Reproducing human and cross-species drug toxicities using a Liver-Chip

Nonclinical rodent and nonrodent toxicity models used to support clinical trials of candidate drugs may produce discordant results or fail to predict complications in humans, contributing to drug failures in the clinic. Here, we applied microengineered Organs-on-Chips technology to design a rat, dog, and human Liver-Chip containing species-specific primary hepatocytes interfaced with liver sinusoidal endothelial cells, with or without Kupffer cells and hepatic stellate cells, cultured under physiological fluid flow. The Liver-Chip detected diverse phenotypes of liver toxicity, including hepatocellular injury, steatosis, cholestasis, and fibrosis, and species-specific toxicities when treated with tool compounds. A multispecies Liver-Chip may provide a useful platform for prediction of liver toxicity and inform human relevance of liver toxicities detected in animal studies to better determine safety and human risk.

Hepatocyte-Derived Exosomes Promote Liver Immune Tolerance: Possible Implications for Idiosyncratic Drug-Induced Liver Injury

Most idiosyncratic drug-induced liver injury appears to result from an adaptive immune attack on the liver. Recent evidence suggests that the T-cell response may be facilitated by the loss of immune tolerance. In this study, we explored the hypothesis that constitutively released hepatocyte-derived exosomes (HDE) are important for maintaining normal liver immune tolerance. Exosomes were isolated from the conditioned medium of primary human hepatocytes via polymer precipitation. Mock controls were prepared by processing fresh medium that was not hepatocyte exposed with precipitation reagent. THP-1 monocytes were then treated with HDE or an equivalent volume of mock control for 24 h, followed by a 6-h stimulation with LPS. HDE exposure resulted in a significant decrease in the LPS-induced media levels of interleukin-1β and interleukin-8. Gene expression profiling performed in THP-1 cells just prior to LPS-induced stimulation identified a significant decrease among genes associated with innate immune response. MicroRNA (miRNA) profiling was performed on the HDE to identify exosome contents that may drive immune suppression. Many of the predicted mRNA target genes for the most abundant microRNAs in HDE were among the differentially expressed genes in THP-1 cells. Taken together, our data suggest that HDE play a role in maintaining normal liver immune tolerance. Future experiments will explore the possibility that drugs causing idiosyncratic liver injury promote the loss of homeostatic HDE signaling.

Liver microphysiological systems development guidelines for safety risk assessment in the pharmaceutical industry

The liver is critical to consider during drug development because of its central role in the handling of xenobiotics, a process which often leads to localized and/or downstream tissue injury. Our ability to predict human clinical safety outcomes with animal testing is limited due to species differences in drug metabolism and disposition, while traditional human in vitro liver models often lack the necessary in vivo physiological fidelity. To address this, increasing numbers of liver microphysiological systems (MPS) are being developed, however the inconsistency in their optimization and characterization often leads to models that do not possess critical levels of baseline performance that is required for many pharmaceutical industry applications. Herein we provide a guidance on best approaches to benchmark liver MPS based on 3 stages of characterization that includes key performance metrics and a 20 compound safety test set. Additionally, we give an overview of frequently used liver injury safety assays, describe the ideal MPS model, and provide a perspective on currently best suited MPS contexts of use. This pharmaceutical industry guidance has been written to help MPS developers and end users identify what could be the most valuable models for safety risk assessment.

Organ-on-Chip Recapitulates Thrombosis Induced by an anti-CD154 Monoclonal Antibody: Translational Potential of Advanced Microengineered Systems

Clinical development of Hu5c8, a monoclonal antibody against CD40L intended for treatment of autoimmune disorders, was terminated due to unexpected thrombotic complications. These life-threatening side effects were not discovered during preclinical testing due to the lack of predictive models. In the present study, we describe the development of a microengineered system lined by human endothelium perfused with human whole blood, a "Vessel-Chip." The Vessel-Chip allowed us to evaluate key parameters in thrombosis, such as endothelial activation, platelet adhesion, platelet aggregation, fibrin clot formation, and thrombin anti-thrombin complexes in the Chip-effluent in response to Hu5c8 in the presence of soluble CD40L. Importantly, the observed prothrombotic effects were not observed with Hu5c8-IgG2σ designed with an Fc domain that does not bind the FcγRIIa receptor, suggesting that this approach may have a low potential risk for thrombosis. Our results demonstrate the translational potential of Organs-on-Chips, as advanced microengineered systems to better predict human response.

