Abstract 1061: Characterization of synergistic selinexor combinations with dexamethasone, pomalidomide, elotuzumab, and daratumumab in primary MM cells

Introduction. Multiple myeloma (MM) is an all but incurable plasma cell malignancy without predictive biomarkers for approved therapies. Selinexor (SELI), a nuclear export inhibitor targeting exportin 1 (XPO1), is approved with dexamethasone (DEX) with promising SELI-combination studies ongoing. We investigated SELI combinations ex vivo to identify synergistic combinations and companion biomarkers. Methods. We established a platform to perform parallel RNA/exome sequencing and ex vivo drug sensitivity assessment on CD138+ cells from MM patient bone marrow aspirates. At the time of this analysis, 844 different samples with clinical, WES and RNA sequencing data were treated ex vivo with the following agents: SELI (n=75), DEX (192), pomalidomide (POM, 268), elotuzumab (ELO, 21), daratumumab (DARA, 117), SELI+DEX (22), SELI+POM (20), SELI+ELO (21), SELI+DARA (27). Cells were cultured with autologous macrophages, stroma, collagen matrix and patient-derived serum. Cell death (LD50 and AUC) was assessed through digital image analysis. Sequencing was performed through ORIEN/AVATAR. Links between non-synonymous mutations in coding genes and cell death were calculated using T-tests with multiple test correction. Results. Our analysis identified SELI+DEX (number of samples=60, p<1E-9), SELI+POM (57, p<0.001) and SELI+ELO (55, p<0.01) as the most synergistic combinations (BLISS model). SELI+DARA showed synergy in 23 out of 50 samples tested. Notably, both direct drug toxicity and phagocytosis were observed. RNAseq found gene expression associations with drug resistance/response. In turn, gene set enrichment analysis (GSEA) showed that SELI resistance was associated with expression of cell adhesion, inflammatory cytokines, and EMT pathways, while the MYC targets were associated with SELI sensitivity. SELI+ELO resistance was associated with expression of hedgehog signaling pathway, while expression of ribosomal subunits was associated with sensitivity. SELI+POM resistance was linked with lysosome and cell adhesion molecules, while sensitivity was tied to ribosome, spliceosome and RNA polymerase. GSEA also identified G2M, MTORC1, MYC targets, E2F and glycolysis as biomarkers for the SELI+DARA synergistic subgroup. WES also identified mutations associated with SELI sensitivity. Mutation of BCL7A, a protein involved in chromatin remodeling, was associated with sensitivity, and mutation of CEP290, which encodes a microtubule binding protein, was associated with resistance (p<0.05). Both BCL7A and CEP290 contain predicted nuclear export sequences, suggesting they are XPO1 cargoes. Conclusions. We observed ex vivo synergy between SELI and DEX, POM, ELO and DARA, and identified expression signatures and mutations associated with response to these agents. Ongoing analysis of additional samples is being performed to validate these results. Citation Format: Praneeth Reddy Sudalagunta, Mark B. Meads, Rafael Renatino Canevarolo, Maria Coelho Silva, Christopher Cubitt, Gabriel DeAvila, Raghunandan Reddy Alugubelli, Constantine N. Logothetis, Amit Kulkarni, Qi Zhang, Oliver Hampton, Christopher J. Walker, Yosef Landesman, Kenneth Shain, Ariosto Siqueira Silva. Characterization of synergistic selinexor combinations with dexamethasone, pomalidomide, elotuzumab, and daratumumab in primary MM cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1061.