MDR1 gene polymorphisms and imatinib response in chronic myeloid leukemia: a meta-analysis

ABCG2 Single Nucleotide Polymorphism Affects Imatinib Pharmacokinetics in Lower Alpha-1-Acid Glycoprotein Levels in Humans

Imatinib is transported extracellularly by ABCB1 and ABCG2 efflux transporters and bound to alpha-1-acid glycoprotein (AGP) in the bloodstream. However, the clinical and pharmacokinetic effects of ABCB1 and ABCG2 on imatinib were inconsistent in the previous literature and have not been confirmed. Therefore, in the present study, we explored the effects of the ABCG2 and ABCB1 genetic polymorphisms on imatinib pharmacokinetics in association with plasma AGP levels in healthy subjects. Twenty-seven healthy individuals were recruited, genotyped for ABCG2 and ABCB1, and given a single oral dose of 400 mg imatinib. Plasma imatinib concentrations were measured and its pharmacokinetics was assessed with respect to ABCG2 (c.421C>A and c.34G>A) and ABCB1 (c.1236C>T, c.2677C>T/A, and c.3435C>T) genotypes, and plasma AGP levels. AGP levels showed a strong positive correlation with imatinib pharmacokinetics. ABCG2 c.421C>A single nucleotide polymorphism showed a statistically significant effect on imatinib pharmacokinetics in low plasma AGP levels groups (<80 mg/dl); subjects with high plasma AGP levels (n = 5, ≥80 mg/dl) were excluded. The results indicate that plasma AGP levels and ABCG2 polymorphisms modulated imatinib pharmacokinetics; however, the effects of the ABCG2 transporter was masked at high plasma AGP levels.

Clinically-Relevant ABC Transporter for Anti-Cancer Drug Resistance

Multiple drug resistance (MDR), referring to the resistance of cancer cells to a broad spectrum of structurally and mechanistically unrelated drugs across membranes, severely impairs the response to chemotherapy and leads to chemotherapy failure. Overexpression of ATP binding cassette (ABC) transporters is a major contributing factor resulting in MDR, which can recognize and mediate the efflux of diverse drugs from cancer cells, thereby decreasing intracellular drug concentration. Therefore, modulators of ABC transporter could be used in combination with standard chemotherapeutic anticancer drugs to augment the therapeutic efficacy. This review summarizes the recent advances of important cancer-related ABC transporters, focusing on their physiological functions, structures, and the development of new compounds as ABC transporter inhibitors.

MDR1 gene polymorphisms and imatinib response in chronic myeloid leukemia: A meta-analysis

BACKGROUND

Our study aimed to investigate the association between multidrug resistance (MDR1) C1236T, C3435T and G2677T/A polymorphisms and the response to imatinib (IM) in chronic myeloid leukemia (CML).

MATERIALS AND METHODS

An electronic databases in PubMed, Embase, Web of Knowledge, Scopus and Cochrane were searched using combinations of keywords relating to MDR1 polymorphisms and the response to IM in CML. Studies retrieved from database searches were screened using strict inclusion and exclusion criteria.

RESULTS

In total, 37 studies were initially identified, and 17 studies, involving 4494 CML patients, were eventually included in this meta-analysis.Results of our study revealed significant association between MDR1 G2677T/A and C3435T polymorphisms and response to IM in Caucasian population under recessive model (T or A vs G; OR = 1.43,95%CI [1;06-1.93]; T vs C;OR = 1.13; 95%IC [0.79; 1.63]), dominant (T or A vs G; OR = 0.94; 95%CI [0.74-1.21]; T vs C; OR = 1.49; 95%CI [1.02-2.17]) and heterozygous models (T or A vs G; OR = 0.83; 95%CI [0.64; 1.09]; T vs C; OR = 1.52; 95%CI [1.01-2.28]); respectively. However, never significative association was found between IM response and the MDR1 C1236T polymorphism (OR = 1.25; 95%CI [0.46; 3.33]).

CONCLUSION

The MDR1 G2677T/A and C3435T polymorphisms might be a risk factor for resistance to IM in Caucasian CML patients.

