Patient-derived small intestinal myofibroblasts direct perfused, physiologically responsive capillary development in a microfluidic Gut-on-a-Chip Model

The development and physiologic role of small intestine (SI) vasculature is poorly studied. This is partly due to a lack of targetable, organ-specific markers for in vivo studies of two critical tissue components: endothelium and stroma. This challenge is exacerbated by limitations of traditional cell culture techniques, which fail to recapitulate mechanobiologic stimuli known to affect vessel development. Here, we construct and characterize a 3D in vitro microfluidic model that supports the growth of patient-derived intestinal subepithelial myofibroblasts (ISEMFs) and endothelial cells (ECs) into perfused capillary networks. We report how ISEMF and EC-derived vasculature responds to physiologic parameters such as oxygen tension, cell density, growth factors, and pharmacotherapy with an antineoplastic agent (Erlotinib). Finally, we demonstrate effects of ISEMF and EC co-culture on patient-derived human intestinal epithelial cells (HIECs), and incorporate perfused vasculature into a gut-on-a-chip (GOC) model that includes HIECs. Overall, we demonstrate that ISEMFs possess angiogenic properties as evidenced by their ability to reliably, reproducibly, and quantifiably facilitate development of perfused vasculature in a microfluidic system. We furthermore demonstrate the feasibility of including perfused vasculature, including ISEMFs, as critical components of a novel, patient-derived, GOC system with translational relevance as a platform for precision and personalized medicine research.

Effect of Low-Intensity vs Standard-Intensity Warfarin Prophylaxis on Venous Thromboembolism or Death Among Patients Undergoing Hip or Knee Arthroplasty: A Randomized Clinical Trial

IMPORTANCE

The optimal international normalized ratio (INR) to prevent venous thromboembolism (VTE) in warfarin-treated patients with recent arthroplasty is unknown.

OBJECTIVE

To determine the safety and efficacy of a target INR of 1.8 vs 2.5 for VTE prophylaxis after orthopedic surgery.

DESIGN, SETTING, AND PARTICIPANTS

The randomized Genetic Informatics Trial (GIFT) of Warfarin to Prevent Deep Vein Thrombosis enrolled 1650 patients aged 65 years or older initiating warfarin for elective hip or knee arthroplasty at 6 US medical centers. Enrollment began in April 2011 and follow-up concluded in October 2016.

INTERVENTIONS

In a 2 × 2 factorial design, participants were randomized to a target INR of 1.8 (n = 823) or 2.5 (n = 827) and to either genotype-guided or clinically guided warfarin dosing. For the first 11 days of therapy, open-label warfarin dosing was guided by a web application.

MAIN OUTCOMES AND MEASURES

The primary outcome was the composite of VTE (within 60 days) or death (within 30 days). Participants underwent screening duplex ultrasound postoperatively. The hypothesis was that an INR target of 1.8 would be noninferior to an INR target of 2.5, using a noninferiority margin of 3% for the absolute risk of VTE. Secondary end points were bleeding and INR values of 4 or more.

RESULTS

Among 1650 patients who were randomized (mean age, 72.1 years; 1049 women [63.6%]; 1502 white [91.0%]), 1597 (96.8%) received at least 1 dose of warfarin and were included in the primary analysis. The rate of the primary composite outcome of VTE or death was 5.1% (41 of 804) in the low-intensity-warfarin group (INR target, 1.8) vs 3.8% (30 of 793) in the standard-treatment-warfarin group (INR target, 2.5), for a difference of 1.3% (1-sided 95% CI, -∞ to 3.05%, P = .06 for noninferiority). Major bleeding occurred in 0.4% of patients in the low-intensity group and 0.9% of patients in the standard-intensity group, for a difference of -0.5% (95% CI, -1.6% to 0.4%). The INR values of 4 or more occurred in 4.5% of patients in the low-intensity group and 12.2% of the standard-intensity group, for a difference of -7.8% (95% CI, -10.5% to -5.1%).

