AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was ...AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was detected in 27 sporadic colorectal adenomas,62 sporadic colorectal carcinomas and 20 normal colorectal mucosa tissues by methylation-specific PCR. At the same time, the expression of MGMT protein was carried out in the same samples using immunohistochemistry. Mutantallele-specific amplification was used to detect K-rasG to A point mutation in codon 12.RESULTS: None of the normal colorectal mucosa tissues showed methylated bands. Promoter hypermethylation was detected in 40.7% (11 of 27) of adenomas and 43.5% (27 of 62) of carcinomas. MGMT proteins were expressed in nucleus and cytoplasm of normal colorectal mucosa tissues. Loss of MGMT expression was found in 22.2% (6 of 27) of adenomas and 45.2% (28 of 62) of carcinomas. The difference between them was significant (P = 0.041). In the 6 adenomas and 28 carcinomas losing MGMT expression, 5 and 24 cases presented methylation,respectively (P = 0.027, P＜0.001). Thirteen of the 19 colorectal tumors with K-rasG to A point mutation in codon 12 had methylated MGMT(P = 0.011). The frequencies of K-rasG to A point mutation were 35.3% (12 of 34) and 12.7% (7 of 55) in tumors losing MGMT expression and with normal expression, respectively.CONCLUSION: Promoter hypermethylation and loss of expression of MGMT gene were common events in colorectal tumorigenesis, and loss of expression of MGMT occurs more frequently in carcinomas than in adenomas in sporadic patients. Hypermethylation of the CpG island of MGMT gene was associated with loss of MGMT expression and K-ras G to A point mutation in colorectal tumor. The frequency of K-ras G to A point mutation was increased in tumors losing MGMT expression. It suggests that epigenetic inactivation of MGMT plays an important role in colorectal neoplasia.展开更多
O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-ni...O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-nitrosourea (ACNU) of 20 Chinese tumor cell strains were assayed. A linear response between MGMT activity and ACNU sensitivity (D10) was observed. The lower the MGMT activity In the cells, the more the sensitivity to ACNU killing. It suggested that assay of MGMT activity in tumor biopsy could be used as a guide to predict the effectiveness of ACNU treatment in chemotherapy of human cancer.展开更多
The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity bein...The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included 1) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, 2) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and 3) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumorselective reduction in MGMT activity exist in human tissue.展开更多
Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to respons...Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to response,time to progression (TTP),and overall survival (OS) in newly diagnosed glioblastoma multiforme (GBM) patients treated with temozolomide (TMZ) concomitant with and adjuvant to radiotherapy (RT).Methods:From June 2005 to August 2008,34 adult patients (18-65 years),PS ≥70,with newly diagnosed GBM received TMZ 75 mg/m2 plus RT up to 60 Gy,followed by TMZ 175 mg/m2 5 days every 4 weeks for 12 doses.MGMT Methylation-specific PCR assay,MGMT protein expression,and Ki-67 expression using immunohistochemistry (IHC) were performed on the tissue blocks.The patients were followed by MRI while MR spectroscopy (MRS) was performed for the stable cases or to confirm progression and accordingly Bevacizumab 10 mg/kg every 2 weeks was added to 7 patients till further progression was proved.Results:31 cases were evaluable,12 (38.7%) had unmethylated MGMT,while 19 (61.3%) were methylated.Seventeen cases (55%) were MGMT immunonegative while 14 cases (45%) were immunopositive.The cut off value of Ki-67 LI in relation to survival was 17%,where 15 were < 17% (48.4%),and 16 were ≥ 17% (51.6%).Response evaluation started after the second dose of the adjuvant TMZ and was repeated every 2 months.The overall disease control rate (ODC) was 74.2%,where 2 patients had complete response (CR),14 had partial response (PR),and 7 had stable disease (SD),while 8 (25.8%) had progressive disease (PD).The ODC was significantly higher among methylated patients and in those with Ki-67 < 17% (P=0.0003).The median overall TTP was 12 months and the median OS was 20 months for all the patients including those who received Bevacizumab for some stable cases or as a salvage treatment in patients with good PS,the MGMT-methylated patients had a higher median TTP of 13 months (range 8 to 18 months,95% CI of 9.36 to 12.9),and OS of 24 months (range 12 to 31 months,95% CI of 16.1 to 21.32),while the unmethylated patients had a median TTP of 6.5 months and a median OS of 12 months,such correlations were highly significant (P=0.0001).MGMT immunoexpression failed to show significant correlation with MGMT promotor methylation or the outcome of the patients.Patients with Ki-67 < 17% had a median TTP of 16 months and median OS of 24 months compared to 7 and 12.5 months respectively for the patients with Ki-67 ≥17%.Significant correlation was found between the ODC,TTP,and OS with age < 52,near total excision,and TMZ doses received ≥ 10.The commonest grade 3 and 4 toxicities was neutropenia recorded in 3 patients (9.67%),thrombocytopenia in 4 patients (12.9%),and one patient with G3 nausea,vomiting,and constipations (3%),all were medically manageable.Conclusion:MGMT promotor methylation status and Ki-67 LI (but not the MGMT protein expression),could serve as prognostic markers for survival,also MGMT could identify the newly diagnosed GBM patients who will have better response to TMZ.展开更多
BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group...BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group to a cysteine residue in its active site and became inactive.The chemical carcinogen N-nitroso compounds(NOCs)can directly bind to the DNA and induce the O_(6)-methylguanine adducts,which is an important cause of gene mutation and tumorigenesis.However,the underlying regulatory mechanism of MGMT involved in NOCs-induced tumorigenesis,especially in the initiation phase,remains largely unclear.AIM To investigate the molecular regulatory mechanism of MGMT in NOCs-induced gastric cell malignant transformation and tumorigenesis.METHODS We established a gastric epithelial cell malignant transformation model induced by N-methyl-N’-nitro-N-nitrosoguanidine(MNNG)or N-methyl-N-nitroso-urea(MNU)treatment.Cell proliferation,colony formation,soft agar,cell migration,and xenograft assays were used to verify the malignant phenotype.By using quantitative real-time polymerase chain reaction(qPCR)and Western blot analysis,we detected the MGMT expression in malignant transformed cells.We also confirmed the MGMT expression in early stage gastric tumor tissues by qPCR and immunohistochemistry.MGMT gene promoter DNA methylation level was analyzed by methylation-specific PCR and bisulfite sequencing PCR.The role of MGMT in cell malignant transformation was analyzed by colony formation and soft agar assays.RESULTS We observed a constant increase in MGMT mRNA and protein expression in gastric epithelial cell malignant transformation induced by MNNG or MNU treatment.Moreover,we found a reduction of MGMT gene promoter methylation level by methylation-specific PCR and bisulfite sequencing PCR in MNNG/MNU-treated cells.Inhibition of the MGMT expression by O_(6)-benzylguanine promoted the MNNG/MNU-induced malignant phenotypes.Overexpression of MGMT partially reversed the cell malignant transformation process induced by MNNG/MNU.Clinical gastric tissue analysis showed that MGMT was upregulated in the precancerous lesions and metaplasia tissues,but downregulated in the gastric cancer tissues.CONCLUSION Our finding indicated that MGMT upregulation is induced via its DNA promoter hypomethylation.The highly expressed MGMT prevents the NOCs-induced cell malignant transformation and tumorigenesis,which suggests a potential novel approach for chemical carcinogenesis intervention by regulating aberrant epigenetic mechanisms.展开更多
High grade gliomas are always the research focus in the field of neurosurgery due to their poor prognosis despite the current standard therapeutic regimen of surgical resection followed by radiation therapy and chemot...High grade gliomas are always the research focus in the field of neurosurgery due to their poor prognosis despite the current standard therapeutic regimen of surgical resection followed by radiation therapy and chemotherapy. Alkylating agent temozolomide has been established as the standard chemotherapy while its resistance inevitable during treatment. This phenomenon seriously influences the prognosis of patients suffering from high grade gliomas. This review aims to elucidate temozolomide chemoresistance mechanisms through three chapters including O^6-methylguanine-DNA methyltransferase(MGMT) methylation, mismatch repair mutation and epigenetic regulation consisting of p21, chromatin and histone, Y-box binding protein-1 and micro RNAs.展开更多
The emergence of drug resistance is a major obstacle limiting the successful chemotherapy of malignant tumors. Our previous studies have demonstrated that O^6-methylguanine-DNA methyltransferase (MGMT, EC 2.1.1.63) is...The emergence of drug resistance is a major obstacle limiting the successful chemotherapy of malignant tumors. Our previous studies have demonstrated that O^6-methylguanine-DNA methyltransferase (MGMT, EC 2.1.1.63) is an important contributor to tumor cellular resistance toward mono- and bifunctional alkylating agents, such as 1- (4-amino-2-methyl-5-pyrimidinyl) methyl-3- (2-chloroethyl) -3-nitrosourea (ACNU) and N-methyl-N’-nitro-N-nitrosoguanidine (MNNG). Mechanistically, MGMT can specifically remove the induced alkyl groups at the O^6-position of guanine which finally would lead to a G→ A transition or a lethal DNA interstrand cross-link unless repaired. Cells展开更多
