IN-VITRO STUDIES ON CELLULAR AND MOLECULAR MECHANISMS OF ARSENIC TRIOXIDE (AS2O3) IN THE TREATMENT OF ACUTE PROMYELOCYTIC LEUKEMIA - AS2O3 INDUCES NB4 CELL APOPTOSIS WITH DOWN-REGULATION OF BCL-2 EXPRESSION AND MODULATION OF PML-RAR-ALPHA PML PROTEINS/

It has been shown recently in China that arsenic trioxide (As2O3) is a very effective treatment for acute promyelocytic leukemia (APL). APL patients resistant to all-trans retinoic acid (ATRA) and conventional chemotherapy can still respond to As2O3. In this study, we addressed t he possible cellular and molecular mechanisms of this treatment by usi ng NB4 cells as a model. The results show that: (1) As2O3 triggers rel atively specific NB4 cell apoptosis at micromolar concentration, as pr oved by morphology, histogramic related nuclear DNA contents, and DNA gel eletrophoresis. (2) As2O3 does not influence bar, bcl-x, c-myc, an d p53 gene expression, but downregulates bcl-2 gene expression at both mRNA and protein levels. (3) As2O3 induces a significant modulation o f the PML staining pattern in NE, cells and HL-60 cells. The micropunc tates characteristic of PML-RAR alpha in NB4 cells dissappear after tr eatment with As2O3, whereas a diffuse PML staining occurs in the perin uclear cytoplasmic region. In addition, a low percentage of untreated NB4 cells exhibits an accumulation of PML positive particles in a comp artment of cytoplasm. The percentage of these cells can be significant ly increased after As2O3 treatment. A similar PML staining pattern is observed in apoptotic cells. (4) ATRA pretreatment does not influence As2O3-induced apoptosis. These results suggest that induction of cell apoptosis can he one of the mechanisms of the therapeutic effect of As 2O3. Moreover, this apoptosis induction occurs independently of the re tinoid pathway and may be mediated, at least partly, through the modul ation of bcl-2, as well as PML-RAR alpha and/or PML proteins. (C) 1996 by The American Society of Hematology.