Hypermethylation of CpG island in O^6-methylguanine-DNA methyltransferase gene was associated with K-rasG to A mutation in colorectal tumor

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.

Expression of O⁶-Methylguanine-DNA Methyltransferase Examined by Alkyl-Transfer Assays, Methylation-Specific PCR and Western Blots in Tumors and Matched Normal Tissue

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.

Temozolomide and radiotherapy in newly diagnosed glioblastoma patients:O^6-methylguanine-DNA methyltransferase (MGMT) promotor methylation status and Ki-67 as biomarkers for survival and response to treatment

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.

O6-methylguanine DNA methyltransferase is upregulated in malignant transformation of gastric epithelial cells via its gene promoter DNA hypomethylation

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.

O^6-METHYLGUANINE-DNA METHYLTRANSFERASE ACTIVITY AND SENSITIVITY OF 20 CHINESE TUMOR CELL STRAINS TO 1-(4-AMINO-2-METHYL-5-PYRIMIDINYL) METHYL-3-(2-CHLOROETHYL)-3-NITROSOUREA

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.

Promoter methylation status of hMLH1,MGMT,and CDKN2A/p16 in colorectal adenomas

AIM:To investigate aberrant DNA methylation of CpG islands and subsequent low-or high-level DNA microsatellite instability(MSI)which is assumed to drive colon carcinogenesis. METHODS:DNA of healthy individuals,adenoma(tu-bular or villous/tubulovillous)patients,and colorectal carcinoma patients who underwent colonoscopy was used for assessing the prevalence of aberrant DNA methylation of human DNA mismatch repair gene mutator L homologue 1(hMLH1),Cyclin-dependent kinase inhibitor 2A(CDKN2A/p16),and O-6-methylguanine DNA methyltransferase(MGMT),as well as their rela- tion to MSI. RESULTS:The frequency of promoter methylation for each locus increased in the sequence healthy tissue/adenoma/carcinoma.MGMT showed the highest frequency in each group.MGMT and CDKN2A/p16 presented a statistically significant increase in promoter methylation between the less and more tumorigenic forms of colorectal adenomas(tubular vs tubullovillous and villous adenomas).All patients with tubulovillous/villous adenomas,as well as all colorectal cancer patients,showed promoter methylation in at least one of the examined loci.These findings suggest a potentially crucial role for methylation in the polyp/adenoma to cancer progres- sion in colorectal carcinogenesis.MSI and methylation seem to be interdependent,as simultaneous hMLH1, CDKN2A/p16,and MGMT promoter methylation was present in 8/9 colorectal cancer patients showing the MSI phenotype. CONCLUSION:Methylation analysis of hMLH1,CD- KN2A/p16,and MGMT revealed specific methylation profiles for tubular adenomas,tubulovillous/villous adenomas,and colorectal cancers,supporting the use of these alterations in assessment of colorectal tumorigenesis.

MGMT is down-regulated independently of promoter DNA methylation in rats with all-trans retinoic acidinduced spina bifida aperta

O6-methylguanine DNA methyltransferase(MGMT), a DNA repair enzyme, has been reported in some congenital malformations, but it is less frequently reported in neural tube defects. This study investigated MGMT mRNA expression and methylation levels in the early embryo and in different embryonic stages, as well as the relationship between MGMT and neural tube defects. Spina bifida aperta was induced in rats by a single intragastric administration of all-trans retinoic acid on embryonic day(E) 10, whereas normal control rats received the same amount of olive oil on the same embryonic day. DNA damage was assessed by detecting γ-H2 A.X in spina bifida aperta rats. Real time-polymerase chain reaction was used to examine mRNA expression of MGMT in normal control and spina bifida aperta rats. In normal controls, the MGMT mRNA expression decreased with increasing embryonic days, and was remarkably reduced from E11 to E14, reaching a minimum at E18. In the spina bifida aperta model, γ-H2 A.X protein expression was increased, and mRNA expression of MGMT was markedly decreased on E14, E16, and E18. Bisulfite sequencing polymerase chain reaction for MGMT promoter methylation demonstrated that almost all CpG sites in the MGMT promoter remained unmethylated in both spina bifida aperta rats and normal controls, and there was no significant difference in methylation level between the two groups on either E14 or E18. Our results show that DNA damage occurs in spina bifida aperta rats. The mRNA expression of MGMT is downregulated, and this downregulation is independent of promoter DNA methylation.

