Effect of ABCB1 C3435T polymorphism on docetaxel pharmacokinetics according to menopausal status in breast cancer patients

Genetic determinants of paclitaxel-induced peripheral neuropathy: a review of current literature

Paclitaxel is a widely used chemotherapeutic agent recognized for its efficacy against various malignancies. However, its clinical utility is often limited by paclitaxel-induced peripheral neuropathy (PIPN), a dose-dependent and debilitating side effect that significantly impacts patient quality of life. Genetic predisposition plays a critical role in individual susceptibility to PIPN, influencing both drug metabolism and neuropathic responses. This review examines the genetic basis of PIPN, focusing on polymorphisms in key genes associated with paclitaxel metabolism, transport, neuroinflammation, and neuronal signaling. Variants in CYP2C8, CYP3A4, and CYP2C9 affect drug metabolism, while polymorphisms in ABCB1 and SLCO1B1 influence drug transport. Genes involved in neuroinflammatory pathways (TNF-α, IL-6, IL-1β), peripheral nerve integrity (MAPT, TUBB2), and neuronal signaling (SCN9A) have also been implicated in PIPN susceptibility. Understanding genetic contributions to PIPN is essential for unraveling its pathophysiology and developing targeted interventions. Integrating genetic markers into clinical practice can facilitate personalized treatment strategies, minimizing PIPN risk and enhancing therapeutic outcomes. Further studies are needed to validate these findings across diverse populations and uncover novel genetic determinants.

SNP's use as a potential chemotoxicity stratification tool in breast cancer: from bench to clinic

Breast cancer (BC) remains one of the most prevalent malignancies affecting women worldwide, necessitating ongoing research to improve treatment outcomes and minimize adverse effects associated with chemotherapy. This article explores the role of genetic variations, particularly single nucleotide polymorphisms (SNPs), in influencing the efficacy and toxicity of chemotherapeutic agents used in BC treatment. It highlights the impact of polymorphisms in drug metabolism and transport genes, such as UDP-glucuronosyltransferase 1A1 (UGT1A1), carbonyl reductase 1 (CBR1), and ATP-binding cassette multidrug transporter (ABCB1) on the risk of adverse effects, including cardiotoxicity and hematological toxicities. By identifying specific SNPs associated with drug response and toxicity, this research underscores the potential for personalized medicine approaches to optimize treatment regimens, enhance therapeutic efficacy, and minimize side effects in BC patients. The findings advocate for the integration of genetic screening in clinical practice to improve patient outcomes and tailor chemotherapy based on individual genetic profiles.

Impact of loperamide on the pharmacokinetics and tissue disposition of ritonavir-boosted oral docetaxel therapy; a preclinical assessment

PURPOSE

An oral docetaxel formulation boosted by the Cytochrome P450 (CYP) 3 A inhibitor ritonavir, ModraDoc006/r, is currently under clinical investigation. Based on clinical data, the incidence of grade 1-2 diarrhea is increased with this oral docetaxel formulation compared to the conventional intravenous administration. Loperamide, a frequently used diarrhea inhibitor, could be added to the regimen as symptomatic treatment. However, loperamide is also a substrate of the CYP3A enzyme, which could result in competition between ritonavir and loperamide for this protein. Therefore, we were interested in the impact of coadministered loperamide on the pharmacokinetics of ritonavir-boosted oral docetaxel.

METHODS

We administered loperamide simultaneously or with an 8-hour delay to humanized CYP3A4 mice (with expression in liver and intestine) receiving oral ritonavir and docetaxel. Concentrations of docetaxel, ritonavir, loperamide and two of its active metabolites were measured.

RESULTS

The plasma exposure (AUC and Cmax) of docetaxel was not altered during loperamide treatment, nor were the ritonavir plasma pharmacokinetics. However, the hepatic and intestinal dispositions of ritonavir were somewhat changed in the simultaneous, but not 8-hour loperamide treatment groups, possibly due to loperamide-induced delayed drug absorption. The pharmacokinetics of loperamide itself did not seem to be influenced by ritonavir.

