title: Combined inhibition of DNA methyltransferase and histone deacetylase restores caspase-8 expression and sensitizes SCLC cells to TRAIL.
abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising drug for the treatment of tumors; however, a number of cancer cells are resistant to this cytokine. Among the mechanisms of resistance of small cell lung carcinomas (SCLCs) to TRAIL is the lack of caspase-8 expression. Although methylation of the caspase-8 promoter has been suggested as the main mechanism of caspase-8 silencing, we showed that reduction of the enzymes involved in DNA methylation, DNA methyltransferases (DNMT) 1, 3a and 3b, was not sufficient to significantly restore caspase-8 expression in SCLC cells, signifying that other mechanisms are involved in caspase-8 silencing. We found that combination of the DNMT inhibitor decitabine with an inhibitor of histone deacetylase (HDAC) significantly increased caspase-8 expression in SCLC cells at the RNA and protein levels. Among all studied HDAC inhibitors, valproic acid (VPA) and CI-994 showed prolonged effects on histone acetylation, while combination with decitabine produced the most prominent effects on caspase-8 re-expression. Moreover, a significant reduction of survivin and cIAP-1 proteins level was observed after treatment with VPA. The combination of two drugs sensitized SCLC cells to TRAIL-induced apoptosis, involving mitochondrial apoptotic pathway and was accompanied by Bid cleavage, activation of Bax, and release of cytochrome c. Both initiator caspase-8 and -9 were required for the sensitization of SCLC cells to TRAIL. Thus, efficient restoration of caspase-8 expression in SCLC cells is achieved when a combination of DNMT and HDAC inhibitors is used, suggesting a combination of decitabine and VPA or CI-994 as a potential treatment for sensitization of SCLC cells lacking caspase-8 to TRAIL.
authors.affiliation: Division of Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Vitaliy O
authors.initials: VO
authors.lastname: Kaminskyy
authors.forename: Olga V
authors.initials: OV
authors.lastname: Surova
authors.forename: Alena
authors.initials: A
authors.lastname: Vaculova
authors.forename: Boris
authors.initials: B
authors.lastname: Zhivotovsky
mesh_terms: D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D015153:Blotting, Western; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D000090205:DNA Methyltransferase 3A; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D006655:Histone Deacetylases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055752:Small Cell Lung Carcinoma / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014635:Valproic Acid / Q000494:pharmacology; D000097584:DNA Methyltransferase 3B
chemical_list: D001374:Azacitidine; D053181:Caspase 8; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D000077209:Decitabine; D004791:Enzyme Inhibitors; D006655:Histone Deacetylases; D051034:Inhibitor of Apoptosis Proteins; D012333:RNA, Messenger; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand; D014635:Valproic Acid; D000097584:DNA Methyltransferase 3B; C107489:BIRC5 protein, human; C000717967:DNMT3A protein, human; C505653:TNFSF10 protein, human