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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...

The effect of transient global ischemia on the ultrastructural features of synaptic mitochondria at the distal dendrites of CA1 hippocampal neurons was investigated in 3-month-old rats. Sham surgery was performed on age-matched controls. The number of mitochondria/microm3 of neurophils (Nv: numeric density), the mitochondrial average size (average volume: V), and longer diameter (Fmax) as well as the overall fraction of neurophils occupied by mitochondria (volume density: Vv) were measured by computer-assisted morphometry. In ischemic rats, a 10% nonsignificant decrease of Nv was found, V increased nonsignificantly by 11%, and Fmax increased nonsignificantly by 5% versus controls. As a final outcome of these balanced changes, Vv remained unchanged between the two experimental groups investigated. In ischemic animals, the percentage distribution of V showed that the population of CA1 synaptic mitochondria was composed by an increased fraction of oversized organelles, while the Fmax distribution revealed that this enlargement was due to an increased percentage of elongated organelles. Thus, the observed increase in size should not be considered as a swelling phenomenon; on the contrary, it may represent a physiological and well-documented step in mitochondrial biogenesis. The above parameters are currently supposed to provide information on the adaptive structural reorganization of mitochondrial morphology under different environmental stimulations. Conceivably, these findings document a positive reactive response to ischemia of the mitochondrial structural dynamics at CA1 synaptic terminals and suggest consideration of these organelles as reliable targets in the development of neuroprotective therapeutic interventions to treat vascular brain diseases, for example, stroke.

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