Abstract
Activation of BCR::ABL1 tyrosine kinase is the main pathogenic mechanism underlying chronic myeloid leukemia (CML) in 90% of affected patients. The prognosis for individuals with CML who receive treatment with BCR::ABL1 tyrosine kinase inhibitors (TKIs) such as imatinib, is promising, with a 5-year survival rate of >90%. However, unfortunately, 20-30% of patients who are treated with imatinib may become resistant to the BCR::ABL1 TKIs. The objective of the present study was to determine whether inhibitors of E3 ubiquitin-protein ligase Mdm2 (MDM2), a regulator of p53 that promotes apoptosis and is highly expressed in CML, could induce cell death in imatinib-resistant CML cells. Apoptosis and cell viability were evaluated using Annexin-V-positive cell count and caspase-3 activity, as well as trypan blue dye exclusion assay. Expression levels of MDM2, p53, Bax, Puma, Noxa, p21, and cleaved caspase-3 were determined via western blotting. MDM2 levels in both the cytoplasm and nucleus were found to be ~3-fold higher in K562/IR cells compared with K562 cells, while the levels of p53 in both cell structures were markedly lower. In addition, an examination of a publicly accessible database revealed that the levels of MDM2 were evidently greater in patients who did not respond to imatinib compared with those who did respond to the drug. NSC-66811 and Nutlin-3, MDM2 inhibitors, increased the percentage of Annexin-positive cells in K562/IR cells by 43 and 62% at concentrations of 10 and 25 µM, respectively. Furthermore, the MDM2 inhibitors increased the levels of Bax, Puma, Noxa, and p21 by increasing the expression of p53 and decreasing the expression of MDM2 in K562/IR cells. Additionally, pifithrin-α, a p53 inhibitor, suppressed MDM2 inhibitor-induced cell death in K562/IR cells. Overall, the findings of the present study highlight the therapeutic potential of MDM2 inhibitors for imatinib-resistant CML.