Prediction of the pharmacokinetics of succinylated human serum albumin in man from in vivo disposition data in animals and in vitro liver slice incubations

Liver uptake of cefditoren is mediated by OATP1B1 and OATP2B1 in humans and Oatp1a1, Oatp1a4, and Oatp1b2 in rats

OATPs and Oatps mediated liver uptake of cefditoren in humans and in rats.

OATP and MRP2-mediated hepatic uptake and biliary excretion of eprosartan in rat and human

BACKGROUND

Eprosartan is an angiotensin II receptor antagonist, used in the treatment of hypertension and heart failure in clinical patients. The objective of this study was to clarify the mechanism underlying hepatic uptake and biliary excretion of eprosartan in rats and humans.

METHODS

Perfused rat liver in situ, rat liver slices, isolated rat hepatocytes and human organic anion-transporting polypeptide (OATP)-transfected cells in vitro were used in this study.

RESULTS

Extraction ratio of eprosartan was decreased by rifampicin in perfused rat livers. Uptake of eprosartan in rat liver slices and isolated rat hepatocytes was significantly inhibited by Oatp modulators such as ibuprofen, digoxin, rifampicin and cyclosporine A, but not by tetraethyl ammonium or p-aminohippurate. Uptake of eprosartan in rat hepatocytes indicated a saturable process. Although uptake of eprosartan in OATP1B3-human embryonic kidney cells (HEK) 293 cells was not observed, significant differences in cellular accumulations of eprosartan between vector- and OATP1B1-Madin-Darby canine kidney strain (MDCK) II cells were found in transcellular transport study. Moreover, cumulative biliary excretion rate of eprosartan in the presence of probenecid (Multidrug resistance-associated protein 2 (Mrp2) inhibitor) was significantly decreased in perfused rat livers. Vectorial basal-to-apical transport of eprosartan was also observed in OATP1B1/MRP2 double transfectants.

CONCLUSIONS

Eprosartan was transported by multiple Oatps (at least Oatp1a1 and Oatp1a4)/Mrp2 in rat and OATP1B1/MRP2, at least, in human.

Translation of central nervous system occupancy from animal models: application of pharmacokinetic/pharmacodynamic modeling

Translation of central nervous system receptor occupancy from animal models to humans has been elusive for many therapeutic targets. However, this may represent a valuable link to clinical efficacy for drugs acting within the brain and spinal cord. The introduction of positron emission tomography marked a significant noninvasive advance in determination of target engagement in the central nervous system. Pharmacokinetic/pharmacodynamic (PK/PD) modeling represents a valuable tool to translate ex vivo receptor occupancy from relevant animal models to humans. Whereas PK properties usually are reasonably scaled across species using standard allometric principles, PD properties related to receptor occupancy are usually species-independent. The translational value and applicability of PK/PD approaches are more directly evident when comparable modeling assumptions and mathematical model structures are employed across experiments and analyses. The purpose of this article is to review the basic principles of PK/PD analysis of receptor occupancy determined using noninvasive positron emission tomography imaging and first principles of allometric PK scaling and PD prediction based on animal data. By use of the data from the area of pain management, we also provide a case study of PK/PD analysis showcasing the importance of PK/PD model assumptions in predicting receptor occupancy in humans based on data from animal models.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Involvement of organic anion-transporting polypeptides in the hepatic uptake of dioscin in rats and humans

The objective of this study was to clarify the mechanism underlying hepatic uptake of dioscin (diosgenyl 2,4-di-O-a-L-rhamnopyranosyl-p-D-glucopyranoside), an herbal ingredient with antihepatitis activity, in rats and humans. The liver uptake index (LUI) in vivo, perfused rat liver in situ, rat liver slices, isolated rat hepatocytes, and human organic anion-transporting polypeptide (OATP)-transfected cells in vitro were used to evaluate hepatic uptake of dioscin. Values of 11.9% ± 1.6% and 15.0% ± 0.9% of dose for uptake of dioscin were observed by LUI in vivo and perfused rat livers in situ, respectively. The time course of dioscin uptake by rat liver slices was temperature-dependent. Uptake of dioscin by rat liver slices and isolated rat hepatocytes was inhibited significantly by Oatp modulators, such as ibuprofen (Oatp1a1 inhibitor), digoxin (Oatp1a4 substrate), and glycyrrhizic acid (Oatp1b2 inhibitor), but not by TEA or p-aminohippurate. Uptake of dioscin in rat hepatocytes and OATP1B3-human embryonic kidney (HEK) 293 cells indicated a saturable process with a Km of 3.75 ± 0.51 μM and 2.08 ± 0.27 μM, respectively. (-)-Epigallocatechin gallate, cyclosporin A, rifampicin, and telmisartan inhibited transport of dioscin in OATP1B3-HEK293 cells. However, transcellular transport of dioscin in OATP1B1- or OATP1B1/multidrug resistance-associated protein 2-Madin-Darby canine kidney strain II cells was not observed. These results indicate that hepatic uptake of dioscin is involved in OATP1B3 in humans, and multiple Oatps might participate in this process in rats.

Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies

Precision-cut tissue slices (PCTS) are viable ex vivo explants of tissue with a reproducible, well defined thickness. They represent a mini-model of the organ under study and contain all cells of the tissue in their natural environment, leaving intercellular and cell-matrix interactions intact, and are therefore highly appropriate for studying multicellular processes. PCTS are mainly used to study the metabolism and toxicity of xenobiotics, but they are suitable for many other purposes. Here we describe the protocols to prepare and incubate rat and human liver and intestinal slices. Slices are prepared from fresh liver by making a cylindrical core using a drill with a hollow bit, from which slices are cut with a specially designed tissue slicer. Intestinal tissue is embedded in cylinders of agarose before slicing. Slices remain viable for 24 h (intestine) and up to 96 h (liver) when incubated in 6- or 12-well plates under 95% O(2)/5% CO(2) atmosphere.

