Chemigenetic analysis and efficacy of novel antifungal drugs that target fungal pH signalling

Collectively, fungal diseases pose a greater threat to animals, plants and ecosystems than other types of infectious micro-organism. Fungal infections of man kill millions and most often occur in patients with severe underlying health conditions such as cancer, or chronic lung disorders such as cystic fibrosis. Fungal infections of plants destroy enough crops annually to feed many millions of people. However, there are a very limited number of antifungal drugs available for use agriculturally or in the clinic and some classes of antifungal drugs, for example the azoles. are therefore used to treat both human and plant fungal infections. In 2018 azole-based fungicides accounted for 34% of the antifungal agents used to treat crops. Worryingly, resistance to all classes of available antifungal drugs is increasing and azole resistance occurring in agricultural settings crosses over into the clinic in around 40% of cases in some settings. This project builds on decades of previous genetic and infection studies, including a PhD project where a new set of chemicals were showed as having antifungal activity. These chemicals attack a fungal signalling mechanism needed for infection and invasion by fungal pathogens in man, plants, animals and we will now work to understand how they work. We will also try to make them more potent, and work with industry to develop them for use in agriculture or in the clinic.

The repertoire of antifungal agents available to treat fungal diseases is sparse, the rate at which we discover new antifungal modes of action (MOAs) is unacceptably slow, and antifungal resistance is on the rise.

The focus of this project is a highly conserved and fungus-specific signalling pathway used by fungi to adapt to the pH of the extracellular environment. Extracellular pH profoundly influences the production and functionality of fungal secreted proteases, toxins, and substrate degrading enzymes, as well as ion and nutrient transporters. As such, fungal viability is heavily dependent upon versatile adaptations to pH flux. pH adaptation is driven by the fungus-specific PacC/Rim signalling pathway which we discovered, and extensively characterised, in the model ascomycete Aspergillus nidulans. PacC/Rim signalling is highly conserved, and indispensable for full infectivity, in the overwhelming majority of fungal pathogens.

With recent BBSRC iCASE funding we devised a powerful genetic screen with which to seek chemical inhibitors of PacC/Rim signalling. We achieved this by repurposing of a genetic selection technique which was initially devised to seek novel regulators of PacC processing in A. nidulans. The aim of this programme is to identify novel antifungal MOAs which inhibit fungal pH signalling. To this end we have assembled an integrated workflow comprising phenotypic, genetic and chemical profiling intended to maximise efficiency of lead discovery and mitigate attrition due to off target or toxic activities.

The programme is comprised of four research objectives.

1. Screen reference libraries for hit-like chemistries and extant drugs which inhibit PacC/Rim signalling
2. Establish proof of on-target and pan-fungal activity and low toxicity
3. Pursuit and definition of Structure-Activity Relationships (SARs)
4. Identify targets and modes of action, and study antifungal efficacy