Gram-Negative Pneumonia Augments Non–Small Cell Lung Cancer Metastasis through Host Toll-like Receptor 4 Activation

Abstract

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.

Human umbilical cord mesenchymal stem cells suppress lung cancer via TLR4/NF-κB signalling pathway

“…TLR4 is widely expressed in lung cells, bone marrow and infiltrating cells. TLR1-6 and TLR9 are highly expressed in airway epithelial cells [16][17][18]. The expression of TLR2, TLR4, TLR7/8 and TLR9 in lung cancer was significantly higher than that in normal lung [19,20].…”

Non-Human Determinants of Lung Cancer Outcome: A Target for Inhibition of Pro-Metastatic Effect of Surgery, Triggered by Postoperative Bacterial Pneumonia

“…The results reported by Gowing et al 6 not only contribute to the understanding of adverse consequences of sepsis in lung cancer patients and propose a possible strategy to maximize the therapeutic benefit of surgery, they also provide a new insight on the interaction between microbial species present in the lungs, pre-existing inflammation, and ultimate cancer spread. TLRs, indeed, besides detecting pathogens, are highly important sensors of commensal micro-organisms, which have been recently found essential in regulating pulmonary immune microenvironment and tumor progression.…”

“…In this issue of the Journal, Gowing et al 6 investigated the role of TLR4 activation in promoting experimental cancer metastasis after induction of gram-negative pneumonia. Using a well-established NSCLC metastatic preclinical mouse model, they induced pneumonia in mice by Escherichia coli intranasal inoculation.…”

“…13 Therefore, TLR2 and 4 might represent potential therapeutic targets to counteract pneumonia-induced NSCLC dissemination. Because TLR blockade does not affect the mortality risk of patients with severe sepsis, a combination of antibiotics with TLR2/4 antagonists could be a suitable strategy for NSCLC patients who develop postoperative pneumonias, as proposed by Gowing et al 6 who used Eritoran, a synthetic lipid A TLR4 antagonist interfering with LPS binding to TLR4. 14 So far, data emerging from clinical trials investigating TLR4 antagonists/inhibitors in patients with severe sepsis do not appear very promising, as these drugs were unable to reduce the serum levels of inflammatory cytokines involved in the metastatic tumor processes, such as IL-6, IL-8, and tumor necrosis factor a.…”

The Airway Microbiota of Non-small-cell Lung Cancer Patients and its Relationship to Tumor Stage and EGFR Gene Mutation

“…Previous studies suggested that specific genera might be engaged with the metastasis of lung cancer patients [13,14]. In vivo mechanistic investigations found that certain species might contribute to the development of extrathoracic or intrathoracic metastasis via enhancement of adhesion of lung cancer cell or regulation of lung immune system [15][16][17]. Therefore, it is plausible to hypothesize that the lung microbiota may be identified as relevant to N and M classification.…”