Abstract LB-302: Inhibition of STAT3 following systemic delivery of STAT3 antisense oligonucleotide results in target inhibition in tumor and tumor-associated stromal cells and dramatic reduction in circulating pro-tumorigenic cytokines

Abstract

Abstract Constitutive activation of STAT3 has been documented in a broad range of neoplastic tissues. STAT3 is a transcription factor that regulates the expression of numerous genes involved in the proliferation, survival, and metastasis of tumor cells. In addition, STAT3 contributes to tumorigenesis by modulating immune responses mediated by tumor stromal cells in the tumor microenvironment. The immuno-suppressive, pro-tumorigenic effects of STAT3 are regulated by induction or inhibition of several key cytokines. However STAT3 remains a difficult target to drug with conventional approaches. Here, we have studied the effects of selective downregulation of STAT3 in various cancer settings by optimized antisense oligonucleotides (ASOs). We assessed the effects of STAT3 downregulation on the expression of cytokines and the progression of cancer. Initially, the safety of inhibiting STAT3 was demonstrated in tolerability studies, where no notable toxicities were observed despite near complete abrogation of STAT3 expression in the liver following systemic delivery of ASO in both rodents and in non-human primate. ASO treatment led to STAT3 inhibition in tumor cells and several non-tumor stromal cell populations of the tumor. In addition, dramatic reduction in key pro-tumorigenic cytokines including IL-6 and IL-1b was observed in C26 colon cancer-bearing animals, which correlated with the decrease of STAT3 level in tumor and stromal cells. This result suggests that STAT3 might not only transmit the IL-6 signal from upstream pathway, but regulates IL-6 level possibly in an auto-feedback manner. Downregulation of STAT3 also led to the inhibition of IL-6-induced C-reactive protein (CRP) expression, which was recently reported to play a key role in the progression of multiple myeloma (MM). Moreover, inhibition of STAT3 resulted in a significant delay in tumor growth in STAT3-dependent MDA-MB-231 breast cancer and U251 glioblastoma xenograft models following systematic ASO treatment. The results from this study collectively suggest that STAT3 expression can be specifically modulated by ASOs in vivo tumor models and that in addition to effects in tumor cells STAT3 ASOs regulate the balance of tumorigenic cytokines in the tumor microenvironment. 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 LB-302. doi:10.1158/1538-7445.AM2011-LB-302