In-silico approach as a tool for selection of excipients for safer amphotericin B nanoformulations

Safer and efficacious Amphotericin B (AmB) nanoformulations can be designed by augmenting AmB in the monomeric or super-aggregated state, and restricting the aggregated state, by choosing the appropriate excipient, which can be facilitated by employing in-silico prediction as a tool. Excipients selected for the study included linear fatty acids from caprylic (C₈) to stearic(C₁₈) and the stearate based amphiphilic surfactants polyoxyl-15-hydroxystearate (PS15) and polyoxyl-40-stearate (PS40). Blend module was employed to determine the two miscibility parameters mixing energy (E_mix) and interaction parameter (χ). AmB-excipient interactions were modelled using molecular docking software. The fatty acids revealed a decrease in E_mix and χ values with increase in carbon chain length, suggesting enhanced affinity with increase in fatty acid hydrophobicity. Significantly higher affinity was observed with amphiphilic surfactants, in particular PS40 which exhibited negative values of E_mix and χ proposing very high degree of miscibility. Molecular docking study confirmed extensive interaction of all the excipients with the AmB polyene chain. PS15 and PS40 displayed in addition hydrophilic interactions with the mycosamine and polyol moieties with PS40 exhibiting complete wrapping of the AmB molecule. PS15 demonstrated only partial wrapping, attributed to the shorter ethylene oxide chain. AmB nanosuspensions (NS) were prepared by in situ nanoprecipitation using the excipients and the AmB state identified by UV scanning between 300-500 nm. AmB NS with fatty acids and PS15-AmB NS revealed a high intensity peak between 330-350 nm of aggregated AmB and low intensity monomeric peaks between 405-415 nm reflecting predominance of the aggregated state. PS40-AmB NS on the other hand revealed complete absence of aggregated state and a high intensity peak between 321-325 nm which corresponded to the super-aggregated state. Also, the super-aggregated state slowly released the safe monomeric form without aggregate formation. Furthermore, very low hemolysis seen with PS40-AmB NS confirmed low toxicity attributed to the safer super-aggregated state and while higher hemolysis as anticipated was seen with PS15-AmB NS (aggregated state). The basis for selection of the appropriate excipient for design of safer AmB nanoformulations would be those excipients that exhibit negative values of miscibility parameters E_mix and χ, exhibit interaction with the hydrophobic and hydrophilic regions of AmB and demonstrate complete wrapping of AmB in the molecular docking study. Our study thus demonstrates feasibility of in-silico prediction as a practical tool for excipient selection for safer AmB nanoformulations.