The MEK1/2 inhibitor U0126 reverses imatinib resistance through down-regulating activation of Lyn/ERK signaling pathway in imatinib-resistant K562R leukemia cells.

Chronic myelogenous leukemia (CML) is triggered by the constitutively activated BCR-ABL oncoprotein and multiple downstream signaling pathways, including the Raf/MEK/ERK, Akt/mTOR, SRC, and STAT5 pathways. The BCR-ABL tyrosine kinase inhibitor imatinib is the standard treatment for CML. However, the development of imatinib resistance has become a new challenge for CML treatment. Here, we investigated the expression levels of the signaling pathways to explore the cause of imatinib resistance and seek new reversing drugs. Our results showed that abnormal activation of the BCR-ABL-independent Lyn/ERK signaling pathway was involved in imatinib-resistance of K562R cells. Furthermore, p-Lyn and p-ERK were up-regulated after treatment with imatinib alone. However, U0126, a MEK1/2 inhibitor, could counteract the up-regulation induced by imatinib, and the combination of imatinib and U0126 could overcome the resistance to imatinib in K562R cells. In conclusion, our studies suggest that the combination of imatinib and an inhibitor of the ERK signaling pathway may be effective in imatinib-resistant CML patients.