Molecular insights into recognition of GUCY2C by T-cell engaging bispecific antibody anti-GUCY2CxCD3

The intestinal epithelial receptor Guanylyl Cyclase C (GUCY2C) is a tumor-associated cell surface antigen expressed across gastrointestinal malignancies that can serve as an efficacious target for colorectal cancer immunotherapy. Here, we describe a yeast surface-display approach combined with an orthogonal peptide-based mapping strategy to identify the GUCY2C binding epitope of a novel anti-GUCY2CxCD3 bispecific antibody (BsAb) that recently advanced into the clinic for the treatment of cancer. The target epitope was localized to the N-terminal helix H2 of human GUCY2C, which enabled the determination of the crystal structure of the minimal GUCY2C epitope in complex with the anti-GUCY2C antibody domain. To understand if this minimal epitope covers the entire antibody binding region and to investigate the impact of epitope position on the antibody's activity, we further determined the structure of this interaction in the context of the full-length extracellular domain (ECD) of GUCY2C. We found that this epitope is positioned on the protruding membrane-distal helical region of GUCY2C and that its specific location on the surface of GUCY2C dictates the close spatial proximity of the two antigen arms in a diabody arrangement essential to the tumor killing activity of GUCY2CxCD3 BsAb.

Crystal structure of ultra-humanized anti-pTau Fab reveals how germline substitutions humanize CDRs without loss of binding'

Administration of therapeutic antibodies can elicit adverse immune responses in patients through the generation of anti-drug antibodies that, in turn, reduce the efficacy of the therapeutic. Removal of foreign amino acid content by humanization can lower the immunogenic risk of the therapeutic mAb. We previously developed the ultra-humanization technology "Augmented Binary Substitution" (ABS) which enables single-step CDR germlining of antibodies. The application of ABS to a chicken anti-pTau antibody generated an ultra-humanized variant, anti-pTau C21-ABS, with increased human amino acid content in the CDRs and reduced in-silico predicted immunogenicity risk. Here, we report the high-resolution crystal structure of anti-pTau C21-ABS Fab in complex with the pTau peptide (7KQK). This study examines how ultra-humanization, via CDR germlining, is facilitated while maintaining near-identical antigen affinity (within 1.6-fold). The co-complex structure reveals that the ABS molecule targets the same antigenic epitope, accommodated by structurally-similar changes in the paratope. These findings confirm that ABS enables the germlining of amino acids within CDRs by exploiting CDR plasticity, to reduce non-human amino acid CDR content, with few alterations to the overall mechanism of binding.

Discovery and optimization of a novel anti-GUCY2c x CD3 bispecific antibody for the treatment of solid tumors

We report here the discovery and optimization of a novel T cell retargeting anti-GUCY2C x anti-CD3ε bispecific antibody for the treatment of solid tumors. Using a combination of hybridoma, phage display and rational design protein engineering, we have developed a fully humanized and manufacturable CD3 bispecific antibody that demonstrates favorable pharmacokinetic properties and potent in vivo efficacy. Anti-GUCY2C and anti-CD3ε antibodies derived from mouse hybridomas were first humanized into well-behaved human variable region frameworks with full retention of binding and T-cell mediated cytotoxic activity. To address potential manufacturability concerns, multiple approaches were taken in parallel to optimize and de-risk the two antibody variable regions. These approaches included structure-guided rational mutagenesis and phage display-based optimization, focusing on improving stability, reducing polyreactivity and self-association potential, removing chemical liabilities and proteolytic cleavage sites, and de-risking immunogenicity. Employing rapid library construction methods as well as automated phage display and high-throughput protein production workflows enabled efficient generation of an optimized bispecific antibody with desirable manufacturability properties, high stability, and low nonspecific binding. Proteolytic cleavage and deamidation in complementarity-determining regions were also successfully addressed. Collectively, these improvements translated to a molecule with potent single-agent in vivo efficacy in a tumor cell line adoptive transfer model and a cynomolgus monkey pharmacokinetic profile (half-life>4.5 days) suitable for clinical development. Clinical evaluation of PF-07062119 is ongoing.

