Research progresses of small molecule inhibitors targeting TGF-β and its receptors

Transforming growth factor-β (TGF-β) belongs to a group of biologically active cytokines that bind to its receptors to activate Smad signaling and non-Smad signaling pathways. The biological functions of TGF-β include promoting cell epithelial-mesenchymal transition, tissue fibrosis, angiogenesis and tumor immune evasion, as well as dual effects of cancer suppression and cancer promotion. Given the fact that the ligand-and receptors-mediated abnormal activation of TGF-β signaling pathways play an important role in the pathogenesis of multiple diseases such as malignant tumors and tissue fibrosis, more than a dozen small-molecule inhibitors have been developed to block the TGF-β signaling pathways, providing a novel method for controlling the development of these diseases. At present, pirfenidone, an inhibitor for TGF-β production, has been approved for treatment of idiopathic pulmonary fibrosis, while the inhibitors of TGFβRI/ALK5 for therapeutics of tumors or myelodysplastic syndromes, including LY2157299, EW-7197 and LY3200882, are in the phase I to Ⅲ clinical trials, with additional ones inhibiting TGFβRs such as SB-431542, LY2109761, TP-0427736, and IN-1130 being in the preclinical phase. This paper reviews recent advances in research of small-molecule inhibitors targeting TGF-β and its receptors.