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Abstract 5928: Suicide gene therapy of ovarian cancer

Purpose: The objective of this study was to develop a gene directed enzyme prodrug therapy (GDEPT) method that can effectively kill both differentiating and cancer stem-like cells (CSCs) in ovarian cancer. Methods: Ovarian cancer cell lines including A2780, A2780-Cis, SKOV-3, OVCAR-3 and OVASC-1 (malignant cells from ascitic fluid of an ovarian cancer patient) were examined to identify the most drug resistant one. Various chemotherapeutic drugs which are used for suicide gene therapy were tested to identify one that is the most effective against ovarian cancer cells. These include 6-Methylpurine, 5-Fluorouracil, and SN-38. Cisplatin was used as a standard of care control. The anticancer activities of the drugs were studied by a cell toxicity assay and clonogenic assay. Flow cytometry was performed to study surface stem markers, such as CD133, CXCR4, HER2. ALDH1 activity in ovarian cancer cells was studied by ALDH assay kit. The ability of the most effective enzyme/prodrug system to kill drug resistant ovarian cancer cells was studied by a cell viability assay. Results: The results of in vitro dose-response experiments on various ovarian cancer cells showed that SN-38 was the most efficient drug with IC50 in a range of 10 -100 nM, in comparison to 10-500 μM range of all other selected active drugs. OVASC-1 and OVCAR-3 cell lines showed a higher resistance to drug therapy as compared with other cell lines. It was observed that these two cell lines have a higher number of drug resistant cancer cells in their populations. It was also observed that CSCs are strongly associated with resistance to chemotherapy. ALDH assay, clonogenic assay and sphere formation assay showed a direct correlation between the therapy resistance and the percentage of CSCs. OVASC-1 cells in comparison to the other cell lines were found to be a suitable model for therapy resistant studies. After treatment by 100 nM SN-38, no visible colonies of Ascites were observed. Adipose-derived stem cells (ADSCs) were genetically modified to express Carboxylesterase-2 (CE2) and thus could convert CPT-11 to its active form (SN-38). Using this enzyme/prodrug system an effective eradication of highly resistant OVASC-1 ovarian cancer cells was demonstrated. Conclusions: Our findings suggest that Carboxylesterase/CPT-11 enzyme/prodrug system is the most effective GDEPT method against highly drug resistant ovarian cancer cells. Citation Format: Obeid M. Malekshah, Siddik Sarkar, Arash Hatefi. Suicide gene therapy of ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5928.