Protective Effect of Anti-Phosphatidylserine Antibody in a Guinea Pig Model of Advanced Hemorrhagic Arenavirus Infection.

Objective: Host derived markers on virally infected cells or virions may provide targets for the generation of antiviral agents. Recently, we identified phosphatidylserine (PS) as a host marker of virions and virally-infected cells.

Methods And Materials: Under normal physiological conditions, PS is maintained on the inner leaflet of the plasma membrane facing the cytosol.

Granulocyte-Colony Stimulating Factor Receptor, Tissue Factor, and VEGF-R Bound VEGF in Human Breast Cancer In Loco.

Background: Doxorubicin and docetaxel-based chemotherapy regimens used in breast cancer patients are associated with high risk of febrile neutropenia (FN). Granulocyte colony-stimulating factors (G-CSF) are recommended for both treating and preventing chemotherapy-induced neutropenia. Increased thrombosis incidence in G-CSF treated patients was reported; however, the underlying mechanisms remain unclear.

Identification of a Monoclonal Antibody That Attenuates Antiphospholipid Syndrome-Related Pregnancy Complications and Thrombosis.

In the antiphospholipid syndrome (APS), patients produce antiphospholipid antibodies (aPL) that promote thrombosis and adverse pregnancy outcomes. Current therapy with anticoagulation is only partially effective and associated with multiple complications. We previously discovered that aPL recognition of cell surface β2-glycoprotein I (β2-GPI) initiates apolipoprotein E receptor 2 (apoER2)-dependent signaling in endothelial cells and in placental trophoblasts that ultimately promotes thrombosis and fetal loss, respectively.

Antibody-Mediated Blockade of Phosphatidylserine Enhances the Antitumor Effect of Sorafenib in Hepatocellular Carcinomas Xenografts.

Background: Currently, the only FDA-approved systemic therapy for hepatocellular carcinoma (HCC) is the multi-receptor tyrosine kinase inhibitor, sorafenib, which provides only modest clinical benefit. We recently showed that treatment with a phosphatidylserine (PS) targeting agent suppresses tumor growth by targeting tumor vasculature and reactivating antitumor immunity.

Methods: We tested the hypothesis that sorafenib increases PS exposure on tumor vasculature, thereby enhancing the antitumor efficacy of PS targeting.

Tumor-specific targeting by Bavituximab, a phosphatidylserine-targeting monoclonal antibody with vascular targeting and immune modulating properties, in lung cancer xenografts.

Bavituximab is a chimeric monoclonal antibody with immune modulating and tumor-associated vascular disrupting properties demonstrated in models of non-small cell lung cancer (NSCLC). The molecular target of Bavituximab, phosphatidylserine (PS), is exposed on the outer leaflet of the membrane bi-layer of malignant vascular endothelial cells and tumor cells to a greater extent than on normal tissues. We evaluated the tumor-targeting properties of Bavituximab for imaging of NSCLC xenografts when radiolabeled with (111)In through conjugation with a bifunctional chelating agent, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA).

Phosphatidylserine-targeting antibody induces M1 macrophage polarization and promotes myeloid-derived suppressor cell differentiation.

Multiple tumor-derived factors are responsible for the accumulation and expansion of immune-suppressing myeloid-derived suppressor cells (MDSC) and M2-like tumor-associated macrophages (TAM) in tumors. Here, we show that treatment of tumor-bearing mice with docetaxel in combination with the phosphatidylserine-targeting antibody 2aG4 potently suppressed the growth and progression of prostate tumors, depleted M2-like TAMs, and MDSCs, and increased the presence of M1-like TAMs and mature dendritic cells in the tumors. In addition, the antibody markedly altered the cytokine balance in the tumor microenvironment from immunosuppressive to immunostimulatory.

A novel "salting-out" procedure for the isolation of tumor-derived exosomes.

The last decade has seen an exponential growth in the number of exosome-related publications. Although many of these studies have used exosomes from biological fluids (blood, and ascites or pleural effusions) the vast majority employed vesicles isolated from large volumes of tissue culture supernatants. While several techniques are available for their isolation, all require a significant reduction in volume to obtain sufficient concentrations for study.

Phosphatidylserine-targeted molecular imaging of tumor vasculature by magnetic resonance imaging.

Phosphatidylserine (PS), normally restricted to the inner leaflet of the plasma membrane, becomes exposed on the outer surface of viable endothelial cells in tumor vasculature, but not in normal blood vessels. In the present study, we report the use of PGN635, a novel human monoclonal antibody that specifically targets PS, for in vivo molecular MRI of tumor vasculature. The F(ab')2 fragments of PGN635 were conjugated to polyethylene glycol (PEG) coated iron oxide nanoparticles (IO).