Promoter Hypermethylation of DNA Repair Gene MGMT in Laryngeal Squamous Cell Carcinoma

The relationship between hypermethylation of CpG islands in the promoter regions of O^6- methylguanine DNA methyhransferase （MGMT） genes and laryngeal squamous cell carcinoma was explored. Methylation-specific PCR and semi-quantitative RT-PCR were used to study the promoter methylation and mRNA expression of the MGMT gene in laryngeal carcinoma tissues, tissues adjacent to the tumor and normal laryngeal tissues. Hypermethylation of MGMT gene was detected in 16 samples of 46 （34.8 %） laryngeal squamous cell carcinoma samples. However, the MGMT hypermethylation was not detected in all tissues adjacent to the tumors and normal tissues. No significant difference in MGMT gene hypermethylation was found in samples with different histological grades （χ^2= 3. 130, P=0. 077） or in samples from patients with different TNM status （χ^2= 3. 957, P=0. 138）. No expression of MGMT mRNA was detected in all hypermethylated laryngeal carcinoma tissues. The expression of MGMT mRNA was detected in all unmethylated laryngeal carcinoma tissues, tissues adjacent to the tumors and normal tissues. It suggests that MGMT gene promoter hypermethylation is associated with MGMT gene transcription loss in laryngeal carcinoma tissues and possibly plays an important role in carcinogenesis of laryngeal tissues.

O^6-methylguanine-DNA methyltransferase gene expression confers alkylation resistance to tumor cells

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

死亡相关蛋白激酶1、KLF4、6-氧-甲基鸟嘌呤-DNA甲基转移酶甲基化状态检测及与宫颈癌人乳头瘤病毒16感染的关系

目的检测宫颈癌组织死亡相关蛋白激酶1(DAPK1)、KLF4、6-氧-甲基鸟嘌呤-DNA甲基转移酶(MGMT)启动子区域甲基化状态,初步探讨其甲基化状态与宫颈癌人乳头瘤病毒16(HPV16)感染的关系。方法选取宫颈癌患者103例为宫颈癌组,另选取同期年龄相匹配的慢性子宫颈炎患者110例为对照组。检测2组宫颈脱落组织DAPK1、KLF4、MGMT基因甲基化状态。通过人乳头瘤病毒检测HPV16感染情况,分析宫颈癌组织DAPK1、KLF4、MGMT基因甲基化与HPV16感染相关性。结果与对照组相比,宫颈癌组患者HPV16感染阳性率升高,差异有统计学意义(P<0.05);与对照组相比,宫颈癌组DAPK1、KLF4、MGMT基因异常甲基化率升高,差异有统计学意义(P<0.05)。分化程度低、TNM分期Ⅲ~Ⅳ期、有淋巴结转移及有远处转移患者宫颈癌组织DAPK1、KLF4、MGMT甲基化率高于分化程度高、中及TNM分期Ⅰ~Ⅱ、无淋巴结转移、无远处转移患者,差异有统计学意义(P<0.05)。与HPV16感染阴性相比,HPV16感染阳性患者中APK1、KLF4、MGMT甲基化比例升高,差异有统计学意义(P<0.05)。HPV16感染情况与APK1、KLF4、MGMT甲基化相关(r=0.454,0.497,0.307,P<0.05)。结论HPV16感染可能与APK1、KLF4、MGMT甲基化有关,HPV16感染可能通过影响APK1、RAR-β、MGMT基因甲基化促进宫颈癌的发展。

铀矿工GSTP1基因多态与MGMT基因和p16基因甲基化的关系

目的探讨氡职业暴露人群谷胱甘肽S-转移酶P1(GSTP1)基因多态与痰细胞6-氧-甲基嘌呤-DNA甲基转移酶(MGMT)和p16基因甲基化的关系。方法用聚合酶链反应-限制性片段长度多态性法(PCR-RFLP)确定70例氡职业暴露人群GSTP1的基因型;用聚合酶链反应-甲基化特异性法(MSP)确定痰细胞中MGMT和p16基因的甲基化与非甲基化状态。结果在70名铀矿工中,GSTP1基因A105G位点的纯合子(Ile/Ile)42例,杂合子(Ile/Val)25例和纯合子(Val/Val)3例。MGMT、p16基因甲基化率和总甲基化率分别为14.2%、8.6%和18.6%。与携带Ile/Ile人群相比,携带异常等位基因(Ile/Val与Val/Val)的人群MGMT基因甲基化和总甲基化率增加[P=0.037,OR=4.8,95%CI(1.1~21.0);P=0.016,OR=5.1,95%CI(1.4~19.6)];p16基因甲基化率差异无统计学意义[P=0.057,OR=4.6,95%CI(0.8~29.2)]。结论GSTP1(A105G)基因多态性与氡致MGMT基因甲基化和总甲基化的易感性有关。

