John G. Luz

Structural comparison of allogeneic and syngeneic T cell receptor-peptide-major histocompatibility complex complexes: a buried alloreactive mutation subtly alters peptide presentation substantially increasing V(beta) Interactions.

The crystal structures of the 2C/H-2Kbm3–dEV8 allogeneic complex at 2.4 Å and H-2Kbm3–dEV8 at 2.15 Å, when compared with their syngeneic counterparts, elucidate structural changes that induce an alloresponse. The Asp77Ser mutation that imbues H-2Kbm3–dEV8 with its alloreactive properties is located beneath the peptide and does not directly contact the T cell receptor (TCR). However, the buried mutation induces local rearrangement of the peptide itself to preserve hydrogen bonding interactions between the peptide and the α1 77 residue. The COOH terminus of the peptide main chain is tugged toward the α1-helix such that its presentation to the TCR is altered. These changes increase the stability of the allogeneic peptide-major histocompatibility complex (pMHC) complex and increase complementarity in the TCR–pMHC interface, placing greater emphasis on recognition of the pMHC by the TCR β-chain, evinced by an increase in shape complementarity, buried surface area, and number of TCR–pMHC contacting residues. A nearly fourfold increase in the number of β-chain–pMHC contacts is accompanied by a concomitant 64% increase in β-chain–pMHC shape complementarity. Thus, the allogeneic mutation causes the same peptide to be presented differently, temporally and spatially, by the allogeneic and syngeneic MHCs.

The 2.5 Å crystal structure of the SIRT1 catalytic domain bound to nicotinamide adenine dinucleotide (NAD+) and an indole (EX527 analogue) reveals a novel mechanism of histone deacetylase inhibition.

The sirtuin SIRT1 is a NAD(+)-dependent histone deacetylase, a Sir2 family member, and one of seven human sirtuins. Sirtuins are conserved from archaea to mammals and regulate transcription, genome stability, longevity, and metabolism. SIRT1 regulates transcription via deacetylation of transcription factors such as PPARγ, NFκB, and the tumor suppressor protein p53. EX527 (27) is a nanomolar SIRT1 inhibitor and a micromolar SIRT2 inhibitor. To elucidate the mechanism of SIRT inhibition by 27, we determined the 2.5 Å crystal structure of the SIRT1 catalytic domain (residues 241-516) bound to NAD(+) and the 27 analogue compound 35. 35 binds deep in the catalytic cleft, displacing the NAD(+) nicotinamide and forcing the cofactor into an extended conformation. The extended NAD(+) conformation sterically prevents substrate binding. The SIRT1/NAD(+)/35 crystal structure defines a novel mechanism of histone deacetylase inhibition and provides a basis for understanding, and rationally improving, inhibition of this therapeutically important target by drug-like molecules.

Structural Context of Disease-Associated Mutations and Putative Mechanism of Autoinhibition Revealed by X-Ray Crystallographic Analysis of the EZH2-SET Domain.

The enhancer-of-zeste homolog 2 (EZH2) gene product is an 87 kDa polycomb group (PcG) protein containing a C-terminal methyltransferase SET domain. EZH2, along with binding partners, i.e., EED and SUZ12, upon which it is dependent for activity forms the core of the polycomb repressive complex 2 (PRC2). PRC2 regulates gene silencing by catalyzing the methylation of histone H3 at lysine 27. Both overexpression and mutation of EZH2 are associated with the incidence and aggressiveness of various cancers. The novel crystal structure of the SET domain was determined in order to understand disease-associated EZH2 mutations and derive an explanation for its inactivity independent of complex formation. The 2.00 Å crystal structure reveals that, in its uncomplexed form, the EZH2 C-terminus folds back into the active site blocking engagement with substrate. Furthermore, the S-adenosyl-L-methionine (SAM) binding pocket observed in the crystal structure of homologous SET domains is notably absent. This suggests that a conformational change in the EZH2 SET domain, dependent upon complex formation, must take place for cofactor and substrate binding activities to be recapitulated. In addition, the data provide a structural context for clinically significant mutations found in the EZH2 SET domain.

Crystal Structures of mPGES-1 Inhibitor Complexes Form a Basis for the Rational Design of Potent Analgesic and Anti-Inflammatory Therapeutics.

Microsomal prostaglandin E synthase 1 (mPGES-1) is an α-helical homotrimeric integral membrane inducible enzyme that catalyzes the formation of prostaglandin E2 (PGE2) from prostaglandin H2 (PGH2). Inhibition of mPGES-1 has been proposed as a therapeutic strategy for the treatment of pain, inflammation, and some cancers. Interest in mPGES-1 inhibition can, in part, be attributed to the potential circumvention of cardiovascular risks associated with anti-inflammatory cyclooxygenase 2 inhibitors (coxibs) by targeting the prostaglandin pathway downstream of PGH2 synthesis and avoiding suppression of antithrombotic prostacyclin production. We determined the crystal structure of mPGES-1 bound to four potent inhibitors in order to understand their structure-activity relationships and provide a framework for the rational design of improved molecules. In addition, we developed a light-scattering-based thermal stability assay to identify molecules for crystallographic studies.

Discovery and Characterization of 2-Acylaminoimidazole Microsomal Prostaglandin E Synthase-1 Inhibitors.

