Serapha Bio to take control of Boundless Bio (NASDAQ: BOLD) in cash-dividend merger

Rhea-AI Filing Summary

Boundless Bio agreed to an all-stock merger with private biotech Serapha Bio, creating a combined company focused on Serapha’s in vivo base-editing therapy SERP-01 for Alpha‑1 Antitrypsin Deficiency. Based on the merger exchange ratio, Serapha equityholders are expected to own about 96.3% of the combined company on a fully diluted basis, with Boundless Bio equityholders owning about 3.7%.

Before closing, Boundless Bio may declare a cash dividend to its pre‑merger stockholders, currently expected to total roughly $44–$48 million, reflecting excess net cash. Serapha has already raised approximately $138 million in Series A preferred financing and secured an additional $92 million PIPE commitment, giving the combined company expected cash runway into the second half of 2029.

In connection with the merger, Boundless Bio will cut about 75% of its workforce, incurring one‑time charges of approximately $3.0–$5.0 million, and will wind down its BBI‑940 oncology program after early clinical data showed human exposure below preclinical expectations. CEO Zachary Hornby and several senior R&D leaders will depart, with Chief Legal Officer Jessica Oien becoming principal executive officer during the transition. All outstanding employee stock options have been fully vested and their exercise period extended, while underwater Boundless Bio options with exercise prices above $8.00 will be cancelled at closing.

Positive

• Serapha has secured approximately $230 million in private financing (about $138 million Series A plus a $92 million PIPE), giving the combined company projected cash runway into the second half of 2029 through key SERP‑01 clinical milestones.

Negative

• Boundless Bio will reduce its workforce by approximately 75% and discontinue further development of BBI‑940 after unfavorable pharmacokinetic exposure data, indicating a major strategic retreat from its original oncology focus.

Insights

Biotech M&A and capital markets analyst

Reverse-merger style deal shifts control to Serapha while returning cash to Boundless holders.

The transaction effectively turns Boundless Bio into a public-market vehicle for Serapha Bio. Serapha equityholders are expected to control about 96.3% of the combined company, while Boundless stockholders retain a small equity stake plus a pre-closing cash dividend expected around $44–$48 million.

Serapha brings a lead base-editing asset, SERP‑01, backed by a $138 million Series A and a $92 million PIPE, with combined cash projected to fund operations into the second half of 2029. That implies runway through planned Phase 2 completion and Phase 3 initiation, but execution depends on regulatory progress and continued favorable clinical data.

For Boundless, the deal follows disappointing pharmacokinetic data for oncology asset BBI‑940, a roughly 75% workforce reduction and a leadership transition. Investors will watch upcoming Form S‑4 and proxy materials, which will detail final exchange mechanics, dividend amount and risk factors tied to SERP‑01’s clinical and regulatory pathway.

8-K Event Classification

8 items: 1.01, 2.05, 3.02, 5.01, 5.02, 7.01, 8.01, 9.01

8 items

Item 1.01 Entry into a Material Definitive Agreement Business

The company signed a significant contract such as a merger agreement, credit facility, or major partnership.

Item 2.05 Costs Associated with Exit or Disposal Activities Financial

The company committed to an exit plan involving layoffs, facility closures, or restructuring charges.

Item 3.02 Unregistered Sales of Equity Securities Securities

The company sold equity securities in a private placement or other unregistered transaction.

Item 5.01 Changes in Control of Registrant Governance

A change in control of the company occurred, such as through a merger, takeover, or management buyout.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers Governance

Key personnel changes including departures, elections, or appointments of directors and executive officers.

Item 7.01 Regulation FD Disclosure Disclosure

Material non-public information disclosed under Regulation Fair Disclosure, often investor presentations or guidance.

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

Item 9.01 Financial Statements and Exhibits Exhibits

Financial statements, pro forma financial information, and exhibit attachments filed with this report.

Key Figures

Serapha Series A financing: $138,000,000 Serapha PIPE commitment: $92,000,000 Total private placement: $230,000,000 +5 more

8 metrics

Serapha Series A financing $138,000,000 Aggregate purchase price for Serapha Series A preferred stock

Serapha PIPE commitment $92,000,000 Aggregate purchase price for Pre-Closing Financing PIPE Securities

Total private placement $230,000,000 Concurrent private placement supporting merger and SERP-01 development

Expected cash dividend $44–$48 million Pre-closing dividend to pre-merger Boundless Bio stockholders

Workforce reduction Approximately 75% Portion of Boundless Bio workforce to be laid off

Restructuring charges $3.0–$5.0 million One-time costs tied to workforce reduction

Serapha ownership post-merger Approximately 96.3% Pro forma fully diluted ownership of combined company

Boundless Bio ownership post-merger Approximately 3.7% Pre-merger Boundless equityholders’ expected stake in combined company

Key Terms

Pre-Closing Financing, Exchange Ratio, Regenerative Medicine Advanced Therapy Designation, investigator-initiated trial, +2 more

6 terms

Pre-Closing Financing financial

"pre-closing shares of Serapha capital stock (the PIPE Securities) for an aggregate purchase price of approximately $92,000,000 in a private placement (the Pre-Closing Financing)"

Exchange Ratio financial

"calculated in accordance with the exchange ratio as set forth in the Merger Agreement (the Exchange Ratio)"

The exchange ratio is the number used to decide how many shares of one company you get for each share you own in another company during a merger or acquisition. It’s like a recipe that tells you how to swap shares fairly, ensuring both companies’ values are balanced. This ratio matters because it determines how ownership divides between the companies' shareholders.

Regenerative Medicine Advanced Therapy Designation regulatory

"SERP-01 has received Orphan Drug Designation and Regenerative Medicine Advanced Therapy Designation from the FDA"

A U.S. regulatory designation that expedites development and review of certain cell, gene and tissue-based therapies designed to repair, replace or restore damaged tissue or organ function. It matters to investors because receiving the designation can shorten the path to approval, increase interaction with regulators, and make a program more attractive to partners or buyers — like giving a promising product a VIP pass through regulatory traffic, reducing time and risk to potential revenue.

investigator-initiated trial medical

"YolTech has been enrolling AATD patients in an Investigator-Initiated Trial (IIT) in Renji Hospital, Shanghai, China"

A clinical study led and managed by an independent researcher or physician rather than the company that makes the drug or device; the investigator designs the protocol, runs the study at their site(s), and often controls the data even if the company supplies the product or funding. For investors, these trials can produce important third‑party validation or new uses for a product — like an independent test drive revealing strengths or limits — and their outcomes can change a product’s commercial and regulatory prospects.

material adverse effect regulatory

"no Boundless Bio material adverse effect or Serapha material adverse effect since the date of the Merger Agreement"

A material adverse effect is a significant negative change or event that substantially reduces a company’s business, financial condition, or future prospects — think of it like a sudden major engine failure that makes a car unreliable. Investors care because such an event can lower expected profits, trigger contract clauses (allowing counterparties to renegotiate or walk away), and prompt swift stock-price reassessment based on the higher risk and uncertainty.

termination fee financial

"Serapha may be required to pay to Boundless Bio a termination fee of $1,000,000"

A termination fee is a payment required if one party ends a contract before its agreed-upon end date. It acts like a penalty or compensation to the other party for canceling early, similar to a fee you might pay for breaking a lease or canceling a service contract. For investors, it matters because it can influence a company's decisions and financial obligations related to ending agreements prematurely.

