Using an orthotopic mouse model of renal cell carcinoma, we showed previously that IL-2/αCD40 combination immunotherapy resulted in synergistic anti-tumor responses. In contrast, the use of either IL-2 or αCD40 as single agents mediated only partial, transient anti-tumor effects. We now show that treatment of tumor-bearing mice with IL-2/αCD40, but not either IL-2 or αCD40 alone, induces significant nitric oxide synthase (NOS2) expression within the tumor microenvironment through an interferon gamma-dependent pathway. In saline-control treated mice (low NO levels), NO inhibition reduced lung metastases by itself. However, in the context of immunotherapy (high NO levels), NOS2 inhibition completely abrogated the ability of IL-2/αCD40 treatment to reduce lung metastases but had no effect on the ability of IL-2/αCD40 to reduce primary kidney tumor burden. We further show that IL-2/αCD40 induces the NO-dependent decrease in matrix metalloproteinase (MMP) expression and activity, concomitant with an increase in the expression of tissue-inhibitor of metalloproteinase (TIMP)-1 within the tumor microenvironment. Finally, the treatment of tumor-bearing mice with the NO donor, JS-K significantly reduced lung metastases but had no effect on primary tumor size. These data distinguish the primary anti-tumor effects of IL-2/αCD40 immunotherapy, which are independent of NO expression, from the important ability of IL-2/αCD40 to inhibit lung metastases through the NO-dependent regulation of MMP and TIMP functions. Furthermore, the reduced MMP9 activity may be indicative of M1 polarized macrophages within the tumor microenvironment after IL-2/αCD40 treatment. Our data demonstrate the mechanistic basis for the IL-2/αCD40-mediated control of lung metastases and indicate that the context-dependent application of NO-inducing agents may hold considerable promise for the treatment of metastastic disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5594.