The Novel mTOR Complex 1/2 Inhibitor P529 Inhibits Human Lung Myofibroblast Differentiation.

Idiopathic pulmonary fibrosis is a progressive and deadly disorder with very few therapeutic options. Palomid 529 (8-(1-hydroxyethyl)-2-methoxy-3-(4-methoxybenzyloxy)-benzo[c]chromen-6-one; P529) is a novel dual inhibitor of mechanistic target of rapamycin complex 1/2 (mTORC1/2). In these studies, we investigated the effect of P529 on TGF-β-dependent signaling and myofibroblast differentiation. TGF-β-induced phosphorylation of the mTORC1 targets, p70 S6 kinase 1 (S6K1), and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), were both dose dependently inhibited by P529 in human lung fibroblasts with maximal inhibition occurring between 10 and 20 μM. mTORC2-mediated phosphorylation of Akt at the S473 site was partially inhibited with a similar dose dependency, as was TGF-β-induced myofibroblast differentiation. Protein levels of TGF-β-induced fibronectin and collagen were similarly decreased by P529. At this dose, there was also inhibition of mRNA transcript levels for Col1 and α-SMA, suggesting inhibition of transcriptional activation. However, there was no effect of P529 on canonical TGF-β-induced Smad signaling, as assessed by receptor-associated Smad2/3 phosphorylation, Smad2/3/4 translocation, or Smad-driven gene expression, as assessed by Smad-binding element driven luciferase. Conversely, activation of mTORC1/2 signaling was dependent on TGF-β type I receptor (ALK5) signaling and on Smad2/3 expression. P529 treatment disrupted TGF-β-induced actin stress fiber formation during myofibroblast differentiation, the deposition of new extracellular fibronectin matrix, and linear wound closure by fibroblasts. Likewise, mTOR knockdown inhibited TGF-β-induced myofibroblast differentiation. In conclusion, P529 inhibits TGF-β-induced myofibroblast differentiation, actin stress fiber formation, and matrix protein expression and deposition. Inhibition of mTORC1/2 by P529 may be a promising approach to inhibit in vivo fibrosis. J. Cell. Biochem. 118: 2241-2249, 2017.