Polymorphisms of ABCG2 and its impact on clinical relevance

The role of ABCG2 in health and disease: Linking cancer therapy resistance and other disorders

All biological systems have adenosine triphosphate (ATP) binding cassette (ABC) transporters, one of the significant protein superfamilies involved in transport across membranes. ABC transporters have been implicated in the etiology of diseases like metabolic disorders, cancer, and Alzheimer's disease. ATP-binding cassette superfamily G member 2 (ABCG2), one of the ABC transporters, is necessary for the ATP-dependent efflux of several endogenous and exogenous substances. Consequently, it maintained cellular homeostasis and shielded tissue from xenobiotic substances. ABCG2 was initially identified in an Adriamycin-selected breast cancer cell line (MCF-7/AdrVp) and was linked to the emergence of multidrug resistance (MDR) in cancerous cells. Under many pathophysiological conditions, including inflammation, disease pathology, tissue injury, infection, and in response to xenobiotics and endogenous substances, the expression of ABCG2 undergoes alterations that result in modifications in its function and activity. Genetic variants in the ABCG2 transporter can potentially impact its expression and function, contributing to the development of many disorders. This review aimed to illustrate the impact of ABCG2 expression and its variants on oral drug bioavailability, MDR in specific cancer cells, explore the relationship between ABCG2 expression and other disorders such as gout, Alzheimer's disease, epilepsy, and erythropoietic protoporphyria, and demonstrate the influence of various synthetic and natural compounds in regulating ABCG2 expression.

Inhibition of ABCG2 prevents phototoxicity in a mouse model of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is a genetic disease characterized by protoporphyrin IX-mediated painful phototoxicity. Currently, options for the management of EPP-associated phototoxicity are limited and no oral medication is available. Here, we investigated a novel therapy against EPP-associated phototoxicity by targeting the ATP-binding cassette subfamily G member 2 (ABCG2), the efflux transporter of protoporphyrin IX. Oral ABCG2 inhibitors were developed, and they successfully prevented EPP-associated phototoxicity in a genetically engineered EPP mouse model. Mechanistically, ABCG2 inhibitors suppress protoporphyrin IX release from erythroid cells and reduce the systemic exposure to protoporphyrin IX in EPP. In summary, our work establishes a novel strategy for EPP therapy by targeting ABCG2 and provides oral ABCG2 inhibitors that can effectively prevent protoporphyrin IX-mediated phototoxicity in mice.

GSK2606414 Sensitizes ABCG2-Overexpressing Multidrug-Resistant Colorectal Cancer Cells to Chemotherapeutic Drugs

Colorectal cancer is a common malignant tumor. A major factor in the high mortality rate of colorectal cancer is the emergence of multidrug resistance (MDR). Overexpression of the ABCG2 gene in cancer cells directly leads to MDR. Finding new inhibitors of ABCG2 may be an effective way to overcome drug resistance. We found that the compound GSK2606414 enhanced the sensitivity of the ABCG2 substrate to the chemotherapeutic drugs mitoxantrone and doxorubicin in ABCG2-overexpressing multidrug-resistant colorectal cancer cells by increasing their intracellular accumulation without affecting the protein expression of ABCG2. Molecular docking experiments predicted that GSK2606414 could stably bind in the drug-binding pocket of ABCG2. In conclusion, GSK2606414 can sensitize ABCG2-overexpressed multidrug-resistant colorectal cancer cells to chemotherapy drugs and can be used as a potential inhibitor of ABCG2.

