PODOPHYLLOTOXIN-RESISTANT MUTANTS OF CHINESE-HAMSTER OVARY CELLS - CROSS-RESISTANCE STUDIES WITH VARIOUS MICROTUBULE INHIBITORS AND PODOPHYLLOTOXIN ANALOGS

  • 1 January 1983
    • journal article
    • research article
    • Vol. 43  (2) , 505-512
Abstract
The cross-resistances of several mutants of Chinese hamster ovary [CHO] cells which were obtained after 1 and 2 selection steps in the presence of the microtubule inhibitor podophyllotoxin (PodRI and PodRII mutants, respectively) towards various inhibitors of microtuble assembly were examined. Based upon their specific patterns of cross-resistance/sensitivity to various microtubule inhibitors, the PodRI and PodRII classes of mutants appear to be of more than one kind. Studies on the binding of [3H]podophyllotoxin to cytoplasmic extracts indicate that one of the PodRII mutants which has been shown previously to be affected in a MW 66,000-68,000 microtubule-associated protein shows reduced binding of the drug in comparison to the parental PodS and PodRI cells. The different PodRI and PodRII mutants exhibited proportionally increased cross-resistances to various podophyllotoxin analogs (e.g., deoxypodophyllotoxin, epipodophyllotoxin, .beta.-peltatin, 4''-demethylpodophyllotoxin, .alpha.-peltatin, podophyllotoxin-.beta.-D-glucoside, .beta.-peltatin-.beta.-D-glucoside, picropodophyllotoxin, and podophyllic acid) which possess microtubule-inhibitory activity. With the exception of one PodRI class of mutant, none of the mutants exhibited any cross-resistance to 4''-demethylepipodophyllotoxin thenylidine-.beta.-D-glucoside and 4''-demethylepipodophyllotoxin ethylidine-.beta.-D-glucoside, the 2 podophyllotoxin analogs which lack microtubule-inhibitor activity. The cross-resistance studies with these mutants, which, based upon the biochemical studies and their highly specific patterns of cross-resistance, are presumably affected in microtubules, provide some very novel insights into the mechanisms of action of various microtubule inhibitors. The cross-resistance studies with the set of podophyllotoxin-resistant mutants provide a sensitive and highly specific screening procedure for identifying compounds which possess podophyllotoxin-like activity and for investigating the structure-activity relationship among them. The results of structure-activity relationship studies for the various podophyllotoxin analogs examined are discussed.