Inhibition of antitumor effects of flavone acetic acid by cortisone.

The effect of cortisone (2 mg/mouse) on the effect of the antitumour agent flavone acetic acid (NSC 347512) was measured in four different murine tumours, growing subcutaneously. Response was measured by histological assessment of haemorrhagic necrosis after 24 h, and by assessment of tumour growth delay. In C57B1/6 x DBA/2)F1 hosts, cortisone pre-treatment prevented FAA-induced haemorrhagic necrosis in Lewis lung (sub-line LLTC) tumours but did not inhibit necrosis induction in Colon 38 tumours. Similarly in C3H/HeN mice, cortisone pre-treatment prevented FAA-induced necrosis of Spon-2 and partially prevented necrosis induction in mammary M-16/C tumours. Since corticosteroids are often administered, or generated internally, in the course of clinical treatment, this result has implications for the clinical use of FAA and other compounds, which act on tumour vasculature as part of their antitumour action.