Abstract 3943: Inhibition of ribosomal protein RPS6KB1 as a strategy to improve conventional therapy for prostate cancer
Authors: Clark Alison D. , Hussain Suleman S. , Huang Shih-Bo , Bedolla Roble G. , Obeidat Mohammad A. , Papanikolaou Niko , Lin Chun Lin , Huang Tim H. , Gupta Yogesh , Chen Yidong , Miyamoto Hiroshi , Ghosh Rita , Kumar Addanki P. 
Published: August 2019

Abstract
Radiation therapy (RT) is a standard treatment for organ confined prostate cancer (PCa). Although dose escalation increases local control, further escalation hampers effectiveness due to toxicity. Additionally, intrinsic and acquired resistance to radiation causes progression to advanced metastatic PCa. Therefore, there is an urgency for addition of adjuvant therapies that synergize with radiation to improve therapeutic efficacy. We have identified a novel combination regimen (Nexrutine, Nx, a natural compound plus radiation) that demonstrated strong synergistic tumor growth inhibition in vitro (in multiple prostate cancer cell lines) and in transgenic adenocarcinoma of mouse prostate (TRAMP) model in part through downregulation of ribosomal protein S6K (RPS6KB1). To understand the precise molecular mechanism of synergy between Nx and radiation, we conducted transcriptome profiling of prostate cancer cells treated with single and combination modalities and followed up with pathway analysis, clinical validation, and in vitro gain and loss of function studies. Analyses of these data identified significant alterations in expression of genes across all experimental groups and genes that were unique to each group. Functional annotation using DAVID analysis of the top 200 genes in the combination group revealed ‘cell cycle regulation’ as the top pathway altered in the combination treatment. Remarkably, 22 genes enriched in the cell cycle pathway (including RPS6KB1) showed significant upregulation in high Gleason human prostate tumors. Interestingly cBioportal data indicated that alterations of RPS6KB1 in human prostate tumors is mutually exclusive with expression changes of AKT or NFκB. Computational molecular modeling studies showed that Berberine (Ber), one of the active constituents of Nx, interacts with RPS6KB1 in a novel mode. Additional biochemical and molecular investigations using RPS6KB1 KO cells divulged that KO cells are relatively (i) resistant to Ber and (ii) more sensitive to NFκB inhibitor-induced proliferation inhibition compared to wild type LNCaP cells. Collectively, our findings (i) identified RPS6KB1 as a direct target of Ber; and (ii) demonstrate that RPS6KB1 is a clinically relevant target of prostate cancer with possible role in radiosensitization. This work is supported in part by SABER*IRACDA grant K12GM11726 (ADC) and VA-Merit Award I01 BX 003876 (APK).
Citation Format: Alison D. Clark, Suleman S. Hussain, Shih-Bo Huang, Roble G. Bedolla, Mohammad A. Obeidat, Niko Papanikolaou, Chun Lin Lin, Tim H. Huang, Yogesh Gupta, Yidong Chen, Hiroshi Miyamoto, Rita Ghosh, Addanki P. Kumar. Inhibition of ribosomal protein RPS6KB1 as a strategy to improve conventional therapy for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3943.