MDR1 single nucleotide polymorphisms predict response to vinorelbine-based chemotherapy in patients with non-small cell lung cancer

Genetic polymorphisms as potential pharmacogenetic biomarkers for platinum-based chemotherapy in non-small cell lung cancer

Platinum-based chemotherapy (PBC) is a widely used treatment for various solid tumors, including non-small cell lung cancer (NSCLC). However, its efficacy is often compromised by the emergence of drug resistance in patients. There is growing evidence that genetic variations may influence the susceptibility of NSCLC patients to develop resistance to PBC. Here, we provide a comprehensive overview of the mechanisms underlying platinum drug resistance and highlight the important role that genetic polymorphisms play in this process. This paper discussed the genetic variants that regulate DNA repair, cellular movement, drug transport, metabolic processing, and immune response, with a focus on their effects on response to PBC. The potential applications of these genetic polymorphisms as predictive indicators in clinical practice are explored, as are the challenges associated with their implementation.

Genetic variations in ABC transporter genes as a predictive biomarker for toxicity in North Indian lung cancer patients undergoing platinum-based doublet chemotherapy

ATP-binding cassette (ABC) transporters are expressed in various human tissues and play a vital role in the efflux of various chemotherapeutic drugs. The current study has assessed genetic variants of ABCB1, ABCC1, ABCC2, and ABCG2 genes in 407 lung cancer patients undergoing platinum-based doublet chemotherapy. The association of ABCB1 (C¹²³⁶ T, C³⁴³⁵ T, and G²⁶⁷⁷ T/A), ABCC1 (G³¹⁷³ A and G²¹⁶⁸ A),ABCC2 (G⁴⁵⁴⁴ A), and ABCG2 (C⁴²¹ A) polymorphisms with chemotherapy-induced adverse events were assessed, and statistical analysis was conducted. Our data showed that patients harboring heterozygous (GA) genotype for ABCC1 G³¹⁷³ A had an increased risk of developing leukopenia (odds ratio [OR] = 1.88, p = 0.04) and anemia (adjusted odds ratio [AOR] = 2.70, p = 0.03). For ABCC2 G⁴⁵⁴⁴ A polymorphism, patients harboring one copy of the mutant (GA) allele showed an increased risk of developing anemia (OR = 4.24, p = 0.03). After adjusting with various confounding factors, the heterozygous (GA) genotype showed a 5.63-fold increased risk of developing anemia (AOR = 5.63, p = 0.03). The ABCB1 G²⁶⁷⁷ A (OR = 0.37, p = 0.008) and ABCC1 G³¹⁷³ A (OR = 0.54, p = 0.04) polymorphism showed a lower incidence of developing nephrotoxicity. In ABCG2 C⁴²¹ A polymorphism, patients harboring heterozygous (CA) genotype had a lower incidence of having diarrhea (OR = 0.25, p = 0.04). An increased risk of having diarrhea was observed in the heterozygous genotype (GA) for ABCC1 G³¹⁷³ A polymorphism (AOR = 2.78, p = 0.04). An increased risk of liver injury was found in the patients carrying heterozygous genotype of the ABCC1 G³¹⁷³ A (OR = 2.06, p = 0.02) and ABCB1 C¹²³⁶ T (OR = 1.85, p = 0.01). This study demonstrates the role of polymorphic variations in ABCB1, ABCC1, ABCC2, and ABCG2 in predicting hematological, nephrotoxicity, gastrointestinal, and hepatotoxicity.

Impact of pharmacogenetics on variability in exposure to oral vinorelbine among pediatric patients: a model-based population pharmacokinetic analysis

PURPOSE

Better understanding of pharmacokinetics of oral vinorelbine (VNR) in children would help predicting drug exposure and, beyond, clinical outcome. Here, we have characterized the population pharmacokinetics of oral VNR and studied the factors likely to explain the variability observed in VNR exposure among young patients.

DESIGN/METHODS

We collected blood samples from 36 patients (mean age 11.6 years) of the OVIMA multicentric phase II study in children with recurrent/progressive low-grade glioma. Patients received 60 mg/m² of oral VNR on days 1, 8, and 15 during the first 28-day treatment cycle and 80 mg/m², unless contraindicated, from cycle 2-12. Population pharmacokinetic analysis was performed using nonlinear mixed-effects modeling within the Monolix^® software. Fifty SNPs of pharmacokinetic-related genes were genotyped. The influence of demographic, biological, and pharmacogenetic covariates on pharmacokinetic parameters was investigated using a stepwise multivariate procedure.

RESULTS

A three-compartment model, with a delayed double zero-order absorption and a first-order elimination, best described VNR pharmacokinetics in children. Typical population estimates for the apparent central volume of distribution (V_c/F) and elimination rate constant were 803 L and 0.60 h^-1, respectively. Following covariate analysis, BSA, leukocytes count, and drug transport ABCB1-rs2032582 SNP showed a dramatic impact on V_c/F. Conversely, age and sex had no significant effect on VNR pharmacokinetics.

CONCLUSION

Beyond canonical BSA and leukocytes, ABCB1-rs2032582 polymorphism showed a meaningful impact on VNR systemic exposure. Simulations showed that the identified covariates could have an impact on both efficacy and toxicity outcomes. Thus, a personalized dosing strategy, using those covariates, could help to optimize the efficacy/toxicity balance of VNR in children.

