Combined inhibition of DNA methyltransferase and histone deacetylase restores caspase-8 expression and sensitizes SCLC cells to TRAIL

• Published in: Carcinogenesis (New York) 2011-10, Vol.32 (10), p.1450-1458
• Main Authors: Kaminskyy, Vitaliy O., Surova, Olga V., Vaculova, Alena, Zhivotovsky, Boris
• Format: Article
• Language: English
• Subjects: 5-aza-2'-deoxycytidine; Azacitidine - analogs & derivatives; Azacitidine - pharmacology; Biological and medical sciences; Blotting, Western; Carcinogenesis, carcinogens and anticarcinogens; Caspase 8 - genetics; Caspase 8 - metabolism; Decitabine; DNA (Cytosine-5-)-Methyltransferase 1; DNA (Cytosine-5-)-Methyltransferases - antagonists & inhibitors; DNA (Cytosine-5-)-Methyltransferases - genetics; DNA (Cytosine-5-)-Methyltransferases - metabolism; DNA Methyltransferase 3A; DNA Methyltransferase 3B; Enzyme Inhibitors - pharmacology; Fluorescent Antibody Technique; Histone Deacetylases - chemistry; Histone Deacetylases - genetics; Histone Deacetylases - metabolism; Humans; Inhibitor of Apoptosis Proteins - genetics; Inhibitor of Apoptosis Proteins - metabolism; Lung Neoplasms - enzymology; Lung Neoplasms - pathology; Lung Neoplasms - prevention & control; Medical sciences; Membrane Potential, Mitochondrial - drug effects; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; Small Cell Lung Carcinoma - enzymology; Small Cell Lung Carcinoma - pathology; Small Cell Lung Carcinoma - prevention & control; Survivin; TNF-Related Apoptosis-Inducing Ligand - genetics; TNF-Related Apoptosis-Inducing Ligand - metabolism; Tumor Cells, Cultured; Tumors; Valproic Acid - pharmacology
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgr135

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.