Inhibition of PIM kinase with fractionated radiation and docetaxel in preclinical prostate cancer models.

Abstract

e17534 Background: PIM kinases are highly expressed in high risk prostate cancer and are associated with aggressiveness and poor prognosis, presenting a therapeutic target. Methods: We studied PIM inhibition (PIMi) in both hormone-dependent (LNCaP) and -independent (DU145, 22Rv1) prostate cancer cell lines and mouse xenografts. We evaluated PIMi effects via Western blotting, immunofluorescence, and RNAseq of multiple relevant pathways, and performed radiosensitization analysis with colony formation assays. We also investigated xenograft tumor growth with PIMi +/- radiation (RT) or docetaxel. Results: Pretreating the cell lines with PIMi prior to RT caused marked changes in H2AX phosphorylation compared to no PIMi + RT, with most significant alteration in DU145. However, in colony formation assays, 22Rv1 showed greatest radiosensitization with colony survival reduced from 23% to 15% with PIMi. 22Rv1 xenografts were grown in castrated mice, which were randomized to 30 Gy in 15 treatments vs no RT over 3 weeks, -/+ PIMi on RT days. RT + PIMi eliminated gross tumor, compared to an average of 78% and 51% of initial tumor volumes remaining with PIMi alone and RT alone, respectively. Immunofluorescence and Western blotting of harvested tumors showed PIMi altered patterns in proteins involved with hypoxic response (COX-2), cell survival (MDM2), and androgen receptor and suggested interactions between RT and PIMi for both MDM2 and androgen receptor but not COX-2. RNAseq analysis of xenografts showed daily PIMi affected multiple pathways involved in metabolism, growth, and DNA repair. Finally, we tested PIMi -/+ docetaxel in castrated mice with hormone-sensitive (LNCaP) or -resistant (22Rv1) xenografts treated with PIMi -/+ docetaxel. With both xenografts, PIMi + docetaxel reduced tumor size best, with 22Rv1 xenografts most dramatically showing 74% volume reduction from baseline with PIMi + docetaxel compared to 50% and 25% reduction in volumes with PIMi alone and docetaxel alone, respectively. Conclusions: PIMi has multiple pathway effects in prostate cancer. PIMi significantly reduces disease burden, particularly in combination with RT or docetaxel. Our data provide rationale for testing PIMi in clinical trials for prostate cancer.