Assessment of whole blood thrombosis in a microfluidic device lined by fixed human endothelium

The vascular endothelium and shear stress are critical determinants of physiological hemostasis and platelet function in vivo, yet current diagnostic and monitoring devices do not fully incorporate endothelial function under flow in their assessment and, therefore, they can be unreliable and inaccurate. It is challenging to include the endothelium in assays for clinical laboratories or point-of-care settings because living cell cultures are not sufficiently robust. Here, we describe a microfluidic device that is lined by a human endothelium that is chemically fixed, but still retains its ability to modulate hemostasis under continuous flow in vitro even after few days of storage. This device lined with a fixed endothelium supports formation of platelet-rich thrombi in the presence of physiological shear, similar to a living arterial vessel. We demonstrate the potential clinical value of this device by showing that thrombus formation and platelet function can be measured within minutes using a small volume (0.5 mL) of whole blood taken from subjects receiving antiplatelet medications. The inclusion of a fixed endothelial microvessel will lead to biomimetic analytical devices that can potentially be used for diagnostics and point-of-care applications.

Primary Human Lung Alveolus-on-a-chip Model of Intravascular Thrombosis for Assessment of Therapeutics

Pulmonary thrombosis is a significant cause of patient mortality; however, there are no effective in vitro models of thrombi formation in human lung microvessels that could also assess therapeutics and toxicology of antithrombotic drugs. Here, we show that a microfluidic lung alveolus-on-a-chip lined by human primary alveolar epithelium interfaced with endothelium and cultured under flowing whole blood can be used to perform quantitative analysis of organ-level contributions to inflammation-induced thrombosis. This microfluidic chip recapitulates in vivo responses, including platelet-endothelial dynamics and revealed that lipopolysaccharide (LPS) endotoxin indirectly stimulates intravascular thrombosis by activating the alveolar epithelium, rather than acting directly on endothelium. This model is also used to analyze inhibition of endothelial activation and thrombosis due to a protease activated receptor-1 (PAR-1) antagonist, demonstrating its ability to dissect complex responses and identify antithrombotic therapeutics. Thus, this methodology offers a new approach to study human pathophysiology of pulmonary thrombosis and advance drug development.

4-Methyl-6,7-dihydro-4H-triazolo[4,5-c]pyridine-Based P2X7 Receptor Antagonists: Optimization of Pharmacokinetic Properties Leading to the Identification of a Clinical Candidate

The synthesis and preclinical characterization of novel 4-(R)-methyl-6,7-dihydro-4H-triazolo[4,5-c]pyridines that are potent and selective brain penetrant P2X7 antagonists are described. Optimization efforts based on previously disclosed unsubstituted 6,7-dihydro-4H-triazolo[4,5-c]pyridines, methyl substituted 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyrazines, and several other series lead to the identification of a series of 4-(R)-methyl-6,7-dihydro-4H-triazolo[4,5-c]pyridines that are selective P2X7 antagonists with potency at the rodent and human P2X7 ion channels. These novel P2X7 antagonists have suitable physicochemical properties, and several analogs have an excellent pharmacokinetic profile, good partitioning into the CNS and show robust in vivo target engagement after oral dosing. Improvements in metabolic stability led to the identification of JNJ-54175446 (14) as a candidate for clinical development. The drug discovery efforts and strategies that resulted in the identification of the clinical candidate are described herein.

Regulatory Forum Opinion Piece*: Use and Utility of Animal Models of Disease for Nonclinical Safety Assessment: A Pharmaceutical Industry Survey

An Innovation and Quality (IQ) Consortium focus group conducted a cross-company survey to evaluate current practices and perceptions around the use of animal models of disease (AMDs) in nonclinical safety assessment of molecules in clinical development. The IQ Consortium group is an organization of pharmaceutical and biotechnology companies with the mission of advancing science and technology. The survey queried the utilization of AMDs during drug discovery in which drug candidates are evaluated in efficacy models and limited short-duration non-Good Laboratory Practices (GLP) toxicology testing and during drug development in which drug candidates are evaluated in GLP toxicology studies. The survey determined that the majority of companies used AMDs during drug discovery primarily as a means for proactively assessing potential nonclinical safety issues prior to the conduct of toxicology studies, followed closely by the use of AMDs to better understand toxicities associated with exaggerated pharmacology in traditional toxicology models or to derisk issues when the target is only expressed in the disease state. In contrast, the survey results indicated that the use of AMDs in development is infrequent, being used primarily to investigate nonclinical safety issues associated with targets expressed only in disease states and/or in response to requests from global regulatory authorities.

