O(6)-methylguanine-DNA-methyltransferase (MGMT) is a DNA repair protein removing mutagenic and cytotoxic adducts from O(6)-guanine in DNA. Approximately 40% of colorectal cancers (CRC) display MGMT deficiency due to the promoter hypermethylation leading to silencing of the gene. Alkylating agents, such as dacarbazine, exert their antitumor activity by DNA methylation at the O(6)-guanine site, inducing base pair mismatch; therefore, activity of dacarbazine could be enhanced in CRCs lacking MGMT. We conducted a phase II study with dacarbazine in CRCs who had failed standard therapies (oxaliplatin, irinotecan, fluoropyrimidines, and cetuximab or panitumumab if KRAS wild-type).
All patients had tumor tissue assessed for MGMT as promoter hypermethylation in double-blind for treatment outcome. Patients received dacarbazine 250 mg/m(2) intravenously every day for four consecutive days, every 21 days, until progressive disease or intolerable toxicity. We used a Simon two-stage design to determine whether the overall response rate would be 10% or more. Secondary endpoints included association of response, progression-free survival, and disease control rate with MGMT status.
Sixty-eight patients were enrolled from May 2011 to March 2012. Patients received a median of three cycles of dacarbazine (range 1-12). Grades 3 and 4 toxicities included: fatigue (41%), nausea/vomiting (29%), constipation (25%), platelet count decrease (19%), and anemia (18%). Overall, two patients (3%) achieved partial response and eight patients (12%) had stable disease. Disease control rate (partial response + stable disease) was significantly associated with MGMT promoter hypermethylation in the corresponding tumors.
Objective clinical responses to dacarbazine in patients with metastatic CRC are confined to those tumors harboring epigenetic inactivation of the DNA repair enzyme MGMT.
"Also, DNA methylation status has been reported to correlate with clinicopathological features of many types of cancers (Brait et al. 2008; Kim et al. 2013; Sato et al. 2002; Yang and Park 2012). Taking these advantages, DNA methylation markers for the prediction of a response to a cancer therapy have been identified in other types of cancers (Amatu et al. 2013; Giovannetti et al. 2012; Hegi et al. 2005; Mikeska et al. 2012; Park et al. 2009; Toyota et al. 2009). However, in ESCC, few studies have demonstrated an association between DNA methylation status and response to dCRT (Brabender et al. 2009). "
[Show abstract][Hide abstract] ABSTRACT: Purpose:
Definitive chemoradiotherapy (dCRT) is one of the standard treatments for esophageal squamous cell carcinoma. Patients with a response to dCRT have a better prognosis than those resistant to dCRT while survival benefits for patients with residual tumors are limited. Nevertheless, few molecular markers to predict the response to dCRT are currently available. Here, we aimed to establish a DNA methylation marker to predict the response to dCRT.
A total of 104 patients were divided into screening (n = 43) and validation (n = 61) sets. A genome-wide DNA methylation analysis was performed using an Infinium HumanMethylation450 BeadChip array. Methylation levels were measured by quantitative methylation-specific PCR and normalized by the fraction of cancer cells in a sample.
The genome-wide methylation analysis of seven responders and eight non-responders identified 18 genomic regions specifically (un)methylated in the responders. Among these, methylation of the promoter CpG island of ZNF695 was significantly associated with the response to dCRT in the screening set (P = 0.004), and a cutoff value was determined. In the validation set, the association was successfully validated (P = 0.021), and a high specificity (90 %) for the prediction of responders was obtained using the prefixed cutoff value. In addition, a multivariate analysis showed that ZNF695 methylation was an independent predictive factor for the response to dCRT (OR 7.55, 95 % CI 2.12-26.9, P = 0.002).
ZNF695 methylation was significantly associated with the response to dCRT and is a promising predictive marker for the response to dCRT.
Journal of Cancer Research and Clinical Oncology 10/2014; 141(3). DOI:10.1007/s00432-014-1841-x · 3.08 Impact Factor
"However, given the effect of MGMT loss in sensitizing cancer cells to alkylating agents, recently several attempts were made to select suitable patients for these medications. In a phase II clinical trial study with dacarbazine in metastatic CRC patients who had failed standard therapies, objective clinical response was limited to those patients with MGMT methylation (47). Similar findings were seen in metastatic patients with MGMT methylation who were treated with single agent Temozolomide (48). "
[Show abstract][Hide abstract] ABSTRACT: O(6)-methylguanine DNA methyltransferase (MGMT) is a DNA repair enzyme with the ability to protect cells from DNA mutations by removing alkyl groups from the O(6) position of guanine. Colon mucosa is exposed to the direct effects of environmental carcinogens and therefore maintaining a proficient DNA repair system is very important to stay protected against DNA mutagenesis. Loss of MGMT expression is almost exclusively associated with methylation of CpG islands in the MGMT gene promoter region which is found in approximately 40% of colorectal cancers. The role of MGMT loss in colorectal tumorigenesis is complex but numerous studies have documented methylation of this gene even in the normal appearing mucosa as well as in aberrant crypt foci, suggesting that MGMT methylation can be regarded as an early event or "field defect" in colon cancer neoplasia. The focus of this perspective is the role of MGMT in different pathways of colorectal carcinogenesis as well as the implication of this molecule in treatment decisions in colorectal cancer patients.
Frontiers in Oncology 10/2013; 3:266. DOI:10.3389/fonc.2013.00266
[Show abstract][Hide abstract] ABSTRACT: Colorectal cancer (CRC) is among the leading causes of cancer death worldwide, involving multiple dietary and non-dietary risk factors. A growing body of evidence suggests that N-nitroso compounds play a pivotal role in the etiology of CRC. N-nitroso compounds are present in food and are also formed endogenously in the large intestine. Upon metabolic activation and also spontaneously they form electrophilic species that methylate the DNA, producing N-methylated purines and O(6)-methylguanine, the latter of which bears high mutagenic and carcinogenic potential. Methylated DNA bases are removed by base excision repair initiated by the alkyladenine-DNA glycosylase, the family of AlkB homologues proteins, and the suicide enzyme O(6)-methylguanine-DNA methyltransferase (MGMT), which is the main focus of this review. We present animal models with a deficiency of MGMT that display a tremendously enhanced sensitivity towards alkylation-induced colorectal carcinogenesis, highlighting its role in the protection against the cytotoxic and mutagenic effects of alkylating agents. In line with these studies, MGMT was linked to the formation of human sporadic CRC. Colorectal tumors and precursor lesions frequently display epigenetic inactivation of MGMT resulting from promoter hypermethylation, which is tightly associated with the occurrence of G:C to A:T transition mutations in the KRAS oncogene. We also discuss clinical data, which identified the MGMT status of CRC patients as promising parameter for the treatment of metastasized CRC using alkylating anticancer drugs such as temozolomide.
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