Purpose: The topoisomerase I inhibitor irinotecan (CPT-11) is widely used for the treatment of metastatic colorectal cancer. However, mechanism to determine pharmacological response to CPT-11 is still unclear. We reported the application of a novel metabolomic analysis using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) on the study of metabolic responses to anticancer agents (AACR #2563 and #4785, 2008 and #3764, 2009). The purpose of this study is to compare the metabolomic responses to SN-38, the active metabolite of CPT-11, between high-sensitive and low-sensitive colorectal cancer cells, for finding new biomarkers that can predict CPT-11 response.

Experimental Procedures: To elucidate metabolomic responses to SN-38, human colorectal carcinoma, HCT116 and HT29 cells were exposed to 50 nM SN-38. At time 0, 3, 8, and 24 h after SN-38 exposure, all intracellular metabolites were extracted by liquid-liquid extraction and simultaneously analyzed by CE-TOFMS. To find out low molecular weight compounds related to the sensitivity to SN-38, the metabolomic profiles were compared across the 8 colorectal cancer cell lines and sensitivity to SN-38 was investigated.

Results: The HCT116 cells were more sensitive to SN-38 than HT29. The intracellular metabolites of key pathways for cellular activity were quantitatively analyzed by CE-TOFMS, which included glycolysis, tricarboxylic acid (TCA) cycles, urea cycles, amino acid metabolism and pyrimidine metabolism. The intracellular levels of endogenous deoxyribonucleotides (dTTP and dCTP) increased after SN-38 exposure in both cells. In contrast, ribonucleotides such as CTP and UTP of RNA synthesis pathway were not affected by SN-38 exposure in either cell. These results imply the change in deoxyribonucleotide pool due to the disruption of DNA synthesis by topoisomerase I inhibition, the main anti-cancer mechanism of SN-38. It was also found that lactate and glycerol-3-phosphate were accumulated to a greater extent in HCT116 than in HT29. Furthermore, correlation analysis using 8 colorectal cancer cell lines revealed that the intracellular level of γ-aminobutyric acid (GABA) strongly correlated with cellular sensitivity to SN-38.

Conclusions: The present CE-TOFMS metabolome analysis created a new finding on metabolomic mechanisms for response to SN-38 by colorectal cancer cells with different chemosensitivities. GABA was found to be a potential low molecular weight biomarker that may be used for predicting CPT-11 response.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2605.