New drugs are required to counter the tuberculosis (TB) pandemic. Here, we describe the synthesis and characterization of 1,3-benzothiazin-4-ones (BTZs), a new class of antimycobacterial agents that kill Mycobacterium tuberculosis in vitro, ex vivo, and in mouse models of TB. Using genetics and biochemistry, we identified the enzyme decaprenylphosphoryl-beta-d-ribose 2'-epimerase as a major BTZ target. Inhibition of this enzymatic activity abolishes the formation of decaprenylphosphoryl arabinose, a key precursor that is required for the synthesis of the cell-wall arabinans, thus provoking cell lysis and bacterial death. The most advanced compound, BTZ043, is a candidate for inclusion in combination therapies for both drug-sensitive and extensively drug-resistant TB.

, and 38 to 100,000 mg/kg (CIP) were performed with a murine aerosol infection model. MXF was the most efficacious agent (3.0 ؎ 0.2 log 10 CFU/lung reduction), followed by SPX (1.4 ؎ 0.1) and OFX (1.5 ؎ 0.1). CIP showed no effect. The ratio of the AUC to the MIC was the pharmacodynamic parameter that best described the in vivo efficacy. In summary, a lack of intracellular killing predicted the lack of in vivo activity of CIP. The in vivo rank order for maximal efficacy of the three active fluoroquinolones was not clearly predicted by the in vitro assays, however.

We report 1,4-azaindoles as a new inhibitor class that kills Mycobacterium tuberculosis in vitro and demonstrates efficacy in mouse tuberculosis models. The series emerged from scaffold morphing efforts and was demonstrated to noncovalently inhibit decaprenylphosphoryl-β-D-ribose2'-epimerase (DprE1). With "drug-like" properties and no expectation of pre-existing resistance in the clinic, this chemical class has the potential to be developed as a therapy for drug-sensitive and drug-resistant tuberculosis.

Limited data exist on the pharmacokinetic-pharmacodynamic (PK-PD) parameters of the bactericidal activities of the available antimycobacterial drugs. We report on the PK-PD relationships for isoniazid. Isoniazid exhibited concentration (C)-dependent killing of Mycobacterium tuberculosis H37Rv in vitro, with a maximum reduction of 4 log 10 CFU/ml. In these studies, 50% of the maximum effect was achieved at a C/MIC ratio of 0.5, and the maximum effect did not increase with exposure times of up to 21 days. Conversely, isoniazid produced less than a 0.5-log 10 CFU/ml reduction in two different intracellular infection models (J774A.1 murine macrophages and whole human blood). In a murine model of aerosol infection, isoniazid therapy for 6 days produced a reduction of 1.4 log 10 CFU/lung. Dose fractionation studies demonstrated that the 24-h area under the concentration-time curve/MIC (r 2 ‫؍‬ 0.83) correlated best with the bactericidal efficacy, followed by the maximum concentration of drug in serum/MIC (r 2 ‫؍‬ 0.73).No new drugs for the treatment of tuberculosis have been registered in the last 40 years. Discovery of new antimycobacterial agents is in part limited by the laborious and slow nature of the in vitro and in vivo studies required. Knowledge of the pharmacokinetic (PK)-pharmacodynamic (PD) properties of candidate drugs could be used to facilitate drug discovery and evaluation of the effects of combinations of agents. As a step toward such a strategy, we have recently identified the PK-PD parameter that correlated with the in vivo efficacy of rifampin in a murine aerosol model of tuberculosis (7). In the present study, we have extended this work to include isoniazid. MATERIALS AND METHODSReagents. Isoniazid (lot 36H1179) and carboxymethyl cellulose (lot 77H1077) were purchased from Sigma, St. Louis, Mo. Isoniazid stock solutions were prepared in 100% dimethyl sulfoxide (DMSO; Sigma) and diluted in normal saline prior to final use. ETDA (lot 5-4514) was purchased from Hi-Media Labs, Mumbai, India. Acetonitrile (high-pressure liquid chromatography [HPLC] grade) and trichloroacetic acid (TCA) were obtained from Spectrochem Pvt. Ltd., Mumbai, India. Cinnamaldehyde (lot 96320) was obtained from Fluka Biochemika, Bucks, Switzerland.Microbial cultures and cell lines. Mycobacterium tuberculosis H37Rv (ATCC 27294) and J774A.1 macrophages were prepared for in vitro, macrophage, and animal infection studies by previously described methods (7).Blood from healthy volunteers. Group O-positive blood from healthy volunteers collected in citrate phosphate dextrose adenine anticoagulant was obtained from a registered blood bank (TTK Blood Bank, Bangalore, India). It was stored at 4°C and was used for assays up to 1 month from the date of collection.Animals. The Institutional Animal Ethics Committee, registered with the Government of India (registration no. CPCSEA 1999/5), approved all experimental protocols with animals and the use of animals. Ethical practices recommend the use of equal numbers of animals of both sexes w...

The modern definition of enzymology is synonymous with the Michaelis-Menten equation instituted by Leonor Michaelis and Maud Menten. Most textbooks, or chapters within, discussing enzymology start with the derivation of the equation under the assumption of rapid equilibrium (as done by Michaelis-Menten) or steady state (as modified by Briggs and Haldane) conditions to highlight the importance of this equation as the bedrock on which interpretation of enzyme kinetic results is dependent. However, few textbooks or monographs take the effort of placing the equation within its right historical context and discuss the assumptions that have gone into its institution. This guide will dwell on these in substantial detail. Further, this guide will attempt to instil a sense of appreciation for the mathematical curve rectangular hyperbola, its unique attributes and how ubiquitous the curve is in biological systems. To conclude, this guide will discuss the limitations of the equation, and the method it embodies, and trace the journey of how investigators are attempting to move beyond the steady-state approach and the Michaelis-Menten equation into full progress curve, pre-steady state and single-turnover kinetic analysis to obtain greater insights into enzyme kinetics and catalysis.