Abstract 342: Analysis of Mechanism of a Novel Drug Candidate using an Organ-level Functional Microdevice that Reconstitutes Human Pulmonary Thrombosis

Pulmonary microvascular thrombosis is a catastrophic medical condition and yet, it is very difficult to predict response and study mechanism of action of potential drug candidates to humans. This is partly so because currently available in vitro assays do not recapitulate physiologically-relevant forces and animal models can also be very complex, making it impossible to analyze intercellular signaling within the lung that occurs under coagulation or drug administration. We designed a model of lung thrombosis in which human primary alveolar and endothelial cells are co-cultured and maintained up to 2 weeks. The device consists of a top chamber seeded with human alveolar epithelial cells (AE) and a lower chamber seeded with endothelial cells, separated by a porous matrix-coated membrane. Whole blood was perfused at a physiological shear stress through the vascular channel and clots were visualized in real-time. When healthy cells were cultured, no intravascular blood clotting was observed, even when lipopolysaccharide (LPS) endotoxin was administered. In contrast, when LPS was added to the AE channel, it caused a significant increase in platelet adhesion at the endothelium, demonstrating that the presence of alveolar epithelium is critical to LPS-induced intravascular thrombosis in vitro . We evaluated this device by analyzing a novel protease activator receptor-1 (PAR1) antithrombotic compound, termed parmodulin 2 (PM2). When the endothelium was cultured along with PM2 under the condition of LPS stimulated AE, we found inhibition of clotting, demonstrating the therapeutic effect of PM2 in the presence of epithelial-endothelial-blood cell signaling. Finally, to test if PM2 performs the therapeutic function of Activated Protein C (APC) that has been reported to stimulate its cytosolic effects via the β-arrestin pathway, we knocked down β-arrestin in the endothelium and analyzed clot formation again. We found that clotting reoccurred in vascular channel, thus showing that PM2 acts like an APC-like drug candidate. In conclusion, the lung alveolus-on-a-chip reconstitutes organ-level responses to blood clotting and may offer a valuable platform for drug development by allowing to dissect contributions of various cells in their mechanism of action.

A role for protein kinase C-delta in the regulation of ornithine decarboxylase expression by oxidative stress

The expression of genes that regulate cell growth, such as ornithine decarboxylase (ODC), can be modulated by oxidant tumor promoters. Treatment of murine papilloma PE cells with H2O2 led to a transient induction of ODC enzyme activity, which could be blocked by calphostin, a nonspecific inhibitor of protein kinase C (PKC). Peak activity (11-fold) occurred 5-6 h after treatment, followed by a rapid decline. The increase in ODC activity was associated with an elevation of both ODC mRNA (3-fold) and protein (7-fold). Direct involvement of PKC in the regulation of ODC by oxidants was determined by stable transfection of PE cells with a dominant-negative PKC-delta mutant. PKC-delta activity was completely inhibited in response to H2O2 in cells overexpressing mutant PKC-delta compared with cells transfected with a blank plasmid. Induction of ODC mRNA, protein, and activity was also completely inhibited in cells expressing the PKC-delta mutant after H2O2 treatment. Activation of an ODC promoter-luciferase reporter construct by H2O2 was attenuated in mutant cells compared with control cells, further confirming that ODC is regulated transcriptionally by PKC-delta. However, fold-increases in ODC mRNA and protein were much less than the increase in activity, suggesting that ODC may also undergo posttranscriptional regulation in the presence of oxidants. Taken together, these studies provide new insight into the regulation of ODC by oxidants and suggest that PKC-delta may play a critical role in this regulation.

