Amphotericin primarily kills yeast by simply binding ergosterol

Abstract

Amphotericin B (AmB) is a prototypical small molecule natural product that can form ion channels in living eukaryotic cells and has remained refractory to microbial resistance despite extensive clinical utilization in the treatment of life-threatening fungal infections for more than half a century. It is now widely accepted that AmB kills yeast primarily via channel-mediated membrane permeabilization. Enabled by the iterative cross-coupling-based synthesis of a functional group deficient derivative of this natural product, we have discovered that channel formation is not required for potent fungicidal activity. Alternatively, AmB primarily kills yeast by simply binding ergosterol, a lipid that is vital for many aspects of yeast cell physiology. Membrane permeabilization via channel formation represents a second complementary mechanism that further increases drug potency and the rate of yeast killing. Collectively, these findings (i) reveal that the binding of a physiologically important microbial lipid is a powerful and clinically validated antimicrobial strategy that may be inherently refractory to resistance, (ii) illuminate a more straightforward path to an improved therapeutic index for this clinically vital but also highly toxic antifungal agent, and (iii) suggest that the capacity for AmB to form proteinlike ion channels might be separable from its cytocidal effects.small molecules | protein-like functions | N-methyliminodiacetic acid boronates

Polyene antibiotic that inhibits membrane transport proteins

“…This finding pointed to the importance of this hydroxyl group for pore formation and led to the conclusion that channel formation is a necessary condition for the antifungal activity of amphotericin B. However, no explanation was given for the residual activity of the compound, and the residual membrane permeabilization that was observed in this study was likely attributable to an aspecific effect caused by the positively charged nature of the methyl-ester version of the Carreira group, as previously suggested (24). Interestingly, the antifungal activity of natamycin is comparable to the activities of both amphotericin derivatives (24,26).…”

“…However, no explanation was given for the residual activity of the compound, and the residual membrane permeabilization that was observed in this study was likely attributable to an aspecific effect caused by the positively charged nature of the methyl-ester version of the Carreira group, as previously suggested (24). Interestingly, the antifungal activity of natamycin is comparable to the activities of both amphotericin derivatives (24,26). This implies that these amphotericin B derivatives are also able to inhibit a broad class of essential membrane transport proteins by binding to ergosterol, thus explaining their antifungal activities.…”

“…Gray et al (24) concluded that amphotericin B primarily kills yeast by simply binding ergosterol and that membrane permeabilization via pore formation represents a second complementary mechanism. Earlier studies from the laboratory of Carreira showed that substituting the hydroxyl group at position 35 of the methyl-ester version of amphotericin B led to a significant but not complete reduction in K + efflux from model membrane vesicles (25,26).…”

Polyene macrolide biosynthesis in streptomycetes and related bacteria: recent advances from genome sequencing and experimental studies

“…The mechanisms of antibiotic action are complex and still incompletely understood, even after five decades of research. However, recent studies with non-permeabilising amphotericin analogues suggest that transmembrane channels are not essential for antifungal activity, sequestering of ergosterol disrupts multiple cellular processes and may be sufficient (Szpilman et al, 2008;Gray et al, 2012). The new "sponge model" proposes that aggregates of amphotericin B align on the membrane surface and extract ergosterol from the lipid bilayer (Anderson et al, 2014).…”

Antifungal Drug Development: Challenges, Unmet Clinical Needs, and New Approaches

“…The oldest class of antifungal drugs is the polyenes, of which amphotericin B is the only example used to treat systemic infections. Amphotericin B binds to ergosterol, a membrane sterol that is unique to fungi, as part of its mechanism of action (Gray et al 2012). Amphotericin B is fungicidal and is the most broad spectrum antifungal available.…”