The inhibitory effect of canine interferon gamma on the growth of canine tumors.

Recombinant canine interferon-γ (rc-IFNγ; Interdog) was exclusively approved as a therapeutic for canine atopic dermatitis. However, it has been used off-label for the treatment of canine cancer. We examined the inhibitory effect of rc-IFNγ on the growth of canine tumor cell lines and analyzed its mechanism of action. Three (CTB-p, CTB-m, and CNM-m) out of seven mammary gland tumor cell lines and two (VIMC and CoMS) out of four mast cell tumor cell lines showed remarkable growth inhibition after treatment with rc-IFNγ. However, one (CLBL-1) out of nine lymphoma cell lines showed a significant amount of cell death. Using CTB-p and CTB-m cell lines, we showed that STAT1 was essential for inducing the growth inhibitory effect of rc-IFNγ. Although rc-IFNγ induced G1 growth arrest in CTB-p cell line, treatment with rc-IFNγ did not alter the expression of cell cycle regulatory proteins. In this study, we observed direct cytotoxicity or cytostatic effects of rc-IFNγ in canine tumor cell lines. However, the detailed mechanisms responsible for these effects need to be elucidated in the future.