Development of PF-06671008, a Highly Potent Anti-P-cadherin/Anti-CD3 Bispecific DART Molecule with Extended Half-Life for the Treatment of Cancer

Bispecific antibodies offer a promising approach for the treatment of cancer but can be challenging to engineer and manufacture. Here we report the development of PF-06671008, an extended-half-life dual-affinity re-targeting (DART®) bispecific molecule against P-cadherin and CD3 that demonstrates antibody-like properties. Using phage display, we identified anti-P-cadherin single chain Fv (scFv) that were subsequently affinity-optimized to picomolar affinity using stringent phage selection strategies, resulting in low picomolar potency in cytotoxic T lymphocyte (CTL) killing assays in the DART format. The crystal structure of this disulfide-constrained diabody shows that it forms a novel compact structure with the two antigen binding sites separated from each other by approximately 30 Å and facing approximately 90° apart. We show here that introduction of the human Fc domain in PF-06671008 has produced a molecule with an extended half-life (-4.4 days in human FcRn knock-in mice), high stability (Tm1 > 68 °C), high expression (>1 g/L), and robust purification properties (highly pure heterodimer), all with minimal impact on potency. Finally, we demonstrate in vivo anti-tumor efficacy in a human colorectal/human peripheral blood mononuclear cell (PBMC) co-mix xenograft mouse model. These results suggest PF-06671008 is a promising new bispecific for the treatment of patients with solid tumors expressing P-cadherin.

Three-dimensional structure and biophysical characterization of Staphylococcus aureus cell surface antigen-manganese transporter MntC

MntC is a metal-binding protein component of the Mn²⁺-specific mntABC transporter from the pathogen Staphylococcus aureus. The protein is expressed during the early stages of infection and was proven to be effective at reducing both S. aureus and Staphylococcus epidermidis infections in a murine animal model when used as a vaccine antigen. MntC is currently being tested in human clinical trials as a component of a multiantigen vaccine for the prevention of S. aureus infections. To better understand the biological function of MntC, we are providing structural and biophysical characterization of the protein in this work. The three-dimensional structure of the protein was solved by X-ray crystallography at 2.2Å resolution and suggests two potential metal binding modes, which may lead to reversible as well as irreversible metal binding. Precise Mn²⁺-binding affinity of the protein was determined from the isothermal titration calorimetry experiments using a competition approach. Differential scanning calorimetry experiments confirmed that divalent metals can indeed bind to MntC reversibly as well as irreversibly. Finally, Mn²⁺-induced structural and dynamics changes have been characterized using spectroscopic methods and deuterium-hydrogen exchange mass spectroscopy. Results of the experiments show that these changes are minimal and are largely restricted to the structural elements involved in metal coordination. Therefore, it is unlikely that antibody binding to this antigen will be affected by the occupancy of the metal-binding site by Mn²⁺.

Atypical antigen recognition mode of a shark immunoglobulin new antigen receptor (IgNAR) variable domain characterized by humanization and structural analysis

The immunoglobulin new antigen receptors (IgNARs) are a class of Ig-like molecules of the shark immune system that exist as heavy chain-only homodimers and bind antigens by their single domain variable regions (V-NARs). Following shark immunization and/or in vitro selection, V-NARs can be generated as soluble, stable, and specific high affinity monomeric binding proteins of ∼12 kDa. We have previously isolated a V-NAR from an immunized spiny dogfish shark, named E06, that binds specifically and with high affinity to human, mouse, and rat serum albumins. Humanization of E06 was carried out by converting over 60% of non-complementarity-determining region residues to those of a human germ line Vκ1 sequence, DPK9. The resulting huE06 molecules have largely retained the specificity and affinity of antigen binding of the parental V-NAR. Crystal structures of the shark E06 and its humanized variant (huE06 v1.1) in complex with human serum albumin (HSA) were determined at 3- and 2.3-Å resolution, respectively. The huE06 v1.1 molecule retained all but one amino acid residues involved in the binding site for HSA. Structural analysis of these V-NARs has revealed an unusual variable domain-antigen interaction. E06 interacts with HSA in an atypical mode that utilizes extensive framework contacts in addition to complementarity-determining regions that has not been seen previously in V-NARs. On the basis of the structure, the roles of various elements of the molecule are described with respect to antigen binding and V-NAR stability. This information broadens the general understanding of antigen recognition and provides a framework for further design and humanization of shark IgNARs.

