Background: Cellular heterogeneity within tumors is increasingly recognized as a source of therapeutic failure. However, the molecular mechanisms driving intratumor heterogeneity, drug-resistance and relapse in neuroblastoma remain ill-defined.
Results: Here we characterized neuroblastoma as a biphasic tumor. In new patient-derived cell lines, two phenotypically divergent cellular subtypes were detected, regardless of the shared genetic defects. One cell type is referred to as neuro-epithelial (NE) and expresses classic neuroblastoma markers from the peripheral sympathetic nervous system. In contrast, a newly characterized mesenchymal (MES) cell type lacks NE markers, instead expresses mesenchymal genes and is motile. Moreover, MES-type cells are resistant to a wide variety of chemotherapeutics used in clinical management of neuroblastoma.
The identification of a drug-resistant MES-type subpopulation of cells urged identification of the molecular pathways that control them. Analysis of mRNA gene expression and cis-regulatory elements of four MES-NE cell line pairs uncovered signaling routes (e.g. NOTCH, WNT) and a transcription factor module associated with the MES-state. The top transcription factors PRRX1 and NOTCH each efficiently converted NE-type cells to induced-MES (iMES) cells. iMES cells acquired many features of MES-cells including motility, mesenchymal gene expression and –histone modifications as well as chemo-resistance. Immunohistochemical analysis of primary neuroblastoma detected a small fraction of PRRX1-positive MES-type cells. Importantly, MES-type cells enriched after chemotherapy treatment and in relapsed tumors, compared to the primary tumor.
Conclusions: Neuroblastoma is a biphasic tumor with classic NE-type cells and chemo-resistant MES-type cells. A subpopulation of MES-type cells is detected in vivo and can enrich after therapy and in relapses. Delineation of the core MES-regulatory network identified new pathways that induce the MES-state. A detailed understanding of MES-regulatory pathways will uncover new avenues for therapeutic intervention.