# An Antifungal with a Novel Mechanism of Action Discovered via Resistance Gene-Guided Genome Mining

## TL;DR

A new antifungal drug with a unique mechanism was discovered by targeting an enzyme crucial for fungal amino acid production.

## Contribution

Acetolactate synthase (ALS) is validated as a novel antifungal target, with a new inhibitor discovered via resistance gene-guided genome mining.

## Key findings

- HB-35018, a novel compound, potently inhibits ALS and outperforms existing inhibitors against pathogenic fungi.
- HB-35018 forms a unique covalent bond with ALS, distinct from known inhibitors, revealed by cryo-electron microscopy.
- ALS is essential for fungal virulence in a mouse model of invasive aspergillosis.

## Abstract

Invasive fungal infections claim over two million lives
annually,
a problem exacerbated by rising resistance to current antifungal treatments
and an increasing population of immunocompromised individuals. Despite
this, antifungal drug development has stagnated, with few novel agents
and fewer novel targets explored in recent decades. Here, we validate
acetolactate synthase (ALS), an enzyme critical for branched-chain
amino acid biosynthesis and absent in humans, as a promising target
for new therapeutics. Using resistance gene-guided genome mining,
we discovered a biosynthetic gene cluster in Aspergillus terreus encoding HB-35018 (1), a novel spiro-cis-decalin tetramic acid that
potently inhibits ALS. Biochemical and antifungal assays demonstrate
that 1 surpasses existing ALS inhibitors in efficacy
against Aspergillus fumigatus and other pathogenic
fungi. Structural studies via cryo-electron microscopy reveal a unique
covalent binding interaction between compound 1 and ALS,
distinct from known inhibitors, and finally, we demonstrate that ALS
is essential for virulence in a mouse model of invasive aspergillosis.
These findings position ALS as a promising target for antifungal development
and demonstrate the potential of resistance gene-guided genome mining
for antifungal discovery.