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Understanding 8-K Material Events →

false 0001782303 0001782303 2026-06-22 2026-06-22

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): June 22, 2026

Boundless Bio, Inc.

(Exact Name of Registrant as Specified in Its Charter)

Delaware		001-41989		83-0751369
(State or Other Jurisdiction of Incorporation)		(Commission File Number)		(IRS Employer Identification No.)

11099 North Torrey Pines Road, Suite 150
La Jolla, California		92037
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s Telephone Number, Including Area Code: (858) 766-9912

N/A

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☒ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, par value $0.0001 per share		BOLD		Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

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

Item 1.01 Entry into a Material Definitive Agreement.

Merger Agreement

On June 22, 2026, Boundless Bio, Inc., a Delaware corporation (Boundless Bio), entered into an Agreement and Plan of Merger and Reorganization (the Merger Agreement) with Serapha Bio, Inc., a Delaware corporation (Serapha), and Boulder Merger Sub Corp., a Delaware corporation and wholly owned subsidiary of Boundless Bio (Merger Sub). Upon the terms and subject to the satisfaction of the conditions described in the Merger Agreement, Merger Sub will be merged with and into Serapha, with Serapha surviving as a wholly owned subsidiary of Boundless Bio (the Merger and, together with all of the other transactions contemplated by the Merger Agreement, the Contemplated Transactions). The Merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended.

Subject to the terms and conditions of the Merger Agreement, at the effective time of the Merger (the Effective Time), each then-outstanding share of common stock or preferred stock of Serapha (including any shares of capital stock issued pursuant to the Pre-Closing Financing (as defined below)) outstanding immediately prior to the Effective Time (each such share, a Serapha Share) (excluding any share described in clause (b) below) will be converted into the right to receive a number of shares of Boundless Bio common stock, par value $0.0001 per share (Boundless Bio Common Stock), calculated in accordance with the exchange ratio as set forth in the Merger Agreement (the Exchange Ratio). Each then-outstanding option to purchase Serapha Shares will be converted into an option to purchase Boundless Bio Common Stock, and each then-outstanding warrant to purchase shares of Serapha capital stock (including any pre-funded warrants issued pursuant to the Pre-Closing Financing) will be converted into a warrant to purchase shares of Boundless Bio Common Stock, in each case subject to adjustment as set forth in the Merger Agreement. Each option to purchase Boundless Bio Common Stock outstanding immediately prior to the Effective Time with an exercise price greater than $8.00 will be cancelled for no consideration.

Pursuant to the Exchange Ratio formula in the Merger Agreement, upon the Closing (as defined in the Merger Agreement), on a pro forma basis and based upon the number of shares of Boundless Bio Common Stock expected to be issued in the Merger (including following the consummation of the Pre-Closing Financing and Serapha’s Series A preferred financing), pre-Merger equityholders of Serapha are expected to own approximately 96.31% of the combined company and pre-Merger equityholders of Boundless Bio are expected to own approximately 3.69% of the combined company, in each case, calculated on a fully diluted basis. The percentage of the combined company that each party’s equityholders will own following the Closing is subject to certain adjustments as described in the Merger Agreement, including the final amount of the Boundless Bio Net Cash at Closing. Prior to the Closing, Boundless Bio may declare a cash dividend (the Pre-Closing Dividend) to holders of Boundless Bio Common Stock outstanding prior to the Effective Time up to an amount equal to the aggregate of Boundless Bio’s reasonable, good faith approximation of the amount by which Boundless Bio Net Cash will exceed $0, subject to the terms of the Merger Agreement.

The Merger Agreement contains representations and warranties of the parties regarding their respective businesses. The Merger Agreement also contains certain covenants made by each of Boundless Bio and Serapha, including non-solicitation restrictions binding each party (and subject to certain exceptions as further described in the Merger Agreement) and its representatives and restrictions on the operation of each party’s business between the date of the Merger Agreement and the Closing.

In connection with the Merger, Boundless Bio will prepare and file a registration statement on Form S-4, which will contain a proxy statement and prospectus, to register the shares issued pursuant to the Merger Agreement (the Form S-4) and will seek the approval of Boundless Bio’s stockholders of, among other matters, (i) the issuance of the shares of Boundless Bio Common Stock pursuant to the Merger and the change of control of Boundless Bio resulting from the Merger, (ii) a reverse stock split of Boundless Bio Common Stock at a ratio to be mutually agreed upon by Boundless Bio and Serapha and (iii) an increase in the number of authorized shares of Boundless Bio Common Stock to a number determined by Serapha (the Boundless Bio Stockholder Matters).

The Closing is subject to certain closing conditions, including: (i) the approval by the Boundless Bio stockholders of the Boundless Bio Stockholder Matters; (ii) approval by the requisite Serapha stockholders of the adoption and approval of the Merger Agreement and the Contemplated Transactions; (iii) the existing shares of Boundless Bio Common Stock having been continually listed on the Nasdaq Stock Market (Nasdaq) and Nasdaq’s

approval of the initial listing application of shares of Boundless Bio Common Stock to be issued in the Merger; (iv) the Securities Purchase Agreement (as defined below) being in full force and effect with cash gross proceeds of not less than $200 million having been received by Serapha; (v) the effectiveness of the Form S-4; (vi) that certain Exclusive License Agreement, dated June 12, 2026, by and between Serapha and YolTech Therapeutics Co., Ltd. being in full force and effect; and (vii) no legal restraint. The Closing is also subject to other specified customary closing conditions of each party, including the accuracy of each party’s representations and warranties, subject to applicable materiality qualifications, compliance by each party with its covenants under the Merger Agreement in all material respects, respectively, delivery of certain customary closing documents by each of Boundless Bio and Serapha, and no Boundless Bio material adverse effect or Serapha material adverse effect since the date of the Merger Agreement that is continuing, respectively.

The Merger Agreement contains certain termination rights of each of Boundless Bio and Serapha. Upon termination of the Merger Agreement in certain circumstances, Serapha may be required to pay to Boundless Bio a termination fee of $1,000,000, including (i) where Serapha’s board of directors changes or withdraws its recommendation in favor of the Merger or recommends to enter into an alternative transaction or (ii) if (a) the Merger Agreement is terminated because Serapha (1) fails to obtain the requisite stockholder approval of the Merger Agreement and the Contemplated Transactions or (2) breaches the Merger Agreement, (b) an alternative acquisition proposal was announced or disclosed prior to obtaining Serapha’s stockholder approval, and (c) within 12 months of the termination of the Merger Agreement, Serapha enters into a definitive agreement with respect to an alternative transaction.