Genomic stability at the coding regions of the multidrug transporter gene ABCB1: insights into the development of alternative drug resistance mechanisms in human leukemia cells

AIM

Despite considerable efforts to reverse clinical multidrug resistance (MDR), targeting the predominant multidrug transporter ABCB1/P-glycoprotein (P-gp) using small molecule inhibitors has been unsuccessful, possibly due to the emergence of alternative drug resistance mechanisms. However, the non-specific P-gp inhibitor cyclosporine (CsA) showed significant clinical benefits in patients with acute myeloid leukemia (AML), which likely represents the only proof-of-principle clinical trial using several generations of MDR inhibitors. Nevertheless, the mutational mechanisms that may underlie unsuccessful MDR modulation by CsA are not elucidated because of the absence of CsA-relevant cellular models. In this study, our aims were to establish CsA-resistant leukemia models and to examine the presence or absence of ABCB1 exonic mutations in these models as well as in diverse types of human cancer samples including AMLs.

METHODS

Drug-resistant lines were established by stepwise drug co-selection and characterized by drug sensitivity assay, rhodamine-123 accumulation, [3H]-labeled drug export, ABCB1 cDNA sequencing, and RNase protection assay. The genomic stability of the ABCB1 coding regions was evaluated by exome sequencing analysis of variant allele frequencies in human populations. Moreover, the mutational spectrum of ABCB1 was further assessed in diverse types of cancer samples including AMLs in the Cancer Genome Atlas (TCGA) at the National Cancer Institute.

RESULTS

We report the development of two erythroleukemia variants, RVC and RDC, which were derived by stepwise co-selection of K562/R7 drug-resistant leukemia cells with the etoposide-CsA and doxorubicin-CsA drug combinations, respectively. Interestingly, both RVC and RDC cell lines, which retained P-gp expression, showed altered multidrug-resistant phenotypes that were resistant to CsA modulation. Strikingly, no mutations were found in the ABCB1 coding regions in these variant cells even under long-term stringent drug selection. Genomically, ABCB1 displayed relatively low variant allele frequencies in human populations when compared with several ABC superfamily members. Moreover, ABCB1 also exhibited a very low mutational frequency in AMLs compared with all types of human cancer. In addition, we found that CsA played a role in undermining the selection of highly drug-resistant cells via induction of low-level and unstable drug resistance.

CONCLUSION

Our data indicate that ABCB1 coding regions are genomically stable and relatively resistant to drug-induced mutations. Non-ABCB1 mutational mechanisms are responsible for the drug-resistant phenotypes in both RVC and RDC cell lines, which are also prevalent in clinical AML patients. Accordingly, we propose several relevant models that account for the development of alternative drug resistance mechanisms in the absence of ABCB1 mutations.

Impact of ABCB1 Gene Polymorphisms and Smoking on the Susceptibility Risk of Chronic Myeloid Leukemia and Cytogenetic Response

Background:

IM, a strong and selective TKI, has been approved as the front line of treatment in CML patients. In spite of satisfactory results of imatinib in the treatment of patients with CML, patients with treatment failure or suboptimal response developed resistance that might be because of pharmacogenetic variants. This study attempted to evaluate the influence of ABCB1 gene polymorphisms and smoking on CML risk and resistance to imatinib.

Methods:

ABCB1 (c.1236C>T, c.3435C>T) polymorphisms were genotyped in 98 CML patients and 100 sex- and age-matched healthy subjects by PCR-RFLP method, followed by sequencing. The patients were evaluated for cytogenetic response by the standard chromosome banding analysis in regular intervals.

Results:

Our results showed that c.1236CC genotype was significantly associated with imatinib resistance (OR = 3.94; p = 0.038). Analysis of the joint of SNP-smoking combination showed that smokers with c.1236TT/CT and c.1236CC genotypes had the increased risk of CML (OR = 6.04; p = 0.00 and OR = 4.95, p = 0.005) and treatment failure (OR = 5.36, p = 0.001 and OR = 15.7, p = 0.002), respectively. Smokers with c.3435TT/CT and c.3435CC genotypes also displayed the elevated risk of CML development (OR = 6.01, p = 0 and OR = 4.36, p = 0.011) and IM resistance (OR = 5.61, p = 0.001 and OR = 13.58, p = 0.002), respectively.

