Kinome and Druggable Genome Vulnerabilities in Multiple Myeloma Identified by Systematic RNA Interference Screening.

We have conducted systematic small interfering RNA (siRNA) lethality screening of the kinome and “druggable genome” in human myeloma cell lines (HMCL) to functionally generate a comprehensive map of critical genes and vulnerabilities in human myeloma tumors. KMS11 human myeloma cells were screened with both an 1800 oligo (639 gene) siRNA library targeting the kinome and with a 13,984 oligo (6,791 gene) library targeting the druggable genome in duplicate using optimized conditions that resulted in >95% transfection efficiency and <5% background cytotoxicity. siRNA were used at low concentration (13nM) to minimise off-target cellular effects. Each gene was initially screened with at least 2 distinct siRNA. Universally lethal and non-silencing siRNA were tested in parallel as controls. Viability was measured at 96 hours by ATP-dependent luminescence and was normalized to the mean and distribution of controls by the B-score method. Approximately 14% of kinome siRNA and 5.8% of druggable genome siRNA caused important reductions in HMCL viability (greater than three standard deviations from control samples treated with non-silencing siRNA), compared with an anticipated rate due to chance of only 0.135%. Short-listed kinome vulnerabilities were validated by repeat targeting in a second lethality screening experiment in KMS11 using a total of four independent siRNA per gene. Forty-two kinases were confirmed as critical for myeloma cell survival. Unsupervised pathway analysis indicates that approximately half are concentrated within established pathways involved in cytokine (VEGFR, FGFR3, IGFR/IL6R) signaling and regulation of cell cycle, apoptosis or metabolism. The role of other survival kinases in myeloma are novel. The selectivity of kinome vulnerabilities identified in KMS11 for myeloma cells versus other tissues was examined by parallel silencing of these targets in KMS11 and JJN3 myeloma cells and in non-myeloma 293 and A549 epithelial cells. The most lethal kinase targets in myeloma that simultaneously show experimental evidence of tumor selectivity include aurora kinase A (AURKA), G-protein receptor coupled kinase 6 (GRK6) and protein kinase N1 (PKN1). By gene expression analyses, PKN1 and GRK6 are both preferentially expressed in plasma cells, compared with an analysis of >50 somatic tissues in which they are absent or only weakly expressed. The extent to which the kinome vulnerabilities identified in KMS11 occur in other HMCL was assessed by tertiary siRNA screening and by lentiviral shRNA techniques. More than 75% of kinases vulnerable in KMS11 cells are recurrently vulnerable in other myeloma tumor lines. Secondary validation studies of all genomic vulnerabilities identified from the much larger siRNA lethality screen of the druggable genome in myeloma cells is ongoing, however, to date 134 genes have been validated as essential myeloma survival factors during primary screening by concordant lethality of 2/2 independent siRNA (compared with an expected rate due to chance of n<1 genes). Significantly, proteosome subunits and specific ubiquitin ligases number amongst the most potently lethal genomic vulnerabilities in KMS11. Overall, this attempt to systematically and functionally document all genetic vulnerabilities in myeloma provides a strong rational impetus for the development of novel therapies that optimally target susceptibilities inherent within myeloma tumors.