Multidrug resistance-1 gene polymorphisms associated with treatment outcomes in de novo acute myeloid leukemia

Can pharmacogenetics impact the therapeutic effect of cytarabine and anthracyclines in adult acute myeloid leukaemia patients?: A Serbian experience

Background

Cytarabine-anthracycline-based induction chemotherapy remains the standard of care for remission induction among patients with newly diagnosed acute myeloid leukaemia (AML). There are remarkable differences in therapy response among AML patients. This fact could be partly explained by the patients' genetic variability related to the metabolic paths of cytarabine and anthracyclines. This study aims to evaluate the effect of variants in pharmacogenes SLC29A1, DCK, ABCB1, GSTM1, and GSTT1, as well as laboratory and AML-related parameters on clinical outcomes in adult AML patients.

Methods

A total of 100 AML patients were included in the study. Pharmacogenetic variants SLC29A1 rs9394992, DCK rs12648166, ABCB1 rs2032582, and GSTM1 and GSTT1 gene deletions were detected by methodology based on PCR, fragment analysis and direct sequencing. The methods of descriptive and analytic statistics were used. Survival analysis was done using the Kaplan-Meier method using the Log-Rank test.

Results

This is the first study of adult AML pharmacogenetics in the Serbian population. Clinical outcomes in our cohort of AML patients were not impacted by analysed variants in SLC29A1, DCK, ABCB1 and GSTT1, and GSTM1 genes, independently or in combinations. Achievement of complete remission was identified as an independent prognostic indicator of clinical outcome.

Conclusions

The population-specific genomic profile has to be considered in pharmacogenetics. Since the data on AML pharmacogenetics in European populations is limited, our results contribute to knowledge in this field and strongly indicate that a high-throughput approach must be applied to find particular pharmacogenetic markers of AML in the European population.

ABC transporters are predictors of treatment failure in acute myeloid leukaemia

INTRODUCTION

To date, no chemoresistance predictors are included in acute myeloid leukaemia (AML) prognostic scoring systems to distinguish responding and refractory AML patients prior to chemotherapy. ABC transporters have been described as altering AML chemosensitivity; however, a relevant study investigating their role at various molecular levels was lacking.

METHODS

Gene expression, genetic variants, methylation and activity of ABCA2, ABCA5, ABCB1, ABCB6, ABCC1, ABCC3 and ABCG2 were analysed in AML blasts and healthy myeloblasts. Differences between responding and refractory AML in a cohort of 113 patients treated with 3 + 7 induction therapy were explored.

RESULTS

ABCC3 variant rs2301837 (p = 0.049), ABCG2 variant rs11736552 (p = 0.044), higher ABCA2 (p = 0.021), ABCC1 (p = 0.017), and ABCG2 expression (p = 0.023) and a higher number of concurrently overexpressed transporters (p = 0.002) were predictive of treatment failure by multivariate analysis. Expression of ABCA5 (p = 0.003), ABCB6 (p = 0.001) and ABCC3 (p < 0.0001) increased significantly after chemotherapy. Higher ABCG2 promoter methylation correlated with lower ABCG2 expression (p = 0.0001). ABCC1 was identified as the most active transporter in AML blasts by functional analysis.

CONCLUSIONS

ABC transporters, especially ABCC1 seem to contribute substantially to AML chemoresistance. A detailed understanding of chemoresistance mechanisms and the clinical implications of chemosensitivity predictors may lead to alternative therapeutic approaches for AML patients with unveiled chemoresistance signatures.

Role of Pharmacogenetics in the Treatment of Acute Myeloid Leukemia: Systematic Review and Future Perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by remarkable toxicity and great variability in response to treatment. Plenteous pharmacogenetic studies have already been published for classical therapies, such as cytarabine or anthracyclines, but such studies remain scarce for newer drugs. There is evidence of the relevance of polymorphisms in response to treatment, although most studies have limitations in terms of cohort size or standardization of results. The different responses associated with genetic variability include both increased drug efficacy and toxicity and decreased response or resistance to treatment. A broad pharmacogenetic understanding may be useful in the design of dosing strategies and treatment guidelines. The aim of this study is to perform a review of the available publications and evidence related to the pharmacogenetics of AML, compiling those studies that may be useful in optimizing drug administration.

Functional Genetic Variants in ATG10 Are Associated with Acute Myeloid Leukemia

Simple Summary

Acute myeloid leukemia (AML) is a hematological neoplasm with a very poor survival rate. To date, diagnostic tools to monitor individuals at higher risk of developing AML are scarce. Single nucleotide polymorphisms (SNPs) have emerged as good candidates for disease prevention. AML is characterized by altered autophagy, a vital mechanism to remove and recycle unnecessary or dysfunctional cellular components. ATG10 is one of the autophagy core genes involved in the autophagosome formation. We hypothesize that SNPs located in regulatory regions of the ATG10 gene could predispose individuals to AML development. We therefore genotyped three SNPs within the ATG10 locus. We identified the ATG10_rs3734114 as a potential risk factor for developing AML, whereas the ATG10_rs1864182 was associated with decreased risk. These findings highlight ATG10 as a key regulator of susceptibility to AML. Furthermore, we believe that ATG10 SNPs could be exploited in the clinical setting as an AML prevention strategy.

