Plasma Concentrations Of Paclitaxel Research Articles

Near Infrared Spectroscopic Combined with Partial Least Squares and Radial Basis Function Neural Network to Analyze Paclitaxel Concentration in Rat Plasma.

Paclitaxel is known as one of the most effective anticancer drugs. Near Infrared Spectroscopy (NIRS), a rapid, precise and non-destructive approach of analysis, has been widely used for qualitative and quantitative detection. The present study aims to analyze the plasma paclitaxel concentration with NIRS. Various batches of plasma samples were prepared and the concentration of paclitaxel was determined via high performance liquid chromatography tandem mass spectrometry (LC-MS/MS). The outliers and the number of calibration set were confirmed by Monte Carlo algorithm combined with partial least squares (MCPLS). Since NIR spectra may be contaminated by signals from background and noise, a series of preprocessing were performed to improve signal resolution. Moving window PLS and radical basis function neural network (RBFNN) methods were applied to establish calibration model. Although both PLS and RBFNN models are well-fitting, RBFNN-established model displayed better qualities on stability and predictive ability. The correlation coefficients of calibration curve and prediction set (Rc(2) and Rp(2)) are 0.9482 and 0.9544, respectively. Moreover, independent verification test with 20 samples confirmed the well predictive ability of RBFNN model.

Enhanced oral bioavailability of paclitaxel by solid dispersion granulation

The main objective of this study was to develop novel orally administrable tablets containing solid dispersion granules (SDG) of amorphous paclitaxel (PTX) prepared by fluid bed technology, and to evaluate its in vitro dissolution and in vivo pharmacokinetics (PK) in beagle dogs. The SDG were prepared using optimized composition by fluid bed technology, and characterized for solid-state properties. The release study of SDG tablet (SDG-T) in simulated gastric fluid showed a rapid release of PTX, reaching maximum dissolution within 20 min. Finally, the PK profile of SDG-T and a reference formulation Oraxol™ (oral solution formulation used in Phase I clinical study) at a dose of 60 mg orally with co-administration of P-gp inhibitor HM38101, and Taxol® at a dose of 10 mg intravenously (i.v.) was investigated in beagle dogs. The mean absolute BA% of PTX following SDG-T and Oraxol™ solution was 8.23 and 6.22% in comparison to i.v. administration of Taxol®. The relative BA% of PTX from SDG-T in comparison to Oraxol™ solution was 132.25% at a dose of 60 mg following oral administration. In conclusion, we have successfully prepared PTX tablets with solid dispersion granules (SDG) of amorphous PTX using fluid bed technology that could provide plasma PTX concentration in the range of 10–150 ng/mL for a period of 24 h following oral administration in dogs with a P-gp inhibitor. Hence, this could be a promising formulation for PTX oral delivery and could be used in our intended clinical studies following pre-clinical efficacy studies.

Pharmacokinetically based dosing of weekly paclitaxel to reduce drug-related neurotoxicity based on a single sample strategy.

The present simulation study was initiated to develop a limited sampling strategy and pharmacokinetically based dosing algorithm of weekly paclitaxel based on pharmacokinetic (PK) and chemotherapy-induced peripheral neuropathy (CIPN) data from a large database. We used paclitaxel plasma concentrations from 200 patients with solid tumors receiving weekly paclitaxel infusions to build a population PK model and a proportional odds model on CIPN. Different limited sampling strategies were tested on their accuracy to estimate the individual paclitaxel time-above-threshold-concentration of 0.05µmol/L (T c>0.05µM), which is a common threshold for paclitaxel. A dosing algorithm was developed based on the population distribution of paclitaxel T c>0.05µM and the correlation between paclitaxel T c>0.05µM and CIPN. A trial simulation based on paclitaxel PK and CIPN was performed using empirical Bayes estimations, applying the proposed dosing algorithm and a single 24-h paclitaxel PK sample. A single paclitaxel plasma concentration taken 18-30h after the start of chemotherapy infusion adequately predicted T c>0.05µM. By using an empirical dosing algorithm to target an average paclitaxel T c>0.05µM between 10 and 14h, Bayesian simulations of repetitive (adapted) dosing suggested a potential reduction of grade 2 CIPN from 9.6 to 4.4%. This simulation study proposes a pharmacokinetically based dosing algorithm for weekly paclitaxel and shows potential improvement of the benefit/risk ratio by using empirical Bayesian models.

