O6-methylguanine-DNA-methyltransferase expression and gene polymorphisms in relation to chemotherapeutic response in metastatic melanoma

Ma, Shen; Egyházi, Suzanne; Ueno, Takayuki; Lindholm, Christer; Kreklau, Emiko L.; Stierner, Ulrika; Ringborg, Ulrik; Hansson, Johan

doi:10.1038/sj.bjc.6601270

Cited by 64 publications

(42 citation statements)

References 34 publications

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“…However, conflicting data have been reported. Thus, the pretreatment levels of MGMT in biopsies of cutaneous tumours were not related to the outcome (Middleton et al, 1998) whereas a later study showed that MGMT expression in melanoma metastases was related to the clinical response of the patients to DTIC-based therapy (Ma et al, 2002a(Ma et al, , 2003. Conversely, MGMT promoter methylation was not clearly related to the patients response upon TMZ treatment, although methylation threshold levels were also discussed to have an impact on therapy (Rietschel et al, 2008).…”

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confidence: 99%

Temozolomide- and fotemustine-induced apoptosis in human malignant melanoma cells: response related to MGMT, MMR, DSBs, and p53

Naumann¹,

Roos²,

Jöst³

et al. 2009

Br J Cancer

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Malignant melanomas are highly resistant to chemotherapy. First-line chemotherapeutics used in melanoma therapy are the methylating agents dacarbazine (DTIC) and temozolomide (TMZ) and the chloroethylating agents BCNU and fotemustine. Here, we determined the mode of cell death in 11 melanoma cell lines upon exposure to TMZ and fotemustine. We show for the first time that TMZ induces apoptosis in melanoma cells, using therapeutic doses. For both TMZ and fotemustine apoptosis is the dominant mode of cell death. The contribution of necrosis to total cell death varied between 10 and 40%. The O 6 -methylguanine-DNA methyltransferase (MGMT) activity in the cell lines was between 0 and 1100 fmol mg À1 protein, and there was a correlation between MGMT activity and the level of resistance to TMZ and fotemustine. MGMT inactivation by O 6 -benzylguanine sensitized all melanoma cell lines expressing MGMT to TMZ and fotemustine-induced apoptosis, and MGMT transfection attenuated the apoptotic response. This supports that O 6 -alkylguanines are critical lesions involved in the initiation of programmed melanoma cell death. One of the cell lines (MZ7), derived from a patient subjected to DTIC therapy, exhibited a high level of resistance to TMZ without expressing MGMT. This was related to an impaired expression of MSH2 and MSH6. The cells were not cross-resistant to fotemustine. Although these data indicate that methylating drug resistance of melanoma cells can be acquired by down-regulation of mismatch repair, a correlation between MSH2 and MSH6 expression in the different lines and TMZ sensitivity was not found. Apoptosis in melanoma cells induced by TMZ and fotemustine was accompanied by double-strand break (DSB) formation (as determined by H2AX phosphorylation) and caspase-3 and -7 activation as well as PARP cleavage. For TMZ, DSBs correlated significantly with the apoptotic response, whereas for fotemustine a correlation was not found. Melanoma lines expressing p53 wild-type were more resistant to TMZ and fotemustine than p53 mutant melanoma lines, which is in marked contrast to previous data reported for glioma cells treated with TMZ. Overall, the findings are in line with the model that in melanoma cells TMZ-induced O 6 -methylguanine triggers the apoptotic (and necrotic) pathway through DSBs, whereas for chloroethylating agents apoptosis is triggered in a more complex manner.

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confidence: 99%

Temozolomide- and fotemustine-induced apoptosis in human malignant melanoma cells: response related to MGMT, MMR, DSBs, and p53

Naumann¹,

Roos²,

Jöst³

et al. 2009

Br J Cancer

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“…However, at present, these are not clearly established. There are a substantial number of epidemiological and biochemical reports on the properties of these variants (reviewed in [48]) but these do not provide a consistent picture with some studies showing increased risk of tumor development and others not [19,20,22,23,25,26,29,31,[45][46][47]. This may be a consequence of the small sample size in most of these studies.…”

Section: Discussionmentioning

confidence: 72%

“…The Ile143 is located in the active site pocket and is very close to the Cys145 acceptor site. However, this protein appears not to differ from wild type in the repair of methylated DNA [19,24,39]. This is not surprising since the position equivalent to Ile143 in hAGT is variable when sequences from a wide range of organisms are compared with the most common alteration being the presence of Val rather than Ile.…”

