PURPOSE: Pediatric sarcomas are bone and soft tissue tumors that often exhibit high metastatic potential and refractory stem-like phenotypes, resulting in poor outcomes. Aggressive sarcomas frequently harbor a disrupted p53 pathway. However, whether pediatric sarcoma stemness is associated with abrogated p53 function and might be attenuated via p53 reactivation remains unclear. METHODS: We utilized a unique panel of pediatric sarcoma models and tumor tissue cohorts to investigate the correlation between the expression of stemness-related transcription factors, p53 pathway dysregulations, tumorigenicity in vivo, and clinicopathological features. TP53 mutation status was assessed by next-generation sequencing. Major findings were validated via shRNA-mediated silencing and functional assays. The p53 pathway-targeting drugs were used to explore the effects and selectivity of p53 reactivation against sarcoma cells with stem-like traits. RESULTS: We found that highly tumorigenic stem-like sarcoma cells exhibit dysregulated p53, making them vulnerable to drugs that restore wild-type p53 activity. Immunohistochemistry of mouse xenografts and human tumor tissues revealed that p53 dysregulations, together with enhanced expression of the stemness-related transcription factors SOX2 or KLF4, are crucial features in pediatric osteosarcoma, rhabdomyosarcoma, and Ewing's sarcoma development. p53 dysregulation appears to be an important step for sarcoma cells to acquire a fully stem-like phenotype, and p53-positive pediatric sarcomas exhibit a high frequency of early metastasis. Importantly, reactivating p53 signaling via MDM2/MDMX inhibition selectively induces apoptosis in aggressive, stem-like Ewing's sarcoma cells while sparing healthy fibroblasts. CONCLUSIONS: Our results indicate that restoring canonical p53 activity provides a promising strategy for developing improved therapies for pediatric sarcomas with unfavorable stem-like traits.

1st Department of Pathology St Anne's University Hospital and Faculty of Medicine Masaryk University Brno Czech Republic

Central European Institute of Technology Masaryk University Brno 625 00 Czech Republic

Department of Experimental Biology Faculty of Science Masaryk University Brno 625 00 Czech Republic

Department of Internal Medicine Hematology and Oncology and Institute of Medical Genetics and Genomics University Hospital Brno and Faculty of Medicine Masaryk University Brno 625 00 Czech Republic

Department of Pediatric Oncology University Hospital Brno and Faculty of Medicine Masaryk University Brno 613 00 Czech Republic

International Clinical Research Center St Anne's University Hospital Brno 656 91 Czech Republic

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