A high affinity recombinant antibody to the human EphA3 receptor with enhanced ADCC activity.

EphA3 is expressed in solid tumors and leukemias and is an attractive target for the therapy. We have generated a panel of Humaneered® antibodies to the ligand-binding domain using a Fab epitope-focused library that has the same specificity as monoclonal antibody mIIIA4. A high-affinity antibody was selected that competes with the mIIIA4 antibody for binding to EphA3 and has an improved affinity of ∼1 nM. In order to generate an antibody with potent cell-killing activity the variable regions were assembled with human IgG1k constant regions and expressed in a Chinese hamster ovary (CHO) cell line deficient in fucosyl transferase. Non-fucosylated antibodies have been reported to have enhanced binding affinity for the IgG receptor CD16a (FcγRIIIa). The affinity of the antibody for recombinant CD16a was enhanced approximately 10-fold. This resulted in enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) activity against EphA3-expressing leukemic cells, providing a potent antibody for the evaluation as a therapeutic agent.

Targeting EphA3 inhibits cancer growth by disrupting the tumor stromal microenvironment.

Eph receptor tyrosine kinases are critical for cell-cell communication during normal and oncogenic tissue patterning and tumor growth. Somatic mutation profiles of several cancer genomes suggest EphA3 as a tumor suppressor, but its oncogenic expression pattern and role in tumorigenesis remain largely undefined. Here, we report unexpected EphA3 overexpression within the microenvironment of a range of human cancers and mouse tumor xenografts where its activation inhibits tumor growth. EphA3 is found on mouse bone marrow-derived cells with mesenchymal and myeloid phenotypes, and activation of EphA3(+)/CD90(+)/Sca1(+) mesenchymal/stromal cells with an EphA3 agonist leads to cell contraction, cell-cell segregation, and apoptosis. Treatment of mice with an agonistic α-EphA3 antibody inhibits tumor growth by severely disrupting the integrity and function of newly formed tumor stroma and microvasculature. Our data define EphA3 as a novel target for selective ablation of the tumor microenvironment and demonstrate the potential of EphA3 agonists for anticancer therapy.

The eosinophil surface receptor epidermal growth factor-like module containing mucin-like hormone receptor 1 (EMR1): a novel therapeutic target for eosinophilic disorders.

BACKGROUND: Although several novel agents are currently in clinical trials for eosinophilic disorders, none has demonstrated efficacy in reducing blood and tissue eosinophilia in all subjects. Additional approaches are clearly needed. OBJECTIVE: We sought to explore the potential of the human eosinophil surface receptor epidermal growth factor-like module containing mucin-like hormone receptor 1 (EMR1) as a therapeutic target for eosinophilic disorders. METHODS: EMR1 expression was assessed in blood and bone marrow specimens from eosinophilic and healthy subjects, cell lines, CD34(+) cells differentiated in vitro, and tissue biopsy specimens by using flow cytometry, quantitative PCR, and immunostaining. Eosinophil targeting by a novel, humanized, afucosylated anti-EMR1 IgG1 was evaluated in vitro by using a natural killer cell-mediated killing assay and in vivo in cynomolgus monkeys. RESULTS: Analysis of blood and bone marrow cells from healthy and eosinophilic donors and in vitro-differentiated CD34(+) cells confirmed restriction of human EMR1 surface and mRNA expression to mature eosinophils. Tissue eosinophils also expressed EMR1. Although EMR1 was highly expressed on eosinophils from all subjects, surface expression was negatively correlated with absolute eosinophil counts (r = -0.46, P < .001), and soluble plasma levels correlated positively with absolute eosinophil counts (r = 0.69, P < .001), suggesting modulation of EMR1 in vivo. Nevertheless, afucosylated anti-EMR1 mAb dramatically enhanced natural killer cell-mediated killing of eosinophils from healthy and eosinophilic donors and induced a rapid and sustained depletion of eosinophils in monkeys. CONCLUSION: EMR1 expression is restricted to mature blood and tissue eosinophils. Targeting of eosinophils with afucosylated anti-EMR1 antibody shows promise as a treatment for eosinophilic disorders.

GM-CSF-dependent pSTAT5 sensitivity is a feature with therapeutic potential in chronic myelomonocytic leukemia.

Granulocyte-macrophage-colony-stimulating factor (GM-CSF) hypersensitivity is a hallmark of juvenile myelomonocytic leukemia (JMML) but has not been systematically shown in the related human disease chronic myelomonocytic leukemia (CMML). We find that primary CMML samples demonstrate GM-CSF-dependent hypersensitivity by hematopoietic colony formation assays and phospho-STAT5 (pSTAT5) flow cytometry compared with healthy donors. Among CMML patients, the pSTAT5 hypersensitive response positively correlated with high-risk disease, peripheral leukocytes, monocytes, and signaling-associated mutations. When compared with IL-3 and G-CSF, GM-CSF hypersensitivity was cytokine specific and thus a possible target for intervention in CMML. To explore this possibility, we treated primary CMML cells with KB003, a novel monoclonal anti-GM-CSF antibody, and JAK2 inhibitors. We found that an elevated proportion of immature GM-CSF receptor-α(R) subunit-expressing cells were present in the bone marrow myeloid compartment of CMML. In survival assays, we found that myeloid and monocytic progenitors were sensitive to GM-CSF signal inhibition. Our data indicate that a committed myeloid precursor expressing CD38 may represent the progenitor population with enhanced GM-CSF dependence in CMML, consistent with results in JMML. These preclinical data indicate that GM-CSF signaling inhibitors merit further investigation in CMML and that GM-CSFR expression on myeloid progenitors may be a biomarker for this therapy.

