Alternative strategies for proof-of-principle studies of antibacterial agents

Selective toxicity of antibacterial agents-still a valid concept or do we miss chances and ignore risks?

BACKGROUND

Selective toxicity antibacteribiotics is considered to be due to interactions with targets either being unique to bacteria or being characterized by a dichotomy between pro- and eukaryotic pathways with high affinities of agents to bacterial- rather than eukaryotic targets. However, the theory of selective toxicity oversimplifies the complex modes of action of antibiotics in pro- and eukaryotes.

METHODS AND OBJECTIVE

This review summarizes data describing multiple modes of action of antibiotics in eukaryotes.

RESULTS

Aminoglycosides, macrolides, oxazolidinones, chloramphenicol, clindamycin, tetracyclines, glycylcyclines, fluoroquinolones, rifampicin, bedaquillin, ß-lactams inhibited mitochondrial translation either due to binding to mitosomes, inhibition of mitochondrial RNA-polymerase-, topoisomerase 2ß-, ATP-synthesis, transporter activities. Oxazolidinones, tetracyclines, vancomycin, ß-lactams, bacitracin, isoniazid, nitroxoline inhibited matrix-metalloproteinases (MMP) due to chelation with zinc and calcium, whereas fluoroquinols fluoroquinolones and chloramphenicol chelated with these cations, too, but increased MMP activities. MMP-inhibition supported clinical efficacies of ß-lactams and daptomycin in skin-infections, and of macrolides, tetracyclines in respiratory-diseases. Chelation may have contributed to neuroprotection by ß-lactams and fluoroquinolones. Aminoglycosides, macrolides, chloramphenicol, oxazolidins oxazolidinones, tetracyclines caused read-through of premature stop codons. Several additional targets for antibiotics in human cells have been identified like interaction of fluoroquinolones with DNA damage repair in eukaryotes, or inhibition of mucin overproduction by oxazolidinones.

CONCLUSION

The effects of antibiotics on eukaryotes are due to identical mechanisms as their antibacterial activities because of structural and functional homologies of pro- and eukaryotic targets, so that the effects of antibiotics on mammals are integral parts of their overall mechanisms of action.

Early Clinical Assessment of the Antimicrobial Activity of Finafloxacin Compared to Ciprofloxacin in Subsets of Microbiologically Characterized Isolates

Two phase II studies were performed with patients with uncomplicated urinary tract infections (uUTIs) and complicated urinary tract infections (cUTIs) or acute pyelonephritis (PN) to compare finafloxacin (300 mg twice a day [b.i.d.] orally for uUTI and 800 mg once a day [q.d.] intravenously [i.v.] for cUTI/PN) and ciprofloxacin (250 mg b.i.d. orally for uUTI and 400 mg b.i.d. i.v. for cUTI/PN). The early response to the study medications was evaluated in the microbiological intent-to-treat population (mITT) at day 3. A total of 21% of the isolates were ciprofloxacin resistant, 13.7% were primed pathogens carrying a mutation(s) potentially fostering fluoroquinolone resistance development, and 7.1% produced extended-spectrum β-lactamases (ESBLs). Finafloxacin demonstrated very good early clinical activity, with microbiological eradication rates of 88.6% (n = 132), compared to 78.7% (n = 61) for ciprofloxacin, and 69.6% (n = 23), compared to 35.7% (n = 14) for ciprofloxacin, in patients with ciprofloxacin-resistant uropathogens; 94.1% (n = 17), compared to 80.0% (n = 10) for ciprofloxacin, in patients infected with uropathogens primed for fluoroquinolone resistance uropathogens; and 91.7% (n = 11), compared to 0% for ciprofloxacin, in patients infected with ESBL producers. Finafloxacin demonstrated early and rapid activity against uropathogens, including fluoroquinolone-resistant and/or multiresistant pathogens or ESBL producers, while ciprofloxacin was less active against this subset of resistant pathogens. Susceptibilities of pathogens were quantitated by broth microdilution. Isolates were subgrouped according to their susceptibility patterns, in particular first-step quinolone resistance, quinolone resistance, and ESBL production. Eradication was defined as the elimination or reduction of study entry pathogens to <10³ CFU/ml in urine culture. (The studies described in this paper have been registered at ClinicalTrials.gov under identifiers NCT00722735 and NCT01928433.).

Analysis of effects of MCB3681, the antibacterially active substance of prodrug MCB3837, on human resident microflora as proof of principle

The water-soluble prodrug MCB3837 is rapidly converted to MCB3681, active against Gram-positive bacterial species, after intravenous infusion. The aim of this study was to prove the principle that MCB3681 is efficacious in vivo by demonstrating its effect on the resident microflora or colonizers of the human skin, nose, oropharynx and intestine. MCB3837 was infused at a daily dose of 6 mg/kg for 5 days. MCB3681 was active against clostridia, bifidobacteria, lactobacilli, enterococci and Staphylococcus aureus, thus proving the principle that MCB3681 is antibacterially efficacious in vivo without affecting the Gram-negative microflora.