Temozolomide resistance in high grade gliomas

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.

MRI影像组学无创预测脑胶质母细胞瘤MGMT启动子甲基化状态的价值

目的:探讨MRI影像组学模型术前预测脑胶质母细胞瘤(GBM)O 6-甲基鸟嘌呤-DNA甲基转移酶启动子甲基化(MGMT-PM)状态的价值。方法:回顾性分析2018年1月-2021年10月在本院经病理证实的130例脑GBM患者的临床资料和MRI图像(ADC和对比增强3D-T 1WI)。其中,MGMT-PM阳性组(PM率≥8%)58例,MGMT-PM阴性组(PM率<8%)72例。按7:3的比例将所有患者随机分为训练集(91例)和验证集(39例)。由2位放射科医师独立在ADC和CE-3D-T 1WI图像上逐层勾画ROI,获得病灶的全域容积感兴趣区(VOI),分别提取851个组学特征。然后,采用最小绝对收缩和选择算法(LASSO)进行特征降维,将保留下来的特征与其对应的系数进行线性组合,构建影像组学模型并计算每例患者的影像组学评分(Radscore),得到Radscore ADC、Radscore CE-T 1WI和Radscore联合三组评分。采用ROC曲线评估各组学模型的诊断效能,将最优模型的Radscore和临床特征(年龄、性别)纳入logistic回归分析构建预测MGMT-PM状态的临床-组学综合模型,并绘制其诺模图。采用ROC曲线评价综合模型的预测效能,并采用校准曲线和决策曲线分别评估此模型的校准度和临床实用价值。结果:在训练集中,Radscore联合预测MGMT-PM状态的AUC为0.872,优于单一序列(Radscore ADC:AUC=0.798,P<0.05;Radscore CE-T 1WI:AUC=0.840,P<0.05);在验证集中得到了一致的结论。在影像组学模型中加入临床特征后,可提高预测效能,临床-组学综合模型的AUC、敏感度和特异度分别为0.904、92.50%和78.43%。校准曲线显示临床-组学综合预测模型在训练集和验证集中预测概率与实际概率之间的差异均无统计学意义(P=0.051、0.284)。决策曲线分析表明综合预测模型具有一定的临床实用价值。结论:MRI影像组学模型有助于术前无创性预测GBM的MGMT启动子甲基化状态,多序列结合及引入临床特征能提高模型的预测效能。

人脑胶质瘤干/祖细胞系SU-2放射耐受及其相关机制的初步研究

目的研究胶质瘤干细胞在胶质瘤耐受放射中的作用,为克服恶性胶质瘤放射耐受寻找新的干预靶点。方法干细胞培养条件下培养自建人脑胶质瘤干/祖细胞系SU-2,以及人脑胶质瘤细胞系U251和SHG-44,观察不同剂量直线加速器照射前后细胞形态变化、Hoechst 33342-细胞和CD133+细胞比例、肿瘤细胞存活率和裸小鼠致瘤率等项指标,并以实时荧光定量PCR方法检测人脑胶质瘤细胞系U251和人脑胶质瘤干/祖细胞系SU-2照射前后MGMT基因表达水平。结果当照射剂量为1～15Gy时,人脑胶质瘤干/祖细胞系SU-2中的Hoechst 33342-细胞和CD133+细胞比例明显增加,高达18.73%和13.70%,细胞存活率升高、致瘤率(8/8)增加、侵袭性增强,MGMT基因表达水平轻度升高。结论经一定剂量的X线照射后,胶质瘤干细胞因具有强于其他肿瘤细胞的放射耐受性而出现选择性存活且细胞比例升高,其生物学特性如细胞存活率、体内致瘤率增加,侵袭性增强。可能与胶质瘤干细胞DNA损伤修复能力提高有关,确切的分子学机制值得进一步深入研究。

