Abstract 1064: STAT3 NH2-terminal domain inhibition sensitizes medulloblastoma cells to chemotherapy

Abstract

Abstract Medulloblastoma (MB) is the most common malignant brain tumor in children that arises from cerebellar neuronal progenitor cells. Despite aggressive treatment involving radiation and chemotherapy, the prognosis for high-risk MB remains poor and long-term complications from current therapies are common. Therefore, new effective therapies based on the molecular features of MB are needed to improve therapeutic outcomes. The STAT3 transcription factor is known to be constitutively activated in a variety of human cancers, including MB and functions as an oncoprotein, mediating cancer cell survival, proliferation, migration and drug-resistance. We have delineated the functional role of STAT3 NH2-Terminal Domain (NTD) in MB by using a cell permeable peptide derivative of the STAT3 second helix that specifically binds and perturbs the structure/function of STAT3 and interferes with tetramerization of STAT3 dimers, protein-protein interactions and target genes transcription. Herein, we report that treatment of MB cells with STAT3-NTD inhibitor (S3-NTDi) leads to growth inhibition, cell cycle arrest and apoptosis. The inhibition of STAT3 signaling was also confirmed by downregulation of its downstream targets, including MYC, CCND1, BCl2L1, BCL2, PIM1 and APEX1. Moreover, we observed that S3-NTDi exposure attenuated the migration of MB cells in a wound-healing assay, a prerequisite for tumor invasion and metastasis. We also found that S3-NTDi abrogated IL-6 induced epithelial-mesenchymal transition (EMT) marker protein expression and inhibition of EMT-related transcription factors SNAIL and TWIST. Most importantly, we observed that combination therapy with S3-NTDi and cisplatin significantly decreased the highly aggressive MYC-driven MB cell growth in a dose dependent manner and induced apoptosis by downregulating STAT3 regulated anti-proliferative and anti-apoptotic gene expression. To elucidate the mechanisms of S3-NTDi mediated inhibition, we showed that S3-NTDi upregulated expression of pro-apoptotic gene C/EBP-homologous protein (CHOP) and concomitantly decreased association of the STAT3 transcription factor to endogenous proximal promoter of CCND1 and BCL2 in chromatin immunoprecipitation assay. Furthermore, we determined that S3-NTDi mediated downregulation of miRNA-21 in MB cells, de-repressed Protein Inhibitor of Activated STAT3 (PIAS3), a negative regulator of STAT3 which, in turn, attenuated STAT3 signaling pathway. Overall, our results revealed an important role of STAT3 NTD and its downstream effector molecules in regulating MB pathogenesis and disruption of this pathway with S3-NTDi may serves as a promising new candidate for therapeutic interventions in MB therapy, thereby improving the outcomesin high-risk pediatric MB patients. Citation Format: Sutapa Ray, Don W. Coulter, Shawn D. Gray, Jason A. Sughroue, Nagendra K. Chaturvedi, Shantaram S. Joshi, Kishor K. Bhakat, Timothy R. McGuire, John G. Sharp. STAT3 NH2-terminal domain inhibition sensitizes medulloblastoma cells to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1064. doi:10.1158/1538-7445.AM2017-1064