Fluoroquinolones are potent inhibitors of bacterial topoisomerase II (DNA gyrase). They can also inhibit eukaryotic topoisomerases, which could possibly lead to clastogenicity and/or cellular toxicity. Recent studies have demonstrated a correlation between mammalian cell cytotoxicity of the fluoroquinolones and the potential of these compounds to induce micronuclei, a genetic toxicity endpoint. In an effort to identify potent nontoxic quinolone antibacterials, we have examined the structural features of the fluoroquinolones associated with mammalian cell cytotoxicity. An investigation of a wide variety of substituents at the 1, 5, 7, and 8 positions of a quinolone nucleus was conducted. The results indicate that no one position has a controlling effect on the observed cytotoxicity. Instead, a combination of the various substituents contributes to the effects seen. Certain trends were apparent, such as the fact that compounds with pyrrolidines at the R-7 position were more cytotoxic than those with piperazines, and halogens at R-8 (X-position) were associated with more cytotoxicity relative to hydrogen. A general trend also existed between the cytotoxicity of the compounds and their Gram-positive antibacterial activity. A detailed comparison between the various groups and positional variations as they controlled the cytotoxicity and antibacterial activity is presented.
PD 131628 is a new aminopyrrolidine-substituted fluorocyclopropyl naphthyridine quinolone which possesses high in vitro activity against a wide spectrum of bacterial species. The MICs for .90% of strains were 0.125 to 0.25 ,ug/ml for staphylococci, Streptococcus pyogenes, and S. pneumoniae; 0.5 ,ug/ml for S. agalactiae and Enterococcus faecalis; 0.125 jug/ml for members of the family Enterobacteriaceae and Acinetobacter spp.; 0.5 ,Lg/mI for Pseudomonas aeruginosa; and <0.03 ,ug/ml for Haemophilus influenzae, Moraxella (Branhamella) catarrhalis, and Neisseria gonorrhoeae. In these in vitro comparisons with ciprofloxacin, PD 131628 is more active against gram-positive organisms, approximately equivalent against gram-negative organisms, and, like most other quinolones, relatively inactive against gram-negative anaerobes. In most instances, the in vitro potency of PD 131628 exceeded those of widely used compounds:
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