Effect of thalidomide on tumour necrosis factor production and anti-tumour activity induced by 5,6-dimethylxanthenone-4-acetic acid.

The investigational anti-tumour agent, 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA), an analogue of flavone acetic acid (FAA), has been scheduled for clinical evaluation. Like FAA, 5,6-MeXAA exhibits excellent experimental anti-tumour activity and is an efficient inducer of cytokines in mice. We have examined the effect of pharmacological suppression of tumour necrosis factor (TNF) production on the anti-tumour activity of 5,6-MeXAA, taking advantage of previous observations that TNF production in response to endotoxin in vitro is inhibited by thalidomide. Thalidomide at doses of between 8 and 250 mg kg-1 efficiently suppressed serum TNF activity in response to 5,6-MeXAA at its optimal TNF inducing dose of 55 mg kg-1. Suppression was achieved when thalidomide was administered at the same time as, or up to 4 h before, 5,6-MeXAA. Under conditions in which TNF activity was suppressed, the degree of tumour haemorrhagic necrosis and the proportion of cures in the subcutaneous Colon 38 tumour were increased. In mice administered thalidomide (100 mg kg-1) together with 5,6-MeXAA (30 mg kg-1), complete tumour regression was obtained in 100% of mice, as compared with 67% in mice receiving 5,6-MeXAA alone. The results suggest a possible new application for thalidomide and pose new questions about the action of 5,6-MeXAA and related compounds.