Description

Here is a 2025 powerhouse paper that's redefining the fight against Acute Myeloid Leukemia (AML)—a brutal foe notorious for dodging therapies like BCL-2 inhibitors such as Venetoclax. Enter the game-changer: BH3 mimetics (those clever drugs that ape the BH3 domain, a pro-apoptotic α-helical snippet from the BCL-2 family proteins) supercharged with non-canonical amino acids (ncAAs) for dual takedown of MCL-1 and BCL-xL.

Through savvy site-saturation mutagenesis, the team dialed up binding affinities to impressive IC50s of 2.77 nM for MCL-1 and 10.69 nM for BCL-xL—a fourfold leap in potency. This precision fit—nailed by rigid cyclohexyl side chains for unmatched shape complementarity and hydrophobic packing—simply can't be pulled off with the standard 20 amino acids!

Citation: Wang et al., 2025

The 20 canonical amino acids offer a limited set of side-chain shapes. For targets that require precise geometric complementarity, such as protein-protein interactions in oncology, this limitation constrains drug design. Non-canonical amino acids provide access to molecular geometries that do not exist in nature.

In work targeting acute myeloid leukaemia resistance, researchers used ncAAs with rigid cyclohexyl side chains to optimise BH3 mimetic peptides against MCL-1 and BCL-xL, two anti-apoptotic proteins that drive resistance to venetoclax. Site-saturation mutagenesis with ncAAs achieved IC50 values of 2.77 nM (MCL-1) and 10.69 nM (BCL-xL), a fourfold potency improvement. The rigid side chains provided shape complementarity and hydrophobic packing that standard amino acids could not deliver (Wang et al., 2025).

This demonstrates a general principle: when binding affinity depends on geometric fit, expanding beyond the natural amino acid palette can access potency gains that conventional protein engineering may not reach.

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