Antitumor effects and toxicities of carboxymethylpullulan-peptide-doxorubicin conjugates

In vivo antitumor effects of the conjugates of doxorubicin (DXR) with carboxymethylpullulan (CMPul) through tetrapeptide spacers were compared with those of DXR against tumor-bearing rats. CMPul-DXR conjugates bound through Gly-Gly-Phe-Gly and Gly-Phe-Gly-Gly spacers were found to be more potent than DXR after a single intravenous injection in rats bearing Walker 256 carcinosarcoma. These conjugates were also more effective than DXR in rats bearing Yoshida sarcoma. However, CMPul-DXR conjugate bound through Gly-Gly-Gly-Gly was less effective against Walker 256-bearing rats than DXR. Body weight loss of CMPul-DXR conjugates in rats, on the other hand, was less than that of DXR at a DXR dose of 10 mg/kg. Lethal doses of CMPul-DXR conjugates in CDF1 mice were about 3-times higher than that of DXR. These data suggest that the therapeutic index of CMPul-DXR conjugates bound through appropriate peptide spacers was increased more than that of DXR. However, CMPul-DXR conjugates tested were all less effective than DXR against Walker 256 cells in vitro. Also, 125I-labeled CMPul-DXR conjugate accumulated much less in the cells than 14C-DXR.