A genetic approach was undertaken to identify normal bacterial genes whose products function to limit the effective concentration of antibiotics. In this approach, a multicopy plasmid library containing cloned Escherichia coli chromosomal sequences was screened for transformants that showed increased resistance to a number of unrelated antibiotics. Three such plasmids were identified, and all contained sequences originating from the mar locus. DNA sequence analysis of the minimal complementation unit revealed that the resistance phenotype was associated with the presence of the marA gene on the plasmids. The putative marA gene product is predicted to contain a helix-turn-helix DNA binding domain that is very similar to analogous domains found in three other E. coli proteins. One such similarity was to the SoxS gene product, the elevated expression of which has previously been associated with the multiple antibiotic resistance (Mar) phenotype. Constitutive expression of marA conferred antibiotic resistance even in cells carrying a deletion of the chromosomal mar locus. We have also found that transformants bearing marA plasmids show a significant reduction in ompF translation but not transcription, similar to previously described mar mutants. However, this reduction in ompF expression plays only a minor role in the resistance mechanism, suggesting that functions encoded by genes unlinked to mar must be affected by marA. These results suggest that activation of marA is the ultimate event that occurs at the mar locus during the process that results in multiple antibiotic resistance.

Multiple antibiotic resistance in Escherichia coli has typically been associated with mutations at the mar locus, located at 34 min on the E. coli chromosome. A new mutant, marC, isolated on the basis of a Mar phenotype but which maps to the soxRS (encoding the regulators of the superoxide stress response) locus located at 92 min, is described here. This mutant shares several features with a known constitutive allele of the soxRS gene, prompting the conclusion that it is a highly active allele of this gene. The marC mutation has thus been given the designation soxR201. This new mutant was used to examine the relationship between the mar and sox loci in promoting antibiotic resistance. The results of these studies indicate that full antibiotic resistance resulting from the soxR201 mutation is partially dependent on an intact mar locus and is associated with an increase in the steady-state level of mar-specific mRNA. In addition, paraquat treatment of wild-type cells is shown to increase the level of antibiotic resistance in a dose-dependent manner that requires an intact soxRS locus. Conversely, overexpression of MarA from a multicopy plasmid results in weak activation of a superoxide stress response target gene. These findings are consistent with a model in which the regulatory factors encoded by the marA and soxS genes control the expression of overlapping sets of target genes, with MarA preferentially acting on targets involved with antibiotic resistance and SoxS directed primarily towards components of the superoxide stress response. Furthermore, compounds frequently used to induce the superoxide stress response, including paraquat, menadione, and phenazine methosulfate, differ with respect to the amount of protection provided against them by the antibiotic resistance response.