Genetic polymorphisms are associated with individual susceptibility to dexmedetomidine

Introduction: Dexmedetomidine (DXM) is widely used as an adjuvant to anesthesia or a sedative medicine, and differences in individual sensitivity to the drug exist. This study aimed to investigate the effect of genetic polymorphisms on these differences. Methods: A total of 112 patients undergoing hand surgery were recruited. DXM 0.5 μg/kg was administered within 10 min and then continuously injected (0.4 μg/kg/h). Narcotrend index, effective dose and onset time of sedation, MAP, and HR were measured. Forty-five single nucleotide polymorphisms (SNPs) were selected for genotype. Results: We observed individual differences in the sedation and hemodynamics induced by DXM. ABCG2 rs2231142, CYP2D6 rs16947, WBP2NL rs5758550, KATP rs141294036, KCNMB1 rs11739136, KCNMA1 rs16934182, ABCC9 rs11046209, ADRA2A rs1800544, and ADRB2 rs1042713 were shown to cause statistically significant (p < 0.05) influence on the individual variation of DXM on sedation and hemodynamics. Moreover, the multiple linear regression analysis indicated sex, BMI, and ADRA2A rs1800544 are statistically related to the effective dose of DXM sedation. Discussion: The evidence suggests that the nine SNPs involved in transport proteins, metabolic enzymes, and target proteins of DXM could explain the individual variability in the sedative and hemodynamic effects of DXM. Therefore, with SNP genotyping, these results could guide personalized medication and promote clinical and surgical management.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

A Pan-Cancer Landscape of ABCG2 across Human Cancers: Friend or Foe?

Emerging evidence from research or clinical studies reported that ABCG2 (ATP-binding cassette sub-family G member 2) interrelates with multidrug resistance (MDR) development in cancers. However, no comprehensive pan-cancer analysis is available at present. Therefore, we explore multiple databases, such as TCGA to investigate the potential therapeutic roles of ABCG2 across 33 different tumors. ABCG2 is expressed on a lower level in most cancers and shows a protective effect. For example, a lower expression level of ABCG2 was detrimental to the survival of adrenocortical carcinoma (TCGA-ACC), glioblastoma multiforme (GBM), and kidney renal clear cell carcinoma (KIRC) patients. Distinct associations exist between ABCG2 expression and stemness scores, microenvironmental scores, microsatellite instability (MSI), and tumor mutational burden (TMB) of tumor patients. We observed a significant positive correlation between the ABCG2 mutation site and prognosis in uterine corpus endometrial carcinoma (UCEC) patients. Moreover, transmembrane transporter activity and hormone biosynthetic-associated functions were found to be involved in the functionality of ABCG2 and its related genes. The cDNAs of cancer cell lines were collected to detect exon mutation sequences and to analyze ABCG2 mRNA expression. The mRNA expression level of ABCG2 showed a significant difference among spheres and drug-resistant cancer cell lines compared with their corresponding adherent cancer cell lines in six types of cancer. This pan-cancer study provides, for the first time, a comprehensive understanding of the multifunctionality of ABCG2 and unveils further details of the potential therapeutic role of ABCG2 in pan-cancer.

Association between high-dose methotrexate-induced toxicity and polymorphisms within methotrexate pathway genes in acute lymphoblastic leukemia

Methotrexate (MTX) is a folic acid antagonist, the mechanism of action is to inhibit DNA synthesis, repair and cell proliferation by decreasing the activities of several folate-dependent enzymes. It is widely used as a chemotherapy drug for children and adults with malignant tumors. High-dose methotrexate (HD-MTX) is an effective treatment for extramedullary infiltration and systemic consolidation in children with acute lymphoblastic leukemia (ALL). However, significant toxicity results in most patients treated with HD-MTX, which limits its use. HD-MTX-induced toxicity is heterogeneous, and this heterogeneity may be related to gene polymorphisms in related enzymes of the MTX intracellular metabolic pathway. To gain a deeper understanding of the differences in toxicity induced by HD-MTX in individuals, the present review examines the correlation between HD-MTX-induced toxicity and the gene polymorphisms of related enzymes in the MTX metabolic pathway in ALL. In this review, we conclude that only the association of SLCO1B1 and ARID5B gene polymorphisms with plasma levels of MTX and MTX-related toxicity is clearly described. These results suggest that SLCO1B1 and ARID5B gene polymorphisms should be evaluated before HD-MTX treatment. In addition, considering factors such as age and race, the other exact predictor of MTX induced toxicity in ALL needs to be further determined.

