Genetic variations of hOCT1 gene and CYP3A4/A5 genes and their association with imatinib response in Chronic Myeloid Leukemia

SPK1/S1P axis confers gastrointestinal stromal tumors (GISTs) resistance of imatinib

BACKGROUND

Imatinib mesylate (IM) is highly effective in the treatment of gastrointestinal stromal tumors (GISTs). However, the most of GISTs patients develop secondary drug resistance after 1-3 years of IM treatment. The aim of this study was to explore the IM-resistance mechanism via the multi-scope combined with plasma concentration of IM, genetic polymorphisms and plasma sensitive metabolites.

METHODS

This study included a total of 40 GISTs patients who had been regularly treated and not treated with IM. The plasma samples were divided into three experiments, containing therapeutic drug monitoring (TDM), OCT1 genetic polymorphisms and non-targeted metabolomics. According to the data of above three experiments, the IM-resistant cell line, GIST-T1/IMR cells, was constructed for verification the IM-resistance mechanism.

RESULTS

The results of non-targeted metabolomics analysis suggested that the sphingophospholipid metabolic pathway including the SPK1/S1P axis was inferred in IM-insensitive patients with GISTs. A GIST cell line (GIST-T1) was immediately induced as an IM resistance cell model (GIST-T1/IMR) and we found that blocking the signal pathway of SPK1/S1P in the GIST-T1/IMR could sensitize treatment of IM and reverse the IM-resistance.

CONCLUSIONS

Our findings suggest that IM secondary resistance is associated with the elevation of S1P, and blockage the signaling pathway of SPK1/S1P warrants evaluation as a potential therapeutic strategy in IM-resistant GISTs. The design of this study from blood management, group information collection, IM plasma concentration with different elements, identification of sphingolipid metabolism and lastly verification the function of SPK1/S1P in the IM-resistance GISTs cells.

Association between Germline Single-Nucleotide Variants in ADME Genes and Major Molecular Response to Imatinib in Chronic Myeloid Leukemia Patients

Imatinib is the most common first-line tyrosine kinase inhibitor (TKI) used to treat chronic-phase chronic myeloid leukemia (CP-CML). However, only a proportion of patients achieve major molecular response (MMR), so there is a need to find biological factors that aid the selection of the optimal therapeutic strategy (imatinib vs. more potent second-generation TKIs). The aim of this retrospective study was to understand the contribution of germline single-nucleotide variants (gSNVs) in the achievement of MMR with imatinib. In particular, a discovery cohort including 45 CP-CML patients was analyzed through the DMET array, which interrogates 1936 variants in 231 genes related to the absorption, distribution, metabolism and excretion (ADME) process. Variants statistically significant in the discovery cohort were then tested in an extended and independent cohort of 137 CP-CML patients. Finally, a total of 7 gSNVs (ABCG1-rs492338, ABCB11-rs496550, ABCB11-rs497692, CYP2D6-rs1135840, CYP11B1-rs7003319, MAT1A-rs4934027 and SLC22A1-rs628031) and one haplotype in the ABCB11 gene were significantly associated with the achievement of MMR with first-line imatinibtreatment. In conclusion, we identified a genetic signature of response to imatinib in CP-CML patients that could be useful in selecting those patients that may benefit from starting imatinib as first-line therapy, therefore avoiding the toxicity related to second-generation TKIs.

Genetic Variants of ABC and SLC Transporter Genes and Chronic Myeloid Leukaemia: Impact on Susceptibility and Prognosis