Upon termination of the Merger Agreement in certain circumstances, a termination fee of $1,000,000 may be payable by Boundless Bio to Serapha if (i) the Merger Agreement is terminated because Boundless Bio fails to obtain the requisite stockholder approval of the Boundless Bio Stockholder Matters or a change by board of directors of Boundless Bio in its recommendation regarding the Merger or other Parent Triggering Event (as defined in the Merger Agreement) occurs, (ii) an alternative acquisition proposal was announced or disclosed prior to such termination, and (iii) within 12 months of the termination of the Merger Agreement, Boundless Bio enters into a definitive agreement with respect to an alternative transaction.

The transaction has received approval by the boards of directors of the parties and is expected to close in the fourth quarter of 2026, subject to certain closing conditions, including, among other things, approval by the stockholders of each company and the satisfaction of customary closing conditions.

At the Effective Time, the board of directors of the combined company is expected to consist of a number of directors determined by Serapha, all of whom will be designated by Serapha, and the executive officers of the combined company will consist of officers determined by Serapha.

Series A Preferred Financing

In connection with the execution and delivery of the Merger Agreement, certain institutional and accredited investors entered into a Series A stock purchase agreement with Serapha, pursuant to which such persons invested in a private placement of Serapha’s Series A preferred stock for an aggregate purchase price of approximately $138,000,000.

Pre-Closing Financing

Concurrently with the execution and delivery of the Merger Agreement, certain institutional and accredited investors have also entered into a securities purchase agreement with Serapha (the Securities Purchase Agreement), pursuant to which such persons have agreed to purchase, in the amounts set forth therein, pre-closing shares of Serapha capital stock (the PIPE Securities) for an aggregate purchase price of approximately $92,000,000 in a private placement (the Pre-Closing Financing). The closing of the Pre-Closing Financing is conditioned on the satisfaction or waiver of the conditions set forth in the Merger Agreement (in addition to other customary closing conditions) and is expected to occur substantially concurrently with the Closing of the Merger and prior to the Effective Time.

Pursuant to the terms of the Securities Purchase Agreement, at closing of the Pre-Closing Financing, Serapha will enter into a Registration Rights Agreement (the Registration Rights Agreement) with the purchasers of the PIPE Securities, which will provide for the registration and resale of Boundless Bio Common Stock issuable in exchange for the PIPE Securities upon the Closing of the Merger, in accordance with the terms of the Registration Rights Agreement.

The foregoing descriptions of the Securities Purchase Agreement and Registration Rights Agreement do not purport to be complete and are qualified in their entirety by reference to the Securities Purchase Agreement, and the Registration Rights Agreement the forms of which are filed as Exhibits 10.3 and 10.4, respectively, to this Current Report on Form 8-K and are incorporated herein by reference.

Support Agreements

Concurrently with the execution of the Merger Agreement, the executive officers and directors of Boundless Bio holding approximately 1.7% of the outstanding Boundless Bio capital stock entered into support agreements (the Boundless Bio Support Agreements) in favor of Serapha, providing among other things, that such officers and directors (x) will vote all of their shares of Boundless Bio capital stock, among other things: (i) in favor of approving the Contemplated Transactions, including the Boundless Bio Stockholder Matters and the other actions contemplated by the Merger Agreement, (ii) against any proposal made in opposition to, or in competition with, the Merger Agreement or the Merger and (iii) against any acquisition proposal involving a third party and (y) will not solicit or negotiate alternative acquisition proposals or inquiries in their capacities as stockholders of Boundless Bio.

Concurrently with the execution of the Merger Agreement, certain officers, directors and stockholders of Serapha holding approximately 65% of the outstanding Serapha capital stock entered into support agreements (the Serapha Support Agreements and, together with Boundless Bio Support Agreements, the Support Agreements) in favor of Boundless Bio, providing among other things, that such executive officers, directors and stockholders (x) will vote all of their shares of Serapha capital stock, among other things: (i) in favor of adopting the Merger Agreement and approving the Merger, the other Contemplated Transactions and the other actions contemplated by the Merger Agreement, (ii) against any proposal made in opposition to, or in competition with, the Merger Agreement or the Merger and (iii) against any acquisition proposal involving a third party and (y) will not solicit or negotiate alternative acquisition proposals or inquiries in their capacities as stockholders of Serapha.

In accordance with the terms of the Merger Agreement, the executive officers and directors of Serapha immediately prior to the Effective Time will enter into lock-up agreements, pursuant to which, subject to specified exceptions, such persons will be subject to certain restrictions on transfers of the shares of Boundless Bio Common Stock beneficially held by such persons or such persons’ family members (other than shares received as a result of the conversion of shares received in the Pre-Closing Financing) for the 180-day period following the Effective Time.

The foregoing descriptions of the Merger Agreement, the form of Boundless Bio Support Agreement and the form of the Serapha Support Agreement (collectively, the Agreements), are not complete and are qualified in their entirety by reference to those Agreements, which are filed as Exhibits 2.1, 10.1 and 10.2, respectively, to this Current Report on Form 8-K and incorporated herein by reference. In particular, the assertions embodied in the representations and warranties contained in the Merger Agreement are qualified by information in confidential disclosure schedules provided by each of Boundless Bio and Serapha in connection with the signing of the Merger Agreement. These confidential disclosure schedules contain information that modifies, qualifies and creates exceptions to the representations and warranties and certain covenants set forth in the Merger Agreement. Moreover, certain representations and warranties in the Agreements were used for the purpose of allocating risk between the parties thereto rather than establishing matters as facts. Accordingly, the representations and warranties may not describe the actual state of affairs at the date they were made or at any other time, and investors should not rely on them as statements of fact.

Item 2.05 Costs Associated with Exit or Disposal Activities.

On June 23, 2026, Boundless Bio, in connection with signing of the Merger Agreement, announced a workforce reduction of approximately 75% of Boundless Bio’s workforce. Boundless Bio expects to incur one-time

costs of approximately $3.0 million to $5.0 million in connection with the workforce reduction primarily related to one-time termination benefits (some of which are contractual), including severance and healthcare related benefits. Boundless Bio estimates that the workforce reduction will be substantially completed in the third quarter of 2026 and that the majority of the related charges will be recognized in Boundless Bio’s third quarter financial results of operations.

The estimate of costs that Boundless Bio expects to incur and the timing thereof are subject to a number of assumptions, and actual results may differ materially. Boundless Bio may also incur additional costs not currently contemplated due to events that may occur as a result of, or that are associated with, the implementation of the workforce reduction.

Item 3.02 Unregistered Sales of Equity Securities.

To the extent required by this Item, the information included in Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

The shares of Serapha capital stock to be issued in the Pre-Closing Financing will be issued in private placements exempt from registration under Section 4(a)(2) of the Securities Act of 1933, as amended (the Securities Act), and/or Regulation D promulgated thereunder, because the offer and sale of such securities does not involve a “public offering” as defined in Section 4(a)(2) of the Securities Act, and other applicable requirements were met. Neither this Current Report on Form 8-K nor any of the exhibits attached hereto is an offer to sell or the solicitation of an offer to buy the shares of Serapha capital stock or any other securities of Boundless Bio or Serapha.

