Design, Synthesis, and Biological Evaluation of Efflux-Resistant Imatinib Derivatives.

Resistance to imatinib, a first-line BCR-ABL1 tyrosine kinase inhibitor for chronic myeloid leukemia, is frequently mediated by drug efflux through P-glycoprotein (P-gp) overexpression. We report the design, synthesis, and evaluation of eight novel imatinib derivatives modified at the piperazine terminus with efflux resistance breaker (ERB) fragments to reduce P-gp-mediated efflux. In silico docking against cryo-EM P-gp structures predicted increased hydrophobic interactions and enhanced occupancy at the access tunnel, indicative of efflux inhibition. Compound 8 showed potency comparable to imatinib in BCR-ABL1+ K562 cells and a lower LC50 fold change in resistant K562/DOX cells, suggesting reduced efflux susceptibility. Accumulation assays confirmed the improved intracellular retention of compound 8. Compound 9 displayed increased potency in resistant cells, correlating with higher intracellular levels despite modest kinase inhibition. Verapamil assays confirmed reduced efflux liability for compounds 8 and 13. Compound 8 also showed a positive therapeutic index. These findings support rational design to mitigate efflux-mediated resistance.