Sidewinder Therapeutics closed a $137 million Series B to advance a pipeline of bispecific antibody-drug conjugates (ADCs) targeting multiple solid tumor indications. The round was co-led by Frazier Life Sciences and Novartis Venture Fund, with OrbiMed returning as the sole Series A backer. The company’s lead program SWT012 is on track for an IND filing by the end of 2026, with clinical development expected to begin in 2027. Sidewinder said its other ADC candidates, SWT019 and SWT020, are also planned to enter clinical studies in 2027, with the company emphasizing improved safety and efficacy through next-generation targeting and linker-payload tooling. Sidewinder uses Lonza’s Synaffix site-specific linker-payload technology and reported a multi-target licensing agreement with Lonza signed in January 2026. The financing underscores investor interest in ADC designs that can expand therapeutic index without adding systemic toxicity. The immediate impact for the field is competitive differentiation in bispecific ADCs, with later-stage validation expected as the IND packages and first-in-human results emerge.