The financing was co-led by Leaps by Bayer, the impact investment arm of Bayer AG, and RA Capital Management, with participation from new investors Sectoral Asset Management and Piper Heartland Healthcare Capital.

The Series C financing additionally included participation from existing investors Fidelity Management & Research Company LLC, ARCH Venture Partners, Nextech Invest, Wellington Management, Vertex Ventures HC, Redmile Group, Surveyor Capital (a Citadel company), GT Healthcare Capital Partners, Alexandria Venture Investments, PFM Health Sciences, Logos Capital, and City Hill Ventures.

In a statement, Boundless Bio said that it will use the funds for the clinical development of BBI-355, the first extrachromosomal DNA (ecDNA)-directed therapy (ecDTx) for patients with oncogene-amplified cancers, as a single agent and in combination with other therapies.

BBI-335 is currently being evaluated in the phase I/II POTENTIATE clinical trial. BBI-355 is a selective CHK1 inhibitor, which has been shown preclinically to be lethal to ecDNA-bearing oncogene-amplified cancer cells. Absent in healthy cells, ecDNA is present in 14% of early-stage cancers and up to 40% of metastatic cancers; it drives both oncogenesis and therapeutic resistance.

The funds will also be used to advance Boundless Bio's other ecDTx candidates, as well as its proprietary ecDNA diagnostic clinical trial assay, ECHO (ecDNA Harboring Oncogenes), which is being developed collaboratively with Sophia Genetics.

In addition, Fabio Pucci, PhD, senior director of Venture Investments Health at Leaps by Bayer, will join the Boundless Bio board of directors, the firm added.