We may never succeed in achieving regulatory approval for our ecDTx. Preclinical and clinical development timelines, the probability of success, and total development costs can differ materially from expectations. If the Merger is not completed, we anticipate that we will continue to make determinations as to how much funding to direct to any ecDTx we may decide to develop on an ongoing basis in response to the results of ongoing and future preclinical studies and clinical trials, regulatory developments, and our ongoing assessment of our ecDTx’s commercial potential. We will need to raise substantial additional capital in the future if the Merger is not completed and we decide to develop any ecDTx. In addition, we cannot forecast whether our ecDTx may be subject to future collaborations, when such arrangements will be secured, if at all, and to what degree such arrangements would affect our development plans and capital requirements.

General and Administrative

General and administrative (G&A) expenses consist primarily of personnel-related costs, including salaries, bonuses, benefits, travel, severance, and stock-based compensation for employees in executive, accounting and finance, business development, legal, and other administrative functions. Other significant costs include allocated facility-related expenses, legal fees relating to intellectual property and corporate matters, professional fees for accounting and consulting services, insurance costs, and business development expenses. We also incur costs associated with maintaining compliance with securities exchange listing and SEC requirements, including audit, legal, regulatory, and tax-related services, as well as director and officer insurance premiums and investor relations costs associated with operating as a public company.

If the Merger is not completed and we decide to develop any ecDTx, we anticipate that our G&A expenses will increase in the long-term if we are successful in developing our ecDTx and growing our business and, if our ecDTx receives marketing approval, when we commence commercialization activities.

Other Income, Net

Other income, net consists primarily of interest income earned on our cash, cash equivalents, and investments.

Results of Operations

Comparison of the Three Months Ended June 30, 2026 and 2025

The following table summarizes our results of operations for each of the periods indicated (in thousands):

21

Research and Development Expenses

The following table summarizes our R&D expenses for each of the periods indicated (in thousands):

R&D expenses were $14.0 million and $12.2 million for the three months ended June 30, 2026 and 2025, respectively. The $1.8 million increase was primarily attributable to (i) a $3.2 million increase in facilities-related costs due to the early termination of the 2024 Lease and (ii) a $1.1 million increase related to the impairment of property and equipment as a result of our early termination of the 2024 Lease, partially offset by (iii) a $1.9 million decrease in direct program costs, (iv) a $0.4 million decrease in personnel-related costs, reflecting a decline in ongoing compensation costs resulting from the reduction in workforce, substantially offset by severance costs and stock-based compensation recognized in connection with the amendment of our stock options during the second quarter of 2026, and (v) a $0.2 million decrease in outside services and consulting costs. The increase in BBI-940 direct program costs for the three months ended June 30, 2026 compared with the same period in 2025 was primarily due to costs relating to the KOMODO-1 clinical trial initiated in early 2026, and the decreases in BBI-355 and BBI-825 direct program costs for the three months ended June 30, 2026 compared with the same period in 2025 were primarily due to our decisions to wind down the POTENTIATE and STARMAP clinical trials, as discussed above.

BBI-940 direct program costs are shown as a separate component of R&D expenses in the table above for all periods presented. Such costs were included in “other development programs” in our annual financial statements for the year ended December 31, 2025.

General and Administrative Expenses

G&A expenses were $10.4 million and $4.8 million for the three months ended June 30, 2026 and 2025, respectively. The $5.6 million increase in G&A expenses was primarily attributable to (i) a $1.7 million increase in personnel-related costs, primarily related to severance costs and stock-based compensation recognized in connection with the amendment of our stock options (see Notes 1 and 9 to our condensed financial statements), (ii) a $2.0 million increase in facilities-related costs due to the early termination of the 2024 Lease, (iii) a $1.4 million increase in professional fees, primarily related to legal fees incurred in connection with the Merger, and (iv) a $0.5 million increase in other G&A costs.

Other Income, Net

Other income, net was $0.7 million and $1.4 million for the three months ended June 30, 2026 and 2025, respectively. The $0.7 million decrease resulted from a reduction in interest income generated by our available-for-sale investment securities portfolio due to a decrease in the amount of cash and cash equivalents available for investing purposes as well as a decline in the market yields available for such investment securities compared to the prior year period.

We expect interest income to decrease prior to the Closing as we wind down our research and development activities and incur costs associated with the Merger, and as our investable asset base declines, including the anticipated Pre-Closing Dividend described under “Pre-Closing Dividend” above. Market yields on our investment portfolio may also fluctuate in response to changes in monetary policy and broader interest rate conditions, which could further affect interest income in future periods.

Comparison of the Six Months Ended June 30, 2026 and 2025

The following table summarizes our results of operations for each of the periods indicated (in thousands):

Research and Development Expenses

The following table summarizes our R&D expenses for each of the periods indicated (in thousands):

R&D expenses were $23.7 million and $24.4 million for the six months ended June 30, 2026 and 2025, respectively. The $0.6 million decrease was primarily attributable to (i) a $2.0 million decrease in direct program costs, (ii) a $1.9 million decrease in personnel-related costs, reflecting a decline in ongoing compensation costs resulting from the reduction in workforce, partially offset by severance costs recognized during the second quarter of 2026, and (iii) a $0.8 million decrease in other R&D costs, partially offset by (iv) a $3.0 million increase in facilities-related costs due to the early termination of the 2024 Lease, and (v) a $1.1 million increase related to the impairment of property and equipment as a result of our early termination of the 2024 Lease. The increase in BBI-940 direct program costs for the six months ended June 30, 2026 compared with the same period in 2025 was primarily due to costs relating to the KOMODO-1 clinical trial initiated in early 2026, and the decreases in BBI-355 and BBI-825 direct program costs for the six months ended June 30, 2026 compared with the same period in 2025 were primarily due to our decisions to wind down the POTENTIATE and STARMAP clinical trials, as discussed above.

