ABSTRACT Continued expression of androgen receptor (AR) and its variants, such as AR-V7, despite AR targeted therapy contributes to treatment resistance and cancer progression in advanced CRPC patients. This highlights the need for new strategies to block continued AR signaling. Aldo-keto reductase family 1 member C3 (AKR1C3) is one of the most important genes involved in androgen synthesis and metabolism. Activity of this enzyme cannot be inhibited by abiraterone. Both AR/AR-V7 and AKR1C3 play key roles in cancer progression and driving resistance to current therapies. Therefore, inhibition of both AR/AR-V7 and AKR1C3 would be an ideal strategy for treating advanced prostate cancer (PCa). We have designed a novel strategy to simultaneously target the AR/AR-V7 and AKR1C3 pathways. We designed and synthesized a library of novel dual AKR1C3/AR/AR-variant inhibitors, called LX, according to structure-based computer modeling. Of the LX compounds, LX-1 had the greatest effect at reducing cell number, AR/AR variant expression, and AKR1C3 activity. RNA-seq analysis demonstrated a robust reduction in expression of AR and AR-V7 signaling genes by the selected LX. LX-1 inhibited conversion of the testosterone precursor androstenedione into testosterone in tumor cells which express high levels of AKR1C3 in a dose-dependent manner ex vivo. Furthermore, treatment with LX-1 reduced tumor growth in VCaP and LuCaP35CR PDX xenografts in vivo and decreased intratumoral testosterone. Based on these findings, the overall hypothesis is that concurrent inhibition of AR/AR variants and AKR1C3 using novel LX dual inhibitor suppresses CRPC tumor growth, overcomes resistance and improves treatment response to enzalutamide/abiraterone. This project is to further characterize LX by understanding its mechanism of action (MOA), determining its efficacy, pharmacokinetics and toxicity, and to determine their effects on the sensitivity to anti-androgen therapy with the goal to translate to future clinical development to treat advanced PCa. We hope that completion of the proposed studies will lead to the development of a new class of therapeutic agents that target both intracrine androgen synthesis and the AR signaling.

PROJECT NARRATIVE Increasing evidence showing that AKR1C3 and AR/ARv7 play important roles in promoting prostate cancer progression and resistance. We have developed a number of novel small molecules that function as dual inhibitors of AR/ARv7 and AKR1C3. This application is aimed to determine the efficacy, mechanisms of action, and safety of these small molecules and to develop as novel agents to treat advanced prostate cancer.