Trantinterol, a novel β2-adrenoceptor agonist, noncompetitively inhibits P-glycoprotein function in vitro and in vivo.

P-glycoprotein (P-gp)-mediated drug-drug interactions are important factors causing adverse effects of drugs in clinical use. The aim of this study was to determine whether trantinterol (also known as SPFF), a novel β2-adrenoceptor agonist, was a P-gp inhibitor or substrate. The results showed that trantinterol was not a substrate of P-gp but increased rhodamine 123 (Rho 123) uptake by MDCK-MDR1 cells and decreased the efflux transport of both Rho 123 and cyclosporine A (CsA) in bidirectional transport studies across MDCK-MDR1 cell monolayers. This suggested that trantinterol was a P-gp inhibitor but not a P-gp substrate. The mechanism of inhibition was investigated in the P-gp-Glo assay system, where it was found that trantinterol inhibited P-gp ATPase activity in a dose-dependent manner. A subsequent study using the antibody binding assay with the conformation-sensitive P-gp-specific antibody UIC2 confirmed that trantinterol decreased UIC2 binding at 10 μM in contrast to the competitive inhibitor, verapamil. This suggested that trantinterol was a noncompetitive inhibitor of P-gp. Finally, a pharmacokinetic study in rat showed that trantinterol significantly increased the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of digoxin and paclitaxel (PAC), and the Cmax of cyclosporine A (CsA). In summary, trantinterol is a potent noncompetitive P-gp inhibitor which may increase the bioavailability of other P-gp substrate drugs coadministered with it.

Carotid Artery Infusions for Pharmacokinetic and Pharmacodynamic Analysis of Taxanes in Mice

When proposing the use of a drug, drug combination, or drug delivery into a novel system, one must assess the pharmacokinetics of the drug in the study model. As the use of mouse models are often a vital step in preclinical drug discovery and drug development, it is necessary to design a system to introduce drugs into mice in a uniform, reproducible manner. Ideally, the system should permit the collection of blood samples at regular intervals over a set time course. The ability to measure drug concentrations by mass-spectrometry, has allowed investigators to follow the changes in plasma drug levels over time in individual mice. In this study, paclitaxel was introduced into transgenic mice as a continuous arterial infusion over three hours, while blood samples were simultaneously taken by retro-orbital bleeds at set time points. Carotid artery infusions are a potential alternative to jugular vein infusions, when factors such as mammary tumors or other obstructions make jugular infusions impractical. Using this technique, paclitaxel concentrations in plasma and tissue achieved similar levels as compared to jugular infusion. In this tutorial, we will demonstrate how to successfully catheterize the carotid artery by preparing an optimized catheter for the individual mouse model, then show how to insert and secure the catheter into the mouse carotid artery, thread the end of the catheter out through the back of the mouse's neck, and hook the mouse to a pump to deliver a controlled rate of drug influx. Multiple low volume retro-orbital bleeds allow for analysis of plasma drug concentrations over time.

A Phase I Study of Oral Paclitaxel with a Novel P-Glycoprotein Inhibitor, HM30181A, in Patients with Advanced Solid Cancer.

