Abstract 832: Evaluation of relevance of genes expressed in cancer stem cells and under hypoxia in astrocytic brain tumors

Abstract

Abstract The dismal prognosis of patients suffering from astrocytomas, especially glioblastoma multiforme (GBM) emphasizes the need for more precise expressional characterization of these tumors in order to identify potential prognostic factors and therapeutic targets. Tumor growth leads to formation of low oxygenated regions that are considered as stem cell niches. GBM are described with high cancer stem cell content and with hypoxic and necrotic areas. This study investigates in astrocytomas WHO grade II to IV the transcript levels of genes expressed in cancer stem cells (NANOG, ALDH1A1, ALDH3A1, CD133, NOTCH1, ABCB1, ABCG2) and hypoxia regulators and regulated genes (HIF1α, HIF2α, CA9, VEGF). A relationship between some of these factors and patient survival or tumor grade has been reported in previous studies. Tissue samples (ts) from 46 patients were histologically graded as: 12 diffuse astrocytomas (DA) gr II, 6 anaplastic astrocytomas (AA) gr III and 28 GBM gr IV. RNA was isolated from ts. Gene expression levels measured by real-time qRT-PCR in the separate tumor samples were compared to levels found in 6 non-tumor ts from patients suffering epileptic lesions and to beta actin. Relative quantities were compared between ts groups by Mann-Whitney test and log-transformed for Pearson correlation calculation. Increase of HIF2α (200-fold), CA9 (2.7-fold) and VEGF (3.4-fold) mRNA was observed in GBM compared to non-tumor or DA (p<0.05). HIF1α and NANOG mRNA levels did not change (p>0.05). In contrast, a decrease of expression in GBM compared to DA of ABCB1 (10-fold), ABCG2 (10-fold), NOTCH1 (4.2-fold) and ALDH1A1 (6.8-fold) mRNA was observed (p<0.05). ALDH3A1 mRNA was increased 29-fold in GBM compared to DA, but decreased 270-fold compared to non-tumor (p<0.05). Weak and interesting significant correlations of mRNA levels were observed between NOTCH1, NANOG, ABCG2 and ALDH1A1 (Pearson's coefficient P=0.43 to 0.60), between NANOG and CA9 (P=0.67) and between VEGF and ALDH1A1 (P=-0.43). Primary analysis of expression and survival data indicates a significant connection of overall survival and expression of ALDH1A1. Low ALDH1A1 mRNA correlates with a poor prognosis. Part of our findings could be confirmed by comparison with mRNA levels from public database Rembrandt (Repository of Molecular Brain Neoplasia Data) containing results from experiments with gene expression and copy number arrays. Conclusion: Transcript levels of analyzed genes are significantly related to tumor grade, except are HIF1α and NANOG. Decreased transcript levels of genes expressed in cancer stem cells are in contrast to a high content of cancer stem cells described for GBM. Expression levels of most of the investigated genes can be considered promising candidates as prognostic and diagnostic markers in astrocytomas. This project was supported in part by a grant from the Herzfelder-Familien-Stiftung, Austria. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 832.