Cancer cell death strategies by targeting Bcl-2's BH4 domain.

The Bcl-2-family proteins have long been known for their role as key regulators of apoptosis. Overexpression of various members of the family is associated with oncogenesis. Its founding member, anti-apoptotic Bcl-2 regulates cell death at different levels, whereby Bcl-2 emerged as a major drug target to eradicate cancers through cell death. This resulted in the development of venetoclax, a Bcl-2 antagonist that acts as a BH3 mimetic. Venetoclax already entered the clinic to treat relapse chronic lymphocytic leukemia patients. Here, we discuss the role of Bcl-2 as a decision-maker in cell death with focus on the recent advances in anti-cancer therapeutics that target the BH4 domain of Bcl-2, thereby interfering with non-canonical functions of Bcl-2 in Ca2+-signaling modulation. In particular, we critically discuss previously developed tools, including the peptide BIRD-2 (Bcl-2/IP 3 R-disrupter-2) and the small molecule BDA-366. In addition, we present a preliminary analysis of two recently identified molecules that emerged from a molecular modeling approach to target Bcl-2's BH4 domain, which however failed to induce cell death in two Bcl-2-dependent diffuse large B-cell lymphoma cell models. Overall, antagonizing the non-canonical functions of Bcl-2 by interfering with its BH4-domain biology holds promise to elicit cell death in cancer, though improved tools and on-target antagonizing small molecules remain necessary and ought to be designed. • Anti-apoptotic Bcl-2 prevents cell death through its mitochondrial and endoplasmic reticulum functions. • Anti-apoptotic Bcl-2 via its BH4 domain prevents pro-apoptotic, IP 3 receptor-driven Ca2+ signaling. • Tools that target Bcl-2's BH4 domain such as BIRD-2 elicit cell death in several cancer cell types and are complementary with BH3 mimetics. • BDA-366 was proposed as the first small molecule BH4-domain antagonist, yet triggers cell death independently of Bcl-2. • The first bona fide BH4-domain antagonist small molecule still needs to emerge. [ABSTRACT FROM AUTHOR]