Lung cancer is the most common cause of cancer death in both men and women. Eighty percent of all newly diagnosed lung cancers are non-small cell lung cancers (NSCLC), and over 75 percent present with advanced stage disease. For this reason as well as the predilection for distant recurrence after complete resection, most patients are treated with chemotherapy alone or in combination with other modalities. Unfortunately, the majority of NSCLC are chemoresistant despite treatment regimens with second or third generation of chemotherapeutic agents. Tumor chemoresistance has been attributed to the ability of cells to overcome programmed cell death (apoptosis). Recently, it has been established that chemotherapy upregulates the NF-kappaB transcription factor and this is associated with cellular resistance to chemotherapy-induced apoptosis. With this understanding, experiments were performed to determine whether NF-kappaB provided a similar cell survival signal in NSCLC cell lines following the addition of gemcitabine and cisplatin, two genotoxic agents commonly used to treat NSCLC. Preliminary data demonstrates that these chemotherapeutic agent induce NF-kappaB transcriptional activity. More importantly, the loss of NF- kappaB sensitizes NSCLC cell lines to chemotherapy-induced apoptosis. Although cell death induced by chemotherapy involves death receptor pathways in certain cell types, chemotherapy- induced apoptosis in NSCLC cells did not involve either Fas- or caspase-8-dependent death receptor pathways. In contrast, NF- kappaB was required to overcome mitochondrial-mediated apoptosis following chemotherapy addition. In addition, ceramide has recently been shown to inhibit the anti-apoptotic P13K/Akt pathway as well as activate NFkappaB. Since the loss of NF- kappaB activity sensitizes NSCLC cells to chemotherapy-induced apoptosis, the major goal of this proposal is to examine the cell signaling mechanisms governing apoptosis and chemoresistance following the addition of chemotherapy. To achieve this objective, we will use established (by the P.I.) cell lines which lack NF-kappaB activity and compare them to controls. These cells will be exposed to chemotherapeutic agents and apoptotic and anti-apoptotic signaling pathways will be examined in vitro.
The specific aims of the proposal are to: 1) establish whether chemotherapy kills NSCLC cells through mitochondrial-dependent mechanisms, 2) determine whether the redox status of the cell is responsible for modulating NF-kappaB-dependent cell survival in response to chemotherapy, and 3) determine the role of ceramide as both a pro- and anti-apoptotic mediator following chemotherapy. These studies will provide important insight into how chemotherapy activates apoptotic pathways, as well as mechanisms by which tumors become chemoresistant through upregulation of NF-kappaB. The ultimate goal of this study is to provide the necessary background for the initiation of novel treatment strategies designed to treat patients with advanced lung cancer.