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.

Identification of Potential Biomarkers and Immune Infiltration Characteristics in Ulcerative Colitis by Combining Results from Two Machine Learning Algorithms

Objective

This study was designed to identify potential biomarkers for ulcerative colitis (UC) and analyze the immune infiltration characteristics in UC.

Methods

Datasets containing human UC and normal control tissues (GSE87466, GSE107597, and GSE13367) were downloaded from the GEO database. Then, the GSE87466 and GSE107597 datasets were merged, and the differentially expressed genes (DEGs) between UC and normal control tissues were screened out by the “limma R” package. The LASSO regression model and support vector machine recursive feature elimination (SVM-RFE) were performed to screen out the best biomarkers. The GSE13367 dataset was used as a validation cohort, and the receiver operating characteristic curve (ROC) was used to evaluate the diagnostic performance. Finally, the immune infiltration characteristics in UC were explored by CIBERSORT, and we further analyzed the correlation between potential biomarkers and different immune cells.

Results

A total of 76 DEGs were screened out, among which 56 genes were upregulated and 20 genes were downregulated. Functional enrichment analysis revealed that these DEGs were mainly involved in immune response, chemokine signaling, IL−17 signaling, cytokine receptor interactions, inflammatory bowel disease, etc. ABCG2, HSPB3, SLC6A14, and VNN1 were identified as potential biomarkers for UC and validated in the GSE13367 dataset (AUC = 0.889, 95% CI: 0.797~0.961). Immune infiltration analysis by CIBERSORT revealed that there were significant differences in immune infiltration characteristics between UC and normal control tissues. A high level of memory B cells, γδ T cells, activated mast cells, M1 macrophages, neutrophils, etc. were found in the UC group, while a high level of M2 type macrophages, resting mast cells, eosinophils, CD8+ T cells, etc. were found in the normal control group.

Conclusion

ABCG2, HSPB3, SLC6A14, and VNN 1 were identified as potential biomarkers for UC. There was an obvious difference in immune infiltration between UC and normal control tissues, which may provide help to guide individualized treatment and develop new research directions.

Dysfunction of ABC Transporters at the Surface of BBB: Potential Implications in Intractable Epilepsy and Applications of Nanotechnology Enabled Drug Delivery

Epilepsy is a chronic neurological disorder affecting 70 million people globally. One of the fascinating attributes of brain microvasculature is the (BBB), which controls a chain of distinct features that securely regulate the molecules, ions, and cells movement between the blood and the parenchyma. The barrier's integrity is of paramount importance and essential for maintaining brain homeostasis, as it offers both physical and chemical barriers to counter pathogens and xenobiotics. Dysfunction of various transporters in the (BBB), mainly ATP binding cassette (ABC), is considered to play a vital role in hampering the availability of antiepileptic drugs into the brain. ABC (ATP-binding cassette) transporters constitute a most diverse protein superfamily, which plays an essential part in various biological processes, including cell homeostasis, cell signaling, uptake of nutrients, and drug metabolism. Moreover, it plays a crucial role in neuroprotection by out-flowing various internal and external toxic substances from the interior of a cell, thus decreasing their buildup inside the cell. In humans, forty-eight ABC transporters have been acknowledged and categorized into subfamilies A to G based on their phylogenetic analysis. ABC subfamilies B, C, and G, impart a vital role at the BBB in guarding the brain against the entrance of various xenobiotic and their buildup. The illnesses of the central nervous system have received a lot of attention lately Owing to the existence of the BBB, the penetration effectiveness of most CNS medicines into the brain parenchyma is very limited (BBB). In the development of neurological therapies, BBB crossing for medication delivery to the CNS continues to be a major barrier. Nanomaterials with BBB cross ability have indeed been extensively developed for the treatment of CNS diseases due to their advantageous properties. This review will focus on multiple possible factors like inflammation, oxidative stress, uncontrolled recurrent seizures, and genetic polymorphisms that result in the deregulation of ABC transporters in epilepsy and nanotechnology-enabled delivery across BBB in epilepsy.

