Synergistic Drug Combinations to Overcome Venetoclax Resistance in Multiple Myeloma

We have established a functional precision medicine platform to evaluate the chemosensitivity of 76 FDA-approved and clinical therapeutics relevant to multiple myeloma (MM), alone or in combinations, in human myeloma cell lines (HMCLs) and in primary MM samples. The panel includes the Bcl-2 inhibitor venetoclax, currently in clinical development. There is a pressing need to identify rational drug combinations that select for synergistic activity with venetoclax, overcome its resistance, and provide patients with less toxic treatment options. Here we report the results of a drug screen combining venetoclax with our MM drug panel (MMDP), and examine how venetoclax sensitivity modulates drug synergy profiles. The MMPD was first screened in dose-response format in 25 HMCLs and in 113 primary MM samples using a cellular viability assay (CellTiter Glo, Promega). Single drug response data were used to calibrate concentration ranges for MMDP drugs combined with venetoclax, acoustically dispensed on assay-ready plates in matrix format. Cellular viability was assayed after 72h incubation and synergism quantified using Bliss, HSA, and Loewe scores (Combenefit). Two independent combination screens evaluated synergism of MMDP with venetoclax in a cell line of intermediate (OPM2, EC50 = 690 nM) and low (AMO1, EC50 = 5185 nM) venetoclax sensitivity. Maximum synergism was observed for the HDAC inhibitor panobinostat at 0.80 nM combined to 5.86 nM venetoclax in OPM2, corresponding to a 3.6 and 4.4 fold dose decrease respectively, as compared to single agent response. The most synergistic drug combinations were then confirmed in 3 additional cell lines per class (Intermediate: XG2, NCI-H929, JJN3; Resistant: RPMI-8226, KMS11, KMS26). Five drugs presented concordant synergism in the intermediate class while 10 drugs were found to synergize with venetoclax in the resistant class. The AKT1 inhibitor afuresertib and crenolanib, a PDGFRalpha/beta inhibitor, presented similar patterns of synergism in both groups. Panobinostat, the DNMT inhibitor azacitidine, and dexamethasone had the highest venetoclax synergism in intermediate HMCLs, but had moderate synergism in resistant HMCLs. Eight drugs synergized with venetoclax in resistant HMCLs only. These included carfilzomib, lenalidomide, paclitaxel, and kinase inhibitors cobimetinib, ceritinib, quizartinib, nilotinib, and dovitinib. These