Human brain tumorO6-methylguanine-DNA methyltransferase mRNA and its significance as an indicator of selective chloroethylnitrosourea chemotherapy

Mineura, Katsuyoshi; Yanagisawa, Toshiharu; Watanabe, Katsuo; Kowada, Masayoshi; Yasui, Nobuyuki

doi:10.1002/(sici)1097-0215(19961021)69:5<420::aid-ijc12>3.0.co;2-6

Cited by 44 publications

(24 citation statements)

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“…MGMT is one of the most important genes for ACNU resistance. 6,7,10,30 According to our results, the tumor with RQV of MGMT м1 in real-time quantitative RT-PCR should not be treated by ACNU.…”

Section: Discussionmentioning

confidence: 71%

“…5,10 Some authors, including us, have reported that MGMT expression is closely correlated with the clinical or experimental resistance of brain tumors to ACNU. 30,49 There are at least 2 possible approaches to increase the effectiveness of nitrosoureas in the presence of MGMT; i.e., avoid using nitrosoureas in MGMT active tumors as in our approach and overcome the resistance of MGMT to nitrosoureas. MGMT is different from other enzymes because it is consumed.…”

Section: Discussionmentioning

confidence: 99%

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O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

Tanaka

Kobayashi

Utsuki

et al. 2002

Intl Journal of Cancer

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Key words: MGMT; real-time RT-PCR; ACNU; gliomaNitrosoureas are alkylating agents that cause cell death by binding to DNA. Among nitrosoureas, 1-(4-amino-2-methyl-5-pyrimidynyl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) is widely used in Japan to treat gliomas because of its ability to permeate the blood-brain-barrier and excellent clinical effects in combination with radiation and interferon (IFN)-␤. [1][2][3] Drug-resistance genes are some of the most important elements of tumors themselves in determining drug-resistance, 4 and O 6 -methylguanine-DNA methyltransferase (MGMT) is a drug-resistance gene for nitrosoureas. 5,6 The cross-linking of doublestranded DNA by alkylating agents is inhibited by the cellular DNA-repair protein MGMT. MGMT rapidly reverses alkylation at the O 6 position of guanine, thereby averting lethal cross-linking. 7 This is the mechanism by which MGMT induces resistance to alkylating agents such as ACNU.Protocol studies for malignant gliomas have not provided encouraging therapeutic results because of the heterogeneity and various drug-sensitivities of the tumors. 8,9 Individualization of glioma therapy is recommended. We carried out a new adjuvant therapy that was individualized based on the results of the reverse transcription-polymerase chain reaction (RT-PCR) for MGMT to treat malignant gliomas. 2 Our preliminary individual adjuvant therapies (IAT) based on RT-PCR results regarding MGMT expression seemed to be more effective than conventional therapies for malignant gliomas.The level of MGMT varies widely according to the type of tumor, and even varies among tumors of the same histological classification. 5,10 Approximately 30 -50% of gliomas lack MGMT. 11 The fact that more than 50% of gliomas express MGMT limits the indications for ACNU. In our preliminary IAT, platinum (Pt)-compounds were used instead of ACNU even though Ptcompounds had not been accepted as being effective in gliomas. 12,13 To ensure IAT for gliomas, quantitative evaluation is needed for a higher initial response and prolongation of survival.We carried out the present study to determine more appropriate indications for the use of ACNU in gliomas. Real-time quantitative RT-PCR was used to re-evaluate the treated gliomas. MATERIAL AND METHODS Real-time quantitative RT-PCRIn 100 frozen sample of neuroepithelial tumors (19 low-grade neuroepithelial tumors, 28 Grade III gliomas, 41 glioblastomas, and 12 medulloblastomas), MGMT was quantitated by real-time quantitative RT-PCR using SYBR Green dye. RT-PCR was basically carried out as described previously. 14 -16 Briefly, total RNA was extracted from frozen tissue specimens weighing about 1 g, which had been homogenized using a glass Teflon homogenizer, via the guanidinium thiocyanate-phenol-chloroform single-step extraction method with Isogen (Nippon Gene, Toyama, Japan). 17 After ethanol precipitation, about 100 g of total RNA was extracted. Forty microliters of complementary deoxyribonucleic acid (cDNA) solution was synthesized from 2 g of total RNA wi...