CONCLUSION

These results suggest that delayed loperamide administration can be added to ritonavir-boosted oral docetaxel treatment, without affecting the overall systemic exposure of docetaxel.

ABCB1 genetic polymorphisms affect opioid requirement by altering function of the intestinal P-glycoprotein

The association between polymorphisms of the human ATP binding cassette subfamily B member 1 (ABCB1) gene and opioid response has attracted intense attention recently. As the ABCB1 gene encodes for the transporter P-glycoprotein in the brain and intestine involved in the pharmacokinetics of opioids, we investigated the effects of ABCB1 genetic polymorphisms on doses of opioids for pain relief and determined which pharmacokinetic process was affected in cancer pain patients. Sixty-eight cancer pain patients admitted for intrathecal therapy (ITT) were included. The association between ABCB1 genetic polymorphisms (C3435T, C1236T, G2677T/A and A61G) and systemic doses of opioids before ITT were investigated. Concentrations of oxycodone in plasma and cerebrospinal fluid (CSF) were determined by HPLC-MS/MS in 17 patients treated with oral oxycodone before ITT, and the influences of ABCB1 genetic polymorphisms on plasma-concentration to oral-dose ratios and CSF-concentration to plasma-concentration ratios of oral oxycodone were further analyzed. ABCB1 C3435T and G2677T/A polymorphisms were significantly associated with systemic doses of opioids before ITT, which coincided with the influences of ABCB1 C3435T and G2677T/A polymorphisms on the ratios of plasma-concentration to oral-dose. However, no significant difference was found in ratios of CSF-concentration to plasma-concentration among ABCB1 SNP genotypes. The present study provided the first evidence that ABCB1 C3435T and G2677T/A polymorphisms affect opioid requirement in cancer pain patients via altering transportation function of P-glycoprotein in the intestine, which will further expand our knowledge about pharmacokinetics of opioids and could contribute to the individualization of opioids use.

ABC transporters in breast cancer: their roles in multidrug resistance and beyond

ATP-binding cassette (ABC) transporters are membrane-spanning proteins involved in cholesterol homeostasis, transport of various molecules in and out of cells and organelles, oxidative stress, immune recognition, and drug efflux. They are long implicated in the development of multidrug resistance in cancer chemotherapy. Existing clinical and molecular evidence has also linked ABC transporters with cancer pathogenesis, prognostics, and therapy. In this review, we aim to provide a comprehensive update on all ABC transporters and their roles in drug resistance in breast cancer (BC). For solid tumours such as BC, various ABC transporters are highly expressed in less differentiated subtypes and metastases. ABCA1, ABCB1 and ABCG2 are key players in BC chemoresistance. Restraining these transporters has evolved as a possible mechanism to reverse this phenomenon. Further, ABCB1 and ABCC1 are important in BC prognosis. Newer therapeutic approaches have been developed to target all these molecules to dysregulate their effect, reduce cell viability, induce apoptosis, and increase drug sensitivity. In the future, targeted therapy for specific genetic variations and upstream or downstream molecules can help improve patient prognosis.

Life-Threatening Docetaxel Toxicity in a Patient With Reduced-Function CYP3A Variants: A Case Report

Docetaxel therapy occasionally causes severe and life-threatening toxicities. Some docetaxel toxicities are related to exposure, and inter-individual variability in exposure has been described based on genetic variation and drug-drug interactions that impact docetaxel clearance. Cytochrome P450 3A4 (CYP3A4) and CYP3A5 metabolize docetaxel into inactive metabolites, and this is the primary mode of docetaxel clearance. Supporting their role in these toxicities, increased docetaxel toxicities have been found in patients with reduced- or loss-of-function variants in CYP3A4 and CYP3A5. However, since these variants in CYP3A4 are rare, little is known about the safety of docetaxel in patients who are homozygous for the reduced-function CYP3A4 variants. Here we present a case of life-threatening (grade 4) pneumonitis, dyspnea, and neutropenia resulting from a single dose of docetaxel. This patient was (1) homozygous for CYP3A4*22, which causes reduced expression and is associated with increased docetaxel-related adverse events, (2) heterozygous for CYP3A4*3, a rare reduced-function missense variant, and (3) homozygous for CYP3A5*3, a common loss of function splicing defect that has been associated with increased docetaxel exposure and adverse events. The patient also carried functional variants in other genes involved in docetaxel pharmacokinetics that may have increased his risk of toxicity. We identified one additional CYP3A4*22 homozygote that received docetaxel in our research cohort, and present this case of severe hematological toxicity. Furthermore, the one other CYP3A4*22 homozygous patient we identified from the literature died from docetaxel toxicity. This case report provides further evidence for the need to better understand the impact of germline CYP3A variants in severe docetaxel toxicity and supports using caution when treating patients with docetaxel who have genetic variants resulting in CYP3A poor metabolizer phenotypes.