Highly specific PET imaging of prostate tumors in mice with an iodine-124-labeled antibody fragment that targets phosphatidylserine.

Phosphatidylserine (PS) is an attractive target for imaging agents that identify tumors and assess their response to therapy. PS is absent from the surface of most cell types, but becomes exposed on tumor cells and tumor vasculature in response to oxidative stresses in the tumor microenvironment and increases in response to therapy. To image exposed PS, we used a fully human PS-targeting antibody fragment, PGN635 F(ab')2, that binds to complexes of PS and β2-glycoprotein I.

Pharmacodynamics, tissue distribution, toxicity studies and antitumor efficacy of the vascular targeting fusion toxin VEGF121/rGel.

As a part of an ongoing assessment of its mechanism of action, we evaluated the in vivo pharmacokinetics, tissue distribution, toxicity and antitumor efficacy of VEGF(121)/rGel, a novel fusion protein. Pharmacokinetic studies showed that VEGF(121)/rGel cleared from the circulation in a biphasic manner with calculated half-lives of 0.3 and 6h for the alpha and beta phases, respectively.

IBC's 23rd Antibody Engineering and 10th Antibody Therapeutics Conferences and the Annual Meeting of The Antibody Society: December 2-6, 2012, San Diego, CA.

Now in its 23rd and 10th years, respectively, the Antibody Engineering and Antibody Therapeutics conferences are the Annual Meeting of The Antibody Society. The scientific program covers the full spectrum of challenges in antibody research and development from basic science through clinical development. In this preview of the conferences, the chairs provide their thoughts on sessions that will allow participants to track emerging trends in (1) the development of next-generation immunomodulatory antibodies; (2) the complexity of the environment in which antibodies must function; (3) antibody-targeted central nervous system (CNS) therapies that cross the blood brain barrier; (4) the extension of antibody half-life for improved efficacy and pharmacokinetics (PK)/pharmacodynamics (PD); and (5) the application of next generation DNA sequencing to accelerate antibody research.

Vascular endothelial-targeted therapy combined with cytotoxic chemotherapy induces inflammatory intratumoral infiltrates and inhibits tumor relapses after surgery.

Surgery is the most effective therapy for cancer in the United States, but disease still recurs in more than 40% of patients within 5 years after resection. Chemotherapy is given postoperatively to prevent relapses; however, this approach has had marginal success. After surgery, recurrent tumors depend on rapid neovascular proliferation to deliver nutrients and oxygen.

Near-infrared Optical Imaging of Exposed Phosphatidylserine in a Mouse Glioma Model.

Phosphatidylserine (PS) is normally intracellular but becomes exposed on the luminal surface of vascular endothelial cells in tumors. It also becomes exposed on tumors cells responding to therapy. In the present study, we optically imaged exposed PS in vivo using PGN635, a novel monoclonal antibody that binds PS.

Phosphatidylserine externalization and membrane blebbing are involved in the nonclassical export of FGF1.

The mechanisms of nonclassical export of signal peptide-less proteins remain insufficiently understood. Here, we demonstrate that stress-induced unconventional export of FGF1, a potent and ubiquitously expressed mitogenic and proangiogenic protein, is associated with and dependent on the formation of membrane blebs and localized cell surface exposure of phosphatidylserine (PS). In addition, we found that the differentiation of promonocytic cells results in massive FGF1 release, which also correlates with membrane blebbing and exposure of PS.

Phase I safety and pharmacokinetic study of bavituximab, a chimeric phosphatidylserine-targeting monoclonal antibody, in patients with advanced solid tumors.

Purpose: Bavituximab is a chimeric immunoglobulin G1 phosphatidylserine-targeting monoclonal antibody that triggers vascular disruption and enhances antitumor immune response. This phase I study assessed the safety and pharmacokinetics of bavituximab in patients with advanced solid tumors.

Experimental Design: Patients with refractory advanced solid tumors were enrolled into four sequential dose-escalation cohorts (0.

Cytotoxicity of VEGF(121)/rGel on vascular endothelial cells resulting in inhibition of angiogenesis is mediated via VEGFR-2.

Background: The fusion protein VEGF(121)/rGel composed of the growth factor VEGF(121) and the plant toxin gelonin targets the tumor neovasculature and exerts impressive anti-vascular effects. We have previously shown that VEGF(121)/rGel is cytotoxic to endothelial cells overexpressing VEGFR-2 but not to endothelial cells overexpressing VEGFR-1. In this study, we examined the basis for the specific toxicity of this construct and assessed its intracellular effects in vitro and in vivo.

