Inhibitory effect of NO-releasing ciprofloxacin (NCX 976) on Mycobacterium tuberculosis survival

Abstract

Here, we report the antimycobacterial activity of NCX 976, a new molecule obtained adding a NO moiety to the fluoroquinolone ciprofloxacin, on Mycobacterium tuberculosis H37Rv strain, both in a cell-free model and in infected human macrophages. Unlike unaltered ciprofloxacin, NCX976 displayed a marked activity also at low-nanomolar concentrations.

FIG. 1.

Chemical structure of ciprofloxacin and NCX 976 (2-methoxy-4-(3-[4′-(nitrooxy)butoxy]-3-oxo-1-propenyl]phenyl ester).

FIG. 2.

Morphology of the AFB-stained by the Ziehl-Neelsen protocol. A virulent strain of M. tuberculosis (H37Rv) was treated with 10 nM NCX 976 (A) and 10 nM ciprofloxacin (B) for 2 days. The NO-releasing drug disrupted the normal morphology and red staining of the AFB. No effect was observed in the presence of unaltered ciprofloxacin.

FIG. 3.

Antimycobacterial activity of NCX 976 and ciprofloxacin against M. tuberculosis grown in Sauton's medium. Drugs were added to the indicated concentrations, and incubation was continued for 24 h. Then, cultures were diluted and plated for counting of CFU. Each bar represents the mean ± standard deviation (error bar) (n = 3). (F, 38.43 [P < 0.0001]). For further details see the text.

FIG. 4.

Antimycobacterial activity of NCX 976 and ciprofloxacin against M. tuberculosis in human macrophages. Infection of macrophages was performed at a multiplicity of infection of 10:1 (bacilli:cells). Infected cells were treated for 24 h in the presence of NCX 976 and ciprofloxacin at the indicated concentrations. Then, cells were lysed, and each cell lysate was diluted and plated for counting of CFU after 21 days of culture. Each bar represents the mean ± standard deviation (error bar) (n = 3). (F, 95.09 [P < 0.0001]). For further details see the text.