Section: Discussionmentioning

confidence: 96%

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Differential inactivation of polymorphic variants of human O6-alkylguanine-DNA alkyltransferase

Fang

Loktionova

Moschel

et al. 2008

Biochemical Pharmacology

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The human DNA repair protein O 6 -alkylguanine-DNA alkyltransferase (hAGT) is an important source of resistance to some therapeutic alkylating agents and attempts to circumvent this resistance by the use of hAGT inhibitors have reached clinical trials. Several human polymorphisms in the MGMT gene that encodes hAGT have been described including L84F and the linked double alteration I143V/K178R. We have investigated the inactivation of these variants and the much rarer variant W65C by O 6 -benzylguanine, which is currently in clinical trials, and a number of other second generation hAGT inhibitors that contain folate derivatives (O 4 -benzylfolic acid, the 3' and 5' folate esters of O 6 -benzyl-2'-deoxyguanosine and the folic acid γ ester of O 6 -(p-hydroxymethyl) benzylguanine). The I143V/K178R variant was resistant to all of these compounds. The resistance was due solely to the I143V change. These results suggest that the frequency of the I143V/K178R variant among patients in the clinical trials with hAGT inhibitors and the correlation with response should be considered.

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“…The replacement of Ile by Val has been postulated to affect the acceptance of an alkyl group. However, functional studies of the MGMT 143 V variant protein have found either no difference from the wild-type or a higher activity [32,33]. The 84 F polymorphism has been shown to have similar enzymatic and physicochemical properties to the wild type [34].…”

Section: Discussionmentioning

confidence: 99%

Polymorphisms of phase II xenobiotic-metabolizing and DNA repair genes and in vitro N-ethyl-N-nitrosourea-induced O6-ethylguanine levels in human lymphocytes

Jiao

Chang

Firozi

et al. 2007

Mutation Research/Genetic Toxicology and Environmental Mutagene

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This study tested the hypothesis that genetic variants of phase II detoxification enzymes and DNA repair proteins affect individual response to DNA damage from alkylating agents. In 171 healthy individuals, an immunoslot blot assay was used to measure O 6 -ethylguanosine (O 6 -EtGua) adduct levels in peripheral blood lymphocytes treated with N-ethyl-N-nitrosourea (ENU) in vitro. The genotypes of GSTM1, GSTT1, GSTP1 I 105 V and A 114 V, MGMT L 84 F and I 143 V, XPD D 312 N and K 751 Q, and XRCC3 T 241 M were determined. Demographic and exposure information was collected by in-person interview. Student's t test, analysis of (co)variance, and multiple linear regression models were used in statistical analyses. The mean and median (range) O 6 -EtGua levels were 94.6 and 84.8 (3.2-508.1) fmol/g DNA, respectively. The adduct level was significantly lower in people who smoked ≥ 25 years than that in never-smokers (square-root transformed mean values 8.20 versus 9.37, P = 0.03). Multiple linear regression models revealed that GSTT1 (β = −2.36, P = 0.009) polymorphism was a significant predictor of the level of adducts in 82 never-smokers, whereas the number of years smoked (β = −0.08, P = 0.005) and XRCC3 T 241 M (β = 2.22, P = 0.007) in 89 eversmokers. The association between GSTP1 I 105 V, MGMT I 143 V, and XPD D 312 N with the level of adducts was not conclusive. Each polymorphism could explain 2% to 10% of the variation of the adduct level. These observations suggest that GSTT1 null and XRCC3 T 241 M polymorphism may have some functional significance in modulating the level of ENU-induced DNA damage and these effects are smoking-dependent. Results from this exploratory study need to be confirmed in other experimental systems.

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O6-methylguanine-DNA-methyltransferase expression and gene polymorphisms in relation to chemotherapeutic response in metastatic melanoma

Cited by 64 publications

References 34 publications

Temozolomide- and fotemustine-induced apoptosis in human malignant melanoma cells: response related to MGMT, MMR, DSBs, and p53

Temozolomide- and fotemustine-induced apoptosis in human malignant melanoma cells: response related to MGMT, MMR, DSBs, and p53

Differential inactivation of polymorphic variants of human O6-alkylguanine-DNA alkyltransferase

Polymorphisms of phase II xenobiotic-metabolizing and DNA repair genes and in vitro N-ethyl-N-nitrosourea-induced O6-ethylguanine levels in human lymphocytes

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