Glioblastoma (GB) is the most common type of brain tumor and is usually rapidly fatal. Clinical trials indicate that treatment with temozolomide (TMZ) coupled with chemotherapy is beneficial to patients. Unfortunately, only a small number of patients respond to such treatment and, therefore, there is a critical need to understand the mechanisms responsible for the differing responses among patients. TMZ exerts its therapeutic effect by alkylating tumor DNA to form O6-alkylguanine (O6-AG) which causes apoptosis. O6-AG is repaired by the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT), and, therefore, MGMT levels constitute a critical factor in determining tumor resistance to TMZ treatment. Levels of MGMT vary among individuals due to genetic and epigenetic factors. Single nucleotide polymorphisms (SNPs) in the promoter/enhancer (P/E) region of the gene can affect the expression of the protein by altering the regulation of MGMT transcription. To date, no studies have systematically characterized the relationship between P/E SNPs and MGMT transcription. Our research will address this important unknown, with the overarching long-term goal of ultimately developing sensitive and specific markers that can distinguish those patients who would most likely be responsive to chemotherapy from those who are not. We will test the hypothesis that SNPs in the promoter/enhancer (P/E) region of the MGMT gene alter the regulation of MGMT transcription. Alteration in MGMT transcription would significantly influence sensitivity to alkylation chemotherapy and the outcome of GB treatment. To test our hypothesis, we will first identify the SNPs that exist in the P/E region of the MGMT gene and determine their frequency in the general population. We will then determine the haplotypes that these SNPs encompass, and we will use recombinant DNA and cloning techniques to generate MGMT constructs corresponding to these haplotypes. These constructs will be transiently transfected into the target cell environment (i.e. cultured human glioblastoma cells) to establish the effect each haplotype has on MGMT promoter activity. The information generated from this research will have important translational implications, since it will clarify the role of MGMT promoter polymorphisms as potential modifiers of response to alkylation chemotherapy in cancer patients. The new knowledge gained would ultimately help enhance treatment modalities, which would lead to increasing survival rates and improving functional recovery for GB patients.

Public Health Relevance

The focus of this project is on understanding the significance of the inherited variations in the MGMT gene sequence. The new information generated can explain why some patients with brain tumors respond better than others to alkylation chemotherapy. This information generated will have important clinical implications as it could help in developing therapeutic regimens for patients with brain tumors that are individually tailored or refined, based on a patient's genetic profile, to maximize therapeutic response and reduce deleterious side- effects associated with treatments.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Small Research Grants (R03)
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Special Emphasis Panel (ZRG1-ONC-U (92))
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Fountain, Jane W
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University of Texas Medical Br Galveston
Public Health & Prev Medicine
Schools of Medicine
United States
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Speidel, Jordan T; Xu, Meixiang; Abdel-Rahman, Sherif Z (2017) Differential effect of ABCB1 haplotypes on promoter activity. Pharmacogenet Genomics :
Xu, Meixiang; Nekhayeva, Ilona; Cross, Courtney E et al. (2014) Influence of promoter/enhancer region haplotypes on MGMT transcriptional regulation: a potential biomarker for human sensitivity to alkylating agents. Carcinogenesis 35:564-71
Abdel-Rahman, Sherif Z; El-Zein, Randa A (2011) Evaluating the effects of genetic variants of DNA repair genes using cytogenetic mutagen sensitivity approaches. Biomarkers 16:393-404
Rondelli, Catherine M; El-Zein, Randa A; Wickliffe, Jeffrey K et al. (2010) A comprehensive haplotype analysis of the XPC genomic sequence reveals a cluster of genetic variants associated with sensitivity to tobacco-smoke mutagens. Toxicol Sci 115:41-50