[Effects of Emodin Derivative on Cell Cycle, Apoptosis and NF-κB Pathway in Burkitt Lymphoma Cells]

To investigate the effect and mechanism of a novel emodin derivative YX-18 on Burkitt lymphoma (BL) cells.

MTT assay was used to detect the effect of YX-18 on the proliferation of BL cell lines CA46 and Raji. Annexin V-PE/7-AAD double staining assay was used for detecting the effect of YX-18 on the apoptosis of CA46 and Raji cells. PI/RNase staining was used to test the effect of YX-18 on CA46 and Raji cell cycle. JC-1 method was used to measure the changes of mitochondrial membrane potential after YX-18 treatment, and DAPI staining was used to detect the morphology of apoptotic cells. Western blot was used to analyze the distribution changes of NF-κB pathway protein (P65, P-P65, IκB, P-IκB) in the cytoplasm and cell nucleus, and also the expression changes of cyclin-related protein P21, CDK2, P-CDK2, Cycling D1, Cycling E1, and the apoptosis-related protein Caspase-3, Caspase-8, Caspase-9 and the proliferation-related protein C-MYC, BCL-2 by YX-18. Real-time fluorescence-quantitative PCR was used to evaluate the effects of YX-18 on mRNA levels of C-MYC and Ki-67 genes in CA46 and Raji cells, and EBNA-1 and EBER genes of EBV in Raji (EBV⁺) cells.

Novel Emodin derivative YX-18 could effectively inhibit the proliferation of BL cell lines CA46 and Raji, showing a time-dependent effect (24, 48 and 72 h: r_CA46=0.89, 0.75, 0.75, r_Raji=0.87, 0.73, 0.64). IC₅₀ of CA46 cells and Raji cells treated with YX-18 for 24 h was 1.77±0.04 µmol/L and 1.97±0.22µmol/L, respectively. CA46 cells and Raji cells were treated with YX-18 at concentration of 2.0 and 4.0 µmol/L for 24 h. Compared with the control group, both strains of cells showed a very significant apoptosis at the concentration of 2.0 and 4.0 µmol/L (P<0.01), showing a concentration-dependent effect (r_CA46=0.99, r_Raji=0.92). Moreover, the cleavaged Caspase-3, 8 and 9 proteins were activated by YX-18 into verious degrees in both two cell lines. Both the two cell lines displayed by YX-18 cell cycle arrest at G0/G1 phase (P<0.01) after exposed to YX-18 for 24 hours at the concentration of 1.0, 2.0 µmol/L in CA46 cells and at 0.5 and 1 µmol/L in Raji cells, respectively. YX-18 decreased expression level of cyclin D1, cyclin E1, CDK2, p-cdk2 proteins and increased p21^Waf1/Cip1 level in CA46 and Raji cells. YX-18 significantly declined mitochondrial membrane potential in both cells at the concentration of 2.0 and 4.0 µmol/l (P<0.01) with concentration-dependent manner (r_CA46=-0.96, r_Raji=-0.99). Western blot tests indicated that YX-18 down-regulated nucleus P65 and intracellular cytoplasm P65, P-IκB, P-P65 protein, and upregulated intracellular IκB level with dose-dependent manner. Meanwhile, the expression level of the cell proliferation-related molecules C-MYC and BCL-2 was decreased significantly. YX-18 suppressed mRNA levels of C-MYC and Ki-67 in both cell lines, and EBNA-1 in EBV-positive Raji cells in a concentration-dependent way.

The novel emodin derivative YX-18 can significantly inhibit the proliferation of Burkitt lymphoma cells, and induce the cell apoptosis and cycle arrest. The inhibitory effect of YX-18 on the proliferation of Burkitt lymphoma cells may be related with the effect of Caspase apoptosis pathway, the proliferation and apoptosis-related molecules, such as C-MYC and Ki-67, and also to the inhibition of NF-κB pathway.