ABSTRACT: Glioblastoma multiforme (GBM) is the most common and deadliest glioma, originating from astrocytic progenitors or stem cells and affecting individuals of all ages. Current treatments include surgery, radiation therapy, chemotherapy, and combinations of these modalities. Temozolomide, the first-line chemotherapy for GBM, improves survival when combined with radiation but has limited success due to the tumor's inherent resistance to therapies. Cancer stem cells (CSCs), which exhibit self-renewal and differentiation capabilities, contribute to therapeutic resistance, making them a promising target for GBM therapy. Abemaciclib, a CDK4/6 inhibitor, effectively reduces tumor growth and sphere formation in GBM, although its exact mechanism remains unclear. Our data revealed that Abemaciclib significantly inhibited tumor sphere formation in U87MG and KNS42 cells by downregulating epithelial-mesenchymal transition (EMT)-associated genes, including CD44 and TCF7L2. Notably, silencing CD44 and TCF7L2 also led to a marked reduction in sphere formation. Phospho-kinase array analysis revealed that Abemaciclib reduces pGSK3β and pCREB in sphere cells. Western blotting confirmed that Abemaciclib diminishes pGSK3β-Y216 in parental cells, suggesting reduced kinase activity. Pharmacological inhibition of GSK3β also decreased CD44 and TCF7L2 expression. In an orthotopic animal model, Abemaciclib inhibited tumor formation, with reduced levels of pRB, pGSK3β, Ki67, and CD44 confirmed by immunohistochemistry. Analysis of TCGA and CGGA datasets showed that the mesenchymal GBM subtype (MES-GBM), associated with poor prognosis, has higher EMT gene expression. Treatment of MES-like LN229 cells with Abemaciclib decreased EMT-related genes. These findings suggest that Abemaciclib disrupts GSK3β-mediated EMT pathways, impairing CSC self-renewal and offering a potential therapeutic strategy for GBM.
