Antares Therapeutics, Inc. has registered a first-in-human Phase I/II study of ATX-898, an investigational small molecule whose molecular target has not been publicly disclosed, in patients with advanced solid tumors. The trial, listed on ClinicalTrials.gov as NCT07767474, carries a status of "not yet recruiting" with a planned start date of August 2026.
The study, designated ATX-898-101, is an open-label, non-randomized Phase I/II trial enrolling up to 343 adult patients with histologically confirmed advanced or metastatic solid tumors. It is structured in two sequential parts: Part 1 evaluates ATX-898 as monotherapy across dose-escalation and dose-expansion cohorts targeting ovarian cancer, other gynecologic cancers, and broader solid tumors; Part 2 evaluates ATX-898 in combination with fulvestrant and either abemaciclib (Verzenio) or ribociclib in patients with hormone receptor-positive, HER2-negative (HR+HER2-) advanced or metastatic breast cancer. Primary endpoints in the monotherapy escalation arm include the recommended dose for expansion and occurrence of dose-limiting toxicities over a 12-month window; the combination expansion arm carries objective response rate as a primary endpoint over 36 months. Primary completion is projected for October 2028, with full study completion expected January 2030.
Boston-based Antares Therapeutics was spun out of Scorpion Therapeutics following the sale of Scorpion's mutant-selective PI3Kα inhibitor program to Eli Lilly for up to USD 2.5 billion, launching in June 2025 with a USD 177 million Series A. Led by Scorpion's former executive team, Antares inherited preclinical small-molecule programs and discovery capabilities targeting proteins historically considered difficult to drug. The company said at launch that it planned to advance its first new product candidate into the clinic in 2026, a target the ATX-898 registration now appears set to fulfill.
Although Antares has not disclosed ATX-898's target, the trial design provides some clues to its intended development strategy. The monotherapy program will evaluate activity across ovarian and other gynecologic cancers and broader solid tumors, while Part 2 will add ATX-898 to fulvestrant and either abemaciclib or ribociclib in HR+HER2- advanced breast cancer. The latter cohorts position ATX-898 as an add-on to established endocrine/CDK4/6 inhibitor therapy, although the absence of a disclosed molecular target or public preclinical data makes the biological rationale for the combinations difficult to assess independently.