JAK Inhibitors and Inflammatory DiseasePreclinical IBD studies for JAK inhibitors have largely relied upon oxazolone-induced colitis in mice, a model that histologically and immunologically resembles several aspects of ulcerative colitis. A recent publication from the biopharmaceutical company Incyte has demonstrated the utility of the interleukin 10 (Il10) knockout mouse model for studying JAK inhibition3. This study characterized a novel selective JAK1 inhibitor, itacitinib, in numerous rodent models for inflammatory diseases, including oxazolone- and TNBS-induced colitis and spontaneous colitis in Il10 knockout mice. They demonstrated that selective JAK1 inhibition is highly efficacious in all three of these models despite the varied disease mechanisms and immunological profiles involved, thus suggesting a dominant role for JAK1 in disease pathogenesis across multiple mouse IBD models.
Evaluating Il10 Knockout Mouse ModelsThe Il10 knockout model is characterized by spontaneous and unremitting colitis driven by IL-23 and Th1-like inflammation in response to microbial stimulation4. This phenotype is also highly dependent upon the genetic background of the specific Il10 knockout model, such that permissive strains (e.g., BALB/c or 129/SvEv) develop highly penetrant and severe disease with onset by ~3-4 months of age under specific pathogen free conditions. In contrast, in resistant strains, such as C57BL/6, colitis onset is highly variable and may be significantly delayed. For example, a head-to-head comparison of Il10 knockout mice on BALB/c vs. C57BL/6 backgrounds showed a 100% incidence of colitis in BALB/c by 18 weeks of age, as compared to only 8% in C57BL/6 by 24 weeks of age. Therefore, the BALB/c background Il10 knockout model offers a significant advantage for drug screening studies over the C57BL/6 version as colitis develops more quickly and reliably and with less variable onset. The itacitinib study employed a newly developed Il10 knockout model on the BALB/c background (BALB/cAnNTac-Il10em7Tac) generated by CRISPR/Cas9-mediated gene editing to delete the entire Il10 locus (exons 1 to 5, including the proximal promoter and UTRs). In this study, vehicle-treated BALB/c Il10 knockout mice developed highly penetrant colitis with onset by 15 weeks of age, whereas prophylactic itacitinib treatment was highly efficacious in preventing clinical symptoms, rectal prolapse, colonic hypertrophy, and histopathology.
The BALB/c background Il10 knockout model offers a powerful tool for the preclinical IBD studies and can faithfully recapitulate aspects of chronic colitis within reasonable timeframes. In addition to chemically-induced or other genetically engineered colitis models, BALB/c Il10 knockout mice offer an attractive model to study JAK inhibitors and other preclinical IBD candidates.