Abstract 5424: Combination of decitabine and the tumor-selective CYP450-activated compound ICT2700 produces a synergistic effect in HeLa cells
Authors: Cosentino Laura , Sutherland Mark , Sheldrake Helen , Patterson Laurence H. , Pors Klaus 
Published: February 2011

Over the past decade, much research has been conducted in assessing the role of epigenetics in cancer. Epigenetics refers to transmissible modifications in gene activity, which does not involve any alterations in the DNA sequence. DNA methylation occurs predominantly at CpG sites in the mammalian genome by the DNA methyltransferase (DNMT) enzymes. The interaction of methylated DNA with proteins that detect methylated DNA and other chromatin remodeling proteins render an altered chromatin configuration that prevents the expression of a gene. DNA methylation plays an important role in the expression of oncogenes, tumour suppressor genes and more recently it has also been shown that drug metabolising enzymes are affected by the DNA methylation process. Aberrant alterations in the methylation status of CpG dinucleotides, target sites for DNMT, have been shown in the promoter regions of extrahepatic cytochromes P450 including CYP1A1, CYP1B1 and CYP2W1. We are investigating extra-hepatic CYPs (CYP1A1, 1B1, 2J2, 2S1, 2W1, 4Z1 and 4F11) as targets for tumor-selective prodrug activation. Tumors expressing high levels of active CYP450s could induce their own demise via the conversion of otherwise inert agents into potent cytotoxins. We have identified the aryl-ring-fused chloromethylindolines as a class of agent that possess a pharmacophore capable of undergoing oxidation by CYPs. We have previously shown ICT2700 to be activated by CYP1A1 in vitro and in vivo.

Here we present data that suggest that epigenetic silencing of CYP1A1 affect the cytotoxicity of ICT2700. We have pre-treated MCF-7 and HeLa cell lines with either the demethylating agent decitabine (either 200 nM, 1 or 2 µM, on day 1 or day 1 + 2) or the HDAC inhibitor trichostatin A (100 nM, after day 1) and subsequently exposed the cell lines to ICT2700 (concentration range: 1nM - 200 µM, on days 3, 6 or 9). A higher level of cytotoxic kill by the prodrug ICT2700 in the HeLa cells but not in the MCF-7 cells were observed in combination with decitabine. Combination with trichostatin A had no apparent synergistic effect. In all experiments, a higher level of CYP1A1 mRNA was observed after treatment with decitabine and trichostatin A. Regardless of the pharmacoepigenetic status, ICT2700 exhibited low nM IC50 in the MCF-7 but not in the HeLa cell line, indicating that low levels of CYPs in the former cell line are able to convert the prodrug into a potent cytotoxin.

In conclusion, we have demonstrated that the conversion of the prodrug ICT2700 to some extent is affected by epigenetic silencing and that combination with decitabine can sensitise cells prior to treatment with ICT2700.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5424.