Abstract

Acute myeloid leukemia (AML) is the most common acute leukemia, characterized by a heterogeneous genetic landscape contributing, among others, to the occurrence of metabolic reprogramming. Autophagy, a key player on metabolism, plays an essential role in AML. Here, we examined the association of three potentially functional genetic polymorphisms in the ATG10 gene, central for the autophagosome formation. We screened a multicenter cohort involving 309 AML patients and 356 healthy subjects for three ATG10 SNPs: rs1864182T>G, rs1864183C>T and rs3734114T>C. The functional consequences of the ATG10 SNPs in its canonical function were investigated in vitro using peripheral blood mononuclear cells from a cohort of 46 healthy individuals. Logistic regression analysis adjusted for age and gender revealed that patients carrying the ATG10_rs1864182G allele showed a significantly decreased risk of developing AML (OR [odds ratio] = 0.58, p = 0.001), whereas patients carrying the homozygous ATG10_rs3734114C allele had a significantly increased risk of developing AML (OR = 2.70, p = 0.004). Functional analysis showed that individuals carrying the ATG10_rs1864182G allele had decreased autophagy when compared to homozygous major allele carriers. Our results uncover the potential of screening for ATG10 genetic variants in AML prevention strategies, in particular for subjects carrying other AML risk factors such as elderly individuals with clonal hematopoiesis of indeterminate potential.

Update on drug transporter proteins in acute myeloid leukemia: Pathological implication and clinical setting

Acute myeloid leukemia (AML) is one of the most common hematological neoplasia causing death worldwide. The long-term overall survival is unsatisfactory due to many factors including older age, genetic heterogeneity and molecular characteristics comprising additional mutations, and resistance to chemotherapeutic drugs. The expression of ABCB1/P-glycoprotein, ABCC1/MRP1, ABCG2/BCRP and LRP transporter proteins is considered the major reason for multidrug resistance (MDR) in AML, however conflicting data have been reported. Here, we review the main issues about drug transporter proteins in AML clinical scenario, and highlight the clinicopathological significance of MDR phenotype associated with ABCB1 polymorphisms and FLT3 mutation.

Pharmacogenomics to Predict Tumor Therapy Response: A Focus on ATP-Binding Cassette Transporters and Cytochromes P450

Pharmacogenomics is an evolving tool of precision medicine. Recently, due to the introduction of next-generation sequencing and projects generating "Big Data", a plethora of new genetic variants in pharmacogenes have been discovered. Cancer resistance is a major complication often preventing successful anticancer treatments. Pharmacogenomics of both somatic mutations in tumor cells and germline variants may help optimize targeted treatments and improve the response to conventional oncological therapy. In addition, integrative approaches combining copy number variations and long noncoding RNA profiling with germline and somatic variations seem to be a promising approach as well. In pharmacology, expression and enzyme activity are traditionally the more studied aspects of ATP-binding cassette transporters and cytochromes P450. In this review, we briefly introduce the field of pharmacogenomics and the advancements driven by next-generation sequencing and outline the possible roles of genetic variation in the two large pharmacogene superfamilies. Although the evidence needs further substantiation, somatic and copy number variants as well as rare variants and common polymorphisms in these genes could all affect response to cancer therapy. Regulation by long noncoding RNAs has also been shown to play a role. However, in all these areas, more comprehensive studies on larger sets of patients are needed.

Acid ceramidase promotes drug resistance in acute myeloid leukemia through NF-κB-dependent P-glycoprotein upregulation

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. More than half of older AML patients fail to respond to cytotoxic chemotherapy, and most responders relapse with drug-resistant disease. Failure to achieve complete remission can be partly attributed to the drug resistance advantage of AML blasts that frequently express P-glycoprotein (P-gp), an ATP-binding cassette transporter. Our previous work showed that elevated acid ceramidase (AC) levels in AML contribute to blast survival. Here, we investigated P-gp expression levels in AML relative to AC. Using parental HL-60 cells and drug-resistant derivatives as our model, we found that P-gp expression and efflux activity were highly upregulated in resistant derivatives. AC overexpression in HL-60 conferred resistance to the AML chemotherapeutic drugs, cytarabine, mitoxantrone, and daunorubicin, and was linked to P-gp upregulation. Furthermore, targeting AC through pharmacologic or genetic approaches decreased P-gp levels and increased sensitivity to chemotherapeutic drugs. Mechanistically, AC overexpression increased NF-κB activation whereas NF-kB inhibitors reduced P-gp levels, indicating that the NF-kappaB pathway contributes to AC-mediated modulation of P-gp expression. Hence, our data support an important role for AC in drug resistance as well as survival and suggest that sphingolipid targeting approaches may also impact drug resistance in AML.

Exploring the Structure-Activity Relationship and Mechanism of a Chromene Scaffold (CXL Series) for Its Selective Antiproliferative Activity toward Multidrug-Resistant Cancer Cells

Multidrug resistance (MDR) is one major barrier in cancer management, which urges for new drugs to help treat MDR malignancies and elucidate MDR mechanisms. A series of chromene compounds (the CXL series) demonstrate increased antiproliferative activity toward MDR acute-myeloid-leukemia (AML) cells. The structure-activity relationship (SAR) of the antiproliferative potency has been partly characterized, whereas the structural determinants contributing to selectivity have not been investigated. In this study, three series of CXL compounds were synthesized and evaluated in HL60 and HL60/MX2 leukemia cells. The results not only confirmed previous SAR studies but also, for the first time, provided structural insights into the selectivity for MDR HL60/MX2 cells. Using the lead compounds as probes, we demonstrated that their modulation of intracellular-calcium homeostasis results in their antiproliferative potency and selectivity. Three candidates also demonstrate excellent in vitro safety profiles between cancer cells and normal cells, which will be evaluated in vivo in future studies.

