T5 Toll-like receptor 2 has a tumour suppressor function in non-small cell lung cancer via regulation of the senescence associated secretory phenotype

Background Lung cancer is the leading cause of cancer related deaths worldwide. The value of targeting early stage disease has been widely recognised to improve survival. Oncogene-induced senescence (OIS) is a stress response instigated following the activation of oncogenes and is a well-known tumour suppressor mechanism. OIS is abundant in pre-invasive lesions in murine lung cancer models, however is lost during the progression to malignancy. We previously identified a regulatory role for Toll-like receptor 2 (TLR2) in OIS and expression of the senescence-associated secretory phenotype (SASP), however the functional relevance of this has yet to be established. Methods We used genetically engineered mouse (GEM) models of lung cancer (KrasLSL-G12D/+ and KrasLSL-G12D/+;TP53fl/fl) on both wild-type and Tlr2 null backgrounds. Lung specific activation of mutant KrasG12D and TP53 loss was achieved upon intranasal infection with Cre-recombinase expressing adenovirus. Tumour burden, senescence markers and SASP expression were assessed by immunohistochemistry. Immune cell recruitment was measured using flow cytometry on whole lung single cell suspensions from tumour bearing mice. The expression of Tlr2 and associated SASP components were measured in human pre-invasive lung cancer samples that either progressed to invasive malignancy or regressed to normal epithelium. Results Tlr2 loss was associated with an increased tumour burden and reduced survival in our GEM model. Furthermore, Tlr2 loss caused significantly reduced epithelial expression of key senescence markers and SASP factors. However, immune cell recruitment was not affected suggesting this effect was cell intrinsic. Inhalational administration of a synthetic TLR2 agonist (Pam2CSK4) significantly reduced tumour burden in our GEM model. Molecular profiling of bronchoscopic biopsies of human pre-invasive lung lesions revealed increased TLR2 and SASP expression in samples that did not progress to invasive malignancy, suggesting a tumour suppressor role for TLR2-SASP signalling in human lung cancer. Conclusions We have identified TLR2 as a potential tumour suppressor in lung cancer via regulation of the SASP. Furthermore, we have highlighted a novel therapeutic strategy for the treatment of early stage lung cancer. SASP factors are released into the bloodstream and are ideal candidate biomarkers of pre-invasive disease and thus could potentially aid in stratifying lung cancer screening populations.