IDENTIFICATION OF TOPOISOMERASE-I AS THE CYTOTOXIC TARGET OF THE PROTOBERBERINE ALKALOID CORALYNE

Protoberberine alkaloids (coralyne and its derivatives), which exhibit antileukemic activity in animal models, have been shown to be potent inducers of topoisomerase (topo) I-DNA cleavable complexes using purif ied recombinant human DNA topo I. Different from the structurally simi lar benzophenanthridine alkaloid nitidine (a dual poison of both topos I and II), coralyne and its derivatives have marginal poisoning activ ity against DNA topo II. Yeast cells expressing human DNA topo I are s hown to be specifically sensitive to killing by coralyne derivatives a nd nitidine, suggesting that cellular DNA topo I is their cytotoxic ta rget, Two human camptothecin-resistant cell lines, CPT-KS and A2780/CP T-2000, which are known to express highly camptothecin-resistant topo I, are only marginally resistant to coralyne derivatives and nitidine, Purification of human topo I from Escherichia coli cells overexpressi ng CPT-K5 recombinant topo I has demonstrated similar marginal cross-r esistance to nitidine, It seems possible to develop coralyne and nitid ine derivatives as new topo I-targeted therapeutics to overcome aspect s of camptothecin-related resistance.