Mechanisms of reduction of antitumor drug toxicity by liposome encapsulation.

Actinomycin D, when encapsulated within liposomes, has been previously shown to be less toxic to mice than nonencapsulated actinomycin D, but to retain its tumoricidal activity. We have compared the toxic effects of Act D encapsulated either in the aqueous phase or in the lipid phase of liposomes (APL and LPL, respectively), and the nonencapsulated Act D on the blood forming system, on cell proliferation in the intestine, and on antibody production by spleen lymphocytes. At a single dose of 0.