Intracellular and in vivo evaluation of imidazo [2,1-b]thiazole-5-carboxamide antituberculosis compounds

The imidazo[2,1-b]thiazole-5-carboxamides (ITAs) are a promising class of anti-tuberculosis agents shown to have potent activity in vitro and to target QcrB, a key component of the mycobacterial cytochrome bcc-aa3 super complex critical for the electron transport chain. Herein we report the intracellular macrophage potency of nine diverse ITA analogs with MIC values ranging from 0.0625-2.5 mu M and mono-drug resistant potency ranging from 0.0017 to 7 mu M. The in vitro ADME properties (protein binding, CaCo-2, human microsomal stability and CYP450 inhibition) were determined for an outstanding compound of the series, ND11543. ND-11543 was tolerable at > 500 mg/kg in mice and at a dose of 200 mg/kg displayed good drug exposure in mice with an AUC(0-24h) > 11,700 ng.hr/mL and a >= 24 hr half-life. Consistent with the phenotype observed with other QcrB inhibitors, compound ND-11543 showed efficacy in a chronic murine TB infection model when dosed at 200 mg/kg for 4 weeks. The efficacy was not dependent upon exposure, as pre-treatment with a known CYP450-inhibitor did not substantially improve efficacy. The ITAs are an interesting scaffold for the development of new anti-TB drugs especially in combination therapy based on their favorable properties and novel mechanism of action.