Modulation of topoisomerase activities by tumor necrosis factor

Polymethoxylated flavones derived from citrus suppress tumor necrosis factor-alpha expression by human monocytes

Flavonoids isolated from citrus were evaluated for their ability to affect the inflammation response through suppression of cytokine expression by human monocytes. Several polymethoxylated flavones inhibited lipopolysaccharide-induced monocyte expression of tumor necrosis factor (TNFalpha). Subsequent studies centered on the compound 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) which produced the highest inhibition (IC50 = 5 microM). HMF was also a potent inhibitor of macrophage inflammatory protein-1alpha (MIP-1alpha) and interleukin-10 (IL-10) production, but not of IL-1beta, IL-6, or IL-8 production. Suppression of TNFalpha production was at the level of mRNA induction as determined by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). HMF was also a potent inhibitor of human phosphodiesterase activity and was shown to induce a substantial elevation of cAMP levels in monocytes. The similarity of these results to the inhibition profile of the known phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, suggests that the polymethoxylated flavones inhibit cytokine production in part by suppression of phosphodiesterase activity. The ability of HMF to also inhibit IL-10 production suggests the additional existence of a phosphodiesterase-independent mechanism for this compound.

Flavonoids as inhibitors or enhancers of the cytotoxicity of tumor necrosis factor-alpha in L-929 tumor cells

The effects of some selected flavonoids on tumor necrosis factor-alpha (TNF)-induced cytotoxicity in murine fibroblast L-929 cells were studied. All of the flavanones tested as well as a flavan, epicatechin, protected L-929 cells from TNF-induced cell death of the flavanones tested, hesperetin, isosakuranetin, and pinocembrin failed to modify TNF cytotoxicity, but the 3',4'-dihydroxyflavanones, eriodictyol and taxifolin, showed a protective effect. Eriodictyol was the most potent protective agent of all the flavonoids tested, while a 4'-hydroxyflavanone, naringenin, rather showed enhancement of TNF cytotoxicity. Of the flavones tested, chrysin and apigenin markedly augmented the cytotoxicity of TNF, while luteolin showed a weak protective effect. The magnitude of protection and potentiation by these flavonoids were concentration-dependent and these effects were not altered when the flavonoids were added as much as 2 h after TNF treatment.

Potentiation of the anti-tumor effect of actinomycin D by tumor necrosis factor alpha in mice: correlation between in vitro and in vivo results

The anti-tumor effects of actinomycin D (Act D) and recombinant human tumor necrosis factor (TNF)-alpha have been studied on 4 established murine tumor cell lines: MmB16 melanoma, Lewis lung (LL/2) carcinoma, L1 sarcoma and L1210 leukemia. During short-term incubation (24 hr) Act D produced dose-dependent cytostatic/cytotoxic effects against MmB16, LL/2 and L1 tumor cells but did not reduce the viability of these cells even at high concentration (10 micrograms/ml), below a threshold of 30-60%. However, L1210 leukemic cells were highly susceptible to Act D, and no viable cells were detected in cultures incubated with 1 microgram/ml of Act D. TNF-alpha alone, when used under the same culture conditions, had only a negligible effect on all cell lines tested. However, the combination of this cytokine with Act D produced synergistic cytotoxic effects against MmB16, LL/2 and L1 cells but not against L1210 leukemia cells. In an in vivo model of regional therapy in which tumor-bearing mice were treated with Act D and TNF-alpha, a correlation with in vitro results was observed. In mice bearing MmB16 melanoma, LL/2 carcinoma and L1 sarcoma, the most potent anti-tumor effects were observed in mice treated with Act D and TNF-alpha together. This treatment led to a delay of tumor growth and induced complete tumor regression in some cases. On the contrary, TNF-alpha did not enhance the effect of Act D in mice injected with L1210 leukemia cells. Our results show that TNF-alpha can potentiate the anti-tumor effects of Act D against tumors weakly susceptible to Act D and may be a useful adjuvant to chemotherapy in the local treatment of neoplasia.