Optimization of a Novel DEL Hit That Binds in the Cbl-b SH2 Domain and Blocks Substrate Binding
Jun Liang, Michael J. Lambrecht, Teresita L. Arenzana, Samuel Aubert‐Nicol, Linda Bao, Fabio Broccatelli, Jianping Cai, Céline Eidenschenk, Christine Everett, Thomas P. Garner, Felix Gruber, Pouyan Haghshenas, Malcolm P. Huestis, Peter Hsu, Ponien Kou, Araz Jakalian, Robin Larouche‐Gauthier, Jean‐Philippe Leclerc, Dennis H. Leung, Aaron J. Martin, Jeremy Murray, Madeleine Prangley, Sascha Rutz, Satoko Kakiuchi-Kiyota, Alexander L. Satz, Nicholas J. Skelton, Micah Steffek, Daniel Stoffler, Jawahar Sudhamsu, Sophia T. Tan, Jian Wang, Shouliang Wang, Qiuyue Wang, Timothy J. Wendorff, Moreno Wichert, Arun A. Yadav, Christine Yu, Xiaojing Wang
Abstract
We were attracted to the therapeutic potential of inhibiting Casitas B-lineage lymphoma proto-oncogene-b (Cbl-b), a RING E3 ligase that plays a critical role in regulating the activation of T cells. However, given that only protein–protein interactions were involved, it was unclear whether inhibition by a small molecule would be a viable approach. After screening an ∼6 billion member DNA-encoded library (DEL) using activated Cbl-b, we identified compound 1 as a hit for which the cis -isomer ( 2 ) was confirmed by biochemical and surface plasmon resonance (SPR) assays. Our hit optimization effort was greatly accelerated when we obtained a cocrystal structure of 2 with Cbl-b, which demonstrated induced binding at the substrate binding site, namely, the Src homology-2 (SH2) domain. This was quite noteworthy given that there are few reports of small molecule inhibitors that bind to SH2 domains and block protein–protein interactions. Structure- and property-guided optimization led to compound 27, which demonstrated measurable cell activity, albeit only at high concentrations.