K-rasLA1 Mice Research Articles

040 mTOR inhibition reverses alveolar epithelial neoplasia induced by oncogenic K-ras

Lung adenocarcinomas (ADCs) with k-ras mutation are reported to be resistant to tyrosine kinase inhibitors of the epidermal growth factor receptor. Alternative therapies are needed for these specific ADCs. The serine/threonine kinase AKT and its downstream mediator mammalian target of rapamycin (mTOR) are activated in human lung ADC and clinical trials are underway to test whether mTOR inhibition is useful in treating lung cancer. The goal of this study is to treat the K-ras LAI mice, which undergo somatic activation of the K-ras oncogene and recapitulate morphologic changes of alveolar epithelial cells that precede human lung ADC with an mTOR inhibitor (CCI-779). K-ras LA1 mice were treated for 1 month with CCI-779 at high dose (20 mg/kg/day), low dose (0.1 mg/kg/day) and vehicle. Micro-CT scan was performed before and after completion of treatment. Tumor numbers and volume were evaluated at micro-CT scan and autopsy exam. Expression of downstream mediators of mTOR was studied by immunohistochemistry and western blot on lung tissue. Mechanistic studies were performed on LKR-13, a lung ADC cell line derived from K-ras LA1 mice. The results were extrapolated to human ADC based on samples from a cohort of 400 patients. The levels of phosphorylated AKTSer473 (p-AKT) and S6Ser236/235 (p-S6), a downstream mediator of mTOR, increased with malignant progression (normal alveolar epithelial cells to ADC) in K-ras LAI mice and patients with lung ADC. Macrophages were prominently associated with atypical alveolar hyper-plasia (AAH), an early neoplastic change, and expressed high levels of p-S6. mTOR inhibition in K-ras LAI mice inhibited the progression of AAH to adenoma, decreased the size of adenomas, and induced apoptosis of intra-epithelial macrophages. LKR-13 was resistant to treatment with CCI-779 in vitro . However, as syngeneic tumors in wild type littermates LKR-13 cells recruited intra-epithelial macrophages and regressed in response to treatment with CCI-779. These findings provide evidence that the expansion of lung ADC precursors induced by oncogenic k-ras requires mTOR-dependent signaling and suggest that host factors derived from macrophages may contribute to ADC progression [1].

Inhibition of Mammalian Target of Rapamycin Reverses Alveolar Epithelial Neoplasia Induced by Oncogenic K-ras

The serine/threonine kinase AKT and its downstream mediator mammalian target of rapamycin (mTOR) are activated in lung adenocarcinoma, and clinical trials are under way to test whether inhibition of mTOR is useful in treating lung cancer. Here, we report that mTOR inhibition blocked malignant progression in K-ras(LA1) 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 phospho-S6(Ser236/235), a downstream mediator of mTOR, increased with malignant progression (normal alveolar epithelial cells to adenocarcinoma) in K-ras(LA1) mice and in patients with lung adenocarcinoma. Atypical alveolar hyperplasia, an early neoplastic change, was prominently associated with macrophages and expressed high levels of phospho-S6(Ser236/235). mTOR inhibition in K-ras(LA1) mice by treatment with the rapamycin analogue CCI-779 reduced the size and number of early epithelial neoplastic lesions (atypical alveolar hyperplasia and adenomas) and induced apoptosis of intraepithelial macrophages. LKR-13, a lung adenocarcinoma cell line derived from K-ras(LA1) 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 that host factors derived from macrophages play a critical role in adenocarcinoma progression.