Conclusion:

Our findings suggest that c.1236CC genotype has clinical importance in the prediction of treatment outcome with IM, and smoking could have a synergistic role in CML risk and IM resistance.

Effect of ABC transporter expression and mutational status on survival rates of cancer patients

ATP-binding cassette (ABC) transporters mediate multidrug resistance in cancer. In contrast to DNA single nucleotide polymorphisms in normal tissues, the role of mutations in tumors is unknown. Furthermore, the significance of their expression for prediction of chemoresistance and survival prognosis is still under debate. We investigated 18 tumors by RNA-sequencing. The mutation rate varied from 27,507 to 300885. In ABCB1, three hotspots with novel mutations were in transmembrane domains 3, 8, and 9. We also mined the cBioPortal database with 11,814 patients from 23 different tumor entities. We performed Kaplan-Meier survival analyses to investigate the effect of ABC transporter expression on survival rates of cancer patients. Novel mutations were also found in ABCA2, ABCA3, ABCB2, ABCB5, ABCC1-6, and ABCG2. Mining the cBioPortal database with 11,814 patients from 23 different tumor entities validated our results. Missense and in-frame mutations led to altered binding of anticancer drugs in molecular docking approaches. The ABCB1 nonsense mutation Q856* led to a truncated P-glycoprotein, which may sensitize tumors to anticancer drugs. The search for ABC transporter nonsense mutations represents a novel approach for precision medicine.. Low ABCB1 mRNA expression correlated with significantly longer survival in ovarian or kidney cancer and thymoma. In cancers of breast, kidney or lung, ABC transporter expression correlated with different tumor stages and human populations as further parameters to refine strategies for more individualized chemotherapy.

Pharmacology of tyrosine kinase inhibitors in chronic myeloid leukemia; a clinician's perspective

OBJECTIVE

In this review, we have summarized the pharmacokinetics, pharmacodynamics and adverse effects of imatinib, dasatinib, nilotinib, bosutinib, ponatinib and radotinib with focus on pharmacogenomic studies with clinical end points. We have discussed the key phase 3 trials of tyrosine kinase inhibitors (TKI) comparing with each other, treatment free remission (TFR) and selection of TKI. Upcoming concepts and related trials in the management of chronic myeloid leukemia (CML) along with future directions have been touched upon.

EVIDENCE ACQUISITION

PubMed, Embase, Google, Cochrane library and Medline were searched to identify relevant literature for the review. Clinicaltrial.gov was searched for upcoming data and trials.

RESULTS

There are lot of gap in pharmacokinetics and pharmacodynamics of TKI. Imatinib appears to be the safest TKI. Newer TKI's achieve better achievement of therapeutic milestones, deeper molecular response and less chances of progression of CML compared to imatinib. Newer TKI appears to be better choice for achieving TFR. When the objective is survival, imatinib is still the TKI of choice. Primary prophylaxis with antiplatelet drugs for TKI having cardiovascular and thromboembolic side effects should be considered.

CONCLUSION

Pharmacogenetic data of TKI is still immature to guide in therapeutic decision making in clinical practice. There is need for further research in pharmacology and pharmacogenomics of newer TKI's. Randomized controlled trials are required to decide the optimum TKI for TFR. Safe and effective TKI for targeting T315I mutation, CML accelerated phase and blast crisis are an active area of research.

Association between C1236T Genetic Variant of ABCB1 Gene and Molecular Response to Imatinib in Indonesian Chronic Myeloid Patients

Objective:

Imatinib is the first-line drug used for the treatment of chronic myeloid leukemia (CML) patients due to high molecular response and overall survival rate. However, some patients develop resistance to imatinib even after attaining a response. Mutation in ABCB1 efflux transporters is one of the known mechanisms of resistance to imatinib in chronic myeloid leukemia patients. This study was aimed to investigate the association of ABCB1 C1236T polymorphism in Indonesian chronic myeloid patients with molecular response to imatinib treatment.