Engineering a monomeric Fc domain modality by N-glycosylation for the half-life extension of biotherapeutics

Human IgG is a bivalent molecule that has two identical Fab domains connected by a dimeric Fc domain. For therapeutic purposes, however, the bivalency of IgG and Fc fusion proteins could cause undesired properties. We therefore engineered the conversion of the natural dimeric Fc domain to a highly soluble monomer by introducing two Asn-linked glycans onto the hydrophobic C(H)3-C(H)3 dimer interface. The monomeric Fc (monoFc) maintained the binding affinity for neonatal Fc receptor (FcRn) in a pH-dependent manner. We solved the crystal structure of monoFc, which explains how the carbohydrates can stabilize the protein surface and provides the rationale for molecular recognition between monoFc and FcRn. The monoFc prolonged the in vivo half-life of an antibody Fab domain, and a tandem repeat of the monoFc further prolonged the half-life. This monoFc modality can be used to improve the pharmacokinetics of monomeric therapeutic proteins with an option to modulate the degree of half-life extension.

Discovery of HSD-621 as a Potential Agent for the Treatment of Type 2 Diabetes

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyzes the conversion of inactive glucocorticoid cortisone to its active form, cortisol. The glucocorticoid receptor (GR) signaling pathway has been linked to the pathophysiology of diabetes and metabolic syndrome. Herein, the structure-activity relationship of a series of piperazine sulfonamide-based 11β-HSD1 inhibitors is described. (R)-3,3,3-Trifluoro-2-(5-(((R)-4-(4-fluoro-2-(trifluoromethyl)phenyl)-2-methylpiperazin-1-yl)sulfonyl)thiophen-2-yl)-2-hydroxypropanamide 18a (HSD-621) was identified as a potent and selective 11β-HSD1 inhibitor and was ultimately selected as a clinical development candidate. HSD-621 has an attractive overall pharmaceutical profile and demonstrates good oral bioavailability in mouse, rat, and dog. When orally dosed in C57/BL6 diet-induced obesity (DIO) mice, HSD-621 was efficacious and showed a significant reduction in both fed and fasting glucose and insulin levels. Furthermore, HSD-621 was well tolerated in drug safety assessment studies.

ATP-competitive inhibitors of the mammalian target of rapamycin: design and synthesis of highly potent and selective pyrazolopyrimidines

The mammalian target of rapamycin (mTOR), a central regulator of growth, survival, and metabolism, is a validated target for cancer therapy. Rapamycin and its analogues, allosteric inhibitors of mTOR, only partially inhibit one mTOR protein complex. ATP-competitive, global inhibitors of mTOR that have the potential for enhanced anticancer efficacy are described. Structural features leading to potency and selectivity were identified and refined leading to compounds with in vivo efficacy in tumor xenograft models.

Crystal structures of the two major aggrecan degrading enzymes, ADAMTS4 and ADAMTS5

Aggrecanases are now believed to be the principal proteinases responsible for aggrecan degradation in osteoarthritis. Given their potential as a drug target, we solved crystal structures of the two most active human aggrecanase isoforms, ADAMTS4 and ADAMTS5, each in complex with bound inhibitor and one wherein the enzyme is in apo form. These structures show that the unliganded and inhibitor-bound enzymes exhibit two essentially different catalytic-site configurations: an autoinhibited, nonbinding, closed form and an open, binding form. On this basis, we propose that mature aggrecanases exist as an ensemble of at least two isomers, only one of which is proteolytically active.

