A Phase 1-1b Study to Evaluate the Safety, Efficacy and Dosimetry of Study Drug A9-3408 in Subjects With Metastatic Melanoma

This is a multicenter, open-label Phase 1-1b study of \[225Ac\]Ac-A9-3408 in subjects with unresectable or metastatic melanoma. The primary aim of the Phase 1 portion of the study is to evaluate the safety and tolerability as well as the normal organ and tumor dosimetry of \[225Ac\]Ac-A9-3408 and to select a recommended Phase 2 dose (RP2D). The aim of Phase 1b will be to evaluate the safety, efficacy, and normal organ and tumor dosimetry of \[225Ac\]Ac-A9-3408 administered at the RP2D in subjects with unresectable or metastatic cutaneous melanoma who had confirmed disease progression while receiving an anti-PD-1/PD-L1-containing regimen. The interventional diagnostic \[68Ga\]Ga-A9T-3202 will be administered intravenously (IV) once during screening. The interventional drug \[225Ac\]Ac-A9-3408 will be administered intravenously (IV) once every 6 weeks, for a total of up to 6 cycles.