PO-369 KDM3A/Ets1/MCAM axis in rhabdomyosarcoma and osteosarcoma

Abstract

IntroductionRhabdomyosarcoma (RMS) and Osteosarcoma (OS) are the most common primary malignant tumours of soft tissue and bones, respectively, affecting children, adolescents and young adults. RMS can be divided into two major histopathological and molecular subtypes: driver oncofusion (PAX3/7-FOXO1) positive, alveolar (ARMS), and oncofusion-negative embryonal (ERMS). Oncofusion positive ARMS carries a worse prognosis, in part due to higher propensity for metastasis. OS is also an aggressive disease with high propensity for metastasis. Patients with metastatic RMS and OS have few therapeutic options, including currently no effective targeted therapies, and typically face poor outcomes. Our laboratory has previously identified a novel, potentially druggable, tumour and metastasis-promotional, axis in Ewing Sarcoma, another aggressive bone and soft tissue cancer of childhood, involving the histone demethylase KDM3A, the Ets1 transcription factor, and the cell adhesion protein MCAM. We have additionally observed KDM3A to be overexpressed in RMS, and in a subset of OS. The aim of this study was to examine whether the KDM3A/Ets1/MCAM axis is intact in RMS and OS, and what impact it has on the biology of these diseases.Material and methodsRMS and OS cell lines were analysed for KDM3A, Ets1 and MCAM expression, and selected cell lines were subjected to stable shRNA-mediated KDM3A, Ets1 and MCAM knockdown (KD). Phenotypic effects of knockdown were analysed by clonogenic and transendothelial invasion assays. Preliminary tumour xenograft studies were also performed.Results and discussionsKDM3A is uniformly overexpressed in ERMS and ARMS cell lines and a subset of OS cell lines. KDM3A KD inhibits colony formation and transendothelial invasion in ERMS and ARMS cells and a high-expressing OS cell line. In preliminary studies KDM3A KD also inhibits ARMS tumorigenesis in an orthotopic model. Strikingly, similar to our prior studies in Ewing Sarcoma, a KDM3A/Ets1/MCAM regulatory axis is intact in RMS and OS, and MCAM KD exerts similar phenotypic effects to those achieved with KDM3A KD.ConclusionOur studies indicate that a KDM3A/Ets1/MCAM molecular axis is intact in RMS and OS, and regulates growth and invasive properties. Together with our previous studies in Ewing Sarcoma, these findings suggest that this may be an important tumour and metastasis promotional axis in all three common paediatric sarcomas, despite distinct cellular origins of these cancers.