PDF file 79K, Supplementary Figure S1: Uptake of imatinib and OCT1 probe substrate TEA into OCT1-expressing cells and vector-transfected control cells Supplementary Figure S2: Cellular uptake of the OCT1 probe substrate TEA and imatinib into mOct1- or mOct2-expressing HEK293 cells Supplementary Figure S3: Cellular uptake of imatinib into the CML cell lines Meg-01, LAMA-84 and K562 as well as into OCT1-expressing HEK cells and vector-transfected control cells measured after an incubation period of 120 minutes Supplementary Figure S4: Cellular uptake of imatinib into HEK cells expressing variant V408 in comparison to HEK cells expressing reference sequence M408 and vector-transfected control cells measured after an incubation period of 10 minutes Supplementary Figure S5: Knockdown of OCT1 protein expression by the used shRNA
ARTICLE ABSTRACT
Purpose: In addition to mutated BCR-ABL1 kinase, the organic cation transporter 1 (OCT1, encoded by SLC22A1) has been considered to contribute to imatinib resistance in patients with chronic myeloid leukemia (CML). As data are conflicting as to whether OCT1 transports imatinib and may serve as a clinical biomarker, we used a combination of different approaches including animal experiments to elucidate comprehensively the impact of OCT1 on cellular imatinib uptake.Experimental Design: Transport of imatinib was studied using OCT1-expressing Xenopus oocytes, mammalian cell lines (HEK293, MDCK, V79) stably expressing OCT1, human leukemic cells, and Oct1-knockout mice. OCT1 mRNA and protein expression were analyzed in leukemic cells from patients with imatinib-naïve CML as well as in cell lines.Results: Transport and inhibition studies showed that overexpression of functional OCT1 protein in Xenopus oocytes or mammalian cell lines did not lead to an increased cellular accumulation of imatinib. The CML cell lines (K562, Meg-01, LAMA84) and leukemic cells from patients expressed neither OCT1 mRNA nor protein as demonstrated by immunoblotting and immunofluorescence microscopy, yet they showed a considerable imatinib uptake. Oct1 deficiency in mice had no influence on plasma and hepatic imatinib concentrations.Conclusions: These data clearly demonstrate that cellular uptake of imatinib is independent of OCT1, and therefore OCT1 is apparently not a valid biomarker for imatinib resistance. Clin Cancer Res; 20(4); 985–94. ©2013 AACR.