Structure?Activity Relationships for Three Macrolide Antibiotics in Haemophilus influenzae

Abstract

A prior study examining differences in the activities of erythromycin and azithromycin on cellular functions in the Gram-negative pathogen, Haemophilus influenzae, revealed a marked difference in their inhibitory activities. The study revealed that protein synthesis and 50S ribosomal subunit assembly were equal targets for inhibition by azithromycin while erythromycin was a preferential inhibitor of translation. This contrast in inhibitory activities stimulated a comparative analysis of three additional antibiotics: clarithromycin, flurithromycin and roxithromycin. Each compound was tested over a concentration range for inhibitory effects on cellular processes. Clarithromycin was the most effective inhibitor of protein synthesis with an IC(50) of 5.6 microg/mL, followed by flurithromycin at 6 microg/mL, and roxithromycin at 9 microg/mL. IC(50) values for antibiotic effects on viable cell counts and growth rates were similar to those obtained for protein synthesis. Flurithromycin had the strongest effect on 50S ribosomal subunit formation with an IC(50) of 8 microg/mL, followed by clarithromycin and roxithromycin, at 9.0 microg/mL and 12.5 microg/mL respectively. 30S ribosomal subunit formation in cells treated with flurithromycin and roxithromycin was also reduced to some extent. Pulse-and-chase labeling kinetics examining subunit assembly rates verified the slower synthesis rate of the subunits in the presence of each macrolide. The results are discussed in terms of structural differences of these macrolides and their differential inhibitory effects on both cellular targets.

Erythromycin- and Chloramphenicol-Induced Ribosomal Assembly Defects Are Secondary Effects of Protein Synthesis Inhibition

“…In contrast, in most of their experiments with several protein synthesis inhibitors acting upon the large ribosomal subunit, Champney et al observed the accumulation only of 50S subunit precursors. However, it is noteworthy that 30S subunit assembly is inhibited by some macrolides but not others (11,15,35). One possible explanation is that the sucrose gradient centrifugation conditions used in those studies do not allow 30S assembly intermediates to be separated reliably from the mature subunits.…”

“…The drugs proposed to have such an effect included macrolides and ketolides (10,11,15,35,59), streptogramin B (16), lincosamides (16), aminoglycosides (36), evernimicin (14), linezolid (12), and pleuromutilins (13). However, the indirect mechanism of assembly inhibition cannot be excluded for any of these drugs.…”

Photo Degradation of Cotnaminants of Emerging concern (CECs) under Simulated Solar Radiation: Implications for their Environmental Fate

“…rates of photolysis of roxithromycin in natural waters relative to RODW were enhanced in all light sources whereas rates were not always higher in natural waters for erythromycin. Variation in the behavior between roxithromycin and erythromycin can be attributed to the structural difference at C-9 substituent position (Table 2), which is also responsible for the observed differential effects on growth inhibition in H. influenzae (Mabe et al, 2004a). Macrolides degraded with a half-life of 3-10 days in natural waters in solar simulation which is in agreement with previous studies reporting half-lives in the range of 1-40 days (Vione et al, 2009;Tong et al, 2011).…”

Fluorine in medicinal chemistry: Recent therapeutic applications of fluorinated small molecules

“…Similar to erythromycin and other macrolide antibiotics, flurithromycin inhibits bacterial 50S ribosomal subunit assembly [83]. Improved properties relative to erythromycin include improved acid stability, prolonged serum half-life, higher tissue penetration, and better bioavailability [84]. This is discussed in greater depth in the recent review by Bégué and Bonnet-Delpon [2].…”