Abstract B236: Inhibition of Hedgehog-GLI signaling suppresses tumor growth in squamous lung cancer.

Purpose: Lung squamous cell carcinoma (LSCC) comprises ∼30% of non-small cell lung cancers and currently lacks effective targeted therapies. Previous studies reported overexpression of Hedgehog (HH)-GLI signaling components in LSCC, but the requirement for HH-GLI signaling in regulation of cellular survival and proliferation in LSCC remains unknown. In this study, we investigated the role of HH-GLI signaling in LSCC, and studied the therapeutic potential of HH signaling inhibition. Experimental Design: Gene expression datasets of two independent LSCC patient cohorts were analyzed to study the activation pattern of HH-GLI signaling. Four representative human LSCC cell lines were examined for expression of HH-GLI signaling components. Cell proliferation and apoptosis were assayed in these cells after blocking the HH-GLI pathway by lentiviral-shRNA knockdown or small molecule inhibitors. A xenograft model in immunodeficient mice was used to determine the in vivo therapeutic efficacy of GLI inhibitor GANT61. Results: LSCC has been classified into four distinct mRNA expression subtypes. The classical subtype (∼36% of LSCC) displayed increased expression of positive regulators (PTCH1, SMO, GLI1, GLI2) and decreased expression of negative regulators (SUFU, GLI3) relative to the other three subtypes. GLI2 was consistently highly expressed in the classical subtype, and strong positive correlations between GLI2 and the classical subtype makers (SOX2, TP63 and PIK3CA) were observed, indicating a critical role of GLI2 in LSCC. In three cell lines (NCI-H520, NCI-H226 and SK-MES-1), high level of GLI2 was consistently expressed, whereas GLI1 was hardly detectable. Neither GLI1 nor GLI2 was detected in NCI-H2170. Knockdown of GLI2 by lentiviral-shRNAs caused extensive apoptosis and significant growth inhibition in GLI2-positive cells, suggest an indispensable role of GLI2 in regulating cell survival. Pharmacological inhibition of HH-GLI signaling by GLI inhibitor GANT61 phenocopied the loss of GLI2 in GLI-positive cells, but had little effect on the GLI-negative NCI-H2170. In the xenograft model, GANT61 suppressed tumor progression and led to a significant 40% reduction of tumor weight for GLI-positive cell lines in comparison to solvent control, but had no effects on the GLI-negative NCI-H2170 tumors, suggesting a specific anti-tumor efficacy of GANT61. The expression of HH downstream targets (GLI2, PTCH1, HHIP, and CCND1) was significantly reduced by GANT61, demonstrating a successful blockage of the HH-GLI pathway. In contrast to GANT61, GDC-0449, a clinically available SMO inhibitor, only produced limited cytotoxicity despite the universal expression of SMO. Conclusions: Our studies reveal an important role of GLI2 in LSCC cell survival, and suggest GLI inhibition as a novel and potent strategy to treat patients with classical LSCC. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B236. Citation Format: Lingling Huang, Vonn Walter, Neil Hayes, Mark Onaitis. Inhibition of Hedgehog-GLI signaling suppresses tumor growth in squamous lung cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B236.