Scaling pharmacodynamics from in vitro and preclinical animal studies to humans

An important feature of mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) models is the identification of drug- and system-specific factors that determine the intensity and time-course of pharmacological effects. This provides an opportunity to integrate information obtained from in vitro bioassays and preclinical pharmacological studies in animals to anticipate the clinical and adverse responses to drugs in humans. The fact that contemporary PK/PD modeling continues to evolve and seeks to emulate systems level properties should provide enhanced capabilities to scale-up pharmacodynamic data. Critical steps in drug discovery and development, such as lead compound and first in human dose selection, may become more efficient with the implementation and further refinement of translational PK/PD modeling. In this review, we highlight fundamental principles in pharmacodynamics and the basic expectations for in vitro bioassays and traditional allometric scaling in PK/PD modeling. Discussion of PK/PD modeling efforts for recombinant human erythropoietin is also included as a case study showing the potential for advanced systems analysis to facilitate extrapolations and improve understanding of inter-species differences in drug responses.

Development of translational pharmacokinetic-pharmacodynamic models

Contemporary models in the field of pharmacokinetic-pharmacodynamic (PK-PD) modeling often incorporate the fundamental principles of capacity limitation and operation of turnover processes to describe the time course of pharmacological effects in mechanistic terms. This permits the identification of drug- and system-specific factors that govern drug responses. There is considerable interest in utilizing mechanism-based PK-PD models in translational pharmacology, whereby in silico, in vitro, and preclinical data may be effectively coupled with relevant models to streamline the discovery and development of new therapeutic agents. These translational PK-PD models form the subject of this review.

A Phase I/IIa Study with Succinylated Human Serum Albumin (Suc-HSA), a candidate HIV-1 Fusion Inhibitor

Background

Succinylated human serum albumin (Suc-HAS) is a negatively charged neo-glycoprotein that binds to the positively charged V3–loop of HIV-1 gp120, acting as HIV-1-fusion inhibitor in vitro (IC50: 0.5–5.0 μg/ml). Suc-HSA was safe in rats and monkeys, and showed antiretroviral effect in a human-to-mouse model. We evaluated safety and pharmacokinetics of single and multiple doses of Suc-HSA in HIV-1-infected individuals.

Methods

First, six untreated, chronically HIV-1-infected patients were randomized to a single dose of 1 or 10 mg/kg Suc-HSA intravenously. Second, five consecutive daily doses (10 mg/kg, based on the results of the single dose study) were given to four patients. Safety laboratory assessments, Suc-HSA plasma levels, plasma HIV-1 RNA (pVL), and CD4+ T-cell counts were determined.

Results

Increase of liver transaminases (grade 1/2) occurred in one of six patients in the single-dose phase and in three of four patients in the multiple-dosing phase. Suc-HSA plasma levels were undetectable 4 h after a single dose of 1 mg/kg. After a dose of 10 mg/kg, plasma levels were more sustained, but declined under the target plasma concentration (10 μg/ml) 12–24 h post-dosing. After multiple dosing, plasma levels reached peak values 2h post-dosing as predicted by our kinetic model. However, trough levels were below the target concentrations. There was no change in pVL or CD4+ T-cell count in either the single- or multiple-dosing phase.

Conclusions

At the chosen dosing regimens, adequate antiviral plasma levels were not maintained, probably because the hepatic clearance was more rapid than expected. This may partially explain the lack of effect on pVL and CD4+ T-cell count. The observed liver transaminase increases prohibit further dose escalation.

Pharmacokinetics of a hepatic stellate cell-targeted doxorubicin construct in bile duct-ligated rats

BACKGROUND/AIMS

Inhibition of hepatic stellate cell (HSC) proliferation is a relevant strategy to inhibit liver fibrosis. Coupling of antiproliferative drugs to the HSC-selective drug carrier mannose-6-phosphate-modified human serum albumin (M6PHSA) may lead to cell-selective inhibition of HSC proliferation. We coupled the antiproliferative drug doxorubicin (DOX) to this drug carrier and investigated the pharmacokinetics of this construct in a rat model of liver fibrosis, as well as in cultured HSC.

METHODS/RESULTS

M6PHSA-DOX was cleared from the plasma in a biphasic manner. Upon i.v. injection of 4 microg kg(-1) (tracer), 2 and 20 mg kg(-1), the clearance in the distribution phase of drug disposition (CL(d)) significantly decreased from 9.7+/-0.7 to 4.7+/-2.3 and 1.0+/-0.1 ml kg(-1)min(-1), respectively. This indicates that saturation of clearance mechanisms occurs in this phase of drug disposition, likely reflecting saturable receptor-mediated uptake in the target cells. Gamma-camera studies revealed that the majority of the conjugate accumulated in the liver within 5 min, and immunohistochemical double-staining of liver sections demonstrated co-localization of the construct with HSC-markers. Simulation of the release of DOX from the carrier, after cellular uptake by HSC, showed that a gradual release of the drug takes place over a 9h period. Studies in cultured HSC illustrated that after 24h incubation with the conjugate, DOX was associated with the cell nucleus.

CONCLUSIONS

The rapid distribution of M6PHSA-DOX from the blood to HSC, in combination with the expected gradual release of DOX within these cells, make this construct a promising tool for achieving sustained and selective inhibition of HSC proliferation.