CONCLUSIONS AND RELEVANCE

Among older patients undergoing hip or knee arthroplasty and receiving warfarin prophylaxis, an international normalized ratio goal of 1.8 compared with 2.5 did not meet the criterion for noninferiority for risk of the composite outcome of VTE or death. However, the trial may have been underpowered to meet this criterion and further research may be warranted.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01006733.

Effect of Genotype-Guided Warfarin Dosing on Clinical Events and Anticoagulation Control Among Patients Undergoing Hip or Knee Arthroplasty: The GIFT Randomized Clinical Trial

IMPORTANCE

Warfarin use accounts for more medication-related emergency department visits among older patients than any other drug. Whether genotype-guided warfarin dosing can prevent these adverse events is unknown.

OBJECTIVE

To determine whether genotype-guided dosing improves the safety of warfarin initiation.

DESIGN, SETTING, AND PATIENTS

The randomized clinical Genetic Informatics Trial (GIFT) of Warfarin to Prevent Deep Vein Thrombosis included patients aged 65 years or older initiating warfarin for elective hip or knee arthroplasty and was conducted at 6 US medical centers. Enrollment began in April 2011 and follow-up concluded in October 2016.

INTERVENTIONS

Patients were genotyped for the following polymorphisms: VKORC1-1639G>A, CYP2C9*2, CYP2C9*3, and CYP4F2 V433M. In a 2 × 2 factorial design, patients were randomized to genotype-guided (n = 831) or clinically guided (n = 819) warfarin dosing on days 1 through 11 of therapy and to a target international normalized ratio (INR) of either 1.8 or 2.5. The recommended doses of warfarin were open label, but the patients and clinicians were blinded to study group assignment.

MAIN OUTCOMES AND MEASURES

The primary end point was the composite of major bleeding, INR of 4 or greater, venous thromboembolism, or death. Patients underwent a screening lower-extremity duplex ultrasound approximately 1 month after arthroplasty.

RESULTS

Among 1650 randomized patients (mean age, 72.1 years [SD, 5.4 years]; 63.6% women; 91.0% white), 1597 (96.8%) received at least 1 dose of warfarin therapy and completed the trial (n = 808 in genotype-guided group vs n = 789 in clinically guided group). A total of 87 patients (10.8%) in the genotype-guided group vs 116 patients (14.7%) in the clinically guided warfarin dosing group met at least 1 of the end points (absolute difference, 3.9% [95% CI, 0.7%-7.2%], P = .02; relative rate [RR], 0.73 [95% CI, 0.56-0.95]). The numbers of individual events in the genotype-guided group vs the clinically guided group were 2 vs 8 for major bleeding (RR, 0.24; 95% CI, 0.05-1.15), 56 vs 77 for INR of 4 or greater (RR, 0.71; 95% CI, 0.51-0.99), 33 vs 38 for venous thromboembolism (RR, 0.85; 95% CI, 0.54-1.34), and there were no deaths.

CONCLUSIONS AND RELEVANCE

Among patients undergoing elective hip or knee arthroplasty and treated with perioperative warfarin, genotype-guided warfarin dosing, compared with clinically guided dosing, reduced the combined risk of major bleeding, INR of 4 or greater, venous thromboembolism, or death. Further research is needed to determine the cost-effectiveness of personalized warfarin dosing.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01006733.

Pharmacogenomic assessment of Mexican and Peruvian populations

BACKGROUND

Clinically relevant polymorphisms often demonstrate population-specific allele frequencies. Central and South America remain largely uncategorized in the context of pharmacogenomics.

MATERIALS & METHODS

We assessed 15 polymorphisms from 12 genes (ABCB1 3435C>T, ABCG2 Q141K, CYP1B1*3, CYP2C19*2, CYP3A4*1B, CYP3A5*3C, ERCC1 N118N, ERCC2 K751Q, GSTP1 I105V, TPMT 238G>C, TPMT 460G>A, TPMT 719A>G, TYMS TSER, UGT1A1*28 and UGT1A1 -3156G>A) in 81 Peruvian and 95 Mexican individuals.

RESULTS

Six polymorphism frequencies differed significantly between the two populations: ABCB1 3435C>T, CYP1B1*3, GSTP1 I105V, TPMT 460G>A, UGT1A1*28 and UGT1A1 -3156G>A. The pattern of observed allele frequencies for all polymorphisms could not be accurately estimated from any single previously studied population.

