Last week we described a fragment-derived covalent probe that targets the four closely related TEAD transcription factors, which are part of the Hippo signaling pathway implicated in some cancers. A new paper in J. Med. Chem. by Timo Heinrich and collaborators at Merck KGa, iBET, and Cancer Research Horizons brings us another fragment-derived probe, this one noncovalent.
The researchers started by screening 1930 fragments, each at 2 mM, against TEAD1 and TEAD3 using SPR. Perhaps not surprisingly given the high concentration used, this led to a whopping 560 hits. These were then tested in dose-response format against TEAD1 with or without the coactivator YAP; 254 compounds showed differential affinity, among them compound 1. This molecule was crystallized bound to TEAD3, which revealed that it binds to the hydrophobic pocket normally occupied by a covalently-bound palmitoyl group required for activity. Despite being a fragment, compound 1 was active in a cell reporter assay, and the researchers state that further optimization was done using cellular assays rather than biophysical or biochemical experiments.
Analysis of the crystal structure suggested that enlarging the cyclopentyl moiety could fit more snugly into a hydrophobic pocket, while adding a small propyl moiety could extend into a separate pocket, leading to compound 6, with a 10-fold boost in activity. Replacing the propyl with an additional ring led to sub-micromolar compound 9. Finally, replacing the saturated ring with a substituted phenyl moiety led to MSC-4106, with low nanomolar activity in the cell reporter assay.
Thermal stabilization (specifically, nanoDSF) assays showed that MSC-4106 stabilized TEAD1 and TEAD3 but not TEAD2 or TEAD4. Palmitoylation assays confirmed this selectivity profile. The paper also includes a nice table comparing experimental selectivities of seven other non-covalent TEAD inhibitors, which vary from having activity only against TEAD1 to activity against all four homologs.
MSC-4106 was clean when tested at 10 µM against a panel of 58 receptors and 1 µM against nearly 400 kinases. It did not inhibit hERG or any of the common CYP450s. Finally, PK studies in mice, rats, and dogs showed that the compound is orally bioavailable with a long half-life. Given these favorable properties it was taken into xenograft studies, where it showed tumor growth inhibition at 5 mg/kg and tumor regression at 100 mg/kg. Analysis of tumor tissue showed downregulation of a TEAD-regulated gene, Cyr61.
Can we draw any lessons from comparing covalent MYF-03-176 (discussed last week) with non-covalent MSC-4106? Probably not, given that the former hits all TEAD homologs while the latter is selective for TEAD1 and TEAD3. Both molecules look to be excellent chemical probes for further dissecting Hippo signaling. I look forward to seeing how TEAD inhibitors ultimately fare in the clinic.