MyoD-Cre driven alterations in K-Ras and p53 lead to a mouse model with histological and molecular characteristics of human rhabdomyosarcoma with direct translational applications

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, with overall long-term survival rates of about 65-70%. Thus, additional molecular insights and representative models are critical for further identifying and evaluating new treatment modalities. Using MyoD-Cre mediated introduction of mutant K-RasG12D and perturbations in p53 we have developed a novel genetically engineered mouse model (GEMM) for RMS. Specifically, we directly crossed mice expressing MyoD promoter-regulated Cre-recombinase with germline p53Flox or Lox-Stop-Lox (LSL) knock-in alleles expressing oncogenic p53R172H and/or K-RasG12D mutants. The anatomic sites of primary RMS development observed in these mice recapitulated human disease, with the most frequent sites of tumor growth seen in the head, neck, extremities, and abdomen. We have confirmed RMS histology and diagnosis through hematoxylin and eosin (H&E) staining, as well as positive immunohistochemistry (IHC) staining for desmin, myogenin, and phosphotungstic acid hematoxylin (PTAH). We established cell lines from several of the GEMM tumors with the ability to engraft and develop tumors in immunocompetent mice with similar histological and staining features as the primary tumors. Furthermore, injection of syngeneic RMS lines via tail vein had high metastatic potential to the lungs. Transcriptomic analyses of p53R172H/K-RasG12D GEMM-derived tumors showed evidence of high molecular homology with human RMS. Specifically, we noted alterations in gene ontologies including immune response, metabolism and mRNA processing. Finally, pre-clinical use of these murine RMS lines demonstrated similar therapeutic responsiveness to relevant chemotherapy and targeted therapies as human cell line models. Summary StatementWe have developed a new conditional genetically engineered mouse model of rhabdomyosarcoma (RMS) with homologous molecular signature to human RMS that provides valuable pre-clinical models for evaluating novel therapies.