Boundless Bio Presents Preclinical Breast Cancer Data from its Oral Kinesin Degrader Program at 2026 AACR Annual Meeting

Findings support the ongoing Phase 1 clinical development of BBI-940, an oral, selective kinesin degrader, as a potential first-in-class therapy for select advanced or metastatic breast cancers

SAN DIEGO, April 17, 2026 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, presents preclinical data supporting its lead ecDNA-directed therapy (ecDTx), BBI-940, at the American Association for Cancer Research (AACR) Annual Meeting 2026. Boundless has identified a novel kinesin target ("Kinesin") essential to ecDNA segregation and inheritance in cancer cells, but non-essential in healthy cells. BBI-940, a potentially first-in-class, oral, and selective Kinesin degrader, is currently being evaluated in the Phase 1 KOMODO-1 trial (NCT07408089) in patients with advanced or metastatic ER+/HER2- breast cancer and TNBC-LAR.

"Extrachromosomal DNA is well established as a distinct enabler of chromosomal instability associated with oncogene amplification, therapeutic resistance, and poor outcomes for patients," said Chris Hassig, Ph.D., Chief Scientific Officer of Boundless Bio. "We have discovered and validated a novel kinesin target that plays a critical role in ecDNA segregation during cell division, thereby affording tumors with a high degree of genomic plasticity. Our data demonstrate that selective degradation of this target delivered potent antitumor activity in validated breast cancer models, particularly those with ecDNA. Our genetic, in vitro, in vivo, and toxicity profile of BBI-940 supports our recently initiated, first-in-human KOMODO-1 clinical trial evaluating BBI-940 in ER+/HER2- and TNBC-LAR breast cancer patients."

Details of the presentation are as follows:

Title: Selective degradation of a novel kinesin as a potential therapeutic strategy addressing high-risk extrachromosomal DNA (ecDNA) positive cancers, including breast cancer
Abstract Number: LB361
Session Title: Late-Breaking Research: Experimental and Molecular Therapeutics 3
Session Date and Time: Tuesday April 21, 2026, 2:00 PM - 5:00 PM PT
Location: Poster Section 53
Poster Board Number: 18

Genetic and pharmacologic degradation of Kinesin caused ecDNA mis-segregation, ecDNA depletion, and reduced viability of ecDNA+ cancer cells. Selective degradation of Kinesin in a panel of tumor cell lines demonstrated sensitivity across multiple tumor types and 32% sensitivity in breast cancer cell lines, including those positive for ecDNA and FGFR1 gain. This molecularly defined subgroup for Kinesin degradation was further validated in vivo with demonstrated monotherapy tumor regressions in an ecDNA+ TNBC-LAR model, and significant antitumor activity as monotherapy and combination in an ecDNA+/FGFR1+ ER+ breast cancer model.

About BBI-940
Our lead ecDTx, BBI-940, is a novel, oral, and selective kinesin degrader being evaluated in the ongoing, first-in-human Phase 1 KOMODO-1 (Kinesin Oral Molecular Degrader for Oncology) clinical trial (NCT07408089) in patients with advanced or metastatic estrogen receptor-positive, HER2-negative (ER+/HER2-) breast cancer or triple-negative breast cancer of the luminal androgen receptor subtype (TNBC-LAR). BBI-940 targets a specific kinesin protein, "Kinesin", essential for ecDNA segregation and inheritance in cancer cells, but non-essential in healthy cells. BBI-940 is designed to exploit the heightened dependence of ecDNA-positive tumors on mitotic machinery by degrading Kinesin to induce mitotic catastrophe and cell death.

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. Boundless Bio's research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14% to 17% of cancer patients. Boundless Bio is developing BBI-940, a potentially first-in-class, oral, and selective Kinesin degrader as an ecDNA-directed therapeutic candidate (ecDTx). Boundless Bio is headquartered in San Diego, CA.

For more information, visit www.boundlessbio.com and follow us on LinkedIn and X.

Forward-Looking Statements
Boundless Bio (Company) cautions you that statements contained in this press release that are not a description of historical facts are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as "anticipate," "believe," "contemplate," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "should," "would," "target," or "will" or the negative of these terms or other similar expressions. Forward-looking statements are based on the Company's current beliefs and expectations and include but are not limited to statements regarding: the potential therapeutic benefits of our ecDTx in treating patients with advanced or metastatic estrogen receptor-positive, HER2-negative breast cancer or triple-negative breast cancer of the luminal androgen receptor subtype. The Company's actual results and performance may differ materially from those expressed or implied in any forward-looking statement due to substantial known and unknown risks and uncertainties inherent in our business, including, without limitation: potential delays in the enrollment, data readouts, or completion of clinical trials or in regulatory submissions and responses; the Company is early in its development efforts and its approach to discover and develop ecDTx to treat oncogene amplified cancers is novel and unproven; clinical and preclinical development of therapeutics involves a lengthy and expensive process with inherently uncertain timelines and outcomes; results from preclinical studies or early clinical trials not necessarily being predictive of future results; unexpected adverse side effects or inadequate efficacy of the Company's ecDTx that may limit development, regulatory approval, and/or commercialization; the Company's ability to retain key personnel; the Company's dependence on third parties in connection with clinical trials, preclinical studies, and manufacturing; the potential for the Company's programs and prospects to be negatively impacted by developments relating to its competitors, including the results of studies or regulatory determinations relating to its competitors; regulatory and healthcare reform developments in the United States and foreign countries; disruptions in the FDA's ability to perform routine activities or function in the normal course; macroeconomic and geopolitical events and conditions, including international trade policies and tariffs; and other risks described in the Company's filings with the Securities and Exchange Commission (SEC), including under the heading "Risk Factors" in the Company's annual report on Form 10-K for the year ended December 31, 2025 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date hereof, and, except as required by law, the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.

Contacts: James Lee, Boundless [email protected]

InvestorsBrendan [email protected]