title: Effect of O6-benzylguanine analogues on sensitivity of human tumor cells to the cytotoxic effects of alkylating agents.
abstract: The effect of O6-benzylguanine, O6-(p-chlorobenzyl)guanine, and O6-(p-methylbenzyl)guanine on the sensitivity of various human tumor cell lines to alkylating agents is evaluated. The sensitivity of human colon tumor cells, HT29, to the chloroethylating agents, 1,3-bis(2-chloroethyl)-1-nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 2-chloroethyl(methylsulfonyl) methanesulfonate (clomesone), and chlorozotocin was increased by pretreatment for 2 h with 25 microM of each analogue. O6-Benzylguanine was slightly more effective as a sensitizer in HT29 cells than the p-chlorobenzyl and p-methylbenzyl analogues. However, all analogues sensitized SF767 glioma cells to the cytotoxic effects of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, and clomesone to the same degree. Both cell lines were sensitized to the methylating agents streptozotocin and 5-(3-methyl-1-triazeno)imidazole-4-carboxamide, the active intermediate of 5-(3,3-dimethyl-1-triazenyl)imidazole-4-carboxamide, by pretreatment with 10 microM O6-benzylguanine for 2 h. The number of Raji cells surviving 50 microM clomesone decreased 3-fold upon pretreatment for 2 h with 1 microM O6-benzylguanine. The degree of enhancement was dependent on the amount of alkyltransferase protein present in cell lines. For example, HT29 cells (alkyltransferase activity, 381 fmol/mg protein) exhibited a greater degree of enhancement when treated with O6-benzylguanine than SF767 (77 fmol/mg protein) and M19-MEL melanoma (36 fmol/mg protein) cells. There was no enhancement observed in mer- cell lines, U251 (less than 2 fmol/mg protein), and BE (3 fmol/mg protein), or with alkylating agents which did not produce a cytotoxic lesion at the O6 position of guanine in DNA such as cisplatin or 4-hydroperoxycyclophosphamide. Our studies suggest that O6-benzylguanine analogues may have utility in mer+ tumors as an adjuvant to a variety of alkylating agents which produce a toxic lesion at the O6 position of guanine.
authors.affiliation: Division of Hematology-Oncology, University of Chicago Medical Center, Illinois 60637.
authors.forename: M E
authors.initials: ME
authors.lastname: Dolan
authors.forename: R B
authors.initials: RB
authors.lastname: Mitchell
authors.forename: C
authors.initials: C
authors.lastname: Mummert
authors.forename: R C
authors.initials: RC
authors.lastname: Moschel
authors.forename: A E
authors.initials: AE
authors.lastname: Pegg
mesh_terms: D000477:Alkylating Agents / Q000008:administration & dosage*; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D002330:Carmustine / Q000008:administration & dosage; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000008:administration & dosage; D003520:Cyclophosphamide / Q000008:administration & dosage / Q000031:analogs & derivatives; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004357:Drug Synergism; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D006801:Humans; D066298:In Vitro Techniques; D008130:Lomustine / Q000008:administration & dosage; D008698:Mesylates / Q000008:administration & dosage; D008780:Methyltransferases / Q000378:metabolism; D019853:O(6)-Methylguanine-DNA Methyltransferase; D013311:Streptozocin / Q000008:administration & dosage / Q000031:analogs & derivatives; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000477:Alkylating Agents; D000970:Antineoplastic Agents; D008698:Mesylates; C064976:O(6)-benzylguanine; C041189:clomesone; C007028:chlorozotocin; D013311:Streptozocin; D006147:Guanine; D008130:Lomustine; D003520:Cyclophosphamide; D004247:DNA; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002945:Cisplatin; D002330:Carmustine; C011272:perfosfamide