SYNTHESIS OF CARBOXYMETHYLPULLULAN PEPTIDE DOXORUBICIN CONJUGATES ANDTHEIR PROPERTIES

The amino group of doxorubicin (DXR) was found to be bound to the carb oxyl group of carboxymethylpullulan (CMPul) either directly or through tetrapeptide spacers, including Gly-Gly-Phe-Gly, Gly-Phe-Gly-GIS and Gly-Gly-Gly-Gly. These conjugates had DXR contents of 6.1-7.1%, with t he degree of substitution of carboxymethyl groups being 0.6 per sugar moiety. These conjugates associate in phosphate-buffered saline (PBS) (pH 7.4), forming micelles with hydrophobic DXR inside and hydrophilic CMPul on the outside. The amounts of DXR released from the conjugates in the presence of rat liver lysosomal enzymes were determined by HPL C. The rate of the drug release differed among the conjugates tested. CMPul-DXR conjugate bound through Gly-Gly-Phe-Gly released 35% of its DXR over 24 h. On the other hand, CMPul-DXR conjugate without spacer r eleased no free DXR. The antitumor effect of each conjugate in rats be aring Walker 256 was studied by monitoring the tumor weights after a s ingle intravenous injection. Compared with DXR, CMPul-DXR conjugates b ound through Gly-Gly-Phe-Gly and Gly-Phe-Gly-Gly spacers significantly suppressed the tumor growth, while CMPul-DXR conjugate bound through Gly-Gly-Gly-Gly showed less antitumor effect than DXR. CMPul-DXR conju gate without spacer showed no in vivo antitumor effect even at a dose equivalent to as much as 20 mg/kg of DXR.