Solute carrier (SLC) and ATP-binding cassette (ABC) transporters comprise a variety of proteins expressed on cell membranes responsible for intrusion or extrusion of substrates, respectively, including nutrients, xenobiotics, and chemotherapeutic agents. These transporters mediate the cellular disposition of tyrosine kinase inhibitors (TKIs), and their genetic variants could affect its function, potentially predisposing patients to chronic myeloid leukaemia (CML) and modulating treatment response. We explored the impact of genetic variability (single nucleotide variants—SNVs) of drug transporter genes (ABCB1, ABCG2, SLC22A1, and SLC22A5) on CML susceptibility, drug response, and BCR-ABL1 mutation status. We genotyped 10 SNVs by tetra-primers-AMRS-PCR in 198 CML patients and 404 controls, and assessed their role in CML susceptibility and prognosis. We identified five SNVs associated with CML predisposition, with some variants increasing disease risk, including TT genotype ABCB1 (rs1045642), and others showing a protective effect (GG genotype SLC22A5 rs274558). We also observed different haplotypes and genotypic profiles associated with CML predisposition. Relating to drug response impact, we found that CML patients with the CC genotype (rs2231142 ABCG2) had an increased risk of TKI resistance (six-fold). Additionally, CML patients carrying the CG genotype (rs683369 SLC22A1) presented a 4.54-fold higher risk of BCR-ABL1 mutations. Our results suggest that drug transporters’ SNVs might be involved in CML susceptibility and TKI response, and predict the risk of BCR-ABL1 mutations, highlighting the impact that SNVs could have in therapeutic selection.

GSTT1 null and rs156697 Polymorphism in GSTO2 Influence the Risk and Therapeutic Outcome of B-Acute Lymphoblastic Leukemia Patients

INTRODUCTION

Glutathione S-transferase (GST) gene deletion or polymorphic sequence variations lead to decreased enzyme activity that influences susceptibility and response to chemotherapy in acute lymphoblastic leukemia (ALL). This case-control study investigated the association of GST gene polymorphisms with the etiology and therapeutic outcome of B-ALL among Kashmiri population.

METHODS

A total of 300 individuals including 150 newly diagnosed B-ALL patients and an equal number of age and gender matched controls were genotyped for five GST gene polymorphisms by polymerase chain reaction-restriction fragment length polymorphism technique (PCR-RFLP) and multiplex PCR techniques.

RESULTS

Higher frequency of GSTT1 null, GSTO2-AG, and GSTO2-GG genotypes was observed in ALL cases compared to controls that associated significantly with ALL risk (GSTT1 null: OR = 2.93, p = 0.0001; GSTO2-AG: OR = 2.58, p = 0.01; GSTO2-GG: OR = 3.13, p = 0.01). GSTM1, GSTP1, and GSTO1 SNPs showed no significant association (p > 0.05). Combined genotype analysis revealed significant association of GSTT1 null/GSTM1 null (OR = 4.11, p = 0.011) and GSTT1 null/GSTP1-AG (OR = 4.93, p = 0.0003) with B-ALL susceptibility. Haplotype analysis of rs4925 and rs156697 revealed that carriers of CG haplotype had increased risk of B-ALL (p = 0.04). Kaplan-Meier plots revealed significantly inferior 3-year disease-free survival for GSTO2-GG carriers (p = 0.002). Multivariate analysis confirmed GSTO2-GG as an independent poor prognostic factor for DFS (HR = 4.5, p = 0.034). Among combined genotypes, only GSTT1 null/GSTP1-AG associated significantly with poorer DFS rates (p = 0.032).

CONCLUSION

This study demonstrated that GSTT1 null individually or in combination with GSTM1null and GSTP1-AG genotypes associated with increased B-ALL risk. Also, rs156697 variant genotypes (AG and GG) associated with B-ALL, whereas the GG genotype of rs156697 influenced the treatment outcome.

Resistance to Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia-From Molecular Mechanisms to Clinical Relevance

Simple Summary

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasia associated with a molecular alteration, the fusion gene BCR-ABL1, that encodes the tyrosine kinase oncoprotein BCR-ABL1. This led to the development of tyrosine kinase inhibitors (TKI), with Imatinib being the first TKI approved. Although the vast majority of CML patients respond to Imatinib, resistance to this targeted therapy contributes to therapeutic failure and relapse. Here we review the molecular mechanisms and other factors (e.g., patient adherence) involved in TKI resistance, the methodologies to access these mechanisms, and the possible therapeutic approaches to circumvent TKI resistance in CML.

