Manabu Namba

In vitro tumor cell killing by peritoneal macrophages from mitomycin C-treated rats.

SummaryThe local cellular response induced by intraperitoneal injection of mitomycin C was examined in terms of cell-mediated cytotoxicity for tumor cells. An in vitro cytolysis assay involving 125I-iododeoxyuridine-labeled tumor target cells revealed that treatment of normal ACI/N rats (200 g) with a single intraperitoneal injection of mitomycin C (50, 100, or 200 μg) induced tumoricidal macrophages in the peritoneal cavity. The tumoricidal activity was dependent on the dose of mitomycin C injected and it was detectable as early as 1 day after the intraperitoneal injection of mitomycin C. In addition to the increased tumoricidal activity, the functional activities of the peritoneal macrophages were found to be increased with respect both to uptake of 2-deoxy-d-glucose and to phagocytosis of latex beads. Additional experiments excluded the possibility that the tumor cell cytolysis was the result of direct cytotoxicity by mitomycin C that might have been incorporated in the peritoneal macrophages or of nutrient depletion in the medium during the cytolysis assay. Furthermore, endotoxin contamination of the mitomycin C, which might have produced the activated macrophages, was not detected. The mechanism by which mitomycin C injected intraperitoneally induced the tumoricidal macrophages locally remains uncertain; however, it is possible also in clinical situations.

Analysis of therapeutic effect in experimental chemoimmunotherapy for rat ascites tumor.

SummaryThe lyophilized, squalene-treated Nocardia rubra cell wall skeleton (N-CWS) was confirmed to produce tumoricidal peritoneal macrophages resulting in inhibition of tumor growth when injected locally into the syngeneic ascites fibrosarcoma, AMC 60 in ACI/N rats. Furthermore, N-CWS was found to augment therapeutic effect when administered repeatedly after a single local injection of mitomycin-C (MMC). To analyze the effects, various in vitro cytolysis assays were performed using N-CWS-activated peritoneal macrophages. When tumor target cells were exposed in vitro to MMC, the resulting cytolysis in the presence of N-CWS-activated macrophages was similar to cytolysis of intact target cells. On the other hand, when N-CWS-activated macrophages were exposed to MMC, the tumoricidal activity was lost significantly, depending on exposure to MMC. When tumor target cells and N-CWS-activated macrophages were simultaneously exposed to MMC, tumor-cell cytolysis was strikingly depressed. In the final experiment, combined injection of MMC and N-CWS into the ascites tumor resulted in remarkable increases not only in peritoneal exudate cell number, but also in in vitro tumoricidal activity of peritoneal macrophages as compared to those induced by either agent alone. In addition, the production of tumoricidal macrophages by IP injection of MMC alone was also noticeable, as described previously. These results possibly indicate the involvement of macrophage activation in induction of therapeutic effect in chemoimmunotherapy.