Irradiation Promotes A Mesenchymal Switch In Small Cell Lung Cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Small cell lung cancer (SCLC) is the most aggressive form of lung cancer, with little improvement in therapy options and prognosis over the last few decades. Tumors initially respond well to chemotherapy and radiotherapy; however, when patients relapse, tumors have typically developed resistance to treatment. The aims of this study were to determine how irradiation treatment affects the phenotype of SCLC cells and in particular the neuroendocrine features of SCLC. Xenografts were established by subcutaneous injection of DMS 79 cells into nude mice, before exposure to ionising radiation (IR). Xenograft tumors and IR treated DMS 79 cells were analysed by immunohistochemistry and qPCR for markers of neuroendocrine, mesenchymal and epithelial phenotype. Circulating pro-opiomelanocortin (POMC), a neuroendocrine biomarker, was quantified by ELISA developed in our lab. Irradiation of xenograft tumors led to increased levels of the mesenchymal marker, N-cadherin, unchanged epithelial markers (cytokeratin and E-cadherin), as well as decreased and distinctly heterogeneous expression of POMC. We have previously described POMC as a novel biomarker in SCLC patients and xenografts. However, circulating POMC and tumor POMC protein levels and mRNA were drastically reduced in the irradiated animals. To determine whether the changes in phenotype were associated with resistance, DMS 79 cells were made irradiation resistant (IR-res) through repeated exposure to IR in vitro (total 21Gy). The IR-res cells acquired dramatic changes in morphology and adherence, showed increased proliferation and increased resistance to challenges with both small and larger doses of IR. In addition, cells exhibited increased expression of the mesenchymal markers; N-cadherin and β1 integrin. IR-res cells also showed a significant decrease in expression of the neuroendocrine marker POMC. However, there was no change in expression of other neuroendocrine markers; neuron-specific enolase (NSE), chromogranin A and neural cell adhesion molecule (N-CAM), or the epithelial marker E-cadherin. In summary, irradiation causes a distinct mesenchymal switch in DMS 79 small cell lung cancer cells in vitro and in vivo that does not resemble a classical epithelial to mesenchymal transition (EMT). Therefore, although irradiation is an important treatment paradigm in patients, our data suggests it may promote a phenotype that encourages metastasis. In addition, we have highlighted the need for caution when using biomarkers, as irradiation has modified POMC biomarker expression and secretion so that it no longer predicts tumor burden in relapsed SCLC. Citation Format: Suzanne L. Meredith, Jennifer L. Bryant, Muhammad Babur, Philip Riddell, Kaye J. Williams, Anne White. Irradiation promotes a mesenchymal switch in small cell lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1132. doi:10.1158/1538-7445.AM2014-1132