Association between gene polymorphism and adverse effects in cancer patients receiving docetaxel treatment: a meta-analysis

PURPOSE

Large interindividual variability in the pharmacokinetic properties of docetaxel has been reported, with the clearance of docetaxel varying nearly six fold, in which pharmacogenetics of docetaxel may play an essential role in addition to physiological factors. The association between the gene polymorphism and risk of adverse clinical effects in docetaxel treated patients has been examined in several studies, but their conclusions are, to some extent, controversial. To clarify the role of gene polymorphism in the clinical outcomes of docetaxel treatment, a meta-analysis was performed in the present study.

METHODS

Pooled odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were employed to evaluate the impact of gene polymorphisms of CYP3A4, CYP3A5 and ABCB1. Four studies with 485 subjects were included in this study. Fixed or random-effects model was chosen according to heterogeneity to conduct the meta-analysis. Publication bias was evaluated by fail-safe numbers.

RESULTS

Significant association was identified between the ABCB1 C3435T (rs1045642) polymorphism and risk of short-term recurrent hematological toxicity (TT vs. CC + TC OR = 2.91, 95% CI 1.30-6.52, P = 0.009; TT vs. CC OR = 4.23, 95% CI 1.69-10.57 P = 0.002). The association of the ABCB1 G2677T/A (rs2032582) polymorphism with risk of fluid retention was statistically significant (T(A)/T(A) vs. GG + GT(A) OR = 2.08, 95% CI 1.16-3.73, P = 0.01). No statistically significant association between the CYP3A5 A6986G (rs776746) polymorphism and adverse effects was observed in this study. Due to the limitations of included literature, we did not conduct meta-analysis on CYP3A4 gene polymorphism and adverse effects.

CONCLUSION

An association between the ABCB1 C3435T (rs1045642), ABCB1 G2677T/A (rs2032582) polymorphism and risk of adverse effects of docetaxel was found by our meta-analysis. Namely, the TT homozygotes of the ABCB1 C3435T polymorphism may be associated with the risk of hematological toxicity. ABCB1 G2677T T(A)/T(A) genotype may be associated with the fluid retention.

TRAIL REGISTRATION

PROSPERO 2020 CRD42020203132.

Evaluation of pharmacogenomics and hepatic nuclear imaging-related covariates by population pharmacokinetic models of irinotecan and its metabolites

BACKGROUND

Body surface area (BSA)-based dosing of irinotecan (IR) does not account for its pharmacokinetic (PK) and pharmacodynamic (PD) variabilities. Functional hepatic nuclear imaging (HNI) and excretory/metabolic/PD pharmacogenomics have shown correlations with IR disposition and toxicity/efficacy. This study reports the development of a nonlinear mixed-effect population model to identify pharmacogenomic and HNI-related covariates that impact on IR disposition to support dosage optimization.

METHODS

Patients had advanced colorectal cancer treated with IR combination therapy. Baseline blood was analysed by Affymetrix DMET™ Plus Array and, for PD, single nucleotide polymorphisms (SNPs) by Sanger sequencing. For HNI, patients underwent ^99mTc-IDA hepatic imaging, and data was analysed for hepatic extraction/excretion parameters. Blood was taken for IR and metabolite (SN38, SN38G) analysis on day 1 cycle 1. Population modelling utilised NONMEM version 7.2.0, with structural PK models developed for each moiety. Covariates include patient demographics, HNI parameters and pharmacogenomic variants.

