Enitociclib decreases cell viability in MM cells. (A) Cell viability of small-molecule inhibitors from the pharmaceutical pipeline library treated at 1 μM for 96 hours in OPM-2 cells. A breakdown of molecular targets with a mean cell viability inhibition of >50% are shown. (B) Cell viability values of various CDK inhibitors from the library treated at 1 μM for 96 hours in OPM-2 cells are shown. (C) Western blotting of MM cell lines MM1.S, NCI-H929, OPM-2, and U266B1. Total cell lysates were prepared and analyzed by immunoblotting to detect the level of CDK9. β-actin was used as a loading control. Molecular masses are indicated in kilodaltons (kDa). (D) Dose response curves of MM cell lines treated with increasing concentrations (12.5-200 nM) of enitociclib for 96 hours. Cell viability was measured by Alamar Blue assay. Percent cell viability was normalized to corresponding treatment with dimethyl sulfoxide (DMSO; vehicle control). Mean percentages of cell viability were calculated from 3 technical replicates and standard deviations are shown. BET, Bromodomain and extraterminal; EZH1/2, Enhancer of zeste homolog 1/2; FLT3, Fms-like tyrosine kinase 3; HDAC, Histone deacetylase; HSP, Heat shock protein; IGF-1R, Insulin-like growth factor 1 receptor; KDM5A, Lysine (K)-specific demethylase 5A; mTOR, Mammalian target of rapamycin; NAE, NEDD8-activating enzyme; WNK, With no lysine (K); XPO1, Exportin-1.