March 18, 2013
Epigenetic Changes Play A Key Role In Development Of Chemo Resistance In BCa
At the 28th Annual EAU Congress currently ongoing in Milan until Tuesday, W. Tan and colleagues presented their study on neoadjuvant cisplatin-based chemotherapy which showed that epigenetic changes are potential key drivers in the development of chemo resistance in bladder cancer.
Neoadjuvant cisplatin-based chemotherapy is recommended for patients with muscle invasive bladder cancer. Cisplatin-based regimes have similar efficacy with complete response in 30% a survival advantage if 16% (HR, 0.84;CI 0.72 to 0.99), wrote Tan of the UCL, Dept. of Surgery and Interventional Science in London, the UK.According to the researchers, the ability to identify a biomarker which is able to predict response to treatment would increase pathological complete response rates and spare nonresponders adverse events of chemotherapy. DNA hypermethylation has been implicated in chemotherapy resistance in cancers.
"We hypothesized that DNA methylation may not only represent the mechanisms for the acquisition of resistance, but may also be a potential biomarker to predict response to platinum based chemotherapy in bladder cancer," wrote Tan, lead author of the study titled "Epigenetic alterations associated with neo-adjuvant chemotherapy resistance in bladder cancer."
In the study, DNA was extracted from 48 muscular invasive bladder tumours, taken prior to the patient to receiving a platinum based neo-adjuvant chemotherapy, all tumors had >80% tumor content. 1ug of DNA was bisulphite converted using the EZDNA Bisulfite Conversion Kit (Zymo Research). Genome-wide DNA methylation profiles were generated using the Infinium HumanMethylation 450K BeadChip (Illumina).
According to the researchers, the analysis suggests acquired resistance is associated with global hypermethylation in both primary tumors and paired cell lines. Singular value decomposition (SVD) analysis revealed the strongest methylation signature to be associated with chemotherapy response (p=<0.001).
Supervised analysis identified ~2700 Methylation Variable Positions (MPVs) to be associated with chemotherapy response. Hierarchical clustering of the MVPs associated with chemotherapy response, defined three clusters, 1) chemo sensitive,2) chemo resistant and 3) a mixed cluster with a hypomethylation phenotype. The MVPs associated with resistance include novel genes such as MEIS2, PROM1 and MAP1LC3A, as well as genes previously associated with resistance other tumors, such as MEST and MLH1.
"These data suggest that epigenetic alterations are potential key drivers in the development of chemo resistance in bladder cancer. As well as providing novel insight into mechanisms of drug resistance, we have identified putative candidate biomarkers for further evaluation in future clinical studies, including potential stratification biomarkers in clinical trials of epigenetic therapies that reverse the acquired resistance phenotype," the researchers concluded.
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