Imatinib Is a Substrate for Various Multidrug Resistance Proteins

An increasing resistance to imatinib is an emerging problem in patients with chronic myeloid leukemia. The aim of the study was assessing possible mechanisms of cellular drug resistance in imatinib-resistant derivates of chronic myeloid leukemia K-562 cell line. A parental K-562 and its imatinib-resistant derivate cell lines were used. Cell lines were tested for cytotoxicity of imatinib, cytarabine, busulfan and etoposide. Multidrug resistance proteins expression, rhodamine retention and daunorubicin accumulation were measured for each cell line. Imatinib was cytotoxic to all tested groups of cells. Exposition of K-562 cell line to low concentrations of imatinib caused an increase of IC50 value of imatinib, while exposition of K-562 cell line to higher concentrations of imatinib decreased IC50 value of imatinib. There was a high correlation between PGP, MRP1 and LRP expression and IC50 for imatinib and etoposide. All tested cell lines were highly resistant to cytarabine. Rhodamine retention alone and in the presence of cyclosporine was the lowest in imatinib-resistant K-562R-0.1 cell line, what suggest high PGP activity in this cell line. Daunorubicin accumulation was the highest in parental K-562 cell line and it decreased in imatinib-resistant cell lines, which were characterized by high PGP, MRP1 and LRP expression. These data suggest that imatinib is a substrate for multidrug resistance proteins, and an increased expression of PGP, MRP1 and LRP play a role in resistance to imatinib in chronic myeloid leukemia.