Unpacking amphotericin B toxicity: a critical review of amphotericin B aggregation and its link to toxicity and antifungal activity

Amphotericin B (AmB) is a polyene antifungal that, despite its severe dose-limiting toxicity, is the most effective drug to treating invasive fungal infections. The drug's toxicity arises from its poor selectivity for ergosterol over cholesterol and its tendency to aggregate. Understanding the relationship between toxicity and aggregation is challenging due to the drug's complex mechanism of action, yet imperative to improve the safety profiles of existing and new polyene-based antifungal drugs. In this review, we critically examine and summarise studies that investigate the aggregation of AmB and its relationship to toxicity. As the aggregation behaviour of AmB is highly sensitive to environmental conditions, we provide an in-depth analysis of sample preparation, characterisation of aggregates and control experiments. While data from haemolysis, animal, and cell-based studies consistently show that oligomeric AmB is more toxic than larger aggregates, findings on the toxicity of monomeric AmB inconsistent. Our collated data underscores the need for careful consideration of sample preparation and proper use of vehicle controls when studying the complex relationship between the supramolecular organisation of AmB and its biological effects.