The optimal dose of arsenic trioxide induced opposite efficacy in autophagy between K562 cells and their initiating cells to eradicate human myelogenous leukemia

Arsenic trioxide (As2O3), a main component of arsenolite which is a common traditional Chinese medicine (TCM) wildly used as a therapeutic agent for more than 2400 years in china, has been accepted as a standard treatment for the patients with acute promyelocytic leukemia (APL) based on the principle in TCM of “using a poison to fight against other poisons or malignancy illnesses”. However, it remains unknown that which mechanism is actually responsible for the therapeutic effects against these blood malignancies.The purpose of this study was to explore the actual mechanism that ATO exerts its effects in K562 cells and their initiating cells (K562s).K562s cells were separated and enriched for CD34+/CD38- cells using magnetic microbeads. Cell proliferation was determined by incorporation of BrdU. Cell apoptosis was evaluated by Annexin-V binding and PI uptake. Autophagy was estimated by acridine orange and immunofluorescence staining of LC3-B and p62. MC colonic formation was used to examine cell self-renew. ROS generation inside living cells was measured by DCFH-DA. Cell differentiation was assessed by the benzidine staining. The SA-β-gal assay was used to detect cell senescence. Protein expression was examined by western blotting and immunohistochemical staining.K562s cells were stronger in self-renew and resistance to ATO cytotoxicity and starvation-induced apoptosis than K562 cells. Unexpectedly, we found that ATO at a dose of 0.5μM which had no effect on cell proliferation resulted in maximum suppression on self-renew in both cells and maximum starvation-induced apoptosis in K562s cells but minimum starvation-induced apoptosis in K562 cells. Next, we found that ATO no more than 0.5μM selectively induced K562s cell differentiation indicated by benzidine staining, γ-globin and CD235a expression. More importantly, we found that ATO no more than 0.5μM led to opposite efficacy in autophagy between K562 and K562s cells, and the opposite autophagy could induced late-phase senescence in both cells. Finally, we used the optimal dose of ATO to eradicate leukemia cells and obtained a satisfied therapeutic outcomes in vivo.Our results suggest that the used dose of ATO may determine the fate of cell differentiation senescence or malignant transformation, and the optimal dose of ATO induced opposite efficacy in autophagy between K562 cells and their initiating cells and ultimately leads both cells to late-phase senescence.