PurposeThe purpose of this study is to determine the maximum tolerated dose (MTD), safety, pharmacokinetics, and recommended phase II dose of an oral drug composed of paclitaxel and HM30181A, which is an inhibitor of P-glycoprotein, in patients with advanced cancers.Materials and MethodsPatients with advanced solid tumors received standard therapy were given the study drug at escalating doses, using a 3+3 design. The study drug was orally administered on days 1, 8, and 15, with a 28-day cycle of administration. The dose of paclitaxel was escalated from 60 to 420 mg/m2, and the dose of HM30181A was escalated from 30-210 mg/m2.ResultsA total of twenty-four patients were enrolled. Only one patient experienced a doselimiting toxicity—a grade 3 neutropenia that persisted for more than 2 weeks, at 240 mg/m2 of paclitaxel. MTD was not reached. The maximum plasma concentration was obtained at a dose level of 300 mg/m2 and the area under the curve of plasma concentration- time from 0 to the most recent plasma concentration measurement of paclitaxel was reached at a dose level of 420 mg/m2. The absorption of paclitaxel tends to be limited at doses that exceed 300 mg/m2. The effective plasma concentration of paclitaxel was achieved at a dose of 120 mg/m2. Responses of 23 patients were evaluated; 8 (34.8%) had stable disease and 15 (65.2%) had progressive disease.ConclusionThe study drug appears to be well tolerated, and the effective plasma concentration of paclitaxel was achieved. The recommended phase II dose for oral paclitaxel is 300 mg/m2.

Pharmacokinetic drug interactions between apigenin, rutin and paclitaxel mediated by P-glycoprotein in rats.

The aim of present study was to investigate the effects of apigenin and rutin on the pharmacokinetics of paclitaxel after oral administration of paclitaxel with apigenin and rutin to rats. Paclitaxel (40 mg/kg) was administered orally alone and in combination with apigenin and rutin (10, 20, and 40 mg/kg) for 15 consecutive days. In the single-dose pharmacokinetic study (SDS), blood samples were collected on 1st day whereas on 15th day in the multiple-dose pharmacokinetic study (MDS). The plasma concentrations of paclitaxel were increased dose-dependently in the combination of apigenin and rutin compared to that of paclitaxel control in SDS and MDS (p < 0.01). The areas under the plasma concentration-time curve (AUC) and the plasma peak concentrations (C max) of paclitaxel with apigenin and rutin were significantly higher (p < 0.01) than that of the control. The AUCs and C max of paclitaxel were increased with apigenin and rutin in the dose-dependent manner. The half-life (t 1/2) was significantly longer than that of the control. Non-everted sacs were filled with paclitaxel 100 μM in the presence and absence of verapamil (50 μM), apigenin, and rutin (50, 100 μM) and incubated at 37 ºC for 60 min. The absorption of paclitaxel was increased in the presence of apigenin, rutin, and verapamil, a typical P-glycoprotein and Cyp3A4 inhibitor. If these results are confirmed in humans in a clinical setting, the paclitaxel dose should be adjusted when it is given concomitantly with apigenin and rutin.

Oral co-administration of elacridar and ritonavir enhances plasma levels of oral paclitaxel and docetaxel without affecting relative brain accumulation.

Background:The intestinal uptake of the taxanes paclitaxel and docetaxel is seriously hampered by drug efflux through P-glycoprotein (P-gp) and drug metabolism via cytochrome P450 (CYP) 3A. The resulting low oral bioavailability can be boosted by co-administration of P-gp or CYP3A4 inhibitors.Methods:Paclitaxel or docetaxel (10 mg/kg) was administered to CYP3A4-humanised mice after administration of the P-gp inhibitor elacridar (25 mg kg−1) and the CYP3A inhibitor ritonavir (12.5 mg kg−1). Plasma and brain concentrations of the taxanes were measured.Results:Oral co-administration of the taxanes with elacridar increased plasma concentrations of paclitaxel (10.7-fold, P<0.001) and docetaxel (four-fold, P<0.001). Co-administration with ritonavir resulted in 2.5-fold (paclitaxel, P<0.001) and 7.3-fold (docetaxel, P<0.001) increases in plasma concentrations. Co-administration with both inhibitors simultaneously resulted in further increased plasma concentrations of paclitaxel (31.9-fold, P<0.001) and docetaxel (37.4-fold, P<0.001). Although boosting of orally applied taxanes with elacridar and ritonavir potentially increases brain accumulation of taxanes, we found that only brain concentrations, but not brain-to-plasma ratios, were increased after co-administration with both inhibitors.Conclusions:The oral availability of taxanes can be enhanced by co-administration with oral elacridar and ritonavir, without increasing the brain penetration of the taxanes.