BBI-940 direct program costs are shown as a separate component of R&D expenses in the table above for all periods presented. Such costs were included in “other development programs” in our annual financial statements for the year ended December 31, 2025.

General and Administrative Expenses

G&A expenses were $15.2 million and $10.0 million for the six months ended June 30, 2026 and 2025, respectively. The $5.1 million increase in G&A expenses was primarily attributable to (i) a $1.5 million increase in personnel-related costs, primarily related to severance costs and stock-based compensation recognized in connection with the amendment of our stock options (see Notes 1 and 9 to our condensed financial statements), (ii) a $2.4 million increase in facilities-related costs due to the early termination of the 2024 Lease, and (iii) a $1.2 million increase in professional fees.

Other Income, Net

Other income, net was $1.6 million and $3.0 million for the six months ended June 30, 2026 and 2025, respectively. The $1.4 million decrease resulted from a reduction in interest income generated by our available-for-sale investment securities portfolio due to a decrease in the amount of cash and cash equivalents available for investing purposes as well as a decline in the market yields available for such investment securities compared to the prior year period.

Liquidity and Capital Resources

Sources of Liquidity

On June 22, 2026, Boundless Bio entered into the Merger Agreement pursuant to which, among other matters, Merger Sub will merge with and into Serapha, with Serapha surviving as a wholly owned subsidiary of the Company. The Closing is subject to approval by its stockholders and the stockholders of Serapha and other closing conditions. Boundless Bio’s future operations are highly dependent on the success of the proposed Merger with Serapha.

Through June 30, 2026, we have raised a total of $353.9 million to fund our operations primarily from the gross proceeds from the sale and issuance of shares of our convertible preferred stock prior to our IPO and the sale and issuance of 6,250,000 shares of our common stock in our IPO, which closed in April 2024. Our IPO generated gross proceeds of $100.0 million, which resulted in net proceeds to us of approximately $87.7 million, after deducting underwriting discounts and commissions and other offering expenses.

In April 2025, we entered into an Open Market Sale AgreementSM (the Sales Agreement) with Jefferies LLC (the Agent), pursuant to which we may, from time to time, sell shares of our common stock in “at-the-market” offerings through or to the Agent, acting as sales agent or principal. See Note 1 to our unaudited condensed financial statements included elsewhere in this Quarterly Report on Form 10-Q under the section entitled “ATM Offering” for further information. We are not obligated to sell any shares under the Sales Agreement, and the Agent is not obligated to buy or sell any shares of our common stock. We cannot provide any assurance that we will sell any shares under the Sales Agreement, or, if we do, as to the prices, amounts, or timing of any such sales. As of June 30, 2026, no shares had been sold under the Sales Agreement.

Future Funding Requirements

As of June 30, 2026, we had cash, cash equivalents, and short-term investments of $72.6 million. In April 2026, we terminated the 2024 Lease, and entered into a new, shorter-term lease, the term of which commenced June 1, 2026. The lease termination involved a cash payment of $10.0 million by us to the landlord, and the landlord’s retention of our security deposit of approximately $0.5 million. See Note 7 to our unaudited condensed financial statements included elsewhere in this Quarterly Report on Form 10-Q for further information regarding the lease termination and new lease. Based on our current operating plan, and without giving effect to the anticipated pre-closing cash dividend of approximately $44 to $48 million or the proposed Merger with Serapha described in Note 1 to our unaudited condensed financial statements, we believe that our existing cash, cash equivalents, and short-term investments will be sufficient to fund our operations through the anticipated closing date of the Merger and for a period of at least 12 months from the date hereof. However, our operating plan may change, whether or not the Merger is completed. We have based this estimate on assumptions that may prove to be wrong, and we could deplete our capital resources sooner than we expect. Additionally, the process of conducting preclinical studies, manufacturing any ecDTx or other product candidates, and testing ecDTx or other product candidates in clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain.

Our primary uses of capital were historically compensation and related expenses, research and development costs to support our ecDTx pipeline, legal and other regulatory expenses and general overhead costs. Now that we have suspended and are winding down our research and development activities in anticipation of the Merger with Serapha, our operations will be limited and we expect that Boundless Bio expenses other than those related to the Merger will decrease significantly.

Our future operations are highly dependent on the success of the proposed Merger with Serapha. If the Merger Agreement with Serapha is terminated, Boundless Bio may continue to explore development opportunities for its ecDTx and pursue other strategic alternatives, including collaborations, financing opportunities or a transaction similar to the proposed Merger, or liquidation.

We have incurred significant operating losses since our inception and, as of June 30, 2026, we had an accumulated deficit of $296.9 million. We expect to continue to incur losses for the foreseeable future, and, in general, we anticipate these losses will increase substantially in the future if we decide to develop, seek regulatory approval for, and potentially commercialize any ecDTx, conduct clinical trials and preclinical studies, utilize third parties to manufacture any ecDTx and related raw materials, leverage Spyglass to potentially identify additional development opportunities for our ecDTx and expand our therapeutic pipeline, seek to expand and protect our intellectual property, as well as incur additional costs associated with being a public company. If we obtain regulatory approval for our ecDTx, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing, and distribution. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our clinical trials, preclinical studies, and our other research and development activities and capital expenditures.

