Recent Advances in Cancer Drug Development: Targeting Induced Myeloid Cell Leukemia-1 (Mcl-1) Differentiation Protein.

Background: Anti-apoptotic members of the Bcl-2 family of proteins are upregulated in a majority of cancers and are potential therapeutic targets. Fragment-based design led to the development of clinical candidates that target Bcl-xL/Bcl-2. Although these BclxL/Bcl-2 inhibitors showed promise in pre-clinical studies, resistance to several Bcl-xL inhibitors was observed, when used alone. This is attributed to the over-expression of Mcl-1, another member of the Bcl-2 family of proteins. Indeed, Mcl-1 is highly amplified in numerous cancers, suggesting that it may contribute to malignant cell growth and evasion of apoptosis. Therefore, significant efforts have been made toward the development of direct Mcl-1 inhibitors for cancer therapy. Methods: Following an extensive search of peer-reviewed articles on the development of Mcl-1-selective inhibitors, the literature retrieved is chronologically arranged and discussed in this review article. Results: We have included 147 articles in this review; including articles that describe the development of stapled peptides with improved binding affinity as Mcl-1-selective BH3 mimetics, those describing fragment-based and structure-based design of small molecule Mcl-1 inhibitors by various research groups, and those detailing the use of natural products and their derivatives as potential Mcl-1 inhibitors. Conclusion: The therapeutic potential of targeting the Mcl-1 protein for cancer drug discovery is vast. Stapling BH3 peptides, as well as the development of small molecule inhibitors as BH3 mimetics, are viable strategies to develop selective Mcl-1 inhibitors. With no clinically approved candidate in hand, additional modes of perturbing the biological function of this protein will aid drug discovery efforts.