Overexpression of HURP mRNA in head and neck carcinoma and association with in vitro response to vinorelbine

HURP gene encodes the hepatoma upregulated protein (HURP), a microtubule associated protein regulating mitotic spindle dynamics, which promotes chromosomal congression and alignment during mitosis, with a potential role in tumorigenesis. In the present study, HURP mRNA expression was investigated by reverse transcription-quantitative PCR in oropharyngeal squamous cell carcinoma (OPSCC). Primary OPSCC tumors from 107 patients and 48 adjacent normal tissues, as well as 12 respiratory tract cancer cell lines (9 head and neck squamous cell carcinoma, 2 lung cancer and 1 normal bronchial) were utilised in the present study. mRNA expression levels of HURP were higher in malignant OPSCC tissues compared with in normal mucosa (P<1×10^-5) and significantly associated with sex and smoking status (P<0.0001). Vinorelbine in vitro toxicity at half-maximal inhibitory concentration (IC₅₀) was measured in the 11 cancer cell lines using an MTT assay. Sensitivity to vinorelbine was significantly correlated with HURP expression (r=0.636; P=0.035). The data indicated that HURP overexpression is frequent in OPSCC tissues and associated with smoking. The correlation between HURP mRNA expression and vinorelbine in vitro response suggests that HURP is a potential modulator of vinorelbine response; therefore, it should be explored for its possible predictive value for the efficiency of vinorelbine treatment in this type of cancer.

Effect of Concurrent Chemoradiation With Celecoxib vs Concurrent Chemoradiation Alone on Survival Among Patients With Non-Small Cell Lung Cancer With and Without Cyclooxygenase 2 Genetic Variants: A Phase 2 Randomized Clinical Trial

IMPORTANCE

Treatment of locally advanced non-small cell lung cancer (NSCLC) remains challenging. The rationale of combining a cyclooxygenase 2 (COX-2) inhibitor with concurrent chemoradiation (CCRT) was based on results of preclinical research and prospective clinical studies; however, no randomized clinical trial has provided evidence of a direct comparison with CCRT alone.

OBJECTIVE

To determine the effect of combined selective COX-2 inhibition with standard CCRT on survival among patients with unresectable stage III NSCLC.

DESIGN, SETTING, AND PARTICIPANTS

A single-center, open-label, randomized phase 2 clinical trial was performed among 96 patients who had histologically and cytologically confirmed unresectable stage III NSCLC. Participants were enrolled from November 2011 to August 2015. Data were analyzed from February to October 2018.

INTERVENTION

Patients were randomized to receive thoracic radiation, 60 Gy, for 6 weeks concurrent with etoposide and cisplatin or the same regimen of CCRT combined with 200 mg of celecoxib, taken twice daily.

MAIN OUTCOMES AND MEASURES

The primary end point was overall survival. The secondary end points were the proportion of patients with treatment-related toxic effects, progression-free survival, and overall survival in subgroups with and without the COX-2 genotype.

RESULTS

A total of 100 patients were randomized. Following the exclusion of 4 outliers, 96 participants (96.0%) were analyzed (51 randomized to CCRT alone and 45 randomized to CCRT with celecoxib; mean [SD] age, 60.0 [8.3] years; 73.0 [76.0%] male). The median overall survival time was 32.8 (95% CI, 17.0-48.5) months in the group that received CCRT with celecoxib and 35.5 (95% CI, 25.8-45.2) months in the group that received CCRT alone (P = .88). Celecoxib with CCRT was well tolerated; the incidence of symptomatic radiation pneumonitis was 6.6% (95% CI, 1.4%-18.0%) in the group that received CCRT with celecoxib and 11.8% (95% CI, 4.4%-23.9%) in the group that received CCRT alone (P = .49). Among patients with the high-risk genotype, celecoxib plus CCRT was not associated with higher progression-free survival (hazard ratio, 0.36; 95% CI, 0.13-1.04; P = .05) or overall survival (hazard ratio, 0.50; 95% CI, 0.15-1.72; P = .26) compared with CCRT alone.

CONCLUSIONS AND RELEVANCE

In unresectable stage III NSCLC, adding celecoxib to concurrent chemoradiation did not improve survival. A smaller, not statistically significant proportion of patients in the CCRT with celecoxib group compared with the CCRT alone group developed symptomatic radiation pneumonitis. Among patients with the high-risk genotype, adding celecoxib to CCRT did not improve overall or progression-free survival.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01503385.

Impact of gene polymorphisms on the systemic toxicity to paclitaxel/carboplatin chemotherapy for treatment of gynecologic cancers

PURPOSE

Gynecologic malignancies are often detected in advanced stages, requiring chemotherapy with taxane/platinum combinations, which may cause severe toxicities, such as neutropenia and peripheral neuropathy. Gene polymorphisms are suspected as possible causes for the interindividual variability on chemotherapy toxicities.

OBJECTIVE

To evaluate the role of ABCB1 1236C>T, 3435C>T; CYP2C8*3; CYP3A5*3C variants on paclitaxel/carboplatin toxicities.

METHODS

A cohort of 503 gynecologic cancer patients treated with paclitaxel/carboplatin at the Brazilian National Cancer Institute (INCA-Brazil) was recruited (2013-2017). Polymorphisms were genotyped by real-time PCR, and toxicities were evaluated by patients' interviews at each chemotherapy cycle and by data collection from electronic records. The association of clinical features and genotypes with severe toxicities was estimated using Pearson's Chi square tests and multiple regression analyses, with calculation of adjusted odds ratios (OR_adjusted), and respective 95% confidence intervals (95% CI).

RESULTS

CYP2C8*3 was significantly associated with increased risks of severe (grades 3-4) neutropenia (OR_adjusted 2.11; 95% CI 1.24-3.6; dominant model) and severe thrombocytopenia (OR_adjusted 4.93; 95% CI 1.69-14.35; recessive model), whereas ABCB1 variant genotypes (OR_adjusted 2.13; 95% CI 1.32-3.42), in association with CYP2C8*3 wild type (GG) (OR_adjusted 1.93; 95% CI 1.17-3.19), were predictive of severe fatigue.

CONCLUSIONS

The present study suggests that CYP2C8*3 is a potential predictor of hematological toxicities related to paclitaxel/carboplatin treatment. Since hematological toxicities, especially neutropenia, may lead to dose delay or treatment interruption, such prognostic evaluation may contribute to clinical management of selected patients with paclitaxel-based chemotherapy.

