Abstract LB-435: Double-blind randomized clinical trial of vitamin D3 showing effects on tissue calcitriol levels, gene expression and proliferation immunohistochemistry in prostate cancer

Abstract

Abstract Background: Preclinical data suggest that vitamin D plays a favourable role in prostate cancer prevention and prognosis, but its putative anticancer effects have not been validated in clinical prostate tissue samples. Here, we report the results from a randomized clinical trial (RCT). Objectives: We conducted an RCT to determine whether simple cholecalciferol (vitamin D3) consumed orally elicits effects on prostate cancer pathology in prostate tissue obtained at surgery. Methods: Prostate cancer patients (n=66) with Gleason scores 6 or 7 and scheduled for radical prostatectomy were randomized to daily vitamin D doses of 400, 10,000, or 40,000 IU for 3-8 wk before surgery. Results: Laser-capture microdissected paraffin-embedded prostate tissue showed differential expression, between benign and cancerous regions, for the cancer-related mRNAs and miRNAs, as well as for the Ki-67 proliferation marker (p0.07 among groups). The group consuming 40,000 IU/d vitamin D exhibited the highest levels of both calcitriol and its precursor as measured in frozen prostate tissue and in serum (p<0.02 each). Prostate tissue calcitriol correlated strongly with the expression of androgen receptor mRNA (r = -0.58, p=0.001), NKX3.1 mRNA (r = -0.39, p=0.02), miR-100 (r = 0.44, p=0.01), miR-125b (r = 0.37, p=0.03), Let-7a (r = 0.47, p=0.03), miR-141 (r = 0.51, p=0.002), miR-106b (r = 0.45, p=0.01), and miR-331-3p (r = 0.47, p=0.005). Automated digital analysis of immunohistochemically stained prostate cancer regions showed that prostate tissue calcitriol related negatively with Ki67 intensity (r = -0.38, p =0.02) and percent of nuclei stained strongly positive (3+) for Ki67 (r = -0.41, p=0.008). A threshold effect was evident such that patients at the highest quartile of prostate tissue calcitriol (≥ 37 pmol/kg) had significantly lower AR mRNA (p<0.001), NKX3.1 mRNA (p=0.01), and Ki67 measures (p<0.05), as well as higher levels of the correlated miRNAs (p<0.05), compared to those with lower levels. Conclusions: We provide level-1 clinical evidence that higher oral vitamin D doses produce higher levels of calcitriol within prostate tissue, and that higher prostate calcitriol relates to lower androgen receptor mRNA, higher miRNA signalling, and diminished expression of the proliferation marker Ki67 in prostate cancer. These RCT results justify a need to explore strategies that may maximize calcitriol within prostate for cancer chemoprevention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-435. doi:1538-7445.AM2012-LB-435