Brian Knight

Methapyrilene Toxicity: Anchorage of Pathologic Observations to Gene Expression Alterations

Methapyrilene (MP) exposure of animals can result in an array of adverse pathological responses including hepatotoxicity. This study investigates gene expression and histopathological alterations in response to MP treatment in order to 1) utilize computational approaches to classify samples derived from livers of MP treated rats based on severity of toxicity incurred in the corresponding tissue, 2) to phenotypically anchor gene expression patterns, and 3) to gain insight into mechanism(s) of methapyrilene hepatotoxicity. Large-scale differential gene expression levels associated with the exposure of male Sprague—Dawley rats to the rodent hepatic carcinogen MP for 1, 3, or 7 days after daily dosage with 10 or 100 mg/kg/day were monitored. Hierarchical clustering and principal component analysis were successful in classifying samples in agreement with microscopic observations and revealed low-dose effects that were not observed histopathologically. Data from cDNA microarray analysis corroborated observed histopathological alterations such as hepatocellular necrosis, bile duct hyperplasia, microvesicular vacuolization, and portal inflammation observed in the livers of MP exposed rats and provided insight into the role of specific genes in the studied toxicological processes.

Evaluation of Phosphatidylinositol-4-Kinase IIIα as a Hepatitis C Virus Drug Target

ABSTRACT Phosphatidylinositol-4-kinase IIIα (PI4KIIIα) is an essential host cell factor for hepatitis C virus (HCV) replication. An N-terminally truncated 130-kDa form was used to reconstitute an in vitro biochemical lipid kinase assay that was optimized for small-molecule compound screening and identified potent and specific inhibitors. Cell culture studies with PI4KIIIα inhibitors demonstrated that the kinase activity was essential for HCV RNA replication. Two PI4KIIIα inhibitors were used to select cell lines harboring HCV replicon mutants with a 20-fold loss in sensitivity to the compounds. Reverse genetic mapping isolated an NS4B-NS5A segment that rescued HCV RNA replication in PIK4IIIα-deficient cells. HCV RNA replication occurs on specialized membranous webs, and this study with PIK4IIIα inhibitor-resistant mutants provides a genetic link between NS4B/NS5A functions and PI4-phosphate lipid metabolism. A comprehensive assessment of PI4KIIIα as a drug target included its evaluation for pharmacologic intervention in vivo through conditional transgenic murine lines that mimic target-specific inhibition in adult mice. Homozygotes that induce a knockout of the kinase domain or knock in a single amino acid substitution, kinase-defective PI4KIIIα, displayed a lethal phenotype with a fairly widespread mucosal epithelial degeneration of the gastrointestinal tract. This essential host physiologic role raises doubt about the pursuit of PI4KIIIα inhibitors for treatment of chronic HCV infection.

Scientific and Regulatory Policy Committee (SRPC) Paper Validation of Digital Pathology Systems in the Regulated Nonclinical Environment

Digital Pathology Systems (DPS) are dynamic, image-based computer systems that enable the acquisition, management, and interpretation of pathology information generated from digitized glass slides. This article provides a roadmap for (1) qualification of a whole slide scanner (WSS) during a validation project, (2) validation of software required to generate the whole slide image (WSI), and (3) an introduction to visual digital image evaluation and image analysis. It describes a validation approach that can be utilized when validating a DPS. It is not the intent of this article to provide guidance on when validation of DPS is required. Rather, the article focuses on technical aspects of validation of the WSS system (WSS, IT infrastructure, and associated software) portion of a DPS and covers the processes of setting up the WSS for scanning a glass slide through saving a WSI on a server. Validation of a computerized system, such as a DPS, for use in a regulated nonclinical environment is governed by Code of Federal Regulations (CFR) Title 21 part 11: Electronic Records; Electronic Signature and predicate rules associated with Good Laboratory Practices documents including 21 CFR part 58. Similar regulation and predicate rules apply in the European Union and Japan.

A Twenty-Eight-Day Mechanistic Time Course Study in the Rhesus Monkey with Hepatitis C Virus Protease Inhibitor BILN 2061

BILN 2061 is a potent, reversible inhibitor of hepatitis C virus NS3/NS4A serine protease. Early clinical proof of principle with the drug was offset by the results of subsequent safety studies in Rhesus monkeys revealing cardiotoxicity that featured myocardial vacuolation corresponding to mitochondrial swelling. Here we describe an investigation into the nature, onset, and reversibility of the lesion, and an assessment of potentially predictive biomarkers for the change. Rhesus monkeys were orally administered 1,000 mg/kg/day BILN 2061 and either necropsied after one, three, fourteen, or twenty-eight doses or afforded a ten-week recovery period. The results of electrocardiographic and plasma troponin I and T measurements were unaffected by BILN 2061, but cardiac myocytic vacuolation, correlated with mitochondrial swelling, was observed after three or more doses. Echocardiographic traces obtained after twenty-eight consecutive days of dosing revealed two animals with diminished left ventricular cardiac ejection fraction. One animal was immediately necropsied and exhibited marked cardiotoxicity. The other was afforded a ten-week treatment-free period during which the left ventricular ejection fraction returned to normal. All recovery animal hearts were microscopically and ultrastructurally normal. High-dose BILN 2061 cardiotoxicity in Rhesus monkeys appeared early in the treatment regimen and exhibited reversibility. A reliable biomarker has yet to be identified.

