Design, synthesis, and activity evaluation of broad-spectrum small-molecule inhibitors of anti-apoptotic Bcl-2 family proteins: Characteristics of broad-spectrum protein binding and its effects on anti-tumor activity

A series of class A compounds which have the basic skeleton of ABT-737 and the h2 residues of Bim BH3 were designed, and showed broad-spectrum binding activity to target proteins similar to that of Bim BH3 peptide. Then class B compounds were synthesized by modifying the structure of the most effective class A compound, A-4, and showed better binding affinity to the target proteins. On the basis of the comparison of the structure of the Bim BH3: Bcl-xL complex and that of the ABT-737: Bcl-xL complex, a series of class A compounds were designed. These compounds had the basic skeleton of ABT-737 and the h2 residues of Bim BH3. These residues had shown themselves to be relevant to Bim BH3’s broad-spectrum binding properties in saturation mutagenesis assays. Unlike ABT-737, which is a selective inhibitor of anti-apoptotic members of the Bcl-2 protein family, the class A compounds showed broad-spectrum binding activity to target proteins similar to those of Bim BH3 peptide. Then class B compounds were synthesized by modifying the structure of the most effective class A compound, A-4. Most of these class B compounds showed better binding affinity to the target proteins than the class A compounds had. They also showed themselves more effective than ABT-737 at inhibiting growth in multiple tumor cell lines known to express Bcl-xL, Bcl-2, and Mcl-1 proteins at high levels. Compounds B-11 and B-12 had the strongest anti-tumor activity of any compounds we produced. This study suggests that it is feasible to design small-molecule inhibitors based on the structure of Bim BH3, which shows broad-spectrum binding to Bcl-xL, Bcl-2, and Mcl-1 proteins. Our results also suggest that the broad-spectrum properties of small-molecule inhibitors binding to target proteins play a critical role in inhibiting the growth of many tumor cells. Finally, our study provides a series of lead compounds that merit further research into anti-cancer therapeutics.