The Effect of Fatty Acid Substitution on the in Vitro Release of Amphotericin B from Micelles Composed of Poly(ethylene Oxide)-block-poly(N-hexyl Stearate-L-aspartamide)

The effect of fatty acid substitution on the in vitro release of amphotericin B (AmB) from micelles composed of poly(ethylene oxide)-block-poly[N-(6-hexyl stearate)-L-aspartamide] (PEO-b-PHSA) was investigated. PEO-b-PHSA at 11, 50 and 70% of stearic acid substitution self assembled into micelles that effectively encapsulate AmB by solvent evaporation and dialysis methods. The sustained release of AmB from PEO-b-PHSA micelles was evidenced, by measuring the transfer of the drug to lipid vesicles [dipalmitoyl phosphatidylcholine:cholesterol:dimyristoyl phosphatidyglycerol (3:1:0.25)]. The release of AmB for PEO-b-PHSA micelles was markedly influenced by the degree of fatty acid substitution--as it increased, the release of AmB slowed. Accordingly, drug release was found to correlate with haemolysis induced by AmB encapsulated in PEO-b-PHSA micelles. At 11% stearic acid substitution, encapsulation of AmB had little effect on the drug's ability to induce untoward haemolysis. In contrast, AmB stably encapsulated in PEO-b-PHSA micelles at 50 and 70% caused no hemolysis up to 20 microg/ml. Lastly, PEO-b-PHSA micelles at 50 and 70% were able to elute entirely as micelles during size-exclusion chromatography, indicating their stability toward dissociation after dilution. The results point to a nanoscopic drug depot that may release AmB at controlled rates.