Item 5.01 Changes in Control of Registrant.

To the extent required by this Item, the information included in Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

To the extent required by this Item, the information included in Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

Executive Transitions

In connection with the Contemplated Transaction, effective July 1, 2026, Zachary D. Hornby will cease his role as President and Chief Executive Officer, and as a member of the board of directors of Boundless Bio. Furthermore, effective July 1, 2026, the board of directors of Boundless Bio reduced the size of the board of directors of Boundless Bio from five to four members to remove the vacancy on the board of directors of Boundless Bio created by Mr. Hornby’s resignation from the board of directors.

In connection with Mr. Hornby’s departure, effective July 1, 2026, Jessica Oien, Boundless Bio’s Chief Legal Officer and Corporate Secretary, was appointed to serve as Boundless Bio’s President and “principal executive officer,” in addition to maintaining her current responsibilities as Chief Legal Officer and Corporate Secretary.

The full biography and other information with respect to Ms. Oien required by Item 5.02(c) of Form 8-K are included in Boundless Bio’s proxy statement on Schedule 14A for the 2026 annual meeting of stockholders filed with the SEC on April 28, 2026 under the headings “Executive Officers” and “Certain Relationships and Related Party Transactions,” and such biography and information are incorporated herein by reference.

In connection with the Contemplated Transaction, effective July 1, 2026, Christian Hassig, Ph.D., will cease his role as Boundless Bio’s Chief Scientific Officer, and Robert Doebele, M.D., Ph.D., will also cease his role as Boundless Bio’s Chief Medical Officer.

Separation Agreements and Consulting Agreements with Mr. Hornby and Drs. Doebele and Hassig

In connection with their departures, each of Mr. Hornby and Drs. Doebele and Hassig are expected to enter into a separation agreement with Boundless Bio, effective as of July 1, 2026 (the Separation Agreements). The Separation Agreements will contain a release of claims and will provide for the following severance benefits, subject to, among others, : (i) a lump sum cash severance payment in an amount representing nine months’ (twelve months’ for Mr. Hornby) base salary, (ii) subject to and conditioned upon the occurrence of the Merger, an additional true-up severance payment in an amount representing twelve months’ (eighteen months’ for Mr. Hornby) base salary plus 1.0 times (1.5 times for Mr. Hornby) their respective target bonuses for 2026 less the amount of cash severance previously paid, payable upon the closing of the Merger, and (iii) nine months (twelve months for Mr. Hornby) of COBRA premium payments (increased to twelve months (eighteen months for Mr. Hornby) in the event of the closing of the Merger).

In addition, each of Mr. Hornby and Drs. Doebele and Hassig entered into a consulting agreement with Boundless Bio, pursuant to which they will provide limited transitional services to Boundless Bio.

Amended and Restated Offer Letters with Ms. Oien and David Hinkle

In connection with the Merger, on June 22, 2026, each of Ms. Oien and David Hinkle entered into an amended and restated offer letter with Boundless Bio, to be effective as of July 1, 2026 (the A&R Offer Letters). The A&R Offer Letters provide for, among others, the following additional compensation: (i) in addition to receiving their current base salaries, additional monthly compensation of $50,000 for Ms. Oien and $25,000 for Mr. Hinkle, (ii) a transaction bonus accruing in the amount of $50,000 for Ms. Oien and $25,000 for Mr. Hinkle for each month of employment following July 1, 2026 (provided, that, the transaction bonuses will be capped at $500,000 for Ms. Oien and $250,000 for Mr. Hinkle), and (iii) for Ms. Oien, an additional one-time bonus of $50,000 in the event the Merger Agreement is terminated and Boundless Bio enters into a binding term sheet with a new counterparty to effectuate a similar transaction. The transaction bonuses will be payable to Ms. Oien and Mr. Hinkle upon the closing of the Merger, or, if earlier, upon a termination by Boundless Bio without cause, their resignation for good reason or their death or disability. Neither Ms. Oien nor Mr. Hinkle will be eligible to earn any annual performance bonus for 2026 or thereafter. In addition, Ms. Oien and Mr. Hinkle remain entitled to their existing severance benefits under the Boundless Bio Severance and Change in Control Plan, which severance benefits will be paid upon the closing of the Merger, or if earlier, certain qualifying terminations or employment.

Acceleration of Outstanding Options; Extension of Post-Termination Exercise Period of Options; Acceleration of Premium End Date

Concurrently with the signing of the Merger Agreement, all outstanding stock options to purchase shares of the Boundless Bio Common Stock (the Boundless Options) previously granted to Boundless Bio’s employees, executive officers, directors, and consultants under the 2024 Incentive Award Plan and 2018 Equity Incentive Plan became fully vested and exercisable immediately. In addition, the exercise period of all outstanding Boundless Options was extended to provide that such Options will remain exercisable until the latest to occur of (i) March 31, 2027 (unless the Closing Date occurs prior to such date, in which case the exercise period will expire on the date that is three months following the Closing Date) or (ii) such later date provided in the applicable option agreement. With respect to any outstanding Boundless Options that were repriced by Boundless Bio effective August 19, 2024, the premium end date of the Boundless Options was accelerated to the date of the signing of the Merger Agreement.

Item 7.01 Regulation FD Disclosure.

On June 23, 2026, Boundless Bio and Serapha issued a joint press release announcing the entry into the Merger Agreement. The press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

On June 23, 2026, Boundless Bio and Serapha released a pre-recorded call featuring representatives from both companies discussing the Contemplated Transactions. The pre-recorded call can be accessed by visiting www.boundlessbio.com. Furnished as Exhibit 99.2 hereto is the transcript of the pre-recorded call.

The information in this Item 7.01, including Exhibits 99.1, and 99.2 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the Exchange Act), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 8.01 Other Events.

Based on preliminary exposure data obtained in the early dose escalation cohorts of the KOMODO-1 clinical trial, Boundless Bio 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.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

Exhibit Number		Description
2.1+		Agreement and Plan of Merger and Reorganization, dated June 22, 2026, by and among Boundless Bio, Inc., Boulder Merger Sub Corp., and Serapha Bio, Inc.
10.1		Form of Boundless Bio Support Agreement.
10.2		Form of Serapha Support Agreement.
10.3		Form of Securities Purchase Agreement.
10.4		Form of Registration Rights Agreement.
99.1		Joint Press Release, dated June 23, 2026.
99.2		Pre-Recorded Call Transcript, dated June 23, 2026.
104		Cover Page Interactive Data File (embedded within the Inline XBRL document)

+ Registrant has omitted schedules and exhibits pursuant to Item 601(b)(2) of Regulation S-K. The Registrant agrees to furnish supplementally a copy of the omitted schedules and exhibits to the SEC upon request.