CONCLUSION

This highlights the need to expand the scope of geographic data for use in pharmacogenomics studies.

Differential β3 Integrin Expression Regulates the Response of Human Lung and Cardiac Fibroblasts to Extracellular Matrix and Its Components

Extracellular matrix (ECM) derived from whole organ decellularization has been successfully used in a variety of tissue engineering applications. ECM contains a complex mixture of functional and structural molecules that are ideally suited for the tissue from which the ECM is harvested. However, decellularization disrupts the structural properties and protein composition of the ECM, which may impact function when cells such as the fibroblast are reintroduced during recellularization. We hypothesized that the ECM structure and composition, fibroblast source, and integrin expression would influence the fibroblast phenotype. Human cardiac fibroblasts (HCFs) and normal human lung fibroblasts (NHLFs) were cultured on intact cardiac ECM, collagen gels, and coatings composed of cardiac ECM, lung ECM, and individual ECM components (collagen and fibronectin [FN]) for 48 h. COL1A expression of HCFs and NHLFs cultured on ECM and FN coatings decreased to <50% of that of untreated cells; COL1A expression for HCFs cultured on ECM coatings was one- to twofold higher than HCFs cultured on intact ECM. NHLFs cultured on ECM and FN coatings expressed 12- to 31-fold more alpha-smooth muscle actin (αSMA) than HCFs; the αSMA expression for HCFs and NHLFs cultured on ECM coatings was ∼2- to 5-fold higher than HCFs and NHLFs cultured on intact ECM. HCFs expressed significantly higher levels of β3 and β4 integrins when compared to NHLFs. Inhibition of the β3 integrin, but not β4, resulted in a 16- to 26-fold increase in αSMA expression in HCFs cultured on ECM coatings and FN. Our results demonstrate that β3 integrin expression depends on the source of the fibroblast and that its expression inhibits αSMA expression (and thus the myofibroblast phenotype). We conclude that the fibroblast source and integrin expression play important roles in regulating the fibroblast phenotype.

Pyrosequencing of clinically relevant polymorphisms

Despite the influx of high throughput sequencing techniques, there is still a niche for low-medium throughput genotyping technologies for small-scale screening and validation purposes. Pyrosequencing is a genotyping assay based on sequencing-by-synthesis. Short runs of sequence around each polymorphism are generated, allowing for internal controls for each sample. Pyrosequencing can also be utilized to identify tri-allelic, indel, and short repeat polymorphisms, as well as determining allele percentages for methylation or pooled sample assessment. This range of applications makes it well-suited to the research laboratory as a one-stop system.

Gamma-glutamyl carboxylase and its influence on warfarin dose

Via generation of vitamin K-dependent proteins, gamma-glutamyl carboxylase (GGCX) plays a critical role in the vitamin K cycle. Single nucleotide polymorphisms (SNPs) in GGCX, therefore, may affect dosing of the vitamin K antagonist, warfarin. In a multi-centered, cross-sectional study of 985 patients prescribed warfarin therapy, we genotyped for two GGCX SNPs (rs11676382 and rs12714145) and quantified their relationship to therapeutic dose. GGCX rs11676382 was a significant (p=0.03) predictor of residual dosing error and was associated with a 6.1% reduction in warfarin dose (95% CI: 0.6%-11.4%) per G allele. The prevalence was 14.1% in our predominantly (78%) Caucasian cohort, but the overall contribution to dosing accuracy was modest (partial R2 = 0.2%). GGCX rs12714145 was not a significant predictor of therapeutic dose (p = 0.26). GGCX rs11676382 is a statistically significant predictor of warfarin dose, but the clinical relevance is modest. Given the potentially low marginal cost of adding this SNP to existing genotyping platforms, we have modified our non-profit website (www.WarfarinDosing.org) to accommodate knowledge of this variant.

