Preclinical efficacy and safety of mepolizumab (SB-240563), a humanized monoclonal antibody to IL-5, in cynomolgus monkeys

BACKGROUND

Allergic respiratory diseases are characterized by large numbers of eosinophils and their reactive products in airways and blood; these are believed to be involved in progressive airway damage and remodeling. IL-5 is the principal cytokine for eosinophil maturation, differentiation, and survival. Mepolizumab (SB-240563), a humanized monoclonal antibody (mAb) specific for human IL-5, is currently in clinical trials for treatment of asthma.

OBJECTIVE

The purpose of this study was to characterize the pharmacologic activity and long-term safety profile of an anti--human IL-5 mAb to support clinical trials in asthmatic patients.

METHODS

Naive and Ascaris suum -sensitive cynomolgus monkeys received various dose levels of mepolizumab and were monitored for acute and chronic pharmacologic and toxic responses.

RESULTS

To support preclinical safety assessment, cynomolgus monkey IL-5 was cloned, expressed, and characterized. Although monkey IL-5 differs from human IL-5 by 2 amino acids (Ala27Gly and Asn40His), mepolizumab has comparable inhibitory activity against both monkey IL-5 and human IL-5. In A suum--sensitive monkeys, single doses of mepolizumab significantly reduced blood eosinophilia, eosinophil migration into lung airways, and levels of RANTES and IL-6 in lungs for 6 weeks. However, mepolizumab did not affect acute bronchoconstrictive responses to inhaled A suum. In an IL-2--induced eosinophilia model (up to 50% blood eosinophilia), 0.5 mg/kg mepolizumab blocked eosinophilia by >80%. Single-dose and chronic (6 monthly doses) intravenous and subcutaneous toxicity studies in naive monkeys found no target organ toxicity or immunotoxicity up to 300 mg/kg. Monkeys did not generate anti-human IgG antibodies. Monthly mepolizumab doses greater than 5 mg/kg caused an 80% to 100% decrease in blood and bronchoalveolar lavage eosinophils lasting 2 months after dosing, and there was no effect on eosinophil precursors in bone marrow after 6 months of treatment. Eosinophil decreases correlated with mepolizumab plasma concentrations (half-life = 13 days).

CONCLUSION

These studies demonstrate that chronic antagonism of IL-5 by mepolizumab in monkeys is safe and has the potential, through long-term reductions in circulating and tissue-resident eosinophils, to be beneficial therapy for chronic inflammatory respiratory diseases.

Nonlinear Dynamics in the Progression of Atherosclerotic Fatty Streaks: Morphometric Analysis

Atherosclerotic lesions are heterogeneous in terms of their cellular and lipid composition. While heterogeneity can be the result of stochastic noise, an alternate hypothesis is that the differences observed among individual lesions arise from deterministic chaos. Five New Zealand white rabbits were fed a diet containing 0.15% cholesterol for 6 months. Segments of the aorta were fixed in formalin, stained en bloc with Nile red (NR) and filipin (F), and en face fluorescence microscopy was used to map the distribution of lipids in fatty streaks (FS). The smallest lesions detected stained only with filipin. Larger lesions stained with both Nile red and filipin and two distinct regions of Nile red staining, NR-orange (rich in polar lipids) and NR-yellow (rich in neutral lipids) were observed. Digital overlays revealed a "nested" arrangement of F, NR-orange, and NR-yellow. The lesions also showed marked heterogeneity in their lipid composition. Thus, although initially similar, as FS increased in size, their composition became divergent, suggesting that the ultimate composition of a FS was highly sensitive to its initial composition. Sensitivity to initial condition is one of the hallmarks of deterministic systems. To determine if FS were self-similar, another hallmark of deterministic chaos, the borders of the different regions defined by NR and F staining were subjected to fractal analysis. For each lesion, the borders of the F, NR-orange, and NR-yellow regions were found to be fractal. Return maps were constructed for the differently stained regions. Analysis of the entire 104-lesion data set showed that although the data could be described by a four-parameter logistic model, the population was not chaotic. However, return maps drawn for the maxima of the NR-orange stained regions demonstrated chaos. Taken together, the data suggest that deterministic chaos plays a role in the evolution of atheromatous disease but, in common with most biologic systems, as the lesions progress, chaotic behavior is dampened.

