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Schematic overview of the basic population pharmacokinetic model: a three-compartment model with Michaelis-Menten elimination from the central compartment (V1). V2 and V3 indicate the two peripheral compartments. k12, k21, k13 and k31 indicate the intercompartmental rate constants. Vmax is the maximal elimination rate, and Km is the plasma-concentration of Cremophor EL at half of the Vmax
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The purpose of this study was to develop a population pharmacokinetic model for Cremophor EL used as a formulation vehicle for paclitaxel.
Plasma concentration-time data from 70 patients (85 courses) treated with paclitaxel dissolved in Cremophor EL were used. The nonlinear mixed-effect modelling (NONMEM) program was used for the population pharmac...
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UCN-01 (7-Hydroxystaurosporine) is an investigational anticancer agent that is currently being evaluated as targeted therapy in phase II clinical studies. The aims of this work were to describe the population pharmacokinetics of UCN-01 in patients with advanced solid tumors, and to identify covariates in patients with advanced solid tumors that aff...
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... Data were extracted by digitization. Paclitaxel concentrations were reported as mean data from multiple patients (8,12,13,21,(25)(26)(27)(28)(29)(30), as individual PK profiles from representative patients that were averaged (14,24,31,32), or as unique PK profiles from representative patients (4,16,(33)(34)(35)(36). ...
Nanoparticulate paclitaxel carriers have entered clinical evaluation as alternatives to the Cremophor-based standard Taxol(®) (Cre-pac). Their pharmacokinetics (PK) is complex, and factors influencing their pharmacodynamics (PD) are poorly understood. We aimed to develop a unified quantitative model for 4 paclitaxel carriers that captures systems-level PK, predicts micro-scale PK processes, and permits correlations between carrier properties and observed PD.
Data consisting of 54 PK profiles and 574 observations were extracted from 20 clinical studies investigating Cre-pac, albumin-(A-pac), liposome-(L-pac), and tocopherol-(T-pac) nanocarriers. A population-PK approach was used for data analysis. All datasets were simultaneously fitted to produce a unified model. Model-based simulations explored relationships between predicted PK and myelosuppression for each formulation.
The final model employed nonlinear drug-binding mechanisms to describe Cre-pac and a delayed-release model for A-pac, L-pac, and T-pac. Estimated drug-release rate constants (h(-1)): Cre-pac (5.19), L-pac (1.26), A-pac (0.72), T-pac (0.74). Simulations of equivalent dosing schemes ranked neutropenia severity (highest to lowest): T-pac~Cre-pac>L-pac~A-pac and predicted remarkably well the clinically-observed relationships between neutropenia and free drug exposure relative to a threshold concentration.
Paclitaxel disposition was well-described for all formulations. The derived model predicts toxicodynamics of diverse paclitaxel carriers.
... Disposition of Cremophor was assessed with one-, two-, or three-compartment models with first-order elimination. As Cremophor concentrations were not measured, the volume of distribution for Cremophor was fixed to a literature estimate [38] of 6.01 L. As Cremophor concentrations were not measured in this study, the choice of this volume only affects the estimate for the Cremophor clearance and the parameter(s) for binding of paclitaxel to Cremophor but no other model parameter. Additionally, we incorporated the model from van den Bongard et al. [38] to describe the disposition of Cremophor. ...
... As Cremophor concentrations were not measured, the volume of distribution for Cremophor was fixed to a literature estimate [38] of 6.01 L. As Cremophor concentrations were not measured in this study, the choice of this volume only affects the estimate for the Cremophor clearance and the parameter(s) for binding of paclitaxel to Cremophor but no other model parameter. Additionally, we incorporated the model from van den Bongard et al. [38] to describe the disposition of Cremophor. ...
... As we did not measure Cremophor concentrations, the one-compartment model was chosen following the rule of parsimony. Use of the population PK model for Cremophor from van den Bongard et al. [38] yielded a considerably worse objective function (increase by 118). ...
Our objectives were (1) to compare the disposition and in vivo release of paclitaxel between a tocopherol-based Cremophor-free formulation (Tocosol Paclitaxel) and Cremophor EL-formulated paclitaxel (Taxol) in human subjects, and (2) to develop a mechanistic model for unbound and total paclitaxel pharmacokinetics.
A total of 35 patients (average +/- SD age: 59 +/-13 years) with advanced non-hematological malignancies were studied in a randomized two-way crossover trial. Patients received 175 mg/m(2) paclitaxel as 15 min (Tocosol Paclitaxel) or 3 h (Taxol) intravenous infusion in each study period. Paclitaxel concentrations were determined by LC-MS/MS in plasma ultrafiltrate and whole blood. NONMEM VI was used for population pharmacokinetics.
