O'6-methylguanine-DNA methyltransferase methylation status in canine intracranial glioma tissue samples

Abstract

Gliomas are the second most common intracranial malignancy in dogs. Methylation of the CpG island of the MGMT (O6-methylguanine-DNA-methyltransferase) gene has been associated with an increased clinical response to temozolomide in human glioma. CpG island methylation can silence a gene responsible for a pathway of DNA repair that removes alkyl groups from guanine bases, thereby increasing cytotoxicity. It is currently unknown if methylation of MGMT in dogs creates the same susceptibility. This study was performed to assess the methylation status of chr28:38200334-38201197, a 5' CpG island of 126 nucleotides within the promoter of the MGMT gene in canine intracranial gliomas using the ROS_Cfam_1.0 genome. Samples from 23 histologically confirmed intracranial gliomas were collected and assessed for methylation of the MGMT promoter region via enzyme methyl sequencing. One additional sample of normal brain tissue was used as a control. MGMT methylation was compared to chrX:21989327-21990986, the 5' CpG island of 132 nucleotides of the BCOR gene, a region known to be methylated. The hypothesis of this research was that 30 percent of companion dog gliomas would demonstrate hypermethylation in the promoter CpG 126 that is not seen in normal brain tissue, analogous to the frequency in which the promoter is hypermethylated in human intracranial gliomas. In this study, a 126 bp CpG island in the promoter region of MGMT in canine intracranial glioma tissue samples is hypomethylated when compared to a known hypermethylated CpG island. Companion dog glioma samples were determined to be uniformly hypomethylated when compared to published frequencies of human intracranial glioma methylation. Further research is required to elucidate the impact of the hypomethylated status on MGMT protein functionality, anti-neoplastic therapy, and prognosis.