Transferrin receptor-dependent cytotoxicity of artemisinin–transferrin conjugates on prostate cancer cells and induction of apoptosis

Artemisinin, a natural product isolated from Artemisia annua, contains an endoperoxide group that can be activated by intracellular iron to generate toxic radical species. Cancer cells over-express transferrin receptors (TfR) for iron uptake while most normal cells express nearly undetectable levels of TfR. We prepared a series of artemisinin-tagged transferrins (ART-Tf) where different numbers of artemisinin units are attached to the N-glycoside chains of transferrin (Tf). The Tf bearing ∼16 artemisinins retains the functionality of both Tf and artemisinin. Reduction of TfRs by TfR siRNA transfection significantly impaired the ability of ART-Tf, but not dihydroartemisinin, to kill cells. We also demonstrate that the ART-Tf conjugate kills the prostate carcinoma cell line DU 145 by the mitochondrial pathway of apoptosis.