In vitro activity of DNF-3 against drug-resistant Mycobacterium tuberculosis

Due to the emergence of multidrug-resistant and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis, new antituberculosis drugs are urgently required to improve the efficacy of current tuberculosis (TB) treatment. To achieve this goal, ca. 1000 chemical compounds were screened for potential antimycobacterial activity, among which methyl 5-(2-diethylaminoethoxy)-7,12-dioxo-7,12 dihydrodinaphtho[1,2-b;2',3'-d]furan-6-carboxylate (DNF-3) showed strong activity against all of the tested drug-susceptible and -resistant M. tuberculosis strains, with 50% minimum inhibitory concentrations (MIC₅₀ values) of 0.02-0.39 µg/mL both in culture broth and within murine RAW 264.7 macrophage cells. When DNF-3 was used in combination with rifampicin or streptomycin, it exhibited direct synergy against XDR-TB and an additive effect against M. tuberculosis H37Rv. DNF-3 displayed a long post-antibiotic effect (PAE) that was comparable with rifampicin but was superior to isoniazid, streptomycin and ethambutol. Importantly, DNF-3 showed no cytotoxicity to any cell line tested, with a selectivity index (SI) of >32. DNF-3 was also active against 27 nontuberculous mycobacteria (NTM) strains, Staphylococcus spp. and Streptococcus spp. Taken together, these results indicate that DNF-3 is a promising new candidate drug for treating TB. Further studies are warranted to establish the in vivo effect and therapeutic potential of DNF-3.