Abstract 5277: Non-invasive metabolic biomarkers of histone deacetylase inhibition in human colon cancer cells and tumors

Abstract

Abstract Introduction: Histone deacetylase (HDAC) inhibitors are targeted anti-cancer agents currently approved for cutaneous T-cell lymphoma and in mid-late stage trials for other cancers (Ma et al, Drugs 2009). Developing non-invasive biomarkers of drug activity could provide a useful tool to aid clinical development. We have previously shown that the HDAC inhibitor LAQ824 increases phosphocholine (PC) levels in human colon cancer cells and tumors as detected by magnetic resonance spectroscopy (MRS), a non-invasive method for monitoring tissue metabolism (Chung et al, Neoplasia 2008). Here we sought to confirm this effect using a different chemotype probe (PXD101, belinostat) and investigate the mechanism(s) underlying it. Methods: Human HT29 colon cancer cells were treated for 24h with DMSO or 2 M PXD101 in DMEM ± 28 µM [1,2-13C]-choline. For in vivo evaluation, female nude mice bearing HT29 xenografts were treated i.p. with vehicle (n=6) or 60mg/kg PXD101 (n=6) for 3 days. In vitro metabolism was assessed using 31P or 13C MRS on cell extracts, while in vivo metabolism was evaluated using 1H and 31P MRS pre- (d0) and 3 days post-treatment, followed by analysis of excised tumor extracts. Western blotting for acetyl histone-3 was used to verify inhibitor action. Results: PXD101 treatment in HT29 cells induced histone-3 acetylation and decreased cell counts to 55±6% of controls (p=0.005). In vivo, PXD101 treatment resulted in tumor stasis (grew by 2% from d0) while the control tumors grew by 20% from d0. 31P MRS showed increased cellular PC content to 156±13% (p=0.04) post-PXD101 treatment. In vivo 1H and 31P MRS of tumors revealed rises in total choline/water (169±25%; p=0.02) and phosphomonoester (i.e. PC+phosphoethanolamine)/total phosphate ratios (p=0.01). Ex-vivo analysis attributed this effect to a rise in PC up to 1.4-fold (p=0.03) in the PXD101-treated tumors relative to controls. PC is formed mainly through phosphorylation of choline via choline kinase (de novo route) or hydrolysis of phosphatidylcholine via phospholipases. 13C MRS analysis of cells grown in the presence of the tracer [1,2-13C]-choline showed increased 13C- PC formation post-PXD101 treatment (180±19% of controls, p=0.02) consistent with increased de novo PC synthesis. Conclusions: Our data show that HDAC inhibition with PXD101 increases PC levels in human colon cancer cells and tumors thus confirming our previous findings with the different chemotype agent LAQ824 (Chung et al, Neoplasia 2008). Importantly, we show that this effect is driven by a rise in de novo PC synthesis. These data further support the role of PC as a potential non-invasive biomarker for monitoring the action of HDAC inhibitors. We acknowledge the support received for the CRUK and EPSRC Cancer Imaging Centre in association with the MRC and Department of Health (England). We also acknowledge NHS funding to the NIHR Biomedical Research Centre and NCI for providing PXD101. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5277. doi:10.1158/1538-7445.AM2011-5277