Liposome formulations with prolonged circulation time in blood and enhanced uptake by tumors.

TLDR

Rapid clearance of liposomes from circulation and their preferential uptake by liver and spleen have hindered tumor targeting. The study evaluated how variations in liposome lipid composition affect clearance rates and tissue distribution in normal and tumor‑bearing mice. By optimizing lipid composition while keeping ~100 nm size, the authors achieved a 60‑fold increase in blood retention at 24 h, a four‑fold reduction in liver/spleen accumulation, and a 25‑fold higher tumor concentration, especially with formulations containing a small fraction of negatively charged glycolipids and a neutral phospholipid core, indicating strong therapeutic potential.

Abstract

The rapid clearance of circulating liposomes from the bloodstream, coupled with their high uptake by liver and spleen, has thus far been an obstacle to any attempts at targeting to tumors. We have assessed the impact of liposome composition on their clearance from the circulation in normal and tumor-bearing mice and on their uptake by tumors and various normal tissues. By selective changes in lipid composition, while maintaining a mean particle diameter of approximately equal to 100 nm, we have achieved up to a 60-fold increase in the fraction of recovered dose present in blood 24 hr after i.v. injection. Concomitantly, there was a decrease by a factor of 4 of the recovered dose localizing in the liver and spleen, the major organs of the reticuloendothelial system. Parallel experiments in tumor-bearing mice demonstrated a 25-fold increase of the liposome concentration in the tumor when formulations with long and short blood residence time were compared. The most favorable results were obtained with liposomes containing a small molar fraction of a negatively charged glycolipid, such as monosialoganglioside or phosphatidylinositol, and a solid-phase neutral phospholipid as the bulk component. The bio-distribution of such formulations is of considerable therapeutic potential in cancer for increasing the concentration of cytotoxic agents in tumors while minimizing the likelihood of toxicity to the reticuloendothelial system.