title: Polymyxin permeabilization as a tool to investigate cytotoxicity of therapeutic aromatic alkylators in DNA repair-deficient Escherichia coli strains.
abstract: Chlorambucil (CLB; N,N-bis(2-chloroethyl)-p-aminophenylbutyric acid) and its biologically active beta-oxidation product phenylacetic acid mustard (PAM; N,N-bis(2-chloroethyl)-p-aminophenylacetic acid) are bifunctional aromatic alkylators. CLB is in wide clinical use as an anticancer drug and also as an immunosuppressant. The chemical structures indicate that CLB and PAM are mutagenic, teratogenic and carcinogenic, but the mode of action has remained obscure. We have investigated the biological effects of CLB and PAM with DNA repair-deficient Escherichia coli strains. In contrast to MNNG (N-methyl-N'-nitro-N-nitrosoguanine), CLB and PAM were not toxic to E. coli, but permeabilization of the outer membrane of the cells through use of polymyxin B nonapeptide (PMBN) rendered them susceptible to these compounds. The importance of DNA repair, shown by reversal of damage and attenuation of the toxicity of CLB and PAM, was indicated by the susceptibility of cells lacking O(6)-methylguanine-DNA methyltransferase I and II (ada ogt). Similarly, the protective role of base excision repair (BER) was substantiated by demonstration of an even more increased susceptibility to CLB and PAM of cells lacking 3-methyladenine-DNA glycosylase I and II (alkA1 tag-1). Cells deficient in mismatch repair (mutS) appeared to be slightly more sensitive than normal cells to CLB and PAM, although no such sensitivity to MNNG was observed. This implicates the role of mismatches in CLB- and PAM-related cytotoxicity. It is generally believed that bifunctional alkylating agents, like CLB and PAM, exert their cytotoxic action via DNA cross-linking. Our results with O(6)-methyltransferase- and 3-methyladenine-DNA glycosylase-deficient cells indicate that removal of the adducts prior to the formation of cross-links is an important mechanism maintaining cell viability. We conclude that PMBN permeabilization provides a valuable tool to investigate genetically engineered E. coli cells, whose outer membrane is not naturally permeable to mutagens or other interesting compounds.
authors.affiliation: Laboratory of Molecular Hematology, Department of Clinical Chemistry, Tampere University Hospital and University of Tampere Medical School, FM 2, 3rd floor, P.O. Box 2000, FIN-33521, Tampere, Finland.
authors.forename: C
authors.initials: C
authors.lastname: Salmelin
authors.forename: J
authors.initials: J
authors.lastname: Hovinen
authors.forename: J
authors.initials: J
authors.lastname: Vilpo
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity*; D000970:Antineoplastic Agents / Q000633:toxicity; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D002699:Chlorambucil / Q000633:toxicity; D003470:Culture Media; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects; D005838:Genotype; D008769:Methylnitronitrosoguanidine / Q000633:toxicity; D009152:Mutagenicity Tests; D009588:Nitrogen Mustard Compounds / Q000633:toxicity; D011113:Polymyxins / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D014466:Ultraviolet Rays
chemical_list: D000477:Alkylating Agents; D000970:Antineoplastic Agents; D003470:Culture Media; D009588:Nitrogen Mustard Compounds; D011113:Polymyxins; C008826:phenacid; D008769:Methylnitronitrosoguanidine; D002699:Chlorambucil