Molecular response to imatinib & its correlation with mRNA expression levels of imatinib influx & efflux transporters in patients with chronic myeloid leukaemia in chronic phase

OCT-1 Expression in Patients with Chronic Myeloid Leukemia: A Comparative Analysis with Respect to Response to Imatinib Treatment

The introduction of tyrosine kinase inhibitors (TKI) has resulted in a significant improvement in the treatment of CML patients. However, some CML patients are resistant to imatinib therapy, the initial TKI therapy in the CML. Therefore, it is important to find prognostic markers for resistance. The OCT-1 gene involved in imatinib uptake is also suspected to cause imatinib resistance. The aim of this study was to investigate the role of OCT-1 in imatinib resistance by comparing OCT-1 expression levels in imatinib resistant and imatinib sensitive patients with chronic myeloid leukemia (CML). This study was conducted on 101 patients with CML [imatinib sensitive (n = 51) and imatinib resistant (n = 50)] who were treated with imatinib. Gene expression analysis was done using QRT-PCR. The relative expression levels of OCT-1 were calculated using 2(-ΔΔCT) method. OCT1 mRNA expression levels were 0.149 (0.011-2.532) and 0.119 (0.008-2.868) in imatinib-sensitive group and imatinib-resistant group, respectively. OCT-1 expression levels were not significantly different in the imatinib-sensitive group when compared to imatinib resistant group (p > 0.05). OCT-1 expression was also similar in BCR-ABL1 kinase domain mutation positive and negative cases (p > 0.05). The imatinib-resistant group had a higher rate of hydroxyurea or interferon-alpha treatment prior to imatinib therapy and a lower rate for first-line imatinib as the only treatment than the imatinib-sensitive group (p = 0.002 and p = 0.002, respectively). According to the results of our study, OCT-1 does not have a biomarker feature in the evaluation of imatinib response. In addition, the study should be performed in larger patient groups.

Longer Hydroxyurea Administration Prior to Imatinib Mesylate is Risk Factor for Unsuccessful Major Molecular Response in Chronic-Phase Chronic Myeloid Leukemia: Possibility of P-Glycoprotein Role

Objective:

This study aimed to identify the association between duration of HU administration prior to IM treatment and MMR achievement in chronic-phase CML while evaluating the role of MDA, HIF-1α and P-gp.

Methods:

The study was conducted at Dr. Cipto Mangunkusumo National General Hospital and Dharmais Cancer Hospital, Jakarta using retrospective cohort design to analyse the association between the duration of HU before IM and its MMR achievement and cross-sectional design to analyse the association between MDA, HIF-1α and P-gp expressions with MMR achievement. Main subjects were chronic-phase CML patients treated by HU prior to IM for ≥ 12 months and HU only. The subjects were divided into four main groups: (1) chronic-phase CML patients treated with HU ≤ 6 months + IM ≥ 12 months and (2) HU > 6 months + IM ≥ 12 months (3) HU only (≤ 6 months), (4) HU only ( >6 months). Subjects were obtained from January 2015 to May 2016. Data were gathered through history taking, physical examination, medical record evaluation, and blood sample analysis. Bivariate analysis was conducted using chi square, independent T-test, and Mann-Whitney according to the variables.

Results:

Administration of HU for more than 6 months prior to IM was associated with unsuccessful MMR achievement (RR 1.60; 95%CI 1.29-2.00). MDA level, HIF-1α, P-glycoprotein expression were not associated with MMR achievement but the mean MDA level (0.63±0.31 vs 0.75±0.41 p=0.461) and median P-glycoprotein expressions {16,92 (0,04 – 43,86) vs. 5,15 (0,02–39,64); p=0.311} were found to be higher in patients receiving HU for > 6 months group than in HU ≤ 6 months group consecutively.

Conclusion:

Administration of HU for more than 6 months prior to IM was associated with unsuccessful MMR achievement in chronic-phase CML. The study suggested that P-glycoprotein overexpression as the predictor for unsuccessful MMR achievement.

