Tatsuaki Tsuchiya

Antitumor effects of adriamycin encapsulated in liposomes on chemically induced malignant fibrous histiocytoma in rats: Histological aspects*

We previously reported that, in an experimental animal model (rat), the in vivo growth of chemically induced malignant fibrous histiocytoma (MFH) was inhibited more effectively by adriamycin encapsulated in liposomes (LADM) than by free adriamycin (ADM). To elucidate the histological changes caused by LADM administration, we compared LADM-treated tumor tissues with free ADM-treated tissues. A suspension of chemically induced rat MFH cells was injected subcutaneously into syngeneic rats. After a tumor had developed, free ADM or LADM was administered intravenously. The tumor tissues were then examined histologically. Microscopic examination showed that the number of small round infiltrated cells was greater in the LADM group than in the ADM group. Additionally, an immunohistochemical study with anti-rat lymphocyte or anti-rat macrophage monoclonal antibodies demonstrated that the significant decrease in W3/25+ cells observed in the control and ADM groups was not apparent in the LADM group, and that the percent-ages of cells positive for OX-8, ED2, and ED3 were significantly higher than in the ADM group. These histological changes seem to correlate closely with the inhibition of tumor growth. Our results suggest that LADM possesses the drug-carrying characteristic of liposomes and may also augment certain host defenses against rat MFH, just as biological response modifers do.