The Chemotherapeutic Agent, 5,6-Dimethylxanthenone-4-Acetic Acid,

Vascular disrupting agents (VDA) represent a novel approach to the treatment of cancer, resulting in collapse of tumor vasculature and tumor death. 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is a VDA currently in advanced Phase II clinical trials, yet its precise mechanism of action is unknown despite extensive preclinical and clinical investigations. The data presented herein demonstrate that DMXAA is a novel and specific activator of the TBK1-IRF-3 signaling pathway. DMXAA treatment of primary murine macrophages resulted in robust IRF-3 activation, a ~750-fold increase in IFN-beta mRNA and, in contrast to the potent Toll-like receptor 4 (TLR4) agonist, lipopolysaccharide (LPS), signaling was independent of mitogen-activated protein kinase (MAPK) activation and elicited minimal NF-kappaB-dependent gene expression. DMXAA-induced signaling was critically dependent on the IRF-3 kinase, TBK1, and IRF-3, but MyD88-, TRIF-, IPS-1/MAVS-, and IKKbeta-independent, thus excluding all known TLRs and cytosolic helicase receptors. DMXAA pretreatment of murine macrophages induced a state of tolerance to LPS and vice versa. In contrast to LPS stimulation, DMXAA-induced IRF-3 dimerization and IFN-beta expression were inhibited by salicylic acid (SA). These findings detail a novel pathway for TBK-1-mediated IRF-3 activation and provide new insights into the mechanism of this new class of chemotherapeutic drugs.

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Roberts ZJ, Goutagny N, Perera PY, Kato H, Kumar H, Kawai T, Akira S, Savan R, van Echo D, Fitzgerald KA, Young HA, Ching LM, Vogel SN