Discovery and characterisation of an antibody that selectively modulates the inhibitory activity of plasminogen activator inhibitor-1.

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor (serpin) that regulates fibrinolysis, cell adhesion and cell motility via its interactions with plasminogen activators and vitronectin. PAI-1 has been shown to play a role in a number of diverse pathologies including cardiovascular diseases, obesity and cancer and is therefore an attractive therapeutic target. However the multiple patho-physiological roles of PAI-1, and understanding the relative contributions of these in any one disease setting, make the development of therapeutically relevant molecules challenging. Here we describe the identification and characterisation of fully human antibody MEDI-579, which binds with high affinity and specificity to the active form of human PAI-1. MEDI-579 specifically inhibits serine protease interactions with PAI-1 while conserving vitronectin binding. Crystallographic analysis reveals that this specificity is achieved through direct binding of MEDI-579 Fab to the reactive centre loop (RCL) of PAI-1 and at the same exosite used by both tissue and urokinase plasminogen activators (tPA and uPA). We propose that MEDI-579 acts by directly competing with proteases for RCL binding and as such is able to modulate the interaction of PAI-1 with tPA and uPA in a way not previously described for a human PAI-1 inhibitor.

Potent and selective inhibitors of Helicobacter pylori glutamate racemase (MurI): pyridodiazepine amines.

An SAR study of an HTS screening hit generated a series of pyridodiazepine amines as potent inhibitors of Helicobacter pylori glutamate racemase (MurI) showing highly selective anti-H. pylori activity, marked improved solubility, and reduced plasma protein binding. X-ray co-crystal E-I structures were obtained. These uncompetitive inhibitors bind at the MurI dimer interface.

Exploring 9-benzyl purines as inhibitors of glutamate racemase (MurI) in Gram-positive bacteria.

An early SAR study of a screening hit series has generated a series of 9-benzyl purines as inhibitors of bacterial glutamate racemase (MurI) with micromolar enzyme potency and improved physical properties. X-ray co-crystal EI structures were obtained.

Exploitation of structural and regulatory diversity in glutamate racemases.

Glutamate racemase is an enzyme essential to the bacterial cell wall biosynthesis pathway, and has therefore been considered as a target for antibacterial drug discovery. We characterized the glutamate racemases of several pathogenic bacteria using structural and biochemical approaches. Here we describe three distinct mechanisms of regulation for the family of glutamate racemases: allosteric activation by metabolic precursors, kinetic regulation through substrate inhibition, and D-glutamate recycling using a d-amino acid transaminase. In a search for selective inhibitors, we identified a series of uncompetitive inhibitors specifically targeting Helicobacter pylori glutamate racemase that bind to a cryptic allosteric site, and used these inhibitors to probe the mechanistic and dynamic features of the enzyme. These structural, kinetic and mutational studies provide insight into the physiological regulation of these essential enzymes and provide a basis for designing narrow-spectrum antimicrobial agents.

The devil is still in the details--driving early drug discovery forward with biophysical experimental methods.

This review comments on some recent trends and insights in the field of lead identification and optimization with a bias toward the increased use of biophysical methods, particularly in combination with three-dimensional structural information. While high-throughput screening, combinatorial chemistry and, most recently, in silico virtual screening techniques have made well-resourced but only partially successful attempts to meet the challenge of identifying new drug candidates by playing 'the large numbers game', another group of technologies are now approaching the same challenge from what might be considered the opposite extreme. The common strategy of these technologies is to focus on a smaller set of low-molecular-weight compounds whose interactions with a target are characterized with the aid of sensitive assays, most often high-quality biophysical techniques such as biosensors, calorimetry, nuclear magnetic resonance spectroscopy and X-ray crystallography. The advantages of such an approach include more optimal and chemically attractive starting points, immediate access to reliable measurements of binding properties, the mapping of ligand interactions on the atomic level and, most importantly, a greater control of experimental errors at the initial stages of drug discovery where compounds are either discovered or lost. When correctly supported, this more careful approach appears to deliver quality leads, even for the so-called 'difficult' targets. As these techniques are complementary to traditional methods, companies should be less hesitant to invest in them. The biophysical methods that are used to drive this approach have made something of a return to drug discovery after having been discarded for being too slow, too expensive or too old-fashioned by the over-optimistic supporters of high-throughput and statistical/computational in silico methods.