GLI1 Blockade Potentiates the Antitumor Activity of PI3K Antagonists in Lung Squamous Cell Carcinoma

Abstract

Lung squamous cell carcinoma (SCC), strongly associated with smoking, is treated primarily with traditional cytotoxic chemotherapy due to a lack of FDA-approved targeted agents available. Here we identify the Hedgehog pathway transcription factor GLI1 as a critical driver of lung SCC. Analysis of human lung cancer datasets showed that GLI1 mRNA was highly expressed in human lung SCC and portended a poor prognosis. Inhibition of GLI1 in human lung SCC cell lines suppressed tumor cell clonogenicity and proliferation in culture and in vivo. Addition of SHH ligand, SMO antagonists, or other Hedgehog pathway agonists did not affect GLI1 expression in lung SCC cells. However, GLI1 expression was modulated by either inhibition or activation of the PI3K and MAPK pathways. Furthermore, in vivo growth of SCC harboring amplifications of the PI3K gene PIK3CA was attenuated by antagonizing GLI1 and PI3K. Thus, a combinatorial therapeutic strategy that targets the PI3K-mTOR pathway and GLI1 may lead to effective outcomes for PI3K pathway-dependent cancers, in contrast to recent results of human trials with single-agent PI3K antagonists.

Stromal Hedgehog pathway activation by IHH suppresses lung adenocarcinoma growth and metastasis by limiting reactive oxygen species

“…Cell lysates were generated and analyzed as previously described [31]. Briefly, cells were lysed in ice-cold lysis buffer (M-PER Mammalian Protein Extraction Reagent (Thermo Scientific) with protease inhibitors (Roche) and PhosSTOP phosphatase inhibitors (Roche).…”

“…In lung squamous cell carcinoma (LSCC) tumor-spheres [29], SOX2 activation induced upregulation of Hh acyltransferase (HHAT) [30], a critical component that palmitoylates Hh ligands, and induced autocrine pathway activation to drive growth of LSCC tumor-spheres but not bulk LSCC cells nor LAD tumor-spheres [29]. Alternatively, in PIK3CA-amplified LSCC, PI3K-mTOR pathway activation led to noncanonical GLI1 expression independent of the Hh pathway [31]. GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists induced tumor regression in vivo [31].…”

“…Alternatively, in PIK3CA-amplified LSCC, PI3K-mTOR pathway activation led to noncanonical GLI1 expression independent of the Hh pathway [31]. GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists induced tumor regression in vivo [31]. In LAD tumor-spheres and cell lines, paracrine SHH from LAD epithelia activated the pathway in stroma to express VEGF that in turn, bound to NRP2 receptor to activate the MAPK pathway and express GLI1 in a non-canonical manner [32].…”

Stromal Hedgehog pathway activation by IHH suppresses lung adenocarcinoma growth and metastasis by limiting reactive oxygen species

“…In lung squamous cell carcinoma (LSCC) tumor-spheres (45), SOX2 activation induced upregulation of Hh acyltransferase (HHAT) (46), a critical component that palmitoylates Hh ligands (47, 48), and induces autocrine pathway activation to drive growth of LSCC tumor-spheres but not bulk LSCC cells nor lung adenocarcinoma (LAD) tumor-spheres (45). Alternatively, in PIK3CA -amplified LSCC, PI3K-mTOR pathway activation led to non-canonical GLI1 expression independent of the Hh pathway (49). GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists leads to tumor regression in vivo (49).…”

“…Alternatively, in PIK3CA -amplified LSCC, PI3K-mTOR pathway activation led to non-canonical GLI1 expression independent of the Hh pathway (49). GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists leads to tumor regression in vivo (49). In LAD tumor-spheres and cell lines, paracrine SHH from LAD epithelia activated the pathway in stroma to express VEGF that in turn, bound to NRP2 receptor to activate the MAPK pathway and express GLI1 in a non-canonical manner (50).…”