Abstract 1115: A CRISPR/Cas9 kinome screen identifies GRK5 as a novel regulator of rhabdomyosarcoma (RMS) self-renewal

Abstract

Abstract Rhabdomyosarcoma (RMS) is a devastating pediatric soft tissue sarcoma. Clinical outcome for patients with relapsed or metastatic disease remains poor. However, current treatment options remain relatively unchanged over the last two decades, so there remains an urgent need for more effective treatment options for disease relapse. Cancer stem cells (CSCs), also known as tumor-propagating cells (TPCs), have the capacity for self-renewal and have been proposed to be responsible for tumor relapse and metastasis. RMS has been shown to follow the CSC model of tumor progression. We have previously performed an siRNA library screen against the human kinome (714) and a secondary CRISPR/Cas9 screen of top candidates to narrow down to 11 novel kinase candidates that are potentially essential for self-renewal of human RMS cells. GRK5, a G-protein coupled receptor kinase, was among the top candidate genes. Preliminary data from in vitro cell-based assays and in vivo limiting-dilution experiments in xenografts showed that CRISPR/Cas9-mediated targeted disruption of GRK5 resulted in significant reduction in the self-renewal capacity of RMS cells. GRK5-deficient RMS cells also displayed significant reduction in growth secondary to cell cycle arrest at the G2/M checkpoint. The functional effects on tumor growth and self-renewal appeared unique to GRK5 among the GRK kinase subfamily, as targeted disruption of closely-related GRK4 and GRK6 did not significantly affect RMS tumor cell growth and self-renewal. We propose that targeted disruption of GRK5 by CRISPR/Cas9 results in elevated p53 protein stability and activity, leading to inhibition of proteins required for cell cycle progression. We are also characterizing the loss-of-function effects of GRK5 in a RMS TPC reporter cell line created using a CRISPR/Cas9 knockin approach that will allow for direct assessment of GRK5 and other candidate gene function within the TPC population. By characterizing the biologic role of TPC as well as the function of GRK5 in RMS, we hope to provide new biologic insights into cancer stem cell biology and GRK5 as a novel therapeutic target for the treatment of advanced RMS. Citation Format: Thao Q. Pham, Terra Vleeshouwer-Neumann, Eleanor Chen. A CRISPR/Cas9 kinome screen identifies GRK5 as a novel regulator of rhabdomyosarcoma (RMS) self-renewal [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1115.