The contribution of the ABCG2 C421A polymorphism to cancer susceptibility: a meta-analysis of the current literature

Tumor-acquired somatic mutation affects conformation to abolish ABCG2-mediated drug resistance

ABCG2 is an important ATP-binding cassette transporter impacting the absorption and distribution of over 200 chemical toxins and drugs. ABCG2 also reduces the cellular accumulation of diverse chemotherapeutic agents. Acquired somatic mutations in the phylogenetically conserved amino acids of ABCG2 might provide unique insights into its molecular mechanisms of transport. Here, we identify a tumor-derived somatic mutation (Q393K) that occurs in a highly conserved amino acid across mammalian species. This ABCG2 mutant seems incapable of providing ABCG2-mediated drug resistance. This was perplexing because it is localized properly and retained interaction with substrates and nucleotides. Using a conformationally sensitive antibody, we show that this mutant appears "locked" in a non-functional conformation. Structural modeling and molecular dynamics simulations based on ABCG2 cryo-EM structures suggested that the Q393K interacts with the E446 to create a strong salt bridge. The salt bridge is proposed to stabilize the inward-facing conformation, resulting in an impaired transporter that lacks the flexibility to readily change conformation, thereby disrupting the necessary communication between substrate binding and transport.

Association of ABCB1, ABCG2 drug transporter polymorphisms and smoking with disease risk and cytogenetic response to imatinib in chronic myeloid leukemia patients

BACKGROUND

Despite acceptable results of imatinib in the treatment of chronic myeloid leukemia (CML), some patients fail to acquire a complete cytogenetic response (CCyR), which may be caused by polymorphisms in the pharmacogenetic genes. The study aimed to evaluate the association of two polymorphisms in the ABCB1 and ABCG2 genes with cytogenetic response to imatinib and the risk of CML development.

METHODS

We genotyped ABCB1 (c .2677G/T/A) and ABCG2 (c .421C/A) polymorphisms by PCR-RFLP, T-ARMS-PCR methods in 111 patients with CML and 102 sex- and age-matched healthy subjects. CCyR was determined by standard chromosome banding analysis (CBA).

RESULTS

Analysis of polymorphisms showed significant association of ABCG2 c.421CA genotype (p < 0.0001; OR = 0. 17), and ABCG2c.421A allele (p < 0.0001; OR = 0.31) with decreased risk of CML. Moreover, ABCB1c.2677GT- ABCG2c.421CC combined genotype (p = 0.017; OR = 4.20) was associated with increased risk of CML. Analysis of the joint effect of SNP-smoking combination showed that smoker subjects with the ABCB1c.2677GG/GT (p = 0.001; OR = 15.96, p = 0.001; OR = 8.13, respectively) or ABCG2c.421CC genotypes (p = 0.001; OR = 5.82) had the increased risk of CML, while the risk of the CML in non-smokers carrying the ABCG2c.421CA (p < 0.0001; OR = 0. 18) genotype was strongly decreased compared with reference group. Regarding drug response, ABCG2c.421 CC/CA genotypes in the smoker patients were associated with an increased risk of resistance to imatinib (p < 0.0001; OR = 7.02, p = 0.018; OR = 4.67, respectively).

CONCLUSION

Our results suggest the impact of ABCG2c .421C/A polymorphism on CML development, and smoking may have a synergistic role in the risk of CML and resistance to imatinib.

Study of Breast Cancer Resistance Protein ABCG2 C421A Single Nucleotide Polymorphism RS2231142 in Multiple Myeloma

Breast cancer resistance protein is an adenosine triphosphate-binding cassette (ABC) transporter that belongs to the G-superfamily. It acts as an efflux pump that is crucial for cell protection against toxic compounds and xenobiotics such as procarcinogens. An individual's risk of developing carcinoma depends on genetic variations like single nucleotide polymorphisms (SNPs) that may cause alteration in gene expression and/or reductions in their activities. These changes may influence blood cells' exposure to toxic compounds and increase the susceptibility to multiple myeloma (MM). Our study aimed at investigating polymorphisms at position C421A of the ABCG-2 gene in MM for the first time in Egyptian patients. Peripheral blood mononuclear cells were analyzed for ABCG-2-C421A gene polymorphisms using real-time quantitative polymerase chain reaction in 50 MM patients and 50 control subjects. There is a statistically significant correlation between SNP-C421A of the ABCG-2 gene and the risk for MM (p = 0.0218). Preliminary studies suggest that SNP-C421A of the ABCG-2 gene can be helpful in predicting the risk of developing MM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-022-01523-3.