Acylguanidines as Small-Molecule β-Secretase Inhibitors

BACE1 is an aspartyl protease responsible for cleaving amyloid precursor protein to liberate Abeta, which aggregates leading to plaque deposits implicated in Alzheimer's disease. We have identified small-molecule acylguanidine inhibitors of BACE1. Crystallographic studies show that these compounds form unique hydrogen-bonding interactions with the catalytic site aspartic acids and stabilize the protein in a flap-open conformation. Structure-based optimization led to the identification of potent analogs, such as 10d (BACE1 IC(50) = 110 nM).

Discovery of proline sulfonamides as potent and selective hepatitis C virus NS5b polymerase inhibitors. Evidence for a new NS5b polymerase binding site

Through high throughput screening, substituted proline sulfonamide 6 was identified as HCV NS5b RNA-dependent RNA polymerase inhibitor. Optimization of various regions of the lead molecule resulted in compounds that displayed good potency and selectivity. The crystal structure of 6 and NS5b polymerase complex confirmed the binding near the active site region. The optimization approach and SAR are discussed in detail.

A novel approach to identifying beta-secretase inhibitors: bis-statine peptide mimetics discovered using structure and spot synthesis

Beta-secretase 1 (BACE1) is an aspartic protease believed to play a critical role in Alzheimer's disease. Inhibitors of this enzyme have been designed by incorporating the non-cleavable hydroxyethylene and statine isosteres into peptides corresponding to BACE1 substrate sequences. We sought to develop new methods to quickly characterize and optimize inhibitors based on the statine core. Minimal sequence requirements for binding were first established using both crystallography and peptide spot synthesis. These shortened peptide inhibitors were then optimized by using spot synthesis to perform iterative cycles of substitution and deletion. The present study resulted in the identification of novel "bis-statine" inhibitors shown by crystallography to have a unique binding mode. Our results demonstrate the application of peptide spot synthesis as an effective method for enhancing peptidomimetic drug discovery.

3,5-dioxopyrazolidines, novel inhibitors of UDP-N- acetylenolpyruvylglucosamine reductase (MurB) with activity against gram-positive bacteria

A series of 3,5-dioxopyrazolidines was identified as novel inhibitors of UDP-N-acetylenolpyruvylglucosamine reductase (MurB). Compounds 1 to 3, which are 1,2-bis(4-chlorophenyl)-3,5-dioxopyrazolidine-4-carboxamides, inhibited Escherichia coli MurB, Staphyloccocus aureus MurB, and E. coli MurA with 50% inhibitory concentrations (IC50s) in the range of 4.1 to 6.8 microM, 4.3 to 10.3 microM, and 6.8 to 29.4 microM, respectively. Compound 4, a C-4-unsubstituted 1,2-bis(3,4-dichlorophenyl)-3,5-dioxopyrazolidine, showed moderate inhibitory activity against E. coli MurB, S. aureus MurB, and E. coli MurC (IC50s, 24.5 to 35 microM). A fluorescence-binding assay indicated tight binding of compound 3 with E. coli MurB, giving a dissociation constant of 260 nM. Structural characterization of E. coli MurB was undertaken, and the crystal structure of a complex with compound 4 was obtained at 2.4 A resolution. The crystal structure indicated the binding of a compound at the active site of MurB and specific interactions with active-site residues and the bound flavin adenine dinucleotide cofactor. Peptidoglycan biosynthesis studies using a strain of Staphylococcus epidermidis revealed reduced peptidoglycan biosynthesis upon incubation with 3,5-dioxopyrazolidines, with IC50s of 0.39 to 11.1 microM. Antibacterial activity was observed for compounds 1 to 3 (MICs, 0.25 to 16 microg/ml) and 4 (MICs, 4 to 8 microg/ml) against gram-positive bacteria including methicillin-resistant S. aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae.