Pharmacogenetic Analysis of Voriconazole Treatment in Children

Voriconazole is among the first-line antifungal drugs to treat invasive fungal infections in children and known for its pronounced inter- and intraindividual pharmacokinetic variability. Polymorphisms in genes involved in the metabolism and transport of voriconazole are thought to influence serum concentrations and eventually the therapeutic outcome. To investigate the impact of these genetic variants and other covariates on voriconazole trough concentrations, we performed a retrospective data analysis, where we used medication data from 36 children suffering from invasive fungal infections treated with voriconazole. Data were extracted from clinical information systems with the new infrastructure SwissPK^cdw, and linear mixed effects modelling was performed using R. Samples from 23 children were available for DNA extraction, from which 12 selected polymorphism were genotyped by real-time PCR. 192 (49.1%) of 391 trough serum concentrations measured were outside the recommended range. Voriconazole trough concentrations were influenced by polymorphisms within the metabolizing enzymes CYP2C19 and CYP3A4, and within the drug transporters ABCC2 and ABCG2, as well as by the co-medications ciprofloxacin, levetiracetam, and propranolol. In order to prescribe an optimal drug dosage, pre-emptive pharmacogenetic testing and careful consideration of co-medications in addition to therapeutic drug monitoring might improve voriconazole treatment outcome of children with invasive fungal infections.

Pharmacogenetics of Drug-Resistant Epilepsy (Review of Literature)

Pharmacogenomic studies in epilepsy are justified by the high prevalence rate of this disease and the high cost of its treatment, frequent drug resistance, different response to the drug, the possibility of using reliable methods to assess the control of seizures and side effects of antiepileptic drugs. Candidate genes encode proteins involved in pharmacokinetic processes (drug transporters, metabolizing enzymes), pharmacodynamic processes (receptors, ion channels, enzymes, regulatory proteins, secondary messengers) and drug hypersensitivity (immune factors). This article provides an overview of the literature on the influence of genetic factors on treatment in epilepsy.

Synthesis and biological assessment of new pyrimidopyrimidines as inhibitors of breast cancer resistance protein (ABCG2)

Multidrug resistance constitutes a serious obstacle of the treatment success of cancer by chemotherapy. Mostly it is driven by expression of ABC transport proteins that actively efflux the anticancer agents out of the cell. This work describes the design and synthesis of 12 new pyrimidopyrimidines, as well as their inhibition of ABCG2 a transporter referred also to as breast cancer resistance protein, the selectivity versus ABCB1 (P-glycoprotein/P-gp) and ABCC1 as well as the investigation of their accumulation in single cells. From these results, N-(3,5-dimethoxyphenyl)-2-methyl-7-phenyl-5-(p-tolyl)pyrimido[4,5-d]pyrimidin-4-amine 7 h was identified as promising hit that deserves further investigation showing a selective and effective inhibition of ABCG2 with IC₅₀ equal to 0.493 µM only 2-fold less active than Ko143.

ATP-binding cassette transporters and neurodegenerative diseases

ATP-binding cassette (ABC) transporters are one of the largest groups of transporter families in humans. ABC transporters mediate the translocation of a diverse range of substrates across cellular membranes, including amino acids, nucleosides, lipids, sugars and xenobiotics. Neurodegenerative diseases are a group of brain diseases that detrimentally affect neurons and other brain cells and are usually associated with deposits of pathogenic proteins in the brain. Major neurodegenerative diseases include Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. ABC transporters are highly expressed in the brain and have been implicated in a number of pathological processes underlying neurodegenerative diseases. This review outlines the current understanding of the role of ABC transporters in neurodegenerative diseases, focusing on some of the most important pathways, and also suggests future directions for research in this field.

