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PubMed1987

Structure-activity relationships of podophyllin congeners that inhibit topoisomerase II.

Various analogs of etoposide have been studied and compared in different tests in order to identify which tests best correlate with antitumor activity. These tests included DNA breakage assays using standard alkaline elution procedures as a means of studying topoisomerase II inhibition in intact cells, cytotoxicity studies in naturally sensitive and resistant human carcinoma cell lines, in vitro assays of the effect of the different congeners on topoisomerase II activity, and a preliminary evaluation of the ability of etoposide and teniposide to induce resistance. As in previous studies, a direct correlation was seen between double strand DNA breakage and cytotoxicity but not between single strand DNA breakage and cytotoxicity. Analogs with blocked 4'-hydroxyl groups were poor antitumor agents but were still capable of inhibiting topoisomerase II as evidenced by the production of DNA breaks. However, this DNA breakage was qualitatively different from that produced by VP16. None of the analogs were able to overcome either naive or acquired drug resistance. The dihydroxy analog of VP16, a possible bioactivated analog, was much less potent and possibly less stable than VP16. A model is proposed for the inhibition of topoisomerase II by demethylepipodophyllotoxins that may explain the relationship between double strand DNA breakage and cytotoxicity.

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