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

Tanaka

Kobayashi

Utsuki

et al. 2002

Intl Journal of Cancer

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“…Although the cytotoxicity of chloroethylating agents and methylating agents can be attributed to quite different DNA lesions, both depend upon initial adduct formation at the O 6 -position of guanine (9,55,56). Several preclinical and clinical studies have strongly suggested that the DNA repair enzyme MGMT, with reverse alkylation at the O 6 -position of guanine, plays an important role in cellular resistance to chlorethylation or methylation damage at the O 6 -position of guanine DNA (10,(13)(14)(15)(16)(17)(18)26,(57)(58)(59)(60)(61)(62). In human cancer, the MGMT gene is not commonly mutated or deleted, and loss of MGMT function is most frequently due to epigenetic changes, particularly promoter hypermethylation (22,28,63), which cause MGMT transcriptional silencing in cells with defective O 6 -methylguanine repair (22,28,64,65).…”

Section: Discussionmentioning

confidence: 99%

Effect of IFN-β on human glioma cell lines with temozolomide resistance

Yoshino

Ogino²,

Yachi³

et al. 2009

Int J Oncol

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Abstract. Human interferon-ß (IFN-ß) is known to exhibit pleiotropic biological activities including antitumor effects. On the other hand, temozolomide (TMZ), an oral bioavailable alkylating agent with excellent tolerability, has demonstrated efficacy and has become a key therapeutic agent in patients with malignant gliomas; however, its survival benefit remains unsatisfactory. More recent studies have indicated that there might be favorable therapeutic interactions between IFN-ß and TMZ, although the therapeutic advantages of such a combination have not yet been fully explored. The main aim of the present study was to determine whether an antitumor effect could be potentiated by a combination of IFN-ß and TMZ. The antitumor effect of and cell sensitivity to IFN-ß and TMZ and the synergistic potential of IFN-ß and TMZ in combination were evaluated in six malignant glioma cell lines. Correlations among the MGMT methylation status, quantitative level of MGMT mRNA, MGMT protein expression and the antitumor effect of these agents were also evaluated, since one of the most prominent resistance mechanisms to TMZ involves the DNA repair protein MGMT. The cell growth inhibitory effects of IFN-ß and TMZ on all tumor cell lines were observed in a dose-dependent manner, and the human malignant glioma-derived cell lines differed in their sensitivity to TMZ. The MGMT status, including promoter hypermethylation, quantitative mRNA expression and protein expression, was strongly correlated with TMZ sensitivity. A synergistic cell growth inhibitory effect and down-regulated MGMT mRNA levels were significantly observed when a clinically achievable CNS dose of IFN-ß was combined with TMZ, as compared to treatment with IFN-ß or TMZ alone in TMZ-resistant T98G cells. Furthermore, significant amounts of endogenous IFN-ß protein were detected in TMZ-treated T98G cells by ELISA. These results suggest that the clinical therapeutic efficacy of TMZ might be improved by a combination with IFN-ß in malignant gliomas unmethylated at the MGMT gene. The data provide an experimental basis for future strategies in TMZ chemotherapy, although further studies are needed to determine the detailed role of combined IFN-ß and TMZ chemotherapy in increasing tumor sensitivity.

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“…The majority of trials showed a relationship between low MGMT and better therapeutic response in patients with malignant gliomas on treatment with BCNU 16,17,39,40 or temozolomide. 19,41,42 Some studies, however, failed to show a correlation.…”

Section: Therapeutic Response Of Patientsmentioning

confidence: 99%

MGMT in primary and recurrent human glioblastomas after radiation and chemotherapy and comparison with p53 status and clinical outcome

