The EP3–ZNF488 Axis Promotes Self-Renewal of Glioma Stem-Like Cells to Induce Resistance to Tumor Treating Fields

Tumor treating fields (TTFields) use low-intensity, alternating electric fields to exert antitumor activity and have demonstrated efficacy against multiple cancers, including glioblastoma (GBM). Unfortunately, cancer cells inevitably develop resistance to TTFields, highlighting the need to elucidate the underlying mechanisms to develop approaches to induce durable responses. Using a gene network-based machine learning algorithm, we interrogated TTFields-resistant GBM cells and uncovered a regulatory axis anchored by the prostaglandin E2 receptor 3 (EP3) and the transcription factor zinc finger 488 (ZNF488). Mechanistically, TTFields induced EP3 upregulation and nuclear envelope localization, where it formed a complex with ZNF488 to induce resistance to TTFields by promoting self-renewal of glioma stem-like cells (GSC). Overexpression of EP3 and/or ZNF488 in TTFields-sensitive GSC conferred resistance and enhanced self-renewal, whereas expression of noninteracting mutants of these proteins abrogated the formation of the nuclear complex and prevented resistance. Inhibition of either partner in this protein complex in resistant GSC, including those freshly isolated from TTFields-resistant GBM tumors, resensitized cells to the cytotoxic effects of TTFields, concomitant with reduced self-renewal and in vivo tumorigenicity. Importantly, inhibition of EP3 in TTFields-sensitive GSC preemptively halted the development of resistance. The EP3-ZNF488 axis was significantly upregulated in TTFields-resistant GBM tumors, and coexpression of EP3 and ZNF488 in other cancers correlated with lower survival rates. Collectively, these results indicate that the nuclear EP3-ZNF488 axis is necessary and sufficient to establish TTFields resistance, underscoring the potential to target this axis to prevent or reverse resistance in GBM and possibly other cancers. Significance: The EP3-ZNF488 master regulatory axis in cancer stem-like cells drives resistance to treatments like tumor treating fields, opening avenues for developing strategies to enhance therapeutic efficacy.