Role of ICI-182,780 as a Repurposed Drug to reduce Glioblastoma Stemness sustained by Estrogen signaling: First evidence of GLI-1 as co-activator of ERα

Background Glioblastoma is the most aggressive primary brain tumor in adults, and its poor clinical outcome is largely driven by glioblastoma stem cells (GSCs), which promote tumor progression, therapeutic resistance, and recurrence. Although the renin-angiotensin system has been implicated in GBM progression, the molecular mechanisms linking Angiotensin II (Ang II) signaling to GSC maintenance remain poorly understood. Here, we investigated whether Ang II promotes GBM stemness through estrogen-dependent signaling and assessed the therapeutic potential of the selective estrogen receptor degrader ICI-182,780. Methods Human GBM cell lines, U-87MG and T98G, monolayer and neurosphere-derived GSCs were used to investigate Ang II-mediated signaling. By integrating transcriptomic profiling and pathway enrichment analysis with immunoblotting, qRT-PCR, immunofluorescence and proximity ligation assay, we mapped the Ang II-mediated pathways. Furthermore, we combined chromatin immunoprecipitation (ChIP/Re-ChIP), luciferase reporter assays, spheroid invasion assays, in vivo xenograft analyses, and the interrogation of public datasets (TCGA, CGGA, and GEO) to define the underlying molecular mechanisms and establish their clinical relevance. Results Transcriptomic profiling identified estrogen receptor, PI3K/AKT, Hedgehog, and Notch signaling as major pathways affected by Ang II. Mechanistically, Ang II triggered rapid ERα-dependent activation of PI3K/AKT signaling, leading to SMO-independent activation of GLI-1. Pharmacological inhibition of ERα or PI3K abolished GLI-1 activation, whereas AGTR1 blockade produced only partial effects, suggesting that estrogen signaling is an essential component of the mechanism by which Ang II regulates GLI-1. Functionally, Ang II enhanced neurospheres formation, self-renewal, spheroid invasion, and the expression of stemness-associated markers, including CD133, NOTCH1, OCT4, SOX2 and SOX4, all of which were markedly suppressed by ICI-182,780. Importantly, GLI-1 physically interacted with ERα, cooperatively occupied the Cyclin D1 promoter, and enhanced estrogen-dependent transcription, identifying GLI-1 as a functional transcriptional co-regulator of ERα. In vivo validation and analyses of public clinical datasets confirmed activation of this molecular axis and demonstrated that elevated GLI-1 and ERS1 expression is associated with poor patient survival. Conclusions This study identifies a previously unrecognized Ang II/ERα/PI3K/AKT/GLI-1 signaling circuit that sustains GBM stemness and aggressiveness. By demonstrating that GLI-1 functions as a transcriptional co-regulator of ERα, our finding reveal a novel mechanism linking estrogen signaling to GBM progression and provide a strong rationale for repurposing ICI-182,780 as a therapeutic strategy to target GSCs and overcome disease recurrence.