Abstract 1325: Overexpression of Tribbles 2 enhances prostate cancer cell growth and contributes to enzalutamide resistance

Abstract Background: Enzalutamide, an FDA-approved androgen receptor blocker, is commonly prescribed for advanced prostate cancer which slows down prostate tumor growth. However, therapeutic benefit of enzalutamide is temporary because enzalutamide-resistant prostate cancer (ERPC) invariably develops which is incurable, primarily because currently available therapies cannot effectively kill ERPC cells. Molecular basis behind enzalutamide-resistance is not clearly understood, which is delaying progress towards development of new therapies. Thus, proper molecular characterization of ERPC cells is an urgent and unmet medical need to find appropriate targets to improve the current state of ERPC therapy. Methods: We developed an ERPC model by chronically treating prostate cancer cells to mimic the clinical conditions of Enzalutamide resistance. These ERPC cells were used for comprehensive gene expression analysis by Illumina Hi-Seq whole genome gene-expression array. Hits were confirmed by RT-PCR and Western blot. Regulation of expression and pro-cancer effects of new hits were determined by overexpression and/or treating cells with shRNA and analyzing cell viability, soft-agar colony formation, apoptosis, and effects on downstream targets. Results: Transcriptional profiling revealed that Tribbles 2 (Trib2), a pseudokinase, is overexpressed in ERPC cells. Elevated level of Trib2 was also observed in enzalutamide treated PDX tumors in mice, and in prostate tumors from patients who were treated with enzalutamide. Inhibition of Trib2 by shRNA effectively kills ERPC cells, suggesting that Trib2 plays an important role in ERPC. We found that the Trib2 protein level is especially higher in prostate cancer cells where the AR activity is either low, or absent due to genetic changes. Moreover, transfection and re-expression of the AR gene in AR-negative cells decreases Trib2 protein level, indicating that the expression of Trib2 is negatively regulated by androgenic signaling. Interestingly, forced overexpression of Trib2 results in faster prostate cancer cell growth and makes the cells completely resistant to enzalutamide, and inhibition of Trib2 by shRNA or chemical inhibitor decreases viability and re-sensitizes these cells to enzalutamide. Conclusion: Collectively, our findings reveal that Trib2 is overexpressed in ERPC cells and tumors, and suggest that Trib2 may turn out to be a novel, promising molecular target for therapy of enzalutamide-resistant, lethal prostate cancer. Citation Format: Jitender Monga, Parshva Sanghvi, Jagadananda Ghosh. Overexpression of Tribbles 2 enhances prostate cancer cell growth and contributes to enzalutamide resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1325.