Omega-3 fatty acid-containing liposomes in cancer therapy.

omega-3 fatty acids are associated with reduced growth and incidence of certain cancers, and in this report we demonstrate that a fish oil diet (rich in omega-3 fatty acids) enhances the longevity of mice bearing the myeloid leukemia T27A. We have proposed that the omega-3 fatty acid docosahexaenoic acid (DHA, 22:6 delta 4,7,10,13,16,19) may induce structural changes in tumor cell plasma membranes resulting in reduced tumor growth in vitro. Here, we test whether liposomes containing DHA (18:0, 22:6 PC) have antitumor effects in vivo, leading to enhanced longevity of the tumor-bearing host. Male BALB/c mice (6-8 weeks old) were inoculated intraperitoneally with a T27A tumor dose known to cause 100% mortality of syngeneic (BALB/c) mice in less than 2 weeks. Small unilamellar vesicles (liposomes) were prepared, composed of phosphatidylcholine (PC) with 18:0 in the sn-l position and one of the following fatty acids in the sn-2 position: 18:0, 18:1 omega 9 (oleic), 18:3 omega 3 (alpha-linolenic), 20:4 omega 6 (arachidonic), 22:6 omega 3 (docosahexaenoic). The liposomes were injected intraperitoneally into tumor-bearing mice at various times: concurrently with the tumor inoculum, at select times during tumor growth, and when the mice were moribund. Mouse survival was then charted. DHA-containing lipid vesicles (18:0, 22:6 PC) caused a statistically significant increase in survival of the tumor-bearing mice when compared with 18:0, 18:1 PC. Lipid vesicles of 18:0, 18:0 PC showed no benefit, and 18:0, 20:4 PC was not significantly different than 18:0, 18:1 PC. Lipid vesicles containing a different omega-3 fatty acid, 18:0, 18:3 PC, also effectively enhanced tumor-bearing mouse survival. The greatest benefit was achieved if either the liposome treatments were spaced throughout the tumor growth period, or if the tumor inoculum was suspended in the liposome preparation (without further liposome treatments). Neither lipid peroxidation nor prolonged inflammatory responses appeared to be pertinent, leaving membrane structural changes as a feasible mode of liposome action. With antitumor properties of their own, omega-3 fatty acid-containing lipid vesicles may offer an important new avenue in combination cancer therapies.