Abstract 2350: Inhibition of Gli1 as a novel therapeutic target for lung squamous cell carcinoma

Abstract Purpose: It is clear that Hedgehog (Hh) signaling pathway can promote small cell lung cancer development but is not sufficient to drive tumor formation. However, the functional role of Hh pathway in non-small cell lung cancer remains unclear. We found that Gli1, a transcription factor of Hh pathway, is highly expressed in lung squamous cell carcinoma (SSC). The purpose of our study is to identify the functional importance of Gli1 in lung SCC. Methods: We performed a genome-wide gene expression analysis to examine Hh pathway component expression in 275 lung cancer patient specimens. qRT-PCR and western blot were used to validate their expression in SCC lines. To further explore its biological function in lung SCC we manipulated Gli1 expression genetically or pharmacologically followed by colony formation and tumor formation assays. Results: Microarray analysis revealed that Gli1, Gli2, Gli3, and Smoothened are significantly upregulated in lung SCC compared to lung adenocarcinoma (AD). Consistently we found the increased expression of Glis in lung SCC lines relative to AD lines by real-time PCR and western blot. Knocking down Gli1 by siRNA decreased liquid colony formation ability and Gli1-luciferase reporter activity in SCC lines. A significant reduction of cell proliferation and liquid colony formation was observed in shGli1 expressing SCC cells compared to control cells. Gli1 specific inhibitor GANT61 strongly inhibited SCC cell proliferation through inducing cell apoptosis. However, Gli1 expression or transcriptional activity is not regulated by classical Hh pathway upstream regulators in lung SCC. We found that blocking PI3K or ERK pathways by pharmacological inhibitors significantly reduced Gli1 expression and cell survival. In addition, TGF-β stimulation promoted Gli1 expression and transcriptional activity in SCC cells. Conclusions: Our data suggest that Hh pathway downstream factor Gli1 expression is essential for cell proliferation and colony formation in lung SCC. Gli1 is not regulated by canonical Hh pathway regulators, whereas PI3K, ERK, and TGF pathways are involved in its regulation. Blocking Gli1 function is a novel therapeutic strategy for lung SCC treatment. Citation Format: Chunli Shao. Inhibition of Gli1 as a novel therapeutic target for lung squamous cell carcinoma. [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 2350. doi:10.1158/1538-7445.AM2014-2350