Abstract

Resistance to targeted therapies is a complex and multifactorial process that culminates in the selection of a cancer clone with the ability to evade treatment. Chronic myeloid leukemia (CML) was the first malignancy recognized to be associated with a genetic alteration, the t(9;22)(q34;q11). This translocation originates the BCR-ABL1 fusion gene, encoding the cytoplasmic chimeric BCR-ABL1 protein that displays an abnormally high tyrosine kinase activity. Although the vast majority of patients with CML respond to Imatinib, a tyrosine kinase inhibitor (TKI), resistance might occur either de novo or during treatment. In CML, the TKI resistance mechanisms are usually subdivided into BCR-ABL1-dependent and independent mechanisms. Furthermore, patients’ compliance/adherence to therapy is critical to CML management. Techniques with enhanced sensitivity like NGS and dPCR, the use of artificial intelligence (AI) techniques, and the development of mathematical modeling and computational prediction methods could reveal the underlying mechanisms of drug resistance and facilitate the design of more effective treatment strategies for improving drug efficacy in CML patients. Here we review the molecular mechanisms and other factors involved in resistance to TKIs in CML and the new methodologies to access these mechanisms, and the therapeutic approaches to circumvent TKI resistance.

Association of SLC22A1,SLCO1B3 Drug Transporter Polymorphisms and Smoking with Disease Risk and Cytogenetic Response to Imatinib in Patients with Chronic Myeloid Leukemia

OBJECTIVE

To determine whether polymorphisms of SLC22A1 and SLCO1B3 genes could predict imatinib (IM) response and chronic myeloid leukemia (CML) risk.

METHODS

We genotyped SLC22A1 (c.480G > C, c.1222A > G) and SLCO1B3 (c.334T > G, c.699G > A) polymorphisms in 132 patients with CML and 109 sex- and age-matched healthy subjects. The patients were evaluated for cytogenetic response by standard chromosome banding analysis (CBA).

RESULTS

Polymorphism analysis showed significant increased risk of IM resistance for SLC22A1c.1222AG (P = .03; OR = 2.2), SLCO1B3c.334TT/TG genotypes (P = .007; OR = 4.37) and 334T allele (P = .03; OR = 2.86). The double combinations of SLC22A1c.480CC and c.1222AG polymorphisms with SLCO1B3c.334TT/TG were significantly associated with complete cytogenetic response (CCyR) (P <.05; OR> 7). The interaction between all polymorphisms and smoking were associated with CML development and IM resistance (P ≤.04; OR> 3).

CONCLUSIONS

Our study results suggest the influence of SLC22A1 and SLCO1B3 polymorphisms and the interaction of smoking on CML development and IM response.

Effects of a Common Eight Base Pairs Duplication at the Exon 7-Intron 7 Junction on Splicing, Expression, and Function of OCT1

Organic cation transporter 1 (OCT1, SLC22A1) is localized in the sinusoidal membrane of human hepatocytes and mediates hepatic uptake of weakly basic or cationic drugs and endogenous compounds. Common amino acid substitutions in OCT1 were associated with altered pharmacokinetics and efficacy of drugs like sumatriptan and fenoterol. Recently, the common splice variant rs35854239 has also been suggested to affect OCT1 function. rs35854239 represents an 8 bp duplication of the donor splice site at the exon 7-intron 7 junction. Here we quantified the extent to which this duplication affects OCT1 splicing and, as a consequence, the expression and the function of OCT1. We used pyrosequencing and deep RNA-sequencing to quantify the effect of rs35854239 on splicing after minigene expression of this variant in HepG2 and Huh7 cells and directly in human liver samples. Further, we analyzed the effects of rs35854239 on OCT1 mRNA expression in total, localization and activity of the resulting OCT1 protein, and on the pharmacokinetics of sumatriptan and fenoterol. The 8 bp duplication caused alternative splicing in 38% (deep RNA-sequencing) to 52% (pyrosequencing) of the minigene transcripts when analyzed in HepG2 and Huh7 cells. The alternatively spliced transcript encodes for a truncated protein that after transient transfection in HEK293 cells was not localized in the plasma membrane and was not able to transport the OCT1 model substrate ASP⁺. In human liver, however, the alternatively spliced OCT1 transcript was detectable only at very low levels (0.3% in heterozygous and 0.6% in homozygous carriers of the 8 bp duplication, deep RNA-sequencing). The 8 bp duplication was associated with a significant reduction of OCT1 expression in the human liver, but explained only 9% of the general variability in OCT1 expression and was not associated with significant changes in the pharmacokinetics of sumatriptan and fenoterol. Therefore, the rs35854239 variant only partially changes splicing, causing moderate changes in OCT1 expression and may be of only limited therapeutic relevance.

