FDA Grants Fast Track Designation to AI-Designed Mesothelioma Drug ISM6331
Insilico Medicine has secured FDA fast track designation for ISM6331, a novel, AI-designed pan-TEAD inhibitor. The drug is intended to treat adult patients with unresectable malignant pleural mesothelioma whose disease has progressed following platinum-based chemotherapy and prior anti–PD-1 antibody therapy (with or without anti–CTLA-4 therapy).
This regulatory milestone marks the first fast track designation for Insilico’s AI-driven pipeline. Additionally, early data from the drug's first-in-human Phase 1 trial (NCT06566079) will be featured in an oral presentation at the upcoming 2026 European Society for Medical Oncology (ESMO) Congress.
Mechanism of Action: How ISM6331 Works
Discovered and designed using Insilico’s proprietary generative AI platform, Chemistry42, ISM6331 operates as a potentially best-in-class small-molecule inhibitor. It specifically targets TEAD transcription factors within the Hippo signaling pathway, a network responsible for regulating cell proliferation, tissue homeostasis, and therapeutic resistance in solid tumors. By inhibiting TEAD, the drug is designed to restore balance to this pathway and halt the unchecked proliferation and survival of tumor cells. In preclinical studies, ISM6331 demonstrated broad antitumor efficacy at low doses, a favorable safety profile, and the potential to overcome drug resistance when combined with other agents.
Phase 1 Clinical Trial Overview
ISM6331 is currently being evaluated in a global, multicenter Phase 1 clinical trial involving patients with malignant mesothelioma and other advanced solid tumors. First-in-human data will be shared during a rapid oral presentation at the ESMO Congress in Madrid, Spain, from October 23 to 27, 2026. The trial focuses on establishing the drug's safety profile, with primary endpoints assessing the incidence of dose-limiting toxicities, adverse effects, significant laboratory value abnormalities, and determining the recommended Phase 2 dose. Secondary endpoints aim to measure the drug's preliminary efficacy by tracking the objective response rate (ORR), best objective response (BOR), and duration of response (DOR).
The Impact of Fast Track Designation
The FDA’s fast track program exists to expedite the development and review of drugs that treat serious conditions and fill unmet medical needs. For ISM6331, this designation unlocks several regulatory advantages, including enhanced FDA engagement through more frequent meetings and written feedback on clinical trial designs, biomarker strategies, and overall development plans. Additionally, the drug may become eligible for expedited review processes such as accelerated approval, priority review, and rolling review, which allows completed sections of a new drug application to be submitted to the FDA as they become available.
“Receiving fast track designation validates the strong clinical potential of ISM6331. Moreover, ISM6331 boasts synergistic antitumor effects and potential to overcome drug resistance as combination therapy.” — Halle Zhang, PhD, Vice President of Clinical Development–Oncology, Insilico Medicine
Development and Regulatory Timeline
ISM6331 has steadily progressed through key regulatory and clinical milestones since it was nominated as a development candidate in June 2023. The drug gained visibility when it was featured at the American Association for Cancer Research (AACR) Annual Meeting in April 2024, followed shortly by receiving FDA Orphan Drug Designation for the treatment of mesothelioma in June 2024. Clinical evaluation officially began in January 2025 when the first patient was dosed in the global multicenter Phase 1 trial, paving the way for its recent FDA Fast Track Designation.
Source: Cancer Network | July 29, 2026