Reliable And Reproducible Evaluation Of Therapeutic Interventions In The MDX Mouse Model Of DMD

Abstract

PURPOSE: Preclinical efficacy evaluation in mouse models of human diseases is an important component of drug development. It has been reported that phase II clinical trial success rates have fallen in recent years, with a lack of efficacy being the most frequent reason for failure. Since most of the selected candidate therapeutics have gone through preclinical efficacy testing, this failure could be due to 1) the poor predictive power of disease models, 2) questionable targets, 3) lack of rigor in preclinical trial design, 4) poor control for potential bias, or 5) variable reporting standards. The quality and reproducibility of preclinical trials depend on the thoroughness of the preclinical study, including the design, execution, analysis, and reporting of the preclinical data. Here we have developed a comprehensive phenotyping system to ensure success rate of preclinical candidate evaluations for DMD. METHODS: We subjected mdx mice for following assessments at early (8 weeks) and late (12 months) stages of the disease to represent ambulatory and non-ambulatory stages of the human disease. We assessed Non-Invasive Repeated measures (Open field activity measurement, Grip strength measurement (GSM), Bodyweight, Inflammation assessed by cathepsin activity using optical imaging, and Echocardiography) and Terminal Endpoint measures (Muscle function test (in vitro force contractions), Histological evaluations, Fibrosis measurements, Serum enzymes analysis). RESULTS: Sample size/power estimates showed that EDL muscle specific force, Grip strength and % SF by echocardiography require 5, 11 and 8 mice per group at early stages of the disease and 2 mice/group for all 3 parameters at 12 months’ age. Fibrosis in the heart is less apparent at early stages and require more mice (136/group) in comparison to old age (2mice/group) Cardiac assessment showed that both ejection fraction (EF) and fractional shortening (FS) significantly decreased by 11 months of age in the mdx mice. Evaluation of inflammation in live animals showed that inflammation is more at 2 months than at 12 months. CONCLUSIONS: Our data demonstrates that the quality and reproducibility of preclinical trials depend on not only on the parameter to be analyzed but also on the stage of the disease and sample size required to meaningfully interpret the data.