Overcoming miR-106a induced radioresistance in prostate cancer: Targeting senescence with KU-55933.

Abstract

77 Background: Prostate cancer is a leading cause of cancer related death in men worldwide, with recurrence being a major clinical problem after radiotherapy. There is an unmet need to better characterize radioresistant tumors and identify biomarkers to improve patient outcomes. Methods: We identified that miR-106a was overexpressed in radiation resistant cell lines compared to parental cells. We analyzed The Cancer Genome Atlas dataset to assess miR-106a expression in normal prostate, and low- to high-grade prostate tumors. To assess the functional role of miR-106a, we performed in vitro and in vivo assays for radiation response, including clonogenic survival, proliferation, senescence, and tumor xenograft growth after radiation. We performed gene array and pathway analyses to identify downstream effectors of miR-106a. Results: MiR-106a expression was significantly higher in prostate tumors with Gleason score > 7 compared to Gleason ≤ 7, suggesting miR-106a is involved in high grade disease. MiR-106a overexpression confers radioresistance in vitro and in vivo, by targeting LITAF. We now extend miR-106a’s effects to upregulation of ATM at the promoter level, thereby increasing ATM transcript and protein in the cell. Unexpectedly, we found that miR-106a’s mechanism of radioresistance through ATM upregulation does not alter DNA damage repair. ATM upregulation affects clonogenic survival through reduced senescence. KU-55933, a specific ATM kinase inhibitor, resensitizes miR-106a overexpressing cells to radiation by inducing senescence, a predominant mode of cell death in prostate cancer. Conclusions: Our research challenges the current paradigm of ATM and DNA damage repair by outlining another mechanism of radioresistance through alteration of senescence. Our findings suggest that miR-106a may be a promising biomarker for high-grade disease and radioresistant prostate cancer. In addition, we have identified a therapeutic intervention for miR-106a induced radioresistance. Improvements in bioavailability of KU-55933 may lead to its clinical use in combination with radiation therapy to radiosensitize miR-106a induced radioresistant prostate cancer.