Disrupting STAT3 Signaling in Glioblastoma Stem Cells Using Nitro-Modified Curcumin Analogs

Disrupting STAT3 Signaling in Glioblastoma Stem Cells Using Nitro-Modified Curcumin Analogs

Alvin Sherman Library

Signal Transducer and Activator of Transcription 3 (STAT3) is frequently overactivated in cancers, including glioblastoma (GBM), where its dysregulation is associated with aggressive disease and poor patient survival. STAT3 supports tumor progression by promoting proliferation, resistance to apoptosis, maintenance of cancer stem cells, and immune suppression. Although numerous STAT3 inhibitors are under preclinical and clinical evaluation, none have yet achieved FDA approval. GBM remains a highly lethal brain cancer with limited therapeutic options, underscoring the need for new targeted treatments. Nitro-containing compounds, known for their strong electron-withdrawing characteristics, are emerging as potential anticancer agents. A library of 41 nitro-containing chalcones and cyclic C5-curcumin derivatives was synthesized and screened for cytotoxicity in three glioblastoma stem cell (GSC) lines. Compounds were tested at concentrations ranging from 0.1 to 10 μM, and cell viability was assessed after 72 hours using an MTS assay. Neurosphere-forming assays were conducted to evaluate effects on GSC self-renewal, and Western blotting was used to examine alterations in STAT3-related signaling pathways. SwissDock modeling was employed to predict compound interactions with STAT3. More than half of the synthesized molecules demonstrated average IC50 values ≤ 10 μM in GSCs, and four exhibited IC50s in the low-nanomolar range. Among them, IX-11, a nitro-substituted cyclic C5-curcumin analog, displayed the strongest activity, with an average IC50 of 0.76 μM, outperforming WP1066 (IC50 2.12 μM), a clinical-stage STAT3 inhibitor. IX-11 markedly decreased neurosphere formation, reduced STAT3 phosphorylation, and suppressed downstream gene expression. Docking studies revealed predicted binding to STAT3's SH2 domain, a key site for activation. Nitro groups represent highly effective functional moieties, and IX-11 emerged as a promising STAT3 SH2-domain inhibitor and potential therapeutic candidate for GBM.