Impact of ABC single nucleotide polymorphisms upon the efficacy and toxicity of induction chemotherapy in acute myeloid leukemia

Anthracycline uptake could be affected by efflux pumps of the ABC family. The influence of 7 SNPs of ABC genes was evaluated in 225 adult de novo acute myeloid leukemia (AML) patients. After multivariate logistic regression there were no significant differences in complete remission, though induction death was associated to ABCB1 triple variant haplotype (p = .020). The ABCB1 triple variant haplotype was related to higher nephrotoxicity (p = .016), as well as this haplotype and the variant allele of ABCB1 rs1128503, rs2032582 to hepatotoxicity (p = .001; p = .049; p < .001). Furthermore, the variant allele of ABCC1 rs4148350 was related to severe hepatotoxicity (p = .044), and the variant allele of ABCG2 rs2231142 was associated to greater cardiac (p = .004) and lung toxicities (p = .038). Delayed time to neutropenia recovery was observed with ABCB1 rs2032582 variant (p = .047). This study shows the impact of ABC polymorphisms in AML chemotherapy safety. Further prospective studies with larger population are needed to validate these associations.

Pharmacogenomics and the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a clinically and biologically heterogeneous malignancy that is primarily treated with combinations of cytarabine and anthracyclines. Although this scheme remains effective in most of the patients, variability of outcomes in patients has been partly related with their genetic variability. Several pharmacogenetic studies have analyzed the impact of polymorphisms in genes encoding transporters, metabolizers or molecular targets of chemotherapy agents. A systematic review on all eligible studies was carried out in order to estimate the effect of polymorphisms of anthracyclines and cytarabine pathways on efficacy and toxicity of AML treatment. Other emerging genes recently studied in AML, such as DNA repair genes, genes potentially related to chemotherapy response or AML prognosis, have also been included.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

MPT0B169, a novel tubulin inhibitor, induces apoptosis in taxol-resistant acute myeloid leukemia cells through mitochondrial dysfunction and Mcl-1 downregulation

Acute myeloid leukemia (AML) is a hematological malignant disorder. AML cells are not susceptible to chemotherapeutic drugs because of their multidrug resistance (MDR). Antitubulin agents are currently employed in cancer treatments; however, drug resistance results in treatment failures because of MDR1 expressing cancer cells. We previously synthesized a new tubulin inhibitor, 2-dimethylamino-N-[1-(4-methoxy-benzenesulfonyl)-2,3-dihydro-1H-indol-7-yl]-acetamide (MPT0B169), which inhibits AML cell proliferation by arresting cell cycle at the G2/M phase. In this study, we explored the effect of MPT0B169 on apoptosis in AML HL60 and NB4 cells and MDR1-mediated taxol-resistant HL60/TaxR cells and the underlying mechanism. MPT0B169 induced concentration- and time-dependent apoptosis in these cancer cells, as observed through annexin V/propidium iodide double staining and flow cytometry. Furthermore, DNA fragmentation analysis confirmed MPT0B169-induced apoptosis. MPT0B169 induced a loss of mitochondrial membrane potential, release of cytochrome c into the cytosol, cleavage and activation of caspase-9 and caspase-3, and consequently cleavage of poly (ADP ribose) polymerase. Western blot analysis showed that MPT0B169 markedly reduced Mcl-1 (an antiapoptotic protein) levels; however, it caused no changes in Bcl-2 or BAX (a proapoptotic protein). Knockdown of Mcl-1 using small interfering RNA (siRNA) slightly induced growth inhibition and apoptosis in the HL60 and HL60/TaxR cells. Further investigation revealed that Mcl-1 siRNA enhanced the sensitivity of HL60 and HL60/TaxR cells to MPT0B169-induced growth inhibition and apoptosis. Together, these results demonstrated that MPT0B169-induced apoptosis in nonresistant and MDR1-mediated taxol-resistant AML cells through Mcl-1 downregulation and a mitochondria-mediated pathway. MPT0B169 can overcome MDR1-mediated drug resistance in AML cells.

Association of ABCB1 polymorphisms with prognostic outcomes of anthracycline and cytarabine in Chinese patients with acute myeloid leukemia

PURPOSE

To investigate the influence of ABCB1 polymorphisms on prognostic outcomes in Chinese patients with de novo intermediate-risk acute myeloid leukemia (AML) and to examine the gene expression level in relation to the genetic variation.

METHODS

In total, 263 Chinese intermediate-risk AML patients treated with anthracycline and cytarabine were enrolled. G2677T, C1236T, and C3435T of the ABCB1 gene were analyzed by the allele-specific matrix-assisted laser desorption. Expression of ABCB1 messenger RNA (mRNA) was tested in 101 patients of known genotype and haplotype for ABCB1 polymorphisms. Basic clinical characteristics of these patients were collected from medical records.

RESULTS

Survival analysis showed that patients with AML (TTT haplotype) had a longer overall survival (OS) (p < 0.001, 29.2 months, 95 % confidence interval [CI], 26.9-31.5 months) and relapse-free survival (RFS) (p = 0.005, 21.8 months, 95 % CI, 19.5-24.0 months) compared with those without TTT haplotype (21.9 months, 95 % CI, 19.6-24.2 months; 16.5 months, 95 % CI, 14.6-18.5 months). After adjusting for age; gender; leukocyte count; hemoglobin level; platelet levels; French, American, and British classification; lactate dehydrogenase levels; Eastern Cooperative Oncology Group performance status; nucleophosmin gene; and fms-related tyrosine kinase 3 gene, the multivariate survival analysis showed that the TTT haplotype appeared to be a predicting factor for OS (p = 0.001, hazard ratio = 1.854, 95 % CI, 1.301-2.641) and RFS (p = 0.009, hazard ratio = 1.755, 95 % CI, 1.153-2.671). Moreover, a significant association between the TTT haplotype and relapse in AML patients was observed in this study (p = 0.002, odds ratio = 0.410, 95 % CI, 0.235-0.715). Gene expression level was significantly lower in patients with the TTT haplotype than in the patients with the other haplotypes (p = 0.004).

