Catalase Defines Radiotherapy Resistance and a Therapeutic Vulnerability in Rhabdomyosarcoma

: Therapeutic resistance remains a critical obstacle in rhabdomyosarcoma (RMS), the most common pediatric soft tissue sarcoma. Increasing evidence implicates redox adaptation in tumor survival and treatment failure. Here, we investigated the functional role and clinical relevance of catalase, a primary hydrogen peroxide-detoxifying enzyme, in modulating RMS therapeutic response. Integrated transcriptomic analyses revealed that while catalase is overall downregulated in RMS compared to healthy skeletal muscle, elevated expression strongly correlates with high-risk, metastatic disease and poor overall survival. In human RMS cell lines, catalase was detectable, and its pharmacological inhibition using 3-amino-1,2,4-triazole (3-ATA) promoted reactive oxygen species (ROS) accumulation, sensitizing cells to standard chemotherapeutics. Notably, robust catalase upregulation was observed in RMS cell models characterized by intrinsic and acquired radioresistance, with strong immunoreactivity validated on cell-block sections. Immunohistochemical validation across patient specimens revealed generally weak catalase expression in RMS tumors, whereas strong reactivity was observed in a secondary embryonal RMS (ERMS) arisen following chemoradiotherapy for nasopharyngeal carcinoma. Functionally, targeting catalase with 3-ATA restored both radio- and chemosensitivity in radioresistant RMS lines. Furthermore, co-targeting catalase and Akt using sub-toxic doses of 3-ATA and MK-2206 cooperatively enhanced oxidative stress-mediated cytotoxicity in resistant cells. Together, these findings identify catalase as a pivotal driver of adaptive radioresistance and establish dual catalase/Akt targeting as a promising pro-oxidant strategy to overcome radiotherapy resistance in RMS.