Population Pharmacokinetic Modeling of Etoposide Free Concentrations in Solid Tumor

Purpose

This study aimed to determine free etoposide (ETO) concentrations in two regions of Walker-256 (W256) solid tumor using microdialysis and to establish a population pharmacokinetic (popPK) model to describe simultaneously free tumor and total plasma concentrations.

Methods

W256 tumor-bearing Wistar rats received ETO 10 or 20 mg/kg i.v. bolus. Free ETO concentrations were sampled from central and peripheral regions of the tumor via CMA/20 probes for up to 7 h, whereas blood samples were collected via carotid artery cannulation. Total plasma and free tumor concentration-time profiles were analyzed by non-compartmental approach using WinNonlin® v. 5.3. PopPK modeling was conducted using MONOLIX v.4.3.3.

Results

ETO penetration was higher in the periphery (61?±?15% and 61?±?29%) than in tumor center (34?±?6% and 28?±?11%) following 10 and 20 mg/kg doses, respectively (ANOVA, α?=?0.05). A 4-compartment model fitted ETO concentration-time profiles in all sampling compartments.

Conclusions

The popPK model allowed the simultaneous fitting of plasma and tumor concentrations and a better understanding of ETO distribution in solid tumors. ETO plasma concentrations are not a good surrogate for tumoral exposure, emphasizing the importance of knowing intratumoral concentrations to predict drug response.

     

Testing the validity of<Emphasis Type="Italic"> c-fos</Emphasis> expression profiling to aid the therapeutic classification of psychoactive drugs

Rationale

Different stimuli, including pharmacological stimuli, induce different neuroanatomical profiles of c-fos expression. Can these profiles be used in classifying psychoactive drugs and predicting therapeutic utility?

Objective

To test the validity of c-fos expression profiling to aid therapeutic classification.

Methods

Anxiolytics, antidepressants, antipsychotics and psychostimulants were compared. (i) A meta-analysis was performed and profiles compiled from literature reports of changes in c-fos expression in rat brain regions, measured by in situ hybridisation histochemistry or immunohistochemistry, after acute injection of psychoactive drugs. (ii) Male rat brains were profiled for changes in c-fos mRNA expression induced by acute injection of psychoactive drugs.

Results

(i) The meta-analysis showed that anxiolytics activate few (mostly stress-related) brain regions; antidepressants activate more regions, including the central amygdaloid nucleus; antipsychotics activate more regions still, including the nucleus accumbens and striatal areas; and psychostimulants activate the greatest number of all, including the most cortical regions (especially the piriform cortex). Profiles also varied within drug classes. (ii) Our experimental profiles confirmed and extended meta-analysis profiles, showing more downregulation. (iii) Sites activated by mirtazapine (an antidepressant not previously profiled) matched those of the antidepressant imipramine.

Conclusions

(i) Differences between drug classes support their classification by means of c-fos profiling. Differences within classes may reflect mechanistic variations. (ii) Greater downregulation in our experiments might be because of inclusion of low, clinically relevant, drug doses and fuller coverage of brain regions. (iii) The agreement between mirtazapine and imipramine increases our confidence in the validity of c-fos expression profiling to aid drug classification and predict therapeutic utility.

     

Population Pharmacokinetic Modeling to Describe the Total Plasma and Free Brain Levels of Fluconazole in Healthy and <Emphasis Type="BoldItalic">Cryptococcus neoformans</Emphasis> Infected Rats: How Does the Infection Impact the Drug’s Levels on Biophase?

Purpose

The present work aimed to evaluate the influence of experimental meningitis caused by C. neoformans on total plasma and free brain concentrations of fluconazole (FLC) in Wistar rats.

Method

The infection was induced by the administration of 100 μL of inoculum (1.10⁵ CFU) through the tail vein. Free drug in the brain was assessed by microdialisys (μD). Blood and μD samples were collected at pre-determined time points up to 12 h after intravenous administration of FLC (20 mg/kg) to healthy and infected rats. The concentration-time profiles were analyzed by non-compartmental and population pharmacokinetics approaches.

