Freeze drying of peptide drugs self-associated with long-circulating, biocompatible and biodegradable sterically stabilized phospholipid nanomicelles

The purpose of this study was to determine optimal lipid concentration range for lyophilization of sterically stabilized phospholipid nanomicelles (SSM) and the freeze drying feasibility of self-associated therapeutic peptide–SSM assemblies. SSM at 5–20 mM 1,2-distearoyl-sn-glycero-3-phosphoethanolamine–N-methoxy-poly(ethylene glycol 2000) (DSPE–PEG2000) were analyzed for particle size and viscosity before and after freeze drying which showed no significant changes (p > 0.05). However, a steep increase in viscosity was seen for SSM above 15 mM phospholipid implying micelle–micelle interaction. Greater shrinkage of lyophilized cakes was observed below 10 mM phospholipid while they were more fibrous above 15 mM. Therefore, 10–15 mM DSPE–PEG2000 was chosen as the optimal phospholipid concentration for lyophilized SSM. When vasoactive intestinal peptide (VIP), glucagon-like peptide 1 (GLP-1) or gastric inhibitory peptide (GIP) (each, 67 μM) was added to SSM (10 mM), formulations showed no significant change in particle size, peptide fluorescence and peptide α-helicity before and after lyophilization. In conclusion, we found that peptide drug–SSM interactions are conserved during lyophilization.