Influence of genetic polymorphisms in glutathione-S-transferases gene in response to imatinib among Brazilian patients with chronic myeloid leukemia

Polymorphism in metabolizing enzymes can influence drug response as well as the risk for adverse drug reactions. Nevertheless, there are still few studies analyzing the consequence of polymorphisms for the Glutathione-S-transferases (GST) gene to drug response in chronic myeloid leukemia (CML). This study reports, the influence of GSTP1*B and GSTT1/GSTM1null polymorphisms in response to imatinib in CML patients in a Brazilian population. One hundred thirty-nine CML patients from the Clinical Hospital of Goiânia, Goiás, Brazil, treated with imatinib were enrolled in this study. Genotyping of GSTT1 and GSTM1 genes deletions were performed by qPCR and of GSTP1 gene was performed by RFLP-PCR. The frequency of GSTP1*1B, GSTT1 and GSTM1null polymorphisms were determined for all patients. The influence of each patient's genotypes was analyzed with the patient's response to imatinib treatment. Brazilian CML patients revealed GSTT1 and GSTM1 genes deletions. GSTT1 deletion was found in 19.3% of patients and GSTM1 deletion in 48.7% of patients with CML. GSTT1/GSTM1 deletion was found in 11.7% in Brazilian CML patients. The "G allele" of GSTP1*B, is associated with later cytogenetic response in imatinib therapy. While, the gene presence combined with GG genotype (GSTM1 present/GSTPI-GG) conferred a tend to a later cytogenetic response to patients. GSTP1*B and GSTT1/GSTM1null polymorphisms influence treatment response in CML. Brazilian CML patients presenting GSTP1 AA/AG genotypes alone and in combination with GSTT1 null reach the cytogenetic response faster, while patients presenting GSTP1-GG and GSTMI positive genotypes may take longer to achieve cytogenetic response. As a result, it allows a better prognosis, with the use of an alternative therapy, other than reducing treatment cost.

Glutathione S-transferase gene polymorphic sequence variations: Association with risk and response to Imatinib among Chronic Myeloid Leukemia patients of Kashmir

INTRODUCTION

Glutathione S-transferase (GST) gene deletion or polymorphic sequence variations lead to decreased enzyme activity that influences susceptibility and response to tyrosine kinase inhibitors in chronic myeloid leukemia (CML). We aimed to analyze relation of different GST gene sequence variants with susceptibility and response to Imatinib in CML.

MATERIAL AND METHODS

A total of 150 CML cases and equal number of age and gender matched healthy controls were genotyped for five GST polymorphisms by multiplex-PCR and PCR-RFLP techniques. BCR-ABL1 transcripts were quantified by quantitative Real Time PCR (qRT-PCR).

RESULTS

GSTT1, GSTO1, and GSTO2 SNPs revealed no association, while as GSTM1_null genotype was observed to protect against the development of CML (OR = 0.53, P = .01). GSTP1 variant genotypes AG (OR = 2.1, P = .003) and GG (OR = 5.6, P < .001), significantly associated with increased risk of CML. Combined genotype analysis showed protective impact of GSTT1_present /GSTM1_null (OR = 0.44, P = .003) while as GSTT1_present /GSTP1-GG (OR = 6.92, P < .001) and GSTM1_present /GSTP1-GG (OR = 6.33, P < .001), significantly increased CML risk. GSTM1_null genotype individually and in combination with GSTT1_present associated with superior rate of major molecular response (MMR) and event free survival (EFS) (log-rank P = .029). GSTO2-AG+GG genotype associated with significantly inferior MMR rates at 3, 6, and 12 months. Also, patients with GSTO2-GG genotype showed significantly reduced EFS (log-rank P = .025). Multivariate analysis confirmed GSTM1_null as a better (HR:0.19, P = .029) and GSTO2-GG genotype as an independent poor prognostic factor (HR:2.29, P = .037).

