Abstract 4869: Bone marrow-derived stromal cells contribute to a protumorigenic inflammatory environment that promotes drug resistance
Authors: Borriello Lucia , Nakata Rie , Wu Hong-Wei , Seeger Robert C. , DeClerck Yves A. 
Published: May 2015

Abstract
Therapeutic resistance is a major cause of failure to eradicate cancer. Whereas mutational events are primarily responsible for the development of clones of tumor cells intrinsically resistant to therapy, the tumor microenvironment (TME) plays a critical role in allowing tumor cells to become transiently resistant to therapy before they acquire an irreversible form of resistance. The bone marrow, the site of metastasis of many cancers including neuroblastoma, represents a unique sanctuary for metastatic tumor cells that promotes this form of environment-mediated drug resistance (EMDR). Here we show that when exposed to neuroblastoma cell-derived exosomes, human bone marrow mesenchymal stromal cells (BMMSC) express multiple cytokines and chemokines that have a pro-tumorigenic function including interleukin (IL)-6, IL-8, vascular endothelial cell growth factor (VEGF)-A and macrophage chemotactic protein (MCP)-1 (CCL-2). Exposure of human neuroblastoma cells to conditioned medium (CM) of 48 hour co-cultures of tumor cells and BMMSC increased their resistance to the topoisomerase II inhibitor etoposide (ΔIC 50 = 0.73, p &lt; 0.0001) and activated several signaling pathways, in particular signal transduction and activator of transcription (STAT)-1 and -3 and extracellular signal regulated kinase (ERK1/2). In support of these pathways playing an active role in promoting drug resistance, we demonstrated that the sensitivity of neuroblastoma cells to etoposide in the presence of CM was restored, when tumor cells were pre-treated with a JAK2/STAT3 kinase inhibitor (Ruxolitinib; 1 µM) in combination with a MEK inhibitor (Trametinib; 1µM) whereas alone, each inhibitor had no effect. We also found that in vivo co-injection of human neuroblastoma cells and human BMMSC resulted in a significant increase in tumor formation and tumor growth in NOD/SCID mice compared to tumor cells alone. Interestingly, a similar effect on drug resistance was observed in the presence of mesenchymal-like cells harvested from a fresh primary neuroblastoma tumor. Like BMMSC, these cells expressed the fibroblast-associated protein α, a marker of tumor-associated fibroblasts (TAF), and differentiated into osteoblasts. Our data thus demonstrate that BMMSC contribute to drug resistance in neuroblastoma and support the concept that these cells are a source of TAF in primary tumors. They also suggest that blocking pathways that these cells activate in tumor cells can restore drug sensitivity and increase response to therapy.
Citation Format: Lucia Borriello, Rie Nakata, Hong-Wei Wu, Robert C. Seeger, Yves A. DeClerck. Bone marrow-derived stromal cells contribute to a protumorigenic inflammatory environment that promotes drug resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4869. doi:10.1158/1538-7445.AM2014-4869