Liposomes of different composition have been used to modify macrophage-mediated destruction of syngeneic
cancer cells through a modulation of
membrane lipid content of macrophages and/or
tumor cells.
Dipalmitoylphosphatidylcholine (DPPC)1
liposomes induce
cancer cell lysis by normal, non-tumoricidal, peritoneal macrophages and enhance
tumor cell destruction by BCG-activated macrophages. This effect was produced by large and small
unilamellar liposomes, which are in the 25,000 g supernatant of sonicated preparations. Addition of
cholesterol or negative charges carried by
dicetylphosphate supressed the effect of DPPC
liposomes on macrophage-mediated cytolysis. Enhancement of macrophage-mediated
tumor cell lysis was observed when both
cancer cells and macrophages were incubated with DPPC
liposomes, but not when macrophages and/or
tumor cells were preincubated with
liposomes prior to their coincubation.
Liposomes did not promote the binding of the
cancer cells to the macrophages.
Liposomes could promote formation of
phospholipid domains within the plasma membrane of both
tumor cells and macrophages leading to the destruction of
cancer cells through a temporary fusion with the macrophages.