Preclinical development of keliximab, a Primatized anti-CD4 monoclonal antibody, in human CD4 transgenic mice: characterization of the model and safety studies

The preclinical safety assessment of biopharmaceuticals necessitates that studies be conducted in species in which the products are pharmacologically active. Monoclonal antibodies are a promising class of biopharmaceuticals for many disease indications; however, by design, these agents tend to have limited species cross-reactivity and tend to only be active in primates. Keliximab is a human-cynomolgus monkey chimeric (Primatized) monoclonal antibody with specificity for human and chimpanzee CD4. In order to conduct a comprehensive preclinical safety assessment of this antibody to support chronic treatment of rheumatoid arthritis in patients, a human CD4 transgenic mouse was used for chronic and reproductive toxicity studies and for genotoxic studies. In addition, immunotoxicity studies were conducted in these mice with Candida albicans, Pneumocystis carinii and B16 melanoma cells to assess the effects of keliximab on host resistance to infection and immunosurveillance to neoplasia. The results of these studies found keliximab to be well tolerated with the only effects observed being related to its pharmacologic activity on CD4+ T lymphocytes. The use of transgenic mice expressing human proteins provides a useful alternative to studies in chimpanzees with biopharmaceutical agents having limited species cross-reactivity.

Spontaneous and induced alterations in the cardiac membranous ventricular septum of fetal, weanling, and adult rats

Alterations of the cardiac membranous ventricular septum were studied using macrodissection, scanning electron and light microscopy of fetal, weanling, and adult Sprague-Dawley rats. Membranous ventricular septal defects (VSDs) were observed in 2.0% of fetuses on day 21 postcoitus (pc) but not in weanling or adult rats. The most common observation was a nonpatent depression in the membranous septum with an incidence of 38.1, 10.5, 4.3% for fetuses on days 17, 19, or 21 pc, respectively, 11.8% for weanlings, and 9.1% for adults. VSDs were characterized by a split in the endocardial cushion cells in the interventricular component of the membranous septum. Nonpatent depressions were characterized by a split in the endocardial cushion cells in the atrioventricular component of the septum, and they persisted postnatally as a blind-ended diverticulum directed above the tricuspid valve. The cardiovascular teratogens, trimethadione and trypan blue, produced in fetuses nonpatent depressions and VSDs morphologically similar to untreated fetuses. Maternal diet restriction (25% of controls) lowered fetal (day 21 pc) body weight by 47% but did not affect the incidence of ventricular septal alterations, suggesting that intrauterine growth retardation is not necessarily associated with alterations in the development of the ventricular septum. We conclude that neither VSDs nor nonpatent depressions in Sprague-Dawley rats affect postnatal survival and that VSDs close spontaneously during neonatal life.

Purification and characterization of fully functional human osteoclast precursors

The identification and purification of human osteoclast precursors is essential to further our understanding of the mechanisms that control human osteoclast differentiation. Osteoclastoma tissue potentially provides a rich source of human osteoclast precursors, and in previous studies we have demonstrated the existence of a population of mononuclear cells within this tissue that is reactive with osteoclast-selective vitronectin receptor monoclonal antibodies. In this study, mononuclear cells expressing the vitronectin receptor, as defined by their ability to react with a murine monoclonal antibody to the beta 3 chain of the vitronectin receptor (87MEM1), were isolated from collagenase digests of osteoclastoma tissue using a fluorescence activated cell sorter. Based on their fluorescence signal and size, approximately 2-3% of the viable cells (typically 2 x 10(5)) were obtained and prepared for further phenotyping. The isolated cells demonstrated a number of phenotypic characteristics of osteoclasts: positive tartrate-resistant acid phosphatase (TRAP) activity, reactivity with human osteoclast-selective antibodies, expression of calcitonin receptors, cathepsin K (a novel osteoclast-selective cysteine proteinase) mRNA, and osteopontin mRNA and protein. These phenotypic characteristics were also detected in mononuclear cells within cryostat sections of the native osteoclastoma tissue as well as in resorption lacunae of sections of human bone. In contrast, isolated peripheral blood monocytes were negative for TRAP activity and osteopontin expression and, unlike the osteoclastoma-derived cells, demonstrated strong nonspecific esterase activity. Significantly, when the osteoclastoma-derived 87MEM1 positive cells were cocultured on whale dentine for 1-3 weeks with stromal cells, extensive resorption of the dentine surface was observed. This is the first demonstration of the purification of human osteoclast precursors. These cells provide an homogeneous cell population for studying cellular events that occur during human osteoclast differentiation.

