Effects of liposome dose and the presence of lymphosarcoma cells on blood clearance and tissue distribution of large unilamellar liposomes in mice.
Large unilamellar liposomes (50 to 500 mumol of lipid per kg) were injected i.v. or i.p. into normal and lymphosarcoma-bearing mice. The percentage of the dose remaining in the blood and that accumulated in liver, spleen, and various other organs was measured 4 hr after injection. The results indicate that liposomes cause a dose-dependent saturation of the hepatic and splenic clearance capacities. One day after injection of 10(6) lymphosarcoma cells, the capacity of the tumor-bearing mice to eliminate liposomes from the blood (in a 4-hr period) was inhibited 30 to 50%. This could be ascribed to a decreased activity of the reticuloendothelial system caused by the tumor cells, as was indicated by the simultaneous inhibition of carbon clearance. Six days after injection of the lymphosarcoma cells, the elimination of liposomes from the blood in tumor-bearing mice was restored to the value in normal mice. The possible involvement of tumor cells in the uptake of liposomes by the liver was investigated morphologically after i.v. injection of peroxidase-containing liposomes into lymphosarcoma-bearing mice. Liposome-entrapped peroxidase activity was never observed in the tumor cells. The results presented here indicate that the lymphosarcoma cells do not directly participate in the hepatic accumulation of liposomes, although their mere presence may have significant indirect effects on the elimination of liposomes from the blood and on their tissue distribution.