Mesenchymal progenitors expressing TRAIL induce apoptosis in sarcomas

Sarcomas are frequent tumors in children and young adults that, despite a relative chemo-sensitivity, show high relapse rates with up to 80% of metastatic patients dying in 5 years from diagnosis. The real ontogeny of sarcomas is still debated and evidences suggest they may derive from precursors identified within mesenchymal stromal/stem cells (MSC) fractions. Recent studies on sarcoma microenvironment additionally indicated that MSC could take active part in generation of a supportive stroma. Based on this knowledge, we conceived to use modified MSC to deliver tumor necrosis factor related apoptosis inducing ligand (TRAIL) targeting different sarcoma histotypes. Gene modified MSC expressing TRAIL were co-cultured with different osteosarcoma, rhabdomyosarcoma and Ewing's Sarcoma (ES) cell lines assessing viability and caspase-8 activation. An in vivo model focused on ES was then implemented considering the impact of MSC-TRAIL on tumor size, apoptosis and angiogenesis. MSC expressing TRAIL induced significantly high apoptosis in all tested lines. Sarcoma death was specifically associated with caspase-8 activation starting from 8 hours of co-culture with MSC-TRAIL. When injected into pre-established ES xenotransplants, MSC-TRAIL persisted within its stroma, causing significant tumor apoptosis versus control groups. Additional histological and in vitro studies reveal that MSC-TRAIL could also exert potent anti-angiogenic functions. Our results suggest that MSC as TRAIL vehicles could open novel therapeutic opportunities for sarcoma by multiple mechanisms.