Abstract B15: Human ether-a-go-go-related-1 gene (hERG) K+ channel as a prognostic marker and therapeutic target for glioblastoma
Authors: Pointer Kelli B. , Liu Fang , Jones David K. , Clark Paul A. , Robertson Gail A. , Kuo John S. 
Published: May 2016

Purpose: Glioblastoma multiforme (GBM) is the most malignant primary brain tumor, with a median survival of less than two years despite maximal therapy. Human ether a gò-gò-related-1 gene (hERG) encodes a voltage-dependent K+ channel found overexpressed in GBM cell lines, and linked to aberrant proliferation in other cancers. We analyzed hERG expression in a glioblastoma stem-like cell (GSC)-derived tumor model and a clinically annotated human GBM tissue microarray (TMA) to determine correlation with patient survival. Additionally, since all FDA-approved drugs undergo cardiotoxicity profiling that includes hERG inhibition, GBM patient survival was also analyzed based on whether a patient received hERG inhibitory drugs and their hERG expression levels.

Methods: GSC sphere cultures were isolated from patient GBMs by marker-neutral culture in stem cell media, and validated with progenitor markers, multipotent differentiation, and orthotopic xenograft formation by implanting 2x105 GSCs into right striata of NOD-SCID mice. Tumor xenografts (10-14 weeks) were verified by MRI and animals were sacrificed when moribund. Histology and immunohistochemistry were performed on paraffin-embedded sections for hERG expression and tumor proliferation. Sphere-forming assays with hERG blockers (E-4031, phenytoin) were performed using two low hERG-expressing and two high hERG-expressing GSC lines to test for drug sensitivity. A GBM TMA of 115 patients linked to clinical data was used to correlate hERG expression with patient survival. Clinical data was analyzed to determine if patient survival was affected by incidental administration of drugs with hERG inhibition activity, and the correlative effect of patient GBM hERG expression levels.

Results: hERG expression was upregulated in GBM xenografts with a higher Ki-67 proliferative index. High hERG-expressing GSC lines showed a 50% reduction in sphere formation when treated with known hERG inhibitors at their known hERG channel inactivation IC50 concentrations (E-4031 7.7nM, phenytoin 100uM). GBM TMA analysis showed significantly worse survival for GBM patients with high hERG expression versus low hERG expression (p= 0.0168). In addition, patients who incidentally received at least one hERG blocker drug had significantly better survival compared to patients who did not receive hERG blockers (p=0.0004). Subgroup analysis showed that GBM patients with high hERG expression who also received a hERG blocker had significantly improved survival (p=0.0495);however, there was no significant difference in survival for low hERG-expressing GBM patients who received hERG blocker drugs (p=0.5482).

Conclusions: In this study, we showed that GBM xenografts with higher hERG expression had higher proliferation rates, and treatment with two known hERG inhibitors (phenytoin, E-4031) at IC50 concentrations for inactivating hERG channel activity also inhibited sphere formation in high hERG expressing GSC lines. Furthermore, TMA analyses showed that patients with high hERG-expressing GBMs who received hERG inhibitory drugs had significantly better survival. This data suggest that already FDA-approved drugs with hERG inhibition activity should be tested in patients with high hERG-expressing GBMs.

Citation Format: Kelli B. Pointer, Fang Liu, David K. Jones, Paul A. Clark, Gail A. Robertson, John S. Kuo. Human ether-a-go-go-related-1 gene (hERG) K+ channel as a prognostic marker and therapeutic target for glioblastoma. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B15.