Design,Synthesis And Bioactivity Study Of Selective Mcl-1 Inhibitor

The Bcl-2 family proteins are central regulators of apoptosis. The PPI between anti-apoptotic and pro-apoptotic Bcl-2 members are mediated by the BH3 domain shared by both of them. Anti-apoptotic Bcl-2 proteins are thus attractive targets for developing new anticancer therapies. The specific Bcl-2/Bcl-xL inhibitor ABT-199 was approved by the FDA for marketing in 2016. Mcl-1 protein is overexpressed in a large number of tumors and exhibits unique antitumor properties compared with Bcl-2 and Bcl-xL. They were then documented as two arms of cancer to evade apoptosis. Developing selective Mcl-1 inhibitors may solve the drug resistance to anticancer agents and increase the number of molecule drug candidates.The first selective Mcl-1 inhibitors have been investigated by Fesik until 2012. So far, no drugs in clinical phase were reported. Structural biology and protein mutations studies have shown that the BH3 ?-helix of pro-apoptotic proteins possesses four conserved hydrophobic residues that insert into four hydrophobic sub-pockets, p1-p4 in the BH3-binding groove of anti-apoptotic proteins, while an aspartate makes a salt bridge with a conserved arginyl residue on anti-apoptotic members. These five residues were used as a model for designing small molecule Bcl-2/Mcl-1 inhibitors. Small molecules which can mimic the spatial distribution and physical and chemical properties of hotspots on BH3 ?-helix could competitive combine the BH3 domain of Bcl-2-like proteins and functionally replace the pro-apoptotic protein to induce apoptosis.By analyzing the binding mode of all reports selective Mcl-1 inhibitors, found that none of them could explore the p1 pocket, while we found significant different features between Mcl-1 and Bcl-2 protein that might be exploitable to accomplish Mcl-1 selectivity.Based on a known selective Mcl-1 inhibitor 6-chloro-3-(3-(4-chloro-3,5-dimethylphenoxy)propyl)-1H-indole-2-carboxylic acid, we applied a fragment-based approach to deconstructs the 1H-indole-2-carboxylic acid from the parental molecule, a benzenesulfonyl was substituted at the 1-position to afford an appropriately geometry for engaging into the p1 pocket, a new skeleton A1 was obtained.Compounds A2-A11 were obtained by molecular growth from Al. Finally, we obtained compound A11 with a 7.5-fold selectivity to Mcl-1(Ki=0.48 ?M by FPA) over Bcl-2(Ki=3.6 ?M) which exhibited the selective killing ability on Mcl-1-dependent tumor cells.1H-15N HSQC provide compelling evidence that All can mimic D67 to maintain the interaction with R263 and it mimic 158 and L62 hotspots of the Bim peptide to occupy the p1 and p2 pocket of Mcl-1 protein.Compounds Al-All are the first series of small molecule to probe the p1 pocket of Mcl-1 and Bcl-2 protein. By structure-activity relationships analysis between the compounds, we found that a flexible, polar and relatively small group is more suitable for occupying p1 pocket of Mcl-1 protein. Through analysis of ?G/HAC and MW/pKi of these molecules against the two proteins, we found that the p1 occupation is more favorable for Mcl-1 inhibition than for Bcl-2. Furthermore, we compared our optimization process to other known Mcl-1 selective inhibitors all of which are optimized for p2 pocket, we found that p1 occupation exhibits a higher efficiency to bind to Mcl-1 than occupation of p2 pocket Our evidence illustrated that the p1 could be a key site for selective Mcl-1 inhibitor design.