Enhancing effect ofO6-alkylguanine derivatives on chloroethylnitrosourea cytotoxicity toward tumor cells

Abstract

O6-Alkylguanine derivatives are well known as chemical modulators of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT). Depletion of the enzyme by these derivatives leads to increase sensitivity of tumor cells to chloroethylnitrosoureas. We tested the effect of O6-methylguanine, O6-benzylguanine, O6-(p-methylbenzyl)guanine, O6-(p-chlorobenzyl)guanine, O6-(p-methoxybenzyl)guanine, O6-methylhypoxanthine and O6-benzylhypoxanthine on the sensitivity of tumor cell lines to 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3- nitrosourea hydrochloride (ACNU) using a colorimetric cytotoxicity assay. The sensitivity of MGMT-proficient tumor cells including HeLA S3, C6-1, C6-2/ACNU, U-138 MG and U-373 MG cells was greatly enhanced by 2 hr pretreatment of 10-100 microM O6-benzylguanine, O6-(p-methylbenzyl)guanine and O6-(p-chlorobenzyl)guanine, but not by O6-methylguanine or O6-methylhypoxanthine. O6-(p-methylbenzyl)guanine moderately sensitized the 2 cell lines, HeLa S3 and C6-1, tested in our study to ACNU cytotoxicity. O6-Benzylhypoxanthine at the high concentration (100 microM) sensitized, to some extent, 3 MGMT-proficient cell lines. Lesser degrees of enhancement by the O6-benzylguanine derivatives were noted in MGMT-deficient tumor cells. Biological effects of O6-alkylguanine derivatives on enhancing ACNU cytotoxicity of tumor cells suggest that the exocyclic 2-amino and O6-benzyl groups in O6-benzylguanine skeleton are both essential for the inhibition of MGMT activity.

Cytotoxicity, DNA Damage, and Apoptosis Induced by New Fotemustine Analogs on Human Melanoma Cells in Relation to O6-Methylguanine DNA-Methyltransferase Expression

“…These findings are in agreement with previous immunohistochemistry studies (Ma et al, 2002). Clinical studies demonstrated that the MerϪ phenotype is often associated to a more positive outcome in chemotherapy based on alkylating agents, and several attempts are currently being made to inhibit chemoresistance using MGMT suicide substrates such as O 6 -benzylguanine or O 6 -(4-bromothenyl)guanine (Dolan et al, 1991;Mineura et al, 1994;Middleton et al, 2000b).…”

Aged Garlic Extract Reduces ROS Production and Cell Death Induced by 6-Hydroxydopamine through Activation of the Nrf2-ARE Pathway in SH-SY5Y Cells

“…Three test compounds, 6-OHDA, MPP + and ACNU, that induce cytotoxicity in nerve cells were chosen and the protective effect of AGE (2 and 4 mg/ml) on cell death induced by these compounds was examined. 6-OHDA is a potent neurotoxin and induces cell death associated with ROS generation [20], whereas MPP + is an inducer of Parkinsonism and inhibitor of mitochondrial respiration chain [34] and ACNU is an alkylating anticancer drug used for the therapy of brain cancer [35]. The cytotoxicity of each compound in SH-SY5Y cells was examined and the dose-response curve of each compound was obtained.…”

A mathematical model for intracellular effects of toxins on DNA adduction and repair

“…It is an intracelluIar dynamic model that describes a process of formation of DNA adducts when there is a capacity for removal of those adducts from the DNA by a repair enzyme. Many compounds and metabolities that bind 89 DNA also readily bind existing proteins; some classes of toxins and DNA adducts may inactivate the repair enzyme and subvert the repair process competitively (Chae et al, I994;Lijinsky et al, 1994;Mineura et al, 1994). This particular model illustrates the possible saturation of repair enzyme capacity by the toxin dosage and shows that bistable behavior can sometimes occur, inducing abrupt shifts between two possible steady-state equilibria.…”