Characterization of the colloidal properties, in vitro antifungal activity, antileishmanial activity and toxicity in mice of a di-stigma-steryl-hemi-succinoyl-glycero-phosphocholine liposome-intercalated amphotericin B.

1,2-Di-stigma-steryl-hemi-succinoyl-sn-glycero-3-phosphocholine (DSHemsPC) is a new lipid in which two molecules of stigmasterol (an inexpensive plant sterol) are covalently linked via a succinic acid to glycerophosphocholine. Since amphotericin B (AmB) interacts with sterols, we postulated that DSHemsPC could be used in AmB liposome formulations. Thirty-two DSHemsPC-AmB formulations were prepared using various mole ratios of DSHemsPC, phosphatidylcholine and phosphatidylglycerol at different pH. Most formulations had physical properties similar to AmBisome™: a particle diameter of about 100 nm, a monomodal distribution and a negative zeta potential. The red blood cell potassium release (RBCPR) IC50s for formulations spanned a range, with some being comparable to or greater than the IC50 observed using AmBisome™. A number of formulations had superior in vitro antifungal activity compared to AmBisome™ against all of the tested pathogenic yeasts and molds. The IC50s of formulations against Leishmania major promastigotes and amastigotes for certain formulations were comparable with AmBisome™ and Fungizone™. Most formulations had maximum tolerated intravenous doses (MTD) of less than 10 mg/kg. However the formulation consisting of DSHemsPC/DMPC/DMPG/AmB mole ratio 1.25/5.0/1.5/1.0 (prepared at pH 5.5) had excellent colloidal properties, a high IC50 for RBCPR, antifungal and antileishmanial activity similar to AmBisome™ and an MTD of 60 mg/kg. The characteristics of this DSHemsPC/DMPC/DMPG/AmB formulation make it suitable for further investigation to treat AmB-responsive pathogens.