Pharmacokinetics and pharmacodynamics of nab ‐paclitaxel in patients with solid tumors: Disposition kinetics and pharmacology distinct from solvent‐based paclitaxel

The aim of this study was to characterize population pharmacokinetics and the exposure–neutropenia relationship with nanoparticle albumin-bound (nab)-paclitaxel in patients with solid tumors. Plasma and blood concentrations of paclitaxel and neutrophil data were collected from 150 patients with various solid tumors over the nab-paclitaxel dose range of 80–375 mg/m2. Data were analyzed using nonlinear mixed-effect modeling or logistic regression. Pharmacokinetics of nab-paclitaxel were described by a 3-compartment model with saturable distribution and elimination. The rapid disappearance of circulating paclitaxel was driven by its fast distribution to peripheral compartments; maximum rate for saturable distribution (325000 μg/h) was 40-fold greater than that for saturable elimination (8070 μg/h). Albumin was a significant covariate of paclitaxel elimination (P < .001), while total bilirubin, creatinine clearance, body size, age, sex, and tumor type had no significant or clinically relevant effect. The probability of experiencing a ≥50% reduction in neutrophils was best correlated to the duration above the drug concentration of 720 ng/mL. At a given exposure level, neutropenia development was positively correlated with increasing age but not significantly influenced by hepatic function, tumor type, sex, or dosing schedule. Covariate analyses supports exposure-matched dose adjustments in patients with moderate to severe hepatic impairment.

Systemic Effect of Endoscopic Ultrasonography-Guided Pancreatic Cyst Ablation with Ethanol and Paclitaxel

Endoscopic ultrasonography (EUS)-guided pancreatic cyst ablation is a minimally invasive treatment modality. Local injection of ablative agents may rarely cause systemic effects in patients. This study aimed to evaluate the systemic effect of ablative agents by analyzing the plasma drug concentration. Ten patients with pancreatic cysts were enrolled. Cyst ablation was performed by 99 % ethanol lavage (2.5-70 mL) and paclitaxel (Genexol-polymeric micelle, 6.0-24.0) injection. Blood samples were collected at 0, 2, 4, 7 and 24 h. Plasma paclitaxel concentration was analyzed by a liquid chromatography-tandem mass spectrometry with the lowest limit of quantitation of 0.1 ng/mL. Procedure-related complications were closely monitored. Pancreatic cysts were located at the head in two, body in seven and tail in one patient. Eight cysts were septated. Median diameter and original volume were 39.5 mm (range 2.7-21.8) and 14.79 mL (3.42-343.30). Median cyst fluid CEA and amylase values were 17.10 ng/mL (0.5-14127.5) and 73.50 U/L (3.1-91,590). Peak plasma paclitaxel concentration values were observed between 2 and 7 h, ranging from 0.45 to 14.73 ng/mL. The highest concentration (17.10 ng/mL at 0 h) was observed in a patient who had intracystic bleeding. Mild abdominal pain occurred in five patients and vomiting in one patient during the first 48-h monitoring. Plasma paclitaxel concentration after EUS-guided pancreatic cyst ablation was nearly as low as the undetectable value and rarely caused systemic side-effect.

Anti-Cancer, Pharmacokinetic and Biodistribution Studies of Cremophor EL Free Alternative Paclitaxel Formulation

The aim of the present investigation is to determine the in vivo potential of previously developed and optimized Cremophor EL free paclitaxel (CF-PTX) formulation consisting of soya phosphatidylcholine and biosurfactant sodium deoxycholate. CF-PTX was found to have drug loading of 6 mg/ml similar to Cremophor EL based marketed paclitaxel formulation. In the present study, intracellular uptake, repeated dose 28 days sub-acute toxicity, anti-cancer activity, biodistribution and pharmacokinetic studies were conducted to determine in vivo performance of CF-PTX formulation in comparison to marketed paclitaxel formulation. Intracellular uptake of CF-PTX was studied using A549 cells by fluorescence activated cell sorting assay (FACS) and fluorescence microscopy. In vivo anti-cancer activity of CF-PTX was evaluated using Ehrlich ascites carcinoma (EAC) model in mice followed by biodistribution and pharmacokinetic studies. FACS investigation showed that fluorescence marker acridine orange (AO) solution showed only 19.8±1.1% intracellular uptake where as significantly higher uptake was observed in the case of AO loaded CF-PTX formulation (85.4±2.3%). The percentage reduction in tumor volume for CF-PTX (72.5±2.3%) in EAC bearing mice was found to be significantly (p<0.05) higher than marketed formulation (58.6±2.8%) on 14th day of treatment. Pharmacokinetic and biodistribution studies showed sustained plasma concentration of paclitaxel depicted by higher mean residence time (MRT; 18.2±1.8 h) and elimination half life (12.8±0.6 h) with CF-PTX formulation as compared to marketed formulation which showed 4.4±0.2 h MRT and 3.6±0.4 h half life. The results of the present study demonstrated better in vivo performance of CF-PTX and this formulation appears to be a promising carrier for sustained and targeted delivery of paclitaxel.