Our future capital requirements are difficult to predict and depend on many factors, including but not limited to:

• the costs and timing of the Merger;
• our ability to complete the Merger or, if the Merger is not completed, identify and consummate another strategic transaction;
• the initiation, type, number, scope, progress, expansions, results, costs, and timing of clinical trials and preclinical studies of any ecDTx that we may choose to pursue in the future;
• the costs and timing of manufacturing for any ecDTx, including commercial manufacture at sufficient scale, if our ecDTx is approved;
• the costs and timing of obtaining raw materials for manufacturing sufficient quantities of our ecDTx or obtaining sufficient quantities of any combination agents or other materials needed for use in our clinical trials and preclinical studies;
• the costs and timing of developing diagnostics, if required, and the outcome of their regulatory review;
• the costs, timing, and outcome of regulatory meetings and reviews of our ecDTx;
• changes in regulatory policies or approval pathways;
• disruptions at the FDA that hinder its ability to perform routine activities or function in the normal course;
• the costs, timing, and outcome of seeking to obtain, maintain, expand, enforce, defend, and protect our patents and other intellectual property and proprietary rights or, if necessary, challenging third-party patents and other intellectual property and proprietary rights;
• the costs and timing of purchasing laboratory supplies and equipment and pharmacology supplies for our preclinical activities and clinical trials;
• potential costs not currently contemplated due to events that may occur as a result of, or that are associated with, streamlining our operations as discussed above;
• the costs associated with hiring additional personnel and consultants, as needed, to support our clinical and preclinical development efforts;
• the costs and timing of establishing or securing sales and marketing capabilities if our ecDTx is approved;
• our ability to achieve sufficient market acceptance, coverage, and adequate reimbursement from third-party payors and adequate market share and revenue for any approved products;
• patients’ willingness to pay out-of-pocket for any approved products in the absence of coverage and/or adequate reimbursement from third-party payors;
• the terms and timing of establishing and maintaining collaborations, licenses, and other similar arrangements;
• costs associated with any products or technologies that we may in-license or acquire; and
• the effects of competing technological and market developments as well as disruptions to and volatility in the credit and financial markets.

We have no committed sources of capital. Until we can generate sufficient product revenue to finance our cash requirements, if ever, we expect to finance our future cash needs primarily through equity offerings (including through the Sales Agreement), debt financings, or other capital sources, including potential collaborations, licenses, and other similar arrangements. However, we may be unable to raise additional funds or enter such other arrangements when needed on favorable terms or at all. To the extent that we raise additional capital through the sale of equity or convertible debt securities, the ownership interest of our stockholders will be, or could be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of our common stockholders. Debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures, or declaring dividends. If we raise additional funds through other collaborations or licensing arrangements with third parties, we may have to relinquish valuable rights to our future revenue streams, ecDTx, research programs, intellectual property, or proprietary technology, or grant licenses on terms that may not be favorable to us. Our ability to raise additional funds may be adversely impacted by global economic conditions, disruptions to, and volatility in, the credit and financial markets in the United States, inflation, diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates, and uncertainty about economic stability. If we are unable to raise additional funds through equity or debt financings or other arrangements when needed, we may be required to delay, limit, reduce, or terminate our ecDTx development or other operations, or grant rights to develop and market ecDTx to third parties that we would otherwise prefer to develop and market ourselves, or on less favorable terms than we would otherwise choose.

Cash Flows

The following table summarizes our cash flows for each of the periods indicated (in thousands):

Operating Activities

Net cash used in operating activities was $35.9 million and $26.4 million for the six months ended June 30, 2026 and 2025, respectively. The net cash used in operating activities during the six months ended June 30, 2026 was primarily driven by our reported net loss of $37.2 million, net of noncash charges (including stock-based compensation expense, depreciation, impairment of property and equipment, and right-of-use asset amortization) totaling $14.3 million and a $13.0 million increase of our net operating assets. The net cash used in operating activities during the six months ended June 30, 2025 was primarily driven by our reported net loss of $31.4 million, net of noncash charges (including stock-based compensation expense, depreciation, and right-of-use asset amortization) totaling $4.3 million and a $0.8 million decrease of our net operating assets. The increase in cash used in operations during the six months ended June 30, 2026 in comparison to the six months ended June 30, 2025 was primarily attributable to the $10.0 million cash payment associated with the termination of the 2024 Lease, partially offset by a decrease in third-party spending associated with our discovery, development, and clinical activities.

Investing Activities

Investing activities consist primarily of purchases and maturities of investment securities and purchases of property and equipment. Such activities resulted in a net cash inflow of approximately $37.7 million and $14.4 million during the six months ended June 30, 2026 and 2025, respectively, in each case, primarily from the net maturities of our available-for-sale securities portfolio.

Financing Activities

Financing activities during the six months ended June 30, 2026 consisted of less than $0.1 million in proceeds from the sale of common stock under the ESPP and less than $0.1 million in proceeds from the exercise of stock options. Financing activities during the six months ended June 30, 2025 consisted of $0.1 million in proceeds from the sale of common stock under the ESPP.

Contractual Obligations and Other Commitments

In April 2026, we terminated the 2024 Lease effective May 31, 2026. In connection with the termination, we paid the landlord $10.0 million, and the landlord retained our security deposit of approximately $0.5 million. As of June 30, 2026, we have no remaining obligations under the 2024 Lease. See Note 7 — Lease Agreements for further information.

On April 17, 2026, we entered into a new, shorter-term facility lease for approximately 10,822 square feet of laboratory and office space in La Jolla, California, with an initial term of 12 months commencing June 1, 2026. Monthly base rent payments are approximately $56,000, with two months of base rent abatement during the second and third full calendar months of the lease term. As of June 30, 2026, our remaining obligations under this lease were approximately $0.5 million.

We enter into contracts in the normal course of our business with various third parties for clinical trial and preclinical research services, contract manufacturing services, and professional and other services and products related to our business. These contracts generally provide for termination after a notice period and are therefore cancellable contracts and not separately presented.

Off-Balance Sheet Arrangements

Since our inception, we have not had, and we do not currently have, any off-balance sheet arrangements as defined under rules and regulations of the SEC.

