Richter syndrome (RS) is a rare disease of the lymphohematopoietic system. It is defined as the transformation of a low-grade malignant lymphoproliferative disorder into a more aggressive lymphoproliferative disorder, most commonly, diffuse large B-cell lymphoma (DLBCL). The disease is rare in the clinic and has nonspecific clinical manifestations. An excisional lymph node biopsy is considered the gold standard for diagnosis of RS; 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) can help inform the optimal site for biopsy. The main treatment strategies are chemotherapy, hematopoietic stem cell transplantation (HSCT), participating in a clinical trial of a new medicine, and others, but the overall prognosis is poor. At present, there is no sufficient treatment for the disease. In order to improve the awareness of disease and identify it among a variety of similar diseases, while aiming to discuss treatment strategies, this article reviewed RS in terms of the risk factors, clinical manifestations, diagnosis, treatment, and prognosis.

Objective:To investigate the effects of histone deacetylase inhibitor Chidamide (CS055) and DNA methyltransferase inhibitor decitabine (DAC) on proliferation and apoptosis of acute myeloid leukemia cell line U937 and its possible mechanism.Methods:U937 cells were cultured in vitro and treated with CS055 (CS055 single drug group), DAC (DAC single drug group), combination (combined drug group)and a negative control group. Methyl thiazolyl tetrazolium (MTT) assay was used to detect the proliferation inhibition rate. The apoptosis rate was detected by flow cytometry.The mRNA expression of DNA methyltransferase 1 (DNMT1) was analyzed by real-time fluorescence quantitative polymerase chain reaction (qRT-PCR). Western blot was used to analyze the expression of acetylated histone H3 and DNMT1. Results:The proliferation inhibition rate of U937 cells treated with CS055 and DAC increased significantly in a time-dose-dependent manner. The inhibitory effect of the combination group was more obvious than that of the single drug group. Flow cytometry showed that the 72 h apoptotic rates in the control group, 0.25 μ mol/L CS055 group and 2.5 μ mol/L DAC group were (0.67±0.12)%, (23.43±0.50)%, (8.47±0.32)%, (32.73±0.42)%. The apoptotic rate was significantly increased in the combination group compared with the single drug group. qRT-PCR showed that the expression of DNMT1 mRNA was down-regulated after CS055 and DAC treat alone; the down-regulating effect of the combination group was more significant. Western blot showed that the up-regulation of Ac-H3 and the decrease of DNMT1 in the combination group were significantly higher than those in the single drug group.Conclusions:The application of CS055 and DAC alone could inhibit the proliferation and induce apoptosis of U937 cells. The combination of the two drugs has obvious synergistic effect. The mechanism is that histone deacetylase inhibitors have demethylation effects, and demethylation drugs also have the effect of histone deacetylase inhibitors, which in combination increases demethylation and increases histone deacetylation.