A linear disposition model with three compartments for unbound paclitaxel and a one-compartment model for Cremophor were applied. Total clearance of unbound paclitaxel was 845 L/h (variability: 25% CV). The prolonged release with Tocosol Paclitaxel was explained by the limited solubility of unbound paclitaxel of 405 ng/mL (estimated) in plasma. The 15 min Tocosol Paclitaxel infusion yielded a mean time to 90% cumulative input of 1.14 +/- 0.16 h. Tocosol Paclitaxel was estimated to release 9.8% of the dose directly into the deep peripheral compartment. The model accounted for the presence of drug-containing nanodroplets in blood.
Population pharmacokinetic analysis indicated linear disposition and a potentially higher bioavailability of unbound paclitaxel following Tocosol Paclitaxel administration due to direct release at the target site. The prolonged release of Tocosol Paclitaxel supports 15 min paclitaxel infusions. This mechanistic model may be important for development of prolonged release formulations that distribute in and from the systemic circulation.
... As mentioned previously, the distribution of paclitaxel in patients receiving Taxol is dependent on the duration of infusion and the dose-and time-varying concentrations of Cremophor because of a preferential affinity of paclitaxel for Cremophor in blood (13). In a large group of patients, BSA was shown previously to be a significant covariate on CL in a population model for Cremophor pharmacokinetics (24). Because total blood volume is related to BSA (25), it has been hypothesized that the effect of BSA on variability in paclitaxel CL is caused by the association of paclitaxel in the systemic circulation with Cremophor micelles, of which the distribution is linked to total blood volume and thus to BSA (26). ...
To compare the preclinical and clinical pharmacokinetic properties of paclitaxel formulated as a Cremophor-free, albumin-bound nanoparticle (ABI-007) and formulated in Cremophor-ethanol (Taxol).
ABI-007 and Taxol were given i.v. to Harlan Sprague-Dawley male rats to determine pharmacokinetic and drug disposition. Paclitaxel pharmacokinetic properties also were assessed in 27 patients with advanced solid tumors who were randomly assigned to treatment with ABI-007 (260 mg/m(2), 30 minutes; n = 14) or Taxol (175 mg/m(2), 3 hours; n = 13), with cycles repeated every 3 weeks.
The volume of distribution at steady state and clearance for paclitaxel formulated as Cremophor-free nanoparticle ABI-007 were significantly greater than those for paclitaxel formulated with Cremophor (Taxol) in rats. Fecal excretion was the main elimination pathway with both formulations. Consistent with the preclinical data, paclitaxel clearance and volume of distribution were significantly higher for ABI-007 than for Taxol in humans [21.13 versus 14.76 L/h/m(2) (P = 0.048) and 663.8 versus 433.4 L/m(2) (P = 0.040), respectively].
Paclitaxel formulated as ABI-007 differs from paclitaxel formulated as Taxol, with a higher plasma clearance and a larger volume of distribution. This finding is consistent with the absence of paclitaxel-sequestering Cremophor micelles after administration of ABI-007. This unique property of ABI-007 could be important for its therapeutic effectiveness.
... In addition, a linear increase of CL over time during the postinfusion period was tested but the sigmoidal E max model gave a superior fit to the postinfusion data. Furthermore, this latter postinfusiontime-dependent function is more relevant because of the Michaelis-Menten nature of CrEL elimination [38]. ...
To develop a population pharmacokinetic model for paclitaxel in the presence of a MDR modulator, zosuquidar 3HCl.
The population approach was used (implemented with NONMEM) to analyse paclitaxel pharmacokinetic data from 43 patients who received a 3-h intravenous infusion of paclitaxel (175 mg x m(-2) or 225 mg x m(-2)) alone in cycle 2 or concomitantly with the oral administration of zosuquidar 3HCl in cycle 1.
The structural pharmacokinetic model for paclitaxel, accounting for the Cremophor ELTM impact, was a three-compartment model with a nonlinear model for paclitaxel plasma clearance (CL), involving a linear decrease in this parameter during the infusion and a sigmoidal increase with time after the infusion. The final model described the effect of Zosuquidar 3HCl on paclitaxel CL by a categorical relationship. A 25% decrease in paclitaxel CL was observed, corresponding to an 1.3-fold increase in paclitaxel AUC (from 14829 microg x l(-1) x h to 19115 microg x l(-1) x h following paclitaxel 175 mg x m(-2)) when zosuquidar Cmax was greater than 350 microg x l(-1). This cut-off concentration closely corresponded to the IC50 of a sigmoidal Emax relationship (328 microg x l(-1)). A standard dose of 175 mg x m(-2) of paclitaxel could be safely combined with doses of zosuquidar 3HCl resulting in plasma concentrations known, from previous studies, to result in maximal P-gp inhibition.
