A Fungal-Selective Cytochrome bc1 Inhibitor Impairs Virulence and Prevents the Evolution of Drug Resistance

Abstract

To cause disease, a microbial pathogen must adapt to the challenges of its host environment. The leading fungal pathogen Candida albicans colonizes nutrient-poor bodily niches, withstands attack from the immune system, and tolerates treatment with azole antifungals, often evolving resistance. To discover agents that block these adaptive strategies, we screened 300,000 compounds for inhibition of azole tolerance in a drug-resistant Candida isolate. We identified a novel indazole derivative that converts azoles from fungistatic to fungicidal drugs by selective inhibition of mitochondrial cytochrome bc1. We synthesized 103 analogs to optimize potency (0.4 μM IC50) and fungal selectivity (28-fold over human). In addition to reducing azole resistance, targeting cytochrome bc1 prevents C. albicans from adapting to the nutrient-deprived macrophage phagosome and greatly curtails its virulence in mice. Inhibiting mitochondrial respiration and restricting metabolic flexibility with this synthetically tractable chemotype provides an attractive therapeutic strategy to limit both fungal virulence and drug resistance.

Discovery of a novel and selective fungicide that targets fungal cell wall to treat dermatomycoses: 1,3‐bis(3,4‐dichlorophenoxy)propan‐2‐aminium chloride

“…Usually, a SI value higher than 10 is recommended to ensure the safety of an antimicrobial substance . The higher the SI value of a substance, the better its selective performance against the pathogen and the lower the toxicity against the studied host cell (lymphocytes) . In this study, the only compound with IS > 10 was the 2j , which presented the safest biological profile with selectivity against dermatomycosis fungi.…”

“…The SI for the active compounds presented in Table corresponds to the ratio between the IC 50 (concentration required to inhibit 50% of the human lymphocytes viability) and the average of subinhibitory concentrations (MIC/2; MICs are presented in Table ) for dermatophytes and Candida spp. Usually, a SI value higher than 10 is recommended to ensure the safety of an antimicrobial substance . The higher the SI value of a substance, the better its selective performance against the pathogen and the lower the toxicity against the studied host cell (lymphocytes) .…”

“…23,24,51 The higher the SI value of a substance, the better its selective performance against the pathogen and the lower the toxicity against the studied host cell (lymphocytes). 23,24,51,52 In this study, the only compound with IS > 10 was the 2j, which presented the safest biological profile with selectivity against dermatomycosis fungi. Therefore, this compound was chosen for other toxicity studies, for the mechanism of action investigation and development of a semisolid formulation (hydrogel).…”

Derivatives of the antimalarial drug mefloquine are broad spectrum antifungal molecules with activity against drug-resistant clinical isolates

“…Two recently identified antifungal small molecules that directly target the mitochondria, T-2307 (47) and Inz-1 (48), have increased activity in non-fermentable carbon sources such as glycerol as compared to standard glucose media. If mitochondrial disruption is the process driving the majority of MEF-derivative antifungal activity, we reasoned that the MIC for the MEF-derivatives should be much lower in the presence of glycerol; however, the MICs of the MEF-derivatives were decreased modestly (e.g., 2-fold; data not shown) for some derivatives or were unchanged.…”

Clearing the FoG: Antifungal tolerance is a subpopulation effect that is distinct from resistance and is associated with persistent candidemia

“…Trailing growth is sensitive to environmental conditions, including pH, temperature and nutrients 3,49,50 and is usually detected in liquid cultures. Definitions of ‘tolerance’ vary and generally describe survival or growth above inhibitory concentrations 2,10,28,38,51-56 , detected as slow growth within the zone of inhibition using E-strips or disk diffusion assays 57,58 , or in broth microdilution assays 38,39 . Tolerance can be affected by several adjuvant drugs 19-24 , iron levels 19,59 , genes involved in vacuolar protein sorting 38,47 , as well as calcium flux 28,55,59-61 .…”