title: Mechanisms involved in the potentiation of melphalan by the bioreductive compound THNLA-1 in vitro.
abstract: 9-[3-(2-Nitro-1-imidazolyl)propylamino]-1,2,3,4-tetrahydroacridine hydrochloride (THNLA-1) is a 2-nitroimidazole-based, weakly DNA-intercalating bioreductive agent that significantly potentiates the toxic effects of commonly used antitumor drugs such as melphalan (L-PAM) or cis-DDP in sensitive or resistant cell lines in culture, as well as in solid tumors in mice. Potentiation in vitro was observed when cells were preexposed to THNLA-1 under hypoxic conditions before exposure to L-PAM under aerobic conditions. In this study we investigated possible mechanisms involved in the potentiation of L-PAM by THNLA-1 in V79 Chinese hamster cells. Limited depletion of glutathione with buthionine sulfoximine or THNLA-1 under hypoxic pretreatment conditions accounted for only 8.3% of the potentiation induced by THNLA-1. However, DNA, RNA, and protein synthesis were inhibited in a synergistic way in cells preexposed to THNLA-1 under hypoxic conditions (2 h, 37 degrees C) and then coexposed to various doses of L-PAM under aerobic conditions (1 h, 37 degrees C). Cell cycle analysis by flow cytometry showed a slow traverse through the S phase in the L-PAM-alone-treated cells. However, this phenomenon was more prominent in the THNLA-1 plus L-PAM-treated cells. Under aerobic co-incubation conditions with L-PAM, no difference was observed in the cell cycle of L-PAM-alone-treated cells vs. THNLA-1 plus L-PAM-treated cells. Significantly increased apoptosis was observed in the hypoxia-pretreated cells with THNLA-1, 12 and 24 h posttreatment. Comet and alkaline elution assay analysis showed increased DNA cross-links in the hypoxia-pretreated cells with THNLA-1 compared to the L-PAM-alone-treated cells. Finally, potential lethal damage repair was totally suppressed only in the hypoxia-pretreated cells with THNLA-1. In conclusion, DNA damage and hindrance in its repair are the most important mechanisms in the potentiation of L-PAM by THNLA-1, under hypoxic pretreatment conditions.
authors.affiliation: The Radiation Medicine Institute, Evanston Northwestern Healthcare, IL 60201, USA. mvp499@anima.nums.nwu.edu
authors.forename: M V
authors.initials: MV
authors.lastname: Papadopoulou
authors.forename: M
authors.initials: M
authors.lastname: Ji
authors.forename: S H
authors.initials: SH
authors.lastname: Khan
authors.forename: W D
authors.initials: WD
authors.lastname: Bloomer
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D002460:Cell Line / Q000187:drug effects; D020552:Comet Assay; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004357:Drug Synergism; D005978:Glutathione / Q000378:metabolism; D008558:Melphalan / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011506:Proteins / Q000187:drug effects; D012313:RNA / Q000096:biosynthesis / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013619:Tacrine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D018906:Antineoplastic Agents, Alkylating; D011506:Proteins; D011838:Radiation-Sensitizing Agents; C092966:9-(3-(2-nitro-1-imidazolyl)propylamino)-1,2,3,4-tetrahydroacridine; D013619:Tacrine; D019328:Buthionine Sulfoximine; D012313:RNA; D004247:DNA; D005978:Glutathione; D008558:Melphalan