Pharmacogenetic predictors of adverse events and response to chemotherapy in metastatic colorectal cancer: results from North American Gastrointestinal Intergroup Trial N9741

PURPOSE

With three available chemotherapy drugs for advanced colorectal cancer (CRC), response rate (RR) and survival outcomes have improved with associated morbidity, accentuating the need for tools to select optimal individualized treatment. Pharmacogenetics identifies the likelihood of adverse events or response based on variants in genes involved in drug transport, metabolism, and cellular targets.

PATIENTS AND METHODS

Germline DNA was extracted from 520 patients on the North American Gastrointestinal Intergroup N9741 study. Three study arms were evaluated: IFL (fluorouracil [FU] + irinotecan [IRN]), FOLFOX (FU + oxaliplatin), and IROX (IRN + oxaliplatin). Information on adverse events, response, and disease-free survival was available. Thirty-four variants in 15 candidate genes for analysis based on previous associations with adverse events or outcome were assessed. Genotyping was performed using pyrosequencing.

RESULTS

All variants were polymorphic. The homozygous UGT1A1*28 allele observed in 9% of patients was associated with risk of grade 4 neutropenia in patients on IROX (55% v 15%; P = .002). Deletion in GSTM1 was associated with grade 4 neutropenia after FOLFOX (28% v 16%; P = .02). Patients with a homozygous variant genotype for GSTP1 were more likely to discontinue FOLFOX because of neurotoxicity (24% v 10%; P = .01). The presence of a CYP3A5 variant was significantly associated with RR on IFL (29% v 60%; P = .0074). Most previously published genotype-toxicity or -efficacy relationships were not validated in this study.

CONCLUSION

This study provides a platform to evaluate pharmacogenetic predictors of response or severe adverse events in advanced CRC. Pharmacogenetic studies can be conducted in multicenter trials, and our findings demonstrate that with continued research, clinical application is practical.

A polymorphism in the VKORC1 regulator calumenin predicts higher warfarin dose requirements in African Americans

Warfarin demonstrates a wide interindividual variability in response that is mediated partly by variants in cytochrome P450 2C9 (CYP2C9) and vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1). It is not known whether variants in calumenin (CALU) (vitamin K reductase regulator) have an influence on warfarin dose requirements. We resequenced CALU regions in a discovery cohort of dose outliers: patients with high (>90th percentile, n = 55) or low (<10th percentile, n = 53) warfarin dose requirements (after accounting for known genetic and nongenetic variables). One CALU variant, rs339097, was associated with high doses (P = 0.01). We validated this variant as a predictor of higher warfarin doses in two replication cohorts: (i) 496 patients of mixed ethnicity and (ii) 194 African-American patients. The G allele of rs339097 (the allele frequency was 0.14 in African Americans and 0.002 in Caucasians) was associated with the requirement for a 14.5% (SD +/- 7%) higher therapeutic dose (P = 0.03) in the first replication cohort and a higher-than-predicted dose in the second replication cohort (allele frequency 0.14, one-sided P = 0.03). CALU rs339097 A>G is associated with higher warfarin dose requirements, independent of known genetic and nongenetic predictors of warfarin dose in African Americans.

Ability of VKORC1 and CYP2C9 to predict therapeutic warfarin dose during the initial weeks of therapy

BACKGROUND

CYP2C9 and VKORC1 genotypes predict therapeutic warfarin dose at initiation of therapy; however, the predictive ability of genetic information after a week or longer is unknown. Experts have hypothesized that genotype becomes irrelevant once international normalized ratio (INR) values are available because INR response reflects warfarin sensitivity.

METHODS

We genotyped the participants in the Prevention of Recurrent Venous Thromboembolism (PREVENT) trial, who had idiopathic venous thromboemboli and began low-intensity warfarin (therapeutic INR 1.5-2.0) using a standard dosing protocol. To develop pharmacogenetic models, we quantified the effect of genotypes, clinical factors, previous doses and INR on therapeutic warfarin dose in the 223 PREVENT participants who were randomized to warfarin and achieved stable therapeutic INRs.

