An epigenetic mechanism for capecitabine resistance in mesothelioma

Abstract

Mesothelioma is an uncommon malignancy whose global incidence continues to rise. The therapeutic standard for advanced disease is intravenous pemetrexed and cisplatin. The antifolate capecitabine is significantly less effective than pemetrexed. The balance between thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and Thymidine Phosphorylase (TP) is critical to the efficacy of capecitabine. DNA from mesothelioma cell lines was bisulfite treated and examined by MS-PCR, RNA was obtained for real time PCR analysis, and protein lysates were obtained for Western immunoblot analysis. Cytotoxicity was assessed by MTT assay, comparing 5-aza-CdR pretreated or untreated cells with 5′-Deoxy-5-fluorouridine (DFUR), 5-FU, and pemetrexed. Finally bisulfite sequencing of the extracellular growth factor-1 (ECGF-1) gene was performed on 4 mesothelioma samples and pericardial tissue. One of the four cell lines tested (H290) was methylated for ECGF-1. This corresponded to a lack of TP expression by real time PCR and Western immunoblot. Treatment with 1 μM 5-aza-CdR increased TP mRNA and protein expression in H290. DFUR, the substrate for TP, showed increased cytotoxicity when delivered after 5-aza-CdR exposure in the methylated cell line. There was no difference in any of the unmethylated cell lines when cells were exposed to 5-FU or pemetrexed with or without 5-aza-CdR. Patient tumor samples revealed an increased number of methylated CpG sites in ECGF-1 compared to normal pericardium. Methylation of ECGF-1, leads to transcriptional silencing of TP and may explain the lack of any effect of capecitabine, especially when compared to pemetrexed.

Cancer stem cells and chemoresistance: The smartest survives the raid

“…The antimetabolite drugs such as 5-FU and methotrexate need to be converted further into their most active forms to be therapeutically effective, which does not occur when the target cells lack the enzyme activities (115, 116). For example, in CSCs expression of the thymidine phosphorylase can be inhibited via epigenetically silencing mechanisms such as gene promoter methylation catalyzed by the DNA methyltransferases (DNMTs) , resulting in capecitabine resistance (117). Using inhibitors of DNMTs can thus sensitize the CSCs to capecitabine.…”

How do changes in the mtDNA and mitochondrial dysfunction influence cancer and cancer therapy? Challenges, opportunities and models

“…A study by Moghaddam et al found that Tp has angiogenic properties and, in a MCF7 breast cancer xenograft model, Tp overexpression led to faster tumor growth [227]. In contrast, low Tp expression correlates to the favorable prognosis of gastric cancer treated with chemotherapy [228,229] and promoter methylation has been proposed as a mechanism of its expression down regulation in different cancer cells [230,231].…”

Identifying therapeutic targets in gastric cancer: the current status and future direction

“…The 5-Fu cannot be metabolized into an active ingredient in the absence of appropriate intracellular enzymes. Oral capecitabine only works when it is metabolized to 5-Fu by thymidine phosphorylase, however, methylation of this enzyme-encoding gene can lead to drug resistance [50,51].…”