RESULTS

Analysis included (i) PK data: 32 patients; (ii) pharmacogenomic data: 31 patients: 750 DMET and 22 PD variants; and (iii) HNI data: 32 patients. On initial analysis, overall five SNPs were identified as significant covariates for CL_SN38. Only UGT1A3_c.31 T > C and ABCB1_c.3435C > T were included in the final model, whereby CL_SN38 reduced from 76.8 to 55.1%.

CONCLUSION

The identified UGT1A3_c.31 T > C and ABCB1_c.3435C > T variants, from wild type to homozygous, were included in the final model for SN38 clearance.

Transfer of rhodamine-123 into the brain and cerebrospinal fluid of fetal, neonatal and adult rats

Background

Adenosine triphosphate binding cassette transporters such as P-glycoprotein (PGP) play an important role in drug pharmacokinetics by actively effluxing their substrates at barrier interfaces, including the blood-brain, blood-cerebrospinal fluid (CSF) and placental barriers. For a molecule to access the brain during fetal stages it must bypass efflux transporters at both the placental barrier and brain barriers themselves. Following birth, placental protection is no longer present and brain barriers remain the major line of defense. Understanding developmental differences that exist in the transfer of PGP substrates into the brain is important for ensuring that medication regimes are safe and appropriate for all patients.

Methods

In the present study PGP substrate rhodamine-123 (R123) was injected intraperitoneally into E19 dams, postnatal (P4, P14) and adult rats. Naturally fluorescent properties of R123 were utilized to measure its concentration in blood-plasma, CSF and brain by spectrofluorimetry (Clariostar). Statistical differences in R123 transfer (concentration ratios between tissue and plasma ratios) were determined using Kruskal-Wallis tests with Dunn’s corrections.

Results

Following maternal injection the transfer of R123 across the E19 placenta from maternal blood to fetal blood was around 20 %. Of the R123 that reached fetal circulation 43 % transferred into brain and 38 % into CSF. The transfer of R123 from blood to brain and CSF was lower in postnatal pups and decreased with age (brain: 43 % at P4, 22 % at P14 and 9 % in adults; CSF: 8 % at P4, 8 % at P14 and 1 % in adults). Transfer from maternal blood across placental and brain barriers into fetal brain was approximately 9 %, similar to the transfer across adult blood-brain barriers (also 9 %). Following birth when placental protection was no longer present, transfer of R123 from blood into the newborn brain was significantly higher than into adult brain (3 fold, p < 0.05).

Conclusions

Administration of a PGP substrate to infant rats resulted in a higher transfer into the brain than equivalent doses at later stages of life or equivalent maternal doses during gestation. Toxicological testing of PGP substrate drugs should consider the possibility of these patient specific differences in safety analysis.

Exploring pharmacogenetics of paclitaxel- and docetaxel-induced peripheral neuropathy by evaluating the direct pharmacogenetic-pharmacokinetic and pharmacokinetic-neuropathy relationships

Introduction: Peripheral neuropathy (PN) is an adverse effect of several classes of chemotherapy including the taxanes. Predictive PN biomarkers could inform individualized taxane treatment to reduce PN and enhance therapeutic outcomes. Pharmacogenetics studies of taxane-induced PN have focused on genes involved in pharmacokinetics, including enzymes and transporters. Contradictory findings from these studies prevent translation of genetic biomarkers into clinical practice. Areas covered: This review discusses the progress toward identifying pharmacogenetic predictors of PN by assessing the evidence for two independent associations; the effect of pharmacogenetics on taxane pharmacokinetics and the evidence that taxane pharmacokinetics affects PN. Assessing these direct relationships allows the reader to understand the progress toward individualized taxane treatment and future research opportunities. Expert opinion: Paclitaxel pharmacokinetics is a major determinant of PN. Additional clinical trials are needed to confirm the clinical benefit of individualized dosing to achieve target paclitaxel exposure. Genetics does not meaningfully contribute to paclitaxel pharmacokinetics and may not be useful to inform dosing. However, genetics may contribute to PN sensitivity and could be useful for estimating patients' optimal paclitaxel exposure. For docetaxel, genetics has not been demonstrated to have a meaningful effect on pharmacokinetics and there is no evidence that pharmacokinetics determines PN.

