One way to speed up the TB drug discovery process is to search for antitubercular activity among compound series that already possess some of the key properties needed in anti-infective drug discovery, such as whole-cell activity and oral absorption. Here, we present MGIs, a new series of Mycobacterium tuberculosis gyrase inhibitors, which stem from the long-term efforts GSK has dedicated to the discovery and development of novel bacterial topoisomerase inhibitors (NBTIs). The compounds identified were found to be devoid of fluoroquinolone (FQ) cross-resistance and seem to operate through a mechanism similar to that of the previously described NBTI GSK antibacterial drug candidate. The remarkable in vitro and in vivo antitubercular profiles showed by the hits has prompted us to further advance the MGI project to full lead optimization.

While modern cephalosporins developed for broad spectrum antibacterial activities have never been pursued for tuberculosis (TB) therapy, we identified first generation cephalosporins having clinically relevant inhibitory concentrations, both alone and in synergistic drug combinations. Common chemical patterns required for activity against Mycobacterium tuberculosis were identified using structure-activity relationships (SAR) studies. Numerous cephalosporins were synergistic with rifampicin, the cornerstone drug for TB therapy, and ethambutol, a first-line anti-TB drug. Synergy was observed even under intracellular growth conditions where beta-lactams typically have limited activities. Cephalosporins and rifampicin were 4- to 64-fold more active in combination than either drug alone; however, limited synergy was observed with rifapentine or rifabutin. Clavulanate was a key synergistic partner in triple combinations. Cephalosporins (and other beta-lactams) together with clavulanate rescued the activity of rifampicin against a rifampicin resistant strain. Synergy was not due exclusively to increased rifampicin accumulation within the mycobacterial cells. Cephalosporins were also synergistic with new anti-TB drugs such as bedaquiline and delamanid. Studies will be needed to validate their in vivo activities. However, the fact that cephalosporins are orally bioavailable with good safety profiles, together with their anti-mycobacterial activities reported here, suggest that they could be repurposed within new combinatorial TB therapies.

Here we describe the development and validation of an intracellular high-throughput screening assay for finding new antituberculosis compounds active in human macrophages. The assay consists of a luciferase-based primary identification assay, followed by a green fluorescent protein-based secondary profiling assay. Standard tuberculosis drugs and 158 previously recognized active antimycobacterial compounds were used to evaluate assay robustness. Data show that the assay developed is a short and valuable tool for the discovery of new antimycobacterial compounds.T uberculosis (TB) caused by Mycobacterium tuberculosis affects 9.0 million people annually, with 1.5 million deaths in 2013 (1). Standard TB treatment involves a regimen of four antibiotics taken daily for 6 to 9 months. However, the long treatment duration, toxicity, and interaction with antiretrovirals lead to poor patient compliance and treatment failure. Novel TB drug regimens are therefore urgently needed to treat both standard and drug-resistant forms of TB. Two new drugs, bedaquiline (2) and delamanid (3), were recently approved for the treatment of multidrug-resistant (MDR) TB, and other compounds are in the clinical development pipeline (4). Yet, the search for new TB drug candidates with different modes of action seeks to increase the chances of finding new drugs.Screening of chemical libraries is the first crucial step in the antimicrobial discovery process. Potential antimycobacterial agents are identified by testing chemicals for the ability to inhibit M. tuberculosis growth under in vitro growth conditions in culture medium. However, in vitro screening results are often misleading, as the culture broth does not reflect the environment M. tuberculosis encounters in vivo during the natural course of the disease, neglecting important factors such as compound activation, membrane permeability, removal by efflux pump, and toxicity to mammalian cells (4). Furthermore, adaptive metabolic changes that M. tuberculosis undergoes within the host may affect compound activity (5). Ex vivo screening, in the macrophage, may represent physiological conditions that mimic disease and take into consideration the favorable contribution of host cells in the process of eradicating M. tuberculosis.M. tuberculosis's intracellular lifestyle presents an attractive area for new drug discovery programs. A successful example is the intracellular high-content screening campaign that led to the discovery of Q203 (6). Image-based high-content screening technologies are being adopted more frequently to evaluate the activities of compounds against M. tuberculosis by using various cell types (7-9) or the granuloma infection model (10).High-content screening against M. tuberculosis is a robust and informative assay; however, it is still lacking in terms of speed and simplicity since the endpoint assay requires multiple steps for staining, image acquisition, and cumbersome data analysis. In addition, most of the intracellular compound screening done so far was performed inside e...

As a follow up to the antimycobacterial screening exercise and the release of GSK´s first Tres Cantos Antimycobacterial Set (TCAMS-TB), this paper presents the results of a second antitubercular screening effort of two hundred and fifty thousand compounds recently added to the GSK collection. The compounds were further prioritized based on not only antitubercular potency but also on physicochemical characteristics. The 50 most attractive compounds were then progressed for evaluation in three different predictive computational biology algorithms based on structural similarity or GSK historical biological assay data in order to determine their possible mechanisms of action. This effort has resulted in the identification of novel compounds and their hypothesized targets that will hopefully fuel future TB drug discovery and target validation programs alike.

Global infections by non-tuberculous mycobacteria (NTM) are steadily rising. New drugs are needed to treat NTM infections, but the NTM drug pipeline remains poorly populated and focused on repurposing or reformulating approved antibiotics. We sought to accelerate de novo NTM drug discovery by testing advanced compounds with established activity against Mycobacterium tuberculosis. 3-aminomethyl 4-halogen benzoxaboroles, a novel class of leucyl-tRNA synthetase inhibitors, were recently discovered as active against M. tuberculosis. Here, we report that the benzoxaborole EC/11770 is not only a potent anti-tubercular agent but is active against the M. abscessus and M. avium complexes. Focusing on M. abscessus, which causes the most difficult-to-cure NTM disease, we show that EC/11770 retained potency against drug-tolerant biofilms in vitro and was effective in a mouse lung infection model. Resistant mutant selection experiments showed a low frequency of resistance and confirmed leucyl-tRNA synthetase as the target. This work establishes the benzoxaborole EC/11770 as a novel preclinical candidate for the treatment of NTM lung disease and tuberculosis and validates leucyl-tRNA synthetase as an attractive target for the development of broad-spectrum anti-mycobacterials.