RESULTS

A pharmacogenetic model using data from day 0 (before therapy initiation) explained 54% of the variability in therapeutic dose (R(2)). The R(2) increased to 68% at day 7, 75% at day 14, and 77% at day 21, because of increasing contributions from prior doses and INR response. Although CYP2C9 and VKORC1 genotypes were significant independent predictors of therapeutic dose at each weekly interval, the magnitude of their predictive ability diminished over time: partial R(2) of genotype was 43% at day 0, 12% at day 7, 4% at day 14, and 1% at day 21.

CONCLUSION

Over the first weeks of warfarin therapy, INR and prior dose become increasingly predictive of therapeutic dose, and genotype becomes less relevant. However, at day 7, genotype remains clinically relevant, accounting for 12% of therapeutic dose variability.

Combination of human tumor necrosis factor-alpha (hTNF-alpha) gene delivery with gemcitabine is effective in models of pancreatic cancer

Pancreatic adenocarcinoma is an aggressive and highly lethal malignancy. Currently, gemcitabine is commonly used in patients with pancreatic cancer. However, the life expectancy of pancreatic cancer patients remains poor. We explored the possibility of increased anti-tumor activity by combining human tumor necrosis factor-alpha (hTNF-alpha) with current front-line therapy. Human TNF-alpha displays potent anti-tumor activity, but its use is limited by the toxicity of systemic administration. We developed a gene delivery approach using intratumoral injections of an adenoviral vector expressing hTNF-alpha, AdEgr.TNF.11D (TNFerade), to increase local concentrations of hTNF-alpha within the tumor, thereby maximizing local anti-tumor activity and yet minimizing the systemic toxicities. An ongoing phase III clinical trial is testing the efficacy of AdEgr.TNF.11D-injected intratumorally and combining with chemotherapy in locally advanced pancreatic cancer. In this study, we show that treatment with AdEgr.TNF.11D and gemcitabine results in a high level of hTNF-alpha expression in human pancreatic cancer cell lines. The combined treatment was well tolerated, highly active and produced marked delays in the growth of human pancreatic xenograft tumors relative to either agent alone. Our results strongly suggest that combination of AdEgr.TNF.11D and gemcitabine may be a potentially useful therapeutic approach for the improved treatment of pancreatic cancer.

Laboratory and clinical outcomes of pharmacogenetic vs. clinical protocols for warfarin initiation in orthopedic patients

BACKGROUND

Warfarin is commonly prescribed for prophylaxis and treatment of thromboembolism after orthopedic surgery. During warfarin initiation, out-of-range International Normalized Ratio (INR) values and adverse events are common.

METHODS

In orthopedic patients beginning warfarin therapy, we developed and prospectively validated pharmacogenetic and clinical dose refinement algorithms to revise the estimated therapeutic dose after 4 days of therapy.

RESULTS

The pharmacogenetic algorithm used the cytochrome P450 (CYP) 2C9 genotype, smoking status, peri-operative blood loss, liver disease, INR values and dose history to predict the therapeutic dose. The R(2) was 82% in a derivation cohort (n = 86) and 70% when used prospectively (n = 146). The R(2) of the clinical algorithm that used INR values and dose history to predict the therapeutic dose was 57% in a derivation cohort (n = 178) and 48% in a prospective validation cohort (n = 146). In 1 month of prospective follow-up, the percent time spent in the therapeutic range was 7% higher (95% CI: 2.7-11.7) in the pharmacogenetic cohort. The risk of a laboratory or clinical adverse event was also significantly reduced in the pharmacogenetic cohort (Hazard Ratio 0.54; 95% CI: 0.30-0.97).

CONCLUSIONS

Warfarin dose adjustments that incorporate genotype and clinical variables available after four warfarin doses are accurate. In this non-randomized, prospective study, pharmacogenetic dose refinements were associated with more time spent in the therapeutic range and fewer laboratory or clinical adverse events. To facilitate gene-guided warfarin dosing we created a non-profit website, http://www.WarfarinDosing.org.