Impact of variants in ATP-binding cassette transporters on breast cancer treatment

There has been substantial interest in the impact of ATP-binding cassette (ABC) transporter variability on breast cancer drug resistance. Here, we provide a systematic review of ABC variants in breast cancer therapy. Notably, most studies used small heterogeneous cohorts and their identified associations lack statistical stringency, replication and mechanistic support. We conclude that commonly studied ABC polymorphisms are not suitable to accurately predict therapy response or toxicity in breast cancer patients and cannot guide treatment decisions. However, recent research shows that ABC transporters harbor a plethora of rare variants with individually small effect sizes, and we argue that a shift in strategy from target variant interrogation to comprehensive profiling might hold promise to drastically improve the predictive power of outcome models.

Association of plasma docetaxel levels with ABCB1 gene polymorphisms and tumour response in locally advanced breast cancer patients of South India on neo-adjuvant chemotherapy

BACKGROUND

Genetic factors could be attributed to the variability in docetaxel plasma levels and its subsequent therapeutic response. The objectives of this study were to assess the effect of ABCB1 gene polymorphisms [SNPs rs1045642 (C3435T) and rs1128503 (C1236T)] on docetaxel plasma levels and also to analyze the influence of docetaxel plasma levels on tumour response in the ethnically distinct South Indian population.

METHODS

104 locally advanced breast cancer (LABC) patients on docetaxel-based neo-adjuvant chemotherapy (NACT) were included. The plasma docetaxel levels were estimated using the validated reverse phase liquid chromatography with mass spectrometry (LC-MS/MS). DNA was extracted (phenol-chloroform extraction method) and the real-time PCR system using validated TaqMan® SNP genotyping assay method was used for genotyping. Tumour response was assessed by RECIST criteria based on the MRI images.

RESULTS

Patients with "CT/TT" genotype of the SNP C1236T had a C₀/C_t ratio of 1.6 times higher than those with "CC" genotype (13.5 ± 6.5 vs 8.3 ± 3.1, p = 0.002). Though not significant, patients with "CT/TT" genotype had greater initial plasma concentration (C₀) and area under the plasma concentration-time curve (AUC_0-t). Conversely, the SNP C3435T was not associated with the plasma docetaxel levels. Furthermore, the C₀ and normalized C₀ were found to be higher in tumour responders compared to non-responders (p < 0.05).

CONCLUSIONS

The plasma levels of docetaxel were significantly influenced by the SNP C1236T of ABCB1 gene coding for the MDR1 transporter (P-glycoprotein). The plasma levels of docetaxel were also found to influence its therapeutic effect.

Association between MDR1 gene polymorphisms and the risk of Crohn's disease in a cohort of Algerian pediatric patients

BACKGROUND

The multi-drug resistance gene (MDR1) has raised increasing interest as a susceptibility gene for Crohn's disease (CD). The role of MDR1 single-nucleotide polymorphisms (SNPs) in the predisposition and behavior of CD in the pediatric population is still elusive. Here, we investigated whether SNPs in MDR1 are associated with CD in Algerian pediatric patients.

METHODS

A case-control study was conducted enrolling 47 pediatric CD patients and 100 controls. All subjects were genotyped for the most common MDR1 SNPs (C3434T, C1236T, and G2677A/T) using PCR-RFLP method. We also explored the association between polymorphisms and clinical sub-phenotypes.

RESULTS

We have detected no significant association of C3435T SNP and pediatric CD. However, we observed a significantly higher frequency of the risk alleles, 1236T and 2677T/A among the CD patients compared to controls. Moreover, the risk allele 1236T was associated to a higher risk for resective surgery.

CONCLUSION

Our data suggest that the C1236T and G2677A/T SNPs in the MDR1 gene are associated with CD and the C1236T risk allele with a more severe course of disease in Algerian pediatric patients. Further analysis using larger patients group and functional studies would be interesting to elucidate the role of MDR1 gene in pediatric CD.Pediatric Research (2016); doi:10.1038/pr.2016.163.