Background Our previous study confirmed that oligodendrogliomas had higher frequency of chromosome 1p/19q deletion. In order to improve the diagnostic criteria and to predict the prognosis of oligodendroglioma patient...Background Our previous study confirmed that oligodendrogliomas had higher frequency of chromosome 1p/19q deletion. In order to improve the diagnostic criteria and to predict the prognosis of oligodendroglioma patients, the status of chromosome 1 p/19q deletion, the methylation of O6-methylguanine-DNA methyltransferase （MGMT）, and the expression of p53 protein were evaluated and investigated in relation to patients＇ outcomes.Methods Methylation of MGMT in 73 cases was analyzed by nested methylation-specific PCR （MSP）. The levels of MGMT and p53 protein were tested with immunohistochemistry. Pearson＇s chi-square test and Fisher＇s exact test were used. Multivariate and Kaplan-Meier analysis were performed to determine patients＇ outcomes.Results Both oligodendrogliomas and astrocytic gliomas exhibited frequent methylation of MGMT. However, the results of MSP did not completely correspond to that of the immunohistochemical staining for MGMT. The expression of p53 protein was more frequently observed in patients without a 1 p or 19q deletion in anaplastic oligodendrogliomas （=0.032,0.025）. In low-grade oligodendrogliomas, methylation of MGMT was more frequent in patients with 1 p/19q deletion than in patients with 1p/19q intact （P=0.038）. Patients with oligodendrogliomas with 1p/19q loss of heterozygosity and p53-negative showed a longer progression-free survival.Conclusion Detection of chromosome 1p/19q status combined with p53 protein immunohistochemistry might be beneficial to improve the pathological diagnosis and to determine the prognosis of patients with oligodendrogliomas.展开更多
DNA direct reversal repair(DRR)is unique in that no DNA synthesis is required to correct the error and therefore repair via such mechanisms are error-free.In humans,DRR is carried out by two different pathways:the O6-...DNA direct reversal repair(DRR)is unique in that no DNA synthesis is required to correct the error and therefore repair via such mechanisms are error-free.In humans,DRR is carried out by two different pathways:the O6-methylguanine-DNA methyltransferase(MGMT)and the alkylated DNA repair protein B(AlkB)homologs.The use of alkylating agents is the standard of care for many cancers.However,the use of those drugs is usually halted when resistance develops.This review will examine repair of alkylating agent damage mediated by DRR,resistance mechanisms and potential ways to overcome such resistance.展开更多
基金Supported by the Key Technologies R&D Program of Hubei Province, No. 2002AA301C84
文摘AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was detected in 27 sporadic colorectal adenomas,62 sporadic colorectal carcinomas and 20 normal colorectal mucosa tissues by methylation-specific PCR. At the same time, the expression of MGMT protein was carried out in the same samples using immunohistochemistry. Mutantallele-specific amplification was used to detect K-rasG to A point mutation in codon 12.RESULTS: None of the normal colorectal mucosa tissues showed methylated bands. Promoter hypermethylation was detected in 40.7% (11 of 27) of adenomas and 43.5% (27 of 62) of carcinomas. MGMT proteins were expressed in nucleus and cytoplasm of normal colorectal mucosa tissues. Loss of MGMT expression was found in 22.2% (6 of 27) of adenomas and 45.2% (28 of 62) of carcinomas. The difference between them was significant (P = 0.041). In the 6 adenomas and 28 carcinomas losing MGMT expression, 5 and 24 cases presented methylation,respectively (P = 0.027, P＜0.001). Thirteen of the 19 colorectal tumors with K-rasG to A point mutation in codon 12 had methylated MGMT(P = 0.011). The frequencies of K-rasG to A point mutation were 35.3% (12 of 34) and 12.7% (7 of 55) in tumors losing MGMT expression and with normal expression, respectively.CONCLUSION: Promoter hypermethylation and loss of expression of MGMT gene were common events in colorectal tumorigenesis, and loss of expression of MGMT occurs more frequently in carcinomas than in adenomas in sporadic patients. Hypermethylation of the CpG island of MGMT gene was associated with loss of MGMT expression and K-ras G to A point mutation in colorectal tumor. The frequency of K-ras G to A point mutation was increased in tumors losing MGMT expression. It suggests that epigenetic inactivation of MGMT plays an important role in colorectal neoplasia.
文摘O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-nitrosourea (ACNU) of 20 Chinese tumor cell strains were assayed. A linear response between MGMT activity and ACNU sensitivity (D10) was observed. The lower the MGMT activity In the cells, the more the sensitivity to ACNU killing. It suggested that assay of MGMT activity in tumor biopsy could be used as a guide to predict the effectiveness of ACNU treatment in chemotherapy of human cancer.