CONCLUSION

GSTM1_null genotype seems to have a better prognostic role while GSTP1 variants significantly increase CML risk. Also, results support a correlation between disease outcome and GSTO2 polymorphism.

Factors Influencing the Steady-State Plasma Concentration of Imatinib Mesylate in Patients With Gastrointestinal Stromal Tumors and Chronic Myeloid Leukemia

Imatinib mesylate (IM) is the standard treatment for advanced, metastatic gastrointestinal stromal tumors (GISTs) and chronic myeloid leukemia (CML) with a fixed daily standard dosage via the oral route. Interindividual and intraindividual variability in plasma concentrations have been closely linked to the efficacy of IM therapy. Therefore, this review identifies and describes the key factors influencing the plasma concentration of IM in patients with GISTs and CML. We used the following keywords to search the PubMed, EMBASE, Ovid, Wangfang, and CNKI databases to identify published reports: IM, plasma concentration, GISTs, CML, drug combination/interaction, pathology, and genotype/genetic polymorphism, either alone or in combination. This literature review revealed that only 10 countries have reported the mean concentrations of IM in GISTs or CML patients and the clinical outcomes in different ethnic groups and populations. There were totally 24 different gene polymorphisms, which were examined for any potential influence on the steady-state plasma concentration of IM. As a result, some genotype locus made discrepant conclusion. Herein, the more sample capacity, multicenter, long-term study was worthy to carry out. Eleven reports were enumerated on clinical drug interactions with IM, while there is not sufficient information on the pharmacokinetic parameters altered by drug combinations with IM that could help in investigating the actual drug interactions. The drug interaction with IM should be paid more attention in the future research.

Comprehensive in-silico analysis of damage associated SNPs in hOCT1 affecting Imatinib response in chronic myeloid leukemia

Non-synonymous single nucleotide polymorphisms (nsSNPs) in hOCT1 (encoded by SLC22A1 gene) are expected to affect Imatinib uptake in chronic myeloid leukemia (CML). In this study, sequence homology-based genetic analysis of a set of 270 coding SNPs identified 18 nsSNPs to be putatively damaging/deleterious using eight different algorithms. Subsequently, based on conservation of amino acid residues, stability analysis, posttranscriptional modifications, and solvent accessibility analysis, the possible structural-functional relationship was established for high-confidence nsSNPs. Furthermore, based on the modeling results, some dissimilarities of mutant type amino acids from wild-type amino acids such as size, charge, interaction and hydrophobicity were revealed. Three highly deleterious mutations consisting of P283L, G401S and R402G in SLC22A1 gene that may alter the protein structure, function and stability were identified. These results provide a filtered data to explore the effect of uncharacterized nsSNP and find their association with Imatinib resistance in CML.

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.

Impact of SLC22A1 and CYP3A5 genotypes on imatinib response in chronic myeloid leukemia: A systematic review and meta-analysis

