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.

Long noncoding RNA-HOTAIR affects chemoresistance by regulating HOXA1 methylation in small cell lung cancer cells

“…To further investigate whether aberrant methylation of HOXA1 is necessary in multidrug resistance, we knocked down HOXA1 in the context of 5-aza-CdR treatment, and the results showed that there is no significant difference between control groups and siHOXA1-5-Aza-CdR groups in H446AR cells upon CDDP and ADM treatment. In addition to caspase-8 reported by Kaminskyy et al, 23 our results suggested DNA methylation of HOXA1 was closely associated with chemoresistance of SCLC.…”

“…For example, DNA methylation of caspase-8 in SCLC cells resulted in resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). 23 We found that downregulation of HOXA1 gene affects SCLC cell survival and chemoresistance before. 16 In our study, BSP method showed hypermethylation status of HOXA1 CpG islands in the resistant cells as compared with the parental cells.…”

Reactivation of epigenetically silenced miR-512 and miR-373 sensitizes lung cancer cells to cisplatin and restricts tumor growth

“…5′aza is often used in combination with HDAC inhibitors such as Trichostatin A (TSA), to induce the re-expression of epigenetically silenced genes. 7 MicroRNAs (miRs) are small noncoding RNAs that inhibit protein expression by posttranscriptional inhibition. They are fundamental regulators of diverse cellular processes, whose deregulation contributes to many human diseases including cancer.…”

Sensitization of (colon) cancer cells to death receptor related therapies

“…Moreover, the combination of these two epigenetic drugs sensitized SCLC cells to TRAIL. 38 The most efficient combinatorial treatments are summarized in Table 3.…”