文摘The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included 1) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, 2) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and 3) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumorselective reduction in MGMT activity exist in human tissue.
文摘Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to response,time to progression (TTP),and overall survival (OS) in newly diagnosed glioblastoma multiforme (GBM) patients treated with temozolomide (TMZ) concomitant with and adjuvant to radiotherapy (RT).Methods:From June 2005 to August 2008,34 adult patients (18-65 years),PS ≥70,with newly diagnosed GBM received TMZ 75 mg/m2 plus RT up to 60 Gy,followed by TMZ 175 mg/m2 5 days every 4 weeks for 12 doses.MGMT Methylation-specific PCR assay,MGMT protein expression,and Ki-67 expression using immunohistochemistry (IHC) were performed on the tissue blocks.The patients were followed by MRI while MR spectroscopy (MRS) was performed for the stable cases or to confirm progression and accordingly Bevacizumab 10 mg/kg every 2 weeks was added to 7 patients till further progression was proved.Results:31 cases were evaluable,12 (38.7%) had unmethylated MGMT,while 19 (61.3%) were methylated.Seventeen cases (55%) were MGMT immunonegative while 14 cases (45%) were immunopositive.The cut off value of Ki-67 LI in relation to survival was 17%,where 15 were < 17% (48.4%),and 16 were ≥ 17% (51.6%).Response evaluation started after the second dose of the adjuvant TMZ and was repeated every 2 months.The overall disease control rate (ODC) was 74.2%,where 2 patients had complete response (CR),14 had partial response (PR),and 7 had stable disease (SD),while 8 (25.8%) had progressive disease (PD).The ODC was significantly higher among methylated patients and in those with Ki-67 < 17% (P=0.0003).The median overall TTP was 12 months and the median OS was 20 months for all the patients including those who received Bevacizumab for some stable cases or as a salvage treatment in patients with good PS,the MGMT-methylated patients had a higher median TTP of 13 months (range 8 to 18 months,95% CI of 9.36 to 12.9),and OS of 24 months (range 12 to 31 months,95% CI of 16.1 to 21.32),while the unmethylated patients had a median TTP of 6.5 months and a median OS of 12 months,such correlations were highly significant (P=0.0001).MGMT immunoexpression failed to show significant correlation with MGMT promotor methylation or the outcome of the patients.Patients with Ki-67 < 17% had a median TTP of 16 months and median OS of 24 months compared to 7 and 12.5 months respectively for the patients with Ki-67 ≥17%.Significant correlation was found between the ODC,TTP,and OS with age < 52,near total excision,and TMZ doses received ≥ 10.The commonest grade 3 and 4 toxicities was neutropenia recorded in 3 patients (9.67%),thrombocytopenia in 4 patients (12.9%),and one patient with G3 nausea,vomiting,and constipations (3%),all were medically manageable.Conclusion:MGMT promotor methylation status and Ki-67 LI (but not the MGMT protein expression),could serve as prognostic markers for survival,also MGMT could identify the newly diagnosed GBM patients who will have better response to TMZ.
基金Supported by National Natural Science Foundation of China,No.81472543 and No.81772919Zhejiang Provincial Natural Science Foundation of China,No.LY18H160024 and No.LY20H160040
文摘BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group to a cysteine residue in its active site and became inactive.The chemical carcinogen N-nitroso compounds(NOCs)can directly bind to the DNA and induce the O_(6)-methylguanine adducts,which is an important cause of gene mutation and tumorigenesis.However,the underlying regulatory mechanism of MGMT involved in NOCs-induced tumorigenesis,especially in the initiation phase,remains largely unclear.AIM To investigate the molecular regulatory mechanism of MGMT in NOCs-induced gastric cell malignant transformation and tumorigenesis.METHODS We established a gastric epithelial cell malignant transformation model induced by N-methyl-N’-nitro-N-nitrosoguanidine(MNNG)or N-methyl-N-nitroso-urea(MNU)treatment.Cell proliferation,colony formation,soft agar,cell migration,and xenograft assays were used to verify the malignant phenotype.By using quantitative real-time polymerase chain reaction(qPCR)and Western blot analysis,we detected the MGMT expression in malignant transformed cells.We also confirmed the MGMT expression in early stage gastric tumor tissues by qPCR and immunohistochemistry.MGMT gene promoter DNA methylation level was analyzed by methylation-specific PCR and bisulfite sequencing PCR.The role of MGMT in cell malignant transformation was analyzed by colony formation and soft agar assays.RESULTS We observed a constant increase in MGMT mRNA and protein expression in gastric epithelial cell malignant transformation induced by MNNG or MNU treatment.Moreover,we found a reduction of MGMT gene promoter methylation level by methylation-specific PCR and bisulfite sequencing PCR in MNNG/MNU-treated cells.Inhibition of the MGMT expression by O_(6)-benzylguanine promoted the MNNG/MNU-induced malignant phenotypes.Overexpression of MGMT partially reversed the cell malignant transformation process induced by MNNG/MNU.Clinical gastric tissue analysis showed that MGMT was upregulated in the precancerous lesions and metaplasia tissues,but downregulated in the gastric cancer tissues.CONCLUSION Our finding indicated that MGMT upregulation is induced via its DNA promoter hypomethylation.The highly expressed MGMT prevents the NOCs-induced cell malignant transformation and tumorigenesis,which suggests a potential novel approach for chemical carcinogenesis intervention by regulating aberrant epigenetic mechanisms.
