Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2024 Jun;14(6):2378-2401.
doi: 10.1016/j.apsb.2024.02.010. Epub 2024 Feb 10.

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

Zhenwei Zhang  1 , Linghui Hou  1 , Dan Liu  1 , Shenglin Luan  2 , Min Huang  1 , Linxiang Zhao  1
Affiliations
Review

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

Zhenwei Zhang et al. Acta Pharm Sin B. 2024 Jun.

Abstract

For over two decades, the development of B-cell lymphoma-2 (Bcl-2) family therapeutics has primarily focused on anti-apoptotic proteins, resulting in the first-in-class drugs called BH3 mimetics, especially for Bcl-2 inhibitor Venetoclax. The pro-apoptotic protein Bcl-2-associated X protein (BAX) plays a crucial role as the executioner protein of the mitochondrial regulated cell death, contributing to organismal development, tissue homeostasis, and immunity. The dysregulation of BAX is closely associated with the onset and progression of diseases characterized by pathologic cell survival or death, such as cancer, neurodegeneration, and heart failure. In addition to conducting thorough investigations into the physiological modulation of BAX, research on the regulatory mechanisms of small molecules identified through biochemical screening approaches has prompted the identification of functional and potentially druggable binding sites on BAX, as well as diverse all-molecule BAX modulators. This review presents recent advancements in elucidating the physiological and pharmacological modulation of BAX and in identifying potentially druggable binding sites on BAX. Furthermore, it highlights the structural and mechanistic insights into small-molecule modulators targeting diverse binding surfaces or conformations of BAX, offering a promising avenue for developing next-generation apoptosis modulators to treat a wide range of diseases associated with dysregulated cell death by directly targeting BAX.

Keywords: Apoptosis; Dynamic conformational activation; Pro-apoptotic protein BAX; Small-molecule apoptosis modulators.

