Abstract 653: Gliomas: methylation status of MGMT gene monitoring in plasma DNA of patients receiving chemotherapy with alkylating agents.
Authors: Fiano Valentina , Trevisan Morena , Sacerdote Carlotta , Castiglione Anna , Trevisan Elisa , Senetta Rebecca , Gillio Tos Anna , De Marco Laura , Cassoni Paola , Soffietti Riccardo , Merletti Franco 
Published: August 2014

The protein MGMT (O6-methylguanine-DNA-methyltransferase) is responsible for the DNA repair from damage in O6 position of guanine induced by alkylating agent such as temozolomide, which represent the conventional treatment of gliomas. Silencing of the MGMT gene by epigenetic methylation of its promoter may disable this repair mechanism, thus increasing the cytotoxicity of chemotherapy. Previous studies showed that glioblastama patients, with a methylated MGMT gene promoter in tumour tissue, are more sensitive to the action of alkylating agents and experience higher survival.

The aim of the study was to verify the feasibility and the utility of monitoring the state of methylation of MGMT in circulating DNA as a predictive marker of prognosis and response to treatment.

Fiftyeight patients with glioma (12 with low and 46 with high grade) who underwent surgical resection and who were eligible for therapy with temozolomide, were enrolled in the study. Blood samples for the analysis of MGMT methylation status were collected before any treatment (T0) and during the treatment at the time of each magnetic resonance imaging (about every 3 months). The methylation status of the MGMT gene promoter in circulating DNA was investigated using PCR with a specific probe for the methylated sequence.

The MGMT promoter methylation status in tumour tissue and in plasma was highly concordant: in the 79% of the patients the MGMT promoter was methylated both in tumour tissue and plasma, while in the 21% of patients MGMT promoter was methylated in tissue but not in plasma (Cohen's kappa coefficient = 0.75, p &lt;0.001). The overall survivals (OS) was higher in methylated versus unmethylated MGMT promoter patients both in tumour tissue and plasma, even if with a borderline statistically significance (p = 0.06 by the log-rank test for plasma).

The risk of death increased in patients with unmethylated MGMT promoter both in tumour tissue (Adjusted HR=2.23; 95%CI 0.99-5.04) and in plasma (Adjusted HR1.73; 95%CI 0.92-3.22)

Finally, in all patients after one year from diagnosis we noticed a decrease of the state of methylation of MGMT promoter in plasma. At the end of follow up in the 98% of patients who presented the methylation of the MGMT promoter at T0, a complete unmethylation was observed.

In conclusion the results of this study confirm the feasibility of monitoring the state of methylation of MGMT in circulating DNA in glioma patients. MGMT promoter methylation status may be a prognostic marker of clinical interest in tissue and in plasma. Furthermore the complete unmethylation of MGMT promoter in the 98% of the glioma patients after one year from diagnosis, is a potentially important finding for future researches on biological history and treatment of gliomas.

Citation Format: Valentina Fiano, Morena Trevisan, Carlotta Sacerdote, Anna Castiglione, Elisa Trevisan, Rebecca Senetta, Anna Gillio Tos, Laura De Marco, Paola Cassoni, Riccardo Soffietti, Franco Merletti. Gliomas: methylation status of MGMT gene monitoring in plasma DNA of patients receiving chemotherapy with alkylating agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 653. doi:10.1158/1538-7445.AM2013-653