Identification of Pirin as a Molecular Target of the CCG-1423/CCG-203971 Series of Anti-Fibrotic and Anti-Metastatic Compounds
We have been exploring a series of compounds (including CCG-1423 and CCG-203971) discovered through an MRTF/SRF dependent luciferase screen that can block the “MRTF gene transcription pathway”. They show substantial efficacy in a variety of in vitro and in vivo models of melanoma metastasis and bleomycin-induced skin and lung fibrosis. Recent data show a role for this pathway in melanoma resistance to BRAF inhibitors and our compounds can re-sensitize a subset of resistant melanomas to vemurafenib.
Although these compounds show good activity, their molecular target has been obscure. Our recent target identification efforts reveal that pirin, an iron-dependent co-transcription factor, is a target of this series of compounds. Using biophysical techniques including isothermal titration calorimetry and X-ray crystallography, we verify that pirin binds these compounds in vitro. We also show that pirin is necessary for MRTF-dependent SRE.L Luciferase activation. Finally, using both siRNA and a previously validated pirin inhibitor, we show a role for pirin in TGF-b induced gene expression in primary dermal fibroblasts. These results thus reveal a role for pirin in regulation of MRTF/SRF-regulated gene transcription and suggest that it may be a novel anti-fibrotic target.