Jill Steidl-Nichols

Involvement of β-site APP cleaving enzyme 1 (BACE1) in amyloid precursor protein-mediated enhancement of memory and activity-dependent synaptic plasticity

The amyloid precursor protein (APP) undergoes sequential cleavages to generate various polypeptides, including the amyloid-β protein (Aβ), which forms amyloid plaques in Alzheimers disease (AD), secreted APPα (sAPPα) which enhances memory, and the APP intracellular domain (AICD), which has been implicated in the regulation of gene transcription and calcium signaling. The β-site APP cleaving enzyme 1 (BACE1) cleaves APP in an activity-dependent manner to form Aβ, AICD, and secreted APPβ. Because this neural activity was shown to diminish synaptic transmission in vitro [Kamenetz F, Tomita T, Hsieh H, Seabrook G, Borchelt D, Iwatsubo T, Sisodia S, Malinow R (2003) Neuron 37:925–937], the prevailing notion has been that this pathway diminishes synaptic function. Here we investigated the role of this pathway in vivo. We studied transgenic mice overproducing APP that do not develop AD pathology or memory deficits but instead exhibit enhanced spatial memory. We showed enhanced synaptic plasticity in the hippocampus that depends on prior synaptic activity. We found that the enhanced memory and synaptic plasticity are abolished by the ablation of one or both copies of the BACE1 gene, leading to a significant decrease in AICD but not of any other APP cleavage products. In contrast to the previously described negative effect of BACE1-mediated cleavage of APP on synaptic function in vitro, our in vivo work indicates that BACE1-mediated cleavage of APP can facilitate learning, memory, and synaptic plasticity.

Assessment of Cardiac Troponin I Responses in Nonhuman Primates during Restraint, Blood Collection, and Dosing in Preclinical Safety Studies

Limited information has been published on the use of cardiac troponin I (cTnI) as a biomarker of cardiac injury in monkeys. The purpose of these studies was to characterize the cTnI response seen in cynomolgus macaques during routine dosing and blood collection procedures typically used in preclinical safety studies and to better understand the pathogenesis of this response. We measured cTnI using two different methods, the Siemens Immulite cTnI assay and the more sensitive Siemens Troponin I-Ultra assay. We were able to demonstrate that after oral, subcutaneous, or intravenous dosing of common vehicles, as well as serial chair restraint for venipuncture blood collection, that minimal to mild transient increases in cTnI could be detected in monkeys with both assays. cTnI values typically peaked at 2, 3, 4, or 6 hr after sham dosing and returned to baseline at 22 or 24 hr. In addition, marked increases in heart rate (HR) and blood pressure (BP) occurred in monkeys during the restraint procedures, which likely initiated the cTnI release in these animals. Monkeys that were very well acclimated to the chairing procedures and had vascular access ports for blood sampling did not have marked increases in HRs and BP or increases in cTnI.

From the Cover: Evaluation of the Effects of Tanezumab, a Monoclonal Antibody Against Nerve Growth Factor, on the Sympathetic Nervous System in Adult Cynomolgus Monkeys (Macaca fascicularis): A Stereologic, Histomorphologic, and Cardiofunctional Assessment

Abstract Tanezumab, a humanized monoclonal antibody against nerve growth factor is in development for treatment of chronic pain. Three nonclinical studies assessed effects of clinically relevant and supratherapeutic doses of tanezumab on the sympathetic nervous system (SNS) of adult nonhuman primates. Study 1 evaluated potential effects of subcutaneous (SC) tanezumab (1.2 mg/kg every 8 weeks [Q8W]) on SNS in cynomolgus monkeys for 3 or 6 months and reversibility or persistence of any effects through a nondosing/recovery period. Study 2 evaluated whether neuronal cell death occurs shortly after a single SC tanezumab injection (1.2 mg/kg). Assessments for these two studies included evaluations of superior cervical and cervicothoracic ganglia for neuronal cell death and morphology. Study 3 evaluated effects of SC tanezumab (1.2 mg/kg Q8W and 30 mg/kg/week) over 6 months on sympathetic control of cardiovascular function. Tanezumab exposure was associated with stereologic changes in sympathetic ganglia, including smaller ganglion volume, and smaller average neuron size/area beginning at 2 weeks and reaching maximal levels by 1 month with no further progression through 6 months. These changes were not associated with clinical signs, completely reversed upon tanezumab withdrawal, and were not considered adverse. Tanezumab had no adverse effects on sympathetic control of cardiovascular function. These data support the conclusion that tanezumab administration for up to 6 months has no adverse effects on SNS morphology or function and does not cause neuronal cell death in adult nonhuman primates.

