Sidewinder Therapeutics, a San Diego biotech pursuing bispecific and dual-payload ADC designs, has raised a $137 million Series B led by blue-chip investors. The funding will support preparations for a potential clinical debut in 2027 and further development of its strategy to increase efficacy while reducing toxicities. The company describes its approach as aiming to “double up” antibody-drug conjugate mechanisms within a single construct, targeting fewer toxicities than conventional ADC architectures. The round also provides runway for preclinical work and manufacturing scale-up ahead of first-in-human studies. The investment underscores investor appetite for ADC innovation beyond established players, particularly where platforms promise improved therapeutic index through design-level differentiation (e.g., bispecific targeting and payload configuration). For investors, the key near-term milestone is whether Sidewinder can translate its design goals into early safety and response signals during the lead selection-to-clinic pathway.