Ona Therapeutics closed an oversubscribed $86.6 million Series B to push two antibody-drug conjugates into human testing, including ONA-255 for breast cancer and ONA-389 for colorectal cancer. The funding supports clinical proof-of-concept and first-in-human execution, with co-leads and new backers joining the syndicate. The company’s strategy centers on patient-driven antigen and epitope discovery, aiming to select tumor-specific cell surface targets designed to improve internalization and therapeutic index while lowering on-target/off-tumor toxicity. The financing adds another ADC specialist to the roster of companies seeking differentiated payload delivery and tighter targeting in solid tumors.