Critical Accounting Policies and Significant Estimates and Judgments

Our management’s discussion and analysis of our financial condition and results of operations are based on our unaudited condensed financial statements, which have been prepared in accordance with U.S. generally accepted accounting principles. The preparation of these financial statements requires us to make estimates, assumptions, and judgments that affect the reported amounts of assets, liabilities, and expenses and the disclosure of contingent assets and liabilities in our financial statements. On an ongoing basis, we evaluate our estimates, assumptions, and judgments, including those related to accrued R&D expenses and stock-based compensation expense. 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 value of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions.

There have been no material changes to our critical accounting policies and estimates from those described in “Management’s Discussion and Analysis of Financial Condition and Results of Operations – Critical Accounting Policies and Significant Estimates and Judgments” in our 2025 10-K.

Emerging Growth Company and Smaller Reporting Company Status

As an emerging growth company under the Jumpstart Our Business Startups Act of 2012 (the JOBS Act), we can take advantage of an extended transition period for complying with new or revised accounting standards. This period allows an emerging growth company to delay the adoption of certain accounting standards until those standards would otherwise apply to private companies. We have elected to avail ourselves of this exemption from new or revised accounting standards, and therefore our financial statements may not be comparable to companies that comply with new or revised accounting standards as of public company effective dates. We also intend to rely on other exemptions provided by the JOBS Act, including, without limitation, the exemption from the auditor attestation requirement of Section 404(b) of the Sarbanes-Oxley Act, for so long as we remain eligible.

We will remain an emerging growth company until the earliest of (i) December 31, 2029, which is the last day of the fiscal year following the fifth anniversary of the consummation of our IPO; (ii) the last day of the fiscal year in which we have total annual gross revenue of at least $1.235 billion; (iii) the last day of the fiscal year in which we are deemed to be a “large accelerated filer” as defined in Rule 12b-2 under the Exchange Act, which would occur if the market value of our common stock held by non-affiliates exceeded $700.0 million as of the last business day of the second fiscal quarter of such year; or (iv) the date on which we have issued more than $1.0 billion in nonconvertible debt securities during the prior three-year period.

We are also a smaller reporting company as defined in Rule 12b-2 under the Exchange Act. We may continue to be a smaller reporting company even after we are no longer an emerging growth company. We may take advantage of certain of the scaled disclosures available to smaller reporting companies and will be able to take advantage of these scaled disclosures for so long as our voting and non-voting common stock held by non-affiliates is less than $250.0 million measured on the last business day of our second fiscal quarter, or our annual revenue is less than $100.0 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter.

We are a smaller reporting company, as defined in Rule 12b-2 under the Exchange Act and Item 10(f)(1) of Regulation S-K, and are not required to provide the information under this item.

Evaluation of Disclosure Controls and Procedures

We maintain disclosure controls and procedures that are designed to ensure that information required to be disclosed by us in the reports that we file or submit under the Exchange Act is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms, and that such information is accumulated and communicated to our management, including our principal executive officer and principal financial officer, as appropriate, to allow timely decisions regarding required disclosure. In designing and evaluating the disclosure controls and procedures, management recognized that any controls and procedures, no matter how well designed and operated, can provide only reasonable and not absolute assurance of achieving the desired control objectives. In reaching a reasonable level of assurance, management necessarily was required to apply its judgment in evaluating the cost-benefit relationship of possible controls and procedures. In addition, the design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions; over time, controls may become inadequate because of changes in conditions, or the degree of compliance with policies or procedures may deteriorate. Because of the inherent limitations in a cost-effective control system, misstatements due to error or fraud may occur and not be detected.

Management, with the participation of our principal executive officer and our principal financial officer, evaluated, as of the end of the period covered by this Quarterly Report on Form 10-Q, the effectiveness of our disclosure controls and procedures (as such term is defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act). Based on this evaluation, our principal executive officer and our principal financial officer concluded that, as of such date, our disclosure controls and procedures were effective at the reasonable assurance level.

Changes in Internal Control over Financial Reporting

Management, with the participation of our principal executive officer and our principal financial officer, evaluated any changes in our internal control over financial reporting (ICFR) that occurred during the quarter ended June 30, 2026, as required by Rules 13a-15(d) and 15d-15(d) under the Exchange Act. Management concluded that there was no change in our ICFR that occurred during the quarter ended June 30, 2026 that has materially affected, or is reasonably likely to materially affect, our ICFR.

Investing in our common stock involves a high degree of risk. You should carefully consider the risks and uncertainties described in Part I, Item 1A,“Risk Factors,” of our 2025 10-K, together with all of the information in this Quarterly Report, including the risk factors set forth below, before making an investment decision to purchase or sell shares of our common stock. If any of those risks are realized, our business, financial condition, results of operations, and prospects could be materially and adversely affected. In that event, the trading price of our common stock could decline, and you could lose all or part of your investment. Except as set forth below, there have been no material changes to the risk factors set forth in Part I, Item 1A of our 2025 10-K.

Risks Related to the Proposed Merger

Failure to complete, or delays in completing, the potential Merger with Serapha could materially and adversely affect Boundless Bio’s results of operations, business, financial results and/or common stock price.

On June 22, 2026, Boundless Bio entered into the Merger Agreement with Serapha pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Serapha, with Serapha continuing as a wholly owned subsidiary of Boundless Bio and the surviving corporation of the Merger. Boundless Bio following the Merger is referred to herein as the “Combined Company.” Completion of the Merger is subject to certain closing conditions, a number of which are not within Boundless Bio’s control. Any failure to satisfy these required conditions to closing may prevent, delay or otherwise materially adversely affect the completion of the transaction. Boundless Bio cannot predict with certainty whether or when any of the required closing conditions will be satisfied or if another uncertainty may arise and cannot assure you that it will be able to successfully complete the Merger as currently contemplated under the Merger Agreement or at all.

