Abstract A76: Targeting phosphodiesterase 10A for chemoprevention and treatment of ovarian cancer.

Phosphodiesterase 10A (PDE10A) is a dual cyclic AMP and cyclic GMP phosphodiesterase that is highly expressed in the brain striatum, testis and thyroid and this restricted expression in peripheral tissue has been clinically exploited for the treatment of schizophrenia and Huntington9s disease. Interestingly, our group has recently found that PDE10A is overexpressed in colon, lung and breast tumors when compared to their healthy tissue correlates. Moreover, our studies indicate that PDE10A inhibition in cancer cells by RNA interference or by small molecule inhibitors leads to activation of cGMP/PKG and inhibition of β-catenin signaling pathway that culminates with apoptotic cell death. Here we are investigating the role of PDE10A in ovarian cancer by using genetic approaches (RNA interference and CRISPR/Cas9 genome editing) and novel PDE10A small molecule inhibitors that we generated. We found that PDE10A protein is expressed in various established ovarian cancer cell lines at higher levels than in immortalized ovarian surface epithelial cell lines. Using a known PDE10A inhibitor, Pf-2545920, and novel sulindac derivatives that we generated with high specificity towards the PDE10A isozyme, we observed potent growth inhibition properties (IC50s at low micromolar or sub-micromolar concentrations) for all ovarian cancer cell lines tested. One of our novel PDE10A inhibitors, called MCI-030, which showed IC50~0.5μM for ovarian cancer cells, was orally administered to C57BL/6 mice at a safe dose of 100mg/Kg and revealed a stable concentration of approximately 2μM in the plasma and ovarian tissue for about 8h. Mechanistically, our results showed that PDE10A inhibitors induced apoptosis as measured by PI/Annexin V staining. Pf-2545920 induced phosphorylation of VASP at Ser157 and Ser239 in OV-90, OVCAR3 and SKOV3 cells, indicating activation of cyclic nucleotide signaling pathway. In addition, a decrease in the levels of β-catenin, survivin, c-Myc and cyclin D1 was observed in OV-90 cells treated with Pf-2545920 for 24h. We used CRISPR-Cas9 to delete a 97bp segment in exon 7 of PDE10A in the diploid ovarian cancer cell line OV-90. Homozygous knockout PDE10A clones were obtained and showed decreased clonogenic potential and decreased Pf-2545920-mediated pVASP phosphorylation in vitro. We are currently investigating the expression of PDE10A in clinical specimens of ovarian tumors by qPCR, western-blotting and immunohistochemistry. Our future work includes testing MCI-030 in vivo using xenograft intraperitoneal models of ovarian cancer, as well as in vivo experiments with OV-90 PDE10 knockout cells. Our ultimate goal for the proposed studies of PDE10 as a novel chemoprevention target for ovarian cancer is to develop a potent PDE10 inhibitor with negligible toxicity that can be used as a chemoprevention agent for women at high risk for this malignancy. Citation Format: Luciana Madeira da Silva, Elaine Gavin, Kevin Lee, Ileana Aragon, Veronica Ramirez-Alcantara, Jennifer Scalici, Rodney P. Rocconi, Gary A. Piazza. Targeting phosphodiesterase 10A for chemoprevention and treatment of ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A76.