Strategies for maintaining the particle size of peptide DNA condensates following freeze-drying

The particle size of peptide DNA condensates were studied after freeze-drying and rehydration as a function of sugar excipient, concentration, pH, DNA concentration, and peptide condensing agent. In the absence of an excipient, freeze-dried 50 mu g/ml AlkCWK(18) (iodoacetic acid alkylated Cys-Typ-Lys(18)) DNA condensates formed large fibrous flocculates on rehydration. Of the sugars tested as lyoprotectants, sucrose proved most effective at preserving particle size during rehydration. The addition of 5 wt/vol% sucrose preserved a mean particle diameter of less than 50 nm during rehydration of AlkCWK(18) DNA condensates prepared at DNA concentrations up to 200 mu g/ml; however, higher DNA concentrations led to the formation of insoluble fibrous flocculates. Substitution of polyethylene glycol (PEG)-CWK18 as a DNA condensing peptide eliminated the need for sucrose, resulting in peptide DNA condensates that retained particle size when rehydrated in water or normal saline at concentrations up to 5 mg/ml. The results suggest that sucrose functions primarily as a bulking agent during freeze-drying that only preserves the particle size of AlkCWK(18) DNA condensates up to a maximum concentration of 200 mu g/ml. Alternatively, the steric layer created on the surface of PEG-CWK18 DNA condensates provides far more efficient lyoprotection, preserving their particle size at a concentration of 5 mg/ml without a bulking agent. (C) 2000 Elsevier Science B.V. All rights reserved.