Overexpression of ABCG2 Confers Resistance to MLN7243, a Ubiquitin-Activating Enzyme (UAE) Inhibitor

Overexpression of ATP-binding cassette transporter superfamily G member 2 (ABCG2), is known as a major mechanism mediating multidrug resistance (MDR) in cancer cells. MLN7243 is a small-molecule ubiquitin activating enzyme inhibitor currently under clinical investigation. The aim of the current study is to determine if MLN7243 is a substrate of MDR-related ABCG2 transporter. Our results showed that cancer cells overexpressing ABCG2 transporter were resistant to MLN7243 compared to the parental cells, while knockout of ABCG2 gene or pharmacological inhibition of ABCG2 efflux function completely reversed the drug resistance. Unexpectedly, the endogenous low expression of ABCG2 is sufficient to confer cancer cells resistance to MLN7243. The ABCG2 ATPase assay and HPLC assay suggested that MLN7243 can significantly stimulate ABCG2 ATPase activity and be pumped out from ABCG2-overexpressing cells by ABCG2. The docking analysis also implied that MLN7243 binds to ABCG2 drug-binding pocket with optimal binding affinity. However, MLN7243 did not competitively inhibit the efflux of other ABCG2 substrate drugs, indicating it may not serve as an MDR reversal agent. In conclusion, our study provides direct in vitro evidence to show that MLN7243 is a potent ABCG2 substrate. If our results can be translated to humans, it suggests that combining MLN7243 with ABCG2 inhibitors may enhance the anticancer efficacy for patients with high tumor ABCG2 level.

A systematic review and meta-analysis of the association of ABCC2/ABCG2 polymorphisms with antiepileptic drug responses in epileptic patients

PURPOSE

Accumulating evidence indicates that genetic polymorphisms in ATP-binding cassette superfamily members, such asABCC2 and ABCG2, alter responses to antiepileptic drugs (AEDs); however, this evidence is controversial and inconclusive. To provide strong evidence of the association between common polymorphisms in ABCC2 and ABCG2 and AED responses in patients with epilepsy, we performed a systematic review and meta-analysis.

METHODS

A literature search of electronic databases (PubMed, EBSCO, Ovid and the China National Knowledge Infrastructure) was performed. To evaluate the association of genetic polymorphisms inABCC2 and ABCG2 and risk of AED treatment, we calculated pooled odds ratios (ORs) and 95 % confidence intervals (CIs) using a fixed- or random-effect model.

RESULTS

A significant association of theABCC2 rs717620 polymorphism with resistance to AEDs was found in the overall pooled populations (homozygous comparison: OR = 1.77, 95 % CI, 1.27-2.48; dominant model: OR = 1.23, 95 % CI, 1.06-1.43; recessive model: OR = 1.75, 95 % CI, 1.28-2.40) and Asians (dominant model: OR = 1.21, 95 % CI, 1.03-1.42; recessive model: OR = 1.80, 95 % CI, 1.30-2.50). Using a recessive model, a similarly significant association of ABCC2 rs3740066 with AED resistance was observed in the overall pooled populations (OR = 2.29, 95 % CI, 1.44-3.64) and Asians (OR = 2.53, 95 % CI, 1.56-4.08). However, ABCC2 rs2273697, ABCG2 rs2231137 and rs2231142 were not found to be associated with AED responsiveness.

CONCLUSION

This meta-analysis suggests thatABCC2 rs717620 and rs3740066 are risk factors that predict responses to AEDs in epileptic patients.

