Novel small molecule nucleotide homologs (SMNH) activate human macrophages to kill intracellular Mycobacterium tuberculosis. (VAC6P.949)

Tuberculosis is a major cause of death in mankind and drug resistant tuberculosis has posed a problem for therapy. Immunotherapy is an option for better control of tuberculosis. We discovered two types of novel SMNH compounds which were active as adjuvants since they activated respectively NOD2 and TLR-7 receptors in macrophages. Since these cytosolic pattern recognition pathways lead to bactericidal mechanisms, we tested the efficacy of the SMNHs to activate macrophages to kill mycobacteria. Methods: Human THP1 macrophages were treated with either NOD-2 (SB44, SB44-1) or TLR-7 (SB9922) SMNH followed by infection with M. tuberculosis. Three days later macrophages were lysed and plated for bacterial counts. Cytokines from BMs were estimated using sandwich ELISA and autophagic markers were evaluated using monodansyl cadaverine and fluorescence microscopy. Results: Both NOD2 and TLR-7 activating SMNH compounds reduced the numbers of M. tuberculosis in human macrophages by 1-log10 over 3 days of culture. These SMNHs also reduced the numbers of M. tuberculosis within mouse BMs between 1-2log10 over 3 days. SMNHs activated autophagic processes in macrophages underscoring a new mechanism to kill intracellular M. tuberculosis. Since the main scaffold of SB44 has been used as an adjuvant in human trials, we anticipate that SB44 and SB9922 like compounds can be used as adjuncts to drugs for treating ongoing infections of M. tuberculosis in humans.