Pharmacogenomics of platinum-based chemotherapy response in NSCLC: a genotyping study and a pooled analysis

Published data showed inconsistent results about associations of extensively studied polymorphisms with platinum-based chemotherapy response. Our study aimed to provide reliable conclusions of these associations by detecting genotypes of the SNPs in a larger sample size and summarizing a comprehensive pooled analysis. 13 SNPs in 8 genes were genotyped in 1024 NSCLC patients by SequenomMassARRAY. 39 published studies and our study were included in meta-analysis. Patients with GA or GG genotypes of XRCC1 G1196 had better response than AA genotype carriers (Genotyping study: OR = 0.72, 95%CI: 0.53-0.96, P = 0.028; Meta-analysis: OR = 0.74, 95%CI: 0.62-0.89, P = 0.001). Patients carrying CT or TT genotypes of XRCC1 C580T could be more sensitive to platinum-based chemotherapy compared to patients with CC genotype (OR = 0.54, 95%CI: 0.37-0.80, P = 0.002). CC genotype of XRCC3 C18067T carriers showed more resistance to platinum-based chemotherapy when compared to those with CT or TT genotypes (OR = 0.69, 95%CI: 0.52-0.91, P = 0.009). Our study indicated that XRCC1 G1196A/C580T and XRCC3 C18067T should be paid attention for personalized platinum-based chemotherapy in NSCLC patients.

Genetic Polymorphisms and Platinum-based Chemotherapy Treatment Outcomes in Patients with Non-Small Cell Lung Cancer: A Genetic Epidemiology Study Based Meta-analysis

Data regarding genetic polymorphisms and platinum-based chemotherapy (PBC) treatment outcomes in patients with NSCLC are published at a growing pace, but the results are inconsistent. This meta-analysis integrated eligible candidate genes to better evaluate the pharmacogenetics of PBC in NSCLC patients. Relevant studies were retrieved from PubMed, Chinese National Knowledge Infrastructure and WANFANG databases. A total of 111 articles comprising 18,196 subjects were included for this study. The associations of genetic polymorphisms with treatment outcomes of PBC including overall response rate (ORR), overall survival (OS) and progression-free survival (PFS) were determined by analyzing the relative risk (RR), hazard ration (HR), corresponding 95% confidence interval (CI). Eleven polymorphisms in 9 genes, including ERCC1 rs11615 (OS), rs3212986 (ORR), XPA rs1800975 (ORR), XPD rs1052555 (OS, PFS), rs13181 (OS, PFS), XPG rs2296147 (OS), XRCC1 rs1799782 (ORR), XRCC3 rs861539 (ORR), GSTP1 rs1695 (ORR), MTHFR rs1801133 (ORR) and MDR1 rs1045642 (ORR), were found significantly associated with PBC treatment outcomes. These variants were mainly involved in DNA repair (EXCC1, XPA, XPD, XPG, XRCC1 and XRCC3), drug influx and efflux (MDR1), metabolism and detoxification (GSTP1) and DNA synthesis (MTHFR), and might be considered as potential prognostic biomarkers for assessing objective response and progression risk in NSCLC patients receiving platinum-based regimens.

Pharmacogenomics of platinum-based chemotherapy sensitivity in NSCLC: toward precision medicine

Lung cancer is one of the leading causes of cancer-related death in the world. Platinum-based chemotherapy is the first-line treatment for non-small-cell lung cancer (NSCLC), however, the therapeutic efficiency varies remarkably among individuals. A large number of pharmacogenomics studies aimed to identify genetic variations which can be used to predict platinum response. Those studies are leading NSCLC treatment to the new era of precision medicine. In the current review, we provided a comprehensive update on the main recent findings of genetic variations which can be used to predict platinum sensitivity in the NSCLC patients.

Efflux transporter variants as predictors of drug toxicity in lung cancer patients: systematic review and meta-analysis

Chemotherapeutic drugs are underutilized in lung cancer management due in part to serious adverse drug reactions (ADRs).

AIM

With studies revealing an association between interindividual patient ADR variation and efflux transporter variants, we carried out a meta-analysis and systemic review, in order to highlight current knowledge regarding the strength of association between efflux transporter SNPs variants and chemotherapeutic-drug induced ADRs.

MATERIALS & METHODS

Papers were sourced from MEDLINE, Cochrane Library, CINHL, EMBASE, Web of Knowledge, Scopus. The Cochrane Collaboration Risk of Bias Tool v13 was used to evaluate six types of bias domains for each of the publications reviewed.

RESULTS

Twenty-five publications comprising three randomised control trials, two retrospective case-controls and 20 clinical observation studies, totalling 3578 patients, were deemed eligible for review. Of the known efflux drug transporters, we report findings on the ABC members ABCB1, ABCC1, ABCC2, ABCG2, ABCA1, ABCC4 and ABCC5. Meta-analysis showed an decreased risk of irinotecan-induced neutropenia in patients expressing ABCB1 2677G>T/G (odds ratio [OR]: 0.24; 95% CI: 0.1-0.59; p = 0.002) but increased risk for ABCC2 3972T>T (OR: 1.67; 95% CI: 1.01-2.74; p = 0.04). ABCG2 34G>A was associated with a threefold increased risk of irinotecan-induced diarrhea (95% CI: 1.00-6.24; p = 0.05).

CONCLUSION

The majority of studies have identified a role for variants in effluxdrug transporters in contributing to lung cancer treatment-associated ADRs. However, for implementation of use of these transporter genetic variants as prognostic markers for ADR risk, future studies must incorporate larger patient numbers.

