Mezigdomide (CC-92480), a Novel Cereblon E3 Ligase Modulator, Induces Vulnerability of Multiple Myeloma Cells to T-Cell-Mediated Killing (2022)

Introduction: Mezigdomide (BMS-986348) is a novel cereblon (CRBN) E3 ligase modulator (CELMoD®) that induces potent degradation of IKZF1 (Ikaros) and IKZF3 (Aiolos), transcription factors that contribute to multiple myeloma (MM) survival. The direct tumoricidal effect of mezigdomide is mediated by rapid, deep, and sustained degradation of Ikaros and Aiolos and induction of apoptosis in MM cells. In parallel, mezigdomide induces degradation of Ikaros and Aiolos in peripheral blood mononuclear cells (PBMCs), leading to the activation of T cells. This dual mechanism of cell-autonomous tumor inhibition and immune activation has been invoked to explain the clinical observations highlighting the impact of patient immune status on treatment outcomes. Here, we provide data indicating that these mechanisms may be one and the same: the primary site of action of mezigdomide is in the tumor cell, and results in both cell-autonomous viability loss and sensitization to immune-mediated killing. Methods: To assess the impact of mezigdomide on interactions with T cells, we combined mezigdomide and alnuctamab (BMS-986349; CC-93269), an asymmetric 2-arm, humanized immunoglobulin G1-based T-cell engager that promotes T-cell-mediated killing of target cells by recruiting T cells to BCMA-expressing target cells, leading to immune-synapse formation and T-cell cytotoxic activity. Donor T cells (n = 3) or target MM cells (n = 3 cell lines with various BCMA-expression levels tested: H929 > OPM2 > L363) were pretreated with mezigdomide for 16 or 72 hours, respectively, and after mezigdomide wash off, T cells and MM cells were combined in a co-culture system followed by alnuctamab treatment for 72 hours. BCMA was measured before and after mezigdomide pretreatment. Target-cell viability, T-cell proliferation, and cytokine release were measured at the end of the co-culture period. Primity BioScreen, a flow-cytometry-based assessment of membrane-associated proteins, was performed on target MM cells (n = 5 different cell lines) and PBMCs following mezigdomide pretreatment to profile potential changes in surface proteins important for immune-synapse formation. Results: Pretreatment of target MM cells with mezigdomide for 72 hours led to enhanced cytotoxic activity of alnuctamab. These results were reproducible across 3 healthy donors and various MM cell lines, including lenalidomide- and pomalidomide-resistant derivates, but not in CRBN-deficient cell lines. Profiling of secreted factors associated with T-cell cytotoxic function revealed increased release of interleukin-2 after mezigdomide pretreatment of either T cells only or T cells and MM cells; further experiments utilizing conditioned media showed no effect of mezigdomide-induced secreted factors on T-cell-mediated killing, suggesting a primary role for T-cell-to-target-cell interaction. Primity BioScreen revealed that the profile of adhesion molecules important for T-cell-mediated killing had been shifted both in MM cells and in PBMCs after mezigdomide pretreatment, revealing several candidates potentially mediating the enhanced cytotoxicity of alnuctamab following mezigdomide pretreatment. Conclusions: Collectively, our data demonstrate that pretreatment with mezigdomide induces enhanced immune sensitization in MM cells via upregulation of membrane-associated cell-adhesion molecules leading to increased cytotoxic T-cell activity. These results support the clinical investigation of mezigdomide in combination with T-cell-engaging therapeutic modalities in patients with MM.