title: Murine lymphoma L5178Y cells resistant to purine antagonists: differences in cross-resistance to thioguanine-platinum(II) and selenoguanine-platinum(II).
abstract: To determine whether the antitumor activities of thioguanine-platinum(II) [TG-Pt(II)] and selenoguanine-platinum(II) [SeG-Pt(II)] are due to direct actions of these compounds or to the actions of their hydrolysis products, studies were made on a purine antagonist-resistant, murine lymphoma L5178Y/MP subline that lacked the anabolic enzyme hypoxanthine-guanine phosphoribosyltransferase necessary for tumor inhibition. The L5178Y/MP subline proved to be highly resistant to both TG-Pt(II) and thioguanine; the resistance ratios to the two compounds were almost identical. The subline showed high resistance to selenoguanine, but the cross-resistance to SeG-Pt(II) was negligible. Whether the compounds exhibit the delayed cytotoxicity characteristic of purine antagonists was also investigated. Delayed cytotoxicity was demonstrated for TG-Pt(II) as well as for thioguanine and other purine antagonists but not for SeG-Pt(II) or cis-dichlorodiammineplatinum(II). Experiments on cross-resistance and delayed cytotoxicity showed differences in the cytotoxicities of TG-Pt(II) and SeG-Pt(II): TG-Pt(II) exerted its activity through its hydrolysis product thioguanine, whereas SeG-Pt(II) compound was cytotoxic itself.
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D006147:Guanine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000627:therapeutic use; D007940:Leukemia L5178 / Q000188:drug therapy*; D007942:Leukemia, Experimental / Q000188:drug therapy*; D015122:Mercaptopurine / Q000494:pharmacology; D051379:Mice; D009944:Organoplatinum Compounds / Q000009:adverse effects / Q000627:therapeutic use*; D013866:Thioguanine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D009944:Organoplatinum Compounds; D006147:Guanine; C017935:platinum thioguanine; C025317:selenoguanine platinum(II); D015122:Mercaptopurine; D013866:Thioguanine