P25.01 Metabolic Characterization of Drug Resistance to Antifolate in Malignant Pleural Mesothelioma

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive malignancy that develops due to asbestos exposure. MPM is a diffuse disease with a poor prognosis. MPM develops in the pleural cavity and is highly resistant to a number of therapeutics. A combination of pemetrexed (PMX) and cisplatin (CDDP) is the first-line chemotherapy that remains useful today. PMX inhibits the enzymes dihydrofolate reductase (DHFR), thymidylate synthase (TYMS), and glycinamide ribonucleotide formyltransferase (GART), which are involved in purine and pyrimidine synthesis. However, the median survival is approximately 12 months after treatment with PMX and CDDP, and the response rate is 41.3%. Therefore, patients with MPM show an approximately 60% incidence of resistance to PMX and CDDP. The mechanism of CDDP resistance has been investigated in several studies; however, the mechanism of PMX resistance is poorly understood. There are reports of TYMS overexpression being involved in PMX resistance; on the other hand, there are also reports of a lack of link to clinical results. In a previous study, I reported that the levels of glycine and IMP may be potential biomarkers of chemotherapy with PMX. For this reason, I hypothesized that MPM cells might acquire PMX resistance via changes in metabolic pathways. I established an MPM cell line of PMX resistance and examined the expression levels of PMX-targeted enzymes and intracellular metabolites of acquired PMX-resistant cell lines. In the first study, I changed medium the concentration of PMX was added to increase by 10% so that two PMX-resistant cell lines. Viable cells by WST-8 assay and the dose response curve. In a second study, I investigated the mRNA expression levels of parental cell lines and PMX-resistant cell lines to investigate whether PMX-resistant cell lines might change the expression levels of PMX-targeted enzymes and other enzymes. In the third study, I examined whether differences in intracellular metabolites between PMX-resistant and parent cell lines in the presence of PMX by metabolome analysis. MPM cells in the presence of PMX for a long time, and then established two PMX-resistant cell lines. These cell lines were extremely resistant to PMX. Next, I confirmed that increased TYMS expression levels by RT-qPCR when MPM cells exposed to PMX for a long time; however, DHFR and GART expression levels not change . Furthermore, expression levels of RFC and multidrug resistance protein (MRP) did not change . Next, I analyzed PMX-resistance and parent cell lines of intracellular metabolites in the presence of PMX, and found that glycine and adenosine changed between parental cell lines and PMX-resistant cell lines in the presence of PMX. In this study, I showed that TYMS expression levels, glycine and adenosine were changed by acquired PMX-resistance. Therefore, we think that finding regulatory genes of TYMS expression and glycine, adenosine production might elucidate the mechanism of drug resistance . I report these results, I would like to discuss.