Ona Therapeutics raised an oversubscribed $86.6 million Series B to push two antibody-drug conjugate candidates into human testing. The Barcelona-based biotech said the round will primarily support ONA-255 in breast cancer and advance ONA-389 toward first-in-human studies in colorectal cancer. The funding included co-leads Columbus Venture Partners and Mérieux Equity Partners, with participation from new investors COFIDES and Korys and existing backers. Ona framed its strategy around patient-driven tumor antigen and epitope discovery to improve internalization and targeted payload delivery while aiming to reduce off-target toxicity. For the ADC field, the round adds another clinical entry focused on differentiating targeting biology—at a time when investors continue to reward platforms that can reduce resistance and improve therapeutic index.