CONCLUSIONS

The findings suggested the TTT haplotype was possibly related to the OS, RFS, and relapse in Chinese patients with AML.

Polymorphisms of the drug transporters ABCB1, ABCG2, ABCC2 and ABCC3 and their impact on drug bioavailability and clinical relevance

INTRODUCTION

Human ATP-binding cassette (ABC) transporters act as translocators of numerous substrates across extracellular and intracellular membranes, thereby contributing to bioavailability and consequently therapy response. Genetic polymorphisms are considered as critical determinants of expression level or activity and subsequently response to selected drugs.

AREAS COVERED

Here the influence of polymorphisms of the prominent ABC transporters P-glycoprotein (MDR1, ABCB1), breast cancer resistance protein (BCRP, ABCG2) and the multidrug resistance-associated protein (MRP) 2 (ABCC2) as well as MRP3 (ABCC3) on the pharmacokinetic of drugs and associated consequences on therapy response and clinical outcome is discussed.

EXPERT OPINION

ABC transporter genetic variants were assumed to affect interindividual differences in pharmacokinetics and subsequently clinical response. However, decades of medical research have not yielded in distinct and unconfined reproducible outcomes. Despite some unique results, the majority were inconsistent and dependent on the analyzed cohort or study design. Therefore, variability of bioavailability and drug response may be attributed only by a small amount to polymorphisms in transporter genes, whereas transcriptional regulation or post-transcriptional modification seems to be more critical. In our opinion, currently identified genetic variants of ABC efflux transporters can give some hints on the role of transporters at interfaces but are less suitable as biomarkers to predict therapeutic outcome.

Low MDR1 and BAALC expression identifies a new subgroup of intermediate cytogenetic risk acute myeloid leukemia with a favorable outcome

Treatment optimization in acute myeloid leukemia requires the accurate assignment of patients at diagnosis to specific risk groups to guide subsequent risk-adapted treatment stratification. In this study, we have evaluated the impact of expression of the gene BAALC in conjunction with MDR1 in AML with intermediate cytogenetic risk group to more precisely define risk assessment. Low MDR1/high BAALC, high MDR1/low BAALC, and high MDR1/high BAALC expressers demonstrated a similar clinical outcome with CR rate being 68.75-75% and relapse rate being 40-50% and therefore could be considered as a "combined group". In contrast, low expression of both BAALC and MDR1 identifies an intermediate cytogenetic risk group a distinctly favorable outcome, with higher CR rate being 93.3%, lower relapse rate being 7.1%, and longer OS being 50.3% than that of the "combined group". Moreover, low MDR1/low BAALC expressers in the intermediate cytogenetic risk group also demonstrated a comparable clinical outcome with patients in the favorable-risk group. Thus low MDR1/low BAALC expression identifies a subgroup of intermediate cytogenetic risk AML patients with a remarkably good long-term outcome achieved by chemotherapy alone.

Association analysis of three ABCB1 (MDR1) gene variants (C1236T, G2677A/T and C3435T) and their genotype/haplotype combinations with the familial Mediterranean fever

1. Familial Mediterranean fever (FMF) is considered an autosomal recessive disorder, associated with a single gene named Mediterranean fever (MEFV). The aim of this study was to perform genotyping and haplotyping analysis of the multidrug resistance (ATP-binding cassette, subfamily B, member 1 - ABCB1) gene in FMF patients. 2. Three ABCB1 gene polymorphisms (C1236T, G2677T/A and C3435T) were analyzed in 309 FMF patients and 250 healthy control subjects. All subjects were genotyped by PCR-restriction fragment length polymorphism analysis, and statistical analysis was performed using the Arlequin 3.1.1 and SPSS 16.0 software packages. 3. The CT genotype frequency of the C3435T polymorphism (p = 0.003), the CT-GT-CT (C1236T-G2677T/A-C3435T) triple genotype (p = 0.001) and the C-G (C1236T-G2677T/A) haplotype (p = 0.030) were more common in the FMF patients. The CT-GG-CC triple genotype and T-G-C, C-T-T and T-G-T haplotypes (C1236T-G2677T/A-C3435T) were higher in the control subjects (p = 0.011, 0.001, 0.009 and 0.000, respectively). The CT-GG binary genotype and C-T and T-G haplotypes for C1236T-G2677T/A polymorphisms may have a high degree of protective effect against FMF (p = 0.0005, 0.002 and 0.000, respectively). 4. Our study showed that genotypes and haplotypes of ABCB1 gene polymorphisms may affect patients' FMF susceptibility.

Genotype variability and haplotype frequency of MDR1 (ABCB1) gene polymorphism in Morocco

The multidrug resistance gene (MDR1) plays an important role in the transport of a wide range of drugs and elimination of xenobiotics from the body. Identification of polymorphisms and haplotypes in the MDR1 gene might not only help understand pharmacokinetics and pharmacodynamics of drugs, but also can help in the prediction of drug responses, toxicity, and side effects, especially, in the era of personalized medicine. We have analyzed the genotypic and haplotypic frequencies of the three most common single-nucleotide polymorphisms in the MDR1 gene in a sample of 100 unrelated healthy Moroccan subjects by polymerase chain reaction-restrictive fragment length polymorphism. The observed genotype frequencies were 43% for 1236CC, 49% for 1236CT, and 8% for 1236TT in exon 12; 49% for 2677GG, 47% for 2677GT, and 4% for 2677TT in exon 21; 39% for 3435CC, 51% 3435CT for 3435TT, and 10% for 3435TT in exon 26, respectively. We found that all polymorphisms were in Hardy-Weinberg equilibrium. Moderate linkage disequilibrium (LD) was observed between the three polymorphisms, the strongest LD in our study has been observed between C1236T and G2677T (D'=0.76; r(2)=0.45). We identified eight haplotypes, the most frequent were 1236C-2677G-3435C (53%), 1236T-2677T-3435T (21%), and 1236C-2677G-3435T (10%), respectively. Our findings might facilitate future studies on pharmacokinetics of P-glycoprotein substrate drugs and interindividual variability to drugs in Moroccan patients.

Ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017): a novel scaffold that resensitizes multidrug resistant leukemia cells to chemotherapy

Multidrug resistance (MDR) is a major hurdle in the treatment of cancer, and there is a pressing need for new therapies. We have recently developed ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017), derived from a dual inhibitor of Bcl-2 and SERCA proteins, sHA 14-1, with selective cytotoxicity toward MDR cancer cell lines in vitro. In this study, we present new evidence for its therapeutic potential in treatment of MDR cancers and offer mechanistic insights toward its preferential targeting of drug-resistant cancer. CXL017 selectively suppressed the growth of tumors derived from the MDR cancer cell line, HL60/MX2, in vivo. In addition, even after chronic exposure to CXL017, HL60/MX2 failed to develop stable resistance to CXL017, whereas it acquired >2000-fold resistance to cytarabine (Ara-C), the major first-line chemotherapy for the treatment of acute myeloid leukemia (AML). Remarkably, instead of acquiring further cross-resistance, HL60/MX2 cells exposed to CXL017 were resensitized to standard therapies (10- to 100-fold). Western blotting analyses revealed that CXL017 exposure significantly down-regulated Mcl-1 and Bax and up-regulated Noxa, Bim, Bcl-X(L), SERCA2, and SERCA3 proteins, along with a reduction in endoplasmic reticulum (ER) calcium content. Given the well-established functions of Bcl-2 family proteins and ER calcium in drug resistance, our results suggest that the down-regulation of Mcl-1 and the up-regulation of Noxa and Bim along with the decrease in ER calcium content are likely responsible for CXL017-induced resensitization of MDR cancer cells. These data also demonstrate the unique potential of CXL017 to overcome MDR in cancer treatment.

Idarubicin is superior to daunorubicin in remission induction of de novo acute myeloid leukemia patients with high MDR1 expression

Aim: To investigate whether idarubicin in a cytarabine-based induction regimen was superior to daunorubicin in de novo acute myeloid leukemia patients expressing high MDR1. Patients & methods: The clinicopathological data were analyzed in 125 patients receiving daunorubicin or idarubicin with cytarabine for remission induction. Median MDR1 mRNA expression in pretreated bone marrow cells was used as the cutoff point for high and low MDR1 expression. Results: A total of 59.7% high and 77.8% low MDR1 expressers achieved complete remission (CR; p = 0.029). Idarubicin yielded a higher CR rate than daunorubicin in high MDR1 expressers (82.1 vs 41.2%; p = 0.001), it also demonstrated a higher CR rate than daunorubicin (p < 0.05) in high MDR1 expressers exhibiting favorable or intermediate risk, while there was no difference between the two treatment arms in low MDR1 expressers exhibiting either favorable or intermediate risk. Conclusion: Idarubicin is associated with better remission induction of de novo acute myeloid leukemia patients with high MDR1 expression.

Original submitted 23 May 2012; Revision submitted 10 October 2012

Drug resistance: still a daunting challenge to the successful treatment of AML

Resistance to chemotherapy remains a challenging issue for patients and their physicians. P-glycoprotein (Pgp, MDR1, ABCB1), as well as a family of structurally and functionally related proteins, are plasma membrane transporters able to efflux a variety of substrates from the cell cytoplasm, including chemotherapeutic agents. The discovery of ABCB1 made available a potential target for pharmacologic down-regulation of efflux-mediated chemotherapy resistance. In patients with acute myeloid leukemia (AML), a neoplasm characterized by proliferation of poorly differentiated myeloid progenitor cells, leukemic cells often express ABCB1 at high levels, which may lead to the development of resistance to chemotherapy. Thus, AML seemed to be a likely cancer for which the addition of drug efflux inhibitors to the chemotherapeutic regimen would improve outcomes in patients. Despite this rational hypothesis, the majority of clinical trials evaluating this strategy have failed to reach a positive endpoint, most recently the Eastern Cooperative Oncology Group E3999 trial. Here we review data suggesting the importance of ABCB1 in AML, address the failure of clinical trials to support a therapeutic strategy aimed at modulating ABCB1-mediated resistance, and consider the type of research that should be conducted in this field going forward.

ABCB1 genetic variation and P-glycoprotein expression/activity in a cohort of Brazilian acute myeloid leukemia patients

PURPOSE

Polymorphisms in the ABCB1 gene may influence P-glycoprotein (Pgp) expression and/or activity. Because the population in Brazil is markedly heterogeneous, we analyzed the relationship between ABCB1 polymorphisms and Pgp expression/activity in Brazilian acute myeloid leukemia (AML) patients.

METHODS

Acute myeloid leukemia samples from 109 patients were studied. ABCB1 gene variants rs1128503 (C1236T) and rs1045643 (C3435T) were analyzed by PCR-RFLP assay. Pgp expression and Pgp activity were analyzed by flow cytometry.

RESULTS

There was a similar distribution of Pgp expression and activity on polymorphisms C1236T, C1236C, and T1236T for exon 12, and C3435T, C3435C, and T3435T for exon 26. An exception was observed in the lowest ratio of mean fluorescence intensity (MFI) median for Pgp expression in the TT genotype for both studied exons, and its correspondence to a low MFI median for Pgp activity. Pgp expression did not show impact on the response to remission induction therapy, but the MFI median of Pgp expression in the remission failure group was higher than that of the complete remission (CR) group of patients (p = 0.04). Overall survival (OS) was significantly influenced by CR (p = 0.0001). Better 5-year OS and 5-year event-free survival rates (p = 0.04 and p = 0.007, respectively) were achieved in patients presenting the genetic variant CC in exon 12 followed by those presenting the variant CT in exon 26 (p = 0.001).

