Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.1.1.37 (DNA methyltransferase)
 4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Temozolomide (TMZ) is a methylating agent which prolongs survival when administered during and after radiotherapy in the first-line treatment of glioblastoma and which also has significant activity in recurrent disease. O6-methylguanine DNA methyltransferase (MGMT) is a DNA repair enzyme attributed a role in cancer cell resistance to O6-alkylating agent-based chemotherapy. Using a panel of 12 human glioma cell lines, we here defined the sensitivity to TMZ in acute cytotoxicity and clonogenic survival assays in relation to MGMT, mismatch repair and p53 status and its modulation by dexamethasone, irradiation and BCL-X(L). We found that the levels of MGMT expression were a major predictor of TMZ sensitivity in human glioma cells. MGMT activity and clonogenic survival after TMZ exposure are highly correlated (p < 0.0001, r2 = 0.92). In contrast, clonogenic survival after TMZ exposure does not correlate with the expression levels of the mismatch repair proteins mutS homologue 2, mutS homologue 6 or post-meiotic segregation increased 2. The MGMT inhibitor O6-benzylguanine sensitizes MGMT-positive glioma cells to TMZ whereas MGMT gene transfer into MGMT-negative cells confers protection. The antiapoptotic BCL-X(L) protein attenuates TMZ cytotoxicity in MGMT-negative LNT-229 but not in MGMT-positive LN-18 cells. Neither ionizing radiation (4 Gy) nor clinically relevant concentrations of dexamethasone modulate MGMT activity or TMZ sensitivity. Abrogation of p53 wild-type function strongly attenuates TMZ cytotoxicity. Conversely, p53 mimetic agents designed to stabilize the wild-type conformation of p53 sensitize glioma cells for TMZ cytotoxicity. Collectively, these results suggest that the determination of MGMT expression and p53 status will help to identify glioma patients who will or will not respond to TMZ.
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PMID:O6-methylguanine DNA methyltransferase and p53 status predict temozolomide sensitivity in human malignant glioma cells. 1640 12

Temozolomide (TMZ) is an alkylating chemotherapeutic agent that prolongs the survival of patients with glioblastoma. Clinical benefit is more prominent in patients with methylation of the O(6) -methyl-guanine DNA methyltransferase (MGMT) promoter. However, all patients eventually suffer from tumor progression because their tumors become resistant to TMZ. Here, we modeled acquired TMZ resistance in glioma cells in vitro to identify underlying molecular mechanisms. To this end, the glioma cell lines LNT-229, LN-308, and LN-18 were exposed repetitively to increasing concentrations of TMZ to induce a stable resistant phenotype (R) defined by clonogenic survival assays. The molecular mechanisms mediating acquired resistance were assessed by immunoblot, PCR, and flow cytometry. Rescue experiments were performed with siRNA-mediated candidate gene silencing. We found in LN-18 cells constitutively expressing MGMT a strong up-regulation of MGMT levels in TMZ-resistant cells. TMZ resistance in the MGMT-negative cell lines LNT-229 and LN-308 was not associated with de novo expression of MGMT. Instead, we found a down-regulation of several DNA mismatch-repair proteins in resistant LNT-229 cells. A TMZ-resistant phenotype was also achieved by silencing selected DNA mismatch repair proteins in parental LNT-229 cells. No obvious mechanism of resistance was identified in the third cell line, LN-308, except for reduced methylation of LINE-1 repetitive elements. In conclusion, we demonstrate that different molecular mechanisms may contribute to the development of acquired TMZ resistance in glioma cells, indicating the need to develop distinct strategies to overcome resistance.
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PMID:Distinct molecular mechanisms of acquired resistance to temozolomide in glioblastoma cells. 2256 86