Boundless Bio’s efforts to complete the Merger could cause substantial disruptions in, and create uncertainty surrounding, its business, which may materially adversely affect its results of operation and its business. Uncertainty as to whether the Merger will be completed in a timely manner or at all may affect Boundless Bio’s ability to retain and motivate existing employees or could adversely affect Boundless Bio’s business and its relationship with consultants, suppliers, vendors, regulators and other business partners. The adverse effects of the pendency of the transaction could be exacerbated by any delays in completion of the transaction or termination of the Merger Agreement.

If the conditions to the Merger are not satisfied or waived, the Merger may not occur.

Even if the Merger is approved by the stockholders of Serapha and Boundless Bio, specified conditions must be satisfied or, to the extent permitted by applicable law, waived to complete the Merger. These conditions are set forth in the Merger Agreement. Boundless Bio cannot assure you that all of the conditions to the completion of the Merger will be satisfied or waived. If the conditions are not satisfied or waived, the Merger may not occur or the closing may be delayed.

Boundless Bio and Serapha may mutually agree to waive the Nasdaq listing condition under the Merger Agreement, and if such condition is waived, the Combined Company’s stock may not be listed on Nasdaq following completion of the Merger.

Pursuant to the Merger Agreement, Boundless Bio agreed to use commercially reasonable efforts to maintain the listing of Boundless Bio’s common stock (Boundless Bio Common Stock) on Nasdaq until the Effective Time and, to the extent required by the rules and regulations of Nasdaq, to cause the shares of Boundless Bio Common Stock to be issued in connection with the Contemplated Transactions (as defined in the Merger Agreement) to be approved for listing on Nasdaq. The Merger Agreement also requires the parties, to the extent required by Nasdaq Marketplace Rule 5110, to use commercially reasonable efforts to cause the initial listing application for the Boundless Bio Common Stock and Boundless Bio preferred stock (together, the Boundless Bio Capital Stock) on Nasdaq (including any Boundless Bio Common Stock issuable upon conversion thereof) (the Nasdaq Listing Application) to be conditionally approved prior to the Effective Time (as defined in the Merger Agreement). Additionally, under the Merger Agreement, each of Boundless Bio’s and Serapha’s obligation to complete the Merger is subject to the satisfaction or waiver by each of the parties of various conditions, including that the Nasdaq Listing Application has been approved by Nasdaq. In the event that the Nasdaq Listing Application is not approved by Nasdaq, it is possible (although not likely) that Boundless Bio and Serapha may mutually agree to waive the applicable condition and nonetheless proceed with completing the Merger. If such condition is waived, Boundless Bio will not recirculate an updated proxy statement/prospectus to the one that will be provided in connection with matters related to the Merger, nor will it solicit a new vote of stockholders prior to proceeding with the Merger. If Boundless Bio proceeds with the Merger in these circumstances, the Combined Company’s stock may not be listed on Nasdaq.

If the Combined Company’s stock is not listed on Nasdaq following completion of the Merger, trading of the shares could be conducted in the over‑the‑counter market or on an electronic bulletin board established for unlisted securities such as the Pink Sheets or the OTC Bulletin Board. In such event, it is likely that there would be significantly less liquidity in the trading of the Combined Company common stock, decreases in institutional and other investor demand for the shares, a reduction in coverage by securities analysts, a decrease in market making activity and information available concerning trading prices and volume, and fewer broker dealers willing to execute trades in the Combined Company common stock. Also, it may be difficult for the Combined Company to raise additional capital if the Combined Company common stock is not listed on a major exchange. The occurrence of any of these events could result in a further decline in the market price of the Combined Company common stock and could have a material adverse effect on the Combined Company.

The Exchange Ratio for the Merger will not change or otherwise be adjusted based on the market price of Boundless Bio Common Stock.

Each then-outstanding share of Serapha common stock (Serapha Common Stock) and Serapha preferred stock (together, Serapha Capital Stock) (including shares of Serapha Common Stock issued in the Serapha Pre-Closing Financing), excluding any shares to be cancelled pursuant to the Merger Agreement, will be converted into the right to receive a number of shares of Boundless Bio Common Stock, equal to the Exchange Ratio (as defined in the Merger Agreement), (ii) each then-outstanding Serapha Option will be converted into and become an Assumed Option (as defined in the Merger Agreement) on the existing terms and conditions (including with respect to vesting and accelerated vesting), subject to adjustment as set forth in the Merger Agreement, and (iii) each then-outstanding Serapha warrant, including any Serapha pre-funded warrant issued pursuant to the Serapha Pre-Closing Financing, will be converted into an Assumed Warrant (as defined in the Merger Agreement), subject to adjustment as set forth in the Merger Agreement and the form of warrant. Applying the Exchange Ratio, the former Serapha securityholders immediately before the Merger are expected to own approximately 96.31% of the aggregate number of shares of the Combined Company’s capital stock following the Merger (on a fully‑diluted basis, and subject to dilution from any equity issued by Serapha after June 22, 2026 and before the closing), and Boundless Bio securityholders immediately before the Merger are expected to own approximately 3.69% of the aggregate number of shares of the Combined Company capital stock following the Merger (on a fully‑diluted basis), subject to certain assumptions, including, but not limited to, that Boundless Bio Net Cash (as defined in the Merger Agreement) as of Closing will be approximately $0, after giving effect to the Pre-Closing Dividend, which is expected to be approximately $44 to $48 million.