Forward-Looking Statements

This Current Report on Form 8-K contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to, statements regarding the structure and intended tax treatment of the proposed Merger; expectations regarding the ownership structure of the combined company; the expected management team of the combined company; expectations regarding the structure, size, timing and completion of the Pre-Closing Financing and Nasdaq listing; the potential Pre-Closing Dividend; expectations regarding the clinical development of BBI-940; and other statements that are not historical fact. These forward-looking statements are made as of the date they were first issued, and were based on the then-current expectations, estimates, forecasts, and projections, as well as the beliefs and assumptions of management. There can be no assurance that future developments affecting Boundless Bio, Serapha or the Contemplated Transactions will be those that have been anticipated.

Forward-looking statements are subject to a number of risks and uncertainties, many of which involve factors or circumstances that are beyond Boundless Bio’s and Serapha’s control. Boundless Bio’s actual results could differ materially from those stated or implied in forward-looking statements due to a number of factors, including but not limited to (i) the risk that the conditions to the Closing are not satisfied; (ii) uncertainties as to the timing of the consummation of the proposed Merger and the ability of each of Boundless Bio and Serapha to consummate the proposed Merger; (iii) risks related to Boundless Bio’s ability to manage its operating expenses and its expenses associated with the proposed Merger pending Closing; (iv) risks related to the failure or delay in obtaining required approvals from any governmental or regulatory entity necessary to consummate the proposed Merger, if applicable; (v) the risk that as a result of adjustments to the Exchange Ratio, Boundless Bio’s stockholders and Serapha’s stockholders could own more or less of the combined company than is currently anticipated; (vi) risks related to the

market price of Boundless Bio Common Stock relative to the value suggested by the Exchange Ratio and the anticipated cash dividend; (vii) unexpected costs, charges or expenses resulting from the proposed Contemplated Transactions; (viii) the risk that anticipated ownership percentages or cash dividend amount may change based on adjustments at or prior to closing; (ix) the risk that the Pre-Closing Financing is not consummated; (x) Serapha’s reliance on intellectual property rights under its license agreement with YolTech Therapeutics and risks related to the protection of intellectual property; and (xi) the potential for the occurrence of any event, change or other circumstance or condition that could give rise to the termination of the Merger Agreement and the other agreements entered into in connection therewith. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties. These and other risks and uncertainties are more fully described in periodic filings with the SEC, including the factors described in the section titled “Risk Factors” in Boundless Bio’s Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC, and in other filings that Boundless Bio makes and will make with the SEC in connection with the proposed Merger, including the Proxy Statement (as defined below). You should not place undue reliance on these forward-looking statements, which are made only as of the date hereof or as of the dates indicated in the forward-looking statements. Boundless Bio expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in its expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based. This communication does not purport to summarize all of the conditions, risks and other attributes of an investment in Boundless Bio or Serapha.

Participants in the Solicitation

This Current Report on Form 8-K relates to the proposed Merger and other Contemplated Transactions involving Boundless Bio and Serapha and may be deemed to be solicitation material in respect of the proposed Merger and other Contemplated Transactions. In connection with the proposed Merger and other Contemplated Transactions, Boundless Bio will file relevant materials with the SEC, including the Form S-4 that will contain a proxy statement (the Proxy Statement) and prospectus. This communication is not a substitute for the Form S-4, the Proxy Statement or for any other document that Boundless Bio may file with the SEC and/or send to Boundless Bio’s stockholders in connection with the proposed Merger. Boundless Bio, Serapha, and their respective directors and certain of their executive officers may be considered participants in the solicitation of proxies from Boundless Bio’s stockholders with respect to the proposed Merger and other Contemplated Transactions under the rules of the SEC. Information about the directors and executive officers of Boundless Bio is set forth in its most recent definitive proxy statement filed with the SEC on April 28, 2026. Additional information regarding the persons who may be deemed participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, will also be included in the Form S-4, the Proxy Statement and other relevant materials to be filed with the SEC when they become available. You may obtain free copies of this document as described below. BEFORE MAKING ANY VOTING DECISION, INVESTORS AND SECURITY HOLDERS OF BOUNDLESS BIO ARE URGED TO READ THE FORM S-4, THE PROXY STATEMENT AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT BOUNDLESS BIO, THE PROPOSED MERGER AND OTHER CONTEMPLATED TRANSACTIONS AND RELATED MATTERS.

No Offer or Solicitation

This Current Report on Form 8-K does not constitute an offer to sell or the solicitation of an offer to buy any securities nor a solicitation of any vote or approval with respect to the proposed transactions herein or otherwise. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act and otherwise in accordance with applicable law. BEFORE MAKING ANY VOTING DECISION, INVESTORS AND SECURITY HOLDERS OF BOUNDLESS BIO ARE URGED TO READ THE FORM S-4, THE PROXY STATEMENT AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT BOUNDLESS BIO, THE PROPOSED MERGER AND OTHER CONTEMPLATED TRANSACTIONS AND RELATED MATTERS.

Additional Information and Where to Find It

Investors and security holders will be able to obtain free copies of the Form S-4, the Proxy Statement and other documents filed by Boundless Bio with the SEC through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed by Boundless Bio with the SEC will also be available free of charge on Boundless Bio’s website at investors.boundlessbio.com.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

						BOUNDLESS BIO, INC.
Date:June 23, 2026				By:		/s/ Jessica Oien
						Name: Jessica Oien Title: Chief Legal Officer and Corporate Secretary

Exhibit 99.1

Boundless Bio and Serapha Bio Announce Merger Agreement and $230 Million Concurrent Private Placement

Combined company to operate as Serapha Bio and to advance Serapha’s potential best-in-class in vivo base editing program for Alpha-1 Antitrypsin Deficiency

Serapha’s lead program SERP-01 targets the SERPINA1 E342K (PiZZ) mutation, with proof-of-concept data demonstrating restoration of serum AAT to normal levels

Concurrent $230 million private placement co-led by RTW Investments and RA Capital Management, with participation from syndicate of top healthcare investors and mutual funds

Companies to hold joint webcast on Tuesday, June 23, 2026 at 8:30 a.m. ET

SAN DIEGO and NEW YORK – June 23, 2026 – Boundless Bio, Inc. (Nasdaq: BOLD) and Serapha Bio, Inc., a privately held biotechnology company developing an investigational in vivo base editing therapy for Alpha-1 Antitrypsin Deficiency (AATD), today announced that they have entered into a definitive merger agreement pursuant to which Serapha will combine with Boundless Bio in an all-stock merger. Prior to the closing, Boundless Bio expects to declare a cash dividend to pre-merger Boundless stockholders. Upon completion of the transaction, the combined company plans to operate under the name Serapha Bio, Inc. and is expected to trade on Nasdaq under the ticker symbol “AATD”.

In support of the proposed merger, Serapha has secured commitments for pre-closing private investments of approximately $230 million from a syndicate of investors co-led by RA Capital Management and RTW Investments and includes participation by Janus Henderson Investors, Decheng Capital, Vivo Capital, Casdin Capital, LifeSci Venture Partners, Logos Capital, Balyasny Asset Management, and Eventide Asset Management, of which approximately $138 million has already been funded in a Series A financing. The additional $92 million in funding is expected to close substantially concurrently with the merger, subject to customary closing conditions.

