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 downregulation of Bcl-2 expression and modulation of PML-RAR alpha/PML proteins

Abstract

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 the possible cellular and molecular mechanisms of this treatment by using NB4 cells as a model. The results show that: (1) As2O3 triggers relatively specific NB4 cell apoptosis at micromolar concentration, as proved by morphology, histogramic related nuclear DNA contents, and DNA gel eletrophoresis. (2) As2O3 does not influence bax, bcl-x, c-myc, and p53 gene expression, but downregulates bcl-2 gene expression at both mRNA and protein levels. (3) As2O3 induces a significant modulation of the PML staining pattern in NB4 cells and HL-60 cells. The micropunctates characteristic of PML-RAR alpha in NB4 cells dissappear after treatment with As2O3, whereas a diffuse PML staining occurs in the perinuclear cytoplasmic region. In addition, a low percentage of untreated NB4 cells exhibits an accumulation of PML positive particles in a compartment of cytoplasm. The percentage of these cells can be significantly 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 be one of the mechanisms of the therapeutic effect of As2O3. Moreover, this apoptosis induction occurs independently of the retinoid pathway and may be mediated, at least partly, through the modulation of bcl-2, as well as PML-RAR alpha and/ or PML proteins.

Establishment and characterization of an arsenic‐sensitive monoblastic leukaemia cell line (SigM5)

“…The addition of As 2 O 3 to cultured cells in concentrations similar to plasma levels achieved in APL patients (Chen et al, 1997) triggers apoptotic cell death of SigM5 within 24 h (see Fig 5). As 2 O 3 has been reported to be ineffective in the monoblastic cell line U937 (Chen et al, 1996), and in our hands also HL-60 cells were totally unresponsive to treatment with As 2 O 3 . B-cell chronic lymphocytic leukaemia (B-CLL) lines have been described to undergo apoptosis upon treatment with an organic arsenic, but not with As 2 O 3 (Ko Ènig et al, 1997).…”

“…We show that SigM5 retained many of the characteristics of monocytes±macrophages, although the cells are representative of an early stage of monocytic differentiation. Furthermore, we provide evidence that, in contrast to U937 (Chen et al, 1996) and HL-60 cells, As 2 O 3 induces apoptosis in SigM5 cells, a finding that implicates potential novel strategies for future treatment of a subset of monoblastic leukaemias.…”

“…Thus, the difficulties in determining the differentiation stage of cultured monoblastic cells can be easily understood (Ziegler-Heitbrock et al, 1988;Abrink et al, 1994). Recently, it has been shown that inorganic arsenic trioxide (As 2 O 3 ) induces apoptosis in the acute promyelocytic leukaemia (APL; FAB M3) cell line NB 4 , offering an explanation for the therapeutic effect of As 2 O 3 observed in the treatment of APL (Chen et al, 1996(Chen et al, , 1997. More recently, studies in B-cell chronic lymphocytic leukaemia lines (B-CLL) revealed that an organic arsenical drug promoted programmed cell death associated with down-regulation of bcl-2 protein expression (Ko Ènig et al, 1997).…”

Histone deacetylase inhibitor but not arsenic trioxide differentiates acute promyelocytic leukaemia cells with t(11;17) in combination with all‐trans retinoic acid

“…Treatment with arsenic trioxide (As 2 O 3 ) also can achieve clinical remission in APL patients with t(15;17), and induces apoptosis of the APL cells in vitro (Chen et al, 1996Shen et al, 1997;Soignet et al, 1998). Although As 2 O 3 as well as ATRA induces the degradation of PML-RARa, the effectiveness of As 2 O 3 on ATRA-resistant APL suggests that As 2 O 3 acts on APL cells through a different pathway from ATRA (Kitamura et al, 1997a;Shen et al, 1997;Gianni et al, 1998;Soignet et al, 1998).…”

Current Situation and Perspectives of Clinical Study in Integrative Medicine in China

“…The mechanism of arsenous acid treating APL was illustrated from the perspective of molecular oncology, including degradation of PML/RARa fusion proteins, downregulating gene expression of Bcl2 and inducing apoptosis in leukemia cells. Arsenous acid became the first antileukemia drug of inducing apoptosis in the world arousing the medical research fever of arsenic trioxide [27][28][29]. It was honored as "ancient remedy performs new tricks" in 1996 by Science [30].…”