Pharmacogenomics with red cells: a model to study protein variants of drug transporter genes

The PharmacoScan pharmacogenomics platform screens for variation in genes that affect drug absorption, distribution, metabolism, elimination, immune adverse reactions and targets. Among the 1,191 genes tested on the platform, 12 genes are expressed in the red cell membrane: ABCC1, ABCC4, ABCC5, ABCG2, CFTR, SLC16A1, SLC19A1, SLC29A1, ATP7A, CYP4F3, EPHX1 and FLOT1. These genes represent 5 ATP-binding cassette proteins, 3 solute carrier proteins, 1 ATP transport protein and 3 genes associated with drug metabolism and adverse drug reactions. Only ABCG2 and SLC29A1 encode blood group systems, JR and AUG, respectively. We propose red cells as an ex vivo model system to study the effect of heritable variants in genes encoding the transport proteins on the pharmacokinetics of drugs. Altered pharmacodynamics in red cells could also cause adverse reactions, such as haemolysis, hitherto unexplained by other mechanisms.

A meta-analysis of ABCG2 gene polymorphism and non-small cell lung cancer outcomes

We aimed to analyze the correlation between ABCG2 gene polymorphisms of 34 GG/(GA + AA) loci, 421 CC/(AC + AA) loci, and non-small cell lung cancer (NSCLC) therapeutic effects via meta-analysis. With key words, the databases PubMed and EMBASE were searched for clinical studies on ABCG2 polymorphism and NSCLC. RR and 95% CIs were used to compute combined effects, followed by heterogeneity testing. Publication bias was examined using the funnel plot method. Review Manager 5.3 software was used for the meta-analysis. Ten studies were included. No evidence of heterogeneity exists in these studies. The results indicate that two polymorphic loci of ABCG2 gene (34 G>A, and 421 C>A) had no relationship with the curative effect of chemotherapy for NSCLC, except ABCG2 34G>A, which had a significant relationship with the skin toxicity complication. There was no significant relationship between these polymorphisms and complications (skin toxicity, diarrhea, interstitial pneumonia, liver dysfunction, and neutropenia). Begg’s test and Egger’s test indicated that there was no obvious publication bias. The meta-analysis indicated that there was no significant correlation between ABCG2 gene polymorphism and NSCLC outcomes.

Development of precision medicine approaches based on inter-individual variability of BCRP/ABCG2

Precision medicine is a rapidly-developing modality of medicine in human healthcare. Based on each patient׳s unique characteristics, more accurate dosages and drug selection can be made to achieve better therapeutic efficacy and less adverse reactions in precision medicine. A patient׳s individual parameters that affect drug transporter action can be used to develop a precision medicine guidance, due to the fact that therapeutic efficacy and adverse reactions of drugs can both be affected by expression and function of drug transporters on the cell membrane surface. The purpose of this review is to summarize unique characteristics of human breast cancer resistant protein (BCRP) and the genetic variability in the BCRP encoded gene ABCG2 in the development of precision medicine. Inter-individual variability of BCRP/ABCG2 can impact choices and outcomes of drug treatment for several diseases, including cancer chemotherapy. Several factors have been implicated in expression and function of BCRP, including genetic, epigenetic, physiologic, pathologic, and environmental factors. Understanding the roles of these factors in controlling expression and function of BCRP is critical for the development of precision medicine based on BCRP-mediated drug transport.

