Sidewinder Therapeutics, a San Diego biotech developing bispecific antibody-drug conjugates for cancer, announced on 8 April 2026 that it had closed an oversubscribed $137m Series B financing. No valuation was disclosed.
Frazier Life Sciences and Novartis Venture Fund co-led the round. OrbiMed, which was the company's only Series A investor, returned, and the other participants were Life Sciences at Goldman Sachs Alternatives, DCVC Bio, Samsara BioCapital, Longwood Fund, Astellas Venture Management and Alexandria Venture Investments.
The round brings total funding to $162m, according to the company. Sidewinder was founded in 2023 with OrbiMed's backing. The company did not say how much the Series A raised, and BioSpace likewise reported that the amount was undisclosed.
What Sidewinder does
Antibody-drug conjugates, or ADCs, are drugs built to deliver a payload to cancer cells. Sidewinder's versions are bispecific, meaning each one binds two targets at once. The company aims them at receptor co-complexes that are highly expressed on certain solid tumors. Each co-complex pairs an oncogenic driver receptor with an internalising receptor.
According to the company, targeting both is meant to improve specificity for the tumor and the uptake of the drug into cancer cells, so the payload reaches them while sparing normal cells. The antibodies are engineered from sequences the company discovered itself.
Target indications include squamous cell carcinomas of the lung and of the head and neck, and gastrointestinal cancers including colorectal cancer, where treatment options are limited.
Pipeline and timing
The company said its lead program is expected to enter clinical development in 2027. BioSpace gave more detail from a company presentation: the lead candidate, SWT012, has been tested in animals for bladder cancer, with an investigational new drug (IND) submission planned by the end of 2026. A second candidate, SWT019, is preclinical for lung cancer, with an IND planned for the first half of 2027. A third, SWT020, is preclinical for colorectal cancer, with no IND timing given and the company still settling on a final formula.
Sidewinder also has a partnership with Lonza's Synaffix unit, applying Synaffix's site-specific linker-payload technology across several programs. BioSpace noted that the technology has also been licensed to other companies.
Who is on the board
Four investor representatives joined the board alongside the financing: Daniel Estes of Frazier Life Sciences, Michal Silverberg of Novartis Venture Fund, Josh Richardson of Life Sciences at Goldman Sachs Alternatives and John Hamer of DCVC Bio.
Eric Murphy, co-founder and chief executive, said the ADC field is at an inflection point driven by next-generation bispecific technology, and that Sidewinder intends to lead that wave. Estes said he believes Sidewinder will significantly advance the ADC space.
Sidewinder did not disclose its headcount.
Use of the money
The stated purpose of the financing is to take its precision bispecific ADCs into clinical development for cancer. The company did not break down how the $137m would be divided between programs, manufacturing or staffing.
Company website: sidewinderbio.com