Tumor-Secreted Extracellular Vesicles Counteract Therapy Response by Triggering Inflammatory Mesenchymal Stem Cell Development

Abstract Purpose: Therapy resistance is a major clinical hurdle in bone cancer treatment and seems to be largely driven by poorly understood microenvironmental factors. Recent evidence suggests a critical role for a unique subpopulation of mesenchymal stem cells with inflammatory features (iMSC), though their origin and function remained unexplored. We demonstrate that cancer-secreted extracellular vesicles (EV) trigger the development of iMSCs, which hinder therapy response in vivo, and set out to identify strategies to counteract their function. Experimental Design: The role of iMSCs in therapy resistance was evaluated in an orthotopic xenograft mouse model of osteosarcoma. EV-induced alterations of the MSC transcriptome were analyzed and compared with single-cell RNA sequencing data of biopsies from patients with osteosarcoma and multiple myeloma. Functional assays identified EV components driving iMSC development. We assessed the efficacy of clinical drugs in blocking iMSC-induced resistance in vivo. Results: We found that iMSCs are induced by interaction with cancer EVs and completely abrogate the antimetastatic effect of TGFβ signaling inhibition. Importantly, EV-induced iMSCs faithfully recapitulate the inflammatory single-cell RNA signature of stromal cells enriched in biopsies from patients with multiple myeloma and osteosarcoma. Mechanistically, cancer EVs act through two distinct mechanisms. EV-associated TGFβ induces IL6 production, whereas the EV-RNA cargo enhances TLR3-mediated chemokine production. We reveal that simultaneous blockade of downstream EV-activated pathways with ladarixin and tocilizumab disrupts metastasis formation and overcomes iMSC-induced resistance. Conclusions: Our observations establish iMSCs as major contributors to drug resistance, reveal EVs as triggers of iMSC development, and highlight a promising combination strategy to improve therapy response in patients with bone cancer.