Any changes in the market price of Boundless Bio Common Stock before the completion of the Merger will not affect the number of shares Serapha stockholders will be entitled to receive pursuant to the Merger Agreement. However, the Exchange Ratio remains subject to equitable adjustment as set forth in the Merger Agreement for certain changes in the capitalization of Boundless Bio or Serapha, including any stock dividend, subdivision, reclassification, recapitalization, stock split, including the Nasdaq Reverse Split (as defined in the Merger Agreement) to the extent not previously taken into account in calculating the Exchange Ratio, combination or exchange of shares or other similar change. Therefore, if before the completion of the Merger, the market price of Boundless Bio Common Stock increases from the market price on the date of the Merger Agreement, then Serapha stockholders could receive merger consideration with substantially more value for their shares of Serapha Capital Stock than the parties had negotiated when they established the Exchange Ratio. Similarly, if before the completion of the Merger, the market price of Boundless Bio Common Stock declines from the market price on the date of the Merger Agreement, then Serapha stockholders could receive merger consideration with substantially lower value. The Merger Agreement does not include a price‑based termination right.

The issuance of Boundless Bio Common Stock, including the shares of Boundless Bio Common Stock issued in exchange for shares of Serapha Common Stock issued in the Serapha Pre‑Closing Financing, to Serapha stockholders pursuant to the Merger Agreement and the resulting change in control from the Merger, and the Nasdaq Reverse Split, must be approved by Boundless Bio stockholders, and the Merger Agreement and transactions contemplated thereby must be approved by the Serapha stockholders. Failure to obtain these approvals would prevent the closing of the Merger.

Before the Merger can be completed, Boundless Bio stockholders must approve, among other things, the Boundless Bio Stockholder Matters (as defined in the definition of “Parent Stockholder Matters” in the Merger Agreement), including the issuance of shares of Boundless Bio Common Stock representing (or convertible into) more than 20% of the shares of Boundless Bio Common Stock outstanding immediately prior to the Effective Time to Serapha stockholders in connection with the Contemplated Transactions, the change of control of Boundless Bio resulting from the Contemplated Transactions, the Nasdaq Reverse Split and the increase in authorized shares contemplated by the Parent Charter Amendment (as defined in the Merger Agreement). In addition, Serapha stockholders must adopt the Merger Agreement and approve the Merger and the related transactions. Failure to obtain the required stockholder approvals may result in a material delay in, or the abandonment of, the Merger. Any delay in completing the Merger may materially adversely affect the timing and benefits that are expected to be achieved from the Merger.

The Merger may be completed even though a material adverse effect may result from the announcement of the Merger, industry‑wide changes or other causes.

In general, neither Boundless Bio nor Serapha is obligated to complete the Merger if there is a “material adverse effect” (as defined in the Merger Agreement) affecting the other party between June 22, 2026, the date of the Merger Agreement, and the closing of the Merger. However, certain types of causes are excluded from the concept of a “material adverse effect.” Such exclusions include, but are not limited to, changes in general economic or political conditions, industry‑wide changes, changes resulting from the announcement of the Merger, natural disasters, pandemics, other public health events or force majeure events and changes in U.S. generally accepted accounting principles. Certain of these exclusions are subject to a limitation and will not apply to the extent Boundless Bio or Serapha, as applicable, is disproportionately affected relative to other similarly situated companies in the industries in which they operate. Therefore, if any of these events were to occur and adversely affect Boundless Bio or Serapha, the adverse effect may not constitute a “material adverse effect” under the Merger Agreement, and the other party may still be required to complete the closing of the Merger notwithstanding such “material adverse effect.” If any such adverse effects occur and Boundless Bio completes the closing of the Merger, the stock price of the Combined Company may suffer. This in turn may reduce the value of the Merger to the stockholders of Boundless Bio, Serapha or both.

If the Merger is not completed, Boundless Bio’s stock price may decline significantly.

The market price of Boundless Bio Common Stock is subject to significant fluctuations. Market prices for securities of pharmaceutical, biotechnology and other life science companies have historically been particularly volatile. In addition, the market price of Boundless Bio Common Stock will likely be volatile based on whether stockholders and other investors believe that Boundless Bio can complete the Merger or otherwise raise additional capital to support Boundless Bio’s operations if the Merger is not completed and another strategic transaction cannot be identified, negotiated and completed in a timely manner, if at all. The volatility of the market price of Boundless Bio Common Stock has been and may be exacerbated by low trading volume.

Additional factors that may cause the market price of Boundless Bio Common Stock to fluctuate include:

• announcements of the results of its clinical trials, discussions with regulators, and regulatory approval decisions;
• the entry into, or termination of, key agreements, including commercial partner agreements;
• announcements by commercial partners or competitors of new commercial products, clinical progress or lack thereof, significant contracts, commercial relationships or capital commitments;
• the loss of key employees;
• future sales of Boundless Bio Common Stock;
• general and industry‑specific economic conditions that may affect Boundless Bio’s research and development expenditures; and
• period‑to‑period fluctuations in financial results.

Moreover, the stock markets in general have experienced substantial volatility that has often been unrelated to the operating performance of individual companies. These broad market fluctuations may also adversely affect the trading price of Boundless Bio Common Stock. In the past, following periods of volatility in the market price of a company’s securities, stockholders have often instituted class action securities litigation against such companies.

If Boundless Bio completes the Merger, the Combined Company will need to raise additional capital, including by potentially issuing equity securities or incurring debt, which may cause significant dilution to the Combined Company’s stockholders or restrict the Combined Company’s operations.

