siRNA library screen of human kinases and phosphatases identifies polo-like kinase 1 as a promising new target for the treatment of pediatric rhabdomyosarcomas

摘要

Rhabdomyosarcoma (RMS), consisting of alveolar (aRMS) and embryonal (eRMS) subtypes, is the most common type of sarcoma in children. Currently, there are no targeted drug therapies available for RMS. In searching for new molecular therapeutic targets, we performed genome-wide siRNA library screens targeting human phosphatases (n=206) and kinases (n=691) initially against an aRMS cell line, RH30. Sixteen phosphatases and 50 kinases were identified based on growth inhibition after 72 hours. Inhibiting polo-like kinase 1 (PLK1) had the most remarkable impact on growth inhibition (~80%) and apoptosis on all three RMS cell lines tested including RH30, CW9019 (aRMS) and RD (eRMS), while there was no effect in normal muscle cells. The loss of PLK1 expression and subsequent growth inhibition correlated with decreased p-CDC25C and Cyclin B1. Increased expression of WEE 1 was also noted. The induction of apoptosis after PLK1 silencing was confirmed by increased p-H2AX, propidium iodide uptake, chromatin condensation, as well as caspase-3 and PARP cleavage. Pediatric Ewing’s sarcoma (TC-32), neuroblastoma (IMR32 and KCNR) and glioblastoma (SF188) models were also highly sensitive to PLK1 inhibition. Finally, based upon cDNA microarray analyses, PLK1 mRNA was over-expressed (>1.5 fold) in 10/10 RMS cell lines and in 47% and 51% of primary aRMS (17/36 samples) and eRMS (21/41 samples) tumors, respectively, compared to normal muscles. Similarly, pediatric Ewing’s sarcoma, neuroblastoma and osteosarcoma tumors expressed high PLK1. We conclude that PLK1 could be a promising therapeutic target for the treatment of a wide range of pediatric solid tumors including RMS.