Sidewinder Therapeutics raises $137M to push bispecific ADCs toward the clinic
What's the deal? San Diego-based Sidewinder Therapeutics has closed an oversubscribed $137 million Series B to advance its bispecific antibody-drug conjugates (ADCs) into clinical development for cancer.
The round was co-led by Frazier Life SciencesDealroom has a profile for this one. Try Dealroom → and Novartis Venture FundDealroom has a profile for this one. Try Dealroom →, with OrbiMed — the sole Series A investor — and new participants including Life Sciences at Goldman Sachs Alternatives and DCVC BioDealroom has a profile for this one. Try Dealroom →. The company has raised $162 million in total since its founding in 2023.
Proceeds will fund the advancement of Sidewinder's lead programme toward a clinical trial start targeted for 2027, along with broader pipeline development.
Why now? ADCs have become one of oncology's hottest drug classes, attracting billions in dealmaking from large pharma. But first-generation ADCs carry a known problem: off-tumour toxicity, where the drug damages healthy cells alongside cancerous ones. Sidewinder's bispecific approach — targeting receptor co-complexes found specifically on solid tumours rather than single antigens — is designed to address that limitation directly.
The company is going after cancers with few good treatment options: squamous cell carcinomas in lung and head and neck, as well as gastrointestinal cancers including colorectal cancer. The oversubscription of the round signals investor confidence in the scientific differentiation.
What could go wrong? Sidewinder's lead programme won't enter the clinic until 2027 at the earliest, leaving a long stretch of preclinical risk ahead. Bispecific ADCs are technically complex — engineering two targeting arms alongside a cytotoxic payload introduces more variables and more ways for a programme to fail.
The field is also crowded: established players and well-funded rivals are racing toward the same clinical readouts, and competitive data from a larger company could shift investor and partner attention quickly.
The company relies on LonzaDealroom has a profile for this one. Try Dealroom →'s SynaffixDealroom has a profile for this one. Try Dealroom → platform for its site-specific linker-payload chemistry — a key third-party dependency that adds execution risk.
The signal: Sidewinder's raise reflects an accelerating shift in oncology investment toward next-generation ADCs. GileadDealroom has a profile for this one. Try Dealroom →'s $3.15 billion acquisition of ADC-focused Tubulis, announced in April 2026, underlines how much big pharma is willing to pay for differentiated technology in this space.
The involvement of Novartis Venture Fund is particularly notable: corporate venture arms rarely back companies in a space without strategic intent, and Novartis has its own ADC ambitions. For early-stage biotechs with a credible scientific angle on one of oncology's most commercially active modalities, the funding environment remains unusually receptive.
Sources:
Sidewinder Therapeutics
Business Wire
Fierce Biotech
Endpoints News
J.V.
