Abstract 5042: The mechanism of reversible adaptive plasticity in neuroblastoma.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Neuroblastoma (NB) is a pediatric cancer originating from neural crest-derived progenitors. This disease displays considerable clinical diversity, ranging from spontaneous regression to lethal disease. Heterogeneity within cancer cell populations is common and can arise through multiple mechanisms including genetic/epigenetic changes, microenvironmental influences, resistance to anoikis or presence of cancer stem cells. We have recently described a novel form of tumor cell transformation in NB termed reversible adaptive plasticity. Two defined NB phenotypes with anchorage dependent (AD) and anchorage independent (AI) growth patterns were observed in mouse and human cell lines under distinct culture conditions. These phenotypes are capable of reversible transition and identification of specific molecular markers enabled us to observe both phenotypes in established mouse and human NB tumors. In an effort to investigate the mechanism(s) driving this reversible transition in NB, we sought to determine the gene expression profile of the AD and AI phenotypes. In so doing, we were able to elucidate the molecular patterns and pathways associated with each phenotype. Affymetrix gene array analysis of the mouse Neuro2a cells revealed remarkable differences between the two phenotypes in vitro. 1180 genes were differentially expressed and delineated pathways of proliferation in AD cells or tyrosine kinase activation/ apoptosis inhibition in AI cells. In particular, inhibitor of differentiation 2 (Id2) was found to be 20 fold higher in AD while in AI, genes involved in anoikis resistance like PI3K/Akt, Erk, Bcl2 and integrins were upregulated. We hypothesized that Id2 plays a critical role in mediating phenotypic transition of the NB cells. Down-regulation of Id2 expression in the AD phenotype of NB cells with either antisense Id2 oligonucleotide or Id2-siRNA decreased proliferation, increased cell cycle exit, induced apoptosis and resulted in over-activation of Akt and Integrin/Raf/Erk pathways. This altered phenotype was similar to the AI cells in which anoikis resistance is evident. These findings describe the signaling pathways inducing reversible adaptive plasticity in NB. Id2 appears critical for maintaining the proliferative AD phenotype while down-regulating this pathway results in up-regulation of mechanisms governing transition to the anoikis resistant AI phenotype. In a mouse model of NB, targeting both cell phenotypes with the combination of doxorubicin (AD targeting) and Sorafenib (AI targeting) resulted in significant delay in tumor growth compared to either agent alone, highlighting the importance of adaptive plasticity in NB biology. Citation Format: Lina Chakrabarti, Bi-Dar Wang, Norman H. Lee, Anthony D. Sandler. The mechanism of reversible adaptive plasticity in neuroblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5042. doi:10.1158/1538-7445.AM2013-5042