The lipid composition, particle diameter and dose have been reported to affect the liposomal uptake in the tumor. However, effects of encapsulation amount of drugs in liposomes on the uptakes have scarecely been reported either in vitro or in vivo. In this study, we examined the uptake of liposomes containing CPT-11 by Ehrlich ascites carcinoma in vitro changing the encapsulation amount of CPT-11, and also the tissue distribution of liposomal CPT-11 in vivo with mice. After the addition of high concentration as CPT-11, the uptakes in the tumor cell by liposomes was about 1/3 of that by the solution in vitro. However, after the addition of same level as tissue distribution of CPT-11 in vivo, there is no difference on CPT-11 uptakes between liposome and solution. Thus lipid satulation in the tumor cells was observed by increasing liposomes in the medium. For a definite dose, the decrease of CPT-11 amount in the liposomes reduced the uptake in the tumor cell. Therefore, we thought that the uptake of liposomes in the tumor cell depended on lipid amount of liposomes. The increase of CPT-11 amount in the liposomes enhanced CPT-11 concentration in the serum, liver and tumor after administration of liposomal CPT-11 to the mice. An enhanced antitumor activity was expected from the result of SN-38 concentration in the tumor.
