Quercetin (3,3′,4′,5,7-pentahydroxyflavone) entrapped within phospholipid vesicles inhibited [3H]thymidine incorporation and lactate production in Ehrlich ascites tumor cells. The presence of serum proteins in concentrations of up to 10 mg/ml did not alter the extent of the inhibitory effect of the liposome-entrapped flavone. At the same concentrations, serum proteins eliminated almost completely the inhibitory effects of the free quercetin on these metabolic processes. Prolonged sonication and different lipid compositions of the liposomes did not increase the inhibition of [3H]thymidine incorporation by the entrapped quercetin in the presence of serum albumin. On the other hand, serum albumin eliminated the elevation of the cyclic adenosine 3′:5′-monophosphate level in these cells produced by both free and liposome-entrapped flavone.

Attachment between Ehrlich ascites tumor cells and quercetin-loaded liposomes is demonstrated in negatively stained electron micrographs. The liposomes ranged in size from 50 to 100 nm. After 10 min of incubation, these liposomes were distributed randomly on the cell surface at distances of 100 to 200 nm.

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This work was supported by the B. De Rothschild Foundation for the Advancement of Science in Israel.

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