Ona Therapeutics closed an oversubscribed Series B financing totaling $86.6 million to advance two antibody-drug conjugates targeting treatment-resistant cancers. The money primarily supports ONA-255, an ADC initially built for breast cancer, while also pushing ONA-389 toward first-in-human work in colorectal cancer. The company’s platform aims to discover novel tumor-specific antigens and epitopes, with an engineering focus on payload internalization to improve therapeutic index and reduce off-target toxicity. Ona said the syndicate reflects investor alignment on clinical execution and oncology drug development expertise. Columbus Venture Partners and Mérieux Equity Partners led the round, joined by COFIDES and Korys and supported by existing investors. The funding provides runway to progress multiple programs concurrently rather than sequencing development around a single asset. For the ADC market, the financing adds another entrant emphasizing differentiated antigen discovery and internalization mechanics—an area that remains a key differentiator beyond linker and payload chemistry.