Abstract 1106: Co-administration of the iRGD tumor-penetrating peptide improves the tumor immunostimulatory effects of low-dose IL-2

Abstract

Abstract Background: Recombinant IL-2 at high doses is an effective immunotherapy treatment for various types of solid tumors. However, its clinical utility has been limited by serious mechanism-based side-effects. The clinical-stage iRGD peptide specifically targets tumors and, via activation of the ‘CendR’ trans-tissue transport pathway, increases tumor penetration and accumulation of various types of co-administered drugs. By selectively increasing the drug delivery into tumors, but not to normal tissues, iRGD potentiates the pharmacological activity of various anti-cancer agents within tumor tissue, while reducing their toxicities. In this study we investigate whether co-administration of iRGD with low-dose IL-2 can improve the tumor immune microenvironment by increasing in the ratios of tumor-killing effector CD8 cells vs. the immunosuppressive T-regulatory cells. Methods: Subcutaneous breast tumors (4T1) were generated in immunocompetent mice. Mice were treated with either vehicle control, iRGD, IL-2, or IL-2 + iRGD for 5 days. Tumors were preserved for immunohistochemistry (IHC) or enzymatically digested for fluorescence activated cell sorting (FACS) 16 hours after the last dosing. The FACS and IHC panels were designed to detect the percentage of total T cells, CD4 and CD8 T cells, and Treg cells. Results: Low doses of IL-2 alone were found to increase Tregs within the tumor but had no effect in CD4 or CD8 effector T cells, compared to vehicle treatment. However, when Low dose IL-2 was co-administered with iRGD, we observed a significantly lower percentage of T regs and an increase in CD4 effector T cells. More importantly the ratio of CD8 / Treg cells was increased by at least 10-fold, compared to low dose IL-2 alone. Conclusions: The combination treatment with iRGD and low doses of IL-2 is capable of favorably altering the tumor immune microenvironment such that immunosuppressive T reg cells were reduced, while there was an increase in the effector CD4 and CD8 T-cell populations. The tumor-selective IL-2 pharmacology benefit obtained with iRGD co-administration may provide new options for the use of the well-validated IL-2 in solid tumor patients, including a strategy to overcome the primary resistance to PD-1 blockade. Citation Format: Harri Jarvelainen, Gregory P. Botta, Tatiana Hurtado De Mendoza, Erkki Ruoslahti. Co-administration of the iRGD tumor-penetrating peptide improves the tumor immunostimulatory effects of low-dose IL-2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1106.