Population pharmacokinetics of regorafenib in solid tumours: Exposure in clinical practice considering enterohepatic circulation and food intake.

AIM: Regorafenib is an oral multikinase inhibitor with clinical efficacy in a range of advanced solid tumours. A population pharmacokinetic (PK) model was developed to evaluate the variability of the PK of regorafenib and its pharmacologically active metabolites M-2 and M-5 in solid tumours. METHODS: The model was initially developed using densely sampled phase 1 data and information on food intake to incorporate enterohepatic circulation (EHC) that was identified to considerably contribute to the PK of regorafenib. This was then applied to sparsely sampled data from four phase 3 studies in patients with advanced solid tumours. The need for exact food intake data to estimate individual drug exposure was evaluated. RESULTS: By incorporating EHC, the model adequately described the PK profiles of regorafenib, M-2 and M-5 after single and multiple doses in patients from phase 1 studies. Individual exposure in phase 3 studies was adequately described based on assumptions on the time and frequency of food intake, although exact food intake data are recommended to improve the estimation. Covariate analysis identified sex and body mass index (BMI) as impacting exposure to regorafenib, and sex as strongly impacting exposure to M-2 and M-5 (also influenced by the BMI effect on parent regorafenib in the joint model developed); however, these factors accounted for a small portion of the overall variability in exposure. CONCLUSIONS: The adequate description of regorafenib PK after multiple dosing requires the incorporation of EHC. Neither single nor combined covariates predicted exposures that would warrant a priori regorafenib dose adjustment.

Modeling of pharmacokinetics, efficacy, and hemodynamic effects of macitentan in patients with pulmonary arterial hypertension.

BACKGROUND: Macitentan is the first endothelin receptor antagonist with demonstrated efficacy on morbidity and mortality in pulmonary arterial hypertension (PAH) in the pivotal study SERAPHIN. METHODS: The pharmacokinetics (PK) of macitentan and its active metabolite, ACT-132577, were characterized in a population model. Efficacy and hemodynamics (pharmacodynamics, PD) were related to PK based on PK/PD modeling. RESULTS: Sex, age, and body weight influenced the PK to a statistically significant extent. Model-based simulations showed that these variables are clinically not relevant. Concomitant use of PAH medication (PDE-5 inhibitors) did not influence macitentan trough concentration to a relevant extent. Efficacy and hemodynamics showed clear differences from placebo for macitentan concentrations on 3 and 10 mg with consistent superior effects for 10 mg. After 6 months, PAH patients showed model-predicted 6-min walk distance (6-MWD) improvements of 1.0 m on placebo compared to 29.8 and 34.1 m on 3 and 10 mg of macitentan, respectively. Higher macitentan concentrations were associated with reductions in pulmonary vascular resistance (PVR), mean right atrial and pulmonary arterial pressure, and total pulmonary resistance (TPR) and increases in cardiac index (CI) and mixed venous oxygen saturation. Statistical significance was determined for PVR, TPR, and CI but not for 6-MWD. In addition, PVR showed more pronounced differences between active treatment and placebo than 6-MWD. CONCLUSIONS: Modeling identified statistically significant inter-patient differences; simulations to assess the magnitude of the effects permitted clinical judgment. The same approach will allow for extrapolation to children. Hemodynamic markers might be better markers of treatment effects than 6-MWD. TRIAL REGISTRATION: The SERAPHIN study and its open-label extension are registered with ClinicalTrials.gov with identifiers NCT00660179 (https://www.clinicaltrials.gov/ct2/show/NCT00660179) and NCT00667823 (https://clinicaltrials.gov/ct2/show/NCT00667823) and with EudraCT with identifiers 2007-002440-14 (https://www.clinicaltrialsregister.eu/ctr-search/search?query=2007-002440-14) and 2007-003694-27 (https://www.clinicaltrialsregister.eu/ctr-search/search?query=2007-003694-27).

Challenges in collecting pharmacokinetic and pharmacodynamic information in an intensive care setting: PK/PD modelling of clazosentan in patients with aneurysmal subarachnoid haemorrhage.

