[Antitumor efficacy of activated macrophages against murine glioma cells]

A crucial manifestation of malignant gliomas is the regrowth of already-invaded neoplastic cells after surgical intervention. One possible approach for inhibiting such tumor growth is to utilize the tumoricidal potential of macrophages. In order to investigate the clinical application of this concept, peritoneal exudate cells (PEC) activated in vitro and in vivo by immunomodulating agents were tested for cytotoxic activity against murine glioma (203-glioma) cells. As immunomodulating agents, heat-killed Propionibacterium acnes (P. acnes), OK-432 and Concanavilin A supernatant (Con A sup) were used in these experiments. P. acnes was provided by Kowa Pharmaceutical Co., Tokyo, and OK-432 by Chugai Pharmaceutical Co., Ltd., Tokyo. Klinische Einheit (KE) units were used to express the strength of the preparation, with 1 KE equal to 0.1 mg of dried streptococci. Con A sup was produced by Con A pulsing of BALB/c splenocytes resuspended in complete medium. PEC harvested from mice to which 5% glycogen in saline had been inoculated intraperitoneally 6 d previously were activated in vitro by P. acnes (P. acnes-PEC), OK-432 (OK-432-PEC) and Con A sup (Con A-PEC). The cytotoxic activities of P. acnes-PEC, OK-432-PEC and Con A-PEC were approximately 25%, 65% and 60%, respectively. PEC were then collected from mice into which either 100 micrograms of P. acnes or 1 KE of OK-432 had been injected intraperitoneally several times. The antitumor effects of P. acnes-PEC and OK-432-PEC were about 35% and 50%, respectively. These activated PEC demonstrated cytotoxic activity against murine glioma in the tumor neutralization assay (Winn assay). Also, the antitumor efficacy of OK-432-PEC belonged mainly to adherent cells. Meningeal gliomatosis (MG) models were prepared for clinical studies. Viable 203-glioma cells (5 X 10(6) were injected percutaneously into the cisterna magna of C57BL/6 mice. The median survival time (MST) of the untreated group was 8.5 days. The MST of the groups treated by intraperitoneal and intracisternal administration of P. acnes were 26 and 33 days. This therapy significantly prolonged the survival time of these models, particularly by the intracisternal treatment. The differential cell count by Giemsa staining and latexphagocytic cell findings revealed that macrophages accounted for more than 90% of the P. acnes-PEC. These results may indicate that activated (PEC) macrophages were induced intracisternally by P. acnes and that activated macrophages induced intraperitoneally exerted antitumor effects in MG models.