Treatment of advanced ovarian carcinoma coexistent with peritoneal tuberculosis

Primary ovarian carcinoma is often chemosensitive. Therefore, aggressive treatment is recommended for patients with ovarian carcinoma. Peritoneal tuberculosis is rare and may present with symptoms similar to those of advanced ovarian carcinoma. To the best of our knowledge, this is the first report of a case of primary advanced ovarian carcinoma coexistent with peritoneal tuberculosis. The patient had undergone three courses of neoadjuvant chemotherapy with tri-weekly paclitaxel and carboplatin (TC), followed by total abdominal hysterectomy, bilateral salpingo-oophorectomy, omentectomy and pelvic and para-aortic lymphadenectomy. The postoperative pathological examination confirmed the diagnosis of ovarian serous papillary adenocarcinoma coexistent with peritoneal tuberculosis. The patient was started on antituberculous chemotherapy, followed 2 weeks later by four courses of antitumor chemotherapy with weekly TC. The plasma concentration of paclitaxel was measured after the first administration of TC. We considered that rifampicin may enhance the metabolism of paclitaxel, causing the plasma concentration of paclitaxel to decrease. Therefore, rifampicin administration was discontinued on days 1, 8 and 15. The patient completed the antitumor and antituberculous chemotherapy and has remained alive and recurrence-free for 5-years. Although rifampicin may enhance the metabolism of paclitaxel, we suggest that it may be possible to administer concurrent antituberculous and antitumor chemotherapy under close observation.

A rapid analytical method for the quantification of paclitaxel in rat plasma and brain tissue by high-performance liquid chromatography and tandem mass spectrometry.

Paclitaxel, an antitumor agent for the treatment of several types of cancers, has recently been reported to cause impaired cognitive function and neuropathic pain in humans. To assess the effects of paclitaxel on the central nervous system, a sensitive and accurate method is required to quantify paclitaxel concentrations in plasma and brain tissue obtained from rodents receiving paclitaxel. The biological samples were prepared by liquid-liquid extraction and separated by a 3.5 min reversed-phase liquid chromatography (RPLC) method using a BDS Hypersil C8 column under isocratic conditions. Paclitaxel was quantified using multiple reaction monitoring (MRM) with a triple quadrupole tandem mass spectrometer working in the positive electrospray ionization (ESI+) mode. A stable isotope labeled analogue of paclitaxel was used as the internal standard (IS). The method was validated to be precise and accurate within the dynamic range of 0.5-100 ng/mL based on 100 μL plasma and 1.5-300 ng/g based on 33 mg of brain tissue in homogenate. This method was applied to samples from 2 mg/kg intravenously dosed rats. The plasma concentrations were observed to be 26.62 ± 8.93 ng/mL and brain concentrations 11.08 ± 4.18 ng/g when measured 4 h post-dose. This rapid LC/MS/MS method was validated to be sensitive, specific, precise and accurate for the quantification of paclitaxel in rat plasma and brain tissue homogenate. Application of the method to study samples provided sufficient proof of blood-brain barrier penetration of paclitaxel, allowing further investigation of its influence on the central nervous system.

