In vitro microbiological characterization of novel cyclic homopentapeptides, CP-101,680 and CP-163,234, for animal health use.

Two cyclic homopentapeptides, CP-101,680 and CP-163,234 [6a-(3',4'-dichlorophenylamino) analogs of viomycin and capreomycin, respectively], were identified as novel antibacterial agents for the treatment of animal disease, especially for livestock respiratory disease. The in vitro microbiological characterization of both CP-101,680 and CP-163,234 was carried out using their parent compounds, viomycin and capreomycin, as controls. This characterization included antibacterial spectrum, influence of media, inoculum size, pH, EDTA, polymixin B nonapeptide (PMBN), serum, cell-free protein synthesis inhibition, and time-kill kinetics. Our results indicated that the capreomycin analog, CP-163,234, showed slightly improved in vitro potency over the viomycin analog, CP-101,680. Both analogs showed very potent cell-free protein synthesis inhibition activity and were bactericidal against Pasteurella haemolytica, P. multocida and Actinobacillus pleuropneumoniae at the level of 4 times and 8 times MICs. CP-163,234 was bactericidal at the level of 4x and 8x MIC against E. coli, but re-growth was observed after 24 hours incubation at both concentrations of CP-101,680.