基金Scientific Research Project of Science and Technology Committee of Shanghai Municipality, 14DZ1930303
文摘High grade gliomas are always the research focus in the field of neurosurgery due to their poor prognosis despite the current standard therapeutic regimen of surgical resection followed by radiation therapy and chemotherapy. Alkylating agent temozolomide has been established as the standard chemotherapy while its resistance inevitable during treatment. This phenomenon seriously influences the prognosis of patients suffering from high grade gliomas. This review aims to elucidate temozolomide chemoresistance mechanisms through three chapters including O^6-methylguanine-DNA methyltransferase(MGMT) methylation, mismatch repair mutation and epigenetic regulation consisting of p21, chromatin and histone, Y-box binding protein-1 and micro RNAs.
文摘The emergence of drug resistance is a major obstacle limiting the successful chemotherapy of malignant tumors. Our previous studies have demonstrated that O^6-methylguanine-DNA methyltransferase (MGMT, EC 2.1.1.63) is an important contributor to tumor cellular resistance toward mono- and bifunctional alkylating agents, such as 1- (4-amino-2-methyl-5-pyrimidinyl) methyl-3- (2-chloroethyl) -3-nitrosourea (ACNU) and N-methyl-N’-nitro-N-nitrosoguanidine (MNNG). Mechanistically, MGMT can specifically remove the induced alkyl groups at the O^6-position of guanine which finally would lead to a G→ A transition or a lethal DNA interstrand cross-link unless repaired. Cells
文摘Background Our previous study confirmed that oligodendrogliomas had higher frequency of chromosome 1p/19q deletion. In order to improve the diagnostic criteria and to predict the prognosis of oligodendroglioma patients, the status of chromosome 1 p/19q deletion, the methylation of O6-methylguanine-DNA methyltransferase （MGMT）, and the expression of p53 protein were evaluated and investigated in relation to patients＇ outcomes.Methods Methylation of MGMT in 73 cases was analyzed by nested methylation-specific PCR （MSP）. The levels of MGMT and p53 protein were tested with immunohistochemistry. Pearson＇s chi-square test and Fisher＇s exact test were used. Multivariate and Kaplan-Meier analysis were performed to determine patients＇ outcomes.Results Both oligodendrogliomas and astrocytic gliomas exhibited frequent methylation of MGMT. However, the results of MSP did not completely correspond to that of the immunohistochemical staining for MGMT. The expression of p53 protein was more frequently observed in patients without a 1 p or 19q deletion in anaplastic oligodendrogliomas （=0.032,0.025）. In low-grade oligodendrogliomas, methylation of MGMT was more frequent in patients with 1 p/19q deletion than in patients with 1p/19q intact （P=0.038）. Patients with oligodendrogliomas with 1p/19q loss of heterozygosity and p53-negative showed a longer progression-free survival.Conclusion Detection of chromosome 1p/19q status combined with p53 protein immunohistochemistry might be beneficial to improve the pathological diagnosis and to determine the prognosis of patients with oligodendrogliomas.
基金California Tobacco-Related Disease Research Program Grant:Combined genotoxic effects of alternative tobacco products and alcohol use(No.28IR-0050,TRO)。
文摘DNA direct reversal repair(DRR)is unique in that no DNA synthesis is required to correct the error and therefore repair via such mechanisms are error-free.In humans,DRR is carried out by two different pathways:the O6-methylguanine-DNA methyltransferase(MGMT)and the alkylated DNA repair protein B(AlkB)homologs.The use of alkylating agents is the standard of care for many cancers.However,the use of those drugs is usually halted when resistance develops.This review will examine repair of alkylating agent damage mediated by DRR,resistance mechanisms and potential ways to overcome such resistance.