ABCB1 and BMI1 mRNA expression in patients with chronic myeloid leukemia: impact on imatinib efficacy

Background

ATP-binding cassette transporters are important in the mechanism of multidrug resistance. ABCB1 displays a high affinity for imatinib. BMI1 is a polycomb group protein thought to be overexpressed in leukemic cells.

Methods

This study was conducted to investigate the prognostic value of ABCB1 and BMI1 expressions in chronic myeloid leukemia (CML). Expression levels were measured in 81 patients newly diagnosed with CML and 20 healthy controls by real time reverse transcription- PCR.

Results

The ABCB1 expression levels did not differ between patients with CML and controls. Low ABCB1 mRNA levels were observed in patients who achieved an optimal response compared to suboptimal and resistant cases (P=0.005). Non-responders showed the highest ABCB1 levels. ABCB1 expression did not affect the progression-free survival (PFS) of patients. BMI1 expression was higher in patients than that in controls (P=0.001). Patients in advanced phases expressed higher levels of BMI1 than those in the chronic phase (P=0.004). High BMI1 expression was associated with a shorter PFS.

Conclusion

ABCB1 mRNA expression may serve as a predictor of the optimal response to imatinib treatment in patients with CML. BMI1 expression was higher in the accelerated and blastic crisis phases of CML and associated with a shorter PFS.

Imatinib Uptake into Cells is Not Mediated by Organic Cation Transporters OCT1, OCT2, or OCT3, But is Influenced by Extracellular pH

BACKGROUND

Cancer cells undergo genetic and environmental changes that can alter cellular disposition of drugs, notably by alterations of transmembrane drug transporters expression. Whether the influx organic cation transporter 1 (OCT1) encoded by the gene SLC221A1 is implicated in the cellular uptake of imatinib is still controversial. Besides, imatinib ionization state may be modulated by the hypoxic acidic surrounding extracellular microenvironment.

OBJECTIVE

To determine the functional contribution of OCTs and extracellular pH on imatinib cellular disposition.

METHODS

We measured imatinib uptake in two different models of selective OCTs drug transporter expression (transfected Xenopus laevis oocytes and OCT-expressing HEK293 human cells), incubated at pH 7.4 and 6, using specific mass spectrometry analysis.

RESULTS

Imatinib cellular uptake occurred independently of OCT1- OCT2- or OCT3-mediated drug transport at pH 7.4. Uptake of the OCTs substrate tetraethylammonium in oocytes remained intact at pH 6, while the accumulation of imatinib in oocytes was 10-fold lower than at pH 7.4, irrespectively of OCTs expressions. In OCT1- and OCT2-HEK cells at pH 6, imatinib accumulation was reduced by 2- 3-fold regardless of OCTs expressions. Since 99.5% of imatinib at pH6 is under the cationic form, the reduced cellular accumulation of imatinib at such pH may be explained by the lower amount of uncharged imatinib remaining for passive diffusion across cellular membrane.

CONCLUSION

Imatinib is not a substrate of OCTs 1-3 while the environmental pH modulates cellular disposition of imatinib. The observation that a slightly acidic extracellular pH influences imatinib cellular accumulation is important, considering the low extracellular pH reported in the hematopoietic leukemia/ cancer cell microenvironment.