Co-expression of pregnane X receptor and ATP-binding cassette sub-family B member 1 in peripheral blood: A prospective indicator for drug resistance prediction in non-small cell lung cancer

The aim of the present study was to investigate the protein expression profiling of pregnane X receptor (PXR) and ATP-binding cassette sub-family B member 1 (ABCB1; also known as MDR1 or P-gp), present in the peripheral blood mononuclear cells (PBMCs) and cancerous tissues of cases of non-small cell lung cancer (NSCLC). Furthermore, the study aimed to assess the feasibility of predicting drug resistance through the medium of PBMCs. Of the subjects included in the study, 37 were histopathologically diagnosed with NSCLC and 17 were control patients without cancer. ThinPrep liquid-based smears with cytosine were applied in the examination of the PBMCs and proved quite effective in preserving the morphology and surface antigens of the lymphocytes. Measurements of expression levels in the PBMCs and cancerous tissues were obtained by immunohistochemical means. The results showed that, with the exception of the selective PXR expression in the normal lung tissues, the two types of proteins existed extensively throughout the PBMCs, normal tissues and tumors. Among the cancer patients, prior to chemotherapy, a significant rise in ABCB1 expression could be observed in the PBMCs, together with a similar rise in ABCB1 and PXR expression in the tumor specimens. Marked upregulation of the two proteins was detected in the PBMCs following 1 cycle of first-line chemotherapy. ABCB1 expression, correlated with PXR, persisted mostly in the PBMCs and tissue samples. When bound to and activated by ligands, PXR translocates from the cytoplasm to the nucleus of the cells. PXR subsequently binds to its DNA response elements as a heterodimer with the retinoid X receptor. A PXR translocation of moderate or low differentiation was identified in 3 cases of adenocarcinoma, which were co-expressing the two genes in the PBMCs prior to chemotherapy. During follow-up visits, tumor recurrence was observed within 3 months in 5 cases, which were characterized by PXR translocation. These findings indicate that the combined expression of PXR and ABCB1 in PBMCs may be used as a prospective indicator in diagnosis prior to histopathological diagnosis, and therefore may function as a novel biomarker for the prediction of drug resistance.

Chemotherapy Resistance in Lung Cancer

Despite a growing interest in development of non-cytotoxic targeted agents, systemic chemotherapy is still the mainstay of treatment for both non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). However, chemotherapy resistance limits our ability to effectively treat advanced lung cancer. Some lung tumors are intrinsically resistant to chemotherapy, and in virtually all cases, even the initial responders rapidly develop acquired resistance. While targeting histology could result in enhanced tumor sensitivity to a particular chemotherapeutic agent, better understanding of molecular determinants of chemotherapy sensitivity/resistance would be critically important. Development of predictive biomarkers to personalize chemotherapeutic agents and combining novel agents targeting specific resistance pathways with standard chemotherapy could be some promising strategies to overcome chemotherapy resistance in lung cancer. In this chapter, we will discuss some key mechanisms of resistance for commonly used chemotherapeutic agents in lung cancer.

Inherited variation in the ATP-binding cassette transporter ABCB1 and survival after chemotherapy for stage III-IV lung cancer

BACKGROUND

The ATP-binding cassette transporter gene ABCB1 and the glutathione S-transferase gene GSTP1 code for a multidrug resistance protein and for a detoxifying phase II metabolic enzyme, respectively, with substrate specificities that include chemotherapy drugs often used to treat lung cancer.

METHODS

We genotyped 11 ABCB1 and eight GSTP1 single nucleotide polymorphisms (SNPs) in 698 white lung cancer patients (all current or former cigarette smokers) and used log-rank test statistics and proportional hazards regression to evaluate associations between SNP genotype and survival.

RESULTS

Using data from all 698 cases, one SNP in ABCB1 (rs2235013) was statistically significantly associated with overall survival (p = 0.038, log-rank test). Chemotherapy and stage jointly (p = 0.025) significantly modified the association between rs2235013 and survival, with statistically significant (p = 0.013, log-rank test) association observed in the subgroup of stage III to IV lung cancer patients who received chemotherapy as part of their first course of treatment (n = 160; 93.1% nonsmall cell). Patients who inherited the minor T allele at ABCB1 rs2235013 experienced better overall survival and recurrence-free survival (hazard ratio, per minor T allele, [95% confidence interval]: 0.66 [0.49-0.90] and 0.55 [0.31-0.95], respectively; adjusted for year of diagnosis, sex, age at diagnosis, cigarette pack years, and stage). In addition, in the advanced stage chemotherapy-treated subgroup, four ABCB1 SNPs (rs6949448, rs2235046, rs1128503, and rs10276036) in mutual high linkage disequilibrium with rs2235013 and an independent ABCB1 SNP (rs1045642) showed statistically significant association (p < 0.05) with survival.

CONCLUSIONS

Inherited variation in ABCB1 may affect survival specifically in advanced stage lung cancer patients who receive chemotherapy.

Prognostic value of cyclooxygenase-2 gene polymorphisms in advanced non-small cell lung cancer patients treated with first-line platinum-based chemotherapy

AIM

Cyclooxygenase-2 (COX-2) plays an important role in cell apoptosis, angiogenesis and tumor invasion, and over-expression of COX-2 is associated with tumor development and occurrence. The aim of this study is to investigate the association between COX-2 polymorphisms and clinical outcomes in advanced non-small cell lung cancer (NSCLC) patients treated with first-line platinum-based chemotherapy.

METHODS

A total of 190 patients with IIIB or IV NSCLC who received platinum-based chemotherapy were recruited in this study. Four functional COX-2 polymorphisms, including rs689465, rs689466, rs3218625 and rs20417, were genotyped by PCR-based restriction fragment length polymorphism methods. Kaplan-Meier methods were used to compare survival by different genotypes. Cox proportional hazard models were used to identify independently significant variables.

RESULTS

The rs689465 AA genotype was significantly associated with longer overall survival (OS) (13.0 months vs 8.8 months, P = 0.019 for log-rank test; hazard ratio [HR] 0.624; 95% confidence internal [CI] 0.418-0.931) and progression-free survival (5.3 months vs 4.0 months, P = 0.018 for log-rank test; HR 0.627; 95% CI 0.421-0.934) compared with AG or GG genotype, especially in patients with adenocarcinoma (P = 0.002), performance status of 1 (P = 0.009) and stage IV disease (P = 0.012), and treated with gemcitabine-based chemotherapy (P = 0.012). Multivariate regression analysis showed that COX-2 rs689465 polymorphism had a significantly independent prognostic value for OS (P = 0.017, HR = 1.637, 95% CI = 1.093-2.453).

