Target-sensitive immunoerythrocytes: interaction of biotinylated red blood cells with immobilized avidin induces their lysis by complement

AbstractRed blood cells (RBC) coated with antibody (immunoerythrocytes) may be useful for drug targeting. Previously we have developed a methodology for avidin (streptavidin)-mediated attachment of biotinylated antibodies (b-Ab) to biotinylated RBC (B-RBC). We have observed that binding of avidin to B-RBC in suspension leads to their complement-mediated lysis by autologous serum. In the present work we have studied the interaction of B-RBC, which are not complement susceptible, with immobilized avidin and their consequent susceptibility to lysis by complement. B-RBC adhered tightly to avidin-coated surfaces and were rendered susceptible to lysis by autologous serum. A long biotin ester provided more effective binding of the B-RBC to immobilized avidin and greater lysis by complement, than a short biotin ester. Based on these results, we have hypothesized that targeting of serum-stable drug-loaded B-RBC attained by step-wise administration of b-Ab and streptavidin may provide target-sensitive lysis of B-RBC. To confirm this hypothesis, we have studied b-Ab and streptavidin mediated targeting of B-RBC to immobilized antigen. Step-wise addition of biotinylated antibody, avidin or streptavidin and b-RBC caused specific binding of B-RBC to immobilized antigen and their subsequent lysis by autologous serum. Therefore, our results obtained in an in vitro model demonstrate that B-RBC might be used for targeting and local release of drug

Anti-Inflammatory Effect of Targeted Delivery of SOD to Endothelium: Mechanism, Synergism with NO Donors and Protective Effects In Vitro and In Vivo

Pro-inflammatory activation of vascular endothelium is implicated in pathogenesis of severe conditions including stroke, infarction and sepsis. We have recently reported that superoxide dismutase (SOD) conjugated with antibodies (Ab/SOD) that provide targeted delivery into endothelial endosomes mitigates inflammatory endothelial activation by cytokines and agonists of Toll-like receptors (TLR). The goal of this study was to appraise potential utility and define the mechanism of this effect. Ab/SOD, but not non-targeted SOD injected in mice alleviated endotoxin-induced leukocyte adhesion in the cerebral vasculature and protected brain from ischemia-reperfusion injury. Transfection of endothelial cells with SOD, but not catalase inhibited NFκB signaling and expression of Vascular Cell Adhesion Molecule-1 induced by both cytokines and TLR agonists. These results affirmed that Ab/SOD-quenched superoxide anion produced by endothelial cells in response to proinflammatory agents mediates NFκB activation. Furthermore, Ab/SOD potentiates anti-inflammatory effect of NO donors in endothelial cells in vitro, as well as in the endotoxin-challenged mice. These results demonstrate the central role of intracellular superoxide as a mediator of pro-inflammatory activation of endothelium and support the notion of utility of targeted interception of this signaling pathway for management of acute vascular inflammation

Immunotargeting of tumor vasculature: preclinical development of novel antibody-based imaging and therapy against TEM1/CD248

