Integrity of zinc finger motifs in PML protein is necessary for inducing its degradation by antimony.

Antimony (Sb) belongs to the same group as arsenic (As) in the periodic table, and both share similar characteristics. However, Sb2O3 (SbIII) has no methylation capacity, unlike arsenic trioxide (As2O3). In the present study, we determined the effect of SbIII on NB4 cells and found that antimony could induce PML-RARα fusion protein degradation, reorganization of PML-NBs, and NB4 cell differentiation with low cytotoxicity. On the other hand, zinc finger motifs in PML protein are considered to be a key target binding site for arsenic-induced PML-RARα protein degradation. Interestingly, antimony and arsenic lost their ability to degrade PML-RARα fusion protein in NB4 cells following pretreatment with phenanthroline (i.e., chelator of zinc ions), indicating that the integrity of zinc finger motifs in PML-RARα fusion protein is a fundamental condition for inducing the protein's degradation by antimony and arsenic. Moreover, we found that SbIII could not induce mutant PML (e.g., A126V and L218P) solubility change and degradation, similar to As2O3. In contrast, we found that the organic antimony compound phenylstibine oxide (PSO) could induce mutant PML protein degradation. In conclusion, our results indicate that SbIII might also be a promising agent to treat acute promyelocytic leukemia, in the same manner as As2O3.

Phenylarsine Oxide Can Induce the Arsenite-Resistance Mutant PML Protein Solubility Changes.

Arsenic trioxide (As2O3) has recently become one of the most effective drugs for treatment of patient with acute promyelocytic leukemia (APL), and its molecular mechanism has also been largely investigated. However, it has been reported that As2O3 resistant patients are frequently found in relapsed APL after consolidation therapy, which is due to the point mutations in B-box type 2 motifs of promyelocytic leukemia (PML) gene. In the present study, we for the first time establish whether organic arsenic species phenylarsine oxide (PAO) could induce the mutant PML-IV (A216V) protein solubility changes and degradation. Here, three different PML protein variants (i.e., PML-IV, PML-V and mutant PML-A216V) were overexpressed in HEK293T cells and then exposed to PAO in time- and dose-dependent manners. Interestingly, PAO is found to have potential effect on induction of mutant PML-IV (A216V) protein solubility changes and degradation, but no appreciable effects were found following exposure to high concentrations of iAsIII, dimethylarsinous acid (DMAIII) and adriamycin (doxorubicin), even though they cause cell death. Our current data strongly indicate that PAO has good effects on the mutant PML protein solubility changes, and it may be helpful for improving the therapeutic strategies for arsenic-resistant APL treatments in the near future.

Effect of arsenic compounds on the in vitro differentiation of mouse embryonic stem cells into cardiomyocytes.

Arsenic is a known carcinogen; however, there is no information on the toxic effects of inorganic arsenic and its intermediate metabolites, monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), during the differentiation of embryonic stem (ES) cells into cardiomyocytes. The objective of this study was to evaluate the effects of arsenic compounds on ES cell differentiation into cardiomyocytes in vitro and to predict the associated toxic effects. Although iAs(III) is known to be toxic, here we found that iAs(III) and DMA(III) did not influence ES cellular differentiation, whereas MMA(III) inhibited ES cell differentiation into cardiomyocytes, suggesting that MMA(III) has adverse effects on embryonic stem cells.