Fragment-based screening and discovery of small molecule ligands for TIGIT and TIM-3.

Abstract

Immune co-stimulatory and co-inhibitory receptors play a critical role in the maintenance of immune homeostasis. These checkpoint proteins have been proven to be effective targets in a cancer setting where constitutive co-inhibitory receptor expression on T cells dampens effector T cell responses. TIGIT and TIM-3 are highly validated co-inhibitory receptor cancer targets that are currently being explored in therapeutic antibody clinical trials. Despite the potential advantages of small molecule inhibitors over antibody-based therapeutics, the discovery of small molecules that target TIGIT and TIM-3 has lagged behind the development of antibodies. We have utilized a fragment-based drug discovery approach to identify fragment hits that bind to TIGIT and TIM-3 for hit-to-lead optimization. While TIGIT was largely refractory to fragment binding resulting in a low hit rate and suboptimal starting compounds, TIM-3 had a much larger hit rate and is likely druggable by small molecules. Fragments were identified that bind to TIM-3 at both the cognate ligand binding FG-CC’ cleft and a novel C”D binding site. SAR by NMR and co-crystal structures of fragments bound to TIM-3 facilitated structure-based design to develop more potent analogs. The fragment screening results, preliminary SAR, and nanomolar affinity compounds discussed in this dissertation serve as important starting points for the further development of small molecule-based TIM-3 inhibitors.