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The MCL-1 BH3 helix is an exclusive MCL-1 inhibitor and apoptosis sensitizer

Nature Chemical Biology volume 6, pages 595–601 (2010)Cite this article

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Abstract

The development of selective inhibitors for discrete anti-apoptotic BCL-2 family proteins implicated in pathologic cell survival remains a formidable but pressing challenge. Such precisely tailored compounds would serve as molecular probes and targeted therapies to study and treat human diseases driven by specific anti-apoptotic blockades. In particular, MCL-1 has emerged as a major resistance factor in human cancer. By screening a library of stabilized alpha-helix of BCL-2 domains (SAHBs), we determined that the MCL-1 BH3 helix is itself a potent and exclusive MCL-1 inhibitor. X-ray crystallography and mutagenesis studies defined key binding and specificity determinants, including the capacity to harness the hydrocarbon staple to optimize affinity while preserving selectivity. MCL-1 SAHB directly targets MCL-1, neutralizes its inhibitory interaction with pro-apoptotic BAK and sensitizes cancer cells to caspase-dependent apoptosis. By leveraging nature's solution to ligand selectivity, we generated an MCL-1–specific agent that defines the structural and functional features of targeted MCL-1 inhibition.

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Figure 1: Identification of an MCL-1–selective BH3 domain.
Figure 2: Binding and specificity determinants of the MCL-1 BH3 helix.
Figure 3: Crystal structure of the MCL-1 SAHBD–MCL-1ΔNΔC complex.
Figure 4: MCL-1 SAHBD dissociates the inhibitory MCL-1–BAK complex in vitro and in situ and sensitizes BAK-dependent mitochondrial cytochrome c release.
Figure 5: Selective MCL-1 targeting by MCL-1 SAHBD sensitizes death receptor signaling and induces caspase-dependent cancer cell apoptosis.

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Acknowledgements

We thank E. Smith (Dana-Farber Cancer Institute) for editorial and graphics support, R.A. Grant (Massachussets Institute of Technology) for input on the crystallography experiments, X-ray data collection and structural analysis, and C.H. Yun and M.J. Eck (Dana-Farber Cancer Institute) for assistance in generating the hydrocarbon staple parameter file used in the structural refinement. This work was supported by US National Institutes of Health grant 5P01CA92625 and a Burroughs Wellcome Career Award in the Biomedical Sciences to L.D.W., a Ruth L. Kirschstein National Research Service Award 1F31CA144566 to M.L.S. and US National Institutes of Health award 5RO1GM084181 to A.E.K. X-ray diffraction data were acquired at the Advanced Photon Source on the Northeastern Collaborative Access Team beamlines, which are supported by award RR-15301 from the National Center for Research Resources at the US National Institutes of Health. Use of the Advanced Photon Source is supported by the US Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

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Authors and Affiliations

  1. Department of Pediatric Oncology, Dana-Farber Cancer Institute and Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts, USA

    Michelle L Stewart & Loren D Walensky

  2. Program in Cancer Chemical Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA

    Michelle L Stewart & Loren D Walensky

  3. Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

    Emiko Fire & Amy E Keating

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Contributions

M.L.S. and L.D.W. designed, synthesized and characterized SAHB compounds for biochemical, structural and cellular analyses. M.L.S. performed the X-ray crystallography experiments with E.F. in the laboratory of A.E.K., who supervised the structural analyses. M.L.S. conducted all biochemical and cellular analyses, with guidance from L.D.W. L.D.W. and M.L.S. wrote the manuscript, which was reviewed and edited by E.F. and A.E.K.

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Correspondence to Loren D Walensky.

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Competing interests

L.W. is a scientific advisor board member and consultant for Aileron Therapeutics.

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Stewart, M., Fire, E., Keating, A. et al. The MCL-1 BH3 helix is an exclusive MCL-1 inhibitor and apoptosis sensitizer. Nat Chem Biol 6, 595–601 (2010). https://doi.org/10.1038/nchembio.391

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