No abstract

Interleukin-4 (IL-4) has been demonstrated to possess anti-tumourigenic properties in vivo which is initially attributed to the infiltration of eosinophils proposed to occur by IL-4 binding to its receptors on endothelial cells, thereby mediating eosinophil adhesion. We have investigated whether the binding of IL-4 to receptors on endothelial cells could elicit other biological responses which may also play a role in tumour inhibition, such as angiogenesis. We have demonstrated that mouse IL-4 (mIL-4) down-regulates the expression of one of the receptors for VEGF, VEGF-R2, on endothe-lial cells in vitro. By generating stable transfectants of C6 glioma cells that express mIL-4 under a tetracycline-responsive promoter system, we were able to apply tight regulatory control of mIL-4 expression in vivo. Subcutaneous implantation of mIL-4/C6 cell lines in nu/nu mice revealed that tumour growth is inhibited by mIL-4 expression. mIL-4-expressing tumours were demonstrated to have a reduced level of vascularisation compared with controls, in addition to a high degree of eosinophil infiltration. Our results suggest that mIL-4 has bimodal biological roles in potentiating tumour inhibition in athymic mice: the suppression of angiogen-esis and the augmentation of the host local immune response.

Angiogenesis is a vital component of the development and progression of many human solid tumors. Glioblastoma multiforme is one of the most highly vascularised class of solid tumors. Thus, we have investigated the potential antitumourigenic activity of endostatin, an angiogenic inhibitor, in the rat C6 glioma model. We have engineered C6 cells that endogenously express mouse endostatin in order to assess the growth of C6 tumors in vivo when endostatin is constitutively expressed. Endostatin secreted by stably transfected C6 cells is biologically active as shown by its inhibition (26%) of bFGF-stimulated proliferation of BAECs in culture. The subcutaneous implantation of endostatin-C6 cells in athymic (nu/nu) mice resulted in a reduced tumor growth rate (90% inhibition) compared to control cell lines throughout the duration of our experiments. Tumor inhibition was associated with a 50% reduction in the number of vessels, which were also smaller in morphology. However, endostatin-C6 tumors were no more necrotic than control tumors. The implantation of endostatin-C6 cells into immunocompetent Wistar rat brains also resulted in reduced tumor volumes (71% inhibition) compared to controls. Tumor cells were sparsely localised along the injection tract but had not formed discrete tumors. Despite the inhibitory response mediated by endostatin on C6 growth, complete tumor inhibition or dormancy was not observed in either the athymic or immunocompetent tumor models. These findings demonstrate that the endogenous expression of endostatin by C6 glioma cells results in a reduced tumor growth rate in vivo that is associated with an inhibition of tumor angiogenesis. Our data suggest that endostatin should be developed as an adjuvant gene therapy for the effective treatment of gliomas. © 2002 Wiley-Liss, Inc. Key words: endostatin; glioma; angiogenesis; inhibitionAngiogenesis is the sprouting of capillaries from preexisting blood vessels by the proliferation, differentiation and migration of endothelial cells. 1 This physiologic process is tightly regulated and involves a delicate balance between proangiogenic and antiangiogenic factors. 2 Angiogenesis is a fundamental aspect of many physiologic processes such as embryogenesis, wound healing and corpus luteum formation. 3 An imbalance of the angiogenic process contributes to the development of a number of disorders such as diabetic retinopathy 4 and chronic arthritis. 5 It is now well established that the requirement of angiogenesis is a vital component in the development, progression and metastasis of many human solid tumors. 6 -10 The growth and progression of solid tumors beyond 2 mm 3 is dependent on the recruitment of angiogenic vessels and an expansion of the tumor vasculature. 3,11 Investigations have focused on defining the different stimulators and inhibitors of angiogenesis that are required for tumor growth and metastases. By understanding the roles and interactions of these factors and their regulation, effective antiangiogenic therapies may be developed. Studies h...

Current treatments for malignant gliomas are still largely ineffective in significantly improving prognosis. We have investigated the efficacy of treating established rat C6 glioma by in situ retroviral delivery of IFN-␥ cDNA. Ecotropic retrovirus packaging cells were transfected with a retroviral vector containing the mouse IFN-␥ gene. The IFN-␥ packaging cells were stereotactically implanted into established intracranial C6 glioma in immunocompetent Wistar rats, resulting in the eradication of these tumors. All IFN-␥-treated rats survived to 92 days after C6 implantation (an arbitrary