Actinium Pharmaceuticals launches clinical trial for Actimab-A in combination

Actinium Pharmaceuticals (ATNM) announced a clinical program comprising of trials studying Actimab-A in combination with either Keytruda – pembrolizumab -or Opdivo – nivolumab – which are blockbuster immunotherapies known as PD-1 inhibitors which are approved in multiple solid tumor indications. Keytruda, developed and commercialized by Merck (MRK) and Opdivo developed and commercialized by Bristol Myers Squibb (BMY), collectively generated $38.8B in sales in 2024 across several solid tumor cancer indications. However, the efficacy of these drugs has shown to be limited by a certain type of cell known as MDSCs or Myeloid Derived Suppressor Cells which accumulate in the tumor microenvironment. MDSCs express the CD33 antigen which is targeted by Actimab-A. Actinium believes that in the clinic Actimab-A can deplete CD33 expressing MDSCs and hence improve the outcomes with PD-1 inhibitors such as Keytruda and Opdivo. Based on its safety and tolerability, Actimab-A is under clinical development via an NCI CRADA in the front-line AML setting with an expected registrational study in combination with CLAG-M in relapsed/refractory AML expected to initiate in 2025. Actinium expects to present initial proof of concept clinical data from the first of these trials in the second half of 2025 as well as provide an update on the outlook for the rest of the trials in the Actimab-A solid tumor program.