Abstract 3880: Assessment of ALDH activity in neuroblastoma patient-derived xenograft cells as a potential marker of neuroblastoma stem cells

Abstract

Abstract Neuroblastoma is a tumor derived from immature neuroblasts predestined to form the sympathetic nervous system. Children with aggressive neuroblastoma are at high-risk of disease relapse despite their initial response to treatment. The molecular mechanisms underlying these relapses are poorly understood, although clonal expansion and de novo mutations have been suggested as potential mechanisms. An alternative hypothesis is that neuroblastoma initiating capacity and resistance to chemotherapy reside in a subpopulation of tumor initiating cells or cancer stem cells, which are not genetically different from most tumor bulk cells but through unknown mechanisms differ phenotypically and functionally. Here we examine aldehyde dehydrogenase (ALDH) expression and activity in neuroblastoma patient-derived xenograft (PDX) cells, cultured under stem cell-promoting conditions, as a potential marker for neuroblastoma stem cells. We found that neuroblastoma PDX cells in general expressed higher levels of various ALDH isoforms as compared to an aggressive classical serum-grown neuroblastoma cell line. Also, a distinct subgroup with high ALDH activity was observed in PDX cells but not in the serum-grown cell line. Growing the PDX cells in serum induced neuronal differentiation accompanied with lower expression of ALDH1 isoforms and reduced ALDH activity. The change in ALDH expression and activity was reversible, implying phenotypic plasticity. Re-analyzing cells initially sorted on ALDH activity also confirmed an inter-conversion of cells with low and high ALDH activity. Furthermore, in vitro clonogenic capacity was significantly higher in cells with high ALDH activity. Serial in vivo passaging of PDXs allowed us to compare PDX cells isolated from different in vivo generations. Interestingly, cells derived from later in vivo generations contained a higher frequency of cells with high ALDH activity. Finally, orthotopic injection of cells with either low or high ALDH activity showed that both subgroups led to tumor formation, however a higher tumor take was observed when injecting cells with high ALDH activity. In conclusion, our results suggest that ALDH activity is associated with an immature phenotype, which is of clinical importance since less differentiated tumors are more aggressive and associated with poor prognosis. Also, cells with high ALDH activity showed higher in vivo tumor initiating capacity. We are currently pursuing a more extensive characterization of neuroblastoma cells with high ALDH activity. Citation Format: Camilla Persson, Kristoffer von Stedingk, Daniel Bexell, My Merselius, Noémie Braekeveldt, Sven Påhlman, Caroline Wigerup. Assessment of ALDH activity in neuroblastoma patient-derived xenograft cells as a potential marker of neuroblastoma stem cells [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 3880. doi:10.1158/1538-7445.AM2017-3880