Strategies for Covalent Attachment of Doxorubicin to Poly(PEG-Lys), a New Water-Soluble Poly(ether urethane

Abstract

Poly(PEG-Lys) is a new, water soluble poly(ether urethane) that has shown promise as an injectable drug carrier. To evaluate the possible use of this drug carrier in chemotherapy, three different approaches for the covalent attachment of doxorubicin to the pendent carboxylic acid groups of poly(PEG- Lys) were developed. In one approach, the pendent carboxylic acid groups of poly(PEG-Lys) were converted to N-hydroxysuccinimide active esters, which spontaneously formed hydrolytically stable amide bonds upon reaction with the amino group located on the daunosamine ring of doxorubicin. The amount of amide-bound doxorubicin was about 7.3 mg/100 mg of conjugate. In a second approach, the degradable hydrazone linkage was formed by reaction of the polymeric hydrazide derivative of poly(PEG-Lys), designated as poly(PEG-Lys hydrazide), with the 13-keto group of doxorubicin. After purification, the amount of carrier-bound doxorubicin was 13.5 mg/100 mg of conjugate. In the third approach, the conjugation of doxorubicin via secondary amine linkages was explored. In this approach, the aldehyde derivative of poly(PEG Lys), desig nated as poly(PEG-Lys-aldehyde), was reacted with doxorubicin, followed by re duction of the intermediate Schiff base with sodium cyanoborohydride. After extensive purification of the carrier, the amount of bound doxorubicin was 10 mg/100 mg of conjugate. All conjugates were characterized by UV/Vis and FTIR spectroscopy and by thin layer chromatography. The conjugates were free of de tectable contamination by unbound drug.