Identification and optimization of pyridine carboxamide-based scaffold as a drug lead for Mycobacterium tuberculosis.

New drugs with novel mechanisms of action are urgently needed to tackle the issue of drug-resistant tuberculosis. Here, we have performed phenotypic screening using the Pathogen Box library obtained from the Medicines for Malaria Venture against Mycobacterium tuberculosis in vitro. We have identified a pyridine carboxamide derivative, MMV687254, as a promising hit. This molecule is specifically active against M. tuberculosis and Mycobacterium bovis Bacillus Calmette-Guérin (M. bovis BCG) but inactive against Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Escherichia coli pathogens. We demonstrate that MMV687254 inhibits M. tuberculosis growth in liquid cultures in a bacteriostatic manner. Surprisingly, MMV687254 was as active as isoniazid in macrophages and inhibited M. tuberculosis growth in a bactericidal manner. Mechanistic studies revealed that MMV687254 is a prodrug and that its anti-mycobacterial activity requires AmiC-dependent hydrolysis. We further demonstrate that MMV687254 inhibits M. tuberculosis growth in macrophages by inducing autophagy. In the present study, we have also carried out a detailed structure-activity relationship study and identified a promising novel lead candidate. The identified novel series of compounds also showed activity against drug-resistant M. bovis BCG and M. tuberculosis clinical strains. Finally, we demonstrate that in contrast to MMV687254, the lead molecule was able to inhibit M. tuberculosis growth in a chronic mouse model of infection. Taken together, we have identified a novel lead molecule with a dual mechanism of action that can be further optimized to design more potent anti-tubercular agents.

Pore-forming proteins and their role in cancer and inflammation: Mechanistic insights and plausible druggable targets.

Perforin is a granular effector pore-forming protein formed in NK cells and Cytotoxic T lymphocytes. These cytotoxic proteins are part of the first-line immune defense in the human body. They ensure apoptosis of pathogen-infected cells or tumor cells in the human body. Activation of receptors on NK cell or T cell triggers secondary proteins in these cells. Further, it leads to Ca2+ dependent perforin egress towards the target cell, ensued by PI3K signaling pathway. Perforin undergoes oligomerization over the target cell membrane and forms transmembrane pores with the membrane-spanning domain-MACPF domain. Granzymes, proapoptotic serine proteases are released through these pores and initiate the target cell apoptotic pathway leading to the cell death. Although perforin is a savior for humans from tumor and viral infections, uncontrolled expression of the perforins leads to the autoimmune conditions, including Familial Hemophagocytic lymphohistiocytosis, insulin-dependent diabetes, and cerebral myocarditis. The present review is the concerted effort to highlight the mechanistic pathways concerning perforin secretion, NK cell and T cell-mediated cytotoxicity towards virus-infected and transformed cells. This is followed by the discussion on synthetic derivatives tested so far to inhibit the perforin in pre and clinical arena for certain unusual conditions.