Activation of LPS-inducible genes by the antitumor agent 5,6-dimethylxanthenone-4-acetic acid in primary murine macrophages. Dissection of signaling pathways leading to gene induction and tyrosine phosphorylation.

The synthetic flavone analogue 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA) has shown promise as an antitumor agent and is currently a candidate for clinical trials. Because 5,6-MeXAA has been shown in a murine macrophage and a human myelomonocytic cell line to induce TNF-alpha mRNA and to activate macrophages to become tumoricidal, actions that are shared with bacterial LPS, we sought to determine the level of LPS mimetic activity exhibited by this low m.w. macrophage-activating agent. To elucidate its mechanisms of action, the capacity to induce a panel of LPS-inducible genes was assessed. 5,6-MeXAA was found to induce a subset of LPS-inducible genes within the panel in both Lpsn and Lpsd primary murine macrophages. Of the six LPS-inducible genes examined, there was marked induction of IP-10, D8, and D3; low induction of TNF-alpha gene expression; and insignificant induction of TNFR-2 and IL-1 beta genes. 5,6-MeXAA was also found to be a potent inducer of IFNs in macrophages of both strains, and of increased expression of the genes that encode the IFN regulatory factors IRF-1, IRF-2, and ICSBP. In contrast with LPS, 5,6-MeXAA failed to induce significantly any of the 40- to 45-kDa tyrosine phosphoproteins induced by LPS. These data suggest that 5,6-MeXAA shares with LPS certain biochemical pathways that lead to gene induction and allow for the additional dissection of the relationship of tyrosine phosphorylation and the expression of specific genes.