(P 15) HISTONE DEACETYLASE-3 PLAYS A ROLE IN THE METASTATIC POTENTIAL OF A SUBPOPULATION OF CELLS IN UNDIFFERENTIATED PLEOMORPHIC SARCOMA

Objective: Undifferentiated Pleomorphic Sarcoma (UPS) is among the most commonly diagnosed soft tissue sarcoma in adults. About ⅓ of patients will eventually develop metastatic UPS, with the lung as the most common metastatic site. UPS consists of a heterogeneous population of cells which can significantly impact the effect of therapeutic interventions. In mesenchymal tumors, it is poorly understood how these different tumor clones functionally impact tumor evolution, specifically how they may contribute to primary tumor growth and metastasis. In previous studies, histone deacetylases have been identified as drivers of metastasis. My objective is to identify and elucidate the epigenetic mechanisms of histone deacetylase 3 (HDAC3) on the metastatic potential of a specific subpopulation of cells driving metastatic UPS.

Methods: We model UPS tumors in mice through activation of oncogenic KrasG12D and knockout of p53 and lineage tracing systems. CRISPR barcoding and fluorescent reporters enable us to label individual tumor clones, providing insight on the clonal dynamics of UPS. To initiate tumorigenesis, an adenovirus containing cre recombinase is injected into the hind limb of the mouse. The tumor bearing limb is amputated and metastasis is observed over a period of time. Primary tumors in these mice exhibit the clonal heterogeneity typical of UPS. Excitingly, the metastatic lesions were shown to arise from a single clone. This specific subpopulation of cells, that can migrate and form distant lesions, are identified as metastatic initiating cells or MCs.

Results: Transcriptomic analysis and whole genome sequencing revealed no discernable differences between the MC and non-MC populations, prompting our investigation into the role of epigenetic factors. Results from a Selleck Bioactive Drug Screen identified histone deacetylase (Hdac) inhibitors were among the most selective of the MC population over the nMCs, as indicated by significant decrease in cell viability. More specifically, RNA sequencing and an in vivo CRISPR screen show upregulation of Hdac3 in the MCs and impaired metastatic function in Hdac3KO cells, respectively.

Conclusion: Previous data has shown that a single subpopulation of cells is responsible for the formation of these distant lesions. HDAC3 may play a role in the metastatic potential of a specific subpopulation of UPS cells. Loss of Hdac3 in vivo resulted in impaired migrative and invasive properties. Ongoing studies aim to elucidate the functional significance and underlying mechanism of HDAC3 in metastatic UPS.