Methods:

We analyzed 120 samples from chronic myeloid leukemia patients in the chronic phase, who had been on imatinib treatment for at least 12 months. We analyzed the C1236T variant of the ABCB1 gene using PCR, followed by direct sequencing, and associate them with the achievement of major molecular response (MMR).

Results:

The major molecular response was achieved in 28% of patients. The frequencies of the SNPs were CC (40%), CT (46%), and TT (14%). Our result showed that there was a lack of association between polymorphism of ABCB1 C1236T and imatinib response in Indonesian patients, with OR = 0.646 (95% CI: 0.283, 1.471; p>0.05).

Conclusion:

There was no association between ABCB1 C1236T variants with the major molecular response in Indonesian chronic myeloid leukemia patients receiving imatinib treatment.

Genetic polymorphisms in ABCG2 and CYP1A2 are associated with imatinib dose reduction in patients treated for gastrointestinal stromal tumors

Imatinib has a mild toxicity profile, although severe adverse events may develop. In this pharmacogenetic pathway analysis the need for dose reduction and cessation of therapy was tested for an association with single nucleotide polymorphisms (SNPs) in genes related to imatinib pharmacology. Retrospective data from 315 patients with a gastrointestinal stromal tumor who received imatinib 400 mg o.d. was associated with 36 SNPs. SNPs that showed a trend in univariate testing were tested in a multivariate model with clinical factors and correction for multiple testing was performed. Dose reduction was associated with carriership of the A-allele in rs2231137 in ABCG2 (OR 7.35, p = 0.0002) and two C-alleles in rs762551 in CYP1A2 (OR 7.12, p = 0.001). Results remained significant after correction for multiple testing. Therapy cessation did not show an association with any of the tested SNPs. These results may help identifying patients at increased risk for toxicity who could benefit from intensified follow-up.

Revisiting the role of ABC transporters in multidrug-resistant cancer

Most patients who die of cancer have disseminated disease that has become resistant to multiple therapeutic modalities. Ample evidence suggests that the expression of ATP-binding cassette (ABC) transporters, especially the multidrug resistance protein 1 (MDR1, also known as P-glycoprotein or P-gp), which is encoded by ABC subfamily B member 1 (ABCB1), can confer resistance to cytotoxic and targeted chemotherapy. However, the development of MDR1 as a therapeutic target has been unsuccessful. At the time of its discovery, appropriate tools for the characterization and clinical development of MDR1 as a therapeutic target were lacking. Thirty years after the initial cloning and characterization of MDR1 and the implication of two additional ABC transporters, the multidrug resistance-associated protein 1 (MRP1; encoded by ABCC1)), and ABCG2, in multidrug resistance, interest in investigating these transporters as therapeutic targets has waned. However, with the emergence of new data and advanced techniques, we propose to re-evaluate whether these transporters play a clinical role in multidrug resistance. With this Opinion article, we present recent evidence indicating that it is time to revisit the investigation into the role of ABC transporters in efficient drug delivery in various cancer types and at the blood-brain barrier.

Pharmacogenetics and Pharmacogenomics of Targeted Therapeutics in Chronic Myeloid Leukemia

The advent of targeted therapeutics has greatly improved outcomes of chronic myeloid leukemia (CML) patients. Despite increased efficacy and better clinical responses over cytotoxic chemotherapies, many patients receiving targeted drugs exhibit a poor initial response, develop drug resistance, or undergo relapse after initial success. This inter-individual variation in response has heightened the interest in studying pharmacogenetics and pharmacogenomics (PGx) of cancer drugs. In this review, we discuss the influence of various germline and somatic factors on targeted drug response in CML. Specifically, we examine the role of genetic variants in drug metabolism genes, i.e. CYP3A family genes, and drug transporters, i.e. ABC and SLC family genes. Additionally, we focus on acquired somatic variations in BCR-ABL1, and the potential role played by additional downstream signaling pathways, in conferring resistance to targeted drugs in CML. This review highlights the importance of PGx of targeted therapeutics and its potential application to improving treatment decisions and patient outcomes.

