Dennis M. Zaller

Transgenic mice that express a myelin basic protein-specific T cell receptor develop spontaneous autoimmunity

We constructed a transgenic mouse model that mimics the human autoimmune disease multiple sclerosis in its spontaneous induction and pathology. Transgenic mice were constructed expressing genes encoding a rearranged T cell receptor specific for myelin basic protein (MBP). T cell tolerance was not induced in the periphery, and functional, autoreactive T cells were found in the spleen and lymph nodes of these mice. Transgenic mice developed experimental allergic encephalomyelitis (EAE) following immunization with MBP and adjuvant plus pertussis toxin as well as with administration of pertussis toxin alone. Spontaneous EAE can develop in transgenic mice housed in a non-sterile facility but not in those maintained in a sterile, specific pathogen-free facility. This model system affords a unique opportunity to dissect the genetic and environmental variables that may contribute to the development of spontaneous autoimmune disease.

X-Ray Crystal Structure of HLA-DR4 (DRA*0101, DRB1*0401) Complexed with a Peptide from Human Collagen II

Genetic predisposition to rheumatoid arthritis (RA) is linked to the MHC class II allele HLA-DR4. The charge of the amino acid at DRbeta71 in the peptide-binding site appears to be critical in discriminating DR molecules linked to increased disease susceptibility. We have determined the 2.5 A x-ray structure of the DR4 molecule with the strongest linkage to RA (DRB1*0401) complexed with a human collagen II peptide. Details of a predicted salt bridge between lysine DRbeta71 and aspartic acid at the P4 peptide position suggest how it may participate in both antigen binding and TCR activation. A model is proposed for the DR4 recognition of collagen II (261-273), an antigen immunodominant in human-transgenic mouse models of RA.

Anthrax lethal factor inhibition

The primary virulence factor of Bacillus anthracis is a secreted zinc-dependent metalloprotease toxin known as lethal factor (LF) that is lethal to the host through disruption of signaling pathways, cell destruction, and circulatory shock. Inhibition of this proteolytic-based LF toxemia could be expected to provide therapeutic value in combination with an antibiotic during and immediately after an active anthrax infection. Herein is shown the crystal structure of an intimate complex between a hydroxamate, (2R)-2-[(4-fluoro-3-methylphenyl)sulfonylamino]-N-hydroxy-2-(tetrahydro-2H-pyran-4-yl)acetamide, and LF at the LF-active site. Most importantly, this molecular interaction between the hydroxamate and the LF active site resulted in (i) inhibited LF protease activity in an enzyme assay and protected macrophages against recombinant LF and protective antigen in a cell-based assay, (ii) 100% protection in a lethal mouse toxemia model against recombinant LF and protective antigen, (iii) ≈50% survival advantage to mice given a lethal challenge of B. anthracis Sterne vegetative cells and to rabbits given a lethal challenge of B. anthracis Ames spores and doubled the mean time to death in those that died in both species, and (iv) 100% protection against B. anthracis spore challenge when used in combination therapy with ciprofloxacin in a rabbit “point of no return” model for which ciprofloxacin alone provided 50% protection. These results indicate that a small molecule, hydroxamate LF inhibitor, as revealed herein, can ameliorate the toxemia characteristic of an active B. anthracis infection and could be a vital adjunct to our ability to combat anthrax.

Structural basis for p38alpha MAP kinase quinazolinone and pyridol-pyrimidine inhibitor specificity.

The quinazolinone and pyridol-pyrimidine classes of p38 MAP kinase inhibitors have a previously unseen degree of specificity for p38 over other MAP kinases. Comparison of the crystal structures of p38 bound to four different compounds shows that binding of the more specific molecules is characterized by a peptide flip between Met109 and Gly110. Gly110 is a residue specific to the α, β and γ isoforms of p38. The δ isoform and the other MAP kinases have bulkier residues in this position. These residues would likely make the peptide flip energetically unfavorable, thus explaining the selectivity of binding. To test this hypothesis, we constructed G110A and G110D mutants of p38 and measured the potency of several compounds against them. The results confirm that the selectivity of quinazolinones and pyridol-pyrimidines results from the presence of a glycine in position 110. This unique mode of binding may be exploited in the design of new p38 inhibitors.

Naturally processed T cell epitopes from human glutamic acid decarboxylase identified using mice transgenic for the type 1 diabetes-associated human MHC class II allele, DRB1*0401.

The identification of class II binding peptide epitopes from autoimmune disease-related antigens is an essential step in the development of antigen-specific immune modulation therapy. In the case of type 1 diabetes, T cell and B cell reactivity to the autoantigen glutamic acid decarboxylase 65 (GAD65) is associated with disease development in humans and in nonobese diabetic (NOD) mice. In this study, we identify two DRB1*0401-restricted T cell epitopes from human GAD65, 274-286, and 115-127. Both peptides are immunogenic in transgenic mice expressing functional DRB1*0401 MHC class II molecules but not in nontransgenic littermates. Processing of GAD65 by antigen presenting cells (APC) resulted in the formation of DRB1*0401 complexes loaded with either the 274-286 or 115-127 epitopes, suggesting that these naturally derived epitopes may be displayed on APC recruited into pancreatic islets. The presentation of these two T cell epitopes in the islets of DRB1*0401 individuals who are at risk for type 1 diabetes may allow for antigen-specific recruitment of regulatory cells to the islets following peptide immunization.