Bisphenol A Inhibits the Transporter Function of the Blood-Brain Barrier by Directly Interacting with the ABC Transporter Breast Cancer Resistance Protein (BCRP)

The breast cancer resistance protein (BCRP) is an important efflux transporter in the blood-brain barrier (BBB), protecting the brain from a wide range of substances. In this study, we investigated if BCRP function is affected by bisphenol A (BPA), a high production volume chemical used in common consumer products, as well as by bisphenol F (BPF) and bisphenol S (BPS), which are used to substitute BPA. We employed a transwell-based in vitro cell model of iPSC-derived brain microvascular endothelial cells, where BCRP function was assessed by measuring the intracellular accumulation of its substrate Hoechst 33342. Additionally, we used in silico modelling to predict if the bisphenols could directly interact with BCRP. Our results showed that BPA significantly inhibits the transport function of BCRP. Additionally, BPA was predicted to bind to the cavity that is targeted by known BCRP inhibitors. Taken together, our findings demonstrate that BPA inhibits BCRP function in vitro, probably by direct interaction with the transporter. This effect might contribute to BPA’s known impact on neurodevelopment.

AZ32 Reverses ABCG2-Mediated Multidrug Resistance in Colorectal Cancer

Colorectal cancer is a common malignancy with the third highest incidence and second highest mortality rate among all cancers in the world. Chemotherapy resistance in colorectal cancer is an essential factor leading to the high mortality rate. The ATP-binding cassette (ABC) superfamily G member 2 (ABCG2) confers multidrug resistance (MDR) to a range of chemotherapeutic agents by decreasing their intracellular content. The development of novel ABCG2 inhibitors has emerged as a tractable strategy to circumvent drug resistance. In this study, an ABCG2-knockout colorectal cancer cell line was established to assist inhibitor screening. Additionally, we found that ataxia-telangiectasia mutated (ATM) kinase inhibitor AZ32 could sensitize ABCG2-overexpressing colorectal cancer cells to ABCG2 substrate chemotherapeutic drugs mitoxantrone and doxorubicin by retaining them inside cells. Western blot assay showed that AZ32 did not alter the expression of ABCG2. Moreover, molecule docking analysis predicted that AZ32 stably located in the transmembrane domain of ABCG2. In conclusion, our result demonstrated that AZ32 could potently reverse ABCG2-mediated MDR in colorectal cancer.

Clinical utility of ABCB1 and ABCG2 genotyping for assessing the clinical and pathological response to FAC therapy in Mexican breast cancer patients

PURPOSE

Resistance to neoadjuvant chemotherapy with 5-fluorouracil, doxorubicin, and cyclophosphamide (FAC) in some patients with locally advanced breast cancer remains one of the main obstacles to first-line treatment. We investigated clinical and pathological responses to FAC neoadjuvant chemotherapy in Mexican women with breast cancer and their possible association with SNPs present in ABC transporters as predictors of chemoresistance.

MATERIALS

A total of 102 patients undergoing FAC neoadjuvant chemotherapy were included in the study. SNP analysis was performed by RT-PCR from genomic DNA. Two SNPs were analyzed: ABCB1 rs1045642 (3435 C > T) and ABCG2 rs2231142 (421 G > T).

RESULTS

In clinical response evaluation, significant associations were found between the ABCB1 C3435T genotype and breast cancer chemoresistant and chemosensitive patients (p < 0.05). In the early clinical response, patients with genotype C/C or C/T were more likely to be chemosensitive to neoadjuvant therapy than patients with genotype T/T (OR = 4.055; p = 0.0064). Association analysis between the ABCB1 gene polymorphism and the pathologic response to FAC chemotherapy showed that the C/C + C/T genotype was a protective factor against chemoresistance (OR = 3.714; p = 0.0104). Polymorphisms in ABCG2 indicated a lack of association with resistance to chemotherapy (p = 0.2586) evaluating the clinical or pathological response rate to FAC neoadjuvant chemotherapy.

CONCLUSION

The early clinical response and its association with SNPs in the ABCB1 transporter are preserved until the pathological response to neoadjuvant chemotherapy; therefore, it could be used as a predictor of chemoresistance in locally advanced breast cancer patients of the Mexican population.

