GSK plc has agreed to acquire IDRx, a Boston-based, clinical-stage biopharmaceutical company dedicated to developing precision therapeutics for the treatment of GIST.

Under the agreement, GSK will pay $1 billion upfront, with potential for an additional $150 million success-based regulatory approval milestone payment. The acquisition includes lead molecule, IDRX-42, a highly selective KIT TKI being developed as a first- and second-line therapy for the treatment of GIST.

GIST typically presents in the GI tract with 80% of cases driven by mutations in the KIT gene that lead to the growth, proliferation, and survival of tumor cells (primary or activating mutations). 90% of patients treated in the first-line develop new KIT mutations (secondary or resistance mutations) that typically lead to relapse with limited therapeutic options. Currently, there are no approved TKIs that inhibit the full spectrum of clinically relevant primary and secondary mutations in KIT.

IDRX-42 has demonstrated activity against all key primary and secondary KIT mutations, designed to improve outcomes for patients with GIST. This breadth of mutational coverage, in addition to high selectivity which could improve tolerability, provides potential for a best-in-class profile.

Tony Wood, Chief Scientific Officer, GSK, said: “We are excited by the early data from IDRX-42 and its unique ability to target all clinically relevant KIT mutations present in GIST, a major gap in the current standard of care. We look forward to accelerating its development in 2025 to redefine treatment.”

Tim Clackson, CEO, IDRx, added: “We are looking forward to working with GSK to advance IDRX-42 for patients with GIST given there have been no major advances to the standard of care for almost 20 years. Combining our experience to date with GSK’s expertise in GI cancers, global clinical development capability, and strong commercial presence in oncology will help to accelerate the development of this novel medicine for patients.”

This agreement reflects GSK’s portfolio approach of identifying potentially best-in-class molecules with targeted mechanisms of action. The transaction supports GSK’s ambitions for growth through 2031 and beyond.