Activated vitronectin as a target for anticancer therapy with human antibodies.

The formation of a provisional extracellular matrix represents an important step during tumor growth and angiogenesis. Proteins that participate in this process become activated and undergo conformational changes that expose biologically active cryptic sites. Activated matrix proteins express epitopes not found on their native counterparts. We hypothesized that these epitopes may have a restricted tissue distribution, rendering them suitable targets for therapeutic human monoclonal antibodies (huMabs). In this study, we exploited phage antibody display technology and subtractive phage selection to generate human monoclonal antibody fragments that discriminate between the activated and native conformation of the extracellular matrix protein vitronectin. One of the selected antibody fragments, scFv VN18, was used to construct a fully human IgG/kappa monoclonal antibody with an affinity of 9.3 nM. In immunohistochemical analysis, scFv and huMab VN18 recognized activated vitronectin in tumor tissues, whereas hardly any activated vitronectin was detectable in normal tissues. Iodine 123-radiolabeled huMabVN18 was shown to target to Rous sarcoma virus-induced tumors in chickens, an animal model in which the epitope for huMab VN18 is exposed during tumor development. Our results establish activated vitronectin as a potential target for tumor therapy in humans.

Dynamic (18F)-2-fluoro-2-deoxy-D-glucose (FDG) scintigraphy of normal and tumor-bearing rats.

Five normal rats, 14 rats bearing the Rous sarcoma intrarenally, and four rats with DMBA-induced mammary carcinomas were imaged by dynamic (18F)-2-fluoro-2-deoxy-D-glucose ((18F)FDG) scintigraphy and (99mTc)DTPA renography. The brain, heart, liver, kidneys, and tumor were selected as regions of interest (ROI) for time activity curves; exponential functions were fitted to the decay-corrected curves, which yielded biologic half-lives of (18F)FDG in the ROI. It was found that all organs ROI's exhibited average elimination of activity, whereas activity accumulated in the tumor ROI for the duration of the study (5 h). The (99mTc)DTPA renographies showed that the excretory function in kidneys bearing the Rous sarcoma is severely impaired. This study shows that small laboratory animals can be successfully scintigraphied with a conventional gamma camera using (18F)FDG and that the pharmacokinetics of this radiopharmaceutical may be evaluated.

Establishment of a brain-tumor model in adult monkeys.

A brain-tumor model in adult monkeys may be significant because of the biological similarity to humans as well as the feasibility for surgical manipulation and for sequential computerized tomography (CT) scanning. In the present study, brain tumors were successfully produced in Japanese monkeys (Macaca fuscata), each weighing 2 to 10.8 kg, with an average age of 5.1 years old. Tumor cells were implanted by intracerebral inoculation of 4 X 10(7) chick embryo fibroblasts infected with the Schmidt-Ruppin strain of Rous sarcoma virus (RSV). With a 15- to 67-day latency, brain tumors were induced in 11 (73.3%) of 15 RSV-inoculated monkeys. Contrast-enhanced CT scans delineated all solitary intracerebral tumors greater than 4 to 6 mm in diameter. The CT images were proved at autopsy to be accurate within 2 mm in determining the size of tumor. Five of the 11 monkeys with intracerebral tumors died, with an average survival time of 26.6 days after RSV inoculation. The induced tumors were classified as either glioma or sarcoma by the presence or absence of glial fibrillary acidic protein (GFAP) and S-100 protein. A chromosome analysis of cultured tumor cells showed a diploid number of 42, indicating monkey origin. It is concluded that the reproducible brain tumor in the adult Japanese monkey inoculated with RSV can serve as a good experimental brain-tumor model for the further study of human malignant brain tumors.

Detection of experimental brain tumor in rat by computed tomography.

The feasibility of the use of computerized tomographic (CT) scanning for detecting an experimental brain tumor in rats was evaluated. Tumors were induced in newborn rats by intracerebral inoculation of Rous sarcoma virus. At varying times contrast-enhanced scans were obtained on an Ohio Nuclear 2010 scanner, the brains examined, and the findings at autopsy correlated with the CT findings. Five tumors were demonstrated by CT scans and their presence confirmed at autopsy. Four small tumors were not detected by CT scans. In 1 animal, multiple tumors were demonstrated by a CT scan, and in another a large cyst was correctly diagnosed. It is concluded that the technology currently available can be used to identify some tumor-bearing animals and should be useful for following the change in size of tumors in response to therapy. Further improvements in scanner resolution should make this technique more useful for animal research.

BCNU and steroids in the viral-induced dog brain tumor.

Schmidt-Ruppin strain of Rous Sarcoma was inoculated intracerebrally into 27 newborn beagle dogs. Fourteen days after viral inoculation, 13 of the dogs were given intravenous BCNU (1 mg/kg). The other 14 were given the same volume of intravenous saline in a randomized, double-blinded fashion. Ninety percent of all dogs developed intracranial tumors. Radionuclide (mercury 197) brain scans were done on each dog at 2-week intervals. Median survival was 113 days in the BCNU group and 115 days in the placebo group (P > .99). Unequivocally positive radionuclide brain scans were detected in 5 dogs treated with BCNU and in 2 of the controls. There were no gross or microscopic differences at autopsy between treated and nontreated animals. BCNU, as given in this animal brain tumor model, did not demonstrate any oncolytic effect. An improvement in sequential brain scans was detected in 2 other dogs in response to Dexamethasone, which was given in a double-blinded, cross-over controlled fashion. Computerized tomography clearly demonstrated the tumor in two cases.