Synergistic Antitumor Activity of Alnuctamab (ALNUC; BMS-986349; CC-93269), a BCMA 2+1 T Cell Engager (TCE), and Celmod Agents in Multiple Myeloma (MM) Preclinical Models

Background: Cereblon E3 ligase modulator (CELMoD®) agents, including classic immunomodulatory (IMiD®) agents, have demonstrated antitumor activity in MM. ALNUC is an asymmetric 2-arm, humanized IgG TCE that binds to B-cell maturation antigen (BCMA) and CD3ε in a 2+1 format (Seckinger A et al. Cancer Cell 2017;31:396-410). ALNUC mediates myeloma tumor cell killing by recruiting T cells to BCMA-expressing target cells, leading to immune synapse formation and T cell cytotoxic activity. We hypothesized that combining CELMoD agents with ALNUC could enhance antitumor activity. Using preclinical models of MM, we evaluated the anti-MM potential of ALNUC in combination with pomalidomide (POM) and the novel CELMoD agents mezigdomide (MEZI; BMS-986348; CC-92480) and iberdomide (IBER).

Methods: To evaluate the effects of CELMoD agents on ALNUC-mediated T cell anti-MM activity, healthy donor (HD) T cells and/or BCMA-expressing MM cell lines (H929, OPM-2, and L363) were pretreated with biologically active concentrations of POM, MEZI, IBER, or dimethyl sulfoxide (DMSO) for 16 h (T cells) or 72 h (MM cells) prior to co-culture. Following CELMoD agent pretreatment, ALNUC was added for 72 h and anti-MM activity was assessed by measuring T cell activation and MM target cell depletion. To assess the effects of CELMoD agents on artificially exhausted T cells, HD CD3+ T cells were pretreated with anti-CD3/CD28 beads and POM, MEZI, IBER, or DMSO for 7 days prior to co-culture with MM cells and ALNUC. To determine if CELMoD agent treatment could reverse T cell dysfunction in patients (pts) with relapsed/refractory MM, pre-treatment PBMCs from pts with MM in a phase 1 trial of ALNUC (NCT03486067) were co-cultured with H929 cells. PBMC samples were selected based on pts’ response to ALNUC (response, n=2; nonresponse, n=3). Co-cultures were pretreated with MEZI 1 nM for 24 h prior to the addition of ALNUC. Functional readouts in all co-culture models used flow cytometry to evaluate T cell proliferation, T cell activation, and MM-cell apoptosis. Additional readouts included measurement of soluble factors associated with T cell activation and antitumor function, including IL-2, IFNγ, TNFα, and Granzyme B. The effects of concurrent treatment and sequential priming with MEZI and ALNUC were investigated in a humanized mouse H929 MM xenograft model. Antitumor activity was assessed by tumor growth, analysis of tumor infiltrating lymphocytes, and tumor histology.

Results: In co-culture experiments with HD T cells, pretreatment of MM cells with MEZI, IBER, and POM increased ALNUC-induced tumor-cell killing potency and efficacy, resulting in IC₅₀ value reductions and a greater reduction of MM cells across all cell lines compared with ALNUC alone. ALNUC antitumor activity against the OPM-2 cell line was also enhanced by the pretreatment of T cells with MEZI and IBER, but not POM. Overall, MEZI demonstrated the greatest enhancement of ALNUC-mediated activity in this in vitro co-culture model. In artificially exhausted HD T cells, enhanced antitumor activity was observed with MEZI and IBER, but not POM, compared with DMSO. Based on the strong activity of MEZI in these in vitro models, its ability to enhance ALNUC effects was examined in a humanized mouse MM xenograft model. Priming or concurrent treatment with MEZI enhanced T cell activation, promoted T cell infiltration of tumor tissue, and increased ALNUC-induced tumor clearance in the xenograft model. The ability of MEZI to enhance ALNUC-mediated T-cell function was examined in a co-culture model using MM pt-derived PBMCs harvested before ALNUC treatment. Pretreatment with MEZI increased ALNUC-mediated antitumor activity vs controls in samples from both responder and nonresponder pts.

Conclusions: The combination of ALNUC and novel CELMoD agents demonstrated enhanced T cell mediated antitumor activity both in vitro and in ex vivo MM models. MEZI showed the greatest ability to enhance TCE-mediated antitumor activity while reversing artificial T cell dysfunction/exhaustion in vitro. Priming and concurrent treatment with MEZI enhanced ALNUC-induced T cell infiltration and activation in the MM xenograft model. The ability of MEZI to enhance ALNUC T cell antitumor function was confirmed using PBMCs from ALNUC monotherapy-treated pts with MM. These results provide a strong biological rationale for combining MEZI (or IBER) with ALNUC in the clinic to enhance responses in pts with MM.

Paiva:Sanofi: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb-Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; GSK: Honoraria, Research Funding; EngMab: Research Funding; Roche: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Adaptive: Honoraria; Amgen: Honoraria; Gilead: Honoraria; Oncopeptides: Honoraria. Gaffney:Bristol Myers Squibb: Current Employment. Burnett:Bristol Myers Squibb: Current Employment. Castiglioni:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Angelo:Bristol Myers Squibb: Current Employment. Pierce:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Patents & Royalties. Boss:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Current holder of stock options in a privately-held company.