The combined company’s cash and cash equivalents balance at closing, including the funds from the private placement, is expected to fund Serapha’s operations into the second half of 2029 and provide runway through Phase 2 completion and Phase 3 initiation for SERP-01.

“This transaction provides Serapha with the public-market platform and capital to advance SERP-01 through a U.S. clinical program with conviction,” said Roderick Wong, MD, Managing Partner and Chief Investment Officer at RTW Investments. “The early clinical data generated with SERP-01 give us confidence that this is a potentially best-in-class base editing therapy that can restore AAT to physiologic levels in patients with the most severe form of this disease.”

Serapha licensed SERP-01, developed as YOLT-202 in Greater China, from YolTech Therapeutics in June 2026, in exchange for an upfront cash payment and a minority equity stake in Serapha. YolTech is also eligible to receive regulatory and commercial milestones totaling over $2 billion and tiered royalties on net sales of SERP-01. YolTech has been enrolling AATD patients in an Investigator-Initiated Trial (IIT) in Renji Hospital, Shanghai, China and retains development and commercialization rights for the Greater China territory.

“SERP-01 has a highly differentiated clinical profile, and, with this financing and merger agreement, Serapha is well positioned to deliver meaningful benefit for the up to 100,000 Americans – and many more around the world – who suffer from the life-threatening effects of severe AATD,” said Rajeev Shah, Managing Partner at RA Capital. “Serapha will hit the ground running with company building support from RTW Investments and RA Capital, including RA Capital’s Blackbird clinical development accelerator.”

“Since our founding, Boundless has pioneered a novel approach rooted in extrachromosomal DNA (ecDNA) biology to attempt to treat some of the most aggressive and difficult cancers. While we’ve deepened our understanding of ecDNA’s foundational role in certain cancers, the early clinical data for BBI-940 did not support continuing to advance this program,” said Zachary Hornby, President and Chief Executive Officer of Boundless Bio. “I am incredibly proud of our Boundless Bio team and their rigorous advancement of our novel science over the past seven years. We believe this transaction represents a strong opportunity to deliver meaningful value for our stakeholders, while providing Serapha with a public-market platform to advance novel therapies for people with rare diseases.”

The combined company will focus on the development and commercialization of Serapha’s lead clinical-stage candidate, SERP-01, for the treatment of severe AATD. AATD is a hereditary disorder most commonly caused by the SERPINA1 E342K point mutation, which causes the liver to produce a misfolded form of AAT, known as Z-AAT, in place of the normal M-AAT. The resulting toxic accumulation of Z-AAT polymers in the liver can lead to hepatitis, fibrosis, and cirrhosis, while reduced levels of functional AAT in circulation leave the lungs vulnerable to progressive emphysema and COPD. There is estimated to be up to 100,000 individuals with the severe PiZZ genotype in the United States, and current treatment is limited to supportive care, liver transplantation for end-stage disease, and weekly intravenous augmentation therapy that does not address the underlying liver pathology.

SERP-01 is an investigational in vivo base editing therapy designed to correct the SERPINA1 E342K mutation at its source. By restoring production of functional M-AAT while reducing toxic Z-AAT, SERP-01 has the potential to address both the liver and lung manifestations of the disease with a single administration.

The Proposed Transaction

Under the terms of the merger agreement, as of the closing and subject to the assumptions and adjustments set forth in the merger agreement, the pre-merger Boundless Bio stockholders are expected to own approximately 3.7% of the combined company and the pre-merger Serapha stockholders (inclusive of those investors participating in the pre-closing financings) are expected to own approximately 96.3% of the combined company. Prior to closing, Boundless Bio expects to declare a cash dividend to pre-merger Boundless Bio stockholders to distribute excess net cash, which is currently expected to be approximately $44 to $48 million, subject to adjustment based on Boundless Bio’s net cash at closing and the terms of the merger agreement.

The transaction has received unanimous approval by the Board of Directors of both companies and is expected to close in the fourth quarter of 2026, subject to certain closing conditions, including, among others, approval by the stockholders of each company, approval of the Nasdaq listing application, the effectiveness of a registration statement to be filed with the U.S. Securities and Exchange Commission (SEC) to register the securities to be issued in connection with the proposed merger, expiration, or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, if applicable, and the satisfaction of other customary closing conditions.

Lucid Capital Markets is serving as exclusive financial advisor and Latham & Watkins LLP is serving as legal counsel to Boundless Bio. Wedbush Securities Inc. is serving as exclusive financial advisor and Gibson, Dunn & Crutcher LLP and Goodwin Procter LLP are serving as legal counsel to Serapha.

Conference Call Information

Boundless Bio and Serapha Bio will host a joint conference call and webcast on June 23, 2026 at 8:30 a.m. ET. Please access the presentation by clicking on the following link: https://edge.media-server.com/mmc/p/w8sgnrsw

About Serapha Bio

Serapha Bio is a clinical-stage biotechnology company developing a novel base editing therapy for patients with AATD. Correcting the PiZ allele, the most common gene variant associated with severe AATD, could address a large population in the U.S. and Europe. Serapha Bio was co-founded in 2026 by RTW Investments, LP and RA Capital Management. For more information, visit https://www.seraphabio.com/.

About Boundless Bio

Boundless Bio is 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. For more information, visit https://boundlessbio.com/.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding the proposed merger between Boundless Bio and Serapha, the expected timing and completion of the transaction and the concurrent financing and Nasdaq listing, the anticipated ownership of the combined company, the expected amount and timing of the cash dividend to be paid to pre-merger Boundless Bio stockholders, the expected cash runway, and the potential, development plans, anticipated clinical milestones and therapeutic benefits of SERP-01, including whether SERP-01 will achieve or maintain restoration of serum AAT to normal levels, reduce toxic Z-AAT, address the liver and lung manifestations of AATD, demonstrate a favorable safety and tolerability profile, or achieve regulatory approval. In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “milestone,” “opportunity,” “plan,” “potential,” “project,” “should,” “target,” “will,” “would” and similar expressions (including the negatives of

these terms or variations of them) may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These statements are based on current expectations and are subject to risks and uncertainties that could cause actual results to differ materially, including the risk that the transaction or financing may not be completed on the anticipated terms or at all, the risk that required stockholder approval may not be obtained, the failure to satisfy the other conditions to the closing of the proposed merger, including the effectiveness of the registration statement to be filed with the SEC and the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, if applicable, the risk that the anticipated ownership percentages or cash dividend amount may change based on adjustments at or prior to closing, the uncertainties inherent in clinical development and the regulatory approval process, the combined company’s ability to successfully develop and, if approved, commercialize SERP-01, the combined company’s reliance on third parties in connection with manufacturing, research, and clinical and preclinical testing, Serapha’s reliance on intellectual property rights under its license agreement with YolTech Therapeutics, risks related to the protection of intellectual property, the combined company may use its capital resources sooner than it anticipates and, in any event, the combined company will continue to require substantial additional funding, and other risks described in Boundless Bio’s filings with the SEC, including its most recent Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q, and in the registration statement and proxy statement/prospectus to be filed in connection with the proposed transaction. Should one or more of these risks or uncertainties materialize, or should any of the parties’ assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. You should not place undue reliance on these forward-looking statements. Forward-looking statements speak only as of the date of this release, and neither company undertakes any obligation to update them except as required by law.