The Structure of HLA-DM, the Peptide Exchange Catalyst that Loads Antigen onto Class II MHC Molecules during Antigen Presentation

The three-dimensional structure of the soluble ecto-domain of HLA-DM has been determined to 2.5 A resolution by X-ray crystallography. HLA-DM has both peptide exchange activity and acts as a chaperone to peptide-free class II MHC molecules. As predicted, the structure is similar to that of classical class II MHC molecules except that the peptide-binding site is altered to an almost fully closed groove. An unusual cavity is found at the center of the region that binds peptides in class II MHC molecules, and a tryptophanrich lateral surface is identified that is a candidate both for binding to HLA-DR, to effect catalysis, and to HLA-DO, an inhibitor.

FGF21 Analogs of Sustained Action Enabled by Orthogonal Biosynthesis Demonstrate Enhanced Antidiabetic Pharmacology in Rodents

Fibroblast growth factor 21 (FGF21) mitigates many of the pathogenic features of type 2 diabetes, despite a short circulating half-life. PEGylation is a proven approach to prolonging the duration of action while enhancing biophysical solubility and stability. However, in the absence of a specific protein PEGylation site, chemical conjugation is inherently heterogeneous and commonly leads to dramatic loss in bioactivity. This work illustrates a novel means of specific PEGylation, producing FGF21 analogs with high specific activity and salutary biological activities. Using homology modeling and structure-based design, specific sites were chosen in human FGF21 for site-specific PEGylation to ensure that receptor binding regions were preserved. The in vitro activity of the PEGylated FGF21 ana-logs corresponded with the site of PEG placement within the binding model. Site-specific PEGylated analogs demonstrated dramatically increased circulating half-life and enhanced efficacy in db/db mice. Twice-weekly dosing of an optimal FGF21 analog reduced blood glucose, plasma lipids, liver triglycerides, and plasma glucagon and enhanced pancreatic insulin content, islet number, and glucose-dependent insulin secretion. Restoration of insulin sensitivity was demonstrated by the enhanced ability of insulin to induce Akt/protein kinase B phosphorylation in liver, muscle, and adipose tissues. PEGylation of human FGF21 at a specific and preferred site confers superior metabolic pharmacology.

HLA-DR1 (DRB1*0101) and DR4 (DRB1*0401) Use the Same Anchor Residues for Binding an Immunodominant Peptide Derived from Human Type II Collagen

Rheumatoid arthritis is an autoimmune disease in which susceptibility is strongly associated with the expression of specific HLA-DR haplotypes, including DR1 (DRB1*0101) and DR4 (DRB1*0401). As transgenes, both of these class II molecules mediate susceptibility to an autoimmune arthritis induced by immunization with human type II collagen (hCII). The dominant T cell response of both the DR1 and DR4 transgenic mice to hCII is focused on the same determinant core, CII(263–270). Peptide binding studies revealed that the affinity of DR1 and DR4 for CII(263–270) was at least 10 times less than that of the model Ag HA(307–319), and that the affinity of DR4 for the CII peptide is 3-fold less than that of DR1. As predicted based on the crystal structures, the majority of the CII-peptide binding affinity for DR1 and DR4 is controlled by the Phe263; however, unexpectedly the adjacent Lys264 also contributed significantly to the binding affinity of the peptide. Only these two CII amino acids were found to provide binding anchors. Amino acid substitutions at the remaining positions had either no effect or significantly increased the affinity of the hCII peptide. Affinity-enhancing substitutions frequently involved replacement of a negative charge, or Gly or Pro, hallmark amino acids of CII structure. These data indicate that DR1 and DR4 bind this CII peptide in a nearly identical manner and that the primary structure of CII may dictate a different binding motif for DR1 and DR4 than has been described for other peptides that bind to these alleles.

Design and synthesis of potent, orally bioavailable dihydroquinazolinone inhibitors of p38 MAP kinase.

The development of potent, orally bioavailable (in rat) and selective dihydroquinazolinone inhibitors of p38alpha MAP kinase is described. These analogues are hybrids of a pyridinylimidazole p38alpha inhibitor reported by Merck Research Laboratories and VX-745. Optimization of the C-5 phenyl and the C-7 piperidinyl substituents led to the identification of 15i which gave excellent suppression of TNF-alpha production in LPS-stimulated whole blood (IC(50)=10nM) and good oral exposure in rats (F=68%, AUCn PO=0.58 microM h).

Chemical genetics define the roles of p38alpha and p38beta in acute and chronic inflammation.

The p38 MAP kinase signal transduction pathway is an important regulator of proinflammatory cytokine production and inflammation. Defining the roles of the various p38 family members, specifically p38α and p38β, in these processes has been difficult. Here we use a chemical genetics approach using knock-in mice in which either p38α or p38β kinase has been rendered resistant to the effects of specific inhibitors along with p38β knock-out mice to dissect the biological function of these specific kinase isoforms. Mice harboring a T106M mutation in p38α are resistant to pharmacological inhibition of LPS-induced TNF production and collagen antibody-induced arthritis, indicating that p38β activity is not required for acute or chronic inflammatory responses. LPS-induced TNF production, however, is still completely sensitive to p38 inhibitors in mice with a T106M point mutation in p38β. Similarly, p38β knock-out mice respond normally to inflammatory stimuli. These results demonstrate conclusively that specific inhibition of the p38α isoform is necessary and sufficient for anti-inflammatory efficacy in vivo.