Combination of BBI-355 and abemaciclib to be evaluated in Boundless Bio’s ongoing Phase 1/2 clinical trial (POTENTIATE) in patients with CDK4/6 amplifications

Boundless Bio, a clinical stage, next-generation precision oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced a clinical trial collaboration and supply agreement with Eli Lilly and Company for supply of their CDK4/6 inhibitor Verzenio^® (abemaciclib) for use in combination with BBI-355 in a clinical trial of patients with locally advanced or metastatic solid tumors with oncogene amplifications. BBI-355 is an orally administered, novel, selective small molecule inhibitor of CHK1 and represents what Boundless Bio believes is the first ecDNA-directed therapy (ecDTx) in development for oncogene amplified cancers.

“We are pleased to enter this supply agreement with Lilly to evaluate the combination of BBI-355 and abemaciclib in patients with ecDNA-driven solid tumors harboring CDK4 or CDK6 amplifications in our ongoing POTENTIATE trial,” said Zachary Hornby, President and Chief Executive Officer of Boundless Bio. “To date, CDK4/6 inhibitors have only been approved in HR+/HER2- breast cancer. Based on preclinical data, we believe BBI-355 has the potential to disable the underlying ecDNA driving oncogene amplification and unlock synergistic anti-tumor activity when combined with abemaciclib, potentially providing an important new treatment option for patients with CDK4 or CDK6 amplified solid tumors.”

Under the terms of the agreement, Lilly will provide abemaciclib clinical drug supply at no cost for Boundless Bio’s ongoing Phase 1/2 clinical trial (POTENTIATE), which will assess BBI-355 in combination with certain selected targeted therapies, including abemaciclib, in patients with specific oncogene amplified solid tumors.

About the POTENTIATE Trial

BBI-355 is being evaluated in a first-in-human Phase 1/2 clinical trial (“POTENTIATE”: Precision Oncology Trial Evaluating Novel Therapeutic Interrupting Amplifications Tied to ecDNA) in patients with locally advanced or metastatic solid tumors with oncogene amplifications, whose disease has progressed despite all standard therapies or for whom no further standard or clinically acceptable therapy exists.

The open-label, non-randomized, 3-part trial involves: BBI-355 single agent dose escalation and expansion in cancer patients with oncogene amplification, dose escalation of BBI-355 in combination with certain selected targeted therapies in cancer patients with specific oncogene amplifications, and dose expansion of BBI-355 in combination with certain selected targeted therapies in cancer patients with specific oncogene amplification on ecDNA. BBI-355 is administered orally every other day. In part 3 of the trial, an ecDNA diagnostic clinical trial assay (CTA), which we call ECHO (ecDNA Harboring Oncogenes), will be implemented to determine the presence of oncogenes amplified on ecDNA in patient tumor samples. ECHO is a proprietary bioinformatic diagnostic algorithm designed by Boundless Bio and developed into a CTA in collaboration with SOPHiA GENETICS to detect oncogenes amplified on ecDNA from tumor biopsy samples using routine clinical NGS assays.

About BBI-355

BBI-355 is an orally administered, novel, selective checkpoint kinase 1 (CHK1) inhibitor and, what we believe, is the first ecDNA-directed therapy (ecDTx) being investigated to treat patients with oncogene amplified cancer. CHK1 is a master regulator of the cellular response to DNA replication stress (RS), which frequently arises from oncogene amplification on ecDNA. By disrupting proper CHK1 function in oncogene amplified cancer cells, we believe BBI-355 facilitates catastrophic RS, and preferentially kills cancer cells relative to healthy cells. CHK1 was identified as an ecDNA essential target via Boundless Bio’s proprietary Spyglass research platform.

About Boundless Bio

Boundless Bio is a clinical stage, next-generation precision oncology company dedicated to the discovery and development of new drugs targeting a novel area of cancer biology, extrachromosomal DNA (ecDNA), to deliver transformative therapies intended to improve and extend the lives of patients with oncogene amplified cancers. Boundless Bio is developing what it believes is the first ecDNA-directed therapy (ecDTx), BBI-355, which is being evaluated in a Phase 1/2 clinical trial and has multiple other pipeline programs advancing in preclinical development and discovery. To date, Boundless Bio has raised more than $250 million from leading life sciences investors.

For more information, visit www.boundlessbio.com.

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Verzenio^® is a registered trademark owned or licensed by Eli Lilly and Company, its subsidiaries, or affiliates.

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