Anti-neoplastic effect of avian reovirus σ C protein on Rous sarcoma virus-induced tumors in chicken.

This study investigated the anti-neoplastic potential of avian reovirus σC (sigma C) protein on Rous sarcoma virus-induced fibrosarcoma in chicken. The recombinant vector expressing σC protein was injected intra-tumorally into specific pathogen free chicken with fibro-sarcoma at the dose 100µg per bird, while control birds were mock-treated with 100µg of empty vector per bird. Recombinant σC protein induced apoptosis in tumors of treated birds resulting in progressive tumor regression, while similar changes were absent in tumors of mock-treated controls. The σC protein-induced apoptosis in tumors was quantified by flow cytometry and the mean level of apoptosis up to 66% was observed in treated tumors, whereas any significant level of apoptosis was absent in mock-treated controls.

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.

src-specific immune regression of Rous sarcoma virus-induced tumors.

We have developed an oncogene-specific tumor regression system in chickens. Injection s.c. of chicken wing webs with either rASV1702 or rASV157, mutants of Rous sarcoma virus (RSV) that express nonmyristolyated src product containing novel N-terminal domains, results in noninvasive fibrosarcomas that regress fully. The ability of challenge infections with wild-type RSV to form tumors is suppressed. This protective effect was shown to be specific for determinants encoded or induced by v-src (I. Gelman and H. Hanafusa, J. Virol., 61: 2461-2468, 1989). In the current study, we used SC chickens, inbred for major histocompatibility complex Class I haplotype B2/B2, to investigate whether this protection results from active immunity. Preinoculation of chickens with either replication-defective rASV1702 virus or non-virus-producing syngeneic chicken embryo fibroblasts expressing 1702src conferred protection against challenge infections with RSV. Thus, viremia was not required for this protection. Splenic lymphocytes from rASV1702-infected donors could transfer protective immunity against RSV tumor challenge to naive chickens. These lymphocytes were cytotoxic in vitro against RSV- or rASV1702-infected SC-chicken embryo fibroblasts, but not against SC-chicken embryo fibroblasts infected with helper virus, suggesting a specificity for src-encoded or -induced determinants. In contrast, splenic lymphocytes from RSV-infected chickens transferred protective immunity poorly and exhibited low in vitro cytotoxic potential for src determinants, suggesting possible suppression mechanisms. Finally, murine cell lines expressing 157src or 1702src produced tumors in nude mice that failed to regress. Thus, although cells expressing 157src or 1702src are inherently tumorigenic, the tumors they induce most likely regress due to immune mechanisms. These results suggest that 1702src and 157src induce src-specific tumor Ag that potently prime an oncogene-specific protective cellular immunity.

[Treatment of autochthonous rat brain tumors with chemotherapy and radiotherapy].

The authors tried to establish a model of primary, autochthonous avian sarcoma virus-induced rat glioma for experimental chemotherapy and radiotherapy. It was found that the intracerebral inoculation of 2 X 10(6) FFU/5 microliter of an infectious cells-free homogeneous sub-group D Schmidt-Ruppin avian sarcoma virus into 3-day-old inbred Fischer rats induced brain tumors in all rats. The mean survival time of the inoculated rats was 58.7 +/- 12 days. With regard to the classification of the induced brain tumors in Fischer rats, astrocytoma accounted for 70%. This ASV-induced tumor in rats fulfills the following criteria for a desirable animal model. Spontaneously arising. Glial origin. Intraparenchymal growth. Uniformly fatal within a reasonable time period. In the present study, the therapeutic effects of anticancer drugs, such as ACNU and vincristine were evaluated and additionally, the effect of ACNU used in conjunction with radiation was also evaluated in this model. The mean survival time of rats was prolonged significantly with ACNU (20 mg/kg) or radiation therapy (1,000 rads), respectively, and in cases where ACNU was used together with radiation, the mean survival time was prolonged further still, but not very significantly, in comparison with radiation therapy alone. In conclusion, the ASV-induced rat glioma model was considered to be closely akin to a spontaneous brain tumor in terms of morphology, blood supply and kinetics of the primary tumor. Moreover, the therapeutic sensitivity of this model to anticancer drugs was fairly similar to that of human anaplastic astrocytoma. Considering these observations, this model seems to be an excellent experimental brain tumor model which is useful for evaluating the effect of new therapies against malignant brain tumors.

Effect of methylprednisolone on radiotherapy of F344 rats with avian sarcoma virus induced gliomas.

We have examined the impact of methylprednisolone acetate (MPA) on survival of F344 rats that were bearing avian sarcoma virus (ASV)-induced gliomas and that were treated optimally with radiotherapy. Toxicity of MPA (dose range of 0.2-5.0 mg/kg X 7 over 3 weeks) was first established in non-tumor bearing rats as assessed by their relative failure to gain weight. Doses of 2.0 or 5.0 mg/kg X 7 caused animals to be 21.8 or 43.9%, respectively, underweight compared with vehicle controls. In rats bearing ASV-induced gliomas, treatment with 3,000 cGY (nine fractions over a 3-week period) alone or with 0.2 or 1.0 mg MPA/kg (X 6 during the 3-week radiotherapy course) produced a significantly prolonged survival compared with that of untreated, tumor bearing rats. However, MPA did not enhance survival when given concurrently with radiotherapy; indeed, at the higher of these two doses, median survival of tumor-bearers was slightly less than with radiotherapy alone. This trend towards interference with the beneficial effects of radiotherapy was more pronounced with the highest dose of MPA studied, 5.0 mg/kg body weight X 6. These animals had a median survival time that was significantly less than that of tumor-bearers receiving radiotherapy alone, but not significantly different from untreated rats with gliomas. The possible significance of these observations is discussed.

Transfer of blood lymphocytes and macrophages between histocompatible progressor and regressor chickens infected with Rous sarcoma virus.

The development of histocompatible White Leghorn (progressor) and Arkansas Regression (regressor) chicken lines was described. When challenged with Rous sarcoma virus, progressor chickens developed fatal tumors while the regressor chickens eliminated the sarcoma. When sensitized histocompatible peritoneal macrophages and blood lymphocytes were transferred from regressor donors to progressor recipients, they both eradicated growing tumors. Histoincompatible cells were ineffective in inducing tumor remission. Within the two age groups tested, the sensitized blood lymphocytes and macrophages were only effective when transferred between age-matched donor and recipient chickens.