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.

Prolyl-tRNA synthetase:18.3nM(Ki)

In mammals, halofuginone at 10 ng/ml down-regulates Smad3, blocking TGF-β signaling and preventing both the differentiation of fibroblasts to myofibroblasts and the transitioning of epithelial cells to mesenchymal cells[2].

Halofuginone clearly extends the survival times of the parasite-infected mice. Oral treatment with halofuginone at doses of 0.2 and 1 mg/kg has an apparent curative effect for the infected mice. The subcutaneous administration of 0.2 mg of halofuginone per kg likewise extends the survival times of the infected mice, but none of the mice is cured. The mice in the 5-mg/kg dose groups die before the completion of treatment with the drug either orally or subcutaneously. Subcutaneous treatment with halofuginone appears to be more toxic to mice than oral treatment[3].

Assay of ProRS activity: The prolyl tRNA synthetase domain of human EPRS (ProRS) is expressed in E.coli with a 6-his tag and purified. Enzymatic activity is assayed using incorporation of 3H Pro into the tRNA fraction essentially, except that the charged tRNA fraction is isolated by rapid batchwise binding to Mono Q sepharose and quantitated by liquid scintillation counting. For all kinetic assays, the concentration of active enzyme in the reaction is 40 nM. Similar inhibition by HF is seen using the human ProRS domain purified from bacteria and full length EPRS purified from rat liver.

Primary murine CD4+ CD25− T cells are activated through the TCR in Th17 polarizing conditions in the presence of either 10 nM MAZ1310 or HF and amino acid supplements. Th17 differentiation is assayed in the absence or presence of HF or borrelidin, with or without 1 mM threonine or proline supplementation. MEFs are treated with or without HF (50 nM) and/or Proline (2 mM) for 4 hours (CHOP, S100A4) or 24 hours (ColIA1, Col1A2).  (Only for Reference)