Nonclinical Safety of the Sodium-Glucose Cotransporter 2 Inhibitor Empagliflozin

Empagliflozin, a selective inhibitor of the renal tubular sodium-glucose cotransporter 2, was developed for treatment of type 2 diabetes mellitus. Nonclinical safety of empagliflozin was studied in a battery of tests to support global market authorization. Safety pharmacology studies indicated no effect of empagliflozin on measures of respiratory or central nervous system function in rats or cardiovascular safety in telemeterized dogs. In CD-1 mouse, Wistar Han rat, or beagle dogs up to 13, 26, or 52 weeks of treatment, respectively, empagliflozin exhibited a toxicity profile consistent with secondary supratherapeutic pharmacology related to glucose loss and included decreased body weight and body fat, increased food consumption, diarrhea, dehydration, decreased serum glucose and increases in other serum parameters reflective of increased protein catabolism, gluconeogenesis, and electrolyte imbalances, and urinary changes such as polyuria and glucosuria. Microscopic changes were consistently observed in kidney and included tubular nephropathy and interstitial nephritis (dog), renal mineralization (rat) and tubular epithelial cell karyomegaly, single cell necrosis, cystic hyperplasia, and hypertrophy (mouse). Empagliflozin was not genotoxic. Empagliflozin was not carcinogenic in female mice or female rats. Renal adenoma and carcinoma were induced in male mice only at exposures 45 times the maximum clinical dose. These tumors were associated with a spectrum of nonneoplastic changes suggestive of a nongenotoxic, cytotoxic, and cellular proliferation-driven mechanism. In male rats, testicular interstitial cell tumors and hemangiomas of the mesenteric lymph node were observed; both tumors are common in rats and are unlikely to be relevant to humans. These studies demonstrate the nonclinical safety of empagliflozin.

Assessment of Inhibin B as a Biomarker of Testicular Injury Following Administration of Carbendazim, Cetrorelix, or 1,2-Dibromo-3-Chloropropane in Wistar Han Rats

Although histopathology is considered the gold standard for assessing testicular toxicity in the nonclinical setting, identification of noninvasive biomarkers for testicular injury are desirable to improve safety monitoring capabilities for clinical trials. Inhibin B has been investigated as a noninvasive biomarker for testicular toxicity. This study investigates the correlation of Inhibin B in Wistar Han rats with the onset and reversibility of testicular histopathology from classical testicular toxicants carbendazim, cetrorelix acetate (CTX), and 1,2-dibromo-3-chloropropane (DBCP). The dose regimen included Interim (day 8), Drug (day 29), and nondosing Recovery (day 58) Phases. Inhibin B was not effective at predicting the onset of carbendazim- or CTX-mediated testicular pathology in rats. Inhibin B was reduced by DBCP administration at the end of the Drug Phase only, acting as a leading indicator of the onset of testicular toxicity before the onset of germ cell depletion. However, since Inhibin B was only decreased at the end of the Dosing Phase and not at the Recovery Phase, when the onset of testicular pathology occurred, it is unclear if monitoring Inhibin B would provide sufficient advanced warning for the onset of testicular pathology. Furthermore, follicle stimulating hormone was decreased following CTX and DBCP administration in the Interim Phase and CTX in the Drug Phase. Inhibin B has limited predictive capacity as a leading testicular biomarker in rats.

Genomic-Derived Markers for Early Detection of Calcineurin Inhibitor Immunosuppressant–Mediated Nephrotoxicity

