De-Novo Designed Library of Benzoylureas as Inhibitors of BCL‑X_L: Synthesis, Structural and Biochemical Characterization

The prosurvival BCL-2 proteins are attractive yet challenging targets for medicinal chemists. Their involvement in the initiation and progression of many, if not all, tumors makes them prime targets for developing new anticancer therapies. We present our approach based on de novo structure-based drug design. Using known structural information from complexes engaging opposing members of the BCL-2 family of proteins, we designed peptidomimetic compounds using a benzoylurea scaffold to reproduce key interactions between these proteins. A library stemming from the initial de novo designed scaffold led to the discovery of ligands with low micromolar potency (<i>K</i>_D = 4 μM) and selectivity for BCL-X_L. These compounds bind in the canonical BH3 binding groove in a binding mode distinct from previously known BCL-2 inhibitors. The results of our study provide insight into the design of a new class of antagonists targeting a challenging class of protein–protein interactions

Discovery of Potent and Selective Benzothiazole Hydrazone Inhibitors of Bcl‑X_L

Developing potent molecules that inhibit Bcl-2 family mediated apoptosis affords opportunities to treat cancers via reactivation of the cell death machinery. We describe the hit-to-lead development of selective Bcl-X_L inhibitors originating from a high-throughput screening campaign. Small structural changes to the hit compound increased binding affinity more than 300-fold (to IC₅₀ < 20 nM). This molecular series exhibits drug-like characteristics, low molecular weights (<i>M</i>_w < 450), and unprecedented selectivity for Bcl-X_L. Surface plasmon resonance experiments afford strong evidence of binding affinity within the hydrophobic groove of Bcl-X_L. Biological experiments using engineered Mcl-1 deficient mouse embryonic fibroblasts (MEFs, reliant only on Bcl-X_L for survival) and Bax/Bak deficient MEFs (insensitive to selective activation of Bcl-2-driven apoptosis) support a mechanism-based induction of apoptosis. This manuscript describes the first series of selective small-molecule inhibitors of Bcl-X_L and provides promising leads for the development of efficacious therapeutics against solid tumors and chemoresistant cancer cell lines