The effect of angiotensin receptor neprilysin inhibitor, sacubitril/valsartan, on central nervous system amyloid-ß concentrations and clearance in the cynomolgus monkey.

Sacubitril/valsartan (LCZ696) is the first angiotensin receptor neprilysin inhibitor approved to reduce cardiovascular mortality and hospitalization in patients with heart failure with reduced ejection fraction. As neprilysin (NEP) is one of several enzymes known to degrade amyloid-ß (Aß), there is a theoretical risk of Aß accumulation following long-term NEP inhibition. The primary objective of this study was to evaluate the potential effects of sacubitril/valsartan on central nervous system clearance of Aß isoforms in cynomolgus monkeys using the sensitive Stable Isotope Labeling Kinetics (SILK™)-Aß methodology. The in vitro selectivity of valsartan, sacubitril, and its active metabolite sacubitrilat was established; sacubitrilat did not inhibit other human Aß-degrading metalloproteases. In a 2-week study, sacubitril/valsartan (50mg/kg/day) or vehicle was orally administered to female cynomolgus monkeys in conjunction with SILK™-Aß. Despite low cerebrospinal fluid (CSF) and brain penetration, CSF exposure to sacubitril was sufficient to inhibit NEP and resulted in an increase in the elimination half-life of Aß1-42 (65.3%; p=0.026), Aß1-40 (35.2%; p=0.04) and Aßtotal (29.8%; p=0.04) acutely; this returned to normal as expected with repeated dosing for 15days. CSF concentrations of newly generated Aß (AUC(0-24h)) indicated elevations in the more aggregable form Aß1-42 on day 1 (20.4%; p=0.039) and day 15 (34.7%; p=0.0003) and in shorter forms Aß1-40 (23.4%; p=0.009), Aß1-38 (64.1%; p=0.0001) and Aßtotal (50.45%; p=0.00002) on day 15. However, there were no elevations in any Aß isoforms in the brains of these monkeys on day 16. In a second study cynomolgus monkeys were administered sacubitril/valsartan (300mg/kg) or vehicle control for 39weeks; no microscopic brain changes or Aß deposition, as assessed by immunohistochemical staining, were present. Further clinical studies are planned to address the relevance of these findings.

Assessment of a nonsteroidal aromatase inhibitor, letrozole, in juvenile rats.

BACKGROUND: The timing and duration of letrozole administration was designed to encompass the majority of postnatal development in the rat with the intent of evaluating the potential for a broad range of effects but with emphasis on expected effects on skeletal maturation. METHODS: Sprague-Dawley rats were administered letrozole via oral gavage at doses of 0.003, 0.03, and 0.3 mg/kg/day beginning on postpartum day (PPD) 7 through 91 followed by a 6-week recovery period. Clinical signs, body weight, food consumption, developmental endpoints, bone, ophthalmology, behavioral assessments, clinical/anatomic pathology, toxicokinetics, and reproductive assessments were conducted. RESULTS: Growth (body weight gain and crown-to-rump length) and food consumption were increased in females at ≥0.03 mg/kg/day and decreased in males at ≥0.003 mg/kg/day. Delayed sexual maturation in both sexes and adverse effects on reproductive function occurred at all doses. Effects on bone growth and maturation were noted in both sexes at all doses. Evidence of recovery was noted for males at 0.003 mg/kg/day and females at 0.003 and 0.03 mg/kg/day upon withdrawal of treatment. Histopathological changes in the pituitary-adrenal-gonadal axis correlated with effects on reproductive function. CONCLUSIONS: The observed effects in juvenile rats were considered predictable and primarily related to the mechanism of action of letrozole upon estrogen synthesis.

Investigation of correlation among safety biomarkers in serum, histopathological examination, and toxicogenomics.

This article addresses the issue of miscorrelation between hepatic injury biomarkers and histopathological findings in the drug development context. Our studies indicate that the use of toxicogenomics can aid in the drug development decision-making process associated with such miscorrelated data. BLZ945 was developed as a Colony-Stimulating Factor 1 Receptor (CSF-1R) inhibitor. Treatment of BLZ945 in rats and monkeys increased serum alanine aminotransferase (ALT) and aspartate transaminase (AST). However, liver hypertrophy was the only histopathological liver finding in rats, and there was no change in the livers of monkeys. Longer treatment of BLZ945 in rats for 6 weeks caused up to 6-fold elevation of ALT, yet hepatocyte necrosis was not detected microscopically. Toxicogenomic profiling of liver samples demonstrated that the genes associated with early response to liver injury, apoptosis/necrosis, inflammation, oxidative stress, and metabolic enzymes were upregulated. Studies are ongoing to evaluate the mechanisms underlying BL945-induced ALT and AST elevations.

Toxicogenomics in biomarker discovery.

In the area of toxicology, the subdiscipline of toxicogenomics has emerged, which is the use of genome-scale mRNA expression profiling to monitor responses to adverse xenobiotic exposure. Toxicogenomics is being investigated for use in the triage of compounds through predicting potential toxicity, defining mechanisms of toxicity, and identifying potential biomarkers of toxicity. Whereas various approaches have been reported for the development of algorithms predictive of toxicity and for the interpretation of gene expression data for deriving mechanisms of toxicity, there are no clearly defined methods for the discovery of biomarkers using gene expression technologies. Ways in which toxicogenomics may be used for biomarker discovery include analysis of large databases of gene expression profiles followed by in silico mining of the database for differentially expressed genes; the analysis of gene expression data from preclinical studies to find differentially expressed genes that correlate with pathology (coincident biomarker) or precede pathology (leading biomarker) within a lead series; or gene expression profiling can be performed directly on the blood from preclinical studies or clinical trials to find biomarkers that can be obtained noninvasively. This chapter broadly discusses the issues and the utility of applying toxicogenomics to biomarker discovery.

Application of toxicogenomics to drug development.

The application of advanced modern biomedical and chemical research technologies in the pharmaceutical industry has led to a significant increase in the number of potential drug targets and lead candidates. Whereas the drug discovery process is enhanced significantly, the failure rate of new compounds due to toxicity remains very high. The pharmaceutical industry is setting high hopes on the new discipline of toxicogenomics to revolutionize the process of drug toxicity assessment by reducing the bottleneck of new drug candidates and minimizing late-stage developmental failures. Toxicogenomics is expected to facilitate the efficient screening of new compounds at an early stage, resulting in significant savings of time and cost associated with new drug development. In this review, a general description of the new discipline of toxicogenomics and its potential impact on the safety assessment of new drugs in the pharmaceutical industry is provided. An overview of the key issues and questions that are confronting investigators in this field today is also given as well as a prospective view of the future of this new discipline.