燃煤污染型砷中毒患者MGMT基因启动区甲基化及MGMT mRNA的表达

[目的]了解燃煤污染型砷中毒患者血中O^6-甲基鸟嘌呤-DNA甲基转移酶基因(MGMT基因)启动区甲基化及患者皮肤组织中MGMT mRNA转录表达的情况,探讨两者间关系及其在砷中毒发生发展乃至癌变中的作用。[方法]采用甲基化特异性PCR法(MSP)检测99例砷中毒患者和103例正常对照MGMT基因启动区甲基化情况;同时采用原位杂交技术检测其中61例砷中毒患者皮肤组织中MGMTmRNA的表达情况。[结果]①砷中毒组MGMT基因启动区甲基化阳性率为40.4%,对照组为2.91%;随病情加重砷中毒患者甲基化阳性率逐渐升高,轻、中、重度砷中毒组甲基化阳性率分别为22.73%、39.02%和52.78%,非癌变组与癌变组甲基化阳性率分别为27.78%和65.00%,均显著高于对照组(P<0.05或P<0.01)。②随着砷中毒患者皮肤病变的加重,MGMTmRNA阳性表达率逐渐降低,其表达率在非癌变组与癌变组分别为71.05%和30.43%,两组间差异有统计学意义(P<0.01)。③MGMT基因启动区甲基化阳性率升高与该基因mRNA表达降低有关联(r=0.456,P=0.01)。[结论]MGMT基因启动区高甲基化是砷中毒发生发展乃至癌变发生的早期事件;MGMT基因启动区高甲基化可导致MGMTmRNA转录水平下降并可能是进一步导致蛋白活性降低的重要原因之一。

毒结清口服液对中晚期肿瘤化疗患者MGMT基因甲基化的影响

目的观察毒结清口服液对中晚期肿瘤化疗患者血浆中O6-甲基鸟嘌呤-DNA-甲基转移酶(O6-methylguanine-DNA methyltransferase,MGMT)基因甲基化状态的影响。方法收集中晚期肿瘤化疗患者60例,随机分为治疗组(30例,常规化疗+毒结清口服液20mL/次,每日3次)和对照组(30例,单用化疗),疗程8周,治疗前后用巢式甲基化特异性聚合酶链反应(MSP)检测中晚期肿瘤化疗患者血浆中MGMT基因的甲基化状态,同时检测外周血常规、KPS评分,评估临床疗效及毒副反应。结果 MGMT基因甲基化检测结果显示治疗组、对照组甲基化率分别为20.00%、46.67%,差异有统计学意义(P<0.05)。与治疗前比较,治疗后治疗组KPS评分显著提高,对照组显著下降,差异均有统计学意义(P<0.05)。两组治疗后比较,差异亦有统计学意义(P<0.01)。化疗后治疗组毒副反应较对照组轻(P<0.01)。结论毒结清口服液对化疗有增效减毒作用,且不影响骨髓造血功能。其作用靶点可能是MGMT,通过对MGMT活性的调控达到增效减毒的作用。

DNA修复基因MGMT启动子区过甲基化与脑胶质瘤

目的在许多肿瘤中发现启动子区过甲基化而导致O6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)的转录失活,本研究拟从胶质瘤患者肿瘤组织和其对应血清中MGMT基因启动子过甲基化是否有一致性对MGMT基因启动子甲基化进行研究。方法采用甲基化特异性PCR法(MSP)进行MGMT基因启动子区甲基化水平的检测。结果27例胶质瘤组织中有14例(51.9%)MGMT甲基化扩增阳性,13例(48.1%)为MGMT去甲基化扩增阳性。相应的血清中有13例(48.1%)MGMT甲基化扩增阳性,14例(51.9%)MGMT去甲基化扩增阳性(P<0.05)。结论胶质瘤患者肿瘤组织和其对应的血清中MGMT基因启动子甲基化状态具有显著相关性。测定血清中MGMT基因启动子区的甲基化状态能反应胶质瘤组织中MGMT基因启动子区甲基化状态。MSP是检测MGMT基因启动子区甲基化灵敏和可靠的方法,可以指导临床脑胶质瘤的个体化化疗方案的设计。