CONCLUSION

Our study suggested that rs689465 polymorphism could be a prognostic biomarker for advanced NSCLC patients treated with first-line platinum-based chemotherapy.

Polymorphisms in arachidonic acid metabolism-related genes and the risk and prognosis of colorectal cancer

Cyclooxygenase-2 (COX-2), 12-lipoxygenase (12-LOX) and phospholipaseA2 (PLA2) played important roles in the modulation of apoptosis, angiogenesis, carcinogenesis and invasion of colorectal cancer (CRC). The polymorphisms in COX-2, 12-LOX and PLA2 may affect their roles. Therefore, we investigated if COX-2 -1195G > A, 12-LOX 261Arg > Gln and PLA2 c.349 + 191A > G polymorphisms were associated with risk and prognosis of CRC as well as possible interactions with the environmental factors on the risk of CRC in Northeast of China. A case-control study with 451 cases and 631 controls were carried out, a cohort with 386 patients were followed up. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Compared with the 261Arg/Arg genotype, 12-LOX 261Arg/Gln genotype and 261Arg/Gln + Gln/Gln genotypes reduced the risk of rectal cancer by 33% (adjusted OR = 0.67, 95% CI 0.47-0.97, p = 0.03) and 32% (adjusted OR = 0.68, 95% CI 0.49-0.96, p = 0.03), respectively. The adjusted HR for the association between 12-LOX 261Gln/Gln genotype and overall survival in patients with CRC was 1.68 (95% CI 1.06-2.68, p = 0.03). There was also evidence of an interaction between the PLA2 c.349 + 191 A > G genotypes and the overnight food consumption (adjusted ORi = 1.92, 95% CI 1.14-3.25, P(interaction) = 0.01). These observations indicate that 12-LOX 261Arg > Gln polymorphism may affect risk of rectal cancer, and it may be a potential predictive marker for prognosis of CRC.

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.

The relative contributions of CYP3A4 and CYP3A5 to the metabolism of vinorelbine

Vinorelbine is a semisynthetic vinca alkaloid used in the treatment of advanced breast and non-small cell lung cancers. Vincristine, a related vinca alkaloid, is 9-fold more efficiently metabolized by CYP3A5 than by CYP3A4 in vitro. This study quantified the relative contribution of CYP3A4 and CYP3A5 to the metabolism of vinorelbine in vitro using cDNA-expressed human cytochrome P450s (P450s) and human liver microsomes (HLMs). CYP3A4 and CYP3A5 were identified as the P450s capable of oxidizing vinorelbine using a panel of human enzymes and selective P450 inhibitors in HLMs. For CYP3A4 coexpressed with cytochrome b5 (CYP3A4+b5) and CYP3A5+b5, the Michaelis-Menten constants for vinorelbine were 2.6 and 3.6 μM, respectively, but the Vmax of 1.4 pmol/min/pmol was common to both enzymes. In HLMs, the intrinsic clearance of vinorelbine metabolism was highly correlated with CYP3A4 activity, and there was no significant difference in intrinsic clearance between CYP3A5 high and low expressers. When radiolabeled vinorelbine substrate was used, there were clear qualitative differences in metabolite formation fingerprints between CYP3A4+b5 and CYP3A5+b5 as determined by NMR and mass spectrometry analysis. One major metabolite (M2), a didehydro-vinorelbine, was present in both recombinant and microsomal systems but was more abundant in CYP3A4+b5 incubations. We conclude that despite the equivalent efficiency of recombinant CYP3A4 and CYP3A5 in vinorelbine metabolism the polymorphic expression of CYP3A5, as shown by the kinetics with HLMs, may have a minimal effect on systemic clearance of vinorelbine.

MDR1 single nucleotide polymorphism C3435T in Turkish patients with non-small-cell lung cancer

We assessed whether single nucleotide polymorphisms (SNPs) in MDR1 gene C3435T predicted the outcome of platinum-based chemotherapies and survival in our non small cell lung cancer (NSCLC) patients. A total of 79 non-small cell lung cancer patients were enrolled to study. We determined the MDR1 C3435T single nucleotide gene polymorphisms. Median age was 60years: 91.7% male, 8.9% female. We found that CC, CT, TT genotype and T, C allele frequencies in lung cancer patients as 24.1%, 62%, 13.9% and 44.3%, 55.7%, respectively. Patients with CT genotype had a higher response rate (11.4%) than the other genotypes. However, this difference is not statistically significant (p=0.743). Cox regression analysis for overall survival showed that ECOG PS status 0 (HR PS 1 vs. 0, 5.68 p=0.002; HR of PS 2 vs. 0 is 21.579, p=0.001; HR of PS 3 vs. 0 is 35.35, p=0.001), stage ≤II (HR of stage III vs. I+II is 17.77; p=0.016, HR of stage IV vs. I+II is 26.97, p=0.006), and albumin level ≥3g/dl (HR of albumin <3g/dl vs. ≥3g/dl is 2.46, p=0.044) were the most important prognostic factors (also, time to progression was related to these factors). There was no significant association between the genotypes and clinicopathologic parameters; however, good performance status, early stage and ≥3g/dl albumin level were found to be the most important prognostic factors for overall survival and progression-free survival.

Meta-analysis on pharmacogenetics of platinum-based chemotherapy in non small cell lung cancer (NSCLC) patients

AIM

To determine the pharmacogenetics of platinum-based chemotherapy in Non Small Cell Lung Cancer (NSCLC) patients.

METHODS

Publications were selected from PubMed, Cochrane Library and ISI Web of Knowledge. A meta-analysis was conducted to determine the association between genetic polymorphisms and platinum-based chemotherapy by checking odds ratio (OR) and 95% confidence interval (CI).

