Abstract PR11: Dysregulation of cholesterol homeostasis through loss of CYP27A1 in prostate cancer; Implications for early detection and prevention of over-treatment

Approximately 200,000 men are annually diagnosed with prostate cancer (PC), making PC the most commonly diagnosed malignancy among men in industrialized countries. On the other hand, only 30,000 men diagnosed with PC will succumb to the disease with the majority of patients dying from other causes. This makes identification of aggressive vs. indolent PCs one of the most important clinical conundrums in the modern health era. Indeed, identification of biomarkers that achieve this distinction would add a huge benefit and would help patients that have indolent disease avoid side effects associated with treatment modalities that should only be provided to patients with aggressive forms of PC. To achieve the above goal, we employed a bioinformatics based search to look for genes that dramatically change in PC relative to benign and can predict progression. Our mined data from eight different publically available clinical datasets clearly indicates that CYP27A1transcript levels (our top candidate) are down-regulated in PC relative to benign and are further downregulated during PC progression. Our bioinformatics data also shows that patients whose tumors express higher levels of CYP27A1 have longer cancer-free survival following local treatment with radical prostatectomy. To validate these findings, we analyzed expression levels of CYP27A1 protein in benign and cancerous prostate tissue microarrays and found that while 90% of benign prostate cores express CYP27A1, 78% of cancerous cores show low to undetectable expression levels. Given the high rate of CYP27A1 loss in PC, we investigated potential mechanisms using data extracted from The Cancer Genome Atlas (TCGA). We found a very strong inverse and nearly linear relationship between levels of CYP27A1 expression and degree of its promoter methylation (R2=0.79). Conversely, the rate of genetic alterations (mutation, deletion) that might explain loss of CYP27A1expression is very low (3%). Taken together, these results indicate that CYP27A1 loss is an epigenetic event caused by promoter hypermethylation. To investigate the role of CYP27A1 in PC, we reintroduced CYP27A1 in LNCaP and 22Rv1 PC cell lines that have silenced its expression via promoter methylation. Overexpressing CYP27A1 in LNCaP cells significantly retards proliferation in vitro and also slows growth of 22Rv1 subcutaneous xenograft tumors. Given that a major function of CYP27A1 is to convert cholesterol into 27hydroxycholesterol (27HC), we treated five different PC cell lines with 27HC and found that 27HC inhibits PC cells viability in vitro in all cell lines and induces cleavage of PARP, a cellular marker for apoptosis. Finally, we found that 27HC treatment reduces cholesterol levels in PC cells and supplementing PC cells with an exogenous source of cholesterol rescues the cells from 27HC mediated effects. Collectively, our results suggest that 27HC may act as an intracellular cholesterol biosensor and PC cells have developed mechanisms to accumulate more cholesterol through silencing of CYP27A1 and stopping the production of 27HC. This is key, as epidemiological and experimental evidence strongly suggests that hypercholesterolemia is associated with an increased risk of lethal PC. Our results highlight CYP27A1 loss as a promising biomarker for PC and also suggest that reduction of intratumoral cholesterol may have a preventative role in PC possibly through treatment with 27HC. Citation Format: Mahmoud A. Alfaqih, Erik R. Nelson, Rachid Safi, Jeff Jasper, Donald P. McDonnell, Stephen J. Freedland. Dysregulation of cholesterol homeostasis through loss of CYP27A1 in prostate cancer; Implications for early detection and prevention of over-treatment. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr PR11.