Category: Preclinical Development
Purpose: Immune checkpoint inhibitors (ICIs) have become standard of care for the treatment of many cancers. Although the spectrum of the response and duration of response are unprecedented, the majority of patients do not respond to ICI treatment. However, in combination with other therapies, ICIs can greatly enhance the response rate. Along with potential therapeutic advantages, combination therapies of small molecules and ICIs can lead to unexpected synergistic adverse events (AEs). For example, combination with a small molecule tyrosine kinase inhibitor (TKI) and an ICI required dose reduction in some patients because AEs were higher than with either therapy alone. The aim of this study is to develop a preclinical mouse model that can predict the propensity of combination therapies of ICIs and small molecules to cause AEs. A preclinical model may potentially elucidate the underlying mechanism of AEs and ultimately enable more patients to benefit from ICI combination therapies.
Methods: Female BALB/c mice were treated with murine anti-PD-1 and murine anti-CTLA-4 monoclonal antibodies combined, with or without coadministration with a small molecule TKI (Drug A) for up to 7 weeks. The development of clinical signs and drug tolerability were assessed during the study. Endpoint measurements included AEs status (clinical signs and histopathological evaluation), blood chemistry, immune phenotyping, gene signature assessment, and drug exposure (PK).
Results: AEs were observed as early as week 3-4 for animals treated with anti-CTLA-4, anti-PD-1 and Drug A combined and by week 5-6 for those treated with anti-CTLA-4 plus anti-PD-1. High drug exposure was maintained until week 4-5 when plasma concentration started to drop for anti-CTLA-4 and anti-PD-1, possibly due to anti-drug antibody responses. Drug plasma levels were stable for Drug A and antibody isotype controls throughout the study. An increase in splenic regulatory T cells (Tregs) observed at weeks 5 and 7 in mice treated with anti-CTLA-4 plus anti-PD-1 was reduced with addition of Drug A. Elevations of several proinflammatory cytokines were observed in both treatment groups. The duodenum rather than the colon was more affected by treatment with ICIs. Anti-CTLA-4 plus anti-PD-1 caused immune cell infiltrates within the duodenum; interestingly, the infiltration was reduced when Drug A was added. More genes associated with gut inflammation were upregulated in the anti-CTLA-4 plus anti-PD-1 treated group in comparison to the group treated with ICIs and Drug A.
Conclusion: Treatment of BALB/c mice with anti-CTLA-4 plus anti-PD-1, with or without Drug A, over 7 weeks was able to recapitulate AE observations from the clinic including elevations of various cytokines, gut inflammation, and changes in several clinical chemistry parameters. While many endpoint measurements were similar, addition of Drug A to anti-CTLA-4 plus anti-PD-1 treated animals reduced inflammation in the colon and reduced splenic Tregs compared to animals only treated with anti-CTLA-4 plus anti-PD-1. This model may allow preclinical assessment of AEs in relationship to ICI therapy in combination with small molecules.
Catherine Boyle– West Point, Pennsylvania
Michael Oropallo– West Point, Pennsylvania
James Monroe– West Point, Pennsylvania
Conrad Raab– West Point, Pennsylvania
Raymond Evers– West Point, Pennsylvania
Liming Liu– Merck, West Point, Pennsylvania