WASHINGTON, DC USA (UroToday.com) - This presentation is the first report that neuropeptides can activate prostate cancer intracrine androgen biosynthesis and that the process is partially blocked by a Src kinase inhibitor.
It is known that neuroendocrine differentiation is associated with castration resistant prostate cancer (CRPC) with detectable increased serum levels of chromogranin A in patients. Neuropeptides secreted from the neuroendocrine cells are believed to activate the androgen receptor (AR) in low or no androgen environments. They hypothesized that neuropeptides sustain CRPC by promoting intracrine androgen synthesis. The investigators engineered LNCaP cells overexpressing gastrin-releasing peptide (GRP) and examined the level of androgen biosynthetic enzymes by RT-PCR and Western blots. Inhibition of androgen-free growth of LNCaP-GRP cells was performed with siRNA to AKR1C3 or CYP17A1 with or without Src inhibitor saracatinib. PSA and total testosterone levels were assessed in LNCaP-GRP cells, serum from tumor-bearing animals and xenografts.
Androgen biosynthetic enzymes were up-regulated in LNCaP-GRP cells, with AKR1C3, CYP17A1 and HSD17B2 displaying over 40-fold increase compared to the control line by real-time RT-PCR analysis. Transfection of siRNA against AKR1C3 and CYP17A1 inhibited LNCaP-GRP cell growth in androgen-free medium. Specific Src family kinase inhibitor saracatinib inhibited androgen-independent LNCaP-GRP cell growth in vitro and tumor metastasis in vivo. Saracatinib also reduced the expression of AKR1C3, AKR1C1/2 and HSD3B1/2 in GRP cells at both RNA and protein levels. When combined with siRNA for AKR1C3 and CYP17A1, saracatinib further inhibited androgen-independent LNCaP-GRP cell growth. Testosterone was detectable by EIA assay in LNCaP-GRP cell lysates (109.1 and 44.5 pg/mg protein vs. 18.3 in control), serum from castrated mice bearing GRP tumors (2235.5 pg/ml serum) and xenograft tissue (59.2 pg/mg tumor). These enhanced T levels were greatly reduced when treated with saracatinib, to 594 pg/ml serum and 12 pg/mg tumor, respectively.
Presented by Allen Gao, et al. at the American Urological Association (AUA) Annual Meeting - May 14 - 19, 2011 - Walter E. Washington Convention Center, Washington, DC USA
Reported for UroToday by Christopher P. Evans, MD, FACS, Professor and Chairman, Department of Urology, University of California, Davis, School of Medicine.