Diaryl-Aminoindazole with Extensive In Vitro Mycobactericidal Activity Dependent on Exposure to Reactive Nitrogen Species

A bromoindazole was reported with the ability to rapidly and extensively kill Mycobacterium tuberculosis (Mtb) in vitro, but only in the presence of sublethal levels of reactive nitrogen species (RNS) (Warrier et al., ACS Infectious Diseases 1:585–560, 2015). After learning that that compound was poorly tolerated in mice, we identified a diaryl-aminoindazole with even more pronounced ability to kill Mtb in vitro in an RNS-dependent manner, along with RNS-dependent mycobactericidal activity against Mycobacterium avium and RNS-dependent mycobacteristatic activity against Mycobacterium abscessus. The compound was orally bioavailable and well tolerated in mice. However, 4- to 8-week treatment of mice with the diaryl-aminoindazole did not reduce their pulmonary burden of Mtb. Possible explanations include the low levels of compound detected in plasma at trough and the low levels of RNS detected in the lungs of these mice.