Overexpression of human ATP-binding cassette transporter ABCG2 contributes to reducing the cytotoxicity of GSK1070916 in cancer cells

The emergence of multidrug resistance (MDR) is one of the main factors that impair therapeutic outcome in cancer therapy. Among all the factors that contribute to MDR, overexpression of ABCG2 transporter has been described as a key factor. GSK1070916 is a potent Aurora kinase inhibitor with broad anticancer effects. The robust efficacy shown in preclinical studies allowed the drug progress to clinical investigation. However, the potential mechanisms of acquired resistance to GSK1070916 remain inconclusive. Since several Aurora kinase inhibitors were reported to be transported substrates of ABCG2, we aimed to identify the potential interaction of GSK1070916 with ABCG2. Our data showed that ABCG2-overexpressing cells demonstrated high resistance-fold to GSK1070916 compared to the parental cells. In addition, combination of GSK1070916 with an ABCG2 inhibitor was able to restore its sensitivity. The multicellular tumor spheroid assay supported this finding by demonstrating attenuated growth inhibition in ABCG2-overexpressing tumor spheroids. In addition, the ABCG2 ATPase assay and computational modeling suggested that GSK1070916 could bind to ABCG2 substrate-binding site. The HPLC assay provided another direct evidence that ABCG2-overexpressing cells showed attenuated intracellular accumulation of GSK1070916, and such phenomenon was abolished by Ko143, a known ABCG2 inhibitor. Furthermore, GSK1070916 was able to hinder the efflux activity of ABCG2, indicating possible drug-drug interactions with other ABCG2 substrate drugs. In summary, we revealed that overexpression of ABCG2 can cause GSK1070916 resistance in cancer cells. The combination of an ABCG2 inhibitor with GSK1070916 may be a rational strategy to overcome the drug resistance and should be considered for clinical investigation.

KD025, an anti-adipocyte differentiation drug, enhances the efficacy of conventional chemotherapeutic drugs in ABCG2-overexpressing leukemia cells

Most patients with advanced leukemia eventually die from multidrug resistance (MDR). Chemotherapy-resistant leukemia cells may lead to treatment failure and disease relapse. Overexpression of ATP-binding cassette subfamily G member 2 (ABCG2) leads to MDR, which serves as a potential biomarker and target of therapeutic intervention for leukemia cells. Targeting ABCG2 is a potential strategy for selective therapy and eradicate MDR cells, thus improving malignant leukemia treatment. KD025 (SLx-2119) is a novel Rho-associated protein kinase 2-selective inhibitor, which has been shown to inhibit adipogenesis in human adipose-derived stem cells and restore impaired immune homeostasis in autoimmunity therapy. The present study demonstrated that KD025 improved the efficacy of antineoplastic drugs in ABCG2-overexpressing leukemia cells and primary leukemia blast cells derived from patients with leukemia. Moreover, KD025 significantly inhibited the efflux of [³H]-mitoxantrone and hence accumulated higher levels of [³H]-mitoxantrone in HL60/ABCG2 cells. However, mechanistic research indicated that KD025 did not alter the protein levels and subcellular locations of ABCG2. KD025 may restrain the efflux activity of ABCG2 by obstructing ATPase activity. Taken together, KD025 can sensitize conventional antineoplastic drugs in ABCG2-overexpressing leukemia cells by blocking the pump function of ABCG2 protein. The present findings may provide a novel and useful combinational therapeutic strategy of KD025 and antineoplastic drugs for leukemia patients with ABCG2-mediated MDR.

Comprehensive Analysis of ABCG2 Genetic Variation in the Polish Population and Its Inter-Population Comparison

