Effector molecules from antitumor macrophages induced with OK-432 and cyclophosphamide

The present study was designed to determine whether antitumor activity of macrophages induced with OK-432 and cyclophosphamide was mainly dependent on their ability to produce a soluble factor, that is, L-arginine-dependent nitric oxide as measured by nitrite concentration. Nitrite production by peritoneal macrophages from NIH Swiss mice pretreated with OK-432 (125 KE/kg) i.p. twice at 1-week intervals and with cyclophosphamide (200 mg/kg) i.p. 2 days before the second OK-432 treatment, increased with time for 24 h, and proportionally depended on macrophage numbers. Nitrite production was inhibited by actinomycin D and puromycin but not by mitomycin C. NG-Monomethyl-L-arginine, a specific competitive inhibitor of L-arginine-dependent nitric oxide synthesis, also inhibited production. There was a close correlation between nitrite production and antitumor activity in macrophages from mice pretreated with either OK-432 and cyclophosphamide, OK-432, or thioglycolate broth. OK-432 increased both nitrite production and antitumor activities when added to the macrophage from mice pretreated with OK-432 but not with thioglycolate broth. Both activities of macrophages from mice pretreated with OK-432 and cyclophosphamide were enhanced with increasing concentrations of L-arginine (0.125-1 mM) in the culture medium. D-Arginine, however, did not substitute for L-arginine. Neither activity was affected by contact between the macrophage and the EL4 cell. The macrophage showed antitumor activity through a membrane filter though the activity was greatly reduced. This antitumor activity of macrophages through a membrane was also inhibited by NG-Monomethyl-L-arginine, and increased by OK-432. However, conditioned media, obtained by culturing macrophages induced with OK-432 and cyclophosphamide, inhibited growth of EL4 cells. This activity was carried out by dialysable and non-dialysable factors. One of the dialysable factors was nitrite, an oxidized product of nitric oxide. The antitumor activity of non-dialysable factors was heat-stable and production of factors was increased by NG-Monomethyl-L-arginine and OK-432. Also, non-dialysable factors increased both antitumor and nitrite production activities of OK-432-elicited macrophages, when incubated with factors. Such activity of factors was also heat-stable. The production of factors increased with incubation time of macrophages, and was not inhibited by NG-Monomethyl-L-arginine. These results indicate that in vitro antitumor activity of macrophages induced with OK-432 and cyclophosphamide was mainly dependent on L-arginine-dependent nitric oxide, and that macrophage-associated soluble factors other than nitric oxide were also needed to inhibit fully tumor growth in vitro.