Targeting tGLI1, a novel mediator of tumor therapeutic resistance, using Ketoconazole sensitizes glioblastoma to CDK4/6 therapy and chemoradiation

Glioblastoma (GBM) remains the most aggressive primary brain tumor in adults, with no effective treatments. While cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) show clinical promise in some cancers, they have not significantly improved survival in GBM patients. This lack of response is attributed to the treatment-resistant glioma stem cell (GSC) population. We previously identified truncated glioma-associated oncogene homolog 1 (tGLI1) as a novel transcription factor promoting GSCs; however, its role in CDK4/6i resistance has never been investigated in any cancer type. Here, we found positive correlations between tGLI1 and CDK4/6 therapeutic resistance in patient datasets and in vitro studies. Pharmacological inhibition of tGLI1 using FDA-approved ketoconazole (KCZ), a tGLI1-specific inhibitor, sensitized GBM and GSCs to CDK4/6is. KCZ+CDK4/6i combination therapy demonstrated synergistic anti-proliferative effects, significantly inhibiting GBM stemness and cell cycle progression while increasing apoptosis. The combination was more efficacious than monotherapies in two orthotopic GBM mouse models. tGLI1 promoted GBM resistance to radiation therapy and temozolomide, while KCZ potentiated effects of these treatments. Collectively, we report for the first time that tGLI1 is a novel mediator of GBM resistance to CDK4/6is, and KCZ sensitizes GBM to CDK4/6is, thereby supporting future clinical utility of novel KCZ+CDK4/6i combinatorial therapy for GBM patients.