Induction of apoptosis in K562 human leukemia cells by 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone

2′,4′-Dihydroxy-6′-methoxy-3′,5′-dimethylchalcone (DMC), isolated from the buds of Cleistocalyx operculatus, was investigated in its cytotoxicity and anti-proliferation on K562 cell line. Our results revealed that the IC50 was equal to 14.2±0.45μM and the EC50 was 3.3±0.14μM. Staining with Hoechst 33258 showed fragmentation and condensation of chromatin in the cells treated with 8μM DMC for 48h. Flow cytometric analysis was performed to determine hypodiploid cells. The results of flow cytometry assay indicated that the percentage of hypodiploid K562 cells was 76.15±3.22% after 48h treatment with 16.0μM DMC. The treatment resulted in the appearance of a hypodiploid peak (A0 region), probably due to the presence of apoptosing cells and/or apoptotic bodies with DNA content less than 2n. Western blot results illustrated that in the same dosage and incubation time, DMC could down-regulate the level of Bcl-2 protein and did not influence the expression of Bax protein. The resulting net effect could thus lead to a lower ratio of Bcl-2/Bax, which might be responsible for the DMC-induced apoptosis in K562 cells.