Drug transporters in breast cancer: response to anthracyclines and taxanes

Despite the advances that have taken place in the past decade, including the development of novel molecular targeted agents, cytotoxic chemotherapy remains the mainstay of cancer treatment. In breast cancer, anthracyclines and taxanes are the two main chemotherapeutic options used on a routine basis. Although effective, their usefulness is limited by the inevitable development of resistance, a lack of response to drug-induced cancer cell death. A large body of research has resulted in the characterization of a plethora of mechanisms involved in resistance; ATP-binding cassette transporter proteins, through their function in xenobiotic clearance, play an important role in resistance. We review here the current evidence for drug transporters as biomarkers and the benefit of adding drug transporter modulators to conventional chemotherapy.

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.

Significant effect of age on docetaxel pharmacokinetics in Japanese female breast cancer patients by using the population modeling approach

PURPOSE

Docetaxel is frequently used in the treatment of a wide variety of solid tumors, including breast cancer. The aim of this study is to obtain the population pharmacokinetic parameters of docetaxel in Japanese female patients with breast cancer.

METHODS

Blood samples from 24 patients were collected sequentially before and after docetaxel infusion. Genomic DNA was isolated from the peripheral blood and genotyped for the selected polymorphisms in the candidate genes of drug transporters and metabolizing enzymes. The influence of patient characteristics on the pharmacokinetics of docetaxel was evaluated using the nonlinear-mixed-effect modeling program, NONMEM. As a basis for comparison, the pharmacokinetics of another taxane paclitaxel in 41 separate female patients with breast cancer was calculated.

RESULTS

A two-compartment model adequately described the pharmacokinetic profiles of docetaxel. The population mean estimates of the total body clearance for patients aged 58 years or less and the central volume of distribution for docetaxel were 32.6 L/h and 5.77 L, respectively. In patients over 58 years, the clearance was 24 % higher than that in the younger patients. No influences of the genotypes examined were noted on the clearance of docetaxel. The clearance of paclitaxel was not affected by patient age.

CONCLUSIONS

Patients over the age of 58 years showed significantly higher clearance of docetaxel than that in patients aged 58 years or less. Since the clearance of paclitaxel was not affected by the age, it is possible that the pharmacokinetic mechanisms of docetaxel might be specifically affected by age in females.

Role of genetic variation in docetaxel-induced neutropenia and pharmacokinetics

Docetaxel is used for treatment of several solid malignancies. In this study, we aimed for predicting docetaxel clearance and docetaxel-induced neutropenia by developing several genetic models. Therefore, pharmacokinetic data and absolute neutrophil counts (ANCs) of 213 docetaxel-treated cancer patients were collected. Next, patients were genotyped for 1936 single nucleotide polymorphisms (SNPs) in 225 genes using the drug-metabolizing enzymes and transporters platform and thereafter split into two cohorts. The combination of SNPs that best predicted severe neutropenia or low clearance was selected in one cohort and validated in the other. Patients with severe neutropenia had lower docetaxel clearance than patients with ANCs in the normal range (P=0.01). Severe neutropenia was predicted with 70% sensitivity. True low clearance (1 s.d.<mean clearance) was identified in 80% of cases. These models however did not reach statistical significance. To improve the predictive value of these models, the addition of non-genetic influencing factors is needed.

Inter-patient variability in docetaxel pharmacokinetics: A review

Docetaxel is a frequently used chemotherapeutic agent in the treatment of solid cancers. Because of the large inter-individual variability (IIV) in the pharmacokinetics (PK) of docetaxel, it is challenging to determine the optimal dose in individual patients in order to achieve optimal efficacy and acceptable toxicity. Despite the established correlation between systemic docetaxel exposure and efficacy, the precise factors influencing docetaxel PK are not yet completely understood. This review article highlights currently known factors that influence docetaxel PK, and focusses on those that are clinically relevant. For example, liver impairment should be taken into account when calculating docetaxel dosages as this may decrease docetaxel clearance. In addition, drug-drug interactions may be of distinct clinical importance when using docetaxel. Particularly, drugs strongly inhibiting CYP3A4 such as ketoconazole should not be concurrently administered without dose modification, as they may decrease the clearance of docetaxel. Gender, castration status, and menopausal status might be of importance as potential factors influencing docetaxel PK. The role of pharmacogenetics in predicting docetaxel PK is still limited, since no polymorphisms of clinical importance have yet been established.

