ABSTRACT
BACKGROUND: Recently, inorganic arsenic trioxide (As2O3) was reported to induce complete remission in a high proportion of patients with refractory acute promyelocytic leukemia (APL). To illustrate cellular and molecular mechanisms of As2O3 in the treatment of APL, many experimental studies were performed on APL-derived cell lines in vitro. Previous studies showed that As2O3 inhibited proliferation and induced apoptosis in the APL-derived cell lines. This study was done to clarify the in vitro mechanisms of As2O3-induced apoptosis in APL-derived NB4 cell lines. METHODS: To determine the effects of As2O3 in the various concentrations, NB4 cells were cultured with 0.1 to 2micro M/L of As2O3. To assay the apoptosis in NB4 cell lines, DNA fragmentation assay and TUNEL were performed. To find out the molecular change of As2O3- induced apoptotic NB4 cell lines, RT-PCR and Western blot analysis for PML-RARalpha chimeric protein expression and flow cytometry for bcl- 2/bax expression were performed. To clarify the caspase activation pathway, Western blot analysis and flow cytometry for procaspase expression were performed. RESULTS: As2O3 induces apoptosis on NB4 cells in relatively high concentration (0.5 to 2 micro M/L) for 2 days. After 2 days of culture the PML-RARalpha chimeric protein expression decreased rapidly by Western blot and RT-PCR analysis and bcl-2 expression also decreased by flow cytometry. The expression of bax by flow cytometry showed a marked increase in high concentration (2micro M/L) but there was no change in low concentration (0.5micro M/L). In the Western blot analysis, the amount of pro`enzyme of caspase-3 was significantly decreased in the cells with high concentration (2micro M/L) compared with that in the cells with low concentration (0.5micro M/L). As2O3 induces proteolytic processing of pro-caspase 7 but not pro-caspase 9 and 8. CONCLUSION: Apoptosis of APL-derived NB4 cell lines was induced by As2O3 and progressed rapidly in higher concentrations. During apoptosis, activation of caspase-7 pathway and degradation of PML-RARalpha chimeric protein, decrease in bcl-2 and increase in bax were shown.