This analysis provides a model which accurately characterized the increase in paclitaxel exposure, which is most likely to be due to P-gp inhibition in the bile canaliculi, in the presence of zosuquidar 3HCl (Cmax > 350 microg x l(-1)) and is predictive of paclitaxel pharmacokinetics following a 3 h infusion. Hence the model could be useful in guiding therapy for paclitaxel alone and also for paclitaxel administered concomitantly with a P-gp inhibitor, and in designing further clinical trials.
While the use of excipients is widespread, a thorough understanding of the drug interaction potential of these compounds remains a frequent topic of current research. Not only can excipients alter the disposition of co‐formulated drugs, but it is likely that these effects on co‐administered drugs can reach to clinical significance leading to potential adverse effects or loss of efficacy. These risks can be evaluated through use of in silico methods of mechanistic modeling, including approaches such as population pharmacokinetic and physiologically‐based pharmacokinetic modeling, which require a comprehensive understanding of the compounds to ensure accurate predictions. We established a knowledgebase of the available compound (or substance) and interaction‐specific parameters with the goal of providing a single source of physiochemical, in vitro, and clinical pharmacokinetic and interaction data of commonly used excipients. To illustrate the utility of this knowledgebase, a model for cremophor EL was developed and used to hypothesize the potential for CYP3A‐ and P‐gp‐based interactions as a proof of concept.
The non-ionic surfactants Cremophor® EL (CrEL; polyoxyethyleneglycerol triricinoleate 35) and polysorbate 80 (Tween® 80; polyoxy-ethylene-sorbitan-20-monooleate) are widely used as drug formulation vehicles, including for the taxane anticancer agents paclitaxel and docetaxel. A wealth of recent experimental data has indicated that both solubilisers are biologically and pharmacologically active compounds, and their use as drug formulation vehicles has been implicated in clinically important adverse effects, including acute hypersensitivity reactions and peripheral neuropathy. CrEL and Tween® 80 have also been demonstrated to influence the disposition of solubilised drugs that are administered intravenously. The overall resulting effect is a highly increased systemic drug exposure and a simultaneously decreased clearance, leading to alteration in the pharmacodynamic characteristics of the solubilised drug. Kinetic experiments revealed that this effect is primarily caused by reduced cellular uptake of the drug from large spherical micellar-like structures with a highly hydrophobic interior, which act as the principal carrier of circulating drug. Within the central blood compartment, this results in a profound alteration of drug accumulation in erythrocytes, thereby reducing the free drug fraction available for cellular partitioning and influencing drug distribution as well as elimination routes. The existence of CrEL and Tween® 80 in blood as large polar micelles has also raised additional complexities in the case of combination chemotherapy regimens with taxanes, such that the disposition of several coadministered drugs, including anthracyclines and epipodophyllotoxins, is significantly altered. In contrast to the enhancing effects of Tween® 80, addition of CrEL to the formulation of oral drug preparations seems to result in significantly diminished drug uptake and reduced circulating concentrations. The drawbacks presented by the presence of CrEL or Tween® 80 in drug formulations have instigated extensive research to develop alternative delivery forms. Currently, several strategies are in progress to develop Tween® 80- and CrEL-free formulations of docetaxel and paclitaxel, which are based on pharmaceutical (e.g. albumin nanoparticles, emulsions and liposomes), chemical (e.g. polyglutamates, analogues and prodrugs), or biological (e.g. oral drug administration) strategies. These continued investigations should eventually lead to more rational and selective chemotherapeutic treatment.
Background:
Peripheral neuropathy is the dose limiting toxicity of paclitaxel, a chemotherapeutic drug widely used to treat solid tumours. This toxicity exhibits great inter-individual variability of unknown origin. The present study aimed to identify genetic variants associated with paclitaxel induced neuropathy via a whole genome approach.
Methods:
A genome-wide association study (GWAS) was performed in 144 white European patients uniformly treated with paclitaxel/carboplatin and for whom detailed data on neuropathy was available. Per allele single nucleotide polymorphism (SNP) associations were assessed by Cox regression, modelling the cumulative dose of paclitaxel up to the development of grade 2 sensory neuropathy.
Results:
The strongest evidence of association was observed for the ephrin type A receptor 4 (EPHA4) locus (rs17348202, p=1.0×10(-6)), and EPHA6 and EPHA5 were among the top 25 and 50 hits (rs301927, p=3.4×10(-5) and rs1159057, p=6.8×10(-5)), respectively. A meta-analysis of EPHA5-rs7349683, the top marker for paclitaxel induced neuropathy in a previous GWAS (r(2)=0.79 with rs1159057), gave a hazard ratio (HR) estimate of 1.68 (p=1.4×10(-9)). Meta-analysis of the second hit of this GWAS, XKR4-rs4737264, gave a HR of 1.71 (p=3.1×10(-8)). Imputed SNPs at LIMK2 locus were also strongly associated with this toxicity (HR=2.78, p=2.0×10(-7)).
