Improved Tumor Targeting by Combined Use of Two Antitenascin Antibodies

Abstract

Purpose: In the pretargeted antibody-guided radioimmunotherapy (PAGRIT) system, the combined use of two different antibodies directed against the same tumor antigen could represent a valid approach for improving tumor targeting and therapeutic efficacy. We developed a novel monoclonal antitenascin antibody, ST2485, and studied its biochemical and functional properties by in vitro and in vivo assays. We then investigated the first of the three-step therapy combining ST2485 with another antitenascin antibody, ST2146, previously described, to increase accumulation of biotinylated antibodies at the tumor site. Experimental Design: Studies of immunoreactivity, affinity, immunohistochemistry, and biodistribution in xenograft model were carried out on ST2485. Analysis of the ST2485 and ST2146 combination was preliminary carried out by ELISA and BiaCore tests and then by in vivo distribution studies after administration of the radiolabeled biotinylated antibodies, followed by a chase with avidin as clearing agent. Results: ST2485 was found to be a suitable antibody for therapeutic applications. Indeed, for its behavior in all tests, it was comparable with ST2146 and better than BC2, an antibody already used for clinical trials. The additivity of ST2146 and ST2485 in tenascin C binding, shown by in vitro tests, was confirmed by biodistribution studies in a xenograft model where tumor localization of the antibodies was near the sum of each antibody alone, with a tumorto-blood ratio higher than 24. Conclusion:The results reported in this study suggest that a monoclonal antitenascin antibody mixture can improve tumor targeting. This strategy could represent progress for therapeutic approaches such as PAGRIT.Radioimmunotherapy using monoclonal antibodies (mAb) is a first-line strategy in cancer treatment because of its ability to specifically target cancer cells. The pretargeted antibody-guided radioimmunotherapy (PAGRIT) consists of the sequential administration of a biotinylated mAb, avidin/streptavidin, and a radiolabeled biotin molecule, leading to specific accumulation of radioactivity at the tumor site implemented by the multiple valence of avidin/streptavidin toward biotin.Among the several tumor antigens identified as possible targets for antibody mediated therapy, tenascin C seems to be a good candidate for the treatment of several solid tumors (1, 2). Tenascin C is an extracellular hexameric glycoprotein whose monomer is composed of repeating epidermal growth factor (EGF)-like units followed by fibronectin-type repeats and a domain with homology to fibrinogen at the carboxy terminus. Alternative splicing in the A-D region of the fibronectin-type repeats gives rise to monomers of different sizes, whose longer form has been correlated with tumor phenotype (3). In the brain tumor, tenascin C is predominantly present in the extracellular matrix and the hyperplastic blood vessels, suggesting some role in the neovascularization of malignant gliomas (4). Both direct and pretargeted therapeutic approaches with lab...

Tumor-Targeting Properties of Novel Antibodies Specific to the Large Isoform of Tenascin-C

“…Furthermore, efficient tumor targeting by anti-tenascin antibodies has been shown clinically using an avidin/biotin-based pretargeting approach (37) or, more recently, with monoclonal antibodies specific for the small isoform of tenascin-C (38,39). However, all these antibodies are of murine origin and may therefore not be suitable for repeated administration to patients and for the development of biopharmaceuticals.…”

Radioimmunoimaging with Mixed Monoclonal Antibodies of Nude Mice Bearing Human Lung Adenocarcinoma Xenografts

“…Several clinicians have tried to seek methods to increase the uptake of radiolabeled antibodies. Mixed radiolabeled antibody imaging (several mAbs of different tumor-specific antigens for the same tumor mixed for imaging after administration, namely, cocktail method of antibodies) may enhance the RII target/non-target ratio in the present study (Hay et al, 2002;Petronzelli et al, 2005). Several studies have shown that the increase in tumor radioactive uptake was not significant with the double dosage of mAb, but it increased significantly with the combined application of mAb.…”

“…Finding tumor-specific high expression antigens and methods to increase the uptake of radioactivity at the tumor site is the key to the development of lung cancer RII. Some studies have demonstrated that the application of mixed labeled antibodies to one type of cancer (called "antibody cocktail") may be an ideal methods to increase the radioactivity uptake in the tumor site (Hay et al, 2002;Petronzelli et al, 2005).…”

Emerging Trends for Radioimmunotherapy in Solid Tumors

“…107 Petronzelli et al also demonstrated improved tumor targeting with a mixture of two antitenascin antibodies in a colon carcinoma xenograft model. 108 Coadministration of 125 Ilabeled and biotinylated antitenascin antibodies ST2146 and ST2485 (directed against distinct epitopes adequately spaced to rule out stearic hindrance) exhibited additive accumulation in HT29 xenografts as compared to the individual antibodies. 108 …”