Influence of polyamine depletion caused by alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, on alkylation- and carbamoylation-induced cytotoxicity in 9L rat brain tumor cells in vitro.
Using a colony-forming efficiency assay, we studied the effect of polyamine depletion on the cytotoxicity of four nitrosoureas with different capacities to alkylate and/or carbamoylate biomolecules. 9L rat brain tumor cells were treated with 10 mM alpha-difluoromethylornithine for 48 hr before a 1-hr treatment with nitrosoureas. The cytotoxicity of 2-[3-(2-chloroethyl)-3-nitrosoureido]-D-glucopyranose, which alkylates and subsequently cross-links DNA but does not carbamoylate, was significantly increased by depletion of intracellular polyamines; the dose enhancement ratio of 1.3 is identical to that found for 1,3-bis(2-chloroethyl)-1-nitrosourea and 1-(2-chloroethyl)-3-trans-4-methylcyclohexyl-1-nitrosourea in previous studies. Addition of exogenous putrescine to polyamine-depleted 9L cells 24 hr before treatment prevented this phenomenon. In contrast, the cytotoxicity of 1,3-bis(trans-4-hydroxycyclohexyl)-1-nitrosourea, which carbamoylates only, was significantly decreased in polyamine-depleted cells. This compound alone reduced intracellular polyamine levels. Polyamine depletion did not affect the cytotoxicity of the monoalkylating nitrosoureas N-ethyl-N-nitrosourea and N-methyl-N-nitrosourea. Thus, polyamine depletion apparently potentiates the cytotoxicity only of chloroethylnitrosoureas that alkylate and cross-link.
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001932:Brain Neoplasms / Q000473:pathology*; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors*; D002330:Carmustine / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D000518:Eflornithine; D005038:Ethylnitrosourea / Q000494:pharmacology; D008130:Lomustine / Q000494:pharmacology; D008770:Methylnitrosourea / Q000494:pharmacology; D009952:Ornithine / Q000031:analogs & derivatives* / Q000494:pharmacology; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000378:metabolism*; D051381:Rats
D000970:Antineoplastic Agents; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D008770:Methylnitrosourea; D008130:Lomustine; D009952:Ornithine; D002262:Carboxy-Lyases; D005038:Ethylnitrosourea; D002330:Carmustine; D000518:Eflornithine