Performance of commercial platforms for rapid genotyping of polymorphisms affecting warfarin dose

Initiation of warfarin therapy is associated with bleeding owing to its narrow therapeutic window and unpredictable therapeutic dose. Pharmacogenetic-based dosing algorithms can improve accuracy of initial warfarin dosing but require rapid genotyping for cytochrome P-450 2C9 (CYP2C9) *2 and *3 single nucleotide polymorphisms (SNPs) and a vitamin K epoxide reductase (VKORC1) SNP. We evaluated 4 commercial systems: INFINITI analyzer (AutoGenomics, Carlsbad, CA), Invader assay (Third Wave Technologies, Madison, WI), Tag-It Mutation Detection assay (Luminex Molecular Diagnostics, formerly Tm Bioscience, Toronto, Canada), and Pyrosequencing (Biotage, Uppsala, Sweden). We genotyped 112 DNA samples and resolved any discrepancies with bidirectional sequencing. The INFINITI analyzer was 100% accurate for all SNPs and required 8 hours. Invader and Tag-It were 100% accurate for CYP2C9 SNPs, 99% accurate for VKORC1 -1639/3673 SNP, and required 3 hours and 8 hours, respectively. Pyrosequencing was 99% accurate for CYP2C9 *2, 100% accurate for CYP2C9 *3, and 100% accurate for VKORC1 and required 4 hours. Current commercial platforms provide accurate and rapid genotypes for pharmacogenetic dosing during initiation of warfarin therapy.

Pharmacogenetic assessment of toxicity and outcome after platinum plus taxane chemotherapy in ovarian cancer: the Scottish Randomised Trial in Ovarian Cancer

PURPOSE

Standard therapy for advanced ovarian cancer consists of a platinum agent in combination with a taxane, which has a 5-year survival rate of approximately 45%. The large individual variability for ovarian cancer patients in both outcome and toxicity risk from chemotherapy makes the identification of pharmacogenetic markers that can be used to screen patients before therapy selection an attractive prospect.

PATIENTS AND METHODS

We assessed 27 selected polymorphisms based on previously described associations or putative functional effects in 16 key genes from pathways that may influence cellular sensitivity to taxanes (ABCB1, ABCC1, ABCC2, ABCG2, CDKN1A, CYP1B1, CYP2C8, CYP3A4, CYP3A5, MAPT, and TP53) and platinum (ABCC2, ABCG2, ERCC1, ERCC2, GSTP1, MPO, and XRCC1) using polymerase chain reaction and Pyrosequencing in 914 ovarian cancer patients from the Scottish Randomised Trial in Ovarian Cancer phase III trial who were treated at presentation with carboplatin and taxane regimens after cytoreductive surgery.

RESULTS

No reproducible significant associations between genotype and outcome or toxicity were found for any of the genes analyzed. Previously reported genotype associations could not be replicated in this large study of a well-defined patient population within one specific clinical trial.

CONCLUSION

There are no clear candidates for taxane/platinum pharmacogenetic markers. This study highlights the need for validation of putative genetic markers in large, well-defined clinical sample sets.

Pyrosequencing: a simple method for accurate genotyping

Pharmacogenetic research benefits first-hand from the abundance of information provided by the completion of the Human Genome Project. With such a tremendous amount of data available comes an explosion of genotyping methods. Pyrosequencing is one of the most thorough yet simple methods to date used to analyze polymorphisms. It also has the ability to identify tri-allelic, indels, short-repeat polymorphisms, along with determining allele percentages for methylation or pooled sample assessment. In addition, there is a standardized control sequence that provides internal quality control. This method has led to rapid and efficient single-nucleotide polymorphism evaluation including many clinically relevant polymorphisms. The technique and methodology of Pyrosequencing is explained in this chapter.

Identification of NR1I2 genetic variation using resequencing

OBJECTIVE

The nuclear receptor NR1I2 (also called PXR or SXR) is primarily expressed in mouse and human liver and intestines. Direct activation of NR1I2 occurs in response to a range of xenobiotics, which causes the formation of a heterodimer with the RXR receptor. This heterodimer binds to the nuclear receptor response elements of downstream genes such as ABCB1, CYP2C, and CYP3A. This study determined the extent of NR1I2 variation in three world populations.

METHODS

Variation in NR1I2 was identified by pooled resequencing in African, Asian, and European populations. Validation was performed in European and African populations using PCR and Pyrosequencing technology. RNA expression of NR1I2, ABCB1 and CYP3A4 was assessed using real-time PCR.