Chemoprotective 3H-1,2-dithiole-3-thione induces antioxidant genes in vivo

Several 1,2-dithiole-3-thiones are potent inhibitors of chemical-induced tumors in multiple tissues. Chemoprotection by 1, 2-dithiole-3-thiones has been associated with induction of detoxication enzymes, although several studies suggest that additional mechanisms may be involved. In this study, we examined the induction of hepatic antioxidant genes in rats treated with 3H-1, 2-dithiole-3-thione (D3T). After a 24 h D3T treatment, a 2.4-fold increase in catalase mRNA was observed, which was accompanied by a 1. 5-fold increase in catalase protein expression and a 2.3-fold increase in catalase activity. D3T also mediated 2.9-, 5.9-, and 3. 7-fold increases in the 1.0, 3.0, and 4.0 kb mRNA species of manganese superoxide dismutase (MnSOD), respectively. The induction of MnSOD mRNA by D3T was coincident with 1.7-fold and 4.6-fold increases in MnSOD protein and enzyme activity, respectively. Induction of gamma-glutamylcysteine synthetase mRNA by D3T was accompanied by an increase in glutathione levels. Nuclear run-on assays provided evidence that D3T enhances the transcription rate from MnSOD, catalase, and gamma-glutamylcysteine synthetase. In support of this view, D3T also activated an MnSOD promoter-reporter construct in transiently transfected HepG2 cells. In light of observations that antioxidant enzyme regulation may be altered during carcinogenesis, induction of these genes could provide a potentially important mechanism of action of chemoprotective 1, 2-dithiole-3-thiones.

Cysteine S-conjugates activate transcription factor NF-kappa B in cultured renal epithelial cells

Activation of NF-kappa B by the nephrotoxic and cytotoxic cysteine S-conjugate S-(1,2-dichlorovinyl)-L-cysteine (DCVC) was investigated in porcine kidney-derived LLC-PK1 cells. DCVC induced binding of nuclear proteins to an NF-kappa B consensus oligonucleotide from the immunoglobulin kappa-light chain enhancer region, as determined by electrophoretic mobility shift assays, and the activated proteins were identified as the p50/RelA heterodimeric complex of NF-kappa B. Transient transfection experiments with a kappa B-controlled luciferase reporter construct showed that the NF-kappa B complex activated by DCVC was transcriptionally active. NF-kappa B transactivation was blocked by inhibition of DCVC bioactivation with the cysteine conjugate beta-lyase inhibitor (aminooxy)acetic acid, by the antioxidants N,N'-diphenyl-p-phenylenediamine and N-acetyl-L-cysteine, and by the protein kinase inhibitor staurosporine. The cysteine S-conjugates S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine and S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine also activated NF-kappa B in LLC-PK1 cells. These results demonstrate that the NF-kappa B pathway is present in LLC-PK1 cells and is induced by cysteine S-conjugates. Inhibition of DCVC-induced transactivation of NF-kappa B by staurosporine and by antioxidants indicate roles for protein kinases and oxidative stress in the NF-kappa B pathway.

Stable transfection of LLC-PK1 cells with human microsomal glutathione S-transferase gene increases haloalkene glutathione S-conjugate formation and cytotoxicity

Nephrotoxic haloalkenes undergo glutathione- and cysteine conjugate beta-lyase-dependent bioactivation, and glutathione S-conjugate formation with haloalkenes as substrates is preferentially catalyzed by the hepatic microsomal glutathione S-transferase (mGST). Porcine kidney-derived LLC-PK1 cells, which are competent to bioactivate glutathione and cysteine S-conjugates of haloalkenes, show low mGST activity. Stable transfection of LLC-PK1 cells with the gene encoding mGST would be expected to increase glutathione S-conjugate formation and, therefore, to increase haloalkene cytotoxicity. Transfection of LLC-PK1 cells with human mGST genes resulted in increased expression of mGST protein in microsomal fractions, in increased glutathione S-conjugate formation with hexachloro-1,3-butadiene and 1-chloro-2,4-dinitrobenzene as the substrates, and in increased cytotoxicity of hexachloro-1,3-butadiene. In addition, transfection with mGST gene also increased the activity of cytosolic glutathione S-transferases.

Immunolocalization of microsomal glutathione S-transferase in rat tissues

Distribution of microsomal glutathione transferase (mGST) protein in rat tissues was investigated by immunohistochemistry. Studies on the localization of mGST are of interest because of its involvement in the detoxication and bioactivation of xenobiotics. mGST antigen was detected in the cytoplasm of some hepatocytes and in bile ducts. In kidney, focal staining of mGST was observed in distal tubules and collecting ducts. Cerebral cortical and cerebellar Purkinje neurons showed good immunoreactivity, and nuclear staining was observed in the choroid plexus. The antigen was detected in epithelial cells of respiratory bronchioles and in the crypt cells of the duodenum. Exocrine cells of the pancreas stained for mGST. Nuclear immunostaining for this protein was observed in primary spermatocytes. mGST antigen was detected in the cytoplasm of the adrenal medulla as a granular stain. Leydig and Sertoli cells in testis also stained for the antigen. Distribution of mGST protein differs from that observed with cytosolic transferases and may be important in determining cell-selective susceptibility to xenobiotics.