Abstract 3195: STAT3 inhibition using shRNA inhibits GBM proliferation, cell migration, anchorage-independent growth of mouse, rat, and human stem-like cells in vitro; and it induces long term survival and anti-GBM immunity in vivo

Abstract

Abstract The purpose of this study was to elucidate the role of Signal Transducers and Activators of Transcription 3 (STAT3) signaling on the tumor microenvironment in the most commonly occurring and aggressive primary brain tumor, Glioblastoma Multiforme (GBM), including preclinical testing of inhibition of STAT3 expression in vivo in syngeneic and patient derived xenograft (PDX) models of GBM. GBM is genetically heterogeneous, but always overexpresses genes that are vital to cell cycle regulation, cell growth and proliferation, cell invasion, and angiogenesis. STAT proteins are transcription factors associated with gene regulation and expression signatures that are implicated in several survival pathways that enable human GBMs to grow in the brain parenchyma. In addition, STAT3 has been identified as a central mechanism in tumor-induced immunosuppression in GBM and other cancers. We studied the effects of STAT3 inhibition via shRNA down-regulation in vivo and in vitro using patient derived primary glioma cells (HF2303 & MGG8) in conjunction with other glioma lines from humans, mice, and rats (U251, GL26, and CNS-1, respectively). In this study, we found that GBM cells harboring down-regulated STAT3 signaling exhibit delayed proliferation, increased apoptosis, and anchorage independence. In vivo, STAT3 inhibition resulted in increased survival rates when tumor cells were treated with the STAT3 shRNA both pre- and post-GBM implantation (syngeneic GBM model). Our data demonstrate that STAT3 has a profound influence on the GBM microenvironment, which prevents the host from clearing the tumor. Down-regulating this signaling pathway using gene therapeutic strategies allows for infiltration of immune cells, decreased invasion, and a decrease in GBM cells’ proliferation that leads to the tumor elimination in ∼83% of the animals, this was associated with the development of an effective anti-tumor immunity that prevents tumor recurrence. Given the phenotype of STAT3 inhibition in in vitro assays and its success in in vivo GBM models, inhibition of STAT3 expression using shRNA and gene therapy technologies constitutes an attractive strategy for preclinical development as a potent therapeutic target for GBM. Citation Format: Nathan T. VanderVeen, Nicholas Raja, Elizabeth Yi, James Curtin, Peter Chockley, Hikmat Assi, Jonathan Savakus, Tom Mikkelsen, Samuel Rabkin, Pedro R. Lowenstein, Maria G. Castro. STAT3 inhibition using shRNA inhibits GBM proliferation, cell migration, anchorage-independent growth of mouse, rat, and human stem-like cells in vitro; and it induces long term survival and anti-GBM immunity in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3195. doi:10.1158/1538-7445.AM2015-3195