Results

A two-compartmental popPK model was able to simultaneously describe plasma and free drug concentrations in the brain for both groups investigated. Analysis of plasma and μD samples showed a better FLC distribution on the brain of infected than healthy animals (1.04?±?0.31 vs 0.69?±?0.14, respectively). The probability of target attainment was calculated by Monte Carlo simulations based on the developed popPK model for 125 mg/kg dose for rats and 400–2000 mg for humans.

Conclusions

FLC showed a limited use in monotherapy to the treatment of criptoccocosis in rats and humans to value of MIC >8 μg/mL.

     

Computational Assessment of Pharmacokinetics and Biological Effects of Some Anabolic and Androgen Steroids

Purpose

The aim of this study is to use computational approaches to predict the ADME-Tox profiles, pharmacokinetics, molecular targets, biological activity spectra and side/toxic effects of 31 anabolic and androgen steroids in humans.

Methods

The following computational tools are used: (i) FAFDrugs4, SwissADME and admetSARfor obtaining the ADME-Tox profiles and for predicting pharmacokinetics;(ii) SwissTargetPrediction and PASS online for predicting the molecular targets and biological activities; (iii) PASS online, Toxtree, admetSAR and Endocrine Disruptomefor envisaging the specific toxicities; (iv) SwissDock to assess the interactions of investigated steroids with cytochromes involved in drugs metabolism.

Results

Investigated steroids usually reveal a high gastrointestinal absorption and a good oral bioavailability, may inhibit someof the human cytochromes involved in the metabolism of xenobiotics (CYP2C9 being the most affected) and reflect a good capacity for skin penetration. There are predicted numerous side effects of investigated steroids in humans: genotoxic carcinogenicity, hepatotoxicity, cardiovascular, hematotoxic and genitourinary effects, dermal irritations, endocrine disruption and reproductive dysfunction.

Conclusions

These results are important to be known as an occupational exposure to anabolic and androgenic steroids at workplaces may occur and because there also is a deliberate human exposure to steroids for their performance enhancement and anti-aging properties.

     

Translational Modeling in Schizophrenia: Predicting Human Dopamine D<Subscript>2</Subscript> Receptor Occupancy

Objectives

To assess the ability of a previously developed hybrid physiology-based pharmacokinetic-pharmacodynamic (PBPKPD) model in rats to predict the dopamine D₂ receptor occupancy (D₂RO) in human striatum following administration of antipsychotic drugs.

Methods

A hybrid PBPKPD model, previously developed using information on plasma concentrations, brain exposure and D₂RO in rats, was used as the basis for the prediction of D₂RO in human. The rat pharmacokinetic and brain physiology parameters were substituted with human population pharmacokinetic parameters and human physiological information. To predict the passive transport across the human blood–brain barrier, apparent permeability values were scaled based on rat and human brain endothelial surface area. Active efflux clearance in brain was scaled from rat to human using both human brain endothelial surface area and MDR1 expression. Binding constants at the D₂ receptor were scaled based on the differences between in vitro and in vivo systems of the same species. The predictive power of this physiology-based approach was determined by comparing the D₂RO predictions with the observed human D₂RO of six antipsychotics at clinically relevant doses.

Results

Predicted human D₂RO was in good agreement with clinically observed D₂RO for five antipsychotics. Models using in vitro information predicted human D₂RO well for most of the compounds evaluated in this analysis. However, human D₂RO was under-predicted for haloperidol.

Conclusions

The rat hybrid PBPKPD model structure, integrated with in vitro information and human pharmacokinetic and physiological information, constitutes a scientific basis to predict the time course of D₂RO in man.

     

General Pharmacokinetic Model for Topically Administered Ocular Drug Dosage Forms

Purpose

In ocular drug development, an early estimate of drug behavior before any in vivo experiments is important. The pharmacokinetics (PK) and bioavailability depend not only on active compound and excipients but also on physicochemical properties of the ocular drug formulation. We propose to utilize PK modelling to predict how drug and formulational properties affect drug bioavailability and pharmacokinetics.

Methods

A physiologically relevant PK model based on the rabbit eye was built to simulate the effect of formulation and physicochemical properties on PK of pilocarpine solutions and fluorometholone suspensions. The model consists of four compartments: solid and dissolved drug in tear fluid, drug in corneal epithelium and aqueous humor. Parameter values and in vivo PK data in rabbits were taken from published literature.

