Epigenetics therapy an introductionR6

DefinitionEpigenetics: all meiotically and mitotically heritable changes in gene expression that are not coded in the DNA sequence itselfDNA methylationRNA associated silencingHistone modificationGenotype and phenotypeNature 2004;429:457-73

GenesChromatinHistonenonhistone chromosomal proteins NucleosomeChromosome

Initiation of DNA transcription

Methods to repress genesCompetitive DNA bindingMasking the activation surfaceDirect interaction with the general transcription factorsRecruitment of repressive chromatin remodeling complexRecruitment of histone deacetylases

Methods to repress genes

MethylationHistone modificationScaffold protein

Epigenetic diseasesNature 2004;429:457-73

DNA methylation

DNA methylationAt promoter, DNA methylation suppresses transcriptionWith deamination, DNA methylation induces C T mutationDNA methyltransferase

DNA methylation in cancerTumor suppressor genes?Nature Clin Pract Oncol 2005;2:S4-S11

Demethylation in cancer therapyNat Rev Drug Discov 2006;5:37-50

DNA methylation inhibitor, nucleoside analogues and non-nucleoside analoguesNat Rev Cancer 2006;5;37-50

Demetheylation effect of cytidine analogs in fibroblast cell linesazacytidinedecitabineCell 1980; 20:85-93DifferentiationMethylation

Demethylation agent for MDSRole of p15ink4bBlood 2002;100:2957-64Blood 2004;103:1635-40p15 protein

Azacitidine improve response rate* and time to leukemia transformation in MDS but not overall survivalTime to leukemia transformation or death P

Decitabine for MDSDecitabine improves quality of life, decreases RBC transfusion for MDSDecitabine didnt improve AML-free survival or overall survival(14.0vs 14.9mo, p= 0.636)Cancer 2006;106:1794-80

NPM-ALK and STAT5 methylationNat Med 2007;13:1341-8NPM-ALK kinase, t(2;5) in ALCLSuppression of STAT 5 in ALCL cell linesiRNA of NPM-ALK reactivate STAT5NPM-ALK transfection results in methlyation of STAT5 promoter inactivate STAT5

AML1/ETO and microRNA-223AML1/ETO = t(8;21) in AM2LLow level of miR-223 in AM2L t(8;21)AML1/ETO induces methylation of miR-223 promoterInhibition of AML1/ETO reverses miR-223 expressionAML1-ETO(+)AML1-ETO(-)Cancer cell 2007;12:457-66

Ras mediates methylation of unrelated genesNature 2007;449:1073-78The specificity of epigenetic change

Histone acetylation (HDAC)

Role of histone modificationDNA transcriptionDNA repairDNA replicationCell 2007;128:693-705

Histone modificationthe histone codeAcetylationMethylationPhosphorylationUbiquitylationsumoylationNature 2007;447:407-12

Nature 2007;447:407-12

Nat Rev Drug Disc 2006;5:769-84

HDAC inhibitorsNat Rev Cancer 2006;5;37-50

SAHA (vorinostat) in cutaneous T-cell lymphomaJCO 2007;25:3109-15

SAHA in ovarian cancerGynecologic Oncology 2008 online published

HDAC inhibitor suppress ER activity in estrogen dependent breast cancer cell lineCCR 2007;13:4882-90

trichostatin A sensitizes estrogen receptor -negative breast cancer cells to tamoxifenOncogene 2004;23:1724-36

HDAC inhibitor Trichostatin A inducesglobal and gene-specific DNA demethylationT24Biochem. Pharmacol 2007;73:1297-1307

Problems in epigenetics agents in cancer therapyDifferentiation or cytotoxic agents?Specificity and Selectivity of the treatment targets?Correction of epigenetic change and underlying gene mutaion?No survival benefit till now!!

Interchromosome regulation of genesNature 2007;447:413-7

Scaffold proteinSATB1More higher structure than chromatinPlay important role in T-cell developmentNat Genetics 2006;38:1229-30SATB1

SATB1 reprogrammes gene expression to promote breast tumour growth and metastasisNature 2008;452:187-193

SummaryNature 2007;447:433-40

SummaryMethylation and HDAC control of transcription through electric change or 3-D conformational change of chromatinControl the phenotypeApplication of cancer therapy?

Thank you for your attention

Decitabine induces ER gene expression in ER(-) breast cancer cell line(MDA-MB-231ELuc.6 cells)Cancer Res 1995;55:2279-83

HDAC inhibitor and azacitidine together induce ER expression in ER(-) breast cancer line (MDA MB-231)Cancer Res 2001;61:7025-29

Nature 2004;429:457-73

Cell 2007;128:655-68

Crosstalk between histone modificationProteins that associate preferentially with modified versions of histone H3 and histone H4.Cell 2007;128:693-705