Pharmacokinetics and Biodistribution Study of Paclitaxel Liposome in Sprague-Dawley Rats and Beagle Dogs by Liquid Chromatography-Tandem Mass Spectrometry

Lipusu is the first paclitaxel liposome preparation approved in the world and has been widely used in China for the treatment of ovary, breast and non-small cell lung cancer. In present study we evaluated the pharmacokinetic and tissue distribution characteristics of paclitaxel liposome in Sprague-Dawley rats and Beagle dogs. A rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed for the determination of paclitaxel in plasma and tissues. The plasma concentrations of paclitaxel in both rats and dogs initially declined steeply, followed by slow elimination after intravenous administration of Lipusu at 5 mg/kg and 1 mg/kg, respectively. The pharmacokinetic parameters calculated by a non-compartmental method in rats and dogs were as follows: AUC0-24: 3 566.5±1 366.1 and 443.2±165.7 μg · h/L, CL: 1.5±0.5 and 2.1±0.6 L/h/kg, Vd: 20.0±7.8 and 38.4±12.5 L/kg, t1/2: 9.3±2.9 and 14.1±6.9 h, respectively. Biodistribution results in rats showed that except for brain and testis, liposomal paclitaxel was extensively distributed into various tissues, especially highly in liver and spleen.

Comparison of pharmacokinetics between paclitaxel emulsion for injection and paclitaxel injection in beagles

Objective:To establish an analytical method for the determination of paclitaxel,and to investigate and compare the pharmacokinetics of paclitaxel emulsion for injection and paclitaxel injection in beagles.Methods:After intravenous administration of paclitaxel emulsion for injection and paclitaxel injection(1.5mg/kg),paclitaxel concentrations in plasma of beagles were determined,and pharmacokinetic parameters were calculated.Paclitaxel and docetaxel(internal standard)were isolated from plasma or tissue samples in 96-well plates by liquid-liquid extraction,and most liquid transfer steps were performed by 96/ 384-channel semi-automatic pipetting tools.Results:The calibration curves were linear over the range of 2-500ng/ml.The lowest limit of quantitation was 2ng/ml.The intra-run and inter-run relative standard deviation(RSD)was less than 15%.The main pharmacokinetic parameters of paclitaxel emulsion for injection and paclitaxel injection were as follows:t1/2were(4.72± 0.53)and(4.50±0.81)h,MRT were(2.46±0.38)and(1.82±0.59)h,AUC0-12hwere(388.90±63.39)and(711.74± 33.70)ng.h.ml-1,AUC0-∞were(411.89±68.44)and(738.35±45.54)ng.h.ml-1,CL were(3.71±0.46)and(2.04±0.11)L.h-1.kg-1,Vdwere(9.07±1.35)and(3.65±0.91)L/kg.Conclusion:The method was sensitive,accurate,specific,simple and convenient for the pharmacokinetic study of paclitaxel emulsion for injection and paclitaxel injection in beagles.There were significant differences in the pharmacokinetic parameters of c0,AUC,CL,Vdof the two preparations(P 0.05).Relative bioavailability of paclitaxel emulsion for injection was(54.93±10.82)%,as calculated by AUC determination.

