A multimodal treatment of carbon ions irradiation, miRNA-34 and mTOR inhibitor specifically control high-grade chondrosarcoma cancer stem cells

•Chondrosarcoma stem cells (ChSCs) are radioresistant and are suppressed by miR-34.•mTOR inhibition by Rapamycin targets ChSCs via FOXO3 and miR-34.•Combination of carbon-ion therapy with mTOR inhibitors effectively controls ChSCs. High-grade chondrosarcomas are chemo- and radio-resistant cartilage-forming tumors of bone that often relapse and metastase. Thus, new therapeutic strategies are urgently needed. Chondrosarcoma cells (CH-2879) were exposed to carbon-ion irradiation, combined with miR-34 mimic and/or rapamycin administration. The effects of treatment on cancer stem cells, stemness-associated phenotype, radioresistance and tumor-initiating properties were evaluated. We show that high-grade chondrosarcoma cells contain a population of radioresistant cancer stem cells that can be targeted by a combination of carbon-ion therapy, miR-34 mimic administration and/or rapamycin treatment that triggers FOXO3 and miR-34 over-expression. mTOR inhibition by rapamycin triggered FOXO3 and miR-34, leading to KLF4 repression. Our results show that particle therapy combined with molecular treatments effectively controls cancer stem cells and may overcome treatment resistance of high-grade chondrosarcoma.