Enhancement of in vitro cytotoxicity of mouse peritoneal exudate cells by flavone acetic acid (NSC 347512).

Flavone acetic acid (FAA), an antitumour agent currently undergoing clinical trials, was found to augment the tumoricidal activity of peritoneal exudate (PE) cells in vitro. Lysis of tumour targets was measured using a standard 18 h 51Cr release assay for activated macrophages. Lytic activity increased with increasing concentrations of FAA up to 100 micrograms/ml before reaching a plateau. At 80 micrograms/ml FAA, 3-fold fewer PE cells were necessary to obtain the same level of activity as in control cultures without FAA. The lytic activity was mediated by Thy-1 negative and glass-adherent cells in the PE population, and was inhibited by dexamethasone. The activity of PE cells against several different tumour targets (P815 mastocytoma, YAC-1 lymphoma, P388 lymphoma, and a Lewis lung carcinoma cell line) were all enhanced by FAA. The results show that FAA can enhance the lytic potential of peritoneal macrophages in vitro to kill a range of tumour cells.