Calcineurin inhibitor (CI) therapy has been associated with chronic nephrotoxicity, which limits its long-term utility for suppression of allograft rejection. In order to understand the mechanisms of the toxicity, we analyzed gene expression changes that underlie the development of CI immunosuppressant-mediated nephrotoxicity in male Sprague-Dawley rats dosed daily with cyclosporine (CsA; 2.5 or 25 mg/kg/day), FK506 (0.6 or 6 mg/kg/day), or rapamycin (1 or 10 mg/kg/day) for 1, 7, 14, or 28 days. A significant increase in blood urea nitrogen was observed in animals treated with CsA (high) or FK506 (high) for 14 and 28 days. Histopathological examination revealed tubular basophilia and mineralization in animals given CsA (high) or FK506 (low and high). We identified a group of genes whose expression in rat kidney is correlated with CI-induced kidney injury. Among these genes are two genes, Slc12a3 and kidney-specific Wnk1 (KS-Wnk1), that are known to be involved in sodium transport in the distal nephrons and could potentially be involved in the mechanism of CI-induced nephrotoxicity. The downregulation of NCC (the Na-Cl cotransporter coded by Slc12a3) in rat kidney following CI treatment was confirmed by immunohistochemical staining, and the downregulation of KS-Wnk1 was confirmed by quantitative real-time-polymerase chain reaction (qRT-PCR). We hypothesize that decreased expression of Slc12a3 and KS-Wnk1 could alter the sodium chloride reabsorption in the distal tubules and contribute to the prolonged activation of the renin-angiotensin system, a demonstrated contributor to the development of CI-induced nephrotoxicity in both animal models and clinical settings. Therefore, if validated as biomarkers in humans, SLC12A3 and KS-WNK1 could potentially be useful in the early detection and reduction of CI-related nephrotoxicity in immunosuppressed transplant patients when monitoring the health of kidney xenographs in clinical practice.

An impedance-based approach using human iPSC-derived cardiomyocytes significantly improves in vitro prediction of in vivo cardiotox liabilities

&NA; Current in vitro approaches to cardiac safety testing typically focus on mechanistic ion channel testing to predict in vivo proarrhythmic potential. Outside of the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative, structural and functional cardiotoxicity related to chronic dosing effects are of great concern as these effects can impact compound attrition. Development and implementation of an in vitro cardiotoxicity screening platform that effectively identifies these liabilities early in the discovery process should reduce costly attrition and decrease preclinical development time. Impedence platforms have the potential to accurately identify structural and functional cardiotoxicity and have sufficient throughput to be included in a multi‐parametric optimization approach. Human induced pluripotent stem cell cardiomyocytes (hIPSC‐CMs) have demonstrated utility in cardiac safety and toxicity screening. The work described here leverages these advantages to assess the predictive value of data generated by two impedance platforms. The response of hIPSC‐CMs to compounds with known or predicted cardiac functional or structural toxicity was determined. The compounds elicited cardiac activities and/or effects on “macro” impedance often associated with overt structural or cellular toxicity, detachment, or hypertrophy. These assays correctly predicted in vivo cardiotox findings for 81% of the compounds tested and did not identify false positives. In addition, internal or literature Cmax values from in vivo studies correlated within 4 fold of the in vitro observations. The work presented here demonstrates the predictive power of impedance platforms with hIPSC‐CMs and provides a means toward accelerating lead candidate selection by assessing preclinical cardiac safety earlier in the drug discovery process. HighlightsAssessment of the impedance platform to predict both chronic and acute in vivo cardiotoxicity.Cardiac functional and structural cardiotoxicity was evaluated.The impedance assay predicted > 80% of known in vivo cardiotoxicity.Data supports utilization of this assay for early drug discovery cardiac safety profiling.

Graphical display of histopathology data from toxicology studies for drug discovery and development: An industry perspective.

Histopathology data comprise a critical component of pharmaceutical toxicology studies and are typically presented as finding incidence counts and severity scores per organ, and tabulated on multiple pages which can be challenging for review and aggregation of results. However, the SEND (Standard for Exchange of Nonclinical Data) standard provides a means for collecting and managing histopathology data in a uniform fashion which can allow informatics systems to archive, display and analyze data in novel ways. Various software applications have become available to convert histopathology data into graphical displays for analyses. A subgroup of the FDA-PhUSE Nonclinical Working Group conducted intra-industry surveys regarding the use of graphical displays of histopathology data. Visual cues, use-cases, the value of cross-domain and cross-study visualizations, and limitations were topics for discussion in the context of the surveys. The subgroup came to the following conclusions. Graphical displays appear advantageous as a communication tool to both pathologists and non-pathologists, and provide an efficient means for communicating pathology findings to project teams. Graphics can support hypothesis-generation which could include cross-domain interactive visualizations and/-or aggregating large datasets from multiple studies to observe and/or display patterns and trends. Incorporation of the SEND standard will provide a platform by which visualization tools will be able to aggregate, select and display information from complex and disparate datasets.

Scientific and Regulatory Policy Committee Points to Consider: Data Visualization for Clinical and Anatomic Pathologists:

Assessment and communication of toxicology data are fundamental components of the work performed by veterinary anatomic and clinical pathologists involved in toxicology research. In recent years, there has been an evolution in the number and variety of software tools designed to facilitate the evaluation and presentation of toxicity study data. A working group of the Society of Toxicologic Pathology Scientific and Regulatory Policy Committee reviewed existing and emerging visualization technologies. This Points to Consider article reviews some of the currently available data visualization options, describes the utility of different types of graphical displays, and explores potential areas of controversy and ambiguity encountered with the use of these tools.