PURPOSE: This paper describes the pharmacokinetic/pharmacodynamic modelling of clazosentan in patients with aneurysmal subarachnoid haemorrhage (aSAH), and the impact of collecting data in an intensive care unit (ICU) setting. Factors influencing data quality, analysis, and interpretation are provided with recommendations for future clinical studies in ICU settings. METHODS: CONSCIOUS-2 was a phase III study involving 1,157 patients with aSAH. Secured by surgical clipping, patients were infused with clazosentan or placebo for up to 14 days post-aSAH. Clazosentan exposure relationships with vital signs, QT intervals, and AST/ALT values as well as efficacy and safety endpoints were characterised using population PK/PD and logistic regression models. RESULTS: Clazosentan clearance was influenced by age, sex, Asian origin, and disease status at baseline, and increased with time. Volume of distribution showed a sex difference. Exposure had no relationship with any efficacy endpoint or ALT/AST values, but was related to the increasing probability of lung complications. Blood pressure decreased proportionally to clazosentan concentrations, and the presence of clazosentan was associated with QT interval increases. Implausible values in the concentration data reflect the specific ICU challenges, possibly arising from PK sampling from the infusion arm or haemodilution. CONCLUSIONS: Population PK/PD modelling of CONCIOUS-2 data provided clinically relevant knowledge about various effects of clazosentan in the aSAH patient population in a real clinical setting. The quality of data and analyses could be improved by the collection of additional data and stricter training of study personnel. Differences in clinical practice between sites and geographical regions are more challenging to overcome.

Absolute oral bioavailability of almorexant, a dual orexin receptor antagonist, in healthy human subjects.

BACKGROUND/AIMS: The aim of this single-center, open-label study was to assess the absolute bioavailability of an oral (tablet) versus intravenous formulation of almorexant in healthy subjects. METHODS: A pilot phase in 3 healthy male subjects, which preceded the main study, consisted of a single 30-min intravenous infusion of 10 mg almorexant. Its objectives were to ensure the tolerability of the intravenous formulation and to select the intravenous dose for the main study. The main study was a randomized, two-way crossover study in 20 healthy subjects (10 males and 10 females). Subjects received a single oral dose of 200 mg almorexant and a single 30-min intravenous infusion of 20 mg almorexant. RESULTS: All 23 subjects completed the study as planned. Almorexant was well tolerated; the main observed adverse events were somnolence and fatigue. A geometric mean total body clearance of 43 l/h (95% CI 39-47) and a volume of distribution of 683 liters (95% CI 552-845) were determined. The absolute oral bioavailability of almorexant was 11.2% (90% CI 9.6-13.1). CONCLUSION: Almorexant seems to possess a pronounced first-pass effect and metabolism.

Relevance of drug uptake and efflux for cisplatin sensitivity of tumor cells.

Platinum sensitivity and platinum resistance may involve altered activity of transport proteins. In order to assess the role of drug uptake and efflux in this phenomenon, we compared the expression of three copper transporters, intracellular platinum accumulation, DNA platination and cytotoxicity of cisplatin in two cisplatin-sensitive and -resistant tumor cell line pairs (ovarian A2780/A2780cis and cervical HeLa/HeLaCK cells). Gene expression of importer CTR1, and ATP7A and ATP7B efflux transporters (with and without cisplatin treatment) was investigated using quantitative real-time PCR and platinum concentrations were determined by flameless atomic absorption spectrometry. After incubation with cisplatin, DNA platination was significantly lower in the resistant variants compared to the respective sensitive cell lines, whereas no obvious difference in DNA repair was found. Accordingly, the resistant variants exhibited lower intracellular platinum concentrations than their respective parental cells (2.5- and 2.9-fold lower in A2780cis and HeLaCK cells, respectively). No differences in efflux were observed. Resistant cells expressed lower levels of CTR1 (1.5-1.8-fold) than their sensitive counterparts. Expression differences of ATP7A and ATP7B between resistant and sensitive cells were cell type-specific. The results highlight the relevance of CTR1 for cisplatin sensitivity as there is a clear relationship between lower CTR1 expression, intracellular concentration, DNA platination and cytotoxicity of cisplatin in both resistant cell lines. Our data provide the basis for a quantitative understanding of alterations in uptake and efflux processes leading to cisplatin resistance and might hence facilitate the development of ex vivo assays that can predict cisplatin sensitivity in tumor specimens of patients.

Pediatric Development of Bosentan Facilitated by Modeling and Simulation.

BACKGROUND: Bosentan is approved for use in adult patients with pulmonary arterial hypertension. The primary aim of the pharmacokinetic modeling was the provision of a systematic guidance for study design and enhanced understanding of pharmacokinetics across the entire pediatric age range. METHODS: A physiologically based pharmacokinetic model was developed for the pediatric population; starting from an adult model, the effects of body weight, age, and maturation of relevant metabolizing enzymes were incorporated to extrapolate the pharmacokinetics to children. A pediatric population pharmacokinetic model was developed to identify relevant covariates. RESULTS: Based on model predictions, a dose of 0.5 mg/kg led to an exposure distinguishable from a dose of 2 mg/kg, and an additional blood sampling time point at 2 h (the predicted time of maximum concentration) allowed more precise estimation of bosentan exposure in children. The lower exposure observed in children compared with adults could be explained by maturation-related changes in clearance. Clinical data confirmed the model predictions. CONCLUSIONS: Maturational changes in drug clearance and developmental changes in body weight were identified as key elements of bosentan pharmacokinetics in pediatric patients. Estimating bosentan exposure using physiologically based and population pharmacokinetic modeling and simulation supported dose selection in pediatric patients. Model-based exposure estimates helped in reducing the number of the youngest pediatric patients to be studied. Pharmacokinetic models can provide a systematic guidance for study design and enhanced understanding of pharmacokinetics across the entire pediatric age range.

