Delayed growth of SK-ES-1 Ewing sarcoma tumor xenografts is associated with reduced Trk and IGF1R pathway markers

Copyright: © 2026 dos Santos et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Ewing sarcoma (ES) is an aggressive childhood tumor. We have previously shown that tropomyosin receptor kinase (Trk) neurotrophin receptors regulate viability, and the Trk and multi-kinase inhibitor K252a restores sensitivity to chemotherapy, in ES cells. Here, we show that administration of K252a in mice transiently delays ES tumor growth and reduces expression and phosphorylation of multiple targets. BALB/c nu/nu nude mice inoculated with SK-ES-1 ES cells were given daily intraperitoneal (i.p.) injections of K252a for 18 days. Immunohistochemical analysis of tumors was performed to quantify the expression and phosphorylation of Trk receptors, phosphoinositide 3-kinase (PI3K), and insulin-like growth factor 1 receptor (IGF1R). Treatment with K252a led to a partial and transient delay in ES tumor growth and reduced the expression and phosphorylation of TrkA, TrkB, PI3K, and IGF1R. Combined treatment with K252a and the IGF1R inhibitor NVP-ADW742 was more effective in reducing ES cell viability than each compound alone. Associations between genes encoding Trks, PI3K, and IGF1R and overall survival (OS) in patients with ES was examined. Significant associations between expression of NTRK genes and patient OS were found, indicating that NTRK genes should be further evaluated as biomarkers for prognosis in patients with ES.