Optimization of a Method to Prepare Liposomes Containing HER2/Neu-Derived Peptide as a Vaccine Delivery System for Breast Cancer

The purpose of this study was to optimize a method for the encapsulation of P5 peptide, a new designed peptide containing MHC class I epitopes from rat HER2/neu protein, into liposomes as an approach for breast cancer vaccine formulation. The efficiency of liposomal encapsulation of peptides is generally low and development of an optimized method to increase encapsulation efficiency is a big challenge. In this study, P5 peptide was encapsulated into liposomes using the following three different methods based on film-hydration procedure. In Method A, the lipid film containing P5 was hydrated using buffer and then extruded to 100 nm using polycarbonate filter. In Method B all the steps were the same as method A except that the lipid film was hydrated in buffer containing 10% (v/v) of DMSO and P5 peptide. In Method C, P5 peptide was added to preformed liposomes (40 mM) in the presence of ethanol (30% v/v) and incubated at 25 ºC for 1h. The highest peptide encapsulation efficiency was achieved using Method C (44%). The presence of P5 peptide in purified liposomes was also confirmed using SDS- PAGE analysis. Investigation on the effects of procedure parameters of method C on encapsulation efficiency demonstrated this method is an optimized procedure for encapsulating P5 peptide. Maximal recovery from liposomes for the accurate quantification of peptide was discovered using acidified isopropanol at 1:2 of sample to solvent ratio (v/v). The optimal methods of encapsulation and peptide content determination in liposomes can accelerate the development of liposomal vaccine formulations.