Pre-clinical targeting of enzalutamide-resistant prostate cancer

• Main Author: Toren, Paul
• Language: English
• Published: University of British Columbia 2017
• Online Access: http://hdl.handle.net/2429/60230

Prostate cancer causes morbidity and mortality for thousands of Canadian men each year. Castration remains the primary treatment for recurrent or metastatic prostate cancer. However, castration is never curative, and the cancer inevitably recurs as castration resistant prostate cancer (CRPC). Newer androgen receptor (AR) antagonists such as enzalutamide(ENZ) demonstrate significant benefit in CRPC patients, but these agents remain non-curative. Therefore, the goal of this thesis was to explore novel strategies to target ENZ-resistant prostate cancer using previously developed models of resistance. Our models suggest that similar resistance patterns to CRPC may be found in ENZ-resistance, including the upregulation of steroidogenesis and activation of survival pathways such as the PI3K/Akt pathway. Unlike inhibition of the AR pathway, we found that inhibition of different nodes of the PI3K/Akt pathway had limited efficacy as monotherapy and we therefore focused on combination strategies to target this prominent survival pathway. We found that combined Akt and MEK pathway inhibition demonstrates only moderate synergy in AR-positive models of prostate cancer, and this did not appear significantly greater in ENZ-resistant than ENZ-sensitive prostate cancer. However, we did find that blockade of Akt signaling in combination with ENZ significantly delays the development of resistance to ENZ through a very significant induction of apoptosis and cell cycle arrest. Further, co-targeting of the Akt and AR pathways appears more effective at earlier stages of prostate cancer progression, when the tumours are still castrate-sensitive. Finally, to further evaluate the combination of PI3K/Akt pathway and AR blockade, we investigated the pre-clinical rationale for the use of bromodomain inhibitors, which indirectly targets both the AR and myc transcription factors. Upregulation of myc was observed following PI3K/Akt inhibition, but overall our studies did not support the combination of bromodomain inhibitors in combination with PI3K/Akt inhibition in prostate cancer models. Taken together, our pre-clinical results highlight several treatment strategies and pitfalls in targeting ENZ-resistant prostate cancer. These studies enhance our understanding of therapeutic approaches to target resistant prostate cancer with several novel agents and combination strategies. Further evaluation in clinical trials is warranted and ongoing. === Medicine, Faculty of === Experimental Medicine, Division of === Graduate