CONCLUSIONS

Polymorphisms in the ABCB1 gene and the levels of Pgp expression could be useful to identify prognostic in AML patients.

Part 2: pharmacogenetic variability in drug transport and phase I anticancer drug metabolism

Equivalent drug doses in anticancer chemotherapy may lead to wide interpatient variability in drug response reflected by differences in treatment response or in severity of adverse drug reactions. Differences in the pharmacokinetic (PK) and pharmacodynamic (PD) behavior of a drug contribute to variation in treatment outcome among patients. An important factor responsible for this variability is genetic polymorphism in genes that are involved in PK/PD processes, including drug transporters, phase I and II metabolizing enzymes, and drug targets, and other genes that interfere with drug response. In order to achieve personalized pharmacotherapy, drug dosing and treatment selection based on genotype might help to increase treatment efficacy while reducing unnecessary toxicity. We present a series of four reviews about pharmacogenetic variability in anticancer drug treatment. This is the second review in the series and is focused on genetic variability in genes encoding drug transporters (ABCB1 and ABCG2) and phase I drug-metabolizing enzymes (CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, DPYD, CDA and BLMH) and their associations with anticancer drug treatment outcome. Based on the literature reviewed, opportunities for patient-tailored anticancer therapy are presented.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

MDR-1 gene polymorphisms G2677T and C3435T in a case of Hodgkin's variant of Richter's syndrome

Richter's syndrome is defined as the transformation of low-grade lymphoma to a more aggressive high-grade malignant form, usually diffuse large B-cell lymphoma. Hodgkin's lymphoma variant of Richter transformation is relatively rare, and only approximately 100 cases have been reported in the literature. This study examined a case of a 53-year-old woman who developed Hodgkin's lymphoma almost 5 years after the diagnosis of chronic lymphocytic leukemia (CLL). The major points of interest regarding CLL with Hodgkin's transformation were also considered, such as the potential role of MDR-1 gene polymorphisms. The patient was evaluated for two MDR-1 gene polymorphisms, G2677T polymorphism in exon 21 and silent C3435T polymorphism in exon 26, to ascertain whether polymorphisms affect the risk of Hodgkin's lymphoma variant of Richter transformation and whether genomic polymorphisms provide prognostic information on the clinical progression of the disease. According to the data obtained, the analysis of polymorphisms in the MDR1 gene exons 21 and 26 revealed that the T2677T and T3435T alleles are not a predisposing factor to Richter transformation, while the presence of the wild-type genotype may be associated with a more favorable response to therapy.

P-glycoprotein: tissue distribution, substrates, and functional consequences of genetic variations

P-glycoprotein (ABCB1, MDR1) belongs to the ABC transporter family transporting a wide range of drugs and xenobiotics from intra- to extracellular at many biological interfaces such as the intestine, liver, blood-brain barrier, and kidney. The ABCB1 gene is highly polymorphic. Starting with the observation of lower duodenal protein expression and elevated digoxin bioavailability in relation to the 3435C>T single nucleotide polymorphism, hundreds of pharmacokinetic and outcome studies have been performed, mostly genotyping 1236C>T, 2677G>T/A, and 3435C>T. Though some studies pointed out that intracellular concentrations of anticancer drugs, for example, within lymphocytes, might be affected by ABCB1 variants resulting in differential outcome, current knowledge of the functional significance genetic variants of ABC membrane transporters does not allow selection of a particular SNP to predict an individual's pharmacokinetics.

MDR-1 polymorphisms (G2677T and C3435T) in B-chronic lymphocytic leukemia: an impact on susceptibility and prognosis

Patients with B-chronic lymphocytic leukemia present diverse clinical features, genetic abnormalities, variable response to treatment, and heterogeneous prognosis. Novel biological markers such as IgVH mutation, CD38, and ZAP-70 expression have shown to offer important prognostic information. An altered expression of the multidrug resistance 1 may represent an additional prognostic marker. Aim of our study was to evaluate two MDR-1 gene polymorphisms: G2677T polymorphism in exon 21 and C3435T polymorphism in exon 26, to evidence if polymorphisms influence the risk of development of B-CLL and whether genomic polymorphisms provide prognostic information on the clinical progression of the disease. A total of 125 patients with B-CLL and 125 healthy subjects were enrolled in this study. The mutant homozygous 2677 TT genotype was found to be associated with the occurrence of B-CLL and higher T allele frequency in patients with B-CLL when compared with controls was observed (P=0.009). When comparing the prognostic patients' characteristics, patients with 2677 GT genotype were statistically linked to the unmutated IgVH genes (r=0.209, P=0.01). Moreover, the same genotype was correlated with lymphocyte number (r=0.269, P=0.02). Finally for the 2677GT polymorphism, the heterozygous status was associated with higher hemoglobin levels (r=0.247, P=0.005). As far the C3435T MDR1 polymorphism, we were not able to identify any significant correlation with IgVH gene status or other variables. In conclusion, MDR1 gene polymorphism could be a factor predisposing to LLC. Moreover, our findings support the possibility of considering these genomic polymorphisms as prognostic markers in patients with B-CLL.