Hormone-related pharmacokinetic variations associated with anti-breast cancer drugs

INTRODUCTION

Breast cancer is the most common female cancer, with more than one million new patients diagnosed annually worldwide. Generally speaking, there are three types of drugs used in management of breast cancer namely: hormonal treatment, chemotherapeutic agents and target-based agents. There is increasing evidence that hormones play an important role in development of both hormone-dependent and hormone-independent breast cancers.

AREAS COVERED

This review summarizes the pharmacokinetics of various types of drugs used to treat breast cancer. Furthermore, the authors discuss hormone-related variations including: the menstrual status, gender and exogenous hormones influencing drug absorption, distribution, metabolism or excretion (ADME). The authors also describe the physiological factors such as body weight and age that affect the pharmacokinetics of several drugs.

EXPERT OPINION

The factors affecting the pharmacokinetics of anti-breast cancer drugs are multifaceted. Hormones appear to be a key factor determining the pharmacokinetics (and efficacy) of hormonal therapy due to their role in cancer progression. In chemotherapy, the effects of hormones on the drug pharmacokinetics are possibly mediated through P-glycoprotein (P-gp) efflux and/or cytochrome P450 metabolism. In many cases, dosing regimen should be adjusted for drugs used in treatment of breast cancers based on the hormone levels in the body.

Prospective evaluation of the drug-metabolizing enzyme polymorphisms and toxicity profile of docetaxel in Korean patients with operable lymph node-positive breast cancer receiving adjuvant chemotherapy

BACKGROUND

Inter-individual variability of pharmacokinetics may account for unpredictable toxicities of docetaxel.

METHODS

From March 2007 to June 2008, female patients with operable lymph node-positive breast cancer receiving docetaxel-containing adjuvant chemotherapy were included in this study. The 4 cycles of planned dose of docetaxel (100 mg/m(2)) was performed as adjuvant chemotherapy, following 4 cycles of adriamycin and cyclophosphamide. We evaluated toxicity profile of docetaxel and single nucleotide polymorphisms (SNPs) of CYP3A5 gene, ABCB1 gene, ABCC2 gene and SCLO1B3 gene. Toxicities during treatment of docetaxel were evaluated and defined according to the NCI CTCAE version 3.0.

RESULTS

Pharmacogenetic analysis was performed in 218 Korean women who had received the uniformly planned chemotherapy. With regard to ABCB1 3435 C>T, ABCB1 3435 T/T had significantly higher risks of neutropenia (P = 0.015). Meanwhile, allele frequencies for CYP3A5 6986 G and ABCB1 3435 T revealed a trend for neutropenia (P = 0.107 and 0.068). We could not find any other association between genotypes and other toxicities.

DISCUSSION

Although ABCB1 3435 T/T was significantly associated with docetaxel-related neutropenia in our study population, polymorphism of pharmacogenetic genes related to docetaxel metabolism did not appear to be evidently associated with docetaxel-related adverse events.

Transporter pharmacogenetics: transporter polymorphisms affect normal physiology, diseases, and pharmacotherapy

Drug transporters mediate the movement of endobiotics and xenobiotics across biological membranes in multiple organs and in most tissues. As such, they are involved in physiology, development of disease, drug pharmacokinetics, and ultimately the clinical response to a myriad of medications. Genetic variants in transporters cause population-specific differences in drug transport and are responsible for considerable inter-individual variation in physiology and pharmacotherapy. The purpose of this review is to provide a broad overview of how inherited variants in transporters are associated with disease etiology, disease state, and the pharmacological treatment of diseases. Given that there are thousands of published papers related to the interplay between transporter genetics and medicine, this review will provide examples that exemplify the broader focus of the literature.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).