Synthesis and Structure−Activity Relationship of Novel 6-Aryl-1,4- dihydrobenzo[d][1,3]oxazine-2-thiones as Progesterone Receptor Modulators Leading to the Potent and Selective Nonsteroidal Progesterone Receptor Agonist Tanaproget

Tanaproget represents a potential first-in-class nonsteroidal PR agonist for contraception with improved safety and side effect profiles versus currently available steroidal oral contraceptives. Additional SAR, biological activity, and structural information from a tanaproget/hPR-LBD (hPR-LBD = human progesterone receptor ligand binding domain) cocrystal structure will also be presented.

Automated systems for protein crystallization

Growth of high quality crystals is often the most difficult step in the determination of protein structures by X-ray diffraction. Automation can improve the success of this process both by reducing the amount of protein required for each screen and by relieving the tedium of setting up crystallization experiments by hand. We have been using an automated system for the design and execution of hanging drop crystallization experiments for the last two years. The system includes robots for the preparation of solutions, setup of hanging drops, and automated imaging, as well as a new software package (RoCKS) for managing all phases of the crystallization process. Here, we review the fundamentals of automated protein crystallization and present results from our comparisons of various approaches to screening.

Catalytically active MAP KAP kinase 2 structures in complex with staurosporine and ADP reveal differences with the autoinhibited enzyme

MAP KAP kinase 2 (MK2), a Ser/Thr kinase, plays a crucial role in the inflammatory process. We have determined the crystal structures of a catalytically active C-terminal deletion form of human MK2, residues 41-364, in complex with staurosporine at 2.7 A and with ADP at 3.2 A, revealing overall structural similarity with other Ser/Thr kinases. Kinetic analysis reveals that the K(m) for ATP is very similar for MK2 41-364 and p38-activated MK2 41-400. Conversely, the catalytic rate and binding for peptide substrate are dramatically reduced in MK2 41-364. However, phosphorylation of MK2 41-364 by p38 restores the V(max) and K(m) for peptide substrate to values comparable to those seen in p38-activated MK2 41-400, suggesting a mechanism for regulation of enzyme activity.

Additional evidence that the K-ras protooncogene is a candidate for the major mouse pulmonary adenoma susceptibility (Pas-1) gene

A locus for mouse pulmonary adenoma susceptibility, Pas-1, has been mapped on distal chromosome 6, where the K-ras gene is located. Allele-specific activation and expression of the K-ras allele from the susceptible parent has been observed in lung tumors from F1 hybrid mice. We report here genetic mapping of lung tumor susceptibility genes in urethane-treated A x B and B x A recombinant inbred (RI) mice using microsatellite markers to seek further evidence for the K-ras gene as candidate for Pas-1. The K-ras genotype differs between the A/J and C57BL/6J progenitors of the RI strains, and distal chromosome 6 contained a major lung tumor susceptibility determinant in the RI mice. Additional evidence that Pas-1 is K-ras involved linkage analysis of (A/JOLaHsd x BALB/ cOLaHsd) F2 intercross mice whose parents shared the same K-ras genotype. In contrast to the results with the A x B and B x A RI strains, no distal chromosome 6 site was significantly associated with tumor development in these F2 mice. In addition to this major locus, linkage analysis of the RI mice revealed additional quantitative trait loci for susceptibility on chromosomes 10, 17, and 19. These loci may serve as modifiers of Pas-1. The relationship between the K-ras genotype and the frequency of K-ras mutations in urethane-induced lung tumors from the RI mice was also explored. All 18 tumor DNAs from RI mice with high susceptibility contained an AT-->TA transversion at the second base of K-ras codon 61. This was also true for DNAs from 27 of 27 (100%) tumors in mice with high intermediate susceptibility. In RI strains with a low intermediate susceptibility, the DNA from 39 of 47 (83%) tumors contained an AT-->TA transversion at codon 61, and only 13 of 21 (62%) tumors had this mutation in the most resistant group. This reflects a positive correlation between the frequency of K-ras mutations in lung tumors of A x B or B x A RI strains and their susceptibility to lung carcinogenesis. Since K-ras appears to be Pas-1, these results suggest that some RI mice that have the resistant K-ras or Pas-1 allele undergo tumor development by a K-ras-independent route.

