Non-small cell lung cancer (NSCLC) has become the leading cause of cancer-related deaths in the United States with a combined 5-year survival rate of only 16%. Even with advancements in aggressive chemotherapeutics, there has been little improvement in patient survival. LKB1 (liver kinase B1)/STK11 (serine-threonine kinase 11) is a tumor suppressor gene mutated in ~30% of NSCLC adenocarcinomas and loss of LKB1 is associated with a more aggressive cancer phenotype. In LKB1-deficient NSCLC, we observe significantly elevated expression and secretion of the chemokines CCL2, CCL5, and CCL20, which are involved in macrophage recruitment. Numerous studies have shown that high infiltration of a unique subset of macrophages called tumor-associated macrophages (TAMs) is associated with poor prognosis in patients with various cancers. mTORC1-HIF1-α and NFκB are two pathways that have been shown to regulate chemokine secretion and are often up-regulated in the absence of LKB1. Dosing LKB1-null cell lines with inhibitors of mTOR and NFκB in addition to silencing HIF1-α gene expression demonstrate that NFκB but not mTORC1-HIF1-α signaling may play a role in regulating chemokine secretion in LKB1-deficient NSCLC. Collectively, these results provide insight into the mechanisms responsible for the aggressive phenotype associated with LKB1-deficient non-small cell lung cancer.

The majority of non-small cell lung cancer (NSCLC) patients (70%) are diagnosed with adenocarcinoma versus other histological subtypes. These patients often present with advanced, metastatic disease and frequently relapse after treatment. The tumor suppressor, Liver Kinase B1, is frequently inactivated in adenocarcinomas and loss of function is associated with a highly aggressive, metastatic tumor (1). Identification of the mechanisms deregulated with LKB1 inactivation could yield targeted therapeutic options for adenocarcinoma patients. Re-purposing the immune system to support tumor growth and aid in metastasis has been shown to be a feature in cancer progression (2). Tumor associated macrophages (TAMs) differentiate from monocytes, which are recruited to the tumor microenvironment via secretion of chemotaxic factors by cancer cells. We find that NSCLC cells deficient in LKB1 display increased secretion of C-C motif ligand 2 (CCL2), a chemokine involved in monocyte recruitment. To elucidate the molecular pathway regulating CCL2 up-regulation, we investigated inhibitors of substrates downstream of LKB1 signaling in A549, H23, H2030 and H838 cell lines. Noticeably, BAY-11-7082 (NF-κB inhibitor) reduced CCL2 secretion by an average 92%. We further demonstrate that a CCR2 antagonist and neutralizing CCL2 antibody substantially reduce monocyte migration to NSCLC (H23) cell line conditioned media. Using an in vivo model of NSCLC, we find that LKB1 deleted tumors demonstrate a discernible increase in CCL2 levels compared to normal lung. Moreover, tumors display an increase in the M2:M1 macrophage ratio and increase in tumor associated neutrophil (TAN) infiltrate compared to normal lung. This M2 shift was significantly reduced in mice treated with anti-CCL2 or a CCR2 antagonist and the TAN infiltrate was significantly reduced with the CCR2 antagonist. These data suggest that deregulation of the CCL2/CCR2 signaling axis could play a role in cancer progression in LKB1 deficient tumors.