ABSTRACT
MCL-1 is an antiapoptotic BCL-2 family protein that has emerged as a major pathogenic factor in human cancer. Like BCL-2, MCL-1 bears a surface groove whose function is to sequester the BH3 killer domains of proapoptotic BCL-2 family members, a mechanism harnessed by cancer cells to establish formidable apoptotic blockades. Although drugging the BH3-binding groove has been achieved for BCL-2, translating this approach to MCL-1 has been challenging. Here, we report an alternative mechanism for MCL-1 inhibition by small-molecule covalent modification of C286 at a new interaction site distant from the BH3-binding groove. Our structure-function analyses revealed that the BH3 binding capacity of MCL-1 and its suppression of BAX are impaired by molecular engagement, a phenomenon recapitulated by C286W mutagenic mimicry in vitro and in mouse cells. Thus, we characterize an allosteric mechanism for disrupting the antiapoptotic BH3 binding activity of MCL-1, informing a new strategy for disarming MCL-1 in cancer.
Subject(s)
Allosteric Regulation/drug effects , Myeloid Cell Leukemia Sequence 1 Protein/chemistry , Myeloid Cell Leukemia Sequence 1 Protein/metabolism , Small Molecule Libraries/pharmacology , Animals , Apoptosis/drug effects , Cell Line , Humans , Mice , Molecular Dynamics Simulation , Mutagenesis , Myeloid Cell Leukemia Sequence 1 Protein/genetics , Neoplasms/genetics , Neoplasms/metabolism , Point Mutation , Protein Binding/drug effects , Protein Conformation/drug effects , Protein Domains , Proto-Oncogene Proteins c-bcl-2/chemistry , Proto-Oncogene Proteins c-bcl-2/metabolism , bcl-2-Associated X Protein/chemistry , bcl-2-Associated X Protein/metabolismABSTRACT
Cancer cells hijack BCL-2 family survival proteins to suppress the death effectors and thereby enforce an immortal state. This is accomplished biochemically by an antiapoptotic surface groove that neutralizes the proapoptotic BH3 α helix of death proteins. Antiapoptotic MCL-1 in particular has emerged as a ubiquitous resistance factor in cancer. Although targeting the BCL-2 antiapoptotic subclass effectively restores the death pathway in BCL-2-dependent cancer, the development of molecules tailored to the binding specificity of MCL-1 has lagged. We previously discovered that a hydrocarbon-stapled MCL-1 BH3 helix is an exquisitely selective MCL-1 antagonist. By deploying this unique reagent in a competitive screen, we identified an MCL-1 inhibitor molecule that selectively targets the BH3-binding groove of MCL-1, neutralizes its biochemical lock-hold on apoptosis, and induces caspase activation and leukemia cell death in the specific context of MCL-1 dependence.
