Abstract 713: Utilizing a potent and selective nonreplicating adenoviral mutant (Ad5-TV-CU), with gene expression controlled by androgen receptor-dependent activation domains in the TMPRSS2 gene, as a novel prodrug-converting enzyme therapy for prostate cancer
Authors: Mercer Emma J. , Imrali Ahmet , Sharpe Kevin , Hallden Gunnel , Lu Yong-Jie 
Published: May 2015

Prostate cancer (PCa) progression is dependent on transcriptional activation of the androgen receptor (AR) in the majority of cases. Therefore, therapies include anti-androgens, which decrease levels of circulating androgens and inhibit AR activity. However, resistance inevitably develops, resulting in more aggressive, incurable late-stage disease with intact or constitutively active AR signaling. There is currently no cure for castration-resistant metastatic PCa and novel therapies are needed.

A major AR-regulated gene is TMPRSS2, which is commonly expressed at higher levels in cancer than normal prostate. In 50% of PCa cases the TMPRSS2 promoter is fused to the oncogenic transcriptional regulator ERG. We generated TMPRSS2 promoter and enhancer constructs to drive the prodrug-converting chimeric enzyme cytosine deaminase uracil phosphoribosyl transferase (CD/UPRT) from an adenoviral vector to investigate the therapeutic efficacy in various PCa models.

The selectivity and transcriptional efficiency of various promoter and enhancer regions containing Androgen response elements (ARE's) were investigated after cloning TMPRSS2 constructs driving Luciferase (Luc) expression into the versatile expression vector ‘VISA’ (VP16-GAL4-WPRE integrated systemic amplifier) (Professor Hung, M.D Anderson, TX,USA) to enhance promoter activity. Comparison with the traditional PSA promoter and the chimeric PSA promoter/enhancer in the VISA vector demonstrated the TMPRSS2 construct to be superior by inducing 3.5 fold and 2.3 fold levels of luciferase expression, respectively. When the Luc-gene was replaced with CD/UPRT, specific and dose-dependent cell killing was observed in 22RV1 (AR+) cells when the non-toxic prodrug 5-flourocytosine (5-FC) was administered. No cell death was observed in primary prostate epithelial cells (PrEC), or immortalized prostate cell lines PNT1A or PNT2 (AR-).

To increase transfection efficiency of the CD/UPRT gene, the TMPRSS2-VISA-CD/UPRT expression cassette was inserted into a non-replicating adenovirus (Ad5-TV-C/U) replacing the E1-genes. Ad5-TV-C/U was characterized and protein expression of the CD/UPRT gene was detected at high levels post infection in 22RV1, LNCaP, and VCaP cells (AR+). Dose-dependent decreases in EC50-values were observed upon infection with Ad5-TV-C/U in combination with low doses of 5-FC in a number of cell lines, for example 22RV1 cells, where EC50-values decreased from 571ppc ±55 to 174ppc ±30.

These results demonstrate that Ad5-TV-C/U is both selective and efficacious in killing AR-positive PCa cells in combination with non-toxic 5-FC. Verification of these findings in preclinical in vivo models is in progress.

Citation Format: Emma J. Mercer, Ahmet Imrali, Kevin Sharpe, Gunnel Hallden, Yong-Jie Lu. Utilizing a potent and selective nonreplicating adenoviral mutant (Ad5-TV-CU), with gene expression controlled by androgen receptor-dependent activation domains in the TMPRSS2 gene, as a novel prodrug-converting enzyme therapy for prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 713. doi:10.1158/1538-7445.AM2014-713