Sidewinder Therapeutics raised $137 million in a Series B to advance a pipeline of bispecific antibody-drug conjugates aimed at improving tumor targeting and safety. The round was co-led by Frazier Life Sciences and Novartis Venture Fund, with OrbiMed returning alongside new investors. Sidewinder said it uses Lonza’s Synaffix site-specific linker-payload and has signed a multi-target licensing agreement with Lonza to help refine the therapeutic index. The company’s lead program, SWT012, is targeting an IND filing with the FDA by the end of 2026 and planned clinical initiation in 2027, with two additional oncology programs on a similar timeline. The financing highlights investor appetite for next-generation ADC formats that can manage efficacy tradeoffs seen in earlier generations.