ABSTRACT
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.
Subject(s)
Antimony/pharmacology , Oncogene Proteins, Fusion/metabolism , Promyelocytic Leukemia Protein/metabolism , Proteolysis/drug effects , Zinc Fingers/drug effects , Antineoplastic Agents/pharmacology , Cell Line, Tumor , Cell Survival/drug effects , Humans , Leukemia, Promyelocytic, Acute/drug therapy , Leukemia, Promyelocytic, Acute/metabolism , Oncogene Proteins, Fusion/chemistry , Promyelocytic Leukemia Protein/chemistryABSTRACT
Arsenic (+3 oxidation state) methyltransferase (AS3MT) is a key enzyme responsible for arsenic metabolism in humans, which facilitates conversion of arsenic trioxide (As2O3) to more reactive metabolites such as monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII). However, it is unclear whether the biotransformation of arsenic by AS3MT contributes to the promotion of acute promyelocytic leukemia (APL) therapy. In order to understand the probable role of AS3MT in APL patients, we evaluated the effects of arsenite (iAsIII) and three mixed arsenicals (i.e., iAsIII, MMAIII and DMAIII, to mimic active arsenic species in the blood) on NB4 cell differentiation and apoptosis. Although the mixed arsenicals exhibited about 2 fold less effect on the induction of NB4 cell differentiation and PML-RARα fusion protein degradation, they showed 5 times stronger ability to induce apoptosis when compared with iAsIII. More importantly, the proliferation of NB4 cells was significantly (p < 0.05) inhibited in a transwell system co-cultured with AS3MT-transfected HepG2 cells after exposure to iAsIII, suggesting that the generation of methylated metabolites restrained cell proliferation. These findings indicate that the therapeutic efficacy of As2O3 (i.e., iAsIII) in APL patients is probably associated with the production of methylated arsenic metabolites (i.e., MMAIII and DMAIII) by AS3MT.
Subject(s)
Antineoplastic Agents/pharmacology , Arsenic Trioxide/pharmacology , Arsenic/metabolism , Leukemia, Promyelocytic, Acute/drug therapy , Leukemia, Promyelocytic, Acute/enzymology , Methyltransferases/metabolism , Apoptosis , Arsenic/chemistry , Cell Differentiation , Cell Proliferation , Hep G2 Cells , Humans , In Vitro Techniques , Leukemia, Promyelocytic, Acute/pathology , Oncogene Proteins, Fusion/metabolism , Tumor Cells, CulturedABSTRACT
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.
