Abstract 5542: Activation of epidermal growth factor receptor potentiates effects of radiation in A549 lung cancer cells

Abstract

Abstract Introduction : For patients with advanced non-small cell lung cancer (NSCLC), chemotherapy alone or in combination with radiation (IR) is considered the standard treatment. However, after the documentation of the over-expression of epidermal growth factor receptor (EGFR) in 50% to 80% of NSCLCs and transforming growth factor-alpha in 81% to 93% of NSCLCs, EGFR has emerged as an important target molecule in NSCLC therapy. The cellular effects of EGFR activation include increased proliferation, promotion of cell motility, adhesion, invasion, angiogenesis and enhanced cell survival. However, activation of EGFR in some tumor cell lines excessively expressing EGFR resulted in cellular apoptosis and growth inhibition. This study attempts to define the role of EGFR kinase activity in sensitizing the responsiveness of EGFR-overexpressed NSCLC cells to IR. Methods: Cell survival, proliferation, cell cycle distribution, reporter activity of EGR-1 and protein expression was studied by colony forming assays, cell counting, flow cytometry, 14Cchloramphenicol acetyl transferase (CAT) reporter assay and Western analysis respectively in A549 and H460 cells. Results: Interestingly, we observed that EGFR activation mediated sensitization of IR effects in A549 cells over-expressing EGFR. Tyrosine kinase inhibitor (TKI), AG1478 blocked EGF effect on sensitization of IR in A549 cells but not in H460 cells. To understand the molecular mechanism underlying the response of A549 cells to IR and EGFR, we investigated the effects of EGFR signaling and IR on expression of early growth response (EGR-1), a transcription factor that sensitizes IR therapy, in both IR-sensitive and insensitive lung cancer cell lines. However, we observed that EGR-1 is not involved in EGFR signaling-mediated IR sensitization since inhibition of Erk (EGFR induces expression of Egr-1 through activation of Erk1/2), did not block EGFR-mediated sensitization of IR effect. Further, we observed that JNK kinase activity mediated EGF-dependent IR effects. Interestingly, acute induction of serum EGF expression level was observed in the patients who responded to IR therapy. Conclusions: Results from this study show that EGFR activation and IR synergistically activate JNK signaling that leads to cellular apoptosis that has important implications for anti-EGFR therapy or IR therapy. Although, preclinical studies have shown that EGFR inhibition can render an additive or synergistic effect with radiotherapy in NSCLCs, clinical benefits are modest. This study suggests that tyrosine kinase activity of EGFR might be required for IR sensitivity. Thus, the inhibition of EGFR by TKIs may lead to reduced responsiveness of NSCLCs to IR thereby compromising the treatment efficacy. Understanding the role of EGFR activity in sensitization of NSCLC cells to IR is therefore extremely important for both radiotherapy and the EGFR TKI-based chemotherapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5542.