Blocking hERG1 enhances radiation sensitization in glioblastoma

Background: Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a median survival of  less than  two  years. Poor outcomes are driven in part by glioma stem cells (GSCs) that resist radiation and repopulate the tumor. The voltage gated potassium channel hERG1 (KCNH2) is upregulated in GBM and linked to therapy resistance, suggesting that its inhibition might improve radiotherapy efficacy. Methods: Human GBM cell line LN‑229 and patient derived GSC line GNS144 were cultured as spheres. IC₅₀ values for the selective hERG1 inhibitor E‑4031 were determined (192.9 µM for LN‑229, 94.23 µM for GNS144). Cells were treated with the respective IC₅₀ concentration of E‑4031 (or vehicle) and irradiated with a single fraction of 0 Gy or 10 Gy. Sphere formation assays were performed and quantified 7-14 days later. Cell‑cycle distribution was assessed by flow cytometry. All experiments were performed in triplicate; statistical significance was evaluated with Tukey's or Fisher's LSD tests (p < 0.05). Results: In LN‑229 spheres, combination therapy with E‑4031 and radiation reduced sphere formation more than radiation alone (+14.4 %, p = 0.0041) or E‑4031 alone (+23.56 %, p = 0.0002). In GNS144, the combination also performed better than radiation alone (+25.80 %, p = 0.0303) and E‑4031 alone (+26.15 %, p = 0.0283). Cell cycle analysis of LN‑229 showed that E‑4031 decreased the S‑phase population by 5.95 % (p = 0.0054) compared with controls, and when combined with radiation it reduced the S‑phase population by an additional 7.36 % (p = 0.0016). Conclusions: Selective blockade of hERG1 with E‑4031 markedly radiosensitizes GBM cells, producing synergistic reductions in sphere forming capacity, a surrogate for stemness. Moreover, hERG1 inhibition decreases the radioresistant S‑phase cell population. These findings suggest that hERG1 blockade may be beneficial for radiosensitization in GBM, and further exploration of hERG1 targeted strategies could improve outcomes for patients diagnosed with glioblastoma.