Abstract P6-01-22: PDE5 as a novel biomarker and a potential therapeutic target for breast cancer

Abstract

Abstract Background: Phosphodiesterases are enzymes responsible for regulating second messenger signaling by hydrolyzing 3’-5’ cyclic guanosine monophosphate (cGMP), that activates specific pathways resulting in protein phosphorylation, ion fluxes, or cyclic nucleotide hydrolysis to affect gene expression or other aspects of cellular activity. Previous studies have reported increased PDE5 expression in multiple human carcinomas, including bladder, colon, lung and breast cancers, suggesting a role for PDE5 in tumorigenesis. In addition, several in vitro observations have shown antiproliferative and proapoptotic effects of sildenafil and other PDE5 inhibitors in cancer cell lines. However, very little is known about PDE5 expression in human breast tumours and its potential role in breast cancer initiation and progression. We therefore propose to determine whether PDE5 expression may be predictor of outcome in breast cancer patients, and examine PDE5 impact on breast cancer phenotype in vitro. Methods: We employed MCF-10A normal breast epithelial cells, estrogen receptor (ER) α-positive (MCF-7/ZR-75/T-47D) and ERα-negative (BT-20/MDA-MB-468/SKBR-3/MDA-MB-435) breast cancer cells. We used RT-PCR, immunoblotting and immunofluorescence analyses for evaluating PDE5 expression. To examine PDE5 impact on breast cancer phenotype, MCF-7 cells were engineered to stably express PDE5 and four clones were selected. Cell proliferation was assessed by MTT and anchorage-independent assays, motility and invasion by wound-healing, transmigration and matrigel-based invasion assays. Retrospective analysis using 1959 breast cancer patients of the Metabric Project was performed to evaluate relationship between PDE5 expression and overall survival by Cox proportional hazard regression. Results: PDE5 mRNA and protein were constitutively expressed at high levels in all the examined tumor cell lines compared to normal breast cells, except for the less motile and non-invasive MCF-7 cells. Interestingly, higher PDE5 expression was found in more aggressive ER-negative cells. Stable overexpression of PDE5 did not affect proliferation of MCF-7 cells, while it significantly increased motility and invasion of all the stable PDE5-transfected clones tested. Patients having high PDE5 expression had a statistically significant poorer survival compared to patients with low PDE5 expression (p=0.014, HR= 1.2). A more relevant discrimination was achieved in lymph node-negative patients (p=0.0015, HR= 1.6), suggesting that assessing PDE5 levels may be helpful to identify a subgroup of early-stage breast cancer patients who are most likely at the highest risk of progression. Conclusions: PDE5 expression may enhance cancer cell invasive potential, thereby representing prospectively a potential molecular candidate as prognostic marker and target for breast cancer therapy. Citation Format: Ines Barone, Antonella Campana, Cinzia Giordano, Marilena Lanzino, Daniela Bonofiglio, Balazs Gyorffy, Stefania Catalano, Sebastiano Andò. PDE5 as a novel biomarker and a potential therapeutic target for breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-01-22.