Tribbles 2 confers resistance to anti-androgenic therapy in prostate cancer via lineage switching

Abstract Background: About 33,000 men will die due to prostate cancer in the US in the year 2021. Prostate cancer initially responds to androgen receptor (AR) targeted therapies (e.g., enzalutamide, darolutamide). However, therapy-resistant, aggressive, lethal malignancy invariably develops for which no effective, targeted treatment options are available. Though failures of AR-targeted therapies remain as major cause for mortality among prostate cancer patients, molecular mechanisms underlying the emergence of resistance are still to be fully characterized. Methods: To understand the molecular basis of enzalutamide resistance, we developed a prostate cancer cell model to mimic the clinical conditions in enzalutamide-resistant disease. These cells were transcriptionally profiled for gene expression analysis by Illumina Hi-Seq whole genome gene-expression array. Hits were validated by RT-qPCR and Western blot. For clinical correlation, samples from enzalutamide treated prostate PDX models as well as surgical prostate tumors from patients were comprehensively analyzed. Role of new hits were determined by lentiviral shRNAs and analysis of cell viability, apoptosis, and downstream targets. Pro-cancer effects were analyzed by cell proliferation, invasion, and soft-agar colony formation. Results: We identified that the Tribbles 2 (TRIB2) pseudokinase is overexpressed in enzalutamide resistant prostate cancer (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. We found that TRIB2 protein level is especially higher in prostate cancer cells where the AR activity is low, or absent due to genetic changes. Forced overexpression of TRIB2 results in aggressive prostate cancer cell growth and makes the cells resistant to enzalutamide. Conversely, inhibition of TRIB2 by shRNA or chemical inhibitor decreases viability and re-sensitizes ERPC cells back to enzalutamide, suggesting that TRIB2 plays an important role as a driver in the resistance mechanism. Interestingly, TRIB2 downregulates luminal markers, but upregulates neuroendocrine markers via the master neuronal transcription factor, BRN2, and the reprogramming factor, SOX2. Inhibition of either BRN2 or SOX2 also re-sensitizes ERPC cells to enzalutamide. Conclusion: These findings suggest that TRIB2 confers resistance to enzalutamide therapy through lineage switching from luminal to neuroendocrine type, involving BRN2 and SOX2. Citation Format: Jitender Monga, Indra Adrianto, Craig Rogers, Shirish Gadgeel, Dhananjay Chitale, Jagadananda Ghosh. Tribbles 2 confers resistance to anti-androgenic therapy in prostate cancer via lineage switching [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 398.