Halofuginone (RU-19110), the competitive inhibitor of prolyl-tRNA synthetase(Ki=18.3 nM), could also down-regulate Smad3 and blocked TGF-β signaling at 10 ng/ml in the mammal.

Halofuginone specifically inhibits collagen type I gene expression and matrix metalloproteinase 2 (MMP-2) gene expression, which may result in the suppression of angiogenesis, tumor stromal cell development, and tumor cell growth. Halofuginone Hydrobromide is the hydrobromide salt of halofuginone, a semisynthetic quinazolinone alkaloid anticoccidial derived from the plant Dichroa febrifuga, with antifibrotic and potential antineoplastic activities. These effects appear to be due to halofuginone-mediated inhibition of the collagen type I and MMP-2 promoters. Collagen type I and MMP-2 play important roles in fibroproliferative diseases.