Chromosomal localization of lipolytic enzymes in the mouse: pancreatic lipase, colipase, hormone-sensitive lipase, hepatic lipase, and carboxyl ester lipase

Several lipases and their cofactors are involved in the absorption, transport, storage, and mobilization of lipids. As part of an effort to examine the role of these enzymes in plasma lipid metabolism and genetic susceptibility to atherosclerosis, we report the chromosomal mapping of their genes in mouse. Restriction fragment length variants for each gene were identified, typed in an interspecific cross, and tested for linkage to known chromosomal markers. The gene for pancreatic lipase resides on chromosome 19, while the gene for its cofactor, colipase, is on chromosome 17. A gene for a protein with sequence similarity to pancreatic lipase was tightly linked (no observed recombination) to the gene for pancreatic lipase, suggesting a gene cluster. The gene for hormone-sensitive lipase is near the gene cluster containing apolipoproteins C-II and E on chromosome 7. The gene for hepatic lipase is near the gene for apolipoprotein A-I on chromosome 9. The carboxyl ester lipase gene resides on chromosome 2. Previously, we have mapped the gene for lipoprotein lipase to chromosome 8. Thus, with the exception of pancreatic lipase and a related protein, these lipase genes, including several that are members of a gene family, are widely dispersed in the genome. Comparison of chromosomal locations for these genes in mouse and humans shows that the previously observed interspecies syntenies are preserved.

Organization of the human lipoprotein lipase gene and evolution of the lipase gene family

The human lipoprotein lipase gene was cloned and characterized. It is composed of 10 exons spanning approximately equal to 30 kilobases. The first exon encodes the 5'-untranslated region, the signal peptide plus the first two amino acids of the mature protein. The next eight exons encode the remaining 446 amino acids, and the tenth exon encodes the long 3'-untranslated region of 1948 nucleotides. The lipoprotein lipase transcription start site and the sequence of the 5'-flanking region were also determined. We compared the organization of genes for lipoprotein lipase, hepatic lipase, pancreatic lipase, and Drosophila yolk protein 1, which are members of a family of related genes. A model for the evolution of the lipase gene family is presented that involves multiple rounds of gene duplication plus exon-shuffling and intron-loss events.

Molecular cloning and sequence of a cholesterol-repressible enzyme related to prenyltransferase in the isoprene biosynthetic pathway

Differential hybridization and molecular cloning have been used to isolate CR39, a cDNA which hybridizes to a 1.2-kilobase (kb) mRNA in rat liver. The level of CR39 mRNA was increased seven- to ninefold over normal levels by dietary cholestyramine and mevinolin and decreased about fourfold compared with normal levels by cholesterol feeding or administration of mevalonate. Similar changes in the mRNA levels of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and HMG-CoA synthase were observed under the various conditions. In vitro translation of either CR39 hybrid selected RNA or 1.2-kb CR39 RNA generated by an SP6 in vitro transcription system produced a polypeptide of 39,000 daltons. As deduced from the nucleotide sequence of a full-length CR39 cDNA, the rat CR39 polypeptide contained 344 amino acids and had a molecular weight of 39,615. The predicted amino acid composition and submit molecular weight of the rat CR39 were very similar to those of prenyltransferases isolated from chicken, pig, and human. The sequence of amino acid residues 173 through 203 in the rat CR39 polypeptide showed that 17 out of 30 matched an active-site peptide of avian liver prenyltransferase. Thus, alterations in the rate of cholesterogenesis resulted in the coordinate regulation of three mRNAs encoding HMG-CoA reductase, HMG-CoA synthase, and CR39, the latter being tentatively identified as prenyltransferase.

