Abstract 6147: Myc-driven osteosarcoma murine model for dissecting the molecular genetics and novel therapeutic strategies for OS
Authors: Nirala Bikesh Kumar , Lyazat Kurenbekova , Patel Tajhal , Shuck Ryan Lane , Kimal Rajapakshe , Yustein Jason T. 
Published: September 2020

Abstract
Osteosarcoma (OS) is the most common bone tumor in pediatric patients, particularly in adolescents and young adults. Unfortunately, over the past four decades, there has been minimal progress towards improving patient outcomes, especially for those with metastatic disease. Currently, no effective molecular targeted therapies are available for the OS, however many OS patients possess genetically defined somatic DNA copy number alterations (SCNAs), including amplification of chromosome 8q24. 8q24.2 region harbors the oncogene c-Myc, and the SCNA is associated with decreased overall survival rates. Furthermore, enhanced c-Myc transcript levels are significantly correlated with worse prognosis. There is a scarcity of reliable and reproducible in vivo animal models that mimic SCNAs and can be used to provide both intrinsic and extrinsic molecular insights into c-Myc-osteosarcoma biology. We have developed a novel conditional c- Myc knock-in mouse model to understand the mechanisms that underlie the ability of c-Myc to drive development and progression of OS and utilize for identification of c-Myc-dependent molecular vulnerabilities. A tissue-specific GEMM for osteosarcoma was developed by altering p53 (f/+) and c-Myc (c- Myc-in) genes in the osteoblast derived cells. Either c-Myc WT or the c-Myc T58A phosphorylation mutant was knocked-in from the constitutively active ROSA26 locus in response to Cre-recombinase. Differential gene expression in c-Myc-driven and non-driven-tumor tissue samples were quantified by RNA sequencing. The protein expression profiles were evaluated for both groups by comprehensive mass spectrometry (MS) analysis and reverse phase proteome analysis (RPPA). Osteosarcoma was confirmed for GEMM tumors by histopathological (H&E) staining. The spontaneous tumor development was significantly accelerated and more aggressive in c-Myc- driven GEMMs as compared to the non-c-Myc-driven. c-Myc expression was significantly higher both at the transcriptional and protein levels in the c-Myc-driven tissue/cells. Expression of 1479 genes (out of 13781 genes) were significantly altered at transcriptional levels in c-Myc driven tumor tissue samples, analyzed by RNA sequencing. Myc-target, E2F, G2M check-point, KRAS and DNA repair associated genes were significantly upregulated whereas the protein secretion, oxidative phosphorylation, adipognenesis, myhogenesis, and E2M transition genes were significantly downregulated when compared with the non-c-Myc-driven group. A significant alteration was observed in the protein expression levels of ribosome biogenesis, DNA replication, nucleotide excision repair, mismatch repair and RNA degradation associated genes in MS data analysis. Our mouse model has high penetrance, short latency, closely resembles human OS and will provide new opportunities for dissecting the molecular genetics of OS and developing novel therapeutic strategies. This model has also provided syngeneic cell lines for future in vivo studies.
Citation Format: Bikesh Kumar Nirala, Kurenbekova Lyazat, Tajhal Patel, Ryan Lane Shuck, Rajapakshe Kimal, Jason T. Yustein. Myc-driven osteosarcoma murine model for dissecting the molecular genetics and novel therapeutic strategies for OS [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6147.