The contribution of ABCG2 G34A and C421A polymorphisms to multiple myeloma susceptibility

Background

Breast cancer resistance protein BCRP, belonging to superfamily G of the adenosine triphosphate-binding cassette (ABC) transporters, is an efflux pump and plays a critical role in protecting cells against xenobiotics and toxic compounds including (pro)carcinogens. BCRP is expressed in many tissues, including hematopoietic stem cells. Genetic variants such as single nucleotide polymorphisms (SNPs) can change the gene expression and/or reduce their products’ activity which may affect an individual’s susceptibility to xenobiotics and the development of carcinoma. These changes may affect the exposure of blood cells to toxic compounds, which increases the risk of multiple myeloma. The aim of this study was to determine polymorphisms at positions G34A and C421A of the ABCG2 gene in multiple myeloma in the Polish population for the first time.

Materials and methods

Material for the study included DNA isolated from nucleus of cells of peripheral blood of patients diagnosed with multiple myeloma (investigated group N=181) and from healthy people (control group N=97). Research into the polymorphisms was conducted using the polymerase chain reaction-restriction fragment length polymorphism technique.

Results

The present study showed a statistically significant association between SNP C421A of the ABCG2 gene and the risk of developing multiple myeloma (P=0.0218). No statistically significant relationship was found for the other parameters analyzed, such as age, gender, or type of secreted immunoglobulin.

Conclusion

Preliminary studies indicate that SNP C421A may become a potential predictor for the development of multiple myeloma.

Identification of ABCG2 as an Exporter of Uremic Toxin Indoxyl Sulfate in Mice and as a Crucial Factor Influencing CKD Progression

Chronic kidney disease (CKD) patients accumulate uremic toxins in the body, potentially require dialysis, and can eventually develop cardiovascular disease. CKD incidence has increased worldwide, and preventing CKD progression is one of the most important goals in clinical treatment. In this study, we conducted a series of in vitro and in vivo experiments and employed a metabolomics approach to investigate CKD. Our results demonstrated that ATP-binding cassette transporter subfamily G member 2 (ABCG2) is a major transporter of the uremic toxin indoxyl sulfate. ABCG2 regulates the pathophysiological excretion of indoxyl sulfate and strongly affects CKD survival rates. Our study is the first to report ABCG2 as a physiological exporter of indoxyl sulfate and identify ABCG2 as a crucial factor influencing CKD progression, consistent with the observed association between ABCG2 function and age of dialysis onset in humans. The above findings provided valuable knowledge on the complex regulatory mechanisms that regulate the transport of uremic toxins in our body and serve as a basis for preventive and individualized treatment of CKD.

ABCB1 3435TT and ABCG2 421CC genotypes were significantly associated with longer progression-free survival in Chinese breast cancer patients

Objective

To investigate the distribution of ABCB1 C3435T and ABCG2 C421A gene polymorphisms in Chinese Han population and their influences on the susceptibility and prognosis of breast carcinoma.

Methods

A total of 200 female subjects were enrolled in this study, comprising 100 breast cancer patients and 100 healthy controls. Carcinoma and para-carcinoma tissues were collected from the breast cancer patients, while peripheral blood was collected from healthy controls. Single nucleotide polymorphisms (SNPs) were detected by the Taqman method. Progression-free survival (PFS) and 5-year survival rate of the patients were calculated.

Results

ABCB1 C3435T and ABCG2 C421A polymorphisms were not associated with disease susceptibility and 5-year survival rate in the study population (p>0.05). However, a high mutation rate of both ABCB1 C3435T and ABCG2 C421A (16% and 17%, respectively) was observed in breast cancer tissues. Patients with ABCB1 3435TT genotype or ABCG2 421CC genotype had longer PFS (p<0.05).

Conclusion

ABCB1 3435TT and ABCG2 421CC were significantly associated with longer PFS in Chinese breast cancer patients.

Associations of the uric acid related genetic variants in SLC2A9 and ABCG2 loci with coronary heart disease risk

Background

Multiple studies investigated the associations between serum uric acid and coronary heart disease (CHD) risk. However, further investigations still remain to be carried out to determine whether there exists a causal relationship between them. We aim to explore the associations between genetic variants in uric acid related loci of SLC2A9 and ABCG2 and CHD risk in a Chinese population.