B3型胸腺瘤和胸腺癌中MGMT蛋白表达缺失的意义及预后分析

目的探讨B3型胸腺瘤和胸腺癌的O6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)蛋白表达缺失的意义以及对预后的影响。方法选取河北医科大学附属第四医院2008年1月—2015年1月行根治性手术切除的胸腺上皮肿瘤标本蜡块60例,按照WHO组织学分型分为B3型胸腺瘤组(20例)、胸腺癌组(28例)、瘤旁组织组(12例);按照Masaoka临床分期分为Ⅰ/Ⅱ组和Ⅲ/Ⅳ组。术后随访截止日期2018年4月。比较B3型胸腺瘤和胸腺癌中MGMT蛋白表达缺失的情况。结果胸腺癌组MGMT蛋白表达缺失高于B3型胸腺瘤组和瘤旁组织组(P <0. 05),B3型胸腺瘤组MGMT蛋白缺失高于瘤旁组织组(P <0. 05)。Ⅲ/Ⅳ期B3型胸腺瘤和胸腺癌发生蛋白表达缺失的比例高于Ⅰ/Ⅱ期(P <0. 05)。MGMT蛋白表达缺失病例5年生存率低于表达正常病例(P <0. 05)。Ⅲ/Ⅳ5年生存率低于Ⅰ/Ⅱ(P <0. 05)。结论 MGMT蛋白表达缺失提示B3型胸腺瘤和胸腺癌恶性程度高,预后差。

脑胶质瘤SHG-44细胞MGMT基因甲基化状态及其与细胞对烷化剂药物耐药性关系的研究

目的探讨人脑胶质瘤SHG-44细胞O(6)-甲基鸟嘌呤DNA甲基转移酶(MGMT)基因启动子甲基化状态与其蛋白表达以及细胞对烷化剂药物耐药性的相关性。方法取处于对数生长期的人脑胶质瘤SHG-44和U251细胞,分别加入5-氮-2’脱氧胞苷(5-Aza-CdR)培养6d后收集细胞,同时以未加5-Aza-CdR的正常培养细胞作为对照。提取细胞基因组DNA,采用甲基化特异性PCR(MSP)检测MGMT基因的甲基化状态,并利用蛋白质印迹方法检测MGMT蛋白的表达。将收集的细胞分为3组,分别加入浓度为125、100、75、50、25、15、10μg/ml的尼莫司汀(ACNU)和50、25、15、10、5、2.5、1μg/ml的替莫唑胺(TMZ)以及等量的完全培养液(阴性对照),采用噻唑蓝(MTT)法分别检测细胞对烷化剂药物的敏感性,以细胞存活50%时所对应的药物浓度(IC50值)作为衡量细胞对药物敏感性的指标,实验重复3次。结果正常培养的SHG-44细胞MGMT基因启动子呈甲基化状态,MGMT蛋白表达缺失,对ACNU和TMZ的IC50值分别为30、11μg/ml,表现为对烷化剂药物敏感;用5-Aza-CdR处理后,SHG-44细胞MGMT基因启动子成功脱甲基化,MGMT蛋白恢复表达,其对ACNU和TMZ的IC50值分别升高了2.5和3.1倍(均P<0.05),对烷化剂药物的敏感性发生逆转。而正常培养和5-Aza-CdR处理的U251细胞MGMT基因启动子均呈未甲基化状态,都能表达MGMT蛋白,并且均表现为对ACNU和TMZ烷化剂药物耐药。结论MGMT基因甲基化状态能稳定地反映细胞诱导MGMT蛋白表达的能力,并有可能成为预测肿瘤组织对烷化剂化疗药物敏感性的分子标记。

胶质瘤MGMT基因启动子甲基化研究及应用进展

O6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)是一种DNA修复酶,MGMT基因启动子CpG岛甲基化是近年研究较多的胶质瘤相关分子标志,既是评价胶质瘤对烷化剂是否敏感的重要分子标志,也是胶质瘤患者预后评价及复发与假性进展鉴别的重要参考指标。尤其是老年恶性胶质瘤患者,MGMT基因启动子CpG岛甲基化是指导其分子分型和制定个性化治疗方案的重要参考依据。本文对MGMT蛋白功能,以及MGMT基因启动子CpG岛甲基化在指导胶质瘤治疗、判断预后及鉴别复发与假性进展中的应用进行概述。