Abstract 5004: In vivo profiling of hypoxic mRNA and miRNA expression in gliomas and head and neck tumors

Abstract

Abstract Hypoxia plays a key role in tumor aggressiveness and radiation resistance, yet little is known regarding hypoxic global gene regulation in vivo. Although the regulation of mRNA and miRNA expression by hypoxia has been investigated in isolation in vitro, it has not yet been analyzed directly in tumor samples. We have used the hypoxia marker EF5 coupled with laser capture microdissection (LCM) to isolate RNA from viable hypoxic and normoxic regions of 9L experimental rat gliomas and from human head and neck (H&N) tumor samples. This was followed by microarray analysis of mRNA expression and comparison of this signature with that obtained from treating 9L cells with hypoxia in vitro. Through this, we have identified several mRNAs (including the HIF targets Vegf, Glut-1 and Hsp27) with increased levels under hypoxia compared to normoxia both in vitro and in vivo. We also found striking differences between the global in vitro and in vivo hypoxic mRNA profiles. An intriguing finding was the hypoxic-downregulation of a number of immunomodulatory and DNA repair proteins including CXCL9, CD3D and RAD51 in vivo, consistent with a pro-tumorigenic role of hypoxia in solid tumors. Immunohistochemical staining verified increased HSP27 and decreased RAD51 protein levels in hypoxic vs. normoxic tumor regions. Moreover, CD8+ T cells which are recruited to tumors upon stimulation by CXCL9 and CXCL10, were largely excluded from viable hypoxic areas in vivo. Global microRNA expression changes have been reported to occur in response to hypoxia in vitro. Hence, our second objective was to identify the cluster of miRNAs differentially expressed in hypoxic vs. normoxic regions of the human tumors using TaqMan® Array MicroRNA Cards. We employed the same technique used with the 9L tumors to analyze miRNA expression patterns in hypoxic vs. normoxic samples from H&N cancer patients who have been administered EF5 prior to surgical removal of the tumor. Consistent with published in vitro studies, miR-210 emerged as a major miRNA robustly induced in the hypoxic regions. We also confirmed miR-210 induction by an individual real time-PCR assay and found it to be upregulated > 2-fold in all hypoxic RNA samples. In addition, we have also found several miRNAs whose levels were upregulated and downregulated in hypoxic vs. normoxic areas. This is the first study to analyze the influence of hypoxia on mRNA and miRNA levels in vivo and can be readily adapted to obtain a comprehensive picture of hypoxic regulation of gene expression and its influence on biological functions in solid tumors. 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 5004. doi:10.1158/1538-7445.AM2011-5004