Results

The model predicted the pilocarpine and fluorometholone concentrations in the corneal epithelium and aqueous humor with a reasonable accuracy for many different formulations. The model includes a graphical user interface that enables the user to modify parameters easily and thus simulate various formulations.

Conclusions

The model is suitable for the development of ophthalmic formulations and the planning of bioequivalence studies.

     

Population Pharmacokinetic Modelling of Morphine,Gabapentin and their Combination in the Rat

Purpose

The combination of morphine and gabapentin seems promising for the treatment of postoperative and neuropathic pain. Despite the well characterised pharmacodynamic interaction, little is known about possible pharmacokinetic interactions. The aim of this study was to evaluate whether co-administration of the two drugs leads to modifications of their pharmacokinetic profiles.

Methods

The pharmacokinetics of morphine, morphine-3-glucuronide and gabapentin were characterised in rats following subcutaneous injections of morphine, gabapentin or their combination. Non-linear mixed effects modelling was applied to describe the pharmacokinetics of the compounds and possible interactions.

Results

The plasma-concentration-time profiles of morphine and gabapentin were best described using a three- and a one-compartment disposition model respectively. Dose dependencies were found for morphine absorption rate and gabapentin bioavailability. Enterohepatic circulation of morphine-3-glucuronide was modelled using an oscillatory model. The combination did not lead to pharmacokinetic interactions for morphine or gabapentin but resulted in an estimated ~33% diminished morphine-3-glucuronide formation.

Conclusions

The finding of a lack of pharmacokinetic interaction strengthens the notion that the combination of the two drugs leads to better efficacy in pain treatment due to interaction at the pharmacodynamic level. The interaction found between gabapentin and morphine-3-glucuronide, the latter being inactive, might not have any clinical relevance.

     

Comparison of Dialysis- and Solvatofluorochromism-Based Methods to Determine Drug Release Rates from Polymer Nanoassemblies

Purpose

To compare traditional dialysis- and novel solvatofluorochromism (SFC)-based methods for accurate determination of drug release profiles for nanoparticle drug carriers.

Methods

Polymer nanoassemblies (PNAs) varying in drug release patterns were prepared using poly(ethylene glycol), poly(ethylenimine), hydrophobic excipients (palmitate and deoxycholate), and model hydrophobic anticancer drugs with clinical relevance (carfilzomib and docetaxel). Nile blue (NB) was used as a model SFC dye quenching fluorescence in water yet emitting strong fluorescence in the presence of hydrophobic drugs within PNAs. Drug release kinetics were measured by dialysis- and SFC-based methods, and analyzed by mathematical modeling of free drug, spiked drug, and encapsulated drug release.

Results

The dialysis method overestimated drug remaining in PNAs because it included released drug in measurements, whereas the SFC method successfully distinguished drugs entrapped in PNAs from released in solution and thus provided more accurate drug release patterns. However, mathematical modeling revealed that the dialysis method would be less influenced than the SFC method by hydrophobic excipients modulating drug diffusion within PNAs.

Conclusions

In comparison to the dialysis-based method, the SFC-based method would allow for real-time spectroscopic determination of drug release from PNAs and potentially other nanoparticle drug carriers with improved convenience and accuracy.

     

Physiologically Based Pharmacokinetic Modeling of Fimasartan,Amlodipine, and Hydrochlorothiazide for the Investigation of Drug–Drug Interaction Potentials

Purpose

To build a physiologically based pharmacokinetic (PBPK) model for fimasartan, amlodipine, and hydrochlorothiazide, and to investigate the drug–drug interaction (DDI) potentials.

Methods

The PBPK model of each drug was developed using Simcyp software (Version 15.0), based on the information obtained from literature sources and in vitro studies. The predictive performance of the model was assessed by comparing the predicted PK profiles and parameters with the observed data collected from healthy subjects after multiple oral doses of fimasartan, amlodipine, and hydrochlorothiazide. The DDI potentials after co-administration of three drugs were simulated using the final model.

Results

The predicted-to-observed ratios of all the pharmacokinetic parameters met the acceptance criterion. The PBPK model predicted no significant DDI when fimasartan was co-administered with amlodipine or hydrochlorothiazide, which is consistent with the observed clinical data. In the simulation of DDI at steady-state after co-administration of three drugs, the model predicted that fimasartan exposure would be increased by ~24.5%, while no changes were expected for the exposures of amlodipine and hydrochlorothiazide.

