Activation by a new synthetic acyltripeptide and its analogs entrapped in liposomes of rat alveolar macrophages to the tumor cytotoxic state

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Abstract
FK-565 (heptanoyl-γ-d-Glu-(l-meso-a, ε-A2pm (l)-d-AlaOH) is a synthetic acyltripeptide closely resembling cell wall peptidoglycan peptides of Streptomyces in structure. Alveolar macrophages (AM) lavaged from lungs of F344 rats were activated by in vitro treatment with FK-565 and its derivatives at concentrations of 1–50 μg/ml medium, and the activated AM killed syngeneic mammary adenocarcinoma cells. When FK-565 and related compounds were encapsulated in multilamellar (MLV) liposomes composed of phosphatidyl-choline and phosphatidylserine, dose-response experiments showed that they were about 800 times more effective than the free compounds in activating AM. Liposome-encapsulated FK-565 and its analogs caused significant activation of AM within 4 h. These data indicated that acyltripeptide and its analogs encapsulated in liposomes are more efficient than the free compounds in rendering AM tumoricidal.