Synergy between histone deacetylase inhibitors and DNA-damaging agents is mediated by histone deacetylase 2 in colorectal cancer

// Samer Alzoubi 1 , Leigh Brody 2 , Sunniyat Rahman 1 , Anne-Laure Mahul-Mellier 3 , Nicolas Mercado 4 , Kazuhiro Ito 4 , Mona El-Bahrawy 5 , Andrew Silver 6 , Alan Boobis 1 , Jimmy D. Bell 2 , Nabil Hajji 1 1 Department of Medicine, Division of Experimental Medicine, Centre for Pharmacology & Therapeutics, Toxicology Unit, Imperial College London, London, UK 2 Department of Life Sciences, Research Centre for Optimal Health, University of Westminster, London, UK 3 Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 4 Airway Disease Section, National Heart and Lung Institute, Imperial College, London, UK 5 Department of Histopathology, Imperial College London, London, UK 6 Colorectal Cancer Genetics, Centre for Genomics & Child Health, Blizard Institute, Barts and The London School of Medicine and Dentistry, London, UK Correspondence to: Nabil Hajji, email: n.hajji@imperial.ac.uk Keywords: colorectal cancer, histone acetylation, drug resistance and in vivo imaging, HDAC2, p53 Received: July 08, 2015 Accepted: May 28, 2016 Published: June 7, 2016 ABSTRACT Previous studies have associated the overexpression of histone deacetylase 2 (HDAC2) and the presence of TP53 mutations with the progression to advanced stage drug resistant colorectal cancer (CRC). However, the mechanistic link between HDAC2 expression and the TP53 mutational status has remained unexplored. Here, we investigated the function of HDAC2 in drug resistance by assessing the synergistic effects of DNA-targeted chemotherapeutic agents and HDAC inhibitors (HDACis) on two TP53 -mutated colorectal adenocarcinoma CRC cell lines (SW480 and HT-29) and on the TP53 -wild type carcinoma cell line (HCT116 p53+/+) and its TP53 deficient sub-line (HCT116 p53-/-). We showed that in the untreated SW480 and HT-29 cells the steady-state level of HDAC2 was low compared to a TP53 -wild type carcinoma cell line (HCT116 p53+/+). Increased expression of HDAC2 correlated with drug resistance, and depletion by shRNA sensitised the multi-drug resistance cell line HT-29 to CRC chemotherapeutic drugs such as 5-fluorouracil (5-FU) and oxaliplatin (Oxa). Combined treatment with the HDACi suberoylanilide hydroxamic acid plus 5-FU or Oxa reduced the level of HDAC2 expression, modified chromatin structure and induced mitotic cell death in HT-29 cells. Non-invasive bioluminescence imaging revealed significant reductions in xenograft tumour growth with HDAC2 expression level reduced to <50% in treated animals. Elevated levels of histone acetylation on residues H3K9, H4K12 and H4K16 were also found to be associated with resistance to VPA/Dox or SAHA/Dox treatment. Our results suggest that HDAC2 expression rather than the p53 mutation status influences the outcome of combined treatment with a HDACi and DNA-damaging agents in CRC.