Lung cancer is currently the leading cause of cancer death in U.S. men and women and surgical resection for cure is often only applicable to early-stage disease. The 5-year survival rate for all stages of lung cancer combined is only 15%. The survival rate is 48% for cases detected when the disease is localized, demonstrating that even when diagnosed at an early stage, relapse and death from disease are common. Thus, finding new therapeutic treatments for lung cancer is critical. We are interested in targeting both the estrogen receptor (ER) pathway and the epidermal growth factor receptor (EGRR) pathway using the pure antiestrogen, ICI 182,780 or Faslodex, and the selective EGFR tyrosine kinase inhibitor, Iressa, in lung cancer cells. We have found that EGFR protein expression is down-regulated in response to estrogen and up-regulated in response to Faslodex in vitro which suggests that the EGFR pathway is turned on when estrogen is depleted in lung cancer cells. This reciprocal control mechanism for estrogen/EGFR regulation provides an ideal model for studying the combination of these two drugs. Treatment of lung cancer with antiestrogenic drugs could give rise to a population of cells with increased levels of EGFR. Therefore, targeting EGFR in combination with traditional hormone therapy could potentially be of benefit by increasing tumor cell death and preventing signaling through this alternate growth pathway.

We examined three non-small cell lung cancer cell lines, A549, 201T, 273T, each which express different levels of EGFR protein. We examined cell growth using a standard MTS assay and apoptosis using the Apo-ONE* Homogeneous Caspase-3/7 Assay. Lung cancer cells were exposed to 10nM estrogen and 1ng/ml EGF and either 1*M Faslodex, 1*M Iressa or a combination of these drugs. In all three cell lines examined, a dramatic decrease in cell proliferation with the combination of Faslodex plus Iressa was observed. This was accompanied by an increase in apoptosis with these treatments. The recent evidence of cross-talk between the EGFR/ER pathways along with the striking efficacy of Iressa in women with lung cancer and the emerging role of estrogens in lung tumorigenesis provides rationale to combine Iressa with antiestrogen therapy for lung cancer treatment in selected patients.

The goal of this proposal is to determine if a combination of Faslodex and Iressa will decrease lung tumor growth in vitro and in vivo and to identify the signaling pathways involved. To study this, we plan to: 1) determine the effects of Iressa and Faslodex on intracellular signaling pathways in lung cancer cells; 2) elucidate the cross-talk pathway between ER and EGFR; 3) determine transcriptional responses to these treatments from estrogen responsive elements in lung cancer cells; 4) test the ability of combination therapy of Iressa and Faslodex in an in vivo lung tumor xenograft model to inhibit tumor growth; and 5) utilize a transgenic mouse model which overexpresses the hepatoctye growth factor gene in the airway as a model to test the ability of Iressa and Faslodex to act as chemopreventive therapeutic agents in vivo. Potentially, these studies will provide the basis for a new type of therapy or chemoprevention in selected female lung cancer patients.