Abstract
Summary
Reciprocal metabolic reprogramming of MSCs and osteosarcoma cells influences tumor-stroma cross talk. Drugs targeting Warburg metabolism may define innovative therapeutic approaches in osteosarcoma.
Introduction
Osteosarcoma (OS) is a malignant primary bone tumour of mesenchymal origin, in which cells with stem-like characteristics (CSCs) have been described. Recent studies have demonstrated a mutual interaction between stroma and tumor cells in exploiting a role in the pathogenesis and progression of cancer, and also in the enhancing stemness phenotype. Here we take in consideration the complex juxtacrine and paracrine intercellular cross talk played by mesenchymal stromal cells (MSCs) with adherent osteosarcoma cells and OS cells with stem-like characteristics (CSCs).
Methods
MSCs were isolated from human adipose tissue and expanded. To evaluate the interaction between the stroma and the cancer cell compartment, we used two different osteosarcoma cancer cell lines (Saos-2 and HOS) and co-cultured them with MSCs. The different cell populations were sorted to study the reciprocal interaction including metabolic reprogramming. CSCs were obtained from SAOS-2 and HOS cell lines using the sphere formation assay and characterised for their self-renewal, mesenchymal stem cell properties and expression of pluripotency markers. CSCs sensitivity to paracrine factors produced by human MSCs was analysed in a model of co-culture system. Mitochondrial activity in the co-culture systems was also evaluated.
Results
Our results revealed that upon intercellular contact, MSCs undergo Warburg metabolism and mitochondrial oxidative stress. In particular, the cell contact activated the stromal component, triggering autophagy and increased expression of monocarboxylate transporter-4 (MCT4) responsible for the extrusion of lactate. Conversely, osteosarcoma cancer cells, upon contact with MSCs, increased their aerobic metabolism and their development. In addition, using a co-culture method without cell contact, we observed that MSCs grown in serum-starvation conditions promoted proliferation of the CSCs obtained from OS cells, probably by secreting one or several soluble factors. By Real Time PCR we evaluated the gene expression of stemness markers like Oct4, Nanog and SOX2, which appeared to have increased in CSCs.
Conclusions
The final goal is to have a better understanding of the role of the stroma on tumor cell metabolism. Apparently, our data show that MSCs may exploit a role in the modulation of tumor metabolic activity and stemness/differentiation in osteosarcoma. Importantly, these findings suggest an adaptation of cancer cells to bioenergetic changes “engaging” stromal cells as their survival strategy. Understanding the interactions in the tumor microenvironment should present new opportunities for the design of cancer therapeutics.
