New target identification of angiogenesis from phenotypic screening of natural products

Unbiased phenotypic screening of natural products has provided a number of unique small molecules with unknown target proteins and modes of action (MOA) in biological context. Target identification of these bioactive natural products is pivotal to address their MOA and to discover better drug candidates that will expedite drug discovery and development. To this aim, we have established chemical genomics and proteomics approach of target identification methods leading to discovery of a number of target protein candidates. Among them, the ubiquinol-cytochrome c reductase binding protein (UQCRB), a subunit protein of Complex III in the mitochondrial respiratory chain was identified as a cellular target of terpesatcin, a natural anti-angoigenic small molecule from fungal metabolites. Terpestacin binding to UQCRB inhibited hypoxia-induced ROS generation, subsequently HIF-1 alpha activation and tumor angiogenesis in vivo, without inhibiting mitochondrial respiration. Functional knock down of UQCRB by siUQCRB as well as UQCRB morpholino dose-dependently inhibited angiogenesis both in vitro and in vivo. Furthermore, vascular endothelial growth factor (VEGF) levels decreased with UQCRB inhibitors treatment and UQCRB morpholino injection in zebrafish model. Based on these new structural and biological information, new synthetic small molecules that specifically regulate the function of UQCRB were also developed by using the smart chemical library designed by pharmacophore-based virtual screening. Collectively, target identification of natural product from phenotypic screening provides both new target and small molecule for exploring new biology of interest and developing new drug candidates.