Identification of a New RXRα Antagonist Targeting the Coregulator-Binding Site

Retinoid X receptor-alpha (RXRα) is implicated in the regulation of many biological processes and also represents a unique intracellular target for pharmacologic interventions. Efforts on discovery of small molecules targeting RXRα have been primarily focused on the molecules that bind to its classical ligand-binding pocket (LBP). Here, we report the identification and characterization of a new RXRα transcriptional antagonist by using structure-based virtual screening. The new antagonist binds with submicromolar affinity to RXRα (K_d = 4.88 × 10^-7 M) and selectively inhibits RXRα transactivation. The compound does not bind to the LBP but to a hydrophobic groove on the surface of RXRα. The new compound also effectively suppresses AKT activation and promotes apoptosis of cancer cells in a RXRα-dependent manner by inhibiting tRXRα interaction with the p85α subunit of PI3K. Thus, the compound represents a new RXRα modulator that regulates the nongenomic actions of RXRα by surface binding.