Pharmacogenetics and the treatment of chronic myeloid leukemia: how relevant clinically? An update

Despite the excellent efficacy and improved clinical responses obtained with imatinib mesylate (IM), development of resistance in a significant proportion of chronic myeloid leukemia (CML) patients on IM therapy have emerged as a challenging problem in clinical practice. Resistance to imatinib can be due to heterogeneous array of factors involving BCR/ABL-dependent and BCR/ABL-independent pathways. Although BCR/ABL mutation is the major contributory factor for IM resistance, reduced bio-availability of IM in leukemic cells is also an important pharmacokinetic factor that contributes to development of resistance to IM in CML patients. The contribution of polymorphisms of the pharmacogenes in relation to IM disposition and treatment outcomes have been studied by various research groups in numerous population cohorts. However, the conclusions arising from these studies have been highly inconsistent. This review encompasses an updated insight into the impact of pharmacogenetic variability on treatment response of IM in CML patients.

The genetic polymorphism and expression profiles of NLRP3 inflammasome in patients with chronic myeloid leukemia

NLRP3 inflammasome has been recently reported as an important risk factor in the development of cancer. But the relationship between polymorphisms of NLRP3 inflammasome related genes and chronic myeloid leukemia (CML) is rarely reported. Therefore, the aim of the present study was to investigate the association of five genetic polymorphisms (NLRP3, IL-1β, IL-18, CARD8 and NF-κB) in 267 CML patients and 344 healthy controls. We found that the AT genotype of CARD8 (rs2043211) was significantly higher compared to TT genotype in high and intermediate risk CML patients. IL-1β (rs16944) polymorphism in early molecular response at 6 months was marginally different, with more GG and less AA genotype in BCR-ABL^IS >1% group. IL-18 (rs1946518) polymorphism was significantly different with more GG genotype in BCR-ABL^IS >1% group at 6 months. We also demonstrated that WBC count of newly diagnosed patients carrying AG genotype was significantly higher than that of GG or AA genotype of IL-1β (rs16944). The onset age of patients carrying ins/ins genotype of NF-κB (rs28362491) was significantly older than that of ins/del and del/del genotype. Moreover, IL-1β or NLRP3 mRNA expression was decreased and IL-18 mRNA expression was increased significantly in CML patients compared with controls. In conclusion, the genetic polymorphisms of NLRP3 inflammasome may be served as potential predictors for CML.

ABCB1 genetic variants in leukemias: current insights into treatment outcomes

Despite improvements in treatment of different types of leukemia, not all patients respond optimally for a particular treatment. Some treatments will work better for some, while being harmful or ineffective for others. This is due to genetic variation in the form of single-nucleotide polymorphisms (SNPs) that affect gene expression or function and cause inherited interindividual differences in the metabolism and disposition of drugs. Drug transporters are one of the determinants governing the pharmacokinetic profile of chemotherapeutic drugs. The ABCB1 transporter gene transports a wide range of drugs, including drugs used in leukemia treatment. Polymorphisms in the ABCB1 gene do affect intrinsic resistance and pharmacokinetics of several drugs used in leukemia treatment protocols and thereby affect the efficacy of treatment and event-free survival. This review focuses on the impact of three commonly occurring SNPs (1236C>T, 2677G>T/A, and 3435C>T) of ABCB1 on treatment response of various types of leukemia. From the literature available, some of the genotypes and haplotypes of these SNPs have been found to be potential determinants of interindividual variability in drug disposition and pharmacologic response in different types of leukemia. However, due to inconsistencies in the results observed across the studies, additional studies, considering novel genomic methodologies, comprehensive definition of clinical phenotypes, adequate sample size, and uniformity in all the confounding factors, are warranted.

