Apoptosis Inducing Novel Anti-Leukemic Agent, Bis(4,7-Dimethyl-1,10 Phenanthroline) Sulfatooxovanadium(IV)[VO(SO₄)(Me₂-Phen)₂] Depolarizes Mitochondrial Membranes

Abstract

Bis(4,7-dimethyl-1,10 phenanthroline) sulfatooxovanadium(IV) [VO(SO₄)(Me₂-Phen)₂] induces apoptosis in human NALM-6 leukemia cells. In the present report, we demonstrate that VO(SO₄)(Me₂-Phen)2-induced apoptosis is mediated through the generation of reactive oxygen species (ROS), depletion of glutathione and depolarization of mitochondrial membrane potential (Δ±m). Using multilaser flow cytometry methods, we further mapped out the death sequence that occurs in VO(SO₄)(Me₂-Phen)2-treated leukemic cells. Triple labeling method to measure ROS, Δ±m and glutathione coupled with multilaser excitation flow cytometry showed that induction of ROS took place before the loss of mitochondrial permeability transition and depletion of glutathione. Correlated two parameter plots of glutathione content versus Δ±m showed that loss of Δ±m and depletion of glutathione closely follows each other. Translocation of phosphatidylserine to the outer leaflet of the cell membrane was the final step in the process before the cells became apoptotic. These results demonstrate that the mitochondrial permeability transition takes place during VO(SO₄)(Me₂-Phen)₂-induced apoptosis and is mediated through induction of ROS and depletion of glutathione.

Key Words:

• oxovanadium
• apoptosis
• mitochondrial membrane transition
• reactive oxygen species
• glutathione