miR-331-3p and Aurora Kinase inhibitor II co-treatment suppresses prostate cancer tumorigenesis and progression

// Michael R. Epis 1, * , Keith M. Giles 1, 4, * , Dianne J. Beveridge 1, * , Kirsty L. Richardson 1 , Patrick A. Candy 1 , Lisa M. Stuart 1 , Jacqueline Bentel 2 , Ronald J. Cohen 5 and Peter J. Leedman 1, 3 1 Laboratory for Cancer Medicine, Harry Perkins Institute of Medical Research and University of Western Australia Centre for Medical Research, Nedlands, WA, 6009, Australia 2 Department of Anatomical Pathology, Fiona Stanley Hospital, Murdoch, WA, 6150, Australia 3 School of Medicine and Pharmacology, University of Western Australia, Nedlands, WA, 6008, Australia 4 Department of Dermatology, New York University Langone Medical Center, New York, NY, 10016, USA 5 Uropath Pty Ltd, West Leederville, WA, 6007, Australia * These authors have contributed equally to this work Correspondence to: Peter J. Leedman, email: peter.leedman@perkins.uwa.edu.au Keywords: miR-331-3p, prostate cancer, Aurora Kinase inhibitor, co-treatment Received: March 26, 2017      Accepted: May 22, 2017      Published: June 27, 2017 ABSTRACT RNA-based therapeutics could represent a new avenue of cancer treatment. miRNA 331-3p (miR-331-3p) is implicated in prostate cancer (PCa) as a putative tumor suppressor, but its functional activity and synergy with other anti-tumor agents is largely unknown. We found miR-331-3p expression in PCa tumors was significantly decreased compared to non-malignant matched tissue. Analysis of publicly available PCa gene expression data sets showed miR-331-3p expression negatively correlated with Gleason Score, tumor stage, lymph node involvement and PSA value, and was significantly down regulated in tumor tissue relative to normal prostate tissue. Overexpression of miR-331-3p reduced PCa cell growth, migration and colony formation, as well as xenograft tumor initiation, proliferation and survival of mice. Microarray analysis identified seven novel targets of miR-331-3p in PCa. The 3’-untranslated regions of PLCγ1 and RALA were confirmed as targets of miR-331-3p, with mutation analyses confirming RALA as a direct target. Expression of miR-331-3p or RALA siRNA in PCa cells reduced RALA expression, proliferation, migration and colony formation in vitro . RALA expression positively correlated with Gleason grade in two separate studies, as well as in a PCa tissue microarray. Co-treatment using siRALA with an Aurora Kinase inhibitor (AKi-II) decreased colony formation of PCa cells while the combination of AKi-II with miR-331-3p resulted in significant reduction of PCa cell proliferation in vitro and PCa xenograft growth in vivo . Thus, miR-331-3p directly targets the RALA pathway and the addition of the AKi-II has a synergistic effect on tumor growth inhibition, suggesting a potential role as combination therapy in PCa.