Abstract
Hypermethylation of 5′-cytosine-guanosine islands of tumor suppressor genes resulting in their silencing has been proposed to be a hallmark of various tumors. Modulation of DNA methylation with DNA methylation inhibitors has been shown to result in cancer cell differentiation or apoptosis and represents a novel strategy for chemotherapy. Currently, effective DNA methylation inhibitors are mainly limited to decitabine and 5-azacytidine, which still show unfavorable toxicity profiles in the clinical setting. Thus, discovery and development of novel hypomethylating agents, with a more favorable toxicity profile, is essential to broaden the spectrum of epigenetic therapy. Parthenolide, the principal bioactive sesquiterpene lactone of feverfew, has been shown to alkylate Cys38 of p65 to inhibit nuclear factor-κB activation and exhibit anti-tumor activity in human malignancies. In this article, we report that parthenolide 1) inhibits DNA methyltransferase 1 (DNMT1) with an IC50 of 3.5 μM, possibly through alkylation of the proximal thiolate of Cys1226 of the catalytic domain by its γ-methylene lactone, and 2) down-regulates DNMT1 expression possibly associated with its SubG1 cell-cycle arrest or the interruption of transcriptional factor Sp1 binding to the promoter of DNMT1. These dual functions of parthenolide result in the observed in vitro and in vivo global DNA hypomethylation. Furthermore, parthenolide has been shown to reactivate tumor suppressor HIN-1 gene in vitro possibly associated with its promoter hypomethylation. Hence, our study established parthenolide as an effective DNA methylation inhibitor, representing a novel prototype for DNMT1 inhibitor discovery and development from natural structural-diversified sesquiterpene lactones.
Footnotes
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This work was supported in part by the National Institutes of Health National Cancer Institute [Grants RO1-CA102031, UO1-CA76576]; the Bio-Medical Mass Spectrometry Laboratory, College of Pharmacy; and the Ohio Supercomputer Center, The Ohio State University.
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Z.L. and S.L. contributed equally to this work.
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This work was presented previously at the following conferences: Cheng D, Xiao JJ, Cheng H, Liu Z, Covey JM, and Chan, KK (2005) at The Annual Meeting of the American Association of Cancer Research; 2005 Apr 16-20; Anaheim, CA; Liu Z, Liu S, Xie Z, Li C, Aimiuwu S, Chen P, Pang J, Marcucci G, and Chan KK (2007) at The Annual Meeting of The American Association of Cancer Research; 2007 April 14-19; Los Angeles, CA; and Liu Z, Xie Z, Wu J, Aimiuwu J, Liu S, Huang H, Plass C, Marcucci G, and Chan KK (2007) at The AAPS Annual Meeting; 2007 Nov 11-15; San Diego, CA. American Association of Pharmaceutical Scientists, Arlington, VA.
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doi:10.1124/jpet.108.147934.
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ABBREVIATIONS: CpG, 5′-cytosine-guanosine; SLs, sesquiterpene lactones; TSGs, tumor suppressor genes; 5mdC, 5-methyl-2′-deoxycytidine; 2dC, 2′-deoxycytidine; 2dG, 2′-deoxyguanosine; DNMT1, DNA methyltransferase 1; hDNMT1, human DNMT1; ds, double strand; RT, reverse transcription; PCR, polymerase chain reaction; ECGC, (-)-epigallocutechin-3-gallate; AA, amino acid; EMSA, electrophoretic mobility shift assay; ChIP, chromatin immunoprecipitation; LC-MS/MS, liquid chromatography-mass spectrometry/mass spectrometry; SAM, S-adenosyl-methionine; MTS, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt; NF-κB, nuclear factor κB; RG-108, b2-(1,3-(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)-3-yl) propanoic acid; MG-98, 5′-UAG CAC CAU UUG AAA UCA GU-3′.
- Received October 24, 2008.
- Accepted February 4, 2009.
- The American Society for Pharmacology and Experimental Therapeutics
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