Cytotoxic effect of venetoclax (ABT 199) and THZ1 alone and in combination on MM cell lines. (A-B) MM cell lines KMS 27 (A) and U266 and MOLP8 cells (B) were treated with varying concentrations of venetoclax (0-15 μM) for 24 hours. Cell viability, expressed as a percentage of untreated control, was assessed using the CellTiter-Glo (CTG) assay on triplicate cultures. (C) U266 and MOLP8 cells and healthy PBMCs (n = 5) were treated with THZ1 (0-300 nM) for 24 hours, with cell viability assessed using the CTG assay. (D) THZ1 and venetoclax synergistically induce cell death in venetoclax-resistant MM cells. The dose-response matrix and synergy map show the percentage inhibition of U266 and MOLP8 cells after 24 hours of treatment with venetoclax alone and in combination with THZ1 at different concentrations. Cell viability was determined using the CTG assay followed by ZIP score analysis. A ZIP score >10 denotes synergistic interaction. (E) U266 and MOLP8 cells were incubated with the indicated concentrations of ABT-199 ± THZ1 for 24 hours, after which PARP and CASPASE3 cleavage was monitored by immunoblotting analysis. β-actin was assayed to ensure equivalent loading and transfer. ABT, Abbott Laboratories; HD PBMC, healthy peripheral blood mononuclear cell.