RESULTS

Data were extracted from 24 publications, which included 11 polymorphisms in 8 genes for meta-analysis. MDR1 C3435T (OR = 1.97, 95% CI: 1.11-3.50, P = 0.02), G2677A/T (OR = 2.61, 95% CI: 1.44-4.74, P = 0.002) and GSTP1 A313G (OR = 0.32, 95% CI: 0.17-0.58, P = 0.0002) were significantly correlated with platinum-based chemotherapy in Asian NSCLC patients.

CONCLUSION

Attention should be paid to MDR1 C3435T, G2677A/T and GSTP1 A313G for personalized chemotherapy treatment for NSCLC patients in Asian population in the future.

Single nucleotide polymorphisms in MDR1 gen correlates with outcome in advanced non-small-cell lung cancer patients treated with cisplatin plus vinorelbine

New therapeutic approaches are being developed based on the findings that several genetic abnormalities underlying NSCLC could influence chemosensitivity. In this study, we assessed whether the presence of polymorphisms in ERCC1, XPD, RRM1 and MDR1 genes can affect the efficacy and the tolerability of cisplatin and vinorelbine in NSCLC patients.

MATERIAL AND METHODS

Eligible patients had histological confirmed stage IV or IIIB (with malignant pleural effusion) non-small-cell lung cancer (NSCLC) previously untreated with chemotherapy; World Health Organization performance status (PS) 0-1. Patients received intravenous doses of vinorelbine 25 mg/m² on day 1 and 8 and cisplatin 75 mg/m² on day 1, every 21 days, for a maximum of eight cycles.

RESULTS

94 patients were included. Median age was 61 years; 84% were male; WHO performance status (PS) was 0 in 24%; and 88% of patients had stage IV disease. The median number of cycles was 6. Overall median survival was 10.92 months (95% CI 9.0-12.9). Overall median time to progression was 5.89 months (95% CI 5.2-6.6). Results of the multivariate analysis for time to progression showed that ECOG 0 (hazard ratio [HR] ECOG 1 vs. ECOG 0, 1.74; p=0.036), MDR13435CC (HR CT vs. CC, 2.01; p=0.017; HR TT vs. CC, 1.54; p=0.22), and decreasing age (HR of age, 0.97; p=0.016) were the most powerful prognostic factors significantly related to lower risk of progression. Whereas ECOG 0 was the only prognostic factor for survival (HR ECOG 1 vs. ECOG 0, 3.02; p=0.001). There was no significant association between any of the SNPs analysed and the occurrence of vinorelbine and cisplatin-related toxicity.

CONCLUSION

In our results, the most important prognostic factors associated with lower risk of progression were MDR1 3435 CC genotype, PS 0 and younger age.

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).

Polymorphisms of ERCC1 C118T/C8092A and MDR1 C3435T predict outcome of platinum-based chemotherapies in advanced non-small cell lung cancer: a meta-analysis

BACKGROUND AND AIMS

With great progress made in individualized chemotherapy, pharmacogenetics is gradually put on the agenda. We performed this meta-analysis to compare outcome to platinum-based chemotherapies in advanced non-small cell lung cancer (NSCLC) with different ERCC1 C118T/C8092A and MDR1 C3435T polymorphisms.

METHODS

Relevant studies were identified according to search strategy in this meta-analysis. Inclusion criteria were patients with advanced NSCLC who were receiving platinum-based chemotherapies. We evaluated the relationship between single nucleotide polymorphisms (SNP) and outcome of platinum-based chemotherapies. RevMan and STATA package were used for the comprehensive quantitative analyses.

RESULTS

Twenty studies were included in the meta-analysis. There was no significant association between SNPs and objective response or overall survival of platinum-based chemotherapies with CC vs. CT/TT: ERCC1 C118T (OR 1.21, 95% CI 0.81-1.82 for objective response; HR 1.09, 95% CI 0.79-1.51 for overall survival); ERCC1 C8092A SNP (OR 0.84, 95% CI 0.59-1.18; HR 1.26, 95% CI 0.68-2.36) and MDR1 C3435T SNP (HR 1.11, 95% CI 0.78-1.56). Ethnic stratification provided the same results. We found a significant difference for MDR1 C3435T (OR 2.22, 95% CI 1.46-3.37; OR 2.63, 95% CI 1.56-4.45 for Asians; OR 1.61, 95% CI 0.79-3.28 for Caucasians).

CONCLUSIONS

We found no evidence to support the use of ERCC1 C118T/C8092A polymorphisms as prognostic predictors of platinum-based chemotherapies in NSCLC. For the MDR1 C3435T SNP, a significant association with objective response was detected for CC genotype in overall and Asian populations stratified. Multiple and large-scale studies with ethnic stratification are required for the correlation between biomarkers and tumor prognosis.

Multi-drug resistance 1 genetic polymorphism and prediction of chemotherapy response in Hodgkin's Lymphoma

Background

The human multi-drug resistance gene (MDR1), which encodes the major trans-membrane transporter P-glycoprotein (P-gp), was found to be associated with susceptibility to cancer and response to chemotherapy. The C3435T Polymorphism of MDR1 gene was correlated with expression levels and functions of P-gp. Here, we studied the association between MDR1 C3435T polymorphism and susceptibility to Hodgkin lymphoma (HL) and patient's response to ABVD chemotherapy regimen.

Methods

a total of 130 paraffin embedded tissue samples collected from HL patients were analyzed to identify the C3435T polymorphism. As a control group, 120 healthy subjects were enrolled in the study. The C3435T Polymorphism was genotyped by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. Data analysis was carried out using the statistical package SPSS version 17 to compute all descriptive statistics. Chi-square and Fisher exact tests were used to evaluate the genotype distribution and allele frequencies of the studied polymorphism.

Results

these studies revealed that the frequency of T allele was significantly higher in HL patients compared to the controls (P < 0.05). In addition, the frequency of CT and TT genotypes were also significantly higher in HL patients compared to the controls (P < 0.05). No association between C3435T polymorphism and response to ABVD was detected among HL patients (P > 0.05).