Conclusions

The developed PBPK model adequately predicted the pharmacokinetics of fimasartan, amlodipine, and hydrochlorothiazide, suggesting that the model can be used to further investigate the DDI potential of each drug.

     

Utility of Göttingen minipigs for Prediction of Human Pharmacokinetic Profiles After Dermal Drug Application

Purpose

Although Göttingen minipigs have been widely used for the evaluation of skin absorption, the correlation of minipig skin permeability with human skin absorption remains unclear. This study was designed to investigate the prediction of human plasma concentrations after dermal application of drug products using skin permeability data obtained from minipigs.

Methods

First, in vitro skin permeabilities of seven marketed transdermal drug products were evaluated in minipigs, and compared with in vitro human skin permeability data. Next, plasma concentration-time profiles in humans after dermal applications were simulated using the in vitro minipig skin permeability data. Finally, the in vitro-in vivo correlation of minipig skin permeability was assessed.

Results

The in vitro skin permeabilities in minipigs were correlated strongly with in vitro human skin permeability data for the same drug products, indicating the utility of minipig skin as an alternative to human skin for in vitro studies. The steady-state plasma concentration or the maximum concentration of drugs was within 2-fold of the clinical data. Bioavailability was approximately 3-fold lower than in vitro permeated fraction.

Conclusions

Predictions using in vitro skin permeability data in Göttingen minipig skin can reproduce the human pharmacokinetic profile, although the prediction of in vivo skin absorption underestimates human absorption.

     

Evaluation of the Utility of Chimeric Mice with Humanized Livers for the Characterization and Profiling of the Metabolites of a Selective Inhibitor (YM543) of the Sodium-Glucose Cotransporter 2

Purpose

YM543 is a novel selective inhibitor of the sodium-glucose cotransporter 2. The objectives of the current study were to evaluate the utility of mice with humanized livers to predict human drug metabolites using YM543 as a case example.

Methods

Metabolites of YM543 generated in humans and experimental animals including chimeric mice with humanized liver, PXB mice, were analyzed via liquid chromatography-mass spectrometry, liquid chromatography-radiometric detector or nuclear magnetic resonance spectrometer.

Results

After oral administration of YM543, metabolites M1–M5 were detected in human plasma and urine. M2–M4 were detected in at least one species while M1 was not generated by experimental animals or in vitro systems. In the metabolite profiling in PXB mice, M1 was detected in both plasma and urine samples.

Conclusions

Metabolite profile of YM543 in PXB mice and humans was closely resemble. and the human specific metabolite was detected in the model mice. The human specific metabolite, M1, was difficult to know in advance to clinical study. The ability to predict the human metabolite profile including presence of human specific metabolites using PXB mice will likely facilitate development of new drug candidates for human use.

     

Preparation and Evaluation of a Novel Class of Amphiphilic Amines as Antitumor Agents and Nanocarriers for Bioactive Molecules

Purpose

We describe a novel class of antitumor amphiphilic amines (RCn) based on a tricyclic amine hydrophilic head and a hydrophobic linear alkyl tail of variable length.

Methods

We tested the lead compound, RC16, for cytotoxicity and mechanism of cell death in several cancer cell lines, anti tumor efficacy in mouse tumor models, and ability to encapsulate chemotherapy drugs.

Results

These compounds displayed strong cytotoxic activity against cell lines derived from both pediatric and adult cancers. The IC50 of the lead compound, RC16, for normal cells including human keratinocytes, human fibroblasts and human umbilical vein endothelial cells was tenfold higher than for tumor cells. RC16 exhibited significant antitumor effects in vivo using several human xenografts and a metastatic model of murine neuroblastoma by both intravenous and oral administration routes. The amphiphilic character of RC16 triggered a spontaneous molecular self-assembling in water with formation of micelles allowing complexation of Doxorubicin, Etoposide and Paclitaxel. These micelles significantly improved the in vitro antitumor activity of these drugs as the enhancement of their aqueous solubility also improved their biologic availability.