Validation and utility of the PhysioTel™ Digital M11 telemetry implant for cardiovascular data evaluation in cynomolgus monkeys and Beagle dogs.

INTRODUCTION The cardiovascular liability of candidate compounds can be evaluated by a number of methods including implanted telemetry, jacketed telemetry and surface lead electrocardiogram (ECG). The utility of the new PhysioTel™ Digital M11 cardiovascular telemetry implant was evaluated in monkeys and dogs. METHODS Eight monkeys and dogs (4 males and 4 females per species) were implanted with the M11 device utilizing a femoral blood pressure catheter and periosteal ECG leads. The signal quality of the ECGs was determined as a percentage of software-matched waveforms and as a percentage of signal loss during the recording periods. To investigate sensitivity for detecting changes in QT/QTc and HR/BP, moxifloxacin and doxazosin were administered to monkeys and dogs implanted with the M11 device. Additionally, histopathological evaluation of the implant site was completed. RESULTS For both monkey and dog, the percentage of recognizable waveforms was high (65% and 85%, respectively), while the average amount of signal loss was low (1% and 3%, respectively), indicating that the M11 implants delivered data of sufficient quality. In monkeys, moxifloxacin (90mg/kg) induced QT and QTc prolongation up to 22 and 12ms, respectively, while at 30mg/kg in dogs, the maximal increases in QT and QTc were 13 and 16ms, respectively. Doxazosin (1.5 and 1.0mg/kg) produced HR increases up to 35 and 29bpm with decreases in blood pressure up to -14 and -26mmHg in monkeys and dogs, respectively. The histopathological impact of the implant, catheter and biopotential leads was limited to expected minor local inflammatory changes as assessed at necropsy and with microscopic examination. DISCUSSION Based upon the results of this study, the PhysioTel™ Digital M11 is a suitable technology for assessing cardiovascular parameters in monkeys and dogs, and because of the size and limited invasiveness of the implant, is well positioned for use on toxicology studies.

Cardiac sodium channel antagonism – Translation of preclinical in vitro assays to clinical QRS prolongation

INTRODUCTION Cardiac sodium channel antagonists have historically been used to treat cardiac arrhythmias by preventing the reentry of the electrical impulse that could occur following myocardial damage. However, clinical studies have highlighted a significant increase in mortality associated with such treatment. Cardiac sodium channel antagonist activity is now seen as an off-target pharmacology that should be mitigated during the drug development process. The aim of this study was to examine the correlation between in vitro/ex vivo assays that are routinely used to measure Nav1.5 activity and determine the translatability of the individual assays to QRS prolongation in the clinic. METHODS A set of clinical compounds with known Nav1.5 activity was profiled in several in vitro/ex vivo assays (binding, membrane potential, patch clamp and the Langendorff isolated heart). Clinical data comprising compound exposure levels and changes in QRS interval were obtained from the literature. Sensitivity/specificity analysis was performed with respect to the clinical outcome. RESULTS The in vitro assays showed utility in predicting QRS prolongation in the clinic. Optimal thresholds were defined for each assay (binding: IC20; membrane potential: IC10; patch clamp: IC20) and sensitivity (69-88%) and specificity (53-84%) values were shown to be similar between assay formats. DISCUSSION The data provide clear statistical insight into the translatability of Nav1.5 antagonism data generated in vitro to potential clinical outcomes. These results improve our ability to understand the liability posed by such activity in novel development compounds at an early stage.