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Antifungal drugs such as amphotericin B (AmB) interact with lipids and phospholipids located on fungal cell membranes to disrupt them and create pores, leading to cell apoptosis and therefore efficacy. At the same time, the interaction can also take place with cell components from mammalian cells, leading to toxicity. AmB was selected as a model antifungal drug due to the complexity of its supramolecular chemical structure which can self-assemble in three different aggregation states in aqueous media: monomer, oligomer (also known as dimer) and poly-aggregate. The interplay between AmB self-assembly and its efficacy or toxicity against fungal or mammalian cells is not yet fully understood. To the best of our knowledge, this is the first report that investigates the role of excipients in the supramolecular chemistry of AmB and the impact on its biological activity and toxicity. The monomeric state was obtained by complexation with cyclodextrins resulting in the most toxic state, which was attributed to the greater production of highly reactive oxygen species upon disruption of mammalian cell membranes, a less specific mechanism of action compared to the binding to the ergosterol located in fungal cell membranes. The interaction between AmB and sodium deoxycholate resulted in the oligomeric and poly-aggregated forms which bound more selectively to the ergosterol of fungal cell membranes. NMR combined with XRD studies elucidated the interaction between drug and excipient to achieve the AmB aggregation states, and ultimately, their diffusivity across membranes. A linear correlation between particle size and the efficacy/toxicity ratio was established allowing to modulate the biological effect of the drug and hence, to improve pharmacological regimens. However, particle size is not the only factor modulating the biological response but also the equilibrium of each state which dictates the fraction of free monomeric form available. Tuning the aggregation state of AmB formulations is a promising strategy to trigger a more selective response against fungal cells and to reduce the toxicity in mammalian cells.

Jim De Yoreo presented some slides on in situ AFM, TEM, dynamic force spectroscopy (DFS) and optical spectroscopy investigations of nucleation in the calcium carbonate system: The free energy barrier to homogeneous nucleation of calcite calculated within the framework of classical nucleation theory (CNT) is prohibitive, even at concentrations exceeding the solubility limits of the amorphous phases. Consistent with this analysis, during nucleation in pure solutions, in our in situ TEM experiments we observed direct formation of all phases, including amorphous calcium carbonate (ACC), as well as the three predominant crystalline phases: calcite, vaterite, and aragonite, even under conditions in which ACC readily forms. In addition to direct formation pathways, we observed indirect pathways in which ACC transforms to aragonite and vaterite through nucleation within or on the precursors, rather than via dissolution and reprecipitation. We also observed aragonate transformation to calcite, but never recorded an instance in which ACC transforms into calcite, except via dissolution–reprecipitation reactions.