Pharmacogenetics of ATP-binding cassette transporters and clinical implications

Drug resistance is a severe limitation of chemotherapy of various malignancies. In particular efflux transporters of the ATP-binding cassette family such as ABCB1 (P-glycoprotein), the ABCC (multidrug resistance-associated protein) family, and ABCG2 (breast cancer resistance protein) have been identified as major determinants of chemoresistance in tumor cells. Bioavailability depends not only on the activity of drug metabolizing enzymes but also to a major extent on the activity of drug transport across biomembranes. They are expressed in the apical membranes of many barrier tissues such as the intestine, liver, blood-brain barrier, kidney, placenta, testis, and in lymphocytes, thus contributing to plasma, liquor, but also intracellular drug disposition. Since expression and function exhibit a broad variability, it was hypothesized that hereditary variances in the genes of membrane transporters could explain at least in part interindividual differences of pharmacokinetics of a variety of anticancer drugs and many others contributing to the clinical outcome of certain leukemias and further malignancies.

The ABCB1 3435 T allele does not increase the risk of paclitaxel-induced neurotoxicity

Paclitaxel is a frequently used anticancer drug with considerable inter-individual variability in terms of drug efficiency and toxicity. The reasons for this variability have not been fully explained. The purpose of this study was to evaluate the possible relationship between paclitaxel-induced neurotoxicity and the distribution of genetic variations with reported functional significance in the ABCB1, CYP2C8 and CYP3A4 genes that are all implicated in taxol metabolism. Women (n=36) experiencing paclitaxel-induced neurotoxicity were included in the study, and the ABCB1 G2677A/T and C3435T as well as CYP2C8(*)3 and CYP3A4(*)1b allele frequencies were determined using PCR-RFLP and DNA sequence analysis. We showed that the ABCB1 3435T allele, previously reported as a risk allele for neurotoxicity, did not correlate with the occurrence of neurotoxicity in our patient sample (Chi-square test, p=0.61). Furthermore, we showed that neither the CYP2C8(*)3 nor CYP3A4(*)1b alleles, that both lead to diminished enzyme activity, correlated with paclitaxel-induced neurotoxicity. The occurrence and variation in severity of neurotoxicity in our Swedish patient sample could therefore not be explained by the reported functional polymorphisms in the ABCB1, CYP2C8 and CYP3A4 genes.

Clinical relevance of a pharmacogenetic approach using multiple candidate genes to predict response and resistance to imatinib therapy in chronic myeloid leukemia

PURPOSE

Imatinib resistance is major cause of imatinib mesylate (IM) treatment failure in chronic myeloid leukemia (CML) patients. Several cellular and genetic mechanisms of imatinib resistance have been proposed, including amplification and overexpression of the BCR/ABL gene, the tyrosine kinase domain point mutations, and MDR1 gene overexpression.

EXPERIMENTAL DESIGN

We investigated the impact of 16 single nucleotide polymorphisms (SNP) in five genes potentially associated with pharmacogenetics of IM, namely ABCB1, multidrug resistance 1; ABCG2, breast-cancer resistance protein; CYP3A5, cytochrome P450-3A5; SLC22A1, human organic cation transporter 1; and AGP, alpha1-acid glycoprotein. The DNAs from peripheral blood samples in 229 patients were genotyped.

RESULTS

The GG genotype in ABCG2 (rs2231137), AA genotype in CYP3A5 (rs776746), and advanced stage were significantly associated with poor response to IM especially for major or complete cytogenetic response, whereas the GG genotype at SLC22A1 (rs683369) and advanced stage correlated with high rate of loss of response or treatment failure to IM therapy.

CONCLUSIONS

We showed that the treatment outcomes of imatinib therapy could be predicted using a novel, multiple candidate gene approach based on the pharmacogenetics of IM.

Influence of the G2677T/C3435T haplotype of MDR1 on P-glycoprotein trafficking and ibutilide-induced block of HERG

The drug efflux pump P-glycoprotein possesses two common and often linked polymorphisms that result in variable drug action. G2677T results in A893S, whereas C3435T is synonymous and has been reported to alter protein folding. We tested the effect of these MDR1 variants on Human Ether-Related A Go-Go (HERG) block by ibutilide in CHO cells 48 h following transient transfection with an IRES-dsRed vector containing MDR1, G2677T MDR1, G2677T/C3435T MDR1 or an empty bicistronic site and an IRES-GFP vector containing HERG (KCNH2). Cotransfection of MDR1 variants had no effect on I(Kr) amplitude at baseline. Cells cotransfected with MDR1-G2677T showed resistance to ibutilide vs HERG alone (IC(50): 105.3+/-1.42 nM vs 27.4+/-2.5 nM; P<0.0001), consistent with the idea that A893S attenuates I(Kr) block by enhancing drug efflux and thus reducing the drug available to interact with the channel binding site. However, G2677T/C3435T cells showed ibutilide sensitivity similar to cells expressing HERG alone (IC(50): 22.2+/-0.9 nM). Immunostaining showed that the C3435T variant did not traffic to the cell surface. Coculture with fexofenadine(1 microM), an MDR1 substrate known to rescue misfolding in other membrane proteins, restored cell surface expression of MDR1 G2677T/C3435T and restored resistance to block HERG by ibutilide 200 nM (98.5+/-0.98% vs 42.3+/-2.2%, P<0.001). The non-synonymous MDR1 variant G2677 T (A893S) confers resistance to ibutilide block of I(Kr), which is mitigated by the C3435T polymorphism through reduced protein expression, an effect that can be restored by coculture with fexofenadine. These data identify ibutilide as an MDR1 substrate and further support the concept that variable drug transport function can modulate the action of HERG blockers.

C3435T polymorphism of the MDR1 gene is not associated with P-glycoprotein function of leukemic blasts and clinical outcome in patients with acute myeloid leukemia

We investigated the association between the MDR1 C3435T polymorphism and P-glycoprotein function of leukemic blasts as well as clinical outcomes in 200 patients with AML, excluding the M3 subtype. The CC, CT and TT genotype frequencies of the C3435T polymorphism among patients were 71, 93 and 36, respectively. The C3435T polymorphism genotypes did not have influence on the P-glycoprotein function of leukemic blasts. Complete remission rates and overall, relapse-free and event-free survival rates were not significantly different among the C3435T polymorphism genotypes. In conclusion, the MDR1 C3435T polymorphism does not appear to have significant clinical implications in AML.

