Improving preclinical to clinical translation in Alzheimer's disease research

Abstract

Introduction: Preclinical testing in animal models is a critical component of the drug discovery and development process. While hundreds of interventions have demonstrated preclinical efficacy for ameliorating cognitive impairments in animal models, none have confirmed efficacy in Alzheimer's disease (AD) clinical trials. Critically this lack of translation to the clinic points in part to issues with the animal models, the preclinical assays used, and lack of scientific rigor and reproducibility during execution. In an effort to improve this translation, the Preclinical Testing Core (PTC) of the Model Organism Development and Evaluation for Late-onset AD (MODEL-AD) consortium has established a rigorous screening strategy with go/no-go decision points that permits unbiased assessments of therapeutic agents.

Methods: An initial screen evaluates drug stability, formulation, and pharmacokinetics (PK) to confirm appreciable brain exposure in the disease model at the pathologically relevant ages, followed by pharmacodynamics (PD) and predictive PK/PD modeling to inform the dose regimen for long-term studies. The secondary screen evaluates target engagement and disease modifying activity using non-invasive positron emission tomography/magnetic resonance imaging (PET/MRI). Provided the compound meets its "go" criteria for these endpoints, evaluation for efficacy on behavioral endpoints are conducted.

Results: Validation of this pipeline using tool compounds revealed the importance of critical quality control (QC) steps that researchers need to be aware of when executing preclinical studies. These include confirmation of the active pharmaceutical ingredient and at the precise concentration expected; and an experimental design that is well powered and in line with the Animal Research Reporting of In vivo Experiments (ARRIVE) guidelines.

Discussion: Taken together our experience executing a rigorous screening strategy with QC checkpoints provides insight to the challenges of conducting translational studies in animal models. The PTC pipeline is a National Institute on Aging (NIA)-supported resource accessible to the research community for investigators to nominate compounds for testing (https://stopadportal.synapse.org/), and these resources will ultimately enable better translational studies to be conducted.

Keywords: Alzheimer's disease; drug screening; mouse models; preclinical testing; translational approaches.

FIGURE 1

The Model Organism Development for Late Onset Alzheimer's Disease (MODEL‐AD) Preclinical Testing Core (PTC) Drug Screening pipeline. The PTC strategy includes a primary screen to determine: drug conformation of active pharmaceutical ingredient; formulation and drug stability; in vivo pharmacokinetics (PK), and target tissue concentrations in models at disease‐relevant ages. A secondary screen evaluates target disease modifying activity using non‐invasive positron emission tomography/magnetic resonance imaging as a pharmacodynamics (PD) readout matched to known disease pathology in the model. Mouse models are best matched to mechanism of action of compound being evaluated relative to model disease trajectory and pathophysiology. Compounds demonstrating positive PD effects in the secondary screen are further interrogated via a tertiary screen of functional assays that assess the compound's ability to normalize a disease‐related phenotype in cognition and neurophysiological tests, as well as a therapeutic index relative to any adverse effects. The final component of the PTC screen includes confirmatory pharmacokinetics, genotyping quality control, and post treatment transcriptomics. The PTC pipeline is a National Institute on Aging‐funded resource accessible to the research community via the Screening the Optimal Pharmaceutical for Alzheimer's Disease (STOP‐AD) program (https://stopadportal.synapse.org)

FIGURE 2

Validation of the active pharmaceutical ingredient of verubecestat. Chromatogram of standard verubecestat (A), catalog S8564, and MK‐2206 (B) the internal standard injected to liquid chromatography‐mass spectrometry (LC/MS/MS) system. The filled peak is the analyte of interest. Chromatogram of custom batch active pharmaceutical ingredient (API) verubecestat (C), catalog S8564, and MK‐2206 (D) the internal standard injected to LC/MS/MS system. The filled peak is the analyte of interest. Chromatogram of standard verubecestat (E) at retention time 8.953 minutes, and custom batch API verubecestat (F) at retention time 9.666 minutes determined not to be the correct API for verubecestat, injected to liquid chromatography/ultraviolet (LC/UV) system