Ona Therapeutics closed an oversubscribed $86.6 million Series B to advance two antibody-drug conjugates toward clinical testing. The capital is primarily earmarked for ONA-255 in advanced treatment-resistant breast cancer, while ONA-389 is set up for first-in-human development in colorectal cancer. The financing includes co-leads Columbus Venture Partners and Mérieux Equity Partners, with new participation from COFIDES and Korys as well as support from existing investors. Ona said the round is intended to fund rapid execution through key clinical and regulatory milestones. The company is building around a patient-driven target discovery platform to identify tumor-specific antigens and epitopes, with the aim of improving internalization and targeted payload delivery in solid tumors.