Important Additional Information and Where to Find it

In connection with the proposed transaction, Boundless Bio intends to file with the SEC a registration statement on Form S-4 that will include a proxy statement of Boundless Bio and a prospectus of Boundless Bio, and each of Boundless Bio and Serapha may file with the SEC or furnish to the SEC other relevant documents concerning the proposed transaction. Investors and securityholders are urged to read the registration statement, including the proxy statement/prospectus contained therein, and all other relevant documents filed with or furnished to the SEC in connection with the proposed transaction when they become available because they will contain important information about Boundless Bio, Serapha and the proposed transaction. Investors and securityholders will be able to obtain free copies of the registration statement and the proxy statement/prospectus, when available, and other relevant documents filed with or furnished to the SEC by Boundless Bio through the website maintained by the SEC at www.sec.gov and on Boundless Bio’s website at https://boundlessbio.com/.

Boundless Bio, Serapha and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from Boundless Bio’s stockholders in connection with the proposed transaction. Information about Boundless Bio’s directors and executive officers and their ownership of Boundless Bio securities is set forth in Boundless Bio’s filings with the SEC, including Boundless Bio’s most recent Annual Report on Form 10-K. Additional information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of proxies in connection with the proposed transaction, including a description of their direct or indirect interests, by security holdings or otherwise, will be included in the registration statement and proxy statement/prospectus when available.

This press release is not intended to and shall not constitute an offer to sell or the solicitation of an offer to buy any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

Contacts

Boundless Bio

Investors: Monique Allaire, THRUST, monique@thrustsc.com

Media: Carly Scaduto, THRUST, carly@thrustsc.com

Serapha Bio / RTW Investments / RA Capital Management

Chris Morrison, RA Capital, cmorrison@racap.com

Exhibit 99.2

Boundless Bio & Serapha BioConference Call Script

Operator

Good morning and welcome to the Boundless Bio conference call to discuss the merger of Boundless and Serapha Bio. This call is being recorded for replay at the company’s request. It’s now my pleasure to turn the call over to Monique Allaire, IR representative for Boundless Bio. Please go ahead.

Monique Allaire

Good morning and thank you for joining us for today’s conference call. The link to this webcast is on the Investor’s page of the Boundless Bio corporate website. Before we begin, I would like to remind you that today’s call will include forward-looking statements, which include, but are not limited to, statements regarding the proposed merger, cash dividend and other contemplated transactions. These forward-looking statements involve significant risks and uncertainties that could cause actual results to differ materially from those expected, including those listed at the bottom of the press release issued this morning.

Please refer to Boundless Bio’s filings with the SEC for additional risks and uncertainties. Boundless intends to file a registration statement containing a proxy statement and a prospectus that will have important information about each company and the transaction, which we advise you to read. These filings are available from the SEC at SEC.gov or on the company’s website.

I’ll now turn the conference over to Zachary Hornby, President and Chief Executive Officer of Boundless Bio.

Zachary Hornby, President and CEO, Boundless Bio

Thank you, Monique.

This morning, we announced that Boundless Bio has entered into a merger agreement with Serapha Bio in an all-stock transaction.

I’ll begin today’s call by sharing a bit of the background leading to this transaction and reviewing the details of the proposed merger with Serapha. I’ll then pass the call over to Dr. Emma Wang, Interim Chief Technology Officer of Serapha, who will provide an overview of the company, its strategy and its pipeline.

Over the last several months, concurrent with reviewing incoming clinical data from our BBI-940 program, we conducted a strategic review to evaluate a range of options that would position us to maximize value for our shareholders. These included assessment of our internal pipeline, financing opportunities, and strategic alternatives.

After a thorough review of our clinical data and strategic options by our Board of Directors, the Board unanimously approved the proposed merger. We believe that this transaction with Serapha offers a compelling opportunity for our stockholders to realize both short and long-term value creation through a cash dividend to Boundless’ pre-merger stockholders that I’ll describe shortly.

I believe Boundless shareholders should be excited about this transaction for several reasons. Serapha is a private clinical-stage company co-founded by premier investors, RTW Investments and RA Capital Management. The company has a lead clinical-stage asset that has the potential to be a best-in-class base editor therapy for the treatment of Alpha-1 Antitrypsin Deficiency with strong early clinical data in patients.

Upon the closing of the transaction, the go-forward company’s cash position is expected to provide cash runway into the second half of 2029, through key late-stage clinical inflection points that Emma will go through. This cash position arises from $230 million in proceeds from a completed Series A financing and expected pre-closing equity financing of Serapha with a syndicate of top-tier healthcare specialists and institutional investors. With this capital, we believe Serapha has the ability to execute its strategy through multiple value-driving clinical catalysts.

Under the terms of the merger agreement, the pre-merger Boundless stockholders are expected to own approximately 3.7% of the combined company. Boundless also expects to pay a cash dividend to pre-merger Boundless stockholders of approximately $44 to 48million immediately prior to the closing of the merger. Pre-merger Serapha stockholders, including the investors participating in the pre-closing financing, are expected to own approximately 96.3% of the combined company.

Following the close of the proposed transaction, the combined company is expected to operate under the name Serapha Bio Incorporated and to begin trading on Nasdaq under the ticker symbol AATD, subject to Nasdaq approval. We expect the merger transaction to close in the 4th quarter of 2026, subject to Boundless stockholder approval and customary closing conditions.

We at Boundless have been impressed with Serapha’s outstanding medical science and the quality of its scientific leadership. We believe in their ability to deliver on their pipeline strategy.

On behalf of the Boundless team, I would like to extend my sincere thanks to our employees for their diligent efforts on our science and programs, to the patients and investigators that participated in our trials, and to our stockholders, advisors, and Board of Directors who have supported us along the way.

As part of our transition planning and our focus on efficient operations through close, I will be stepping down from my role as CEO, President and Director, effective July 1, with our Chief Legal Officer, Jessica Oien, serving as principal executive officer through the transition.

With that, I’m pleased to introduce Dr. Emma Wang, Interim Chief Technology Officer of Serapha Bio.

Emma Wang, Interim CTO, Serapha Bio

Thank you Zach for the introduction. On behalf of Serapha, I want to thank you and the Boundless team for your partnership as we embark on this exciting transaction.

Today, we are thrilled to introduce Serapha Bio and announce our planned merger with Boundless Bio. At Serapha, we are driven to develop transformative therapies to address the profound unmet need in AATD.

