CCR researchers show that blocking the estrogen receptor restores the sensitivity of lung cancer cells to therapy
Expression of estrogen receptor alpha (ERα) is upregulated in mesenchymal-like lung cancer cells that are resistant to chemotherapies (cisplatin and vinorelbine, cis/vin). The chemoresistant cells are also resistant to the cytotoxic effects of natural killer (NK) effector cells or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL); however, their sensitivity can be restored by pretreatment with fulvestrant, an estrogen receptor antagonist.
Tumors become deadly when they spread beyond their tissues of origin or metastasize. Most solid tumors begin in epithelial cells, which line the inner and outer surfaces of the body. In order to metastasize, these cells may lose many epithelial characteristics and become more like mesenchymal cells through a process called epithelial-mesenchymal transition (EMT). Cells that have undergone EMT have greater mobility and can resist chemotherapy and even immunotherapies. Claudia Palena, Ph.D., of CCR’s Laboratory of Tumor Immunology and Biology, and her colleagues wondered if it would be possible to identify compounds that could reverse the therapy resistance imparted by EMT in lung cancer.
The researchers began by generating homogeneous populations of epithelial and mesenchymal lung cancer cells based on the expression of various markers. As expected, the mesenchymal cells were less sensitive to cytotoxic T cells, natural killer (NK) cells, and the deadly immune protein tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Importantly, the mesenchymal cells’ reduced sensitivity to TRAIL was not due to a change in the level of TRAIL receptors.
Using populations of mesenchymal cells, the investigators performed a quantitative high-throughput screening assay to test the ability of several thousand compounds from the NIH Chemical Genomics Center Pharmaceutical Collection to enhance TRAIL-mediated cell death. Of the three compounds identified for further testing, only fulvestrant, an FDA-approved estrogen receptor (ER) antagonist, was confirmed in multiple cell lines as enhancing susceptibility to TRAIL and NK cells at a dose that can be achieved in patients. Fulvestrant alone did not promote cell toxicity. Intriguingly, the scientists found three-times more estrogen receptor alpha (ERα) mRNA in the mesenchymal cells than in the epithelial cells, suggesting estrogen signaling may protect mesenchymal cells from immune-mediated death.
Exposure to chemotherapy also selects for mesenchymal-like cells that are able to resist chemotherapy and immunotherapies. To determine whether fulvestrant could re-sensitize these cells, the researchers generated chemoresistant lung cancer cells by growing cells in the drugs cisplatin and vinorelbine. They found that the chemoresistant cells had increased levels of mesenchymal genes and ERα, and were also resistant to TRAIL, NK- and T-cell-mediated killing. Pretreatment with fulvestrant, however, restored the cells’ sensitivity to immune attack as well as susceptibility to cisplatin and vinorelbine, demonstrating that estrogen signaling is also important in mesenchymal cell chemotherapy resistance.
To further study the role of estrogen signaling in EMT-mediated resistance, the investigators overexpressed ERα in lung cancer cells. These cells resisted TRAIL and NK cell treatment and expressed higher levels of mesenchymal genes. Using samples from The Cancer Genome Atlas, they also found that lung tumors with higher ERα, but not ERβ, had much higher mesenchymal gene expression. Treating lung cancer cells with fulvestrant significantly reduced the expression of the mesenchymal genes and revealed that estrogen promotes the activity of the mesenchymal regulator, brachyury.
Finally, the scientists tested the ability of fulvestrant to restore treatment sensitivity in a mouse model. In mice with lung tumor grafts, treatment with a combination of fulvestrant and the chemotherapeutic docetaxel led to significant tumor shrinkage, though neither drug alone had an effect. Fulvestrant-treated tumors showed reduced levels of ERα and the mesenchymal gene fibronectin, while tumors treated with docetaxel alone actually had increased ERα expression. The combination also led to reduced ERα and fibronectin in tumors that responded, demonstrating that estrogen signaling inhibition decreases mesenchymal features in lung cancer cells, which is associated with increased sensitivity to treatment.
This is the first study to define a role for estrogen signaling in promoting lung cancer resistance to chemotherapy and immunotherapies. These studies suggest fulvestrant combinations may provide a novel, effective method for treating patients with advanced lung cancer.Summary Posted: 06/2016
Hamilton DH, Griner LM, Keller JM, Hu X, Southall N, Marugan J, David JM, Ferrer M, and Palena C. Targeting estrogen receptor signaling with fulvestrant enhances immune and chemotherapy-mediated cytotoxicity of human lung cancer. Clinical Cancer Research. June 7, 2016. PubMed Link