Contrasting results have been reported on the role of rs628031 and rs683369 polymorphisms of SLC22A1 and rs776746 of CYP3A5 on imatinib treatment response in patients with chronic myeloid leukemia (CML). In the present study, we conducted a systematic review and meta-analysis of published studies to estimate the impact of the above-mentioned gene variants on major molecular response (MMR) or complete cytogenetic response (CCyR) in imatinib-treated CML patients. We performed a comprehensive search through PubMed, Web of Knowledge, and Cochrane databases up to September 2017. The pooled analyses showed association between carriers of SLC22A1 rs628031A allele (GA + AA vs GG, OR: 0.58, 95% CI: 0.38-0.88, P = 0.011) or rs683369G allele (CG + GG vs CC, OR: 0.64, 95% CI: 0.42-0.96, P = 0.032) and a lower MMR rate. The combined analyses also revealed a correlation between the dominant (GG + AG vs AA, OR: 2.43, 95%CI: 1.12-5.27, P = 0.024) or the allelic model (G vs A, OR: 1.72, 95% CI: 1.09-2.72, P = 0.020) of CYP3A5 rs776746 with higher CCyR rates. The subsequent sensitivity analysis confirmed the statistical significance of CYP3A5 rs776746 among Asian CML patients (dominant model OR: 3.90; 95%CI: 2.47-6.14, P < 0.001; allelic model OR: 2.08; 95% CI: 1.47-2.95, P < 0.001). In conclusion, the present meta-analysis supports the association of SLC22A1 and CYP3A5 genotypes with clinical imatinib response rates of CML patients, nevertheless further large studies, particularly in Caucasians, are still warranted to provide conclusive evidences.

Fine Mapping and Functional Analysis Reveal a Role of SLC22A1 in Acylcarnitine Transport

Genome-wide association studies have identified a signal at the SLC22A1 locus for serum acylcarnitines, intermediate metabolites of mitochondrial oxidation whose plasma levels associate with metabolic diseases. Here, we refined the association signal, performed conditional analyses, and examined the linkage structure to find coding variants of SLC22A1 that mediate independent association signals at the locus. We also employed allele-specific expression analysis to find potential regulatory variants of SLC22A1 and demonstrated the effect of one variant on the splicing of SLC22A1. SLC22A1 encodes a hepatic plasma membrane transporter whose role in acylcarnitine physiology has not been described. By targeted metabolomics and isotope tracing experiments in loss- and gain-of-function cell and mouse models of Slc22a1, we uncovered a role of SLC22A1 in the efflux of acylcarnitines from the liver to the circulation. We further validated the impacts of human variants on SLC22A1-mediated acylcarnitine efflux in vitro, explaining their association with serum acylcarnitine levels. Our findings provide the detailed molecular mechanisms of the GWAS association for serum acylcarnitines at the SLC22A1 locus by functionally validating the impact of SLC22A1 and its variants on acylcarnitine transport.

The hOCT1 and ABCB1 polymorphisms do not influence the pharmacodynamics of nilotinib in chronic myeloid leukemia

First-line nilotinib in chronic myeloid leukemia is more effective than imatinib to achieve early and deep molecular responses, despite poor tolerability or failure observed in one-third of patients. The toxicity and efficacy of tyrosine kinase inhibitors might depend on the activity of transmembrane transporters. However, the impact of transporters genes polymorphisms in nilotinib setting is still debated. We investigated the possible correlation between single nucleotide polymorphisms of hOCT1 (rs683369 [c.480C>G]) and ABCB1 (rs1128503 [c.1236C>T], rs2032582 [c.2677G>T/A], rs1045642 [c.3435C>T]) and nilotinib efficacy and toxicity in a cohort of 78 patients affected by chronic myeloid leukemia in the context of current clinical practice. The early molecular response was achieved by 81% of patients while 64% of them attained deep molecular response (median time, 26 months). The 36-month event-free survival was 86%, whereas 58% of patients experienced toxicities. Interestingly, hOCT1 and ABCB1 polymorphisms alone or in combination did not influence event-free survival or the adverse events rate. Therefore, in contrast to data obtained in patients treated with imatinib, hOCT1 and ABCB1 polymorphisms do not impact on nilotinib efficacy or toxicity. This could be relevant in the choice of the first-line therapy: patients with polymorphisms that negatively condition imatinib efficacy might thus receive nilotinib as first-line therapy.

