The Focal Adhesion Targeting (FAT) domain of Focal Adhesion Kinase (FAK) is a promising drug target since FAK is overexpressed in many malignancies and promotes cancer cell metastasis. The FAT domain serves as a scaffolding protein, and its interaction with the protein paxillin localizes FAK to focal adhesions. Various studies have highlighted the importance of FAT-paxillin binding in tumor growth, cell invasion, and metastasis. Targeting this interaction through high-throughput screening (HTS) provides a challenge due to the large and complex binding interface. In this report, we describe a novel approach to targeting FAT through fragment-based drug discovery (FBDD). We developed two fragment-based screening assays—a primary SPR assay and a secondary heteronuclear single quantum coherence nuclear magnetic resonance (HSQC-NMR) assay. For SPR, we designed an AviTag construct, optimized SPR buffer conditions, and created mutant controls. For NMR, resonance backbone assignments of the human FAT domain were obtained for the HSQC assay. A 189-compound fragment library from Enamine was screened through our primary SPR assay to demonstrate the feasibility of a FAT-FBDD pipeline, with 19 initial hit compounds. A final total of 11 validated hits were identified after secondary screening on NMR. This screening pipeline is the first FBDD screen of the FAT domain reported and represents a valid method for further drug discovery efforts on this difficult target.

The N-terminal FERM domain of focal adhesion kinase (FAK) contributes to FAK scaffolding and interacts with HER2, an oncogene and receptor tyrosine kinase. The interaction between HER2 and FAK drives resistance to FAK-kinase domain inhibitors through FAK Y397 transphosphorylation and FAK re-activation upon inhibition. As such, FAK FERM remains an attractive drug discovery target. In this report, we detail an alternative approach to targeting FAK through virtual screening-based discovery of chemical probes that target FAK FERM. We validated the binding interface between HER2 and FAK using site-directed mutagenesis and GST pulldown experiments. We assessed the ligandability of key-binding residues of HER2 and FAK utilizing computational tools. We developed a virtual screening method to screen ~200,000 compounds against the FAK FERM domain, identifying 20 virtual chemical probes. We performed GST pull-down screening on these compounds, discovering two hits, VS4 and VS14, with nanomolar IC 50 s in disrupting HER2-FAK. We performed further testing, including molecular docking, immunofluorescence, phosphorylation, and cellular invasion assays to evaluate the compounds' biological effects. One probe, VS14, was identified with the ability to block both auto-and transphosphorylation of Y397. In all, these studies identify two new probes that target FAK FERM, enabling future investigation of this domain. K E Y W O R D SFAK FERM domain, focal adhesion kinase, HER2, high-throughput screening, phosphorylation, virtual screening | 585 STAHL eT AL.