Conclusions

RC16 and related amphiphilic amines may be useful as a novel cancer treatment.

     

A Semi-Physiologically Based Pharmacokinetic Model Describing the Altered Metabolism of Midazolam Due to Inflammation in Mice

Purpose

To investigate influence of inflammation on metabolism and pharmacokinetics (PK) of midazolam (MDZ) and construct a semi-physiologically based pharmacokinetic (PBPK) model to predict PK in mice with inflammatory disease.

Methods

Glucose-6-phosphate isomerase (GPI)-mediated inflammation was used as a preclinical model of arthritis in DBA/1 mice. CYP3A substrate MDZ was selected to study changes in metabolism and PK during the inflammation. The semi-PBPK model was constructed using mouse physiological parameters, liver microsome metabolism, and healthy animal PK data. In addition, serum cytokine, and liver-CYP (cytochrome P450 enzymes) mRNA levels were examined.

Results

The in vitro metabolite formation rate was suppressed in liver microsomes prepared from the GPI-treated mice as compared to the healthy mice. Further, clearance of MDZ was reduced during inflammation as compared to the healthy group. Finally, the semi-PBPK model was used to predict PK of MDZ after GPI-mediated inflammation. IL-6 and TNF-α levels were elevated and liver-cyp3a11 mRNA was reduced after GPI treatment.

Conclusion

The semi-PBPK model successfully predicted PK parameters of MDZ in the disease state. The model may be applied to predict PK of other drugs under disease conditions using healthy animal PK and liver microsomal data as inputs.

     

Combining an <Emphasis Type="Italic">In Vitro</Emphasis> Kinetic Model with a Physiologically-Based Pharmacokinetic Model to Assess the Potential <Emphasis Type="Italic">In Vivo</Emphasis> Fate of Polyvinyl Pyrrolidone-Vinyl Acetate Copolymers

Purpose

To understand hydrolysis and alcoholysis of polyvinylpyrrolidone-co-vinylacetate (PVPVA) during formulation and storage, elucidate the reaction mechanism, establish an intrinsic kinetic model, and apply this model coupled with GastroPlus? modeling to predict the amount of PVPVA degradation in vivo.

Methods

The experimental approach includes the detection of the polymer reaction by solution nuclear magnetic resonance (NMR) and the measurement of reaction product concentration via gas chromatography (GC). The theoretical approach includes the establishment of the intrinsic kinetic model and the application of GastroPlus? to predict the degree of PVPVA degradation.

Results

The kinetic model established is a first order reaction between PVPVA and 2-propanol (IPA) or water under an acidic condition. The application of this kinetic model shows that between 1.7 and 6.8 mg of degradant is formed in the GI tract for a 850 mg dose of PVPVA.

Conclusions

The results from this application provide valuable input for process development and the risk analysis of the degradation of PVPVA.

     

Disease-Induced Alterations in Brain Drug Transporters in Animal Models of Alzheimer’s Disease

Purpose

Alzheimer’s disease (AD) may disturb functions of the blood-brain barrier and change the disposition of drugs to the brain. This study assessed the disease-induced changes in drug transporters in the brain capillaries of transgenic AD mice.

Methods

Eighteen drug transporters and four tight junction-associated proteins were analyzed by RT-qPCR in cortex, hippocampus and cerebellum tissue samples of 12–16-month-old APdE9, Tg2576 and APP/PS1 transgenic mice and their healthy age-matched controls. In addition, microvessel fractions enriched from 1-3-month-old APdE9 mice were analyzed using RT-qPCR and Western blotting. Brain transport of methotrexate in APdE9 mice was assessed by in vivo microdialysis.

Results

The expression profiles of studied genes were similar in brain tissues of AD and control mice. Instead, in the microvessel fraction in APdE9 mice, >2-fold alterations were detected in the expressions of 11 genes but none at the protein level. In control mice strains, >5-fold changes between different brain regions were identified for Slc15a2, Slc22a3 and occludin. Methotrexate distribution into hippocampus of APdE9 mice was faster than in controls.

Conclusions

The expression profile of mice carrying presenilin and amyloid precursor protein mutations is comparable to controls, but clear regional differences exist in the expression of drug transporters in brain.

