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CORRESPONDENCE Stefanie Vogel: svogel{at}som.umaryland.edu
Vascular disrupting agents (VDAs) represent a novel approach to the treatment of cancer, resulting in the 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. Our data demonstrate that DMXAA is a novel and specific activator of the TANK-binding kinase 1 (TBK1)–interferon (IFN) regulatory factor 3 (IRF-3) signaling pathway. DMXAA treatment of primary mouse macrophages resulted in robust IRF-3 activation and
750-fold increase in IFN-ß 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 nuclear factor
B–dependent gene expression. DMXAA-induced signaling was critically dependent on the IRF-3 kinase, TBK1, and IRF-3 but was myeloid differentiation factor 88–, Toll–interleukin 1 receptor domain–containing adaptor inducing IFN-ß–, IFN promoter-stimulator 1–, and inhibitor of
B kinase–independent, thus excluding all known TLRs and cytosolic helicase receptors. DMXAA pretreatment of mouse macrophages induced a state of tolerance to LPS and vice versa. In contrast to LPS stimulation, DMXAA-induced IRF-3 dimerization and IFN-ß expression were inhibited by salicylic acid. These findings detail a novel pathway for TBK1-mediated IRF-3 activation and provide new insights into the mechanism of this new class of chemotherapeutic drugs.
B, inhibitor of
B; IKK, I
B kinase; IP-10, IFN-inducible protein 10; IPS-1, IFN-ß promoter-stimulator 1; IRF-3, IFN regulatory factor 3; MAPK, mitogen-activated protein kinase; MEF, mouse embryonic fibroblast; MyD88, myeloid differentiation factor 88; PAMP, pathogen-associated molecular pattern; PRD, positive regulatory domain; RANTES, regulated on activation, normal T expressed and secreted; RIG-I, retinoic acid–inducible gene I; SA, salicylic acid; TBK1, TANK-binding kinase 1; TIR, Toll–IL-1 resistance; TLR, Toll-like receptor; TRAM, TRIF-related adaptor molecule; TRIF, TIR domain–containing adaptor inducing IFN-ß; VDA, vascular disrupting agent.
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