Gly-Gly-Phe-Gly is a peptide spacer and can be applied to Doxorubicin (DXR) conjugates.
References:
[1]. Shiose Y, et al. Systematic research of peptide spacers controlling drug release from macromolecular prodrug system, carboxymetldextran polyalcohol-peptide-drug conjugates. Bioconjug Chem. 2009 Jan;20(1):60-70.
