Vascular endothelial growth factor (VEGF) gene (VEGFA) polymorphism can predict the prognosis in acute myeloid leukaemia patients

Increased angiogenesis, mediated by vascular endothelial growth factor (VEGF), was associated with poor prognosis in acute myeloid leukaemia (AML) patients. The current study investigated the impact of VEGF gene (VEGFA) single nucleotide polymorphisms (SNPs) on treatment outcomes for AML. Four VEGFA SNPs were analysed for -2578C>A (rs699947), -460T>C (rs833061), +405G>C (rs2010963) and +936 C>T (rs3025039) loci in 138 AML patients. The +936 CC/CT genotype showed strong correlation with favourable leukaemia-free survival (LFS) at 2 years (51.3%) versus with +936 CC genotype (33.6%, P = 0.03). Strong linkage disequilibrium was noted among loci -2578, -460 and +405, but not with +936. Accordingly, four haplotypes were generated based on the genotypes of -2578, -460 and +405 as follows: CTC (40.2%), CTG (35.0%), ACG (22.0%) and ATC (1.2%). The LFS and event-free survival (EFS) inversely correlated with CTG haplotype (P = 0.03 for LFS; P = 0.05 for EFS). We scored the VEGFA polymorphism marker based on +936 C>T genotype and CTG haplotype for -2578, -460 and +405, which demonstrated a good correlation with the treatment outcomes: LFS (P = 0.01), EFS (P = 0.03) and overall survival (P = 0.01). The VEGFA +936 C>T genotype and CTG haplotype seemed to have an additive effect to predict the prognosis in AML patients.

Expression of adenosine triphosphate-binding cassette (ABC) drug transporters in peripheral blood cells: relevance for physiology and pharmacotherapy

Adenosine triphosphate-binding cassette (ABC)-type transport proteins were initially described for their ability to reduce intracellular concentrations of anticancer compounds, thereby conferring drug resistance. In recent years, expression of this type of proteins has also been reported in numerous cell types under physiological conditions; here, these transporters are often reported to alter systemic and local drug disposition (e.g. in the brain or the gastrointestinal tract). In this context, peripheral blood cells have also been found to express several ABC-type transporters. While erythrocytes mainly express multidrug resistance protein (MRP) 1, MRP4 and MRP5, which are discussed with regard to their involvement in glutathione homeostasis (MRP1) and in the efflux of cyclic nucleotides (MRP4 and MRP5), leukocytes also express P-glycoprotein and breast cancer resistance protein. In the latter cell types, the main function of efflux transporters may be protection against toxins, as these cells demonstrate a very high turnover rate. In platelets, only two ABC transporters have been described so far. Besides MRP1, platelets express relatively high amounts of MRP4 not only in the plasma membrane but also in the membrane of dense granules, suggesting relevance for mediator storage. In addition to its physiological function, ABC transporter expression in these structures can be of pharmacological relevance since all systemic drugs reach their targets via circulation, thereby enabling interaction of the therapeutic agent with peripheral blood cells. Moreover, both intended effects and unwanted side effects occur in peripheral blood cells, and intracellular micropharmacokinetics can be affected by these transport proteins. The present review summarises the data available on expression of ABC transport proteins in peripheral blood cells.

Pharmacogenomics of acute leukemia

Pharmacogenomics provides knowledge regarding how genetic polymorphisms affect treatment responses. Such an approach is particularly needed in cancer therapy, as most chemotherapeutics drugs affect both tumor and normal cells, are ineffective in many patients and exhibit serious side effects. Leukemia exists in two different forms, myeloid and lymphoid. Acute lymphoblastic leukemia more frequently occurs in children, whereas the risk of acute myeloid leukemia is more common in adults. Despite significant progress in the treatment of these diseases, therapy is still unsuccessful in many patients. Prognosis is particularly poor in adult acute myeloid leukemia. Treatment failure in childhood acute lymphoblastic leukemia due to drug resistance remains the leading cause of cancer-related death in children. Here, we provide an overview of pharmacogenetics studies carried out in children and adults with acute lymphoblastic leukemia and acute myeloid leukemia, attempting to find the associations between treatment responses and polymorphisms in the genes whose products are needed for metabolism, and effects of drugs used in the treatment of leukemia.

Pharmacogenetics/genomics of membrane transporters in cancer chemotherapy

Inter-individual variability in drug response and the emergence of adverse drug reactions are main causes of treatment failure in cancer therapy. Recently, membrane transporters have been recognized as an important determinant of drug disposition, thereby affecting chemosensitivity and -resistance. Genetic factors contribute to inter-individual variability in drug transport and targeting. Therefore, pharmacogenetic studies of membrane transporters can lead to new approaches for optimizing cancer therapy. This review discusses genetic variations in efflux transporters of the ATP-binding cassette (ABC) family such as ABCB1 (MDR1, P-glycoprotein), ABCC1 (MRP1), ABCC2 (MRP2) and ABCG2 (BCRP), and uptake transporters of the solute carrier (SLC) family such as SLC19A1 (RFC1) and SLCO1B1 (SLC21A6), and their relevance to cancer chemotherapy. Furthermore, a pharmacogenomic approach is outlined, which using correlations between the growth inhibitory potency of anticancer drugs and transporter gene expression in multiple human cancer cell lines, has shown promise for determining the relevant transporters for any given drugs and predicting anticancer drug response.