Phosphatidylinositol 3-kinase mediates bronchioalveolar stem cell expansion in mouse models of oncogenic K-ras-induced lung cancer.

BACKGROUND: Non-small cell lung cancer (NSCLC) is the most common cause of cancer-related death in Western countries. Developing more effective NSCLC therapeutics will require the elucidation of the genetic and biochemical bases for this disease. Bronchioalveolar stem cells (BASCs) are a putative cancer stem cell population in mouse models of oncogenic K-ras-induced lung adenocarcinoma, an histologic subtype of NSCLC. The signals activated by oncogenic K-ras that mediate BASC expansion have not been fully defined. METHODOLOGY/PRINCIPAL FINDINGS: We used genetic and pharmacologic approaches to modulate the activity of phosphatidylinositol 3-kinase (PI3K), a key mediator of oncogenic K-ras, in two genetic mouse models of lung adenocarcinoma. Oncogenic K-ras-induced BASC accumulation and tumor growth were blocked by treatment with a small molecule PI3K inhibitor and enhanced by inactivation of phosphatase and tensin homologue deleted from chromosome 10, a negative regulator of PI3K. CONCLUSIONS/SIGNIFICANCE: We conclude that PI3K is a critical regulator of BASC expansion, supporting treatment strategies to target PI3K in NSCLC patients.

A selective small molecule inhibitor of c-Met, PHA-665752, reverses lung premalignancy induced by mutant K-ras.

The c-Met receptor tyrosine kinase has been implicated in cellular transformation induced by mutant Ras, a commonly activated proto-oncogene in non-small cell lung cancer (NSCLC). However, the role of c-Met has not been defined in K-ras-mutant NSCLC, a disease for which no effective targeted therapeutic options currently exist. To acquire a greater understanding of its role, we used genetic and pharmacologic approaches to inhibit c-Met in mice and cultured cells. In Kras(LA1) mice, which develop premalignant lung lesions that progress to multifocal lung adenocarcinomas owing to somatic mutations in K-ras, c-Met was expressed in multiple cell types within premalignant lung lesions, and high concentrations of HGF were detected in bronchoalveolar lavage samples. Short-term treatment with PHA-665752, a c-Met inhibitor, decreased the numbers of premalignant lung lesions and induced apoptosis in tumor cells and vascular endothelial cells within lesions. In cell culture, PHA-665752 induced apoptosis of a lung adenocarcinoma cell line derived from Kras(LA1) mice (LKR-13) and a murine lung endothelial cell line (MEC). c-Met depletion by siRNA transfection induced apoptosis of MECs but not LKR-13 cells. Collectively, these findings suggest that apoptosis was an on-target effect of PHA-665752 in MECs but not in LKR-13 cells. We conclude that PHA-665752 inhibited lung tumorigenesis in Kras(LA1) mice and may provide a novel therapeutic approach to the prevention of K-ras-mutant NSCLC.

Pten inactivation accelerates oncogenic K-ras-initiated tumorigenesis in a mouse model of lung cancer.

Phosphatase and tensin homologue deleted from chromosome 10 (Pten) is expressed aberrantly in non-small cell lung cancer cells, but the role of Pten in lung neoplasia has not been fully elucidated. In this study, we used a genetic approach to inactivate Pten in the bronchial epithelium of mice. Although, by itself, Pten inactivation had no discernible effect on bronchial epithelial histology, it accelerated lung tumorigenesis initiated by oncogenic K-ras, causing more rapid lethality than that induced by oncogenic K-ras alone (8 weeks versus 24 weeks of median duration of survival, respectively). Lung tumors arose in K-ras mutant, Pten-deficient mice that rapidly obstructed bronchial lumina and replaced alveolar spaces. Relative to K-ras mutant tumors, the K-ras mutant, Pten-deficient tumors exhibited more advanced histologic severity and more prominent inflammation and vascularity. Thus, Pten inactivation cooperated with oncogenic K-ras in promoting lung tumorigenesis.

High expression of ligands for chemokine receptor CXCR2 in alveolar epithelial neoplasia induced by oncogenic kras.

CXCL8, a ligand for the chemokine receptor CXCR2, was recently reported to be a transcriptional target of Ras signaling, but its role in Ras-induced tumorigenesis has not been fully defined. Here, we investigated the role of KC and MIP-2, the murine homologues of CXCL8, in Kras(LA1) mice, which develop lung adenocarcinoma owing to somatic activation of the KRAS oncogene. We first investigated biological evidence of CXCR2 ligands in Kras(LA1) mice. Malignant progression of normal alveolar epithelial cells to adenocarcinoma in Kras(LA1) mice was associated with enhanced intralesional vascularity and neutrophilic inflammation, which are hallmarks of chemoattraction by CXCR2 ligands. In in vitro migration assays, supernatants of bronchoalveolar lavage samples from Kras(LA1) mice chemoattracted murine endothelial cells, alveolar inflammatory cells, and the LKR-13 lung adenocarcinoma cell line derived from Kras(LA1) mice, an effect that was abrogated by pretreatment of the cells with a CXCR2-neutralizing antibody. CXCR2 and its ligands were highly expressed in LKR-13 cells and premalignant alveolar lesions in Kras(LA1) mice. Treatment of Kras(LA1) mice with a CXCR2-neutralizing antibody inhibited the progression of premalignant alveolar lesions and induced apoptosis of vascular endothelial cells within alveolar lesions. Whereas the proliferation of LKR-13 cells in vitro was resistant to treatment with the antibody, LKR-13 cells established as syngeneic tumors were sensitive, supporting a role for the tumor microenvironment in the activity of CXCR2. Thus, high expression of CXCR2 ligands may contribute to the expansion of early alveolar neoplastic lesions induced by oncogenic KRAS.

High expression of ErbB family members and their ligands in lung adenocarcinomas that are sensitive to inhibition of epidermal growth factor receptor.

Recent findings in tumor biopsies from lung adenocarcinoma patients suggest that somatic mutations in the genes encoding epidermal growth factor receptor (EGFR) and Kirsten ras (KRAS) confer sensitivity and resistance, respectively, to EGFR inhibition. Here, we provide evidence that these genetic mutations are not sufficient to modulate the biological response of lung adenocarcinoma cells to EGFR inhibition. We found high expression of ErbB family members, ErbB ligands, or both in three models that were sensitive to EGFR inhibition, including alveolar epithelial neoplastic lesions in mice that develop lung adenocarcinoma by oncogenic KRAS, human lung adenocarcinoma cell lines, and tumor biopsies from lung adenocarcinoma patients. Thus, lung adenocarcinoma cells that depend on EGFR for survival constitutively activate the receptor through a combination of genetic mutations and overexpression of EGFR dimeric partners and their ligands.