Antibody to granulocyte macrophage colony-stimulating factor reduces the number of activated tissue macrophages and improves left ventricular function after myocardial infarction in a rat coronary artery ligation model.

Granulocyte macrophage colony-stimulating factor (GM-CSF) promotes infarct expansion and inappropriate collagen synthesis in a myocardial infarction (MI). This study was designed to determine if treatment with anti-GM-CSF will inhibit macrophage migration, preserve function, and limit left ventricular (LV) remodeling in the rat coronary artery ligation model. Treatment with a monoclonal antibody to GM-CSF (5 mg/kg) was initiated 24 hours before coronary artery ligation and continued every 3 days for 3 weeks. Left coronary arteries of rats were ligated, animals were recovered, and cardiac function was evaluated 3 weeks postligation. Tissue samples were processed for histochemistry. Anti-GM-CSF treatment increased LV ejection fraction (37 ± 3% vs 47 ± 5%) and decreased LV end systolic diameter (0.75 ± 0.12 vs 0.59 ± 0.05 cm) with no changes in LV systolic pressure (109 ± 4 vs 104 ± 5 mm Hg), LV end diastolic pressure (22 ± 4 vs 21 ± 2 mm Hg), LV end diastolic diameter (0.96 ± 0.04 vs 0.92 ± 0.05 cm), or the time constant of LV relaxation tau (25.4 ± +2.4 vs 22.7 ± 1.4 milliseconds) (P < 0.05). Significantly lower numbers of tissue macrophages and significant reductions in infarct size were found in the myocardium of antibody-treated animals (81 ± 21.24 vs 195 ± 31.7 positive cells per 0.105 mm, compared with controls. These findings suggest that inhibition of macrophage migration may be beneficial in the treatment of heart failure after MI.

An engineered human antibody fab fragment specific for Pseudomonas aeruginosa PcrV antigen has potent antibacterial activity.

Pseudomonas aeruginosa is an opportunistic pathogen that can cause acute lung injury and mortality through the delivery of exotoxins by the type III secretion system (TTSS). PcrV is an important structural protein of the TTSS. An engineered human antibody Fab fragment that binds to the P. aeruginosa PcrV protein with high affinity has been identified and has potent in vitro neutralization activity against the TTSS. The instillation of a single dose of Fab into the lungs of mice provided protection against lethal pulmonary challenge of P. aeruginosa and led to a substantial reduction of viable bacterial counts in the lungs. These results demonstrate that blocking of the TTSS by a Fab lacking antibody Fc-mediated effector functions can be sufficient for the effective clearance of pulmonary P. aeruginosa infection.

BCL-3 and NF-kappaB p50 attenuate lipopolysaccharide-induced inflammatory responses in macrophages.

Lipopolysaccharide (LPS) induces expression of tumor necrosis factor alpha (TNFalpha) and other pro-inflammatory cytokines in macrophages. Following its induction, TNFalpha gene transcription is rapidly attenuated, in part due to the accumulation of NF-kappaB p50 homodimers that bind to three kappaB sites in the TNFalpha promoter. Here we have investigated the inhibitory role of BCL-3, an IkappaB-like protein that interacts exclusively with p50 and p52 homodimers. BCL-3 was induced by LPS with delayed kinetics and was associated with p50 in the nucleus. Forced expression of BCL-3 suppressed LPS-induced transcription from the TNFalpha promoter and inhibited two artificial promoters composed of TNFalphakappaB sites that preferentially bind p50 dimers. BCL-3-mediated repression was reversed by trichostatin A and was enhanced by overexpression of HDAC-1, indicating that transcriptional attenuation involves recruitment of histone deacetylase. Analysis of macrophages from p50 and BCL-3 knock-out mice revealed that both transcription factors negatively regulate TNFalpha expression and that BCL-3 inhibits IL-1alpha and IL-1beta. In contrast, induction of the anti-inflammatory cytokine IL-10 was reduced in BCL-3 null macrophages. BCL-3 was not required for the production of p50 homodimers but BCL-3 expression was severely diminished in p50-deficient cells. Together, these findings indicate that p50 and BCL-3 function as anti-inflammatory regulators in macrophages by attenuating transcription of pro-inflammatory cytokines and activating IL-10 expression.

Regulation of CCAAT/enhancer-binding protein (C/EBP) activator proteins by heterodimerization with C/EBPgamma (Ig/EBP).

The CCAAT/enhancer-binding proteins (C/EBPs) are basic leucine zipper transcription factors that play important roles in regulating cell growth and differentiation. C/EBP proteins form leucine zipper-mediated homodimers but are also capable of heterodimerizing with other C/EBPs in vitro. Here we show that C/EBPbeta occurs predominantly as a heterodimer that displays rapid mobility in gel shift assays. Biochemical fractionation and antibody supershift assays demonstrate that the C/EBPbeta heterodimeric partner is C/EBPgamma (Ig/EBP), a C/EBP protein that has been implicated as an inhibitor of other family members. Although most cell types express C/EBPbeta.C/EBPgamma heterodimers, macrophages contain a C/EBPbeta partner that is serologically distinct from C/EBPgamma. We found that C/EBPgamma blocked the ability of C/EBPbeta and C/EBPgamma to activate a reporter gene in L cell fibroblasts but did not inhibit a chimeric C/EBPbeta protein containing the GCN4 leucine zipper. Repression by C/EBPgamma occurs at the level of transactivation and requires heterodimerization with the C/EBP partner. C/EBPgamma was an ineffective repressor in HepG2 hepatoma cells despite forming C/EBP heterodimers, and C/EBPalpha was not effectively inhibited in either L or HepG2 cells. Our findings demonstrate that C/EBPgamma modulates C/EBP activity in a cell- and isoform-specific manner.