Isochamaejasmin induces apoptosis in leukemia cells through inhibiting Bcl-2 family proteins

The biflavonoid isochamaejasmin is mainly distributed in the root of Stellera chamaejasme L. (Thymelaeaceae) that is used in traditional Chinese medicine (TCM) to treat tumors, tuberculosis, and psoriasis. Herein, isochamaejasmin was found to show similar bioactivity against Bcl-2 family proteins to the reference Bcl-2 ligand (-)-gossypol through 3D similarity search. It selectively bound to Bcl-x_l and Mcl-1 with K_i values being 1.93 ± 0.13 μmol·L^-1 and 9.98 ± 0.21 μmol·L^-1, respectively. In addition, isochamaejasmin showed slight growth inhibitory activity against HL-60 with IC₅₀ value being 50.40 ± 1.21 μmol·L^-1 and moderate growth inhibitory activity against K562 cells with IC₅₀ value being 24.51 ± 1.62 μmol·L^-1. Furthermore, isochamaejasmin induced apoptosis of K562 cells by increasing the intracellular expression levels of proteins of the cleavage of caspase-9, caspase-3, and PARP which involved in the Bcl-2-induced apoptosis pathway. These results indicated that isochamaejasmin induces apoptosis in leukemia cells by inhibiting the activity of Bcl-2 family proteins, providing evidence for further studying the underlying anti-cancer mechanism of S. chamaejasme L.