Development of Mcl-1 inhibitors for cancer therapy

The myeloid leukemia cell differentiation protein (Mcl-1) is an anti-apoptotic protein of the B-cell lymphoma 2 (Bcl-2) family, which regulates cellular apoptosis. Mcl-1 expression plays a key role in survival of cancer cells and therefore serves as a promising target in cancer therapy. Besides, its importance as a cancer target, various peptides and small-molecule inhibitors have been successfully designed and synthesized, yet no Mcl-1 inhibitor is approved for clinical use. However, recent development on the understanding of Mcl-1's role in key cellular processes in cancer and an upsurge of reports highlighting its association in various anticancer drug resistance supports the view that Mcl-1 is a key target in various cancers, especially hematological cancers. This review compiles structures of a variety of inhibitors of Mcl-1 reported to date. These include inhibitors based on a diverse range of heterocycles (e.g. indole, imidazole, thiophene, nicotinic acid, piperazine, triazine, thiazole, isoindoline), oligomers (terphenyl, quaterpyridine), polyphenol, phenalene, anthranilic acid, anthraquinone, macrocycles, natural products, and metal-based complexes. In addition, an effort has been made to summarize the structure activity relationships, based on a variety of assays, of some important classes of Mcl-1 inhibitors, giving affinities and selectivities for Mcl-1 compared to other Bcl-2 family members. A focus has been placed on categorizing the inhibitors based on their core frameworks (scaffolds) to appeal to the chemical biologist or medicinal chemist.