ATP-binding cassette sub-family G member 2 (ABCG2), also known as breast cancer resistance protein (BCRP), is one of the key efflux ATP-binding cassette (ABC) transporters of xenobiotics, their metabolites and endogenous compounds such as urate. Some of its genetic variants have been found to influence protein functioning, resulting in serious clinical implications concerning chemotherapy response, as well as gout or blood group phenotype Jr(a-). Previous reports have suggested that the frequencies of certain crucial polymorphisms, such as c.34G>A (p.Val12Met) and c.421C>A (p.Gln141Lys) differ significantly between the Polish population and other Caucasian populations. Thus, to clarify this issue, the present study performs a complete analysis of the genetic variation of ABCG2 coding sequence in the Polish population. The genetic variation in 14 out of 15 coding exons of the ABCG2 gene, as well as their flanking intron sequences, were examined among 190 healthy representatives of the Polish population using scanning with High Resolution Melting (HRM). HRM scanning revealed 17 polymorphisms: eight in the exons (including five missense variants and one point-nonsense mutation) and nine in the intron sequences (eight single nucleotide polymorphisms (SNPs) and one deletion variant). These included variants correlating with the presence of gout and phenotype Jr(a-). Linkage disequilibrium, haplotype blocks and haplotype analyses were also performed. The frequencies of the most common polymorphisms in the Polish population did not differ significantly to those observed for other Caucasian populations, but demonstrated divergence from non-Caucasian populations. We hope that our findings may be helpful for other researchers and clinicians, evaluating the pharmacogenetic role of ABCG2.

Pharmacogenomics of Cognitive Dysfunction and Neuropsychiatric Disorders in Dementia

Symptomatic interventions for patients with dementia involve anti-dementia drugs to improve cognition, psychotropic drugs for the treatment of behavioral disorders (BDs), and different categories of drugs for concomitant disorders. Demented patients may take >6-10 drugs/day with the consequent risk for drug-drug interactions and adverse drug reactions (ADRs >80%) which accelerate cognitive decline. The pharmacoepigenetic machinery is integrated by pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes redundantly and promiscuously regulated by epigenetic mechanisms. CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 geno-phenotypes are involved in the metabolism of over 90% of drugs currently used in patients with dementia, and only 20% of the population is an extensive metabolizer for this tetragenic cluster. ADRs associated with anti-dementia drugs, antipsychotics, antidepressants, anxiolytics, hypnotics, sedatives, and antiepileptic drugs can be minimized by means of pharmacogenetic screening prior to treatment. These drugs are substrates, inhibitors, or inducers of 58, 37, and 42 enzyme/protein gene products, respectively, and are transported by 40 different protein transporters. APOE is the reference gene in most pharmacogenetic studies. APOE-3 carriers are the best responders and APOE-4 carriers are the worst responders; likewise, CYP2D6-normal metabolizers are the best responders and CYP2D6-poor metabolizers are the worst responders. The incorporation of pharmacogenomic strategies for a personalized treatment in dementia is an effective option to optimize limited therapeutic resources and to reduce unwanted side-effects.

Single-nucleotide polymorphisms in a short basic motif in the ABC transporter ABCG2 disable its trafficking out of endoplasmic reticulum and reduce cell resistance to anticancer drugs

ATP-binding cassette (ABC) subfamily G member 2 (ABCG2) belongs to the ABC transporter superfamily and has been implicated in multidrug resistance of cancers. Although the structure and function of ABCG2 have been extensively studied, little is known about its biogenesis and the regulation thereof. In this study, using mutagenesis and several biochemical analyses, we show that the positive charges in the vicinity of the RKR motif downstream of the ABC signature drive trafficking of nascent ABCG2 out of the endoplasmic reticulum (ER) onto plasma membranes. Substitutions of and naturally occurring single-nucleotide polymorphisms within these positively charged residues disabled the trafficking of ABCG2 out of the ER. A representative ABCG2 variant in which the RKR motif had been altered underwent increased ER stress-associated degradation. We also found that unlike WT ABCG2, genetic ABCG2 RKR variants have disrupted normal maturation and do not reduce accumulation of the anticancer drug mitoxantrone and no longer confer resistance to the drug. We conclude that the positive charges downstream of the ABC signature motif critically regulate ABCG2 trafficking and maturation. We propose that single-nucleotide polymorphisms of these residues reduce ABCG2 expression via ER stress-associated degradation pathway and may contribute to reduced cancer drug resistance, improving the success of cancer chemotherapy.