Development and Characterization of Novel Mcl-1 Inhibitors for Treatment of Cancer.

Abstract

Myeloid cell leukemia-1 (Mcl-1) is a potent anti-apoptotic protein, member of the anti-apoptotic Bcl-2 family. Overexpression of Mcl-1 is associated with high tumor grade, resistance to chemotherapy, and poor prognosis in many types of cancers. Thus, Mcl-1 is emerging as a critical survival factor in a broad range of human cancers and represents an attractive molecular target for the development of a new class of cancer therapy. Applying an integrated screening strategy through combining high throughput and virtual screenings, multiple hit compounds with structural diversity were validated as Mcl-1 inhibitors using biochemical and biophysical methods. Based on the confirmed hit molecule and analyzing structure activity relationship (SAR) together with computational docking predicted binding poses supported by HSQC NMR studies, we have designed and optimized a novel class of selective small-molecule inhibitors of Mcl-1 using a 2,4,5 substituted benzoic acid as a scaffold. Several co-crystal structures of this class of inhibitors in complex with Mcl-1 have provided a basis for their further optimization, which ultimately led to the discovery of nanomolar potent and selective ligands that bind to the BH3 hydrophobic groove of the Mcl-1 protein. Mechanistic studies performed in genetically engineered cell lines revealed that our inhibitors have on-target activity and induce Bax/Bak dependent apoptosis; selectively antagonizing Mcl-1 function leading to the induction of the hallmarks of apoptosis. Using functional BH3 profiling assay, we identified heterogeneous dependency on Bcl-2 family members for survival in hematologic malignancies, as well as in solid human cancers. The mitochondrial response to selective Mcl-1 BH3 peptides (Noxa and MS1) predicted the in vitro sensitivity to Mcl-1 inhibitors of several cell lines found to be Mcl-1 dependent, including multiple myeloma cell line H929. 483LM, one of the most potent developed Mcl-1 inhibitors, inhibited the cell growth and induced mechanism-based apoptotic cell death in the H929 cells. Intraperitoneal treatment of the H929 cancer xenograft model with 483LM led to significant dose-dependent tumor regression. Collectively, our data demonstrates that the new class of Mcl-1 inhibitors has promising in vitro and in vivo efficacy, warranting further development toward clinical use in the treatment of human cancers.