Startup Fortitude Bio launches breakthrough in cancer drug resistance, expands ADC to autoimmune diseases
Antibody-drug conjugates have cemented their place as treatment options for many cancers, but one problem with this type of targeted therapy is drug resistance. Scientists at Fortitude Biomedicines believe drug resistance can be overcome by combining an ADC with another emerging cancer therapy. The startup launched on Monday to showcase its approach to the emerging drug sector, which has already sparked investment from the likes of Bristol-Myers Squibb and Pfizer.
ADCs are composed of antibodies associated with toxic drugs. For cancer ADCs, the drug payload is usually chemotherapy. The launch of Fortitude joins a group of companies exploring other uses for drug payloads. The Waltham, Mass.-based startup focuses on ADCs combined with targeted protein degraders, drugs that allow disease-causing proteins to enter cellular systems, eliminating old or damaged proteins. ADCs that use degraders as payloads constitute a new class of drugs called degrader antibody-drug conjugates (DACs).
In order for targeted protein degradation to work, molecular tags need to mark proteins for processing by cellular waste disposal systems. Some proteins lack binding pockets to which small-molecule drugs can attach. This problem can be solved with so-called molecular glues, molecules that facilitate the interaction between the tag and the target protein.
Fortitude's drug comes from a platform technology called GLUE-DAC, which the company describes as a next-generation ADC platform powered by a proprietary molecular glue payload. The startup says the technology has the potential to expand the therapeutic window of ADCs, or the dose range that balances safety and effectiveness. Fortitude also believes its approach can overcome resistance mechanisms and expand ADCs into new therapeutic targets, including those in autoimmune diseases.
So far, no targets have been disclosed. Fortitude Pipeline lists a DAC codenamed FORT-101 as being in the cancer discovery stage. The company said the drug promotes the degradation of transcriptional coactivator, a protein critical for cancer cell survival. Fortitude's most advanced program is FORT-202, a bispecific antibody that has reached Investigational New Drug Application Support Studies.
Fortitude is based on research by Jin Wang, a professor of pharmacology at Baylor College of Medicine and director of the university's Center for Next Generation Therapeutics. Wang co-founded the startup with CEO Jesse Chen, who most recently served as chief technology officer of TRIANA Biomedicines, a startup developing molecular glue degraders for hard-to-treat cancers.
“Drug resistance is increasingly a challenge in the current ADC therapeutic landscape,” Wang said in a prepared statement. “The field is in urgent need of payloads with different mechanisms of action. GLUE-DAC technology addresses this unmet need by combining proven antibody delivery capabilities with the transformative potential of targeted protein degradation.”
Large pharmaceutical companies have shown interest in developing DAC drugs. In 2023, Bristol-Myers Squibb paid $100 million upfront to license DAC from Orum Therapeutics. The drug, BMS-986497 (formerly known as ORM-6151), targets the cancer target CD33. It is currently in phase 1 testing as a potential treatment for acute myeloid leukemia or myelodysplastic syndrome.
Pfizer is developing DAC through its ADC subsidiary Seagen, which is partnering with Nurix Therapeutics, a developer of targeted protein degradation drugs. The agreement, signed in 2023, calls for Nurix to develop targeted protein degraders against Pfizer's nominated targets; the pharmaceutical company will be responsible for combining these degraders with antibodies and advancing the therapies through preclinical and clinical development. The target has not been made public. Seagen paid $60 million to begin the partnership. As of the end of August 2025, Nurix reported having received $10 million toward research milestones. Under the terms of the deal, Pfizer's R&D and milestone payments could total up to $3.4 billion.
Fortitude's seed round was co-led by K2 Bio Partners, Shanghai Medical Angel Capital and Elikon Venture, with participation from Everjoy Fortune and Taihill Venture. The startup said the funding will support the development of its leading immune cell-targeted biologics through preclinical research, which may support investigational new drug applications. The funding will also support the development of the company's technology platform.
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