Abstract 3873: Improving the effectiveness of chemotherapy by combining compounds that suppress drug-induced microsatellite instability

Abstract

Abstract Many chemotherapeutic agents damage DNA and induce DNA damage response (DDR) signaling, resulting in growth arrest or apoptosis. DNA mismatch repair (MMR) system not only maintains genomic stability but also participates in DDR signaling. MMR deficiency leads to genetic hypermutability, manifested as microsatellite instability (MSI), and contributes to cancer pathogenesis and drug resistance. MSI has been linked to chemotherapy and therapy-related secondary cancer. Therefore, it is important to prevent drug-induced MSI to increase the effectiveness of chemotherapy while reducing cancer mortality. The purpose of this study is to characterize the MSI-inducing ability of individual chemotherapeutic agents and identify small compounds that suppress drug-induced MSI. In a human colorectal cancer cell model, all tested drugs individually induced the instability of reporter and endogenous microsatellites while reducing steady-state levels of certain MMR proteins. Relatively, oxaliplatin induced a higher MSI frequency than many tested drugs such as 5-FU. It is known that MMR-deficient tumors are resistant to 5-FU and not oxaliplatin. We then screened a commercially available library for small compounds that suppress oxaliplatin-induced MSI using a dual-fluorescent MSI reporter. We found that the majority of compounds were capable of reducing oxaliplatin-induced MSI. However, they also undesirably decreased the cytotoxicity of oxaliplatin. On the other hand, a small number of compounds such as I-6 and II-13 suppressed oxaliplatin-induced MSI with or without an improvement of drug cytotoxicity. Relative to oxaliplatin alone, co-treatment of 1 μM oxaliplatin with 6-10 μM compound II-13 decreased drug-induced MSI frequency by 45-70% without significantly affecting the cytotoxicity of oxaliplatin. Co-treatment of oxaliplatin with 4-10 μM compound I-6, however, decreased both drug-induced MSI and cell numbers by 50-78% in a dose-dependent manner. To our surprise, compounds such as II-13 suppressed MSI induced by oxaliplatin but not by 5-FU. In conclusion, individual drugs displayed different MSI-inducing abilities whereas MSI-suppressing compounds appear to be drug-specific. Further identification and validation of MSI-suppressing compounds specific for 5-FU or leucovorin, for example, would improve the effectiveness of combination chemotherapy such as FOLFOX. Citation Format: Christina L. Chang, Li-Yan Huang, Chang-Lin Wu, Jhih-Ying Chi. Improving the effectiveness of chemotherapy by combining compounds that suppress drug-induced microsatellite instability. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3873. doi:10.1158/1538-7445.AM2015-3873