Abstract B43: The c-Myc/AKT1/TBX3 axis is important to target in the treatment of embryonal rhabdomyosarcoma

Abstract

Abstract Rhabdomyosarcoma (RMS), a pediatric cancer of the skeletal muscle, is the most common malignant soft-tissue sarcoma in children and adolescents. There are two main subtypes: embryonal RMS (ERMS), which is more prevalent in children and accounts for approximately 75% of RMS cases, and alveolar RMS (ARMS), which presents in adolescents and young adults and accounts for the remaining 25% of cases. Little is known about the molecular mechanisms underpinning ERMS, and there is a need for new and effective therapeutic approaches. Here we investigate the status and role of the T-Box transcription factor 3 (TBX3), which has been well characterized for its function in development and, in particular,r the congenital disorder ulnar mammary syndrome that results from its haploinsufficiency. Conversely, TBX3 has been reported to be overexpressed in numerous cancers including a range of sarcoma subtypes and shown to contribute to oncogenic processes such as cell proliferation, migration, and invasion, in vitro and in vivo tumor-forming ability. To determine the status of TBX3 in ERMS, immunohistochemistry was performed using RMS patient tissue and Western blotting on a panel of RMS cell lines compared to normal myoblast cells. Cell culture models in which TBX3 was either stably knocked down or overexpressed were established, and in vitro and in vivo assays were performed to determine the impact of TBX3 on key hallmarks of cancer including cell proliferation (growth curves), migration (scratch motility assay), as well as tumor formation and invasion in nude mice. Our data showed high TBX3 levels in RMS patient tumor tissue sections as well as in ERMS cell lines tested. Preliminary data reveal that the mechanisms involved in upregulating TBX3 in ERMS involve c-Myc at a transcriptional level and AKT1 at a post-translational level. Importantly, TBX3 was found to promote ERMS cell proliferation and migration, anchorage-independent growth, tumor formation, and metastasis. This study describes for the first time that TBX3 is an oncogene in ERMS and identifies c-Myc/AKT1/TBX3 as an important axis that could be targeted as novel therapeutic approaches for the treatment of this cancer. Citation Format: Danica Anne Sims, Hapiloe Mabaruti Maranyane, Jade Peres, Sharon Prince. The c-Myc/AKT1/TBX3 axis is important to target in the treatment of embryonal rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B43.