     

<Emphasis Type="BoldItalic">In Silico</Emphasis> Absorption Analysis of Valacyclovir in Wildtype and <Emphasis Type="BoldItalic">Pept1</Emphasis> Knockout Mice Following Oral Dose Escalation

Purpose

We developed simulation and modeling methods to predict the in vivo pharmacokinetic profiles of acyclovir, following escalating oral doses of valacyclovir, in wildtype and Pept1 knockout mice. We also quantitated the contribution of specific intestinal segments in the absorption of valacyclovir in these mice.

Methods

Simulations were conducted using a mechanistic advanced compartmental absorption and transit (ACAT) model implemented in GastroPlus?. Simulations were performed for 3 h post-dose in wildtype and Pept1 knockout mice following single oral doses of 10, 25, 50 and 100 nmol/g valacyclovir, and compared to experimentally observed plasma concentration-time profiles of acyclovir.

Results

Good fits were obtained in wildtype and Pept1 knockout mice. Valacyclovir was primarily absorbed from duodenum (42%) and jejunum (24%) of wildtype mice, with reduced uptake from ileum (3%) and caecum/colon (1%), for a total of 70% absorption. In contrast, the absorption of valacyclovir in Pept1 knockout mice was slow and sustained throughout the entire intestinal tract in which duodenum (4%), jejunum (14%), ileum (10%) and caecum/colon (12%) accounted for a total of 40% absorption.

Conclusion

The ACAT model bridged the gap between in situ and in vivo experimental findings, and facilitated our understanding of the complicated intestinal absorption processes of valacyclovir.

     

Human Primary Cell-Based Organotypic Microtissues for Modeling Small Intestinal Drug Absorption

Purpose

The study evaluates the use of new in vitro primary human cell-based organotypic small intestinal (SMI) microtissues for predicting intestinal drug absorption and drug-drug interaction.

Methods

The SMI microtissues were reconstructed using human intestinal fibroblasts and enterocytes cultured on a permeable support. To evaluate the suitability of the intestinal microtissues to model drug absorption, the permeability coefficients across the microtissues were determined for a panel of 11 benchmark drugs with known human absorption and Caco-2 permeability data. Drug-drug interactions were examined using efflux transporter substrates and inhibitors.

Results

The 3D–intestinal microtissues recapitulate the structural features and physiological barrier properties of the human small intestine. The microtissues also expressed drug transporters and metabolizing enzymes found on the intestinal wall. Functionally, the SMI microtissues were able to discriminate between low and high permeability drugs and correlated better with human absorption data (r²?=?0.91) compared to Caco-2 cells (r²?=?0.71). Finally, the functionality of efflux transporters was confirmed using efflux substrates and inhibitors which resulted in efflux ratios of >2.0 fold and by a decrease in efflux ratios following the addition of inhibitors.

Conclusion

The SMI microtissues appear to be a useful pre-clinical tool for predicting drug bioavailability of orally administered drugs.

     

Assessment of a United States pharmaceutical care model for nursing homes in the United Kingdom

Objective

To assess the suitability of an American model of pharmaceutical care for nursing home residents (The Fleetwood model) for application in nursing homes in the United Kingdom.

Method

Pharmacists (those from a hospital setting or involved in prescribing support), general practitioners, nursing home managers and advocates for older people were invited to participate in semi-structured interviews or focus groups. The American Fleetwood model was explained to all participants who were asked for their views and opinions on how such a model could be adapted for use in the UK setting. All interviews and focus groups were tape-recorded, transcribed verbatim and analysed using the framework method.

Main outcome measure

An adapted model of pharmaceutical care for use in UK nursing homes.

Results

There was general concern about prescribing in nursing homes, particularly in relation to psychoactive drugs. All participants were supportive of the proposed model of care and endorsed the greater involvement of pharmacists. However, participants also recognised that unlike pharmacists in the US nursing home setting for which the Fleetwood model had been developed, pharmacists implementing this approach in the UK would face major challenges in relation to access to records (medical and medication), prescribers and residents.

Conclusion

The findings highlighted the key elements of access which will need to be considered if this model of pharmaceutical care is to be applied to nursing home residents in the UK.

Impact of findings on practice

The model has been revised to take account of the challenges relating to access and will be tested in a randomised controlled trial.