Agonist Discovery for Membrane Proteins on Live Cells by Using DNA-encoded Libraries

Identifying
biologically active ligands for membrane proteins is
an important task in chemical biology. We report an approach to directly
identify small molecule agonists against membrane proteins by selecting
DNA-encoded libraries (DELs) on live cells. This method connects extracellular
ligand binding with intracellular biochemical transformation, thereby
biasing the selection toward agonist identification. We have demonstrated
the methodology with three membrane proteins: epidermal growth factor
receptor (EGFR), thrombopoietin receptor (TPOR), and insulin receptor
(INSR). A ∼30 million and a 1.033 billion-compound DEL were
selected against these targets, and novel agonists with subnanomolar
affinity and low micromolar cellular activities have been discovered.
The INSR agonists activated the receptor by possibly binding to an
allosteric site, exhibited clear synergistic effects with insulin,
and activated the downstream signaling pathways. Notably, the agonists
did not activate the insulin-like growth factor 1 receptor (IGF-1R),
a highly homologous receptor whose activation may lead to tumor progression.
Collectively, this work has developed an approach toward “functional”
DEL selections on the cell surface and may provide a widely applicable
method for agonist discovery for membrane proteins.