Profiling Side Population Cells in Malignant Fibrous Histiocytoma

We are currently studying the mechanisms that confer tumour initiating potential upon SP, and as part of this work, we undertook gene profiling studies comparing expression between SP and non-SP cells, initially focusing on the most common soft tissue sarcoma, malignant fibrous histiocytoma (or MFH) Sarcomas contain a subpopulation of cells which exclude Hoechst dye (SP cells) and are enriched for tumor initiating potential. The persistence of SP cells could be responsible for relapse or a failed response to therapy. Expression profiles were compared between the SP and non-SP cells from malignant fibrous histiocytoma (MFH) tumors using microarray. The Hedgehog and Notch pathways were activated in SP cells. Blocking these pathways in MFH xenografts established in NOD-SCID mice depleted the abundance of SP cells and reduced tumor growth. Intriguingly, treatment also substantially inhibited the potential for successful secondary transplantation. The data provides support that SP cells act as tumor initiating cells in sarcomas and suggests targeting the SP as an enticing approach for sarcoma therapy. In this study, we studied six MFH tumours, and identified a number of signaling pathways that were consistently activated in the SP population compared to the non-SP population.