Renal interstitial fibrosis and vascular changes. Occurrence in patients with autoimmune diseases treated with cyclosporine

Histologic examinations of kidney biopsy specimens from six patients with relapsing polychondritis (n = 1), Behçet's syndrome (n = 3), and chronic uveitis (n = 2) were performed after four to 36 months of treatment with cyclosporine. Five of the patients had a variable degree of focal interstitial fibrosis and tubular atrophy, with and without minimal interstitial inflammation. Arteriolar hyalinization was noted in four and glomerular sclerosis in two patients. These renal lesions could not be attributed to underlying autoimmune disease or previous drug therapy but were similar to those recently reported in kidney and heart recipients receiving long-term cyclosporine. The initial cyclosporine doses were 15 mg/kg body weight in one patient and 10 mg/kg in the others. The maintenance cyclosporine doses ranged from 2.5 to 7.5 mg/kg with appropriate trough cyclosporine plasma levels (60 to 130 ng/mL). A rough correspondence between the extent of the histologic renal changes and the cumulative cyclosporine was seen, whereas serum creatinine increase or the development of hypertension during treatment did not predict the degree of interstitial fibrosis or the presence of arteriolar changes. Neither did a rapid fall in the serum creatinine level after withdrawal of cyclosporine exclude focal irreversible renal lesions. Since the histopathologic changes found in the kidneys are potentially progressive, we believe that, until more is known, long-term cyclosporine treatment should be reserved for situations where more established immunosuppression has failed to control an autoimmune process threatening the function of vital organs.

Eosinophil involvement in rheumatoid arthritis as reflected by elevated serum levels of eosinophil cationic protein

Circulating levels of eosinophil cationic protein (ECP), an eosinophil specific granule protein, and numbers of peripheral eosinophils were determined in 42 patients with rheumatoid arthritis. At the time of the investigation the patients were without drug treatment. They had normal blood counts of eosinophils but on average a five-fold increase of the serum ECP values compared with healthy subjects. The intracellular content of ECP in eosinophils isolated from 14 patients was normal. High serum levels of ECP were particularly observed in patients with a disease of rather short duration but with a more aggressive course. Other factors associated with high ECP values were blood eosinophil counts in the upper normal range, high rheumatoid factor titre and increased inflammatory activity as defined by elevated serum haptoglobin and blood platelet counts. No relation was found between serum ECP and circulating immune complexes or serum total IgE. Synovial fluids obtained from 14 patients with rheumatoid arthritis contained very high concentration of ECP; on average nine times higher than those in the circulation of the patients. During corticosteroid but not NSAID therapy serum ECP decreased on average about 50% compared with pre-treatment values. Although eosinophils are not a notable feature of the synovial membrane infiltrate or cellular joint exudate, data obtained indirectly indicates their participation in the inflammatory reaction in RA.

Abnormal calcium and magnesium stores in erythrocytes and granulocytes from patients with inflammatory connective tissue diseases. Relationship to inflammatory activity and effect of corticosteroid therapy

The mass fraction of Ca and Mg in isolated erythrocytes and granulocytes was measured using the nuclear microprobe technique. Conspicuous abnormalities were observed in cells from patients with rheumatoid arthritis and other inflammatory arthritides. Compared with the normal cellular content, total Ca was increased an average of 3 times in erythrocytes and 5 times in granulocytes. Total granulocyte Mg was increased about 3 times, whereas erythrocyte Mg was reduced to as much as 60% of normal. These abnormalities were less prominent or were absent in scleroderma patients, except for levels of granulocyte Ca, which were increased more than 3 times beyond normal in this patient group. A significant positive correlation was found between serum haptoglobin and erythrocyte or granulocyte Ca content among these patients, but not between haptoglobin and erythrocyte or granulocyte Mg values. During corticosteroid treatment, a significant increase in erythrocyte Mg and a significant reduction in erythrocyte Ca were noted, but normalization of these levels was not achieved. Granulocyte Ca was also significantly reduced, while granulocyte Mg remained unaltered. Serum levels of Ca and Mg were within normal ranges and were not influenced by corticosteroid therapy. The results indicate that at least Ca abnormalities in erythrocytes and granulocytes are associated with the intensity of the inflammatory process and that the amounts of Ca and Mg in these cells are influenced by potent antiinflammatory therapy.