CYP3A4*22 Genotype and Systemic Exposure Affect Paclitaxel-Induced Neurotoxicity

Paclitaxel is used for the treatment of several solid tumors and displays a high interindividual variation in exposure and toxicity. Neurotoxicity is one of the most prominent side effects of paclitaxel. This study explores potential predictive pharmacokinetic and pharmacogenetic determinants for the onset and severity of neurotoxicity. In an exploratory cohort of patients (n = 261) treated with paclitaxel, neurotoxicity incidence, and severity, pharmacokinetic parameters and pharmacogenetic variants were determined. Paclitaxel plasma concentrations were measured by high-performance liquid chromatography or liquid chromatography/tandem mass spectrometry, and individual pharmacokinetic parameters were estimated from previously developed population pharmacokinetic models by nonlinear mixed effects modeling. Genetic variants of paclitaxel pharmacokinetics tested were CYP3A4*22, CYP2C8*3, CYP2C8*4, and ABCB1 3435 C>T. The association between CYP3A4*22 and neurotoxicity observed in the exploratory cohort was validated in an independent patient cohort (n = 239). Exposure to paclitaxel (logAUC) was correlated with severity of neurotoxicity (P < 0.00001). Female CYP3A4*22 carriers were at increased risk of developing neurotoxicity (P = 0.043) in the exploratory cohort. CYP3A4*22 carrier status itself was not associated with pharmacokinetic parameters (CL, AUC, Cmax, or T>0.05) of paclitaxel in males or females. Other genetic variants displayed no association with neurotoxicity. In the subsequent independent validation cohort, CYP3A4*22 carriers were at risk of developing grade 3 neurotoxicity (OR = 19.1; P = 0.001). Paclitaxel exposure showed a relationship with the severity of paclitaxel-induced neurotoxicity. In this study, female CYP3A4*22 carriers had increased risk of developing severe neurotoxicity during paclitaxel therapy. These observations may guide future individualization of paclitaxel treatment.

A pharmacogenetic model predicting low paclitaxel clearance based on the DMET platform.

2597 Background: Paclitaxel (PTX) is a commonly used cytotoxic agent. It is metabolized by P450 cytochrome iso-enzymes CYP3A4 and CYP2C8 and has high interindividual variability in pharmacokinetics (PK) and toxicity. Here, we present a genetic prediction model to identify patients with low PTX clearance (CL) using the new Drug-Metabolizing Enzyme and Transporter (DMET; Affymetrix) platform, capable of detecting 1,936 genetic variants (SNPs) in 225 genes. Methods: In a PK study, 270 Caucasian cancer patients were treated with PTX. PK parameters were determined using a limited sampling strategy. HPLC or LC-MS/MS were used to determine PTX plasma concentrations and non-linear mixed effects modelling (NONMEM) was used to estimate individual unbound CL from previously developed PK population models. Subsequently, the cohort of patients was randomly split into a training and validation set. In all patients, the presence of SNPs in metabolic enzymes and transporters was determined using the DMET platform. Selected SNPs were subsequently validated in the validation set. Results: Baseline characteristics were comparable in both sets. The mean CL of the total cohort was 488 ± 149 L/h and the threshold for low CL was set at 339 L/h (1 SD &lt; total mean CL). 14 SNPs were selected to be included in the prediction model and validated in the validation set. For none of these 14 SNPs, evidence for a biological plausible link to taxane metabolism exists. The developed prediction model had a sensitivity of 95% to identify low PTX CL, a positive predictive value of 22% and remained significantly associated with low CL after multivariate analysis correcting for age, gender and Hb levels at start of therapy (P=0.024). Conclusions: This is the first considerably-sized application of the DMET platform to explain PK variability of a widely used anti-cancer drug. Although this validated prediction model for PTX CL had a high sensitivity, its positive predictive value is too low to be of direct clinical use. Likely, genetic variability in DMET genes alone does not sufficiently explain PTX CL, as for example environmental factors may also influence PTX metabolism.

Abstract 986: Sildenafil potentiates the anticancer activity of paclitaxel in ABCB1-mediated multidrug resistance xenograft model.

Abstract The multidrug resistance (MDR) phenotype caused by the overexpression of ATP-binding cassette (ABC) transporters promotes the cellular efflux of a variety of anticancer drugs that may lead to cancer treatment failure. Previous in vitro studies from our group reported sildenafil, a PDE-5 inhibitor, could significantly block the function of ABCB1/P-glycoprotein and reverse ABCB1/P-glycoprotein-mediated MDR. In the current study we investigated the effect of sildenafil on the ABCB1-mediated MDR in vivo. To determine this effect we developed ABCB1-xenograft nude muse model using ABCB1 overexpressing KB-C2 cell line. We found that sildenafil significantly enhanced the chemotherapeutic response of paclitaxel in the ABCB1-xenograft nude mouse model. The combination treatment with sildenafil and paclitaxel attenuated the tumor growth synergistically. In addition, there was no visible toxicity, weight loss or other gross phenotypic changes with combination treatment. The positive effects of sildenafil can be attributed to inhibition of ABCB1-mediated drug efflux. This phenomenon was further supported by increased concentrations of paclitaxel in ABCB1-overexpressing tumors in the combination treatment group compared to paclitaxel alone. In addition, pharmacokinetic analysis showed increase in the plasma paclitaxel concentration in the combination group. These beneficial actions of sildenafil can be considered as viable option for combination therapy with the clinical anticancer drugs that succumb to ABCB1-mediated insensitivity. Citation Format: Kamlesh Sodani, Amit K. Tiwari, Chun-ling Dai, Alaa H. Abuznait, Zhi-jie Xiao, Amal Kaddouni, Zhe-Sheng Chen. Sildenafil potentiates the anticancer activity of paclitaxel in ABCB1-mediated multidrug resistance xenograft model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 986. doi:10.1158/1538-7445.AM2013-986

