Abstract 3650: Anti-MIF gene therapy of murine mammary tumor results in decreased tumor metastasis and reduction of MDSC (Myeloid derived suppressor cells)

Introduction: Macrophage migration inhibitory factor (MIF) is a multifunctional cytokine which has been shown to be secreted by a variety of tumors and results in autocirne tumor growth. The purpose of this study is to determine the effect of down-regulation of MIF expression on primary tumor growth, metastasis and cellular mediators of immune suppression. Methods: Ten days post 4T1-luciferase tumor cells injection into Balb/c mice, nanoparticles with anti-MIF siRNA and controls (PBS and nanoparticles with scrambled siRNA) were directly injected into established tumor daily for 7 days. At different time points, tumor sizes were measured, tumor metastases in live mice were imaged, tumors and blood samples were harvested. The gene expression in tumor slides and 4T1 cells from tumor digest were investigated by FACS and immunofluorescence microscopy. The total number of circulating MDSCs and MDSCs expressing suppressive cytokines were determined by FACS. Results: We have developed a non-viral gene carrier system that contains a biodegradable β-glucan (10 Kda) backbone and protonable imidazole at the reducing end. The nanoparticles at N/P of 8 lead to the high uptake efficiency by 4T1 cells. The imidazole has buffering capacity to induce endosomal escape. Once released into cytosol, the biodegradable glucan shell of nanoparticles is slowly oxidized and degraded so that the siRNAs are sustained released and the target gene MIF is sustained reduced. Applying this intratumoral anti-MIF gene therapy in vivo, we have made the following observations: 1) MIF protein is highly expressed in 4T1 mammary tumors and can be efficiently blocked in vivo; 2) Reduction of MIF production in established tumor in vivo results in reduced primary tumor size and metastasis; 3) Reduction of MIF production in 4T1 tumor cells in vitro results in reduced MIF secretion in 4T1-conditioned medium and enhanced tumor cell apoptosis and death; 4) Reduction of MIF production in established tumor results in a significant reduction in the total number of circulating MDSCs by 37.6%. The MDSCs expressing immune suppressive cytokines including TGF-β, IL-10 and IL-1β was reduced by 43%, 47% and 70%. Significance: Although MIF appears to have recognized autocrine growth activity in a variety of tumors, development of therapeutics directed at MIF have been problematic because it serves a number of functions in normal biological processes. Targeted reduction of MIF by intratumoral injection of siRNA using a non-viral nanoparticle technology alleviates the difficulty of gene delivery. In addition, since the down-regulation of tumor-secreted MIF may reduce mammary tumor-induced immune suppression by reducing MDSCs, the local therapy can result in a favorable systemic antitumor effect by enhancing host immunity. This study represents a first step in developing this therapeutic approach. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3650. doi:10.1158/1538-7445.AM2011-3650