Synthesis and immunostimulating properties of lipophilic ester and ether muramyl peptide derivatives

Macrophages can become cytotoxic toward tumor cells when activated by immunomodulators. Three different muramyl peptides were synthesized: one hydrolyzable lipophilic ester derivative (MTP-Chol) and two nonhydrolyzable lipophilic ether derivatives (MTP-octadecane and MTP-heptadecafluorooctadecane). Activation of the RAW 264.7 cell line was studied by measuring nitrite production as an indication of NO-synthase activity. The lipophilic ester derivative, incorporated within nanocapsules, was as active as free muramyl dipeptide, whereas the lipophilic ether derivatives were unable to activate macrophages. MTP-octadecane in micellar form was not capable of inducing macrophage cytotoxicity either. These results indicate that lipophilic muramyl peptides need to be hydrolyzed to yield a hydrosoluble metabolite in order to activate macrophages.