Targeting kinases in lung cancer prevention

ED09-03 The serine/threonine kinase AKT and its downstream mediator mammalian target of rapamycin (mTOR) are activated in lung adenocarcinoma, and clinical trials are underway to test whether inhibition of mTOR is useful in treating lung cancer. Here we report that mTOR inhibition blocked malignant progression in K-rasLA1 mice, which undergo somatic activation of the K-ras oncogene and display morphologic changes in alveolar epithelial cells that recapitulate those of precursors of human lung adenocarcinoma. Levels of phosphorylated S6Ser236/235 (p-S6), a downstream mediator of mTOR, increased with malignant progression (normal alveolar epithelial cells to adenocarcinoma) in K-rasLA1 mice and in patients with lung adenocarcinoma. Atypical alveolar hyperplasia (AAH), an early neoplastic change, was prominently associated with macrophages and expressed high levels of p-S6. mTOR inhibition in K-rasLA1 mice by treatment with the rapamycin analog CCI-779 reduced the size and number of early epithelial neoplastic lesions (AAH and adenomas) and induced apoptosis of intra-epithelial macrophages. LKR-13, a lung adenocarcinoma cell line derived from K-rasLA1 mice, was resistant to treatment with CCI-779 in vitro. However, LKR-13 cells grown as syngeneic tumors recruited macrophages, and those tumors regressed in response to treatment with CCI-779. Lastly, conditioned medium from primary cultures of alveolar macrophages stimulated the proliferation of LKR-13 cells. These findings provide evidence that the expansion of lung adenocarcinoma precursors induced by oncogenic K-ras requires mTOR-dependent signaling and suggest that host factors derived from macrophages may contribute to adenocarcinoma progression. To further test the role of inflammatory cells in lung tumor progression, we investigated the role of the chemokine receptor CXCR2 and its ligands KC and MIP-2. Recent studies have identified the CXC chemokine receptors and their ligands to be crucial factors in angiogenesis and the recruitment of inflammatory cells. The CXC chemokine family can be divided into two groups according to the presence (ELR+) or absence of (ELR-) of an ELR (Glu-Leu-Arg) motif located immediately before the first cysteine residue at the amino terminus. ELR+ CXC chemokines are known for their potent chemoattraction for neutrophils and macrophages as well as their ability to promote angiogenesis. CXC chemokines promote angiogenesis through the G protein-coupled receptor CXC chemokine receptor 2 (CXCR2) on endothelial cells. The CXCR2 ligand CXCL8 is present in freshly isolated specimens of human NSCLC and has been implicated as the dominant mediator of aberrant angiogenesis in a syngeneic murine Lewis lung cancer model and in human NSCLC/SCID mouse chimera. We investigated the role of CXCR2 and its ligands in the expansion of alveolar epithelial precursors in KrasLA1 mice. Malignant progression was associated with enhanced intra-lesional vascularity. CXCR2 and its ligands were highly expressed in macrophages and epithelial cells within alveolar lesions. Treatment of KrasLA1 mice with a neutralizing antibody against CXCR2 decreased the size and number of early lung lesions and, by histologic criteria, blocked the progression of early hyperplastic lesions to adenomas. Whereas the proliferation of an adenocarcinoma cell line derived from KrasLA1 mice (LKR-13) was resistant to treatment with the anti-CXCR2 antibody in vitro, LKR-13 cells established as syngeneic tumors were sensitive to treatment. Thus, CXCR2 activation was required for the expansion of early alveolar neoplastic lesions by oncogenic Kras, and regression of early lesions by CXCR2 inhibition required components of the tumor microenvironment.