Studies On The Mechanisms Of Sodium Selenite-Induced Apoptosis In Human Promyelocytic Leukemia-Derived NB4 Cells

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia, which is characterized by a specific chromosome translocation t(15;17) and the expression of PML-RAR α fusion protein. Chinese scientists had first introduced all-trans retinoic acid (ATRA) and arsenic trioxide to achieve clinical complete remission (CR) in APL patients via mechanisms of inducing differentiation and apoptosis, respectively. These have been considered as the milestones in the treatment of cancer. However, both drugs have some limitations. Therefore, great efforts have been continuously put into developing new therapeutic agents for APL patients, especially for those who relapsed or became refractory to treatment. Recently, it has been shown that both the content of intracellular reduced glutathione and the levels of some antioxidant enzymes are relatively low in APL-derived NB4 cells. Moreover, data from the same group also suggested that arsenic trioxide might trigger apoptosis in NB4 cells by generation of reactive oxidative species (ROS). In this study, we will verify whether sodium selenite, another inorganic compound with the ability causing oxidative stress, could induce apoptosis or differentiation in NB4 cells. We will also investigate the possible cellular and molecular mechanisms underlying its action, and how this would be influenced by ATRA. In addition, we will see if there is any difference between sodium selenite and arsenic trioxide in their apoptosis-inducing activities as well as in their inhibitory effects on CFU-GM formation of normal hematopoietic progenitors.Methods and Results:1. Sodium selenite was found able to inhibit the proliferation and survival of NB4 cells by Trypan Blue staining and MTT assay. Apoptosis was demonstrated both morphologically by Giemsa staining and by electrophoresis revealing a DNA ladder pattern. Flow cytometry (FCM) assay using TdT-end labeling and PI DNA staining also evidenced DNA fragmentation. The possibility of cell differentiation induced by sodium selenite was addressed using FCM analysis of a differentiation antigen CD11b, however, no increase of CD11b expression was detected, using...