In connection with the execution and delivery of the Merger Agreement, Serapha completed the Series A Financing, raising aggregate gross proceeds of approximately $138 million, and has entered into the Securities Purchase Agreement to complete the Serapha Pre-Closing Financing for aggregate gross proceeds of approximately $92 million. The closing of the Serapha Pre‑Closing Financing is a condition to the Closing, and the closing of the Serapha Pre‑Closing Financing is also conditioned upon satisfaction or waiver of the conditions to the Closing, as well as certain other conditions. The shares of Serapha Common Stock and the Serapha pre‑funded warrants issued in the Serapha Pre‑Closing Financing will result in dilution to all securityholders of the Combined Company (i.e., both Boundless Bio’s pre‑Merger securityholders and former Serapha securityholders).

Additional or alternative financing may not be available to the Combined Company when it is needed or may not be available on favorable terms. To the extent that the Combined Company raises additional capital by issuing equity securities, such financing will cause additional dilution to all securityholders of the Combined Company, including Boundless Bio’s pre‑Merger securityholders and Serapha’s former securityholders. It is also possible that the terms of any new equity securities may have preferences over the Combined Company common stock. Any debt financing the Combined Company enters into may involve covenants that restrict its operations. These restrictive covenants may include limitations on additional borrowing and specific restrictions on the use of the Combined Company’s assets, as well as prohibitions on its ability to create liens, pay dividends, redeem its stock or make investments. In addition, if the Combined Company raises additional funds through licensing arrangements, it may be necessary to grant licenses on terms that are not favorable to the Combined Company.

Some of Boundless Bio’s and Serapha’s directors and executive officers have interests in the Merger that are different from yours and that may influence them to support or approve the Merger without regard to your interests.

Directors and executive officers of Boundless Bio and Serapha have interests in the Merger that are different from, or in addition to, the interests of other Boundless Bio stockholders generally. These interests with respect to Boundless Bio’s directors and executive officers may include, among others, retention bonus payments, acceleration of previously issued equity awards, severance payments if employment is terminated in a qualifying termination in connection with the Merger and rights to continued indemnification, expense advancement and insurance coverage.

Further, certain current members of the Serapha Board of Directors may continue as directors of the Combined Company after the Effective Time, and, following the closing of the Merger, would be eligible to be compensated as non‑employee directors of the Combined Company. These interests, among other factors, may have influenced the directors and executive officers of each company to support or approve the Merger.

The Boundless Bio Board of Directors was aware of and considered those interests, among other matters, in reaching their decisions to approve and adopt the Merger Agreement, approve the Merger, and recommend the approval of the Merger Agreement to Boundless Bio stockholders. These interests, among other factors, may have influenced the directors and executive officers of each company to support or approve the Merger.

Boundless Bio stockholders and Serapha stockholders may not realize a benefit from the Merger commensurate with the ownership dilution they will experience in connection with the Merger, including the conversion of Serapha Common Stock issued in the Serapha Pre‑Closing Financing.

If the Combined Company is unable to realize the full strategic and financial benefits currently anticipated from the Merger, Boundless Bio stockholders and Serapha stockholders will have experienced substantial dilution of their ownership interests without receiving any commensurate benefit, or only receiving part of the commensurate benefit to the extent the Combined Company is able to realize only part of the strategic and financial benefits currently anticipated from the Merger.

Boundless Bio securityholders will generally have a reduced ownership and voting interest in, and will exercise less influence over the management of, the Combined Company following the completion of the Merger as compared to their current ownership and voting interests in the respective companies.

After the completion of the Merger, Boundless Bio’s current stockholders will generally own a smaller percentage of the Combined Company than their ownership of Boundless Bio prior to the Merger. Immediately after the Merger, Boundless Bio securityholders as of immediately prior to the Merger are expected to own approximately 3.69% of the outstanding shares of capital stock of the Combined Company (on a fully‑diluted basis, and subject to dilution from any equity issued by Serapha after June 22, 2026 and before the closing), and former holders of Serapha securities are expected to own approximately 96.31% of the outstanding shares of capital stock of the Combined Company (on a fully‑diluted basis), subject to certain assumptions, including, but not limited to, Boundless Bio Net Cash as of closing being approximately $0, after giving effect to the Pre-Closing Dividend, which is expected to be approximately $44 to $48 million.

Certain provisions of the Merger Agreement may discourage third parties from submitting competing proposals, including proposals that may be superior to the transactions contemplated by the Merger Agreement.

While the Merger Agreement is in effect, each of Boundless Bio and Serapha is generally prohibited from, among other things, soliciting, initiating or knowingly encouraging, inducing or facilitating the communication, making, submission or announcement of any acquisition proposal or acquisition inquiry. In addition, Boundless Bio’s current directors and executive officers have entered into support agreements pursuant to the terms of the Merger Agreement, and as an inducement to Serapha’s willingness to enter into the Merger Agreement, by which they have agreed to vote all of their shares of Boundless Bio Capital Stock in favor of the Contemplated Transactions and against any competing proposals, subject to certain limited exceptions. These provisions could discourage a potential competing acquirer from considering or proposing an acquisition or merger, even if it were prepared to pay consideration with a higher value than that implied by the merger consideration in the combination.

Because the lack of a public market for Serapha Common Stock makes it difficult to evaluate the fair market value of its capital stock, the value of Boundless Bio Common Stock to be issued to Serapha stockholders may be more or less than the fair market value of Serapha Common Stock.

The outstanding capital stock of Serapha is privately held and is not traded on any public market. The lack of a public market makes it difficult to determine the fair market value of Serapha capital stock. Because the percentage of Boundless Bio’s equity to be issued to Serapha stockholders was determined based on negotiations between the parties, it is possible that the value of Boundless Bio Common Stock to be issued to Serapha stockholders will be more or less than the fair market value of Serapha Capital Stock.

Lawsuits may be filed against Boundless Bio, Serapha, or any of the members of their respective boards of directors arising out of the Merger, which may delay or prevent the Merger.

