Kinetics of nirogacestat-mediated increases in B-cell maturation antigen on plasma cells inform therapeutic combinations in multiple myeloma.

Abstract

B-cell maturation antigen (BCMA) is the target of several investigational and approved drugs for multiple myeloma (MM). BCMA expressed on plasma cells (PCs) and MM cells is cleaved by the enzyme gamma secretase, reducing membrane-bound BCMA (mbBCMA) receptor density. Gamma secretase inhibitors (GSIs) have been shown to increase mbBCMA density and may enhance efficacy of BCMA-targeted therapies. The pharmacodynamic profile of the GSI nirogacestat was evaluated in MM cell lines and a phase 1 study in healthy volunteers. In MM cell lines, mbBCMA density and soluble BCMA (sBCMA) concentrations were measured before and after short-duration nirogacestat exposure and at serial timepoints following washout. In the phase 1 study, 23 participants were administered a single oral dose of nirogacestat 50, 150, or 300 mg or repeated doses of 100 mg every 12h for up to 48h; mbBCMA density on PCs (from whole blood and bone marrow) and nirogacestat plasma concentrations were measured at baseline and postdose. After single-dose administration, serum nirogacestat concentrations rapidly increased (Tmax ~1h), and a two-compartment model with linear absorption and clearance best described nirogacestat pharmacokinetics. In MM cells and healthy volunteers' PCs, nirogacestat resulted in rapid and robust increases in mbBCMA density, with increases up to 20-fold within 4-8h of exposure. Concomitant decreases in sBCMA were observed. Nirogacestat is currently being evaluated in combination with several BCMA-directed therapeutic agents in patients with MM. Elucidating the kinetics of BCMA in response to nirogacestat is key to guiding dosing and therapeutic strategies in MM.