A proof-of-concept rat toxicity study highlights the potential utility and challenges of virtual control groups

The virtual control group (VCG) concept provides a potential opportunity to reduce animal use in drug development by replacing concurrent control groups (CCGs) in nonclinical toxicity studies. This work investigated the feasibility and reliability of using VCGs in place of CCGs. A historical control database (HCD), constructed from Genentech Inc. rat toxicity study data, was reviewed to under­stand trends and sources of variability in control animals over time, and to identify data curation requirements for assembling VCGs, e.g., alignment of units of measurement. Several endpoints were investigated and stratified against different study design parameters. Sex, route of administration, fasting status, and body weight at study initiation were among the parameters that were indicated as key matching criteria. With a high-level understanding of potential sources of variability, a retro­spective proof-of-concept (POC) study was designed, evaluating a historical rat pilot toxicity study for test article-related changes. A masked interpretation of the study was conducted using its CCG and two unique VCGs that were constructed from individual animal data pulled from our HCD. While the results of the microscopic pathology assessment and most endpoints were similar across the different control groups, the POC revealed the risk of using VCGs to interpret subtle test article-related changes in clinical pathology parameters. Within the context of our POC, it appears the use of a VCG is not completely equivalent to the CCG, especially with clinical pathology parameters. Additional work is needed to understand the potential utility, and thus, viability of VCGs in other contexts.