The success of antibody-based theranostics depends on the identification of tumor specific biomarkers and the development of corresponding antibodies with high-affinity and specificity. Tumor endothelial marker-1 (TEM1) is highly expressed in tumor vasculature of multiple cancers but not in normal organs. The expression of TEM1 was first evaluated and confirmed by immunohistochemistry from 53 cases of metastatic serous ovarian cancer at HUP. TEM1 positive tumor stroma was observed in >95% of the cases studied. Hence, developing sensitive and effective theranostic agents against TEM1 are of utmost significance in improving diagnosis and treatment of ovarian cancer. Our goals are: 1) engineer TEM1-specific antibodies; 2) evaluate these engineered antibodies in imaging and immunotherapies in preclinical models. To generate TEM1-targeting agents, we designed a panel of multivalent fusion proteins from scFv78, a previously isolated single chain variable fragment specifically recognizing the extracellular domain of TEM1. scFv78 was fused with different huIgG1 Fc region (CH2-, CH3-, or hinge). Proteins were expressed in 293F cells and purified by affinity chromatography. All scFv78 variants exhibited comparable thermo and serum stability in vitro. Among them, the scFv78-Fc fusion (78Fc) has the highest affinity to TEM1 (Kd = 0.15nM, 15X higher than scFv78). Pharmacokinetics (PK) and biodistribution of the protein panel were evaluated in naïve and TEM1+ tumor bearing animals. 78Fc has a t1/2 of 5.1hr, which is suitable for in vivo therapeutic and imaging applications. Therefore, 78Fc was further developed as imaging tool and antibody-drug conjugate (ADC) based on its favorable affinity, stability, half-life and PK profile. In pilot studies with preclinical animal models of tumor vasculature, fluorophore- and [124-I]-labeled 78Fc demonstrated specific enrichment in TEM1+ grafts, but not in control tumor or other organs, by both optical and immunoPET imaging. In addition, 78Fc-MMAE conjugate exerted specific killing of TEM1+ cells. In summary, we have developed a panel of innovative theranostics agents targeting TEM1 on the vasculature of ovarian cancer and several other solid tumors. Our long term goal is to translate such combined approach into the clinic: Using TEM1-antibody as imaging tools to select, and monitor patients for TEM1-antibody based targeted therapies

Collaborative Enhancement of Antibody Binding to Distinct PECAM-1 Epitopes Modulates Endothelial Targeting

Antibodies to platelet endothelial cell adhesion molecule-1 (PECAM-1) facilitate targeted drug delivery to endothelial cells by “vascular immunotargeting.” To define the targeting quantitatively, we investigated the endothelial binding of monoclonal antibodies (mAbs) to extracellular epitopes of PECAM-1. Surprisingly, we have found in human and mouse cell culture models that the endothelial binding of PECAM-directed mAbs and scFv therapeutic fusion protein is increased by co-administration of a paired mAb directed to an adjacent, yet distinct PECAM-1 epitope. This results in significant enhancement of functional activity of a PECAM-1-targeted scFv-thrombomodulin fusion protein generating therapeutic activated Protein C. The “collaborative enhancement” of mAb binding is affirmed in vivo, as manifested by enhanced pulmonary accumulation of intravenously administered radiolabeled PECAM-1 mAb when co-injected with an unlabeled paired mAb in mice. This is the first demonstration of a positive modulatory effect of endothelial binding and vascular immunotargeting provided by the simultaneous binding a paired mAb to adjacent distinct epitopes. The “collaborative enhancement” phenomenon provides a novel paradigm for optimizing the endothelial-targeted delivery of therapeutic agents

Avidin attachment to biotinylated amino groups of the erythrocyte membrane eliminates homologous restriction of both classical and alternative pathways of the complement

AbstractLysis of avidin-coated biotinylated sheep red blood cells (RBC) via the classical pathway of homologous (sheep) and heterologous (guinea pig) complement has been studied. The minimal surface density of avidin inducing antibody-dependent lysis via the classical pathway is smaller than that inducing antibody-independent lysis via the alternative pathway. Heterologous lysis via the classical pathway does not depend on the mode of avidin attachment: both biotinylation of membrane amino groups and insertion of biotinyl-lipid into the membrane provide the same lysis of avidin-coated RBCs by guinea pig serum in the presence of anti-avidin antibody. Avidin-free sheep RBC sensitized with hemolytic anti-RBC antibody were lysed by guinea pig, but not by sheep serum, confirming high efficiency of homologous restriction of the complement. However, avidin-coated RBCs were lysed by homologous serum in the presence of anti-avidin antibody at low surface density of avidin attached. The elimination of the homologous restriction depends on the mode of avidin attachment: biotinylation of membrane amino groups provides antibodymediated lysis via the classical pathway of homologous complement, while insertion of biotinyl-lipid does not provide lysis