The FDA has torpedoed Actinium Pharmaceuticals’ hopes of winning a blood cancer approval based on existing data. With the agency requesting an additional head-to-head randomized clinical trial, Actinium is planning to try to partner the program and switch its attention to other candidates.
Actinium reported phase 3 data on its targeted radiotherapy in February 2023. The study assessed the effect of Iomab-B, which consists of an anti-CD45 antibody conjugated to a radioisotope, on people with acute myeloid leukemia. By delivering a radioisotope to cells that express CD45, Actinium bet it could selectively target blood cancer and stem cells to prepare patients for bone marrow transplants.
The phase 3 SIERRA trial met its primary endpoint, linking Iomab-B to a higher rate of complete remission than standard care after six months. Actinium planned to file for FDA approval in the second half of 2023 but missed that target.
A meeting with the FDA, which was scheduled for the second quarter of 2024, emerged as a key event in the new timeline. Actinium left the meeting with bad news. Rather than getting the green light to file, the biotech learnt that the FDA wants to see an additional head-to-head randomized trial demonstrating overall survival (OS) benefit.
Actinium included OS as a secondary endpoint in the SIERRA trial. The biotech reported a median OS of 6.4 months in the Iomab-B arm and 3.2 months in the control cohort. However, the analysis excluded the 60% of patients in the control arm who crossed over to the Iomab-B cohort, and the difference between the groups fell short of statistical significance.
Disclosing the filing setback, Actinium said crossovers confounded the OS analysis in the intent-to-treat population. The study proposed by the FDA won’t allow patients to cross over from the control cohort.
Actinium is still talking to the FDA to iron out all the details of the study, but the biotech has already decided against taking Iomab-B forward itself. Once it completes its interactions with the FDA, Actinium plans to seek a partner for Iomab-B in the U.S. and focus on the development of its phase 1/2-stage Actimab-A, phase 1 Iomab-ACT and preclinical programs.
Shares in Actinium fell 69% to $1.86 in premarket trading Monday from a Friday closing price of $6.17. The biotech ended March with $84 million in cash and cash equivalents.