With no interaction, knockdown of Apollon and MDR1 reverse the multidrug resistance of human chronic myelogenous leukemia K562/ADM cells

Chemotherapy is the main treatment method for patients with chronic myeloid leukemia (CML) and has achieved marked results. However, the acquisition of multidrug resistance (MDR) has seriously affected the quality of life and survival rate of patients. The overexpression of the inhibitors of apoptosis proteins (IAPs) and the adenosine triphosphate (ATP)-dependent binding cassette (ABC) transporters are the two main causes of MDR. Apollon and MDR1 are the most important and representative members, respectively, among the IAPs and ABC transporters. In the present study, we investigated the role of Apollon and MDR1 in chemotherapy resistance and their mechanism of interaction. We respectively knocked down the expression of Apollon and MDR1 using short hairpin RNA (shRNA) in adriamycin (ADM) resistant human CML K562 cells and examined the drug sensitivity, the consequences with regard to ADM accumulation and the alterations in the expression of Apollon and MDR1. The expression levels of Apollon and MDR1 mRNA were higher in the K562/ADM cells compared with the parental K562 cells as determined by reverse transcription‑polymerase chain reaction (RT-PCR). The plasmids of Apollon and MDR1 shRNA were respectively stably transfected into K562/ADM cells using Lipofectamine 2000. The transfection efficiency was detected by fluorescence microscopy. Cell Counting Kit-8 (CCK-8) assay revealed that Apollon or MDR1 knockdown significantly increased the chemosensitivity of the K562/ADM cells to ADM. Flow cytometric assay revealed that K562/ADM/shMDR1 cells exhibited a significantly increased intracellular accumulation of ADM, and that changes were not found in the K562/ADM/shApollon cells. Compared with the parental K562/ADM cells, a significantly decreased expression of Apollon mRNA and protein was determined in the K562/ADM/shApollon cells without affecting the expression of MDR1 as determined by RT-PCR and western blotting. Likewise, the expression levels of MDR1 mRNA and protein also markedly downregulated in the K562/ADM/shMDR1 cells had no effect on Apollon expression. Collectively, our findings demonstrated, for the first time, that downregulation of Apollon or MDR1 through stable transfection with the Apollon- or MDR1-targeting shRNA induced MDR reversal through respective inhibition of Apollon or MDR1 expression and function. However, the reversal mechanism of Apollon and MDR1 revealed no direct interaction with each other.

Trough concentration and ABCG2 polymorphism are better to predict imatinib response in chronic myeloid leukemia: a meta-analysis

AIM

The present study aimed to conduct a series of meta-analyses to investigate the influence of imatinib trough concentration (C₀), as well as ABCB1 and ABCG2 polymorphisms, on the clinical response in patients with chronic myeloid leukemia (CML).

METHODS

A literature search was conducted using the PubMed and Cochrane electronic databases to locate relevant papers from 2003 onward. Then, an initial meta-analysis of 14 studies involving 2184 patients was conducted to understand the effect of imatinib mesylate (IM) C₀ on clinical outcome in CML patients. Subsequently, a series of meta-analyses were performed, including up to 23 studies with 2577 patients, on the effect of genetic polymorphisms of ABCB1 and ABCG2 on the clinical response to IM.

RESULTS

Meta-analysis revealed that patients who achieved a major molecular response (MMR) have a significantly higher IM C₀ than those who failed to achieve an MMR. We also found that the patients who achieved a complete cytogenic response (CCyR) have a significantly higher IM C₀ than those who did not achieve a CCyR. However, no significant difference in IM C₀ was found between the complete molecular response and non-complete molecular response groups. Additional analysis showed that ABCG2 421 variant A allele was significantly associated with a higher rate of MMR and overall response, especially in Asian patients. Meta-analysis did not reveal a correlation between ABCB1 C3435T and C1236T polymorphisms with any clinical response to IM. However, the G2677T/A polymorphism could play a role in IM response in the recessive model.

CONCLUSION

This meta-analysis demonstrates that there was a significant correlation between the IM trough concentration and clinical responses, especially MMR and CCyR, in CML patients. Furthermore, we found that the probability of successful treatment was correlated with the ABCG2 C421A polymorphism, at least within the Asian population. We failed to determine an association between ABCB1 polymorphisms and IM response, although the G2677T/A polymorphism might be involved. However, further large-scale investigations using more sensitive genotyping methods would be required to confirm this.