Putative stockholder complaints, including stockholder class action complaints, and other complaints may be filed against Boundless Bio, the Boundless Bio Board of Directors, Serapha, the Serapha Board of Directors and others in connection with the transactions contemplated by the Merger Agreement. The outcome of litigation is uncertain, and Boundless Bio or Serapha may not be successful in defending against any such future claims. Lawsuits that may be filed against Boundless Bio, the Boundless Bio Board of Directors, Serapha, or the Serapha Board of Directors could delay or prevent the Merger, divert the attention of Boundless Bio’s and Serapha’s management and employees from their day‑to‑day business and otherwise adversely affect Boundless Bio and Serapha financially.

Boundless Bio has never paid and, other than in connection with the Merger with Serapha, does not intend to pay any cash dividends in the foreseeable future.

Boundless Bio has never paid cash dividends on any of its capital stock. Other than the Pre-Closing Dividend in connection with the Merger, Boundless Bio does not currently anticipate declaring or paying cash dividends on its capital stock in the foreseeable future.

The amount of the Pre-Closing Dividend may change based on the timing to complete the Merger, changes in operating expense levels and other factors.

The Pre-Closing Dividend, which is expected to be approximately $44 to $48 million, is based on Boundless Bio's estimate of the amount by which Boundless Bio Net Cash, as determined pursuant to the terms of the Merger Agreement, will exceed $0. The actual amount of the Pre-Closing Dividend may be higher or lower than the estimated amount and is subject to change based on the timing to complete the Merger, changes in Boundless Bio's operating expense levels, transaction-related costs and expenses, and other adjustments to the components of Boundless Bio Net Cash as set forth in the Merger Agreement. There can be no assurance that the actual amount of the Pre-Closing Dividend will not materially differ from the current estimate.

If Boundless Bio does not successfully complete the Merger or another strategic transaction, the Boundless Bio Board of Directors may decide to pursue a dissolution and liquidation of Boundless Bio. In such an event, the amount of cash available for distribution to Boundless Bio stockholders will depend heavily on the timing of such liquidation as well as the amount of cash that will need to be reserved for commitments and contingent liabilities, as to which Boundless Bio can give you no assurance.

There can be no assurance that the Merger will be completed. If the Merger is not completed, the Boundless Bio Board of Directors may decide to pursue a dissolution and liquidation of Boundless Bio. In such an event, the amount of cash available for distribution to Boundless Bio stockholders will depend heavily on the timing of such decision and, ultimately, such liquidation, since the amount of cash available for distribution continues to decrease as Boundless Bio funds its operations while pursuing the Merger. In addition, if the Boundless Bio Board of Directors were to approve and recommend, and Boundless Bio stockholders were to approve, a dissolution and liquidation of Boundless Bio, Boundless Bio would be required under Delaware law to pay Boundless Bio’s outstanding obligations, as well as to make reasonable provision for contingent and unknown obligations, prior to making any distributions in liquidation to stockholders. Boundless Bio’s commitments and contingent liabilities may include obligations under Boundless Bio’s employment and related agreements with certain employees that provide for severance and other payments following a termination of employment occurring for various reasons, including a change in control of Boundless Bio, litigation against Boundless Bio, and other various claims and legal actions arising in the ordinary course of business, and other unexpected and/or contingent liabilities. As a result of this requirement, a portion of Boundless Bio’s assets would need to be reserved pending the resolution of such obligations.

In addition, Boundless Bio may be subject to litigation or other claims related to a dissolution and liquidation of Boundless Bio. If a dissolution and liquidation were to be pursued, the Boundless Bio Board of Directors, in consultation with Boundless Bio’s advisors, would need to evaluate these matters and make a determination about a reasonable amount to reserve. Accordingly, holders of Boundless Bio Common Stock could lose all or a significant portion of their investment in the event of liquidation, dissolution or winding up of Boundless Bio. A liquidation would be a lengthy and uncertain process with no assurance of any value ever being returned to Boundless Bio stockholders.

Boundless Bio and its stockholders will not have any right to make damage claims against Serapha for the breach of any representation, warranty or covenant made by Serapha in the Merger Agreement.

The Merger Agreement provides that all of the representations, warranties and covenants of the parties contained therein shall not survive the Closing, except for those covenants contained therein that by their terms survive the Closing. Accordingly, there are no remedies available to the parties with respect to any breach of the representations, warranties, covenants or agreements of the parties to the Merger Agreement after the Closing, except for covenants that by their terms survive the Closing. As a result, Boundless Bio and its stockholders will have no remedy available to it if the Merger is completed and it is later revealed that there was a breach of any of the representations, warranties and covenants made by Serapha at the time of the Merger.

Additionally, Boundless Bio cannot assure you that the due diligence conducted in relation to Serapha has identified all material issues or risks associated with Serapha, its business or the industry in which it competes. Furthermore, Boundless Bio cannot assure you that factors outside of its or Serapha’s control will not later arise, or that any previously identified risks will not materialize in a manner inconsistent with the preliminary analysis. As a result of these factors, following the Closing, the Combined Company may be exposed to liabilities and incur additional costs and expenses and it may be forced to later write‑down or write off assets, restructure its operations, or incur impairment or other charges. Boundless Bio and its stockholders have no indemnification rights against Serapha or its stockholders under the Merger Agreement. Accordingly, any stockholders of Boundless Bio that remain stockholders of the Combined Company following the Merger could suffer a reduction in the value of their securities. Such stockholders are unlikely to have a remedy for such reduction in value unless they are able to successfully claim that the reduction was due to the breach by Boundless Bio’s directors or officers of a duty of care or other fiduciary duty owed to them, or if they are able to successfully bring a private claim under securities laws that the registration statement or proxy statement/prospectus relating to the Merger contained an actionable material misstatement or material omission.