Pharmacokinetic/Pharmacodynamic Modelling of Receptor Internalization with CRTH2 Antagonists to Optimize Dose Selection.

BACKGROUND AND OBJECTIVE: The chemoattractant receptor-homologous molecule expressed on T helper-2 cells (CRTH2) is a G-protein-coupled receptor for prostaglandin D2 (PGD2), a key mediator in inflammatory disorders. Two selective and potent CRTH2 antagonists currently in clinical development, ACT-453859 and setipiprant, were compared with respect to their (predicted) clinical efficacy. METHODS: Population pharmacokinetic (PK) and pharmacodynamic (PD) models were developed to characterize how plasma concentrations (PK) of ACT-453859, its active metabolite ACT-463036 and setipiprant related to their effect on blocking PGD2-induced internalization of CRTH2 on eosinophils (PD). Simulations were used to identify doses and dosing regimens leading to 90 % of maximum blockade of CRTH2 internalization at trough. RESULTS: A combined concentration of ACT-453859 and its metabolite ACT-463036, with weights proportional to potency (based on an eosinophil shape change assay), enabled good characterization of the PD effect. The modelling and simulation results facilitated decision making by suggesting an ACT-453859 dose of 400 mg once daily (or 100 mg twice daily) for clinically relevant CRTH2 antagonism. CONCLUSION: Pharmacometric quantification demonstrated that CRTH2 internalization is a useful new biomarker to study CRTH2 antagonism. Ninety percent of maximum blockade of CRTH2 internalization at trough is suggested as a quantitative PD target in clinical studies.

A novel CRTH2 antagonist: Single- and multiple-dose tolerability, pharmacokinetics, and pharmacodynamics of ACT-453859 in healthy subjects.

The chemoattractant receptor-homologous molecule expressed on T-helper 2 cells (CRTH2) is a G-protein-coupled receptor for prostaglandin D2 , a key mediator in inflammatory disorders. In this randomized, double-blind, placebo-controlled study we investigated the single- and multiple-dose tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) up to a dose of 800 mg once a day of ACT-453859, a potent and selective CRTH2 antagonist. ACT-453859 was moderately rapidly absorbed and followed a biphasic elimination pattern, with an elimination half-life between 11 and 20 hours. Steady-state conditions were reached after 1 day, and ACT-453859 did not accumulate. Urinary excretion of unchanged ACT-453859 did not exceed 1.4% of the administered dose. Administration of ACT-453859 resulted in a dose-dependent blockadeof CRTH2 on the surface of eosinophils. The maximum PD effect of ACT-453859 was reached about 2.0 hours after dosing, which corresponded to the highest concentration at which PD were assessed. At steady state, 100 and 800 mg ACT-453859 once a day resulted in blockade of CRTH2 over 24 hours. In this entry-into-humans study, ACT-453859 showed good tolerability at all doses and a PK and PD profile compatible with once-daily dosing.

Drug Development for Pediatric Populations: Regulatory Aspects.

Pediatric aspects are nowadays integrated early in the development process of a new drug. The stronger enforcement to obtain pediatric information by the regulatory agencies in recent years resulted in an increased number of trials in children. Specific guidelines and requirements from, in particular, the European Medicines Agency (EMA) and the Food and Drug Administration (FDA) form the regulatory framework. This review summarizes the regulatory requirements and strategies for pediatric drug development from an industry perspective. It covers pediatric study planning and conduct, considerations for first dose in children, appropriate sampling strategies, and different methods for data generation and analysis to generate knowledge about the pharmacokinetics (PK) and pharmacodynamics (PD) of a drug in children. The role of Modeling and Simulation (M&S) in pediatrics is highlighted-including the regulatory basis-and examples of the use of M&S are illustrated to support pediatric drug development.

The Raf kinase inhibitor BAY 43-9006 reduces cellular uptake of platinum compounds and cytotoxicity in human colorectal carcinoma cell lines.