To that end, we are working to assemble a deeply experienced team of gene editing drug developers who are dedicated to advancing durable, disease-modifying therapies. Our company is singularly focused on advancing a potentially best-in-class in vivo base-editing therapy targeting the SERPINA1 E342K mutation, also known as the PiZ allele, for the treatment of both pulmonary and hepatic disease manifestations in AATD. AATD represents an area of significant unmet need, particularly for patients with the PiZZ genotype, or those who are homozygous for the PiZ allele, with advanced lung and liver disease who are inadequately served by current protein replacement approaches.

Our lead asset SERP-01, known as YOLT-202 in Greater China, is an investigational in vivo base-editing therapeutic in-licensed from YolTech Therapeutics, a Shanghai-based gene editing company. Through this agreement, Serapha has obtained ex-China rights to develop SERP-01 for AATD. SERP-01 employs YolTech’s proprietary adenine base editor delivered via an optimized lipid nanoparticle formulation designed for efficient hepatocyte targeting, to make a precise single-nucleotide correction at the SERPINA1 E342K locus. This correction is designed to address both liver and lung disease manifestations and restore circulating AAT to therapeutically meaningful levels with a single administration. SERP-01 is currently being evaluated in an ongoing investigator-initiated trial, or IIT, in China by YolTech, and data from that study, which we will describe further, have informed our conviction in the program’s differentiated potential.

AATD is one of the most common serious hereditary disorders in populations of Northern European ancestry, with the PiZZ homozygous genotype affecting up to 100,000 individuals in the United States alone, with a significant portion of the patient population being undiagnosed. Progressive obstructive lung disease and chronic liver disease, including fibrosis and cirrhosis, represent the two dominant disease manifestations. The current standard of care for patients with severe pulmonary disease is intravenous AAT augmentation therapy, a burdensome, lifelong infusion regimen that only modestly slows emphysema progression and does not address liver disease. There are no approved therapies that directly correct the underlying genetic defect, and patients with advanced liver disease have no disease-modifying options short of transplantation. We believe a genomic correction therapy is uniquely positioned to address this critical unmet need across both organ manifestations simultaneously.

Because AATD is driven by a single predominant point mutation, this disease is ideally suited to a precise base-editing approach that corrects the single nucleotide, converting the mutant Z-AAT protein to normal or wildtype M-AAT protein. Importantly, SERP-01 has already generated early first-in-human clinical data supporting this compelling approach. In the ongoing China IIT, all three patients dosed at 45 mg have demonstrated restoration of serum M-AAT protein at levels above the accepted protective threshold of 11 µM after week 4, with levels remaining above this threshold through week 22 for one of the patients. One patient received a liver biopsy after SERP-01 therapy, and sequencing of this patient’s liver tissue found there to be no bystander edits. The produced M-AAT protein is the normal or the wildtype form. As of the latest data cutoff, YOLT-202 has been generally well tolerated, with only mild and transient liver enzyme elevations that resolved without intervention.

In parallel with YolTech’s ongoing IIT in China, Serapha intends to advance SERP-01 in the United States and Europe, including CMC technology transfer and initiation of a Phase 2 open-label study in patients at the optimal biologically active dose towards the end of this year. SERP-01 has received Orphan Drug Designation and Regenerative Medicine Advanced Therapy Designation from the FDA, which we believe reflects recognition of the program’s potential to address a serious unmet need with early clinical evidence. We believe the addressable market across the pulmonary and hepatic manifestations of AATD represents a substantial global commercial opportunity. The differentiated target product profile of SERP-01, with its evidence of durable AAT restoration and favorable safety data including lack of observed bystander edits to date, could offer a meaningfully superior alternative to lifelong augmentation therapy for this patient population.

In conclusion, we are excited to advance SERP-01 through the planned merger with Boundless Bio and with the support of our exceptional investor syndicate. We believe this program represents a potential breakthrough for patients living with AATD and a compelling value creation opportunity for our combined shareholder base. We look forward to working closely with the Boundless team in the months ahead to prepare for the successful completion of this merger. With that, I will conclude my remarks and hand the call back to the operator. Thank you for joining.

FAQ

What did Boundless Bio (BOLD) announce in its merger 8-K with Serapha Bio?

Boundless Bio entered an all-stock merger with Serapha Bio, making Serapha the controlling owner of the combined company. The new entity will focus on SERP-01, an in vivo base-editing therapy for Alpha-1 Antitrypsin Deficiency, and will operate under the Serapha Bio name.

How will ownership of the combined Boundless Bio–Serapha company be split?

Pre-merger Serapha equityholders are expected to own about 96.3% of the combined company on a fully diluted basis. Pre-merger Boundless Bio equityholders are expected to hold roughly 3.7%, subject to adjustments described in the merger agreement tied to Boundless Bio’s final net cash.

What cash dividend will Boundless Bio stockholders receive before the Serapha merger?

Before closing, Boundless Bio expects to declare a cash dividend to pre-merger stockholders of approximately $44–$48 million. This distribution reflects excess net cash above a zero-dollar target, with the final amount subject to closing adjustments defined in the merger agreement.

How is the Serapha financing structured in the Boundless Bio merger?

Serapha completed a Series A preferred stock financing of about $138 million and arranged a $92 million PIPE-style pre-closing financing. Together, these private investments total roughly $230 million and, with existing cash, are expected to fund SERP-01 development into the second half of 2029.

What workforce and leadership changes is Boundless Bio making for the Serapha transaction?

Boundless Bio plans a workforce reduction of about 75%, expecting $3.0–$5.0 million in one-time severance and benefit costs. CEO Zachary Hornby and key R&D leaders will depart July 1, 2026, with Chief Legal Officer Jessica Oien becoming president and principal executive officer during the transition.

What happens to Boundless Bio’s BBI-940 oncology program under this merger?

Boundless Bio determined that BBI-940’s human pharmacokinetic exposure was significantly lower than predicted from preclinical studies. Based on early KOMODO-1 data, the company concluded continued clinical development was not supported and is effectively discontinuing the BBI-940 program as it pivots to the Serapha transaction.

How are Boundless Bio employee stock options affected by the Serapha merger?

All outstanding Boundless Bio stock options became fully vested and immediately exercisable upon signing the merger agreement, with exercise periods extended generally to March 31, 2027 or three months post-closing. However, options with exercise prices above $8.00 per share will be cancelled for no consideration at the merger’s effective time.

Filing Exhibits & Attachments

10 documents

Press Releases

• EX-99.1 EX-99.1 21.4 KB
• EX-99.2 EX-99.2 16.1 KB

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• EX-10.1 EX-10.1 53.0 KB
• EX-10.2 EX-10.2 54.5 KB
• EX-10.3 EX-10.3 175.9 KB
• EX-10.4 EX-10.4 131.2 KB

Other Documents

• EX-2.1 EX-2.1 591.2 KB
• EX-101 XBRL TAXONOMY EXTENSION SCHEMA 3.1 KB
• EX-101 XBRL TAXONOMY EXTENSION LABEL LINKBASE 18.3 KB
• EX-101 XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE 11.4 KB