RESULTS

Of 36 single nucleotide polymorphisms (SNPs) identified, 24 were in the untranslated region, 8 were intronic, and 4 exonic. Thirty-six percent were unique to the African population. In comparison with previously published data, we identified 13 novel polymorphisms. The NR1I2 -566A > C polymorphism was significantly associated with ABCB1 and CYP3A4 RNA expression in colon tumor (P = 0.04 in both cases), however, this polymorphism was not associated with NR1I2 expression.

CONCLUSION

With NR1I2 playing such a large role in the regulation of genes involved in drug metabolism and transport, genetic variation contributing to altered NR1I2 function may have an important clinical impact.

Pharmacogenetic analysis of paclitaxel transport and metabolism genes in breast cancer

Paclitaxel is commonly used in the treatment of breast cancer. Variability in paclitaxel clearance may contribute to the unpredictability of clinical outcomes. We assessed genomic DNA from the plasma of 93 patients with high-risk primary or stage IV breast cancer, who received dose-intense paclitaxel, doxorubicin and cyclophosphamide. Eight polymorphisms in six genes associated with metabolism and transport of paclitaxel were analyzed using Pyrosequencing. We found no association between ABCB1, ABCG2, CYP1B1, CYP3A4, CYP3A5 and CYP2C8 genotypes and paclitaxel clearance. However, patients homozygous for the CYP1B1*3 allele had a significantly longer progression-free survival than patients with at least one Valine allele (P=0.037). This finding could reflect altered paclitaxel metabolism, however, the finding was independent of paclitaxel clearance. Alternatively, the role of CYP1B1 in estrogen metabolism may influence the risk of invasive or paclitaxel resistant breast cancer in patients carrying the CYP1B1*3 allele.

Disposition of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite in relation to ABC transporter genotypes

PURPOSE

The source of the pharmacokinetic variability of 9-nitrocamptothecin (9NC) and its 9-aminocamptothecin (9AC) metabolite is unknown. ATP-binding cassette (ABC) transporters have been reported to modulate camptothecin analogues, are associated with camptothecin resistance, and might also affect 9NC and 9AC pharmacokinetics. The aim of this study was to evaluate the functional consequence of known single nucleotide polymorphisms in the transporter genes ABCB1, ABCC2, and ABCG2 on the pharmacokinetic disposition of 9NC and 9AC.

EXPERIMENTAL DESIGN

Pharmacokinetic and genotyping studies were performed in 55 patients as part of two phase I studies of 9NC in patients with refractory solid tumors, a phase II study of 9NC in patients with advanced colon cancer, and a study evaluating the disposition of 9NC after administration of a single dose under fasting conditions. DNA was isolated from plasma and analyzed for variants in ABCB1, ABCC2, and ABCG2 genes. The ABCB1 1236C>T (n = 43), ABCB1 2677G>T/A (n = 43), ABCB1 3435C>T (n = 43), ABCC2 3972C>T (n = 39), and ABCG2 421C>A (n = 42) variants were analyzed using Pyrosequencing.

RESULTS

The ABCG2 421C>A genotype significantly affected the pharmacokinetics of 9AC. The mean 9AC lactone AUC/dose for wild-type (n = 25) and heterozygous (n = 2) patients were 14.3 ng/mL x h and 51.1 ng/mL x h, respectively (P = 0.032). The mean +/- SD 9AC total AUC/dose for wild-type (n = 39) and heterozygous (n = 3) patients were 91.9 +/- 78.3 ng/mL x h and 129.0 +/- 90.5 ng/mL x h, respectively (P = 0.40). 9NC and 9AC disposition were not significantly influenced by variants in ABCB1, ABCC2, and ABCG2, and ABCB1 and ABCC2, respectively (P > 0.05).

CONCLUSION

These findings suggest that inter-individual variability in 9AC disposition, but not 9NC, may be influenced, in part, by ABCG2 genotype. In contrast, there was no evidence for a relationship between ABCG2 and the disposition of 9NC, or for relationships between ABCB1 and ABCC2 genotypes and the disposition of 9NC or 9AC.