Imatinib Affects the Expression of SLC22A1 in a Non-Linear Concentration-Dependent Manner Within 24 Hours

BACKGROUND Imatinib is actively transported into cells by the organic cation transporter (OCT1), encoded by SLC22A1. As a result, the expression of SLC22A1 is considered a prognostic marker for treatment with imatinib in patients with chronic myeloid leukemia (CML). Although limited, there is conflicting evidence indicating that imatinib may affect the expression of SLC22A1. However, thus far, no studies have investigated the effect of imatinib on SLC22A1 expression in an imatinib-sensitive cell line, which would mimic a typical clinical setting. Changes in the expression of SLC22A1 as a result of imatinib could potentially negate its usefulness as a prognostic marker. MATERIAL AND METHODS The K562 CML cell line was exposed to varying concentrations of imatinib for 24, 48, and 72 h and SLC22A1 expression was determined by quantitative real-time PCR. RESULTS Our findings suggest that imatinib affects the expression of SLC22A1 within 24 h in a non-linear concentration-dependent manner. CONCLUSIONS This is the first study to report on the short-term effect of imatinib on the expression of SLC22A1 in an imatinib-sensitive CML cell line. Our results suggest that imatinib affects SLC22A1 mRNA expression in a non-linear dose-dependent manner and that the changes in the expression of SLC22A1 as a result of the concentration of imatinib occur within 24 h of exposure to imatinib and remain stable thereafter for up to 72 h.

Towards Comprehension of the ABCB1/P-Glycoprotein Role in Chronic Myeloid Leukemia

Abstract: The introduction of imatinib (IM), a BCR-ABL1 tyrosine kinase inhibitor (TKI), has represented a significant advance in the first-line treatment of chronic myeloid leukemia (CML). However, approximately 30% of patients need to discontinue IM due to resistance or intolerance to this drug. Both resistance and intolerance have also been observed in treatment with the second-generation TKIs-dasatinib, nilotinib, and bosutinib-and the third-generation TKI-ponatinib. The mechanisms of resistance to TKIs may be BCR-ABL1-dependent and/or BCR-ABL1-independent. Although the role of efflux pump P-glycoprotein (Pgp), codified by the ABCB1 gene, is unquestionable in drug resistance of many neoplasms, a longstanding question exists about whether Pgp has a firm implication in TKI resistance in the clinical scenario. The goal of this review is to offer an overview of ABCB1/Pgp expression/activity/polymorphisms in CML. Understanding how interactions, associations, or cooperation between Pgp and other molecules-such as inhibitor apoptosis proteins, microRNAs, or microvesicles-impact IM resistance risk may be critical in evaluating the response to TKIs in CML patients. In addition, new non-TKI compounds may be necessary in order to overcome the resistance mediated by Pgp in CML.

Molecular study of ABCB1 gene and its correlation with imatinib response in chronic myeloid leukemia

PURPOSE

The introduction and success of imatinib mesylate have become a paradigm shift in chronic myeloid leukemia (CML) treatment. However, despite its high efficiency, resistance to imatinib has emerged as a significant problem, which may in part be caused by pharmacogenetic variability. Three single-nucleotide polymorphisms (C1236T, G2677T/A, C3435T) and/or mRNA expression changes of ABCB1 gene were demonstrated to be associated with inter-individual variability of imatinib response in CML patients. In this study, we aimed to examine whether genetic variations and/or altered expression of ABCB1 gene may influence response to imatinib.

METHODS

Sixty nine CML Tunisian patients, undergoing imatinib therapy, were enrolled in this study. These were divided into two groups: responders and non-responders to imatinib. The relative transcript expression levels of ABCB1 gene and the distribution of allele and genotype frequency of ABCB1 SNPs were compared between these two categories of patients. Linkage disequilibrium tests and haplotypes analysis were also studied.

RESULTS

Our results showed that the mRNA expression level of ABCB1 gene did not differ significantly between the two categories of patients. In addition, results obtained from ABCB1 polymorphisms study and their correlation with imatinib response showed that the optimal response rate to imatinib did not differ significantly between C1236T, G2677T/A or C3435T genotypes. However, haplotype analysis showed that the 1236C-2677A-3435C haplotype was observed only in imatinib non-responders' patients suggesting that CAC haplotype was linked to higher risk of imatinib resistance.

CONCLUSION

Furthermore, analyses of ABCB1 haplotypes should be taken into account to study the relationship between ABCB1 genotypes and imatinib efficacy.