How does a new antimicrobial kill the fungi that invade immunosuppressed patients?

Hard-to-treat fungal infections are a growing problem both UK and worldwide (rates respectively 10,000 and 2M/year; mortality 40% and 25%). Rates are rising because of increased immunosuppression caused by uncontrolled diabetes and cancer therapy (UK), and AIDS (worldwide). Fungal epidemiology is also changing with multidrug resistant species such as Candida auris emerging within the last few years. Other rarer fungi such as Lomentospora spp. have no treatment options, being resistant to all current agents.

Olorofim is a first-in-class anti-fungal developed by the industrial partner F2G Ltd (Eccles, Manchester [1]. Discovery of an antimicrobial with a completely new mode of action is rare. Echinocandins were developed over 20 years ago as the first class of antifungals active against cell walls. The orotomide class represents the only new class of antifungal in Phase 2 clinical trial for 15 years. The value of antifungals worldwide is ~$15B/yr. Anti-cell wall therapy by echinocandins are a successful recent addition (>20 years ago) but imperfect due to fungistatic action, and some fungal species show innate resistance. Fungi also attack crops (>$200B loss / year), so new antifungals are needed to maximise food security. Our work will underpin future development of Olorofim-related compounds to protect plants. Developing understanding of Olorofim, determining its synergy with other antifungals and predicting how drug resistance might develop will maximise its societal benefits. The project will create translational opportunities for inhibitors of other fungal DHODH enzymes, including Mucor and many Candida species.

The project will look into the pathways by which Olorofim kills fungi, a key aspect of its therapeutics [2], which likely contributes to it being highly effective in immunosuppressed invasive fungal models [3]. Olorofim targets the enzyme dihydroorotic acid dehydrogenase (DHODH), an essential ubiquitous enzyme in pyrimidine synthesis, strongly selecting for the Aspergillus isozyme compared to the human (2000:1). In model budding yeast, pyrimidine starvation is lethal more rapidly (t½ 16 hours) than starvation for any other metabolite tested (e.g. phosphate t½ 25 days) because there is no pyrimidine starvation programme [4]. This leaves many possible targets to consider in its killing of cells, as pyrimidines are required for the synthesis of all classes of large biomolecule: DNA, RNA, sugar modifications for proteins, and phospholipids. To some extent the study will therefore also expand our knowledge of the basic biology of how the key pathways under attack by Olorofim signal to each other.

The cell lysis seen with medium term exposure to Olorofim has features that indicate cell wall damage, which fits with an effect via sugar modifications of cell wall proteins. However, another major class of antifungals that target the cell wall, the echinocandins, is only fungistatic. Therefore, this project will focus on what combination of effects gives Olorofim the ability to kill fungi. At UCL we will work with non-pathogenic strains that represent the best models for virulent strains. At F2G, the student will learn techniques in filamentous fungal molecular biology, antifungal screening, fungal biochemistry and chemistry developing target proteins for drug discovery, as well as being immersed in the operations of a small biotechnology company.

Overall Plan
1. Validate S cerevisiae as a model system
2. Determine how cell wall targeting interacts with other pyrimidine pathways
3. Determine how pyrimidine starvation kills fungi with pathogenic potential including both Aspergilli (A. nidulans) and Candida (C. albicans).
4. Confirm these pathways apply in pathogenic filamentous fungi (at F2G)

Applications
Applications must be complete, including both references, by 24th January 2020





Keywords: drugs, small molecule inhibitors, pathways, signaling, infection, infectious disease, antibiotic, antimicrobial, fungi, yeast, biotechnology