Abstract 2865: Characterization of histone deacetylases in embryonal rhabdomyosarcoma

Abstract

Abstract Histone acetylation and deacetylation are key epigenetic modifications that influence gene expression in both normal and neoplastic cells. Histone deacetylases (HDACs) have been the target for cancer therapeutics due to their demonstrated role in modulating tumor onset and progression in a subset of cancers. We have shown that treatment with pan HDAC inhibitors leads to reduced tumor growth and increased tumor cell differentiation of cultured Embryonal Rhabdomyosarcoma (ERMS) cells. However, the role of specific HDACs in ERMS remains unknown. To determine the function specific to each HDAC in ERMS, we have employed the Clustered Regularly Interspersed Short Palindrome Repeats (CRISPR)/Cas9 nuclease-mediated genome editing technology to enable effective knockout of individual HDAC genes in ERMS. Our CRISPR/Cas9 system uses a transient and multiplex gene targeting approach that induces loss-of-function mutations with high efficiency and allows rapid phenotypic analysis. Combining this system with stable selection of mutant clones with null mutations, we have systematically targeted all class I HDAC genes in ERMS cells. Initial characterization reveals distinct functions of class I HDAC genes in ERMS tumorigenesis. HDAC1 loss-of-function in ERMS cells promotes tumor growth. By contrast, HDAC3 or HDAC8 loss-of-function reduces tumor cell viability. HDAC2 loss-of-function does not affect tumor growth but induces robust differentiation of ERMS cells. In future studies, candidate genes/pathways regulated by HDACs will be identified by an integrated approach of Chromatin Immunoprecipitation (ChIP) and gene expression profiling studies. To validate HDAC mutant phenotypes observed in vitro and assess pre-clinical efficacy of targeted HDAC therapies, CRISPR/Cas9 inducible ERMS lines are currently being developed to facilitate tumor xenograft studies in vivo. Overall, our initial gene targeting results reveal distinct roles of class I HDAC genes in modulating ERMS tumor growth and differentiation. Our results suggest that therapeutic efficacy of pan HDAC inhibitors may be compromised by simultaneously inhibiting tumor-promoting and tumor-suppressive functions of HDACs. Targeted HDAC therapies therefore, may have more potent therapeutic benefits. Citation Format: Michael Phelps, Terra Vleeshouwer-Neumann, Jenna Bailey, Nicole Hickman, Eleanor Chen. Characterization of histone deacetylases in embryonal rhabdomyosarcoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2865. doi:10.1158/1538-7445.AM2015-2865