DRUG FEATURES THAT CONTRIBUTE TO THE ACTIVITY OF QUINOLONES AGAINST MAMMALIAN TOPOISOMERASE-II AND CULTURED-CELLS - CORRELATION BETWEEN ENHANCEMENT OF ENZYME-MEDIATED DNA CLEAVAGE IN-VITRO AND CYTOTOXIC POTENTIAL

CP-115,953 roxyphenyl)-1-cyclopropyl-4-quinolone-3-carboxylic acid] is a novel quinolone that is highly active against topoisomerase II in v itro and in mammalian cells in culture (M. J. Robinson, B. A. Martin, T. D. Gootz, P. R. McGuirk, M. Moynihan, J. A. Sutcliffe, and N. Osher off, J. Biol. Chem. 266:14585-14592, 1991). However, the features of t he drug that contribute to its activity towards mammalian systems have not been characterized. Therefore, CP-115,953 and a series of related quinolones were examined for their activity against calf thymus topoi somerase II and cultured mammalian cells. CP-115,953 stimulated DNA cl eavage mediated by the type II enzyme with a potency that was approxim ately 600-fold greater than that of the antimicrobial quinolone ciprof loxacin and approximately 50-fold greater than that of the antineoplas tic drug etoposide. As determined by the ability to enhance enzyme-med iated DNA cleavage, quinolone activity towards calf thymus topoisomera se II was enhanced by the presence of a cyclopropyl group at the N-1 r ing position and by the presence of a fluorine at C-8. Furthermore, th e 4'-hydroxyphenyl substituent at the C-7 position was critical for th e potency of CP-115,953 towards the mammalian type II enzyme. In this regard, the aromatic nature of the C-7 ring as well as the presence an d the position of the 4'-hydroxyl group contributed greatly to drug ac tivity. Finally, the cytotoxicity of quinolones in the CP-115,953 seri es towards mammalian cells paralleled the in vitro stimulation of DNA cleavage by topoisomerase II rather than the inhibition of enzyme-cata lyzed DNA relaxation. This correlation strongly suggests that these qu inolones promote cell death by converting topoisomerase II to a cellul ar poison.