Phase 1 Trial to Assess Safety of Radioactive Anti-CD33 Antibody in Advanced Myeloma

A Phase 1 trial will soon be assessing Actimab-M, an anti-CD33 antibody bound to a radioactive compound, in heavily treated multiple myeloma patients, the compound’s developer, Actinium Pharmaceuticals, announced.

Actimab-M is the CD33 targeting antibody, HuM-195, linked to the radioactive compound actinium 225. CD33 is a protein found in normal blood cells and those of certain blood cancers, particularly acute myeloid leukemia. But studies have shown this protein is also found in 25%–35% of multiple myeloma patients, and is especially evident in those with relapsed or refractory disease.

The Phase 1 trial (NCT02998047) is an open-label, dose-escalation study, designed to assess the safety and efficacy of Actimab-M in about 12 myeloma patients, whose disease progressed despite three prior treatment regimens, or who are refractory to QUAD (caflizomib, lenalidomide, pomalidomide, dexamethasone) therapy. (The trial is recruiting patients at its Dallas test site; more information is available on its clinical trials.gov webpage.)

Patients will be given an infusion  of 0.5 μCi/Kg of Actimab-M on day 1 of up to eight, 42-day cycles as a starting dose. If this dose shows a tolerable safety profile, a second dose of 1 μCi/Kg infused on day 1 of up to four, 42-day cycles, will then be tested.

The trial’s primary goal is to determine the maximum tolerated dose, and the number of treatment-related adverse events. Secondary endpoints include measures of objective response rates, progression-free survival, and overall survival.

“I am very excited to lead in the development of this novel and promising approach,”  Yair Levy, the trial’s principal investigator at Texas Oncology–Baylor Charles A. Sammons Cancer Center in Dallas, said in a news release. “Relapsed and refractory multiple myeloma is an area of high unmet medical need that we hope to address with Actimab-M. … Based on my previous experience with Actimab-A in AML and my research in the area of multiple myeloma, I believe that this targeted treatment could prove efficacious … against this disease.”

Actinium is also conducting studies in acute myeloid leukemia patients: a Phase 3 trial of lomab-B (NCT02665065) and a Phase 2 trial of Actimab-A (NCT02575963). Both these trials are also recruiting participants.

“We are incredibly excited to see the initiation of this trial for Actimab-M in multiple myeloma. Not only does this mark the beginning of the expansion of our clinical pipeline beyond AML, it also demonstrates the broad applicability of our radioimmunotherapy technologies that we intend to progress into new indications and patient populations,” said Sandesh Seth, the company’s executive chairman. “We look forward to providing updates as this trial progresses.”