Background: Preclinical efficacy studies are increasingly required for orphan drug designation by FDA and EMA, and the careful design and choice of outcomes in pre-clinical studies are important in de-risking drug development programs up front of clinical trials. Despite consensus on outcomes, varying protocols and laboratory settings contribute to challenges in data reproducibility and consistency. We have contributed to the development of the TREAT-NMD standard operating procedures for mdx endpoints. Here, we assess the consistency of these outcomes over time in a specialized CRO setting.
Methods: We collected >8,000 data measures from 37 studies, spanning a period of 9 years in a CRO setting. 791 C57BL/10ScSn-Dmdmdx/J and C57BL10/ScSn (WT) mice were studied. Outcomes evaluated were motor (grip strength measures [GSM], exhaustion), functional (in vitro muscle force [EDL]), biomarker (serum creatine kinase) and histological (Picrosirius Red; diaphragm fibrosis) and bodyweights. Projects were grouped by the year conducted, and the consistency of year-to-year data compared over a 9-year time span. Outcomes were also stratified by age of mice (8-16 vs. 16-32 weeks).
Results: The most stable outcomes in both mdx and WT mice were body weight, and grip strength. More variable on a year-to-year basis were exhaustion (2- to 3-fold variation year to year; both mdx and WT), fibrosis (3- to 5-fold in WT, 2-fold in mdx), and serum CK (2- to 10-fold in WT, 2- to 3-fold in mdx). In vitro strength measures were consistent in WT, but a bit less so in mdx (1.5-fold variation).
Conclusion: Our analysis suggests that some outcomes are relatively evaluator-independent with consistent year-to-year project- and year-based assessments; namely, body weight, grip strength, and in vitro force. Body weight consistency is expected, given the mechanical nature of measurement. The consistency of muscle strength outcomes (grip strength, in vitro force) was encouraging, as these are typically primary outcomes for preclinical efficacy studies in mdx. Serum CK and histological assessments of fibrosis were highly variable between project/years, but these outcomes are well-known to show high variability in both mice and humans. The exhaustion outcome seemed quite variable in both WT and mdx, suggesting a strong evaluator-dependent effect of carrying out this technique.