Modulation of MDR1 and MRP3 Gene Expression in Lung Cancer Cells after Paclitaxel and Carboplatin Exposure

Carboplatin-paclitaxel is a reference regimen in the treatment of locally advanced or disseminated non-small cell lung cancer (NSCLC). This paper discusses the multidrug resistance developed with this drug combination, which is one of the major obstacles to successful treatment. In order to understand and overcome the drug resistance pattern of NSCLC after carboplatin plus paclitaxel exposure, levels of mRNA expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated protein 3 (MRP3) were investigated in primary NSCLC cell lines (A-549 and A-427) and a metastasis-derived NSCLC cell line (NODO). Our results showed that exposure of the three NSCLC lines to plasma concentrations of paclitaxel (5 μM) produced an increase in MDR1 expression, while MRP3 showed no alteration in expression. By contrast, the same cells exposed to carboplatin plasma concentrations (30 μM) showed overexpression of MRP3. In these cells, MDR1 showed no expression changes. Interestingly, the combination of both paclitaxel and carboplatin caused increased expression of the MDR1 drug resistance gene rather than the individual treatments. These results suggest that carboplatin and paclitaxel may induce drug resistance mediated by MDR1 and MRP3, which may be enhanced by the simultaneous use of both drugs.

P‐glycoprotein and cytochrome P450 3A act together in restricting the oral bioavailability of paclitaxel

Paclitaxel is avidly transported by P-glycoprotein (P-gp/MDR1/ABCB1). This results in low oral bioavailability, which can be boosted by coadministration of P-gp inhibitors. Unlike paclitaxel, docetaxel is extensively metabolized by CYP3A4 and its oral bioavailability can be enhanced in mice and humans by coadministration of the potent CYP3A inhibitor ritonavir. Unexpectedly, ritonavir also enhances the oral bioavailability of paclitaxel in humans. We aimed to resolve the mechanism underlying this enhancement. Using mice lacking Cyp3a and/or P-gp, we investigated the combined and separate restricting roles of Cyp3a and P-gp in the oral bioavailability of paclitaxel, and the boosting effect of ritonavir. CYP3A4-humanized mice were used for translation to the human situation. P-gp had a dominant effect (11.6-fold, p < 0.001) over Cyp3a (<1.5-fold, n.s.) in limiting plasma concentrations of oral paclitaxel. However, in the absence of P-gp, Cyp3a decreased paclitaxel plasma concentrations twofold (p < 0.001). Coadministered ritonavir inhibited Cyp3a-mediated metabolism, but not P-gp-mediated transport of paclitaxel. Owing to the dominant effect of P-gp, ritonavir enhanced only paclitaxel plasma concentrations in P-gp-deficient mice. Mouse liver microsomes metabolized paclitaxel far less efficiently than human or CYP3A4-transgenic liver microsomes, revealing much lower efficiency of paclitaxel metabolism by mouse than by human CYP3As. Accordingly, ritonavir could enhance the oral bioavailability of paclitaxel in CYP3A4-humanized mice, despite the fact that these mice are P-gp-proficient. Our results show that CYP3A4 inhibition most likely underlies the boosting effect of ritonavir on oral paclitaxel bioavailability in humans. Furthermore, CYP3A4-humanized mice allow improved understanding of CYP3A4-mediated paclitaxel metabolism in humans.