Impact of ABCB1 1236C > T-2677G > T-3435C > T polymorphisms on the anti-proliferative activity of imatinib, nilotinib, dasatinib and ponatinib

Overexpression of ABCB1 (also called P-glycoprotein) confers resistance to multiple anticancer drugs, including tyrosine kinase inhibitors (TKIs). Several ABCB1 single nucleotide polymorphisms affect the transporter activity. The most common ABCB1 variants are 1236C > T, 2677G > T, 3435C > T and have been associated with clinical response to imatinib in chronic myelogenous leukaemia (CML) in some studies. We evaluated the impact of these polymorphisms on the anti-proliferative effect and the intracellular accumulation of TKIs (imatinib, nilotinib, dasatinib and ponatinib) in transfected HEK293 and K562 cells. ABCB1 overexpression increased the resistance of cells to doxorubicin, vinblastine and TKIs. Imatinib anti-proliferative effect and accumulation were decreased to a larger extent in cells expressing the ABCB1 wild-type protein compared with the 1236T-2677T-3435T variant relatively to control cells. By contrast, ABCB1 polymorphisms influenced the activity of nilotinib, dasatinib and ponatinib to a much lesser extent. In conclusion, our data suggest that wild-type ABCB1 exports imatinib more efficiently than the 1236T-2677T-3435T variant protein, providing a molecular basis for the reported association between ABCB1 polymorphisms and the response to imatinib in CML. Our results also point to a weaker impact of ABCB1 polymorphisms on the activity of nilotinib, dasatinib and ponatinib.

A study to explore the correlation of ABCB1, ABCG2, OCT1 genetic polymorphisms and trough level concentration with imatinib mesylate-induced thrombocytopenia in chronic myeloid leukemia patients

PURPOSE

Imatinib mesylate is presently the first-line treatment for chronic myeloid leukemia (CML). Therapeutic drug monitoring (TDM) and pharmacogenetic screening is warranted for better management of imatinib therapy. The present study was framed to explore the influence of common drug transporter gene polymorphisms of ABCB1, ABCG2, OCT1 and trough level concentration on commonly occurring adverse events in CML patients treated with imatinib mesylate.

METHODS

A total number of 111 patients in chronic phase (Philadelphia chromosome +ve) were included in the study. The plasma drug concentration of imatinib was estimated using LC-MS/MS method.

RESULTS

The mean ± SD trough level concentration of imatinib mesylate was found to be 1430.7 ± 438.7 ng/ml. The trough level concentration at steady state (Cmin.ss) was significantly higher in patients with grade 2-4 thrombocytopenia compared with patients without the adverse event (P value 0.033).

CONCLUSION

The drug level of imatinib in plasma correlates with the severity of thrombocytopenia, which adds to the utility of TDM in the management of CML patients.

ABCB1 polymorphisms predict imatinib response in chronic myeloid leukemia patients: a systematic review and meta-analysis

Imatinib mesylate, a competitive tyrosine kinase inhibitor, is considered the first-line therapy drug for Ph+ chronic myeloid leukemia (CML). Three single-nucleotide polymorphisms (SNPs) in the ATP-binding cassette, subfamily B (MDR/TAP), member 1 gene (ABCB1/MDR1), c.1236C>T, c.2677G>T/A and c.3435C>T, have been shown to affect cellular transport/metabolism of imatinib. The associations between these SNPs and imatinib response in CML patients have been widely evaluated, but the results were inconsistent. To derive a conclusive assessment of the associations, we performed a meta-analysis by combining data from a total of 12 reports including 1826 patients. The results showed that the 2677G allele or 3435T allele predicted a worse response to imatinib in CML patients, whereas 1236CC genotype was associated with better response in CML patients from Asian region. In conclusion, this meta-analysis suggests that c.1236C>T, c.2677G>T/A and c.3435C>T can be served as predictive markers for the therapeutical use of imatinib in CML patients.