In vitro and in vivo antibacterial activities of KRM-1648 and KRM-1657, new rifamycin derivatives

Abstract

The in vitro and in vivo antibacterial activities of the new rifamycin derivatives KRM-1648 and KRM-1657 were compared with those of rifampin. Rifabutin, ciprofloxacin, and clarithromycin were also tested for reference. The respective MICs of KRM-1648 and KRM-1657 for 90% of the strains tested (MIC90s) were 0.016 and 0.0078 ,ug/ml, respectively, for methicillin-susceptible Staphylococcus aureus, 0.016 and 0.0039 ,ug/ml, respectively, for methicillin-resistant S. aureus, and 0.0625 and 0.016 ,ug/ml, respectively, for methicillin-and quinolone-resistant S. aureus. These MIC90s of KRM-1657 were equal to or 2-to 64-fold lower than those of rifampin. KRM-1648 and KRM-1657 with MIC90s of between 0.002 and 0.078 ,ug/ml were 2-to 128-fold more active than rifampin against Staphylococcus epidermidis and Streptococcus species, including Streptococcus pneumoniae and Streptococcus pyogenes. The MIC90s of KRM-1657 for Haemophilus influenzae and Neisseria gonorrhoeae were 0.25 and 0.1 ,ug/ml, respectively; KRM-1657 was almost as active as rifampin and was 8-to 16-fold more active than KRM-1648 against these strains. The frequency of occurrence of spontaneous mutations to resistance to KRM-1648 and KRM-1657 was equal to that to rifampin. Against systemic infection with S. aureus in mice, the efficacies of KRM-1648 and KRM-1657 were comparable to that of rifampin.The recently synthesized rifamycin derivatives 3'-hydroxy-5'-(4-isobutyl-1 -piperazinyl)benzoxazinorifamycin (KRM-1648) and 3'-hydroxy-5'-(4-propyl-1-piperazinyl)benzoxazinorifamycin (KRM-1657) (Fig. 1) exhibit potent activity against a variety of mycobacteria including Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium intracellulare (1, 3, 6, 7, 9, 10). These compounds have also been shown to be active against Staphylococcus aureus and Bacillus subtilis but have been shown to be inactive against Escherichia coli and Klebsiella pneumoniae (10). In the study described here, we conducted further testing to determine the in vitro activities of KRM compounds against gram-positive and gram-negative bacteria with the aim of elucidating their antibacterial properties. The frequency of occurrence of spontaneous mutants of S. aureus resistant to these compounds and the therapeutic efficacies of these compounds against S. aureus infections in mice were also determined. KRM-1648, KRM-1657, rifampin, and clarithromycin were dissolved in dimethyl sulfoxide at 3.2 mg/ml. Rifabutin and ciprofloxacin were dissolved in dimethylformamide and 0.1 N NaOH, respectively, at 3.2 mg/ml. Drug solutions were diluted with medium broth for use. All drugs were stored at -20°C. MATERIALS AND METHODSFor in vivo testing, rifampin was dissolved (and the other three rifamycin derivatives were suspended) in 2.5% gum arabic solution containing 0.05% Tween 80 (polysorbate 80) at 1.6 mg/ml and was then diluted with the same vehicle to achieve the appropriate concentrations. The compounds were /\~/ CH3 N NCH2CH

Rifampin-Resistant RNA Polymerase Mutants of Chlamydia trachomatis Remain Susceptible to the Ansamycin Rifalazil

“…Rifalazil has greater potency against Chlamydia than rifampin, which is in contrast to the equivalent MICs that rifampin and rifalazil have against some gram-positive pathogens such as S. aureus (5). The results showing that rifalazil retains activity against Chlamydia strains that are resistant to rifampin was unanticipated, particularly in light of the crossresistance of a high proportion of clinical isolates of both S. (7,10,18,19) and S. aureus (16,17) as well as laboratory isolates of S. aureus (9) are shown within the conserved regions of RpoB known to be involved in resistance to rifampin.…”

Mechanism of action of antimycobacterial activity of the new benzoxazinorifamycin KRM-1648

“…Furthermore, KRM is known to exhibit potent activity in vitro and in vivo against gram-positive bacteria (3, 23) but is not effective against gram-negative bacteria or rapidly growing mycobacteria such as Mycobacterium fortuitum (3,14,23). The spectrum of activity of KRM against gram-positive and gram-negative bacteria is nearly the same as that of RMP (3).…”

In Vitro Activity of Novel Rifamycins against Rifamycin-Resistant Staphylococcus aureus

“…Rifamycins, such as rifampin (RIF), rifabutin (RFB), and rifapentine, inhibit bacterial RNA polymerases isolated from a wide variety of microorganisms (4,8,9,10,21,37,38). This class of drugs has been used in the clinic as one component of multiple drug therapy, predominantly to treat tuberculosis (27) and to treat serious gram-positive infections (15,32,48).…”