ASXL1 and BIM germ line variants predict response and identify CML patients with the greatest risk of imatinib failure

Scoring systems used at diagnosis of chronic myeloid leukemia (CML), such as Sokal risk, provide important response prediction for patients treated with imatinib. However, the sensitivity and specificity of scoring systems could be enhanced for improved identification of patients with the highest risk. We aimed to identify genomic predictive biomarkers of imatinib response at diagnosis to aid selection of first-line therapy. Targeted amplicon sequencing was performed to determine the germ line variant profile in 517 and 79 patients treated with first-line imatinib and nilotinib, respectively. The Sokal score and ASXL1 rs4911231 and BIM rs686952 variants were independent predictors of early molecular response (MR), major MR, deep MRs (MR⁴ and MR^4.5), and failure-free survival (FFS) with imatinib treatment. In contrast, the ASXL1 and BIM variants did not consistently predict MR or FFS with nilotinib treatment. In the imatinib-treated cohort, neither Sokal or the ASXL1 and BIM variants predicted overall survival (OS) or progression to accelerated phase or blast crisis (AP/BC). The Sokal risk score was combined with the ASXL1 and BIM variants in a classification tree model to predict imatinib response. The model distinguished an ultra-high-risk group, representing 10% of patients, that predicted inferior OS (88% vs 97%; P = .041), progression to AP/BC (12% vs 1%; P = .034), FFS (P < .001), and MRs (P < .001). The ultra-high-risk patients may be candidates for more potent or combination first-line therapy. These data suggest that germ line genetic variation contributes to the heterogeneity of response to imatinib and may contribute to a prognostic risk score that allows early optimization of therapy.

Pharmacogenetics of drug transporters in modulating imatinib disposition and treatment outcomes in chronic myeloid leukemia & gastrointestinal stromal tumor patients

The use of imatinib in the treatment of BCR-ABL-positive chronic myeloid leukemia and gastrointestinal stromal tumors has significantly improved survival outcomes in patients afflicted by these malignancies. However, a substantial proportion of imatinib-treated patients still experience treatment failure. Suboptimal concentrations of imatinib have been postulated to contribute at least partially to the development of resistance against imatinib. Indeed, variations in the genes encoding drug transporters have been reported to markedly influence imatinib disposition and treatment outcomes in various populations. This review aims to consolidate and critically assess the studies conducted to date which have investigated the influence of pharmacogenetic variants in drug transporters on the disposition of imatinib and treatment outcomes in Asians and other populations.

GSTM1 and GSTP1, but not GSTT1 genetic polymorphisms are associated with chronic myeloid leukemia risk and treatment response

BACKGROUND

Chronic myeloid leukemia (CML) is associated to the BCR-ABL1 oncogene and can successfully be treated with tyrosine kinase inhibitors (TKIs). However, it remains still under investigation which molecular factors may influence CML risk or varying responses to TKIs. The aim of this study was to assess the role of Glutathione-S-transferases (GSTs) genetic polymorphisms in CML susceptibility and TKI clinical outcome.

MATERIALS

Deletion polymorphisms in GSTM1 and GSTT1 genes and the single nucleotide polymorphism in GSTP1 c.319A>G (rs1695; p.105Ile>Val) were genotyped by PCR methods in 141 CML treated patients and 141 sex- and age-matched healthy individuals.

RESULTS

Individual analysis of each GST gene showed no association with CML risk. A trend toward significance (p=0.07) for a recessive model was found for GSTP1 (OR: 2.04; CI: 0.94-4.4). However, the combined analysis showed that GSTM1-null/GSTP1-GG as well as GSTT1-null/GSTP1-GG were associated with CML development (p=0.03; OR: 3.54 CI: 1.2-14.57; p=0.05; OR: 12.65; CI: 1.17-21.5). The relationship with treatment outcome showed that the presence of GSTM1 gene was significantly linked with an inferior rate of major molecular response (p=0.048) and poor event free-survival (EFS) (p=0.02). Furthermore, a group of patients with GSTP1-GG genotype were significantly associated with reduced EFS comparing to those carrying other GSTP1 genotypes (p=0.049). GSTP1-GG genotypes had short time to treatment failure in a group of patients unresponsive to TKIs comparing to other GSTP1 genotypes (p=0.03).

CONCLUSIONS

This study highlights the significance of GSTM1 and GSTP1 polymorphisms on CML susceptibility and response to TKIs in the Argentinean population.