C2′-OH of Amphotericin B Plays an Important Role in Binding the Primary Sterol of Human Cells but Not Yeast Cells

Abstract

Amphotericin B (AmB) is a clinically vital anti-mycotic but is limited by its severe toxicity. Binding ergosterol, independent of channel formation, is the primary mechanism by which AmB kills yeast, and binding cholesterol may primarily account for toxicity to human cells. The leading structural model predicts that the C2′ hydroxyl group on the mycosamine appendage is critical for binding both sterols. To test this, the C2′ hydroxyl group was synthetically deleted and the sterol binding capacity of the resulting derivative, C2′deOAmB, was directly characterized via isothermal titration calorimetry. Surprisingly, C2′deOAmB binds ergosterol and, within the limits of detection of this experiment, does not bind cholesterol. Moreover, C2′deOAmB is nearly equipotent to AmB against yeast but, within the limits of detection of our assays, is non-toxic to human cells in vitro. Thus, the leading structural model for AmB/sterol binding interactions is incorrect, and C2′deOAmB is an exceptionally promising new antifungal agent.

The Role of Signaling via Aqueous Pore Formation in Resistance Responses to Amphotericin B

“…Recent efforts to improve the AmB therapeutic index have yielded a new derivative (C2=deOAmB), which binds ergosterol but not cholesterol (83). C2=deOAmB is toxic to yeasts but not to human primary kidney cells, confirming the role that cholesterol binding to AmB plays in developing drug nephrotoxicity.…”

New facets of antifungal therapy

“…74 The prototype of these derivatives is amphotericin B with a C'2 hydroxyl group deletion, which allows it to only bind to fungal ergosterol and not mammalian cholesterol. 75 In vivo toxicity and therapeutic experiments using a systemic candidiasis murine model demonstrated that amphotericin B methyl urea (AmBMU) was less toxic and more effective than the traditional deoxycholate amphotericin B formulation. 74 These results contribute to the exciting progress in antifungal drug development linked to the gold standard antifungal agent amphotericin B.…”

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

“…An analogue in which the mirror image of 3, 6 dideoxy 3-amino--D-glucose replaced mycosamine was also inactive (Croatt and Carreira, 2011). Burke and co-workers found that synthetic 2′-deoxy amphotericin B (lacking the 2′ hydroxyl on the mycosamine sugar) was active and had increased specificity for ergosterol-containing membranes (Wilcock et al, 2013). However, this analogue could not be chemically synthesised in large quantities (Davis et al, 2015).…”