NLCQ-1 and NLCQ-2, two new agents with activity against dormant Mycobacterium tuberculosis

4-[3-(2-Nitro-1-imidazolyl)-propylamino]-7-chloroquinoline hydrochloride (NLCQ-1; NSC 709257) and 4-[4-(2-nitro-1-imidazolyl)-butylamino]-7-chloroquinoline hydrochloride (NLCQ-2), two weak DNA-intercalating nitroimidazole-based bioreductive prodrugs, have been tested against dormant Mycobacterium tuberculosis and demonstrated a significant activity comparable with that of the nitroimidazopyran PA-824. Minimum bactericidal concentrations (MBCs) of 3.1–18.4 and 4.9–9.8 μg/mL were obtained for NLCQ-1 and NLCQ-2, respectively. In the same test setting; the corresponding MBC range for PA-824 was 6.4–12.8 μg/mL. For rifampicin, isoniazid, minocycline, streptomycin, clarithromycin and capreomycin, the corresponding MBC values were 2.5, >100, >156.25, >12.5, >312.5 and 37.5 μg/mL, respectively. Toxicity against Vero cells provided 50% inhibitory concentrations (IC50) of 146.7, >640 and >640 μg/mL for NLCQ-1, NLCQ-2 and PA-824, respectively. Therefore, the selectivity index (SI) was 8–47.3, >65.3–130.6 and >50–100 for NLCQ-1, NLCQ-2 and PA-824, respectively. These results suggest the potential usefulness of these compounds in the therapy of the latent form of tuberculosis.