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

Bruna Almeida dos Santos1,2,3, Natália Hogetop Freire1,3,4, Livia Fratini1, Matheus Dalmolin3,5,6, Josimar Macedo de Castro7, Marcelo A. C. Fernandes3,5,6,8, Lauro Gregianin1,3,9,10, André T. Brunetto1,3,4, Algemir Lunardi Brunetto1,3,4, Luis Fernando da Rosa Rivero11, Mariane da Cunha Jaeger1,3,4, Rafael Roesler1,2,3,12,13 and Caroline Brunetto de Farias1,2,3,4 1 Cancer and Neurobiology Laboratory, Experimental Research Center, Clinical Hospital (CPE-HCPA), Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 2 Graduate Program in Biological Sciences: Pharmacology and Therapeutics, Institute for Basic Health Sciences, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 3 National Science and Technology Institute for Children's Cancer Biology and Pediatric Oncology-INCT BioOncoPed, Porto Alegre, RS 90035-003, Brazil 4 Children’s Cancer Institute (ICI), Porto Alegre, RS 90620-110, Brazil 5 InovAI Lab, nPITI/IMD, Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil 6 Bioinformatics Multidisciplinary Environment (BioME), Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil 7 Graduate Program in Medical Sciences, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 8 Department of Computer Engineering and Automation, Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil 9 Department of Pediatrics, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 10 Pediatric Oncology Service, Clinical Hospital, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 11 Department of Pathology, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 12 Department of Pharmacology, Institute for Basic Health Sciences, Federal University of Rio Grande do Sul, Porto Alegre, RS 90035-003, Brazil 13 Center for Biotechnology, Federal University of Rio Grande do Sul, Porto Alegre, RS 91501-970, Brazil Correspondence to: Caroline Brunetto de Farias, email:cbfarias@zielbiosciences.com Keywords: Ewing sarcoma; K252a; Trk; NTRK; insulin-like growth factor 1 receptor Received: November 17, 2025     Accepted: July 06, 2026     Published: August 07, 2026 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. ABSTRACT 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.