Conclusions

these results suggest that MDR1 C3435T polymorphism might play a role in HL occurrence; however this polymorphism is not correlated with the clinical response to ABVD.

Treatment of advanced non-small-cell lung cancer with Chinese herbal medicine by stages combined with chemotherapy

PURPOSE

To observe the effect of Chinese herbal medicine by stages combined with chemotherapy in treating patients with non-small-cell lung cancer (NSCLC) of stage III or IV.

METHODS

Adopting prospective, randomized, controlled, multi-centered trial design, 121 patients enrolled were assigned to the treatment group (n = 65) and the control group (n = 56). All the patients were randomized to receive chemotherapy alone or chemotherapy and Chinese herbal medicine combined (Kangliuzengxiao decoction during chemotherapy and Feiyanning decoction after chemotherapy). The main outcome measures were survival time, Karnofsky score, main clinical symptoms, and adverse reactions.

RESULTS

Five patients discontinued from the trial due to oral administration of Iressa after disease progression or other reasons, and 116 patients were evaluable for clinical efficacy with 63 in the treatment group and 53 in the control group. The overall response rate were 15.87% vs. 7.55% (P = 0.170), and the disease control rate were 85.71% vs. 71.70% in the treatment and control group (P = 0.063), respectively. The median survival time was 16.17 months vs. 12.00 months in the treatment and control group (P = 0.165), respectively. In addition, adverse reactions such as leucopenia in the treatment group were less than those in the control group (P = 0.039).

CONCLUSIONS

Chinese herbal medicine combined with chemotherapy showed favorable effect in improving quality of life and prolonging survival time on patients with advanced NSCLC.

Pharmacogenetics in breast cancer: steps toward personalized medicine in breast cancer management

There is wide individual variability in the pharmacokinetics, pharmacodynamics, and tolerance to anticancer drugs within the same ethnic group and even greater variability among different ethnicities. Pharmacogenomics (PG) has the potential to provide personalized therapy based on individual genetic variability in an effort to maximize efficacy and reduce adverse effects. The benefits of PG include improved therapeutic index, improved dose regimen, and selection of optimal types of drug for an individual or set of individuals. Advanced or metastatic breast cancer is typically treated with single or multiple combinations of chemotherapy regimens including anthracyclines, taxanes, antimetabolites, alkylating agents, platinum drugs, vinca alkaloids, and others. In this review, the PG of breast cancer therapeutics, including tamoxifen, which is the most widely used therapeutic for the treatment of hormone-dependent breast cancer, is reviewed. The pharmacological activity of tamoxifen depends on its conversion by cytochrome P450 2D6 (CYP2D6) to its abundant active metabolite, endoxifen. Patients with reduced CYP2D6 activity, as a result of either their genotype or induction by the coadministration of other drugs that inhibit CYP2D6 function, produce little endoxifen and hence derive limited therapeutic benefit from tamoxifen; the same can be said about the different classes of therapeutics in breast cancer. PG studies of breast cancer therapeutics should provide patients with breast cancer with optimal and personalized therapy.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

Cyclooxygenase-2 genetic variants are associated with survival in unresectable locally advanced non-small cell lung cancer

PURPOSE

Cyclooxygenase-2 (COX-2) plays important roles in the modulation of apoptosis, angiogenesis, immune response, and tumor invasion. Elevated COX-2 expression has been reported to be correlated with reduced survival after radiotherapy. This study examined whether genetic variations in the COX-2 gene are associated with different survival in inoperable locally advanced non-small cell lung cancer (NSCLC) treated with chemoradiotherapy or radiotherapy alone.

EXPERIMENTAL DESIGN

One hundred and thirty-six patients with inoperable stage IIIA-B NSCLC receiving thoracic irradiation between 2004 and 2007 were recruited in this study. Five functional COX-2 polymorphisms were genotyped using DNA from blood lymphocytes. Kaplan-Meier methods were used to compare survival by different genotypes. Cox proportional hazards models were used to identify independently significant variables.

RESULTS

During the median 22.4 months of follow-up, the favorable COX-2 -1195GA and GG genotypes were significantly correlated with better overall survival (20.2 months versus 15.7 months; P = 0.006; hazard ratio (HR), 0.58; 95% confidence interval (CI), 0.39-0.86) and with longer progress-free survival (11.9 months versus 9.5 months; P = 0.034) compared with the -1195AA genotype. No significant associations were found among other COX-2 polymorphisms and clinical outcomes. In the multivariate Cox proportional hazards model, COX-2 -1195G/A polymorphism was independently associated with overall survival after adjusting the clinicopathologic factors (P = 0.008; HR, 0.58; 95% CI, 0.39-0.87).

CONCLUSION

COX-2 -1195G/A polymorphism is a potential predictive marker of survival in locally advanced NSCLC patients treated with chemoradiotherapy or radiotherapy alone.

Association of MDR1 and ERCC1 polymorphisms with response and toxicity to cisplatin-based chemotherapy in non-small-cell lung cancer patients

Among the cancer patient population, resistance to therapy is a major cause for therapeutic failure and for human sufferings, especially for the cancer with poor prognosis. Therefore, finding factors that contribute to drug resistance is a major research interest. In this study, we have investigated whether polymorphisms in genes that control import/export of drugs (MDR1) and that repair DNA adducts (ERCC1) are involved with drug resistance in non-small cell lung cancer (NSCLC) patients. We have recruited 95 patients with advanced NSCLC (stages IIIB-IV) who were specifically treated with platinum-based chemotherapy. We used the ligase detection reactions assay (LDR) to detect polymorphisms in ERCC1 118C/T, and MDR1 2677T/A, E1/-129T/C, and C3435T in peripheral blood lymphocytes from the patients. The haplotype of MDR1 gene single nucleotide polymorphisms (SNPs) were analyzed using the SHEsis software platform on line. We found that none of the single polymorphisms was associated with treatment response or related toxicity. However, patients carrying at least one variant MDR1 2677 T allele was associated with a significantly increased risk of drug resistance (OR=1.844, 95% CI=1.01-3.53, P=0.04) but also with a significantly increased risk of gastrointestinal toxicity (P=0.03) but not hemato-, hepato- or nephro-toxicities. Moreover, we analyzed the haplotypes of the three polymorphisms in MDR1. The patients harboring the E1/-129T-2677T-3435C haplotype had a significantly better response to chemotherapy compared with those having the other haplotypes (P=0.02, 95% CI=1.20-25.87), and a marginally significant association with increased risk of gastrointestinal toxicity (P=0.02, 95% CI=1.15-3.88). Our results suggested that gene polymorphisms in MDR1G2677T/A may be a predictive marker of platinum-based treatment response and of secondary effects, especially gastrointestinal toxicity for advanced NSCLC patients.