PubMed Disclaimer

Figures

Image 1
Graphical abstract
Figure 1
Figure 1
Regulation of apoptosis during health and disease. (A) Diverse cellular stress and cytostatic agents activate pro-apoptotic BH3-only proteins, which sequestrate anti-apoptotic proteins or trigger BAX activation, thereby permeabilizing the mitochondrial outer membrane to activate apoptosis. (B) Tumor cell populations avoid apoptosis through the overexpression of anti-apoptotic proteins during their evolution to the malignant state. (C) The overexpressed anti-apoptotic proteins are neutralized by BH3 mimetics and subsequently reactivate apoptosis in cancer. (D) Diverse BAX agonists directly bind to and conformationally activate BAX to restore apoptosis.
Figure 2
Figure 2
The stepwise mechanism of the BAX conformational activation. BH3-only proteins such as BIM BH3 (cyan) engage the trigger site of inactive BAX monomer (gray) (A) (PDB ID: 1F16), which converts BAX from a closed-loop to an open-loop conformation (B) (PDB ID: 2K7W) via the exposure of the BAX BH3 epitope and allosteric release of the C-terminal α9 helix (C). Following this step, the active BAX monomers translocate to the mitochondrial outer membrane (MOM) via its α9 helix. Then BH3-only proteins such as BIM (cyan) bind to the canonical site of MOM BAX (gray), contributing to the formation of core/latch domain swapped dimer (D) (PDB ID: 4ZIE), initiating a series of conformational changes that result in the formation of BH3-in-groove BAX dimer (E) (PDB ID: 4BDU). These symmetrical dimers can form high-order BAX oligomers (F), which execute MOMP to release cytochrome c.
Figure 3
Figure 3
(A) A novel BAX autoinhibition mechanism related to the BAX activation pathway. BAX inactive dimer (PDB ID: 4S0O, left); BAX inactive monomer (PDB ID: 1F16, right). (B) The crystal structure of BAX-BH3 helix (cyan) bound to anti-apoptotic protein Bcl-XL (gray) (PDB: 3PL7). (C) Bcl-2 BH4 domain (orange) (PDB ID: 1G5M) engages the BH4-binding domain on BAX (green) to inhibit BAX activation (PDB ID: 1F16). (D) NMR solution structure of vMIA's BAX-binding domain (vMIA-BBD) (light magenta) bound to BAX (gray) (PDB ID: 2LR1). (E) The co-crystal structure of 3C10 (gray) with an inactive form of BAX mutant (P168G) (lime) (PDB ID: 5W5X).
Figure 4
Figure 4
Overview of a diversity of functional and potential regulatory sites capable of (A) activating (PDB: 2K7W) and (B) inhibiting (PDB: 1F16) BAX pro-apoptotic activity.
Figure 5
Figure 5
(A) Structural features of the trigger site (PDB: 2K7W). (B) The NMR-derived structure of BIM-BH3 helix (cyan) bound to BAX (gray) (PDB: 2K7W). (C) The iterative structural optimization of BAX agonists bearing pyrazol-3-one core. (D) The design strategy of HDAC-BAX hybrids.
Figure 6
Figure 6
(A) Structural features of the S184 site (PDB: 2K7W). (B) The iterative structural optimization of BAX agonists targeting the S184 site.
Figure 7
Figure 7
(A) BAX agonist 11 engages the canonical site to promote BAX insertion into the MOM and oligomerization (PDB: 1F16). (B) BAX agonist 12 (OICR766A) targets an unrecognized binding site to activate BAX, which requires the presence of C126 (PDB: 2K7W). (C) The chemical reaction of the lipid electrophile trans-2-hexadecenal (t-2-hex) with BAX C126. (D) BAX agonist 13 (BIF-44) specifically binds to the vMIA site and allosterically mobilizes the key regions implicated in BAX activation, thereby sensitizing BH3-only proteins-triggered conformational activation of BAX (PDB: 2K7W).
Figure 8
Figure 8
(A) The trigger site antagonist 14 (Eltrombopag) as well as BAI site antagonists 15 (BAI1), 16, 17 (BAI2), and 18 block the conformational activation of BAX. (B) Structural features of the trigger site and BAI site on inactive BAX (PDB: 1F16).
Figure 9
Figure 9
(A) Several proposed canonical site antagonists 19 (MSN-50), 20 (MSN-125), and 21 (DAN004) inhibit BAX oligomerization via interfering with the BH3-grove dimer (PDB: 4BDU), as probed by chemical crosslinking studies. (B) BAX channel blockers 22 (Bci1) and 23 (Bci2) with an unrecognized binding site block the BAX channel activity to prevent BAX-mediated apoptosis.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Czabotar P.E., Lessene G., Strasser A., Adams J.M. Control of apoptosis by the Bcl-2 protein family: implications for physiology and therapy. Nat Rev Mol Cell Biol. 2014;15:49–63. - PubMed
    1. Oltvai Z.N., Milliman C.L., Korsmeyer S.J. Bcl-2 heterodimerizes in vivo with a conserved homolog, Bax, that accelerates programmed cell death. Cell. 1993;74:609–619. - PubMed
    1. Kiefer M.C., Brauer M.J., Powers V.C., Wu J.J., Umansky S.R., Tomei L.D., et al. Modulation of apoptosis by the widely distributed Bcl-2 homologue Bak. Nature. 1995;374:736–739. - PubMed
    1. Hsu S.Y., Kaipia A., McGee E., Lomeli M., Hsueh A.J. Bok is a pro-apoptotic Bcl-2 protein with restricted expression in reproductive tissues and heterodimerizes with selective anti-apoptotic Bcl-2 family members. Proc Natl Acad Sci U S A. 1997;94:12401–12406. - PMC - PubMed
    1. Tsujimoto Y., Finger L.R., Yunis J., Nowell P.C., Croce C.M. Cloning of the chromosome breakpoint of neoplastic B cells with the t(14;18) chromosome translocation. Science. 1984;226:1097–1099. - PubMed