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Introduction Surgery is essential for cure of early-stage non-small cell lung cancer (NSCLC). Rates of postoperative bacterial pneumonias, however, remain high, and clinical data suggests that post-operative infectious complications confer an increased risk for metastasis. Toll-like receptors (TLRs) mediate the inflammatory response to infection by recognizing evolutionarily conserved bacterial structures at the surface of numerous pulmonary cell types; yet, little is known about how host TLR activation influences NSCLC metastasis. TLR4 recognizes gram-negative bacterium lipopolysaccharide activating the innate immune system. Methods C57BL/6 and TLR4 knockout murine airways were inoculated with Escherichia coli or lipopolysaccharide. Hepatic metastasis assays and intravital microscopy were performed. Bronchoepithelial conditioned media was generated through coincubation of bronchoepithelial cells with TLR4 activating Escherichia coli or lipopolysaccharide. Subsequently, H59 NSCLC were stimulated with conditioned media and subject to various adhesion assays. Results We demonstrate that gram-negative Escherichia coli pneumonia augments the formation of murine H59 NSCLC liver metastases in C57BL/6 mice through TLR4 activation. Additionally, infected C57BL/6 mice demonstrate increased H59 NSCLC in vivo hepatic sinusoidal adhesion compared with negative controls, a response that is significantly diminished in TLR4 knockout mice. Similarly, intratracheal injection of purified TLR4 activating lipopolysaccharide increases in vivo adhesion of H59 cells to murine hepatic sinusoids. Furthermore, H59 cells incubated with bronchoepithelial conditioned medium show increased cell adhesion to in vitro extracellular matrix proteins and in vivo hepatic sinusoids through a mechanism dependent on bronchoepithelial TLR4 activation and interleukin-6 secretion. Conclusion TLR4 is a viable therapeutic target for NSCLC metastasis augmented by gram-negative pneumonia.

Surgical resection of early stage nonsmall cell lung cancer (NSCLC) is necessary for cure. However, rates of postoperative bacterial pneumonias remain high and may confer an increased risk for metastasis. Toll-like receptors (TLRs) mediate the inflammatory cascade by recognizing microbial products at the surface of numerous cell types in the lung; however, little is known about how host TLRs influence NSCLC metastasis. TLR2 recognizes gram-positive bacterial cell wall components activating innate immunity. We demonstrate that lower respiratory tract infection with Streptococcus pneumonia augments the formation of murine H59 NSCLC liver metastases in C57BL/6 mice through host TLR2 activation. Infected mice demonstrate increased H59 and human A549 NSCLC adhesion to hepatic sinusoids in vivo compared with noninfected controls, a response that is significantly diminished in TLR2 knock-out mice. Intra-tracheal injection of purified TLR2 ligand lipoteichoic acid into mice similarly augments in vivo adhesion of H59 cells to hepatic sinusoids. Additionally, H59 and A549 NSCLC cells incubated with bronchoepithelial conditioned media show increased cell adhesion to extracellular matrix components in vitro and hepatic sinusoids in vivo in a manner that is dependent on bronchoepithelial TLR2 activation and interleukin-6 secretion. TLR2 is therefore a potential therapeutic target for gram-positive pneumonia-driven NSCLC metastasis.