INHIBITION OF ANGIOGENESIS IN-VIVO BY INTERLEUKIN-12

Background: In previous animal studies, interleukin 12 (IL 12) was sho wn to inhibit the growth of a wide spectrum of tumors in vivo but to h ave no direct effect on tumor cells in vitro. Also, contrary to the ex pectation of a T-cell-mediated effect, the antitumor activity of IL 12 was not completely abrogated in tests of T-cell-deficient mice. These observations suggest that IL 12 may possess antiangiogenic properties that account for its tumor-inhibitory effects in vivo. Purpose: Our g oal was to investigate the hypothesis that IL 12 has antiangiogenic pr operties. Methods: A model of basic fibroblast growth factor-induced c orneal neovascularization in mice was used to evaluate the effects of IL 12 and interferon gamma (IFN gamma) on angiogenesis in vivo. Differ ent strains of male mice, e.g., immunocompetent C57BL/6 mice, severe c ombined immune-deficient (SCID) mice, natural killer cell-deficient be ige mice, and T-cell-deficient nude mice, were treated with IL 12 (1 m u g/day) intraperitoneally for 5 consecutive days. The extent of neova scularization in response to a basic fibroblast growth factor pellet a nd the inhibition of neovascularization by IL 12 or IFN gamma were ass essed by measuring the maximal vessel length and the corneal circumfer ence involved in new blood vessel formation. The antitumor activities of IL 12 and of the angiogenesis inhibitor AGM-1470 were evaluated in Letvis lung carcinoma-bearing mice. In vitro proliferation studies wer e performed on bovine capillary endothelial cells, mouse pancreatic is let endothelial cells, and mouse hemangioendothelioma cells. Results: IL 12 treatment almost completely inhibited corneal neovascularization in C57BL/6, SCID, and beige mice. This potent suppression of angiogen esis was prevented by the administration of IFN gamma-neutralizing ant ibodies, suggesting that the suppression was mediated through IFN gamm a. In addition, the administration of IFN gamma reproduced the antiang iogenic effects observed during treatment with IL 12. Treatment with I L 12 and AGM-1470 combined did not increase toxicity and showed a tren d toward enhanced antitumor efficacy in Lewis lung carcinoma-bearing m ice. Conclusions: IL 12 strongly inhibits neovascularization. This eff ect is not mediated by a specific cell type of the immune system. Inst ead, IL 12 has been shown to induce IFN gamma, which, in turn, appears to play a critical role as a mediator of the antiangiogenic effects o f IL 12. Implications: Recognition of the mechanisms of the antiangiog enic properties of IL 12 may be crucial in planning its clinical appli cations, including a possibility of coadministration with other inhibi tors of neovascularization.