The discovery of a selective and potent A2a agonist with extended lung retention.

Although the anti-inflammatory role of the A2a receptor is well established, controversy remains with regard to the therapeutic value for A2a agonists in treatment of inflammatory lung diseases, also as a result of unwanted A2a-mediated cardiovascular effects. In this paper, we describe the discovery and characterization of a new, potent and selective A2a agonist (compound 2) with prolonged lung retention and limited systemic exposure following local administration. To support the lead optimization chemistry program with compound selection and profiling, multiple in vitro and in vivo assays were used, characterizing compound properties, pharmacodynamics (PD), and drug concentrations. Particularly, pharmacokinetic-PD modeling was applied to quantify the effects on the cardiovascular system, and an investigative toxicology study in rats was performed to explore potential myocardial toxicities. Compound 2, in comparison to a reference A2a agonist, UK-432,097, demonstrated higher solubility, lower lipophilicity, lower plasma protein binding, high rat lung retention (28% remaining after 24 h), and was efficacious in a lung inflammatory rat model following intratracheal dosing. Despite these properties, compound 2 did not provide a sufficient therapeutic index, that is, separation of local anti-inflammatory efficacy in the lung from systemic side effects in the cardiovascular system. The plasma concentration that resulted in induction of hypotension (half maximal effective concentration; EC50 0.5 nmol/L) correlated to the in vitro A2a potency (rIC50 0.6 nmol/L). Histopathological lesions in the heart were observed at a dose level which is threefold above the efficacious dose level in the inflammatory rat lung model. In conclusion, compound 2 is a highly potent and selective A2a agonist with significant lung retention after intratracheal administration. Despite its local anti-inflammatory efficacy in rat lung, small margins to the cardiovascular effects suggested limited therapeutic value of this compound for treatment of inflammatory lung disease by the inhaled route.

Cytochrome P450-dependent metabolism in HepaRG cells cultured in a dynamic three-dimensional bioreactor.

Reliable and stable in vitro cellular systems maintaining specific liver functions important for drug metabolism and disposition are urgently needed in preclinical drug discovery and development research. The cell line HepaRG exhibits promising properties such as expression and function of drug-metabolizing enzymes and transporter proteins, which resemble those found in freshly isolated human hepatocytes. In this study, HepaRG cells were cultured up to 68 days in a three-dimensional multicompartment capillary membrane bioreactor, which enables high-density cell culture under dynamic conditions. The activity of drug-metabolizing cytochrome P450 (P450) enzymes was investigated by a cocktail of substrates for CYP1A1/2 (phenacetin), CYP2C9 (diclofenac), CYP2B6 (bupropion), and CYP3A4 (midazolam). The model P450 substrates, which were introduced to the bioreactor system mimicking in vivo bolus doses, showed stable metabolism over the entire experimental period of several weeks with the exception of bupropion hydroxylase, which increased over time. Ketoconazole treatment decreased the CYP3A4 activity by 69%, and rifampicin induced the CYP3A4- and CYP2B6-dependent activity 6-fold, which predicts well the magnitude of changes observed in vivo. Moreover, polarity of transporter expression and formation of tissue-like structures including bile canaliculi were demonstrated by immune histochemistry. The long-lasting bioreactor system using HepaRG cells thus provides a promising and stable liver-like in vitro model for continuous investigations of the hepatic kinetics of drugs and of drug-drug interactions, which well predict the situation in vivo in humans.

Scaling down of a clinical three-dimensional perfusion multicompartment hollow fiber liver bioreactor developed for extracorporeal liver support to an analytical scale device useful for hepatic pharmacological in vitro studies.

Within the scope of developing an in vitro culture model for pharmacological research on human liver functions, a three-dimensional multicompartment hollow fiber bioreactor proven to function as a clinical extracorporeal liver support system was scaled down in two steps from 800 mL to 8 mL and 2 mL bioreactors. Primary human liver cells cultured over 14 days in 800, 8, or 2 mL bioreactors exhibited comparable time-course profiles for most of the metabolic parameters in the different bioreactor size variants. Major drug-metabolizing cytochrome P450 activities analyzed in the 2 mL bioreactor were preserved over up to 23 days. Immunohistochemical studies revealed tissue-like structures of parenchymal and nonparenchymal cells in the miniaturized bioreactor, indicating physiological reorganization of the cells. Moreover, the canalicular transporters multidrug-resistance-associated protein 2, multidrug-resistance protein 1 (P-glycoprotein), and breast cancer resistance protein showed a similar distribution pattern to that found in human liver tissue. In conclusion, the down-scaled multicompartment hollow fiber technology allows stable maintenance of primary human liver cells and provides an innovative tool for pharmacological and kinetic studies of hepatic functions with small cell numbers.

Expression of drug metabolizing enzymes in hepatocyte-like cells derived from human embryonic stem cells.

