Antitumor effect of arsenic trioxide in human K562 and K562/ADM cells by autophagy

Abstract

Arsenic trioxide (As₂O₃) has been reported to have potent antitumor effects in vitro and in vivo by inducing cell death via cell cycle arrest and apoptosis in leukemia cells, but the mechanisms of As₂O₃-mediated cell death are not fully understood. In this study, we provided in vitro evidence that As₂O₃ was a potent inducer of autophagy in leukemia K562 and its drug-resistant line K562/ADM cells. As₂O₃ significantly activated autophagic cell death (programmed cell death type II) in leukemia cell lines. Numerous large cytoplasmic inclusions, abundant autophagic vacuoles, phagocytizing cytoplasm and organelles were observed in As₂O₃-treated cells using electron microscope. MDC-labeled autophagic vacuoles were observed by fluorescent inverted phase contrast microscopy and the enhanced MDC fluorescent staining was detected by flow cytometry in As₂O₃-treated cells. Furthermore, real-time quantitative RT-PCR revealed that the expression levels of Beclin-1 and LC3 genes, which play key roles in autophagy, increased in As₂O₃ treated samples than in controls, indicating that autophagy can potentially be involved in the antitumor properties of As₂O₃. The expression level of Bcl-2 gene, an anti-apoptotic molecule, decreased in As₂O₃ treated samples than in controls, suggesting that Bcl-2 may be involved in accumulating Beclin-1 and triggering autophagic cell death in As₂O₃-treated leukemia cells. Western blotting also showed that As₂O₃ up-regulated Beclin-1. Altogether, our data provide direct evidence that autophagic cell death is critical for the effects of As₂O₃ on acute myelogenous leukemia cells.

Keywords::

• Arsenic trioxide
• autophagy
• acute myelogenous leukemia