HDP-101, an antibody-targeted amanitin conjugate to advance to phase I/IIa testing

The U.S. Food and Drug Administration (FDA) has announced that the B-cell maturation antigen (BCMA) antibody–drug conjugate HDP-101 can proceed to phase I/IIa testing.¹ HDP-101 is being assessed for the treatment of patients with multiple myeloma (MM). This agent uses amanitin, derived from Amanita phalloides (death cap mushroom), as the cytotoxic agent in an antibody-targeted conjugate.

The phase I study will evaluate the maximum tolerated dose of HDP-101 by performing a dose escalation study. Then the data from this section will be taken forward into the phase IIa portion which will examine the anticancer efficacy of HDP-101. In the phase IIa trial, patients will be stratified upon their 17p deletion status as this biomarker has been shown to indicate increased sensitivity to amanitin. The expectation is that the first patient will be enrolled and dosed in the second quarter of 2021. The aim will be to enroll 30 patients in the phase I portion and 36 in the phase IIa section.

Preclinical studies have shown positive results with low dose HDP-101 in mouse xenograft models producing durable complete remissions after one intravenous administration. The mechanism of action of this antibody–drug conjugate is thought to involve the inhibition of RNA polymerase II, leading to the initiation of apoptosis in the affected cell. Therefore, as low-level transcription occurs in even dormant cells, HDP-101 was effective at killing active and resting MM cells.²