Phenylhexyl isothiocyanate has dual function as histone deacetylase inhibitor and hypomethylating agent and can inhibit myeloma cell growth by targeting critical pathways

Abstract

Histone deacetylase (HDAC) inhibitors are a new class of chemotherapeutic agents. Our laboratory has recently reported that phenylhexyl isothiocyanate (PHI), a synthetic isothiocyanate, is an inhibitor of HDAC. In this study we examined whether PHI is a hypomethylating agent and its effects on myeloma cells. RPMI8226, a myeloma cell line, was treated with PHI. PHI inhibited the proliferation of the myeloma cells and induced apoptosis in a concentration as low as 0.5 μM. Cell proliferation was reduced to 50% of control with PHI concentration of 0.5 μM. Cell cycle analysis revealed that PHI caused G1-phase arrest of RPMI8226 cells. PHI induced p16 hypomethylation in a concentration-dependent manner. PHI was further shown to induce histone H3 hyperacetylation in a concentration-dependent manner. It was also demonstrated that PHI inhibited IL-6 receptor expression and VEGF production in the RPMI8226 cells, and reactivated p21 expression. It was found that PHI induced apoptosis through disruption of mitochondrial membrane potential. For the first time we show that PHI can induce both p16 hypomethylation and histone H3 hyperacetylation. We conclude that PHI has dual epigenetic effects on p16 hypomethylation and histone hyperacetylation in myeloma cells and targets several critical processes of myeloma proliferation.

Antiproliferative effects of γ-secretase inhibitor, a Notch signalling inhibitor, in multiple myeloma cells and its molecular mechanism of action

“…19 Cells were treated with GSI at concentrations of 0, 10, 20 and 40 mmol/l for 48 h, or with GSI at a concentration of 10 mmol/l for 24, 48 or 72 h. Cells were then lysed in buffer (pH 7.0) containing freshly prepared protease inhibitors. The protein concentration of the cell lysates was determined using the BioRad Protein Assay kit (Bio-Rad Laboratories, Hercules, CA, USA) with a bovine serum albumin standard.…”

“…Cell-cycle analysis was performed using a BD FACScan TM flow cytometer (Becton, Dickinson and Company, Franklin Lakes, NJ, USA) as described previously. 19 The cells were stained with propidium iodide solution (50 mg/ml) on ice and !10 000 cells were analysed for cell-cycle distribution.…”

Bone marrow stromal cells enhance the survival of chronic lymphocytic leukemia cells by regulating HES‑1 gene expression and H3K27me3 demethylation

“…In general, hypermethylation frequently targets genes already silenced in non-tumor cells by repressive histone modifications such as H3K27me3 (28). Thus, although certain tumor-suppressor genes become de novo methylated and silenced in cancer, hypermethylation affects mostly genes already silenced in normal cells (28,29). The H3K27me3 methylation mark is associated with chromatin condensation and transcriptional repression (16).…”

Epigenetic and antioxidant effects of dietary isothiocyanates and selenium: potential implications for cancer chemoprevention

“…Although the growing interest in the epigenetic regulation mediated by ITC has focused mainly on its HDAC inhibitory activity, their potential chemopreventive mechanisms involving DNA methylation mechanisms remain relatively unknown. Studies carried out in a human myeloma cell line have found that phenylhexyl ITC induced histone H3 hyperacetylation and demethylation of the aberrantly methylated p16 promoter in a concentration-dependent manner, suggesting that phenylhexyl ITC has dual epigenetic modulating effects on both DNA methylation and chromatin (55) . Comparable results were obtained in prostate cancer cell lines, where phenethyl ITC inhibited the activity and level of histone deacetylases and promoted glutathione S-transferase pi 1 promoter demethylation (dual action) (56) .…”