Development of bavituximab, a vascular targeting agent with immune-modulating properties, for lung cancer treatment.

Bavituximab is a chimeric monoclonal antibody directed against the membrane phospholipid phosphatidylserine. Phosphatidylserine exposure is increased on endothelial cells and apoptotic cancer cells in solid tumors, allowing tumor-specific targeting of bavituximab. Bavituximab binding results in tumor vessel occlusion and enhanced antitumor immunity.

Enhancing the potency of a whole-cell breast cancer vaccine in mice with an antibody-IL-2 immunocytokine that targets exposed phosphatidylserine.

Phosphatidylserine (PS), an anionic phospholipid normally restricted to the inner leaflet of the plasma membrane, is immunosuppressive when externalized on the outside of cell membranes. Exposed PS inhibits the maturation and function of dendritic cells (DCs), and induces the production of multiple immunosuppressive mediators. In the present study, we determined whether blocking these effects of PS while simultaneously introducing interleukin-2 (IL-2) could improve the immunogenicity of a whole-cell cancer vaccine.

Co-localization of prothrombin fragment F1+2 and VEGF-R2-bound VEGF in human colon cancer.

Background: Colon cancer (CC) is frequently complicated by thromboembolic episodes. Thrombin plays a role in angiogenesis and among others induces the synthesis of vascular endothelial growth factor (VEGF) and its receptors (VEGFR-1 and VEGFR-2). The aim of this study was to assess the expression of prothrombin fragment F1+2 (F1+2), a byproduct in thrombin generation (indicating the presence of thrombin), in relation to the presence of VEGFR-2-bound VEGF (VEGF:VEGFR-2), as an indicator of VEGFR-2 activation in human CC tissue.

Increased exposure of phosphatidylethanolamine on the surface of tumor vascular endothelium.

We have previously shown that oxidative stress within the tumor microenvironment causes phosphatidylserine (PS) to redistribute from the inner to the outer membrane leaflet of the endothelial cells (EC) creating a highly specific marker for the tumor vasculature. Because the distribution of phosphatidylethanolamine (PE) and PS within the membrane is coregulated, we reasoned that PE would also be localized in the outer membrane leaflet of tumor EC. To demonstrate this, the PE-binding peptide duramycin was biotinylated and used to determine the distribution of PE on EC in vitro and in vivo.

Antiphospholipid antibodies promote leukocyte-endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via β2GPI and apoER2.

In antiphospholipid syndrome (APS), antiphospholipid antibodies (aPL) binding to β2 glycoprotein I (β2GPI) induce endothelial cell-leukocyte adhesion and thrombus formation via unknown mechanisms. Here we show that in mice both of these processes are caused by the inhibition of eNOS. In studies of cultured human, bovine, and mouse endothelial cells, the promotion of monocyte adhesion by aPL entailed decreased bioavailable NO, and aPL fully antagonized eNOS activation by diverse agonists.

Anti-phospholipid human monoclonal antibodies inhibit CCR5-tropic HIV-1 and induce beta-chemokines.

Traditional antibody-mediated neutralization of HIV-1 infection is thought to result from the binding of antibodies to virions, thus preventing virus entry. However, antibodies that broadly neutralize HIV-1 are rare and are not induced by current vaccines. We report that four human anti-phospholipid monoclonal antibodies (mAbs) (PGN632, P1, IS4, and CL1) inhibit HIV-1 CCR5-tropic (R5) primary isolate infection of peripheral blood mononuclear cells (PBMCs) with 80% inhibitory concentrations of <0.

Targeting mutant p53 protein and the tumor vasculature: an effective combination therapy for advanced breast tumors.

Breast cancer progression depends upon the elaboration of a vasculature sufficient for the nourishment of the developing tumor. Breast tumor cells frequently contain a mutant form of p53 (mtp53), a protein which promotes their survival. The aim of this study was to determine whether combination therapy targeting mtp53 and anionic phospholipids (AP) on tumor blood vessels might be an effective therapeutic strategy for suppressing advanced breast cancer.

Antiphosphatidylserine antibody combined with irradiation damages tumor blood vessels and induces tumor immunity in a rat model of glioblastoma.

Purpose: The vascular targeting antibody bavituximab is being combined with chemotherapy in clinical trials in cancer patients. Bavituximab targets the membrane phospholipid, phosphatidylserine, complexed with beta2-glycoprotein I. Phosphatidylserine is normally intracellular but becomes exposed on the luminal surface of vascular endothelium in tumors.