TMPRSS2-ERG fusions confer efficacy of enzalutamide in an in vivo bone tumor growth model

Abstract

Background Castrate Resistant Prostate Cancer (CRPC) is an advanced disease resistant to systemic traditional medical or surgical castration, and resistance is primarily attributed to reactivation of AR through multiple mechanisms. TMPRSS2-ERG fusions have been shown to regulate AR signaling, interfere with pro-differentiation functions, and mediate oncogenic signaling. We have recently shown that ERG regulates intra-tumoral androgen synthesis and thereby facilitates AR function in prostate cancer cells. We hypothesize that enzalutamide treatment will be more effective in cells/tumors with TMPRSS2-ERG translocations because these tumors have increased AR signaling. Methods ERG knockdown was performed with VCaP cells using lentiviral infections to generate VCaP ERGshRNA cells and control VCaP scr cells with scrambled shRNA. Cell-growth analysis was performed to determine the effect of enzalutamide. Reverse transcription, quantitative real-time PCR (RT-qPCR) was used to determine the expression of AR responsive genes. Luciferase tagged VCaP scr and shRNA infected cells were used in an intra-tibial animal model for bone tumor growth analysis and enzalutamide treatment used to inhibit AR signaling in bone tumors. Western blotting analyzed VCaP bone tumor samples for ERG, AR, AKR1C3 and HSD3B1 and HSD3B2 expression. Results Enzalutamide inhibited the growth of VCaP scr cells more effectively than shERG cells. Analysis of AR responsive genes shows that Enzalutamide treatment at 5 micromolar concentration inhibited by 85–90% in VCaP Scr cells whereas these genes were inhibited to a lesser extent in VCaP shERG cells. Enzalutamide treatment resulted in severe growth inhibition in VCaP scr shRNA cells compared to VCaP shERG cells. In bone tumor growth experiment, VCaP ERG shRNA cells grew at slower than VCaP scr shRNA cells. Androgen biosynthetic enzyme expression is lower VCaP shERG bone tumors compared to VCaP scr shRNA bone tumors and enzalutamide inhibited the enzyme expression in both types of tumors. Conclusions These data suggest that ERG transcription factor regulates androgen biosynthetic enzyme expression that enzalutamide treatment is more effective against VCaP bone tumors with an intact ERG expression, and that knocking down ERG in VCaP cells leads to a lesser response to enzalutamide therapy. Thus, ERG expression status in tumors could help stratify patients for enzalutamide therapy.

Clinical Efficacy of Enzalutamide vs Bicalutamide Combined With Androgen Deprivation Therapy in Men With Metastatic Hormone-Sensitive Prostate Cancer

“…TMPRSS-ERG fusion gene expression is highly prevalent in patients with prostate cancer. 19 We have previously shown that a prometastatic gene CXCR4 20 and an androgen biosynthetic enzyme AKR1C3 21 are downstream-regulated genes of TMPRSS2-ERG fusions in prostate cancer cells. High baseline ERG levels and changes in androgen metabolism enzymes and resistance pathways such as CXCR4 maybe potential molecular basis for the noted differences.…”

A comprehensive mechanistic basis of prostate cancer advancement & its personalized implementation-bridging the gap: present state and future prospect

“…For example, several lines of pre-clinical and clinical studies suggests for the existence of an oncogenic signaling network involving TMPRSS2, androgen receptor (AR), hepatocyte growth factor (HGF) and c-MET that critically induces early steps of metastatic initiation in association with marked switching of N-cadherin production [91]. In fact, current research strongly supports for the TMPRSS2 associated driver role in overall modulation of metastatic behavior acquisition by prostate cancer cells [86,[89][90][91][92]. On the other hand, TMPRSS2-ERG fusion typically enhances bone metastatic prostate cancer associated cell growth, proliferation and metastatic spread [90].…”

Androgen-Driven Fusion Genes and Chimeric Transcripts in Prostate Cancer

“…The VCaP cell line, due to the TMPRSS2-ERG fusion gene it harbors, has been widely utilized in xenograft drug studies. For example, TMPRSS2-ERG harboring VCaP bone xenograft models were shown to better respond to enzalutamide treatment, suggesting that ERG expression status in tumors could help stratify patients for enzalutamide therapy (Semaan et al, 2019 ). TMPRSS2-ERG-targeted gene silencing therapy using liposomal nanovectors suppressed tumor growth in a VCaP xenograft model and enhanced the efficacy of docetaxel chemotherapy (Shao et al, 2020 ).…”