Ultrastructural evidence of an interaction between Env and Gag proteins during assembly of HIV type 1

Assembly and budding of retroviruses is believed to involve a complex interaction of envelope and capsid proteins at the host cell membrane. The nature of these interactions is, however, incompletely understood. Studies of the topography of the surface of HIV-1 have shown that the envelope glycoprotein projections (knobs) are arranged in a T = 7 levo rotational symmetry. Similarly, an icosahedral structure has been suggested for the p17 matrix of HIV-1. In an effort to investigate whether there is a structural interaction between these molecules, virions whose maturation was blocked by an inhibitor of HIV protease were studied using cytochemistry, morphometry, and 2D fast Fourier transform image enhancement. Analysis of the relationship between core morphology and the topographic distribution of envelope glycoprotein projections on HIV-1 provided structural evidence of an interaction between Env and Gag proteins. Furthermore, image enhancement revealed a periodic substructure in the Pr55gag plaque. Taken together, the data suggest an interaction between Pr55gag and the gp120-gp41 complex during assembly and budding of HIV-1. This interaction may, in part, contribute to determining the amount of Env glycoprotein that will be incorporated into a virion, and therefore play a role in the biology of HIV-1.

Subcellular and ultrastructural localization of alkaline phosphatase in lactating rat mammary glands

The subcellular fractions of lactating rat mammary glands were isolated by differential centrifugation. The mean specific activity of alkaline phosphatase in various fractions was in order greatest to least: microsomes, Golgi, mitochondria, nuclei, and cytosol. Alkaline phosphatase was examined cytochemically by transmission electron microscopy. Alkaline phosphatase activity was localized on myoepithelial membranes, basal and possibly lateral membranes of secretory epithelial cells, and endothelial cells. This finding agreed with biochemical data associating this enzyme activity with microsomes. However, intracellular activities could not be detected on Golgi, secretory vesicles, or apical plasma membranes. Saponin uncovered the activity in that portion of the endoplasmic reticulum of secretory cells adjacent to myoepithelial cells. The identify of this enzyme was further confirmed by selective inhibition studies using dithiothreitol and levamisole. Alkaline phosphatase activities were detected biochemically in lipid droplet "membranes" of secretory epithelium and fat globule membranes. Activity decreased with increasing globule size, indicating that milk alkaline phosphatase originates from lipid droplets of secretory epithelium. The predominance of alkaline phosphatase activity in myoepithelial cell plasma membranes suggests that this enzyme could be involved in cell surface reactions related to oxytocin-mediated milk ejection. In secretory epithelium, it was associated with basal and possibly lateral membranes and lipid droplets that lead to the secretion of milk fat.

Sedimentation field flow fractionation of mitochondrial and microsomal membranes from corn roots

Sedimentation field flow fractionation (sed-FFF) is shown to be a valuable procedure for analysis of a wide variety of subcellular particle preparations. The principles underlying this relatively new separation procedure are described. Separation is based on differences between particles in mass and/or density. As in chromatography, the procedure involves relating on-line or off-line measurements made on the effluent from the separation chamber to the elution (retention) time. In this work effluents were monitored for absorbance at 254, 280, and/or 320 nm; collected fractions were assayed for protein content, total ATPase activity, and/or marker enzyme activities and, when appropriate, were examined by electron microscopy. The ratio of the absorbances at 254 and 320 nm was found to provide a sensitive measure of partial resolution of subcellular particles. Preparations containing all of the subcellular particles of corn roots (exclusive of nuclei, cell walls, and ribosomes), and fractions thereof enriched in mitochondria, microsomes, Golgi membranes, or plasma membranes, were examined by sed-FFF. The subcellular particles appear to remain largely intact. All of the particles observed had a mass less than 2 X 10(11) g/mol. All of the preparations were grossly heterogeneous with respect to effective mass distribution. This is due in part to heterogeneity with respect to the organelle of origin. In microsome preparations, components of low, medium, and high density were present in the unretained peak; the retained region had comparatively more high density particles. Plasma membrane preparations had a very wide effective particle mass distribution. The observations suggest that, in addition to its utility for analytic purposes, sed-FFF is likely to prove useful for micro-preparative fractionation of some subcellular particle preparations. Sed-FFF and density gradient centrifugation can be utilized as complementary methods.