Haplotype-based analysis of MDR1/ABCB1 gene polymorphisms in a Turkish population

The three functional single-nucleotide polymorphisms (SNPs) of the MDR1 gene, C1236T, G2677T/A, and C3435T, exhibit an interpopulation difference. In this study, we analyzed the haplotype frequencies of these three SNPs in 107 unrelated healthy Turkish subjects and compared them with those of other reported populations. We found that C1236T, G2677T/A, and C3435T SNPs are expected to be structured in 10 different haplotypes, with 4 prominent haplotypes T-T-T (33.7%), C-G-C (25.0%), T-G-C (10.9%), and C-T-T (8.7%). There was a statistically significant linkage disequilibrium between all C1236T, G2677T/A, and C3435T SNPs (p < 0.0001); however, our results indicated that only loci 2677 and 3435 show relatively strong linkage disequilibrium (Lewontin's coefficient [D'] = 0.74, Pearson's correlation [r(2)] = 0.47). The haplotype frequency distribution of our study group was found to be significantly different from that in Han Chinese, Uygur Chinese, Kazakh Chinese, Indian, Malay, Japanese, Caucasian, and Ashkenazi Jewish populations (p < 0.0001). The results of this study may contribute to population-specific haplotype data on the MDR1 gene and may serve as a basis for studies on response to P-glycoprotein substrate drugs as well as for future association studies of certain diseases in Turkish population.

Prognostic Significance and Clinicopathological Associations of COX-2 SNP in Patients with Nonsmall Cell Lung Cancer

Background. To further improve the screening, diagnosis, and therapy of patients with nonsmall cell lung cancer (NSCLC) additional diagnostic tools are urgently needed. Gene expression of Cyclooxygenase-2 (COX-2) has been linked to prognosis in patients with NSCLC. The role of the COX-2 926G>C Single Nucleotide Polymorphism (SNP) in patients with NSCLC remains unclear. The aim of this study was to investigate the potential of the COX-2 926G>C SNP as a molecular marker in this disease. Methods. COX-2 926G>C SNP was analyzed in surgically resected tumor tissue of 85 patients with NSCLC using a PCR-based RFLP technique. Results. The COX-2 926G>C SNP genotypes were detected with the following frequencies: GG n = 62 (73%), GC n = 20 (23%), CC n = 3 (4%). There were no associations between COX-2 SNP genotype and histology, grading or gender detectable. COX-2 SNP was significantly associated with tumor stage (P = .032) and lymph node status (P = .016, Chi-square test). With a median followup of 85.9 months, the median survival was 59.7 months. There were no associations seen between the COX-2 SNP genotype and patients prognosis. Conclusions. The COX-2 926G>C SNP is detectable at a high frequency in patients with NSCLC. The COX-2 926G>C SNP genotype is not a prognostic molecular marker in this disease. However, patients with the GC or CC genotype seem more susceptible to lymph node metastases and higher tumor stage than patients with the GG genotype. The results suggest COX-2 926G>C SNP as a molecular marker for lymph node involvement in this disease.

Pharmacokinetics and pharmacogenomics in breast cancer chemotherapy

Locally advanced or metastatic breast cancer is typically treated with chemotherapy. Multiple combinations of chemotherapy regimens are available, including anthracyclines, taxanes, antimetabolites, alkylating agents, platinum drugs and vinca alkaloids. This review discusses the pharmacokinetic and pharmacogenomic information available for commonly used breast cancer chemotherapy drugs. Pharmacogenomic associations for many drugs have yet to be identified or validated in breast cancer. Further work is needed to identify markers to screen breast cancer patients prior to therapy selection.

ABCG2: a perspective

ABCG2, or breast cancer resistance protein (BCRP), is an ABC transporter that has been the subject of intense study since its discovery a decade ago. With high normal tissue expression in the brain endothelium, gastrointestinal tract, and placenta, ABCG2 is believed to be important in the protection from xenobiotics, regulating oral bioavailability, forming part of the blood-brain barrier, the blood-testis barrier, and the maternal-fetal barrier. Notably, ABCG2 is often expressed in stem cell populations, where it likely plays a role in xenobiotic protection. However, clues to its epigenetic regulation in various cell populations are only beginning to emerge. While ABCG2 overexpression has been demonstrated in cancer cells after in vitro drug treatment, endogenous ABCG2 expression in certain cancers is likely a reflection of the differentiated phenotype of the cell of origin and likely contributes to intrinsic drug resistance. Notably, research into the transporter's role in cancer drug resistance and its development as a therapeutic target in cancer has lagged. Substrates and inhibitors of the transporter have been described, among them chemotherapy drugs, tyrosine kinase inhibitors, antivirals, HMG-CoA reductase inhibitors, carcinogens, and flavonoids. This broad range of substrates complements the efficiency of ABCG2 as a transporter in laboratory studies and suggests that, while there are redundant mechanisms of xenobiotic protection, the protein is important in normal physiology. Indeed, emerging studies in pharmacology and toxicology assessing polymorphic variants in man, in combination with murine knockout models have confirmed its dynamic role. Work in pharmacology may eventually lead us to a greater understanding of the physiologic role of ABCG2.