Abstract 4640: High expression of the stem cell marker LGR5 is associated with a poor clinical outcome in patients with Ewing's sarcoma

Abstract

Abstract Ewing's sarcoma family tumors (ESFT) are aggressive bone and soft tissue tumors that are most commonly diagnosed in childhood and adolescence. Unfortunately, drug-resistant relapse is not uncommon and is associated with very poor outcomes. No clinical or pathologic features currently exist that reliably predict chemosensitivity or relapse in newly diagnosed patients. In this study we used whole genome expression microarray profiling to identify potential markers of drug resistance and relapse in ESFT. Affymetrix human exon (HuEx) arrays were used to profile a highly drug resistant case of primary, localized ESFT before and after induction therapy. Comparison of gene summarized data from pre- and post-therapy samples with 10 chemosensitive tumors identified 309 genes to be differentially expressed in the resistant case at diagnosis (fold change>2). Of the 309 differentially expressed genes at diagnosis, 130 demonstrated an even greater change in expression post-induction therapy suggesting that these genes might be markers of the most highly drug-resistant cells. Intriguingly, two stem cell associated genes, PROM1 (prominin 1) and LGR5 (leucine-rich-repeat containing G-protein-coupled receptor 5), were included in the list of putative chemoresistance markers. Expression of PROM1 and LGR5 were 18-fold and 17-fold higher, respectively, at diagnosis and 31-fold and 21-fold higher post-induction therapy in the drug resistant case. To determine if either gene is associated with chemoresistant disease or relapse in ESFT we next evaluated whether their expression correlated with outcome in a large cohort of institutional and Children's Oncology Group patients. Clinical correlates analysis of HuEx gene expression data obtained from 53 tumors revealed no correlation between PROM1 expression and outcome. In contrast, increased expression of LGR5 was associated with worse event-free (p=0.008) and overall survival (p=0.046). Variable but detectable expression of LGR5 in ESFT tumors and cell lines was validated using quantitative RT-PCR. Finally, LGR5 expression in ESFT cells was compared to human embryonic and somatic stem cells and fibroblasts. Significantly, LGR5 was found to be highly expressed by neural crest stem cells but not by bone-marrow derived mesenchymal stem cells, differentiated neural crest cells, or embryonic fibroblasts. These data suggest that LGR5 might be useful as a predictor of outcome in ESFT and implicate a primitive neural crest stem cell phenotype in the developmental origins of drug-resistant and relapsed disease. 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 4640.