Enhanced Stability of PEG-block-poly(N-hexyl stearate L-aspartamide) Micelles in the Presence of Serum Proteins

Polyethylene glycol-phospholipid micelles form a major class of nanocarriers in pharmacy and medicine due to proven capability in drug solubilization, sustained drug release, and evidence for targeted drug delivery in vivo. In this report, we have prepared micelles composed of PEG-block-poly(N-hexyl stearate L-aspartamide) (PEG-b-PHSA), having nine stearic acid side chains, and have studied their stability in the presence of serum proteins by Forster resonance energy transfer (FRET) experiments. In the presence of serum albumin, alpha and beta globulins, or gamma globulins, there are minimal changes in FRET over two hours in vitro, indicating integrity of PEG-b-PHSA micelles. In contrast, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-5000] (PEG-DSPE) micelles lose FRET over two hours in vitro, especially in the presence of alpha and beta globulins, indicating the disruption of PEG-DSPE micelles and leakage of fluorescent probes. Owing to the aliphatic nature of DSPE and PHSA, both PEG-b-PHSA and PEG-DSPE micelles efficiently solubilize amphotericin B (AmB), a poorly water-soluble antifungal agent used to combat systemic mycoses. However, only PEG-b-PHSA micelles gradually liberate AmB in the presence of alpha and beta globulins, based on time-dependent changes in the self-aggregation state of AmB, monitored by UV/vis spectroscopy. PEG-b-PHSA micelles are remarkably stable in the presence of serum proteins and a more stable alternative for poorly water-soluble drugs, which have been solubilized by PEG-DSPE micelles.