As part of a program aimed at the discovery of antinociceptive therapy for inflammatory conditions, a screening hit was found to inhibit microsomal prostaglandin E synthase-1 (mPGES-1) with an IC50 of 17.4 μM. Structural information was used to improve enzyme potency by over 1000-fold. Addition of an appropriate substituent alleviated time-dependent cytochrome P450 3A4 (CYP3A4) inhibition. Further structure-activity relationship (SAR) studies led to 8, which had desirable potency (IC50 = 12 nM in an ex vivo human whole blood (HWB) assay) and absorption, distribution, metabolism, and excretion (ADME) properties. Studies on the formulation of 8 identified 8·H3PO4 as suitable for clinical development. Omission of a lipophilic portion of the compound led to 26, a readily orally bioavailable inhibitor with potency in HWB comparable to celecoxib. Furthermore, 26 was selective for mPGES-1 inhibition versus other mechanisms in the prostanoid pathway. These factors led to the selection of 26 as a second clinical candidate.

Glucocorticoid receptor modulators informed by crystallography lead to a new rationale for receptor selectivity, function, and implications for structure-based design.

The structural basis of the pharmacology enabling the use of glucocorticoids as reliable treatments for inflammation and autoimmune diseases has been augmented with a new group of glucocorticoid receptor (GR) ligands. Compound 10, the archetype of a new family of dibenzoxepane and dibenzosuberane sulfonamides, is a potent anti-inflammatory agent with selectivity for the GR versus other steroid receptors and a differentiated gene expression profile versus clinical glucocorticoids (lower GR transactivation with comparable transrepression). A stereospecific synthesis of this chiral molecule provides the unique topology needed for biological activity and structural biology. In vivo activity of 10 in acute and chronic models of inflammation is equivalent to prednisolone. The crystal structure of compound 10 within the GR ligand binding domain (LBD) unveils a novel binding conformation distinct from the classic model adopted by cognate ligands. The overall conformation of the GR LBD/10 complex provides a new basis for binding, selectivity, and anti-inflammatory activity and a path for further insights into structure-based ligand design.

A Peptide That Antagonizes TCR-Mediated Reactions with Both Syngeneic and Allogeneic Agonists: Functional and Structural Aspects

We identify and consider some characteristics of a peptide antagonist for the Ag-specific receptor on 2C cells (the 2C TCR). The peptide, GNYSFYAL (called GNY), binds to H-2Kb, and a very high-resolution crystal structure of the GNY-Kb complex at 1.35 Å is described. Although the GNY peptide does not bind to Ld, the potency of GNY-Kb as an antagonist is evident from its ability to specifically inhibit 2C TCR-mediated reactions to an allogenic agonist complex (QLSPFPFDL-Ld), as well as to a syngeneic agonist complex (SIYRYYGL-Kb). The crystal structure and the activities of alanine-substituted peptide variants point to the properties of the peptide P4 side chain and the conformation of the Tyr-P6 side chain as the structural determinants of GNYSFYAL antagonist activity.

2-Chloro-4-[[(1R,2R)-2-hydroxy-2-methyl-cyclopentyl]amino]-3-methyl-benzonitrile: A Transdermal Selective Androgen Receptor Modulator (SARM) for Muscle Atrophy.

A transdermal SARM has a potential to have therapeutic benefit through anabolic activity in muscle while sparing undesired effects of benign prostate hyperplasia (BPH) and liver-mediated decrease in HDL-C. 2-Chloro-4-[(2-hydroxy-2-methyl-cyclopentyl)amino]-3-methyl-benzonitrile 6 showed the desired muscle and prostate effects in a preclinical ORX rat model. Compound 6 had minimal effect on HDL-C levels in cynomolgus monkeys and showed human cadaver skin permeability, thus making it an effective tool for proof-of-concept studies in a clinical setting.

Characterization of 3,3-dimethyl substituted N -aryl piperidines as potent microsomal prostaglandin E synthase-1 inhibitors

Here we report on novel, potent 3,3-dimethyl substituted N-aryl piperidine inhibitors of microsomal prostaglandin E synthases-1(mPGES-1). Example 14 potently inhibited PGE2 synthesis in an ex vivo human whole blood (HWB) assay with an IC50 of 7nM. In addition, 14 had no activity in human COX-1 or COX-2 assays at 30μM, and failed to inhibit human mPGES-2 at 62.5μM in a microsomal prep assay. These data are consistent with selective mPGES-1-mediated reduction of PGE2. In dog, 14 had oral bioavailability (74%), clearance (3.62mL/(min*kg)) and volume of distribution (Vd,ss=1.6L/kg) values within our target ranges. For these reasons, 14 was selected for further study.

Structures of PHR domains from Mus musculus Phr1 (Mycbp2) explain the loss-of-function mutation (Gly1092-->Glu) of the C. elegans ortholog RPM-1.

PHR [PAM (protein associated with Myc)-HIW (Highwire)-RPM-1 (regulator of presynaptic morphology 1)] proteins are conserved, large multi-domain E3 ubiquitin ligases with modular architecture. PHR proteins presynaptically control synaptic growth and axon guidance and postsynaptically regulate endocytosis of glutamate receptors. Dysfunction of neuronal ubiquitin-mediated proteasomal degradation is implicated in various neurodegenerative diseases. PHR proteins are characterized by the presence of two PHR domains near the N-terminus, which are essential for proper localization and function. Structures of both the first and second PHR domains of Mus musculus (mouse) Phr1 (MYC binding protein 2, Mycbp2) have been determined, revealing a novel beta sandwich fold composed of 11 antiparallel beta-strands. Conserved loops decorate the apical side of the first PHR domain (MmPHR1), yielding a distinct conserved surface feature. The surface of the second PHR domain (MmPHR2), in contrast, lacks significant conservation. Importantly, the structure of MmPHR1 provides insights into a loss-of-function mutation, Gly1092-->Glu, observed in the Caenorhabditis elegans ortholog RPM-1.