A stapled BIM peptide overcomes apoptotic resistance in hematologic cancers

Abstract

Cancer cells subvert the natural balance between cellular life and death, achieving immortality through pathologic enforcement of survival pathways and blockade of cell death mechanisms. Pro-apoptotic BCL-2 family proteins are frequently disarmed in relapsed and refractory cancer through genetic deletion or interactionbased neutralization by overexpressed antiapoptotic proteins, resulting in resistance to chemotherapy and radiation treatments. New pharmacologic strategies are urgently needed to overcome these formidable apoptotic blockades. We harnessed the natural killing activity of BCL-2-interacting mediator of cell death (BIM), which contains one of the most potent BH3 death domains of the BCL-2 protein family, to restore BH3-dependent cell death in resistant hematologic cancers. A hydrocarbon-stapled peptide modeled after the BIM BH3 helix broadly targeted BCL-2 family proteins with high affinity, blocked inhibitory antiapoptotic interactions, directly triggered proapoptotic activity, and induced dose-responsive and BH3 sequence-specific cell death of hematologic cancer cells. The therapeutic potential of stapled BIM BH3 was highlighted by the selective activation of cell death in the aberrant lymphoid infiltrates of mice reconstituted with BIM-deficient bone marrow and in a human AML xenograft model. Thus, we found that broad and multimodal targeting of the BCL-2 family pathway can overcome pathologic barriers to cell death. IntroductionThe BCL-2 family interaction network lies at the crossroads of the cell's life-death decision (1, 2). Among the oncogenic signals that drive the development and maintenance of cancer, the pathologic reprogramming of the BCL-2 family interaction network has emerged as a formidable barrier to modern day anticancer treatment. Antiapoptotic members of the BCL-2 family contain a surface hydrophobic groove that can bind, sequester, and neutralize the critical BH3 death domains of proapoptotic members (3). Small molecules, such as ABT-737 and ABT-263, that selectively inhibit the antiapoptotic proteins BCL-2 and BCL-X L induce apoptosis of tumors that are especially dependent upon this subset of survival proteins (4, 5). However, the compounds are rendered ineffective by cellular expression of alternate antiapoptotic proteins, such as MCL-1 and BFL1/A1, which lie outside the molecules' range of binding specificity or by the relative or absolute absence of proapoptotic effectors, such as BAX and BAK (6, 7). Thus, a pharmacologic quest is underway to develop nextgeneration agents that simulate broader spectrum BH3-dependent killing activities and effectively deactivate the deflector shields of relapsed and refractory cancers.Chief among the killer BH3-only proteins, Bcl-2-interacting mediator of cell death (BIM) exhibits the most broad-ranging BCL-2 protein interactions, engaging all of the antiapoptotic proteins with high affinity (8, 9) and also directly triggering death effectors, such as BAX (10,11). A recent genetic analysis elegantly demonstrated that only BIM BH3, but not oth...

Evaluation and critical assessment of putative MCL-1 inhibitors

“…38 Such stapled peptides exhibit selectivity in disrupting specific BH3-mediated interactions in vitro, and their sequence-dependent pro-apoptotic activity has been documented in vivo. 39,40 The interaction of an MCL-1-stapled peptide with the BH3-binding groove was employed in a competitive screen to identify a novel MIM-1 that selectively targets the BH3-binding groove of MCL-1. 21 Whereas MIM-1 exhibits BAK-dependent apoptotic activity, its potency may be limited and cell-type dependent, as it failed to induce apoptosis in two MCL-1-dependent cell lines ( Figure 6).…”

Therapeutic potential of a peptide targeting BCL-2 cell guardians in cancer

“…That is the intriguing issue addressed by LaBelle et al in this issue of the JCI (8). This group, directed by Loren Walensky, has previously developed forms of BH3 peptides in which a hydrocarbon staple bridges two nonessential residues separated by a helical turn to force the peptide into the a-helical conformation that favors binding to BCL-2 family members (ref.…”

BH3 Mimetics: Status of the Field and New Developments

“…Given that MCL-1 has emerged as a critical prosurvival factor in a number of malignancies and in drug resistance (17), there is an urgent need to identify MCL-1-specific BH3 mimetics (18,19). The development of small molecules capable of targeting all the main antiapoptotic BCL-2 proteins is also of clear therapeutic interest (8,(20)(21)(22).…”