IGFBP5 is induced by tumor-suppressive naive stromal cells and regulates GAS2-associated apoptosis in rhabdomyosarcoma

Abstract Stromal cells can have either suppressive or stimulatory effects on tumor progression. However, this diverse collection of cells is still poorly characterized in soft-tissue sarcomas. Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood with molecular features of skeletal muscle differentiation. In this study, we explored tumor growth-regulatory signaling between differentially educated non-malignant mesenchymal stromal cells and malignant tumor cells in RMS. Xenograft experiments in mice were designed to provide functional evidence for alterations in tumor behavior linked to tumor-associated stromal cells. Molecular characterization was performed on the Clariom D platform, by gene set enrichment analysis, cell culture validation of deregulated genes, and finally, by clinicopathological validation in a discovery cohort (N=101) and a validation cohort (N=147). The results revealed transient tumor growth-suppressive paracrine effects of naïve orthotopic stromal cells derived from skeletal muscle. These effects were easily abolished if the stromal cells were pre-exposed to RMS cells, either short-term in vitro, or long-term in hindlimb muscle in vivo. Explorative analyses of RMS cells exposed to naïve stromal cells identified insulin-like growth factor binding protein 5 (IGFBP5) as the top upregulated gene, with an ability to induce Caspase 3/7 activation and growth arrest. The gene coding for connective tissue growth factor (CTGF) was identified as the major prosurvival factor being downregulated. Analysis of patient cohorts consistently demonstrated an association between IGFBP5, growth arrest specific protein 2 (GAS2), lower disease stage and favorable survival. Altogether, our study identifies a novel anti-tumor growth mechanism with conditionally deregulated genes linked to apoptosis and differentiation in RMS. The results provide support for continued studies on tumor growth-regulatory mechanisms induced by tumor-surrounding stromal cell subsets at primary and metastatic sites in sarcoma. Citation Format: Monika Ehnman, Karim Katkhada, Liu Zhen Meng, Yue Zhang, Binbin Zhao, Shanlin Tong, Aditi Kallai, Arne Östman, Nick Tobin. IGFBP5 is induced by tumor-suppressive naïve stromal cells and regulates GAS2-associated apoptosis in rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A039.