Raf kinase plays a central role in oncogenic signaling and acts as a downstream effector of Ras in the extracellular signal-regulated (ERK) kinase pathway. BAY 43-9006 (BAY) is a novel signal transduction inhibitor that prevents tumor cell proliferation and angiogenesis through blockade of the Raf/MEK/ERK pathway at the level of Raf kinase and the receptor tyrosine kinases vascular endothelial growth factor receptor-2 and platelet-derived growth factor receptor-beta. The present study evaluates the effects of combining BAY and platinum derivatives on human colorectal cancer cells using different incubation protocols. Our data show that the combination of oxaliplatin or cisplatin with BAY results in marked antagonism irrespective of the used application schedule. Furthermore, BAY abrogates the cisplatin-induced G2 arrest as well as the G1 arrest induced by oxaliplatin. BAY alone arrests cancer cells in their current cell cycle phase and affects cell cycle regulative genes. Specifically, BAY reduced the protein expression of p21Cip1 as well as cyclin D1, and inhibits the expression of cdc2 (cdk1). Utilizing atom absorption spectrometry, BAY significantly reduced cellular uptake of platinum compounds and thereby the generation of DNA adducts. Taken together, co-incubation with BAY results in reduced cellular uptake of platinum compounds and consecutively reduced generation of DNA adducts, and eventually decreased cellular cytotoxicity in human colorectal cancer cells. Our results indicate that the Raf kinase inhibitor BAY 43-9006 might also directly or indirectly interact with platinum transporter proteins in vitro.

Cisplatin nephrotoxicity is critically mediated via the human organic cation transporter 2.

Cis-platin is an effective anti-neoplastic agent, but it is also highly nephrotoxic. Here, we clearly identify the human organic cation transporter 2 (hOCT2) as the critical transporter for cis-platin nephrotoxicity in isolated human proximal tubules and offer a potential mechanism for reducing nephrotoxicity in clinical practice. Interaction of cis-platin with hOCT2 in kidney or hOCT1 in liver was investigated with the fluorescent cation 4-[4-(dimethyl-amino)styril]-methylpyridinium in stably transfected HEK293 cells and for the first time in tissues physiologically expressing these transporters, human proximal tubules, and human hepatocyte couplets. Cis-platin (100 micromol/L) inhibited transport via hOCT2-HEK293 but not hOCT1-HEK293. In human proximal tubules cis-platin competed with basolateral organic cation transport, whereas it had no effect in tubules from a diabetic kidney or in hepatocytes. In hOCT2-HEK293 cells treated for 15 hours, incubation with cis-platin induced apoptosis, which was completely suppressed by contemporaneous incubation with the hOCT2 substrate cimetidine (100 micromol/L). These findings demonstrate that uptake of cis-platin is mediated by hOCT2 in renal proximal tubules, explaining its organ-specific toxicity. A combination of cis-platin with other substrates that compete for hOCT2 offers an effective option to decrease nephrotoxicity in the clinical setting.

Long-term activation of SAPK/JNK, p38 kinase and fas-L expression by cisplatin is attenuated in human carcinoma cells that acquired drug resistance.

Tumor cells chronically exposed to cisplatin (cDDP) acquire cDDP resistance that impacts tumor therapy. To elucidate the mechanism of acquired cDDP resistance (ACR), we compared HeLa cells that gained ACR upon chronic cDDP treatment with the parental strain. We show that ACR is due to a lower level of induced apoptosis. Further, upon cDDP treatment, the levels of Fas, Bax and Bid remained unchanged, whereas Bcl-2 and p-Bad were reduced at late times (120 hr) after treatment. At early times, Fas ligand (fas-L) expression was significantly enhanced in sensitive compared to resistant cells and remained upregulated up to the onset of apoptosis. Thus, activation of the Fas system is critical, which is in line with the finding that in sensitive cells, caspase-8 along with caspase-9 and -3 were activated by cDDP. cDDP provoked the activation of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p38 kinase dose-dependently, with significantly lower levels in ACR cells than in the sensitive parental line. cDDP induces c-Jun and AP-1 activity, as measured by a reporter gene assay, which was again attenuated in ACR cells. Time course analysis revealed that SAPK/JNK and p38 kinase activity was sustained upregulated (> 72 hr postexposure), which occurred at much higher level in sensitive than in ACR cells. Inhibition of either JNK or p38 kinase (by JNK inhibitor II and SB 203580, respectively) attenuated cDDP-induced apoptosis, supporting the role of JNK and p38 kinase in the cDDP response. Since several independently derived cDDP-resistant cell lines displayed attenuated MAPK signaling, sustained SAPK/JNK and p38 kinase activation may be a general mechanism of cDDP-induced cell death. ACR cells displayed a reduced level of DNA damage, indicating long-term stimulation of SAPK/JNK and p38 kinase is triggered by nonrepaired cDDP-induced DNA lesions.