Abstract POSTER-THER-1410: Combining small molecule drugs and standard chemotherapy for treatment of granulosa cell tumour cells
Authors: Crosley Powel , Agopsowicz Kate , Weinfeld Michael , Hitt Mary 
Published: August 2015

Evasion of apoptosis is a hallmark of cancer, and direct induction of apoptosis without dependence on signaling upstream of Caspase-3 (CASP3) is an attractive target for cancer therapy. CASP3 sits at the hub of apoptotic pathways and it is a primary target for inhibition by anti-apoptotic proteins like the X-linked inhibitor of apoptosis (XIAP).

Granulosa cell tumour (GCT) is a rare form of ovarian cancer, highly lethal in the event of recurrence, and has no standard chemotherapy because it is resistant to most common drugs.

A recently discovered small-molecule drug, procaspase activating compound-1 (PAC1), has been shown to effectively cleave procaspase-3 into its active form by removal of an inhibitory zinc ion, facilitating autocleavage of the zymogen and direct induction of apoptosis.

Initial in vitro experiments in our lab have shown PAC1 capable of significantly reducing viability of GCT cells (represented by the KGN cell line), and combining PAC1 with a drug inhibiting XIAP further increases the killing effect. In addition, combining the small-molecule XIAP inhibitor with carboplatin, a standard chemotherapy agent, displays significant drug interaction while killing GCT cells, in vitro.

Results: GCT cell line KGN was treated with various concentrations of PAC1, for 24 and 48 hour time points, and assessed for cell viability using a metabolic assay. Results showed significant reduction of cell viability (p&lt;0.05) in both time and dose-dependent manners. The dose-response curve for these assays indicate an EC50 of ~10 µM PAC1.

High-content screening of PAC1-treated GCT cells produced quantified imagery that suggests treatment with PAC1 is, in fact, inducing activation of CASP3-mediated apoptosis and an assay inhibiting CASP3 displayed reduction in PAC1-induced killing.

Combining 10 µM PAC1 with selected concentrations of embelin, a monovalent XIAP-inhibitor, showed strong additive effect in initial experiments, indicating it is an area worthy of further research. Combination of embelin with carboplatin also displayed significant drug interaction as well as single drug effect (p&lt;0.05).

This presentation suggests that PAC1 reduces viability of GCT cells in a time and dose-dependent manner, in vitro, and the mechanism of that loss of viability is caspase-mediated apoptosis. Furthermore, combining PAC1 with drugs that inhibit XIAP enhances the killing effect.

Combining small molecule drugs that promote apoptosis display strong interaction with carboplatin, a standard chemotherapeutic agent, and may have the potential to allow carboplatin dose reduction. Further research to determine activity in animal models and/or primary human GCT explants is warranted and planned.

Citation Format: Powel Crosley, Kate Agopsowicz, Michael Weinfeld, Mary Hitt. Combining small molecule drugs and standard chemotherapy for treatment of granulosa cell tumour cells [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1410.