PD 0305970 and PD 0326448 are new bacterial gyrase and topoisomerase inhibitors (quinazoline-2,4-diones) that possess outstanding in vitro and in vivo activities against a wide spectrum of bacterial species including quinolone-and multidrug-resistant gram-positive and fastidious organism groups. The respective MICs (g/ml) for PD 0305970 capable of inhibiting >90% of bacterial strains tested ranged from 0.125 to 0.5 versus staphylococci, 0.03 to 0.06 versus streptococci, 0.25 to 2 versus enterococci, and 0.25 to 0.5 versus Moraxella catarrhalis, Haemophilus influenzae, Listeria monocytogenes, Legionella pneumophila, and Neisseria spp. PD 0326448 MIC 90 s were generally twofold higher versus these same organism groups. Comparative quinolone MIC 90 values were 4-to 512-fold higher than those of PD 0305970. In testing for frequency of resistance, PD 0305970 and levofloxacin showed low levels of development of spontaneous resistant mutants versus both Staphylococcus aureus and Streptococcus pneumoniae. Unlike quinolones, which target primarily gyrA and parC, analysis of resistant mutants in S. pneumoniae indicates that the likely targets of PD 0305970 are gyrB and parE. PD 0305970 demonstrated rapid bactericidal activity by in vitro time-kill testing versus streptococci. This bactericidal activity carried over to in vivo testing, where PD 0305970 and PD 0326448 displayed outstanding Streptococcus pyogenes 50% protective doses (PD 50 s) (oral dosing) of 0.7 and 3.6 mg/kg, respectively (ciprofloxacin and levofloxacin PD 50 s were >100 and 17.7 mg/kg, respectively). PD 0305970 was also potent in a pneumococcal pneumonia mouse infection model (PD 50 ‫؍‬ 3.2 mg/kg) and was 22-fold more potent than levofloxacin.The continuing emergence and development of bacterial resistance to existing antibacterial agents (fluoroquinolones, macrolides, and vancomycin) in gram-positive organisms have created the need for new compounds that retain activity against these resistant strains (1, 4, 9, 16). PD 0305970 and PD 0326448 are new bacterial gyrase and topoisomerase inhibitors developed as part of a program to introduce an orally active quinazolinedione (QD), displaying highly potent in vitro and in vivo activities versus susceptible and resistant gram-positive and fastidious organism groups. The structure of PD 0305970, 3-amino-7-{(R)-3-[(S)-1-amino-ethyl]-pyrrolidin-1-yl}-1-cyclopropyl-6-fluoro-8-methyl-1H-quinazoline-2,4-dione, is displayed in Fig. 1. PD 0326448 is the des-3-amino version of PD 0305970 (Fig. 2). The data presented here describe the in vitro susceptibilities, in vivo efficacies, and frequencies of resistance for these compounds compared with quinolones in medically significant bacterial species. MATERIALS AND METHODSAntimicrobial agents. The antibacterial compounds used in these studies were obtained from the following sources: PD 0305970, PD 0326448, and gatifloxacin were obtained from the Chemistry Department at Pfizer Global Research and Development, Ann Arbor, MI; garenoxacin was obtained from Bristol Myers, Prin...

The re-emergence of tuberculosis infections which are resistant to conventional drug therapy has demonstrated the need for alternative chemotherapy against Mycobacterium tuberculosis. As part of a study to optimize the quinolone antibacterials against M. tuberculosis, we have prepared a series of N-1- and C-7-substituted quinolones to examine specific structure-activity relationships between modifications of the quinolone at these two positions and activity against mycobacteria. The compounds, synthesized by literature procedures, were evaluated for activity against Mycobacterium fortuitum and Mycobacterium smegmatis as well as Gram-negative and Gram-positive bacteria. The activity of the compounds against M. fortuitum was used as a barometer of M. tuberculosis activity. The results demonstrate that (i) the activity against mycobacteria was related more to antibacterial activity than to changes in the lipophilicity of the compounds, (ii) the antimycobacterial activity imparted by the N-1 substituent was in the order tert-butyl > or = cyclopropyl > 2,4-difluorophenyl > ethyl approximately cyclobutyl > isopropyl, and (iii) substitution with either piperazine or pyrrolidine heterocycles at C-7 afforded similar activity against mycobacteria.

Due largely to the emergence of multi-drug-resistant HIV strains, the development of new HIV protease inhibitors remains a high priority for the pharmaceutical industry. Toward this end, we previously identified a 4-hydroxy-5,6-dihydropyrone lead compound (CI-1029, 1) which possesses excellent activity against the protease enzyme, good antiviral efficacy in cellular assays, and promising bioavailability in several animal species. The search for a suitable back-up candidate centered on the replacement of the aniline moiety at C-6 with an appropriately substituted heterocyle. In general, this series of heterocyclic inhibitors displayed good activity (in both enzymatic and cellular tests) and low cellular toxicity; furthermore, several analogues exhibited improved pharmacokinetic parameters in animal models. The compound with the best combination of high potency, low toxicity, and favorable bioavailabilty was (S)-3-(2-tert-butyl-4-hydroxymethyl-5-methyl-phenylsulfanyl)-4-hydroxy-6-isopropyl-6-(2-thiophen-3-yl-ethyl)-5,6-dihydro-pyran-2-one (13-(S)). This thiophene derivative also exhibited excellent antiviral efficacy against mutant HIV protease and resistant HIV strains. For these reasons, compound 13-(S) was chosen for further preclinical evaluation.