The tumor distribution and the disposition of serum albumin were investigated in mice bearing Sarcoma 180. The albumin labeled with fluoresceinisothiocyanate(FITC) were administered to the mice. The FITC-labeled albumin acylated with acid anhydrides, such as acetic anhydride, glutaric anhydride, maleic anhydride and succinic anhydride, were also administered to the mice in order to investigate the effect of chemical modification. The plasma concentration of each acylated albumin was significantly lower than that of the non-acylated albumin at 24 h after administration. The tissue distributions of the acylated albumin were also decreased compared to those of the non-acylated albumin. Especially, the accumulation of albumin in the liver and spleen was significantly reduced with the glutarylation and maleylation. Urinary excretion of albumin was significantly increased with the acylation because the degradation rates of the acylated albumins were much faster than that of non-acylated albumin. On the other hand, the acylated and non-acylated albumin were accumulated effectively in the tumor tissue in mice bearing Sarcoma 180. It was found that the tumor distribution of albumin was not impaired by the acylation. It was suggested, therefore, that the glutarylated and maleylated albumin were valuable for relative tumor-selectivity and might be utilized in the macromolecular carrier system of antitumor drugs.