Human embryonic stem cells (hESC) offer a potential unlimited source for functional human hepatocytes, since they can differentiate into hepatocyte-like cells displaying a characteristic hepatic morphology and expressing several hepatic markers. Such cells could be used for, e.g. studies of drug metabolism and hepatotoxicity, which however would require a significant expression of drug metabolising enzymes. Thus, we have investigated the expression of cytochrome P450s (CYPs), UDP-glucuronosyltransferases (UGTs), drug transporters, transcription factors and other liver specific genes in hepatocyte-like cells derived from hESC using a simple direct differentiation protocol. The mRNA and protein expression of several important CYPs were determined using low density arrays, real time PCR and Western blotting. Significant CYP expression on the mRNA level was detected in hepatocyte-like cells derived from one out of two different hESC lines tested, which was much higher than in undifferentiated hESC and generally higher than in HepG2 cells. CYP1A2, CYP3A4/7 and low levels of CYP1A1 and CYP2C8/9/19 protein were detected in both lines. The mRNAs for a variety of CYPs and liver specific factors were shown to be inducible in both cell lines, and this was reflected in induced levels of CYP1A2 and CYP3A4/7 protein. This first report on expression of all major CYPs in hepatocyte-like cells derived from hESC represents an important step towards functional hepatocytes, but efforts to further differentiate the cells using optimized protocols are needed before they exhibit similar levels of drug metabolizing enzymes as primary human hepatocytes and liver.

Glutathione transferases in hepatocyte-like cells derived from human embryonic stem cells.

Human embryonic stem cells (hESCs) offer a potential unlimited source for functional human hepatocytes, since hESCs can differentiate into hepatocyte-like cells displaying a characteristic hepatic morphology and expressing several hepatic markers. These hepatocyte-like cells could be used in various human in vitro hepatocyte assays, e.g. as a test system for studying drug metabolism and drug-induced hepatotoxicity. Since the toxic effect of a compound is commonly dependent on biotransformation into metabolites, the presence of drug metabolising enzymes in potential test systems must be evaluated. We have investigated the presence of glutathione transferases (GSTs) in hepatocyte-like cells by immunocytochemistry and Western blotting. Results show that these cells have high levels of GSTA1-1, whereas GSTP1-1 is not present in most cases. GSTM1-1 is detected by immunocytochemistry but not by Western blotting. In addition, GST activity is detected in hepatocyte-like cells at levels comparable to human hepatocytes. These results indicate that the hepatocyte-like cells have characteristics that closely resemble those of human adult hepatocytes.

Insulin-like growth factor type 1 prevents hyperglycemia-induced uncoupling protein 3 down-regulation and oxidative stress.

Uncoupling proteins (UCPs) have been reported to decrease the mitochondrial production of reactive oxygen species (ROS) by lowering the mitochondrial inner membrane potential (MMP). We have previously shown that UCP3 expression is positively regulated by insulin-like growth factor-1 (IGF-1). The aim of this study was to investigate the role of UCPs in IGF-1-mediated protection from hyperglycemia-induced oxidative stress and neurodegeneration. Human neuroblastoma SH-SY5Y cells were differentiated with retinoic acid for 6 days, after which exposure to 8, 30, or 60 mM glucose with or without 10 nM IGF-1 was started. After 48-72 hr, the number of neurites per cell, UCP3 protein expression, MMP, and intracellular levels of ROS and total glutathione were examined. These studies showed that glucose concentration-dependently reduced the number of neurites per cell, with a 50% reduction at 60 mM. In parallel, the UCP3 protein expression was down-regulated, and the MMP was raised 3.5-fold, compared with those in cells incubated with 8 mM glucose. Also, the ROS levels were increased, showing a twofold maximum at 60 mM glucose. This was accompanied by a twofold elevation of total glutathione levels, confirming an altered cellular redox state. IGF-1 treatment prevented the glucose-induced neurite degeneration and UCP3 down-regulation. Furthermore, the MMP and the intracellular levels of ROS and glutathione were normalized to those of control cells. These data indicate that IGF-1 may protect from hyperglycemia-induced oxidative stress and neuronal injuries by regulating MMP, possibly by the involvement of UCP3.

Visualization of the compartmentalization of glutathione and protein-glutathione mixed disulfides in cultured cells.

Fluorescence microscopy of A549 cells stained with a glutathione (L-gamma-glutamyl-L-cysteinylglycine, GSH)-specific polyclonal antibody displayed uniform staining of the peri-nuclear cytosol, with the nuclear region apparently lacking GSH staining. This discontinuous staining was confirmed in other cell types and also corroborated in A549 cells stained with the thiol-reactive dye mercury orange. The selectivity of antibody binding was confirmed by buthionine sulfoximine (BSO)-dependent inhibition of GSH synthesis. However, confocal visualization of antibody-stained A549 cells in the z-plane revealed the majority of the peri-nuclear staining intensity in the upper half of the cell to be associated with mitochondria, as confirmed by double staining for cytochrome oxidase. Integration of the confocal signals from the nuclear and cytosolic regions halfway down the z-plane showed that the GSH concentrations of these compartments are close to equilibrium. Confirmation of the relatively high levels of mitochondrial glutathione was provided in cells treated with BSO and visualized in z-section, revealing the mitochondrial GSH content of these cells to be well preserved in apposition to near-complete depletion of cytosolic/nuclear GSH. Localized gradients within the cytosolic compartment were also visible, particularly in the z-plane. The antibody also provided initial visualization of the compartmentalization of protein-GSH mixed disulfides formed in A549 cells exposed to diamide. Discontinuous staining was again evident, with heavy staining in membrane blebs and in the nuclear region. Using FACS analysis of anti-GSH antibody-stained Jurkat T lymphocytes, we also demonstrated population variations in the cellular compliment of GSH and protein-GSH mixed disulfides, formed in response to diamide. In addition, we showed cell-cycle variation in GSH content of the cells, with the highest levels of GSH associated with the G2/M mitotic phase of the cell cycle, using double staining with propidium iodide. Similar FACS analyses performed in isolated mitochondria presented a considerable variation in GSH content within mitochondria of uniform granularity from the same preparation.