Variation of O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation in serial samples in glioblastoma
- 264 Downloads
Methylation of the promoter region of the O 6 -methylguanine-DNA methyltransferase (MGMT) gene is known to be predictive of response to temozolomide treatment in patients with glioblastoma. Contrastingly, little is known about variation in the methylation status of the MGMT promoter after treatment or across different regions of the same tumor. About 22 samples from 10 patients who had undergone multiple resections of a glioblastoma were examined with promoter sequencing. Of these, 20 were also analyzed using Methylation Specific PCR (MSP). The methylation status of the MGMT promoter was altered in the specimens obtained pre and post treatment in 2 of 9 samples as assessed by MSP and 7 out of 10 patients as assessed by promoter sequencing. In four patients, the MGMT promoter was unmethylated at primary surgery, but displayed some methylation (32, 44, 12, and 4%) on post-treatment sampling. Alteration in MSP status from unmethylated to methylated was also observed in 2 of these 4 patients. In another patient, methylation increased from 40% on initial sampling to 68% on the second sample. The remaining two patients initially demonstrated some degree of methylation (72% and 12%); subsequent sampling showed no methylation of the MGMT promoter. To ensure variable methylation status was not due to intra-tumoral variability, three to four specimens were sampled from different regions of large glioblastomas (n = 7). Promoter sequencing revealed minimal variation in methylation in all but two sites examined. Immunohistochemistry also demonstrated minimal change in MGMT expression across the tumors. This suggests that variation in MGMT promoter methylation can occur within the same tumor after treatment, necessitating caution in clinical decision-making based on this analysis.
KeywordsGlioma MGMT Temozolomide Methylation DNA repair
We would like to acknowledge the contribution of Dr Anthony Gill, Department of Anatomical Pathology, Pacific Laboratory Medical Services, Royal North Shore Hospital to the optimisation of the immunohistochemistry.
- 1.Kleihues P, Burger PC, Aldape KD, Brat DJ, Biernat W, Bigner DD, Nakazato Y, Plate KH, Giangaspero F, von Deimling A, Ohgaki H, Cavenee WK (2007) Glioblastoma. In: Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (eds) WHO classification of tumours of the central nervous system. International Agency for Research on Cancer, Lyon, pp 33–49Google Scholar
- 4.Stupp R, Mason WP, Van Den Bent MJ, Weller M, Fisher B, Taphoorn M, Belanger K, Brandes AA, Marosi C, Bogdahn U, Curschmann J, Janzer RC, Ludwin SK, Gorlia T, Allgeier A, Lacombe D, Cairncross JG, Eisenhauer E, Mirimanoff RO (2005) Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med 352:987–996PubMedCrossRefGoogle Scholar
- 5.Hegi ME, Diserens A-C, Gorlia T, Hamou M-F, De Tribolet N, Weller M, Kros JM, Hainfellner JA, Mason W, Mariani L, Bromberg JE, Hau P, Mirimanoff RO, Cairncross JG, Janzer RC, Stupp R (2005) MGMT silencing and benefit from temozolomide in glioblastoma. N Engl J Med 352:997–1003PubMedCrossRefGoogle Scholar
- 13.Hegi ME, Diserens A-C, Godard S, Dietrich P-Y, Regli L, Ostermann S, Otten P, Ven Melle G, De Tribolet N, Stupp R (2004) Clinical trial substantiates the predictive value of O-6 Methylguanine-DNA Methyltransferase promoter methylation in glioblastoma patients treated with temozolomide. Clin Cancer Res 10:1871–1874PubMedCrossRefGoogle Scholar
- 15.Brell M, Tortosa A, Verger E, Gil JM, Vinolas N, Villa S, Acebes JJ, Caral L, Pujol T, Ferrer I, Ribalta T, Graus F (2005) Prognostic significance of O6-methylguanine-DNA methyltransferase determined by promoter hypermethylation and immunohistochemical expression in anaplastic gliomas. Clin Cancer Res 11:5167–5174PubMedCrossRefGoogle Scholar
- 18.Grasbon-Frodl EM, Kreth FW, Ruiter M, Schnell O, Bise K, Felsberg J, Reifenberger G, Tonn JC, Kretzschmar HA (2007) Intratumoral homogeneity of MGMT promoter hypermethylation as demonstrated in serial stereotactic specimens from anaplastic astrocytomas and glioblastomas. Int J Cancer 121:2458–2464PubMedCrossRefGoogle Scholar
- 26.Pogribny I, Koturbash I, Tryndyak V, Hudson D, Stevenson SM, Sedelnikova O, Bonner W, Kovalchuk O (2005) Fractionated low-dose radiation exposure leads to accumulation of DNA damage and profound alterations in DNA and histone methylation in the murine thymus. Mol Cancer Res 3:553–561PubMedCrossRefGoogle Scholar