Results

A case–control study including 1,146 CHD cases and 1,146 controls was conducted. Association analysis between two uric acid related variants (SNP rs11722228 in SLC2A9 and rs4148152 in ABCG2) and CHD risk was performed by logistic regression model. Adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Compared with subjects with A allele of rs4148152, those with G allele had a decreased CHD risk and the association remained significant in a multivariate model. However, it altered to null when BMI was added into the model. No significant association was observed between rs11722228 and CHD risk. The distribution of CHD risk factors was not significantly different among different genotypes of both SNPs. Among subjects who did not consume alcohol, the G allele of rs4148152 showed a moderate protective effect. However, no significant interactions were observed between SNP by CHD risk factors on CHD risk.

Conclusions

There might be no association between the two uric acid related SNPs with CHD risk. Further studies were warranted to validate these results.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0162-7) contains supplementary material, which is available to authorized users.

Investigation of the functional single-nucleotide polymorphisms in the BCRP transporter and susceptibility to colorectal cancer

Breast cancer resistance protein (BCRP) protects tissues by actively transporting xenobiotics and their metabolites out of the cells. BCRP is expressed in the apical membrane of normal intestinal and colonic epithelium. The BCRP substrates include a number of structurally unrelated compounds, such as drugs, pesticides, carcinogens and endogenous compounds. Although the functional and common BCRP alleles, 34G>A and 421C>A, are shown to vary by ethnicity, their potential mechanism has not been adequately described with regards to affecting the susceptibility to colorectal cancer. The present study aimed to evaluate the effects of the BCRP variants on the susceptibility to colorectal cancer and to predict the individual responses to xenobiotics transferred by BCRP. BCRP 421C>A was significantly associated with the colorectal cancer risk (odds ratio, 16.12; P=0.005). These findings are the first results of BCRP allele distributions in the Turkish population and provide an understanding of the correlation between therapeutic approaches and etiology of colorectal cancer.

ABC transporter activity linked to radiation resistance and molecular subtype in pediatric medulloblastoma

Background

Resistance to radiation treatment remains a major clinical problem for patients with brain cancer. Medulloblastoma is the most common malignant brain tumor of childhood, and occurs in the cerebellum. Though radiation treatment has been critical in increasing survival rates in recent decades, the presence of resistant cells in a substantial number of medulloblastoma patients leads to relapse and death.

Methods

Using the established medulloblastoma cell lines UW228 and Daoy, we developed a novel model system to enrich for and study radiation tolerant cells early after radiation exposure. Using fluorescence-activated cell sorting, dead cells and cells that had initiated apoptosis were removed, allowing surviving cells to be investigated before extensive proliferation took place.

Results

Isolated surviving cells were tumorigenic in vivo and displayed elevated levels of ABCG2, an ABC transporter linked to stem cell behavior and drug resistance. Further investigation showed another family member, ABCA1, was also elevated in surviving cells in these lines, as well as in early passage cultures from pediatric medulloblastoma patients. We discovered that the multi-ABC transporter inhibitors verapamil and reserpine sensitized cells from particular patients to radiation, suggesting that ABC transporters have a functional role in cellular radiation protection. Additionally, verapamil had an intrinsic anti-proliferative effect, with transient exposure in vitro slowing subsequent in vivo tumor formation. When expression of key ABC transporter genes was assessed in medulloblastoma tissue from 34 patients, levels were frequently elevated compared with normal cerebellum. Analysis of microarray data from independent cohorts (n = 428 patients) showed expression of a number of ABC transporters to be strongly correlated with certain medulloblastoma subtypes, which in turn are associated with clinical outcome.

Conclusions

ABC transporter inhibitors are already being trialed clinically, with the aim of decreasing chemotherapy resistance. Our findings suggest that the inhibition of ABC transporters could also increase the efficacy of radiation treatment for medulloblastoma patients. Additionally, the finding that certain family members are associated with particular molecular subtypes (most notably high ABCA8 and ABCB4 expression in Sonic Hedgehog pathway driven tumors), along with cell membrane location, suggests ABC transporters are worthy of consideration for the diagnostic classification of medulloblastoma.