Fusion Pharmaceuticals Inc. announced that the U.S. Food and Drug Administration (FDA) has cleared the Company's Investigational New Drug (IND) applications for [225Ac]-FPI-2059 (FPI-2059) and the corresponding imaging analogue [111In]-FPI-2058 (FPI-2058). FPI-2059 is a targeted alpha therapy (TAT) designed to use a small molecule to target and deliver actinium-225 to tumor sites expressing neurotensin receptor 1 (NTSR1), a protein that is overexpressed in multiple solid tumor types, including colorectal, pancreatic, gastric, neuroendocrine differentiated prostate, head and neck squamous cell carcinoma, and Ewing sarcoma cancers. Fusion acquired [177Lu]-IPN-1087 (IPN-1087), a lutetium-based beta-emitting radiopharmaceutical, from Ipsen in April 2021, and converted the compound to the alpha-emitting [225Ac]-FPI-2059.

In clinical studies, IPN-1087 showed promising early safety data and good uptake in multiple tumor types. In a head-to-head in vivo comparison of therapeutic efficacy in a mouse xenograft model of colorectal cancer between FPI-2059 and IPN-1087, results show tumor regression with FPI-2059 is achieved at doses of approximately 1500 times lower than IPN-1087. Fusion plans to initiate a Phase 1, non-randomized, open-label clinical trial in patients with solid tumors expressing NTSR1, intended to investigate safety, tolerability and pharmacokinetics and to establish the recommended Phase 2 dose.

The study will prioritize six solid tumor indications, including head and neck squamous cell carcinoma, pancreatic, neuroendocrine prostate, colorectal, gastric and Ewing sarcoma. The study employs a 3 + 3 dose escalation design to evaluate multiple ascending doses of FPI-2059. As part of the screening process, patients will be administered an imaging analogue of FPI-2059, FPI-2058, and only those who meet predefined tumor uptake and safety criteria will go on to receive FPI-2059.

Radiopharmaceuticals are a precision medicine in that the alpha therapeutic can be converted into a corresponding imaging analogue with a different radionuclide (in this case indium), used to screen for a biomarker in patients with tumors that express the cancer target, increasing the likelihood of response to therapy. Fusion plans to provide additional guidance on timelines for the FPI-2059 program following initial experience with patient screening in order to better predict the cadence of patient enrollment. FPI-2059 (FPI-2059) is a targeted alpha therapy combining actinium-225 with a small molecule designed to target neurotensin receptor 1 (NTSR1), in development as a potential treatment for various solid tumors.

NTSR1 is a promising target for cancer treatment that is overexpressed in multiple solid tumors including colorectal, pancreatic, gastric, neuroendocrine differentiated prostate, head and neck squamous cell carcinoma and Ewing sarcoma cancers. FPI-2059 is currently being evaluated in a Phase 1 study.