Wiewrodt

Nagel²,

Dreimüller

et al. 2007

Intl Journal of Cancer

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The DNA repair protein O 6 -methylguanine-DNA methyltransferase (MGMT) plays a pivotal role in alkylating drug resistance. Here, we determined MGMT activity in primary and recurrent glioblastomas (GBM, WHO grade IV) of patients who received radiation therapy (RT) or RT plus chemotherapy with alkylating agents (temozolomide, chloroethylnitrosoureas). The mean MGMT activity of untreated GBM was 37 6 45 (range 0-205) fmol/mg proteins. In the 1st, 2nd and 3rd recurrences, MGMT activity increased from 66 6 50 (13-194) to 68 6 44 (14-143) and 182 6 163 (64-423) fmol/mg protein, respectively. Comparing patients who received RT only with RT plus chemotherapy, a significant increase of MGMT in 1st recurrences was only found after treatment with RT plus chemotherapy, indicating either selection of MGMT expressing cells or induction of the MGMT gene by alkylating agents. The p53 status was not significantly related to the MGMT expression level, although a trend for lower MGMT activity in p53 positively stained tumors was observed. Patients expressing MGMT activity of 30 fmol/mg protein in the pretreatment tumor had a significant better therapeutic response than patients expressing MGMT above this level, which was shown by Kaplan-Meyer curves and the recurrence free interval after primary tumor resection. In patients who received RT only, this correlation was not found. The data revealed a threshold of MGMT expression (30 fmol/mg protein) below which patients respond better to alkylating agents. Therefore, determination of MGMT activity in the primary tumor appears to be useful in predicting the outcome of GBM therapy. ' 2007 Wiley-Liss, Inc.Key words: DNA repair; alkyltransferase; MGMT; glioblastomas; drug resistance; temozolomide Despite the enormous progress in the treatment of various types of tumors, human gliomas still have a low curative response. In the therapy of gliomas, notably the most severe form glioblastoma multiforme (GBM, WHO grade IV), radiation therapy (RT) or RT concomitant with methylating agents such as temozolomide 1 is applied. Methylating and chloroethylating agents such as BCNU (carmustine), CCNU (lomustine) or ACNU (nimustine) are also administered during adjuvant therapy. 2 Unfortunately, only a minority of glioblastoma patients respond to temozolomide and chloroethylating nitrosoureas. A likely explanation for this is the development of either primary or acquired glioblastoma cell resistance that leads to protection of the tumor against alkylating drugs.Methylating and chloroethylating agents attack DNA at nucleophilic sites like the O 6 position of guanine, forming O 6 -alkylguanine. 3 This lesion is considered to be the major cause of mutations and malignant transformation induced by O 6 -alkylating agents. 4 It also provokes cell death by inducing apoptosis 5,6 and, therefore, is considered to be mainly responsible for the antineoplastic effect of O 6 -alkylating agents. O 6 -alkylguanine is repaired by the suicide DNA repair protein O 6 -methylguanine-DNA methyltransferase (MGMT) that transf...

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Human brain tumorO6-methylguanine-DNA methyltransferase mRNA and its significance as an indicator of selective chloroethylnitrosourea chemotherapy

Abstract: , .Akita 010, 'j,,an. 06-methylguanine-DNA methyltransferase (MGMT) removes and repairs chloroethylnitrosourea (CENU)-

Cited by 44 publications

References 6 publications

O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

Effect of IFN-β on human glioma cell lines with temozolomide resistance

MGMT in primary and recurrent human glioblastomas after radiation and chemotherapy and comparison with p53 status and clinical outcome

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Human brain tumorO6-methylguanine-DNA methyltransferase mRNA and its significance as an indicator of selective chloroethylnitrosourea chemotherapy

Abstract: , .Akita 010, 'j,,an. 06-methylguanine-DNA methyltransferase (MGMT) removes and repairs chloroethylnitrosourea (CENU)-

Cited by 44 publications

References 6 publications

O6‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

O6‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

Effect of IFN-β on human glioma cell lines with temozolomide resistance

MGMT in primary and recurrent human glioblastomas after radiation and chemotherapy and comparison with p53 status and clinical outcome

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O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas

O⁶‐methylguanine‐DNA methyltranspherase gene expression in gliomas by means of real‐time quantitative RT‐PCR and clinical response to nitrosoureas