The Gene Expressions of hOCT1 and ABCB1 Change During the Course of CML in Relation to Imatinib Therapy

The intracellular concentration of imatinib (IM) in patients with chronic myeloid leukemia (CML) is supposed to be influenced by the expression of its main cellular transporters, hOCT1 (influx) and ABCB1 (efflux). The assessment of the genes expression may be potentially important in clinical practice to effectively manage the therapy. Our recent results showed the necessity to cautiously interpret results from gene expression measurements of both transporters as their detected mRNA levels are affected by the proportion of different cell types in the sample analyzed (Racil et al. 2010 Am J Hem 85:525, Racil et al. 2011 Leuk & Lymph 52:331). Aims. In this report, we aimed to comprehensively assess differences in the expression of hOCT1 and ABCB1 in total leukocytes of peripheral blood (PB) in relation to the blood cell lineage in CML patients with different responses to IM. Methods. Kruskall Wallis's and Dunn's multiple comparison tests were applied to calculate differences in transcript levels of hOCT1 and ABCB1 in patients at diagnosis (Dg=43), in major molecular response (MMR=27), complete molecular response (BCR-ABL log 4.5 reduction; CMR^4.5 =15), therapy failure (TF=13), accelerated phase (AP=12) and in 75 healthy controls. CMR^4.5 is defined here as either a detectable disease ≤0.0032% BCR-ABL^IS or as undetectable by nested PCR. TF is defined as non CCgR achievement. Additionally, we used the Spearman's correlation test to investigate relationship between expressions and percentage of immature cells and neutrophils in patients with non-physiological blood count (Dg and AP). In patients with normal blood count (CMR^4.5, MMR, TF), we calculated correlation with BCR-ABL transcript level. Finally, we performed in vitro experiments with BCR-ABL negative (SKM-1, MOLM-13) and positive cell lines (K562, MOLM-7) treated with IM to study its effect on ABCB1 expression. Results. We found a significantly lower expression of hOCT1 and ABCB1 at Dg (P<0.001) and in AP (P<0.001 and P<0.01, respectively) in comparison to controls. The lower expression probably depends indirectly on the immature cells count (hOCT1 r = −0.4850, P=0.0002; ABCB1 r = −0.6451, P< 0.0001). Interestingly, while a significant positive correlation of neutrophil count was found with hOCT1 mRNA levels (r=0.6090, P< 0.0001), no correlation was observed with ABCB1. In patients with physiological blood count, we observed significantly elevated expression of ABCB1 in MMR and CMR^4.5 in comparison to controls (P< 0.01). As MMR and CMR^4.5 samples are characterized by the BCR-ABL transcript level <0.1%, this result led us to perform in vitro experiments to test the effect of IM on ABCB1 expression in BCR-ABL negative cell lines showing an elevated expression after incubation with IM. We assume this effect to be a natural defense of BCR-ABL negative cells to get rid of IM. By contrast, we found a drop in ABCB1 expression after BCR-ABL positive cell lines incubation with IM, suggesting inhibitory effects of IM. A significantly reduced expression of hOCT1 was found in TF in comparison to MMR and CMR^4.5 (P< 0.01). These samples did not differ in blood count, but we observed a significant negative correlation of hOCT1 with BCR-ABL transcript levels (r= − 0.5117; P< 0.0001). Conclusion. Cell composition in PB changes during the CML treatment with IM which influences the measurement of hOCT1 and ABCB1 mRNA levels in total leukocytes. However, hOCT1 expression was found to be significantly lower in patients who failed to achieve CCgR but had normal blood count. Interestingly, our data suggest that ABCB1 is differently expressed in BCR-ABL positive and negative cells due to the inhibitory and enhancing effects of IM, respectively. Supported by IGA NT11555 and MZOUHKT2005

Machova Polakova:Novartis: travel grant. Ondrackova:BMS: travel grant.