Conclusions:
This study provides independent support of EPHA5-rs7349683 and XKR4-rs4737264 as the first markers of risk of paclitaxel induced neuropathy. In addition, it suggests that other EPHA genes also involved in axonal guidance and repair following neural injury, as well as LIMK2 locus, may play an important role in the development of this toxicity. The identified SNPs could form the basis for individualised paclitaxel chemotherapy.
Conjugation of boron nanoparticles with porphyrins is an attractive way to create dual agents for anticancer boron neutron capture therapy (BNCT) and photodynamic therapy (PDT). Properties of chlorin e(6) conjugated with two cobalt bis(dicarbollide) nanoparticles (1) or with a closo-dodecaborate nanoparticle (2) are reported. Fluorescent dianionic conjugates 1 and 2 penetrate in A549 human lung adenocarcinoma cells, stain cytoplasm diffusely and accumulate highly in lysosomes but are not toxic themselves for cells. Average cytoplasmic concentration of boron atoms (B) achieves 270 μM (ca. 2 × 10(8) B/cell) and 27 μM (ca. 2 × 10(7) B/cell) at the 1.5 μM extracellular concentration of 1 and 2, respectively, that makes conjugate 1 especially suitable for BNCT. Conjugate 2 causes photoinduced cell death at micromolar concentrations and can be considered also as a photosensitizer for PDT. Conjugates 1 and 2 have high quantum yields of singlet oxygen generation (0.55 and 0.85 in solution, respectively), identical intracellular localization and similar lipid-like microenvironment but conjugate 1 possesses no photoinduced cytotoxicity. A presence of cobalt complexes in conjugate 1 is supposed to be a reason of the observed antioxidative effect in cellular environment, but an exact mechanism of this intriguing phenomenon is unclear. Due to increased intracellular accumulation and absence of photoinduced cytotoxicity conjugate 1 is promising for fluorescence diagnostics of cancer.
Amorphous paclitaxel dissolves rapidly (1 mg mL(-1)) in an isotonic aqueous dispersion of egg lecithin (5% w/w), a new biocompatible submicron drug carrier consisting of structured aggregates with average size 0.5 microm. The solution is physically stable for at least 24 h and can be administered as an intravenous infusion. After a 5 h infusion in rabbits (0.66 mg kg(-1) h(-1)), changes in blood morphology were comparable to those observed in rabbits that received the commercial product Taxol. No changes in the enzyme profiles (alanine/aspartate aminotransferase or alkaline phosphatase) were observed. However, during infusion of the new formulation plasma concentration of paclitaxel (292 +/- 182 ng mL(-1)) was lower than observed after Cremophor-containing Taxol (540 +/- 262 ng mL(-1)). This result may indicate that the tissue distribution is different for the two drug formulations. Daily intraperitoneal administrations (3 doses/day) in mice demonstrated that the new carrier solution was non-toxic and, relative to Taxol, the new formulation exhibited similar or less toxicity.
A 54-year-old patient with primary cerebral lymphoma was treated with two 4-weekly cycles of high-dose intravenous cytarabine (12 g/m2) and methotrexate (3 g/m2). The administration of the first course proceeded without notable complications. Before the administration of methotrexate in the second cycle blood cell counts and chemistry showed no abnormalities except for slightly increased alkaline phosphatase and gamma-glutamyl-transpeptidase levels which was attributed to diphantoin comedication. The patient developed symptoms of acute renal failure 7 h after methotrexate infusion which resulted in a very high serum methotrexate level (39.84 micromol/l) at 20 h after infusion. Rescue therapy was intensified: the leucovorin dosage was increased (1,200 mg continuous i.v. infusion every 24 h) and combined with thymidine rescue therapy (8 g/m2 per day continuous i.v. infusion every 24 h). Urine alkalinization was increased and diphantoin therapy was stopped. Leucovorin eye drops and mouth washes were started 5 days after methotrexate administration to prevent conjunctivitis and mucositis as a result of high methotrexate levels (>2.4 micromol/l). In spite of the fact that serum methotrexate levels remained persistently higher than 0.1 micromol/l for 12 days, the patient experienced no further short-term systemic toxicity except for anaemia (grade 3 according to NCI Common Toxicity Criteria). After day 12 intensified rescue therapy and the frequency of alkalinization were decreased to standard procedures and stopped on day 19. It is concluded that i.v. administration with high-dose methotrexate can result in unpredictable acute toxicity. In our patient, acute methotrexate toxicity was treated successfully by intensification of classical leucovorin rescue therapy in combination with thymidine infusion. In addition, leucovorin mouth washes and eye drops may have prevented mucositis and conjunctivitis, respectively.
