Blocking EZH2 methylation transferase activity by GSK126 decreases stem cell-like myeloma cells.

Delong Zeng,Jingxuan Pan,Maoxing Liu

doi:10.18632/oncotarget.13773

Abstract

EZH2 is a critical epigenetic regulator that is deregulated in various types of cancers including multiple myeloma (MM). In the present study, we hypothesized that targeting EZH2 might induce apoptosis in myeloma cells including stem cell-like cells (CSCs). We investigated the effect of EZH2 inhibition on MM cells using a potent inhibitor (GSK126). The results showed that GSK126 effectively abrogated the methylated histone 3 (H3K27me3) level in MM.1S and LP1 cells, and inhibited the number of live cells and colony formation in soft agar of six MM cell lines. GSK126 induced massive apoptosis in MM.1S, LP1 and RPMI8226 cells. Progressive release of mitochondrial cytochrome c and AIF into the cytosol was detected in GSK126-treated MM cells. GSK126 treatment elicited caspase-3-dependent MCL-1 cleavage with accumulation of proapoptotic truncated MCL-1. These results suggested that GSK126 triggers the intrinsic mitochondrial apoptosis pathway. Enhanced apoptosis was observed in the combination of GSK126 with bortezomib. Using ALDH and side population (SP) assays to characterize CSCs, we found that GSK126 eliminated the stem-like myeloma cells by blocking the Wnt/β-catenin pathway. The in vivo anti-tumor effect of GSK126 was confirmed by using RPMI8226 cells in a xenograft mouse model. In conclusion, our findings suggest that EZH2 inactivation by GSK126 is effective in killing MM cells and CSCs as a single agent or in combination with bortezomib. Clinical trial of GSK126 in patients with MM may be warranted.

Highlights

Multiple myeloma (MM) is a hematological malignancy that originates from long-lived terminally differentiated B cells or plasma cells (PCs) in lymph nodes which are usually colonized in bone marrow (BM) during the disease progression
enhancer of zeste homolog 2 (EZH2) expression has been reported to be absent in normal BM plasma cells, whereas it was increased in MM cells and correlative with tumor burden during the disease progression [17, 21], hinting a role of EZH2 during the tumorigenesis and progression of MM
The cell viability assayed in 6 lines of MM cells exposed to escalating concentrations of GSK126 for 72 h revealed that GSK126 potently inhibited the growth of all tested cell lines, with IC50 values ranging from 12.6 μM to 17.4 μM (Figure 2A), suggesting that the methyltransferase activity of EZH2 may be required for the viability of MM cells and that blocking EZH2 suppressed their viability

Summary

Introduction

Multiple myeloma (MM) is a hematological malignancy that originates from long-lived terminally differentiated B cells or plasma cells (PCs) in lymph nodes which are usually colonized in bone marrow (BM) during the disease progression. Significant progress has been made in the treatment of MM in recent years, increasing the median survival from 3 years to 6 years [1], the disease relapse occurs in most MM patients [2, 3], who display losing response to clinically available agents. The failure of current therapies indicates the existence of a subset of drug-resistant cells which survives during the treatment and replenishes the tumor. Cancer stem-like cells (CSCs) have been suggested in various types of cancers including MM, to be the subset of tumor cells that exhibits features of drugresistance, self-renewal and tumor-initiating.

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Results

Conclusion