Deleting a Potassium Channel Rewires How Glioblastoma Cells Respond to FLASH-Style Radiation

Glioblastoma remains one of the most formidable opponents in clinical oncology. Classified by the World Health Organization as a grade IV astrocytoma, it is the most aggressive and most common primary malignant brain tumor in adults, and despite maximal safe surgical resection followed by radiotherapy and temozolomide chemotherapy, median survival still hovers between twelve and fifteen months. The tumor’s resistance is driven by a formidable arsenal of defenses: robust DNA repair machinery, resistance to apoptosis, surviving populations of glioma stem cells, metabolic plasticity, autophagy, immune evasion and a protective microenvironment. Because the tumor grows within the radiosensitive central nervous system, physicians cannot simply escalate radiation doses without risking devastating injury to healthy brain tissue. Any strategy that widens the therapeutic window between tumor control and normal tissue damage is therefore of intense interest, and a new study published in the Journal of Neuro-Oncology adds an unexpected player to that conversation: a potassium channel.

The research, led by Kamila Maliszewska-Olejniczak of Warsaw University of Life Sciences together with colleagues at the Nencki Institute of Experimental Biology and the National Centre for Nuclear Research in Poland, examined how deleting the large-conductance calcium-activated potassium channel, known as BKCa, alters the way glioblastoma cells respond to ultra-high dose rate electron irradiation. This irradiation regime is the laboratory cousin of FLASH radiotherapy, an emerging modality that delivers radiation at dose rates exceeding 40 Gy per second in millisecond bursts. Preclinical work has repeatedly suggested that FLASH delivery spares normal tissue while preserving tumor kill, a phenomenon called the FLASH effect, thought to involve transient oxygen depletion and reduced reactive oxygen species chemistry. Yet the underlying biology remains stubbornly unclear, and the new findings suggest that ion channels may be part of the answer.

BKCa channels are not passive bystanders in glioblastoma. They are overexpressed in established cell lines such as U87MG and T98G, in glioblastoma stem-like cells, and in primary cells from patient biopsies, and a glioma-specific splice variant called gBKCa is highly expressed in the disease. These so-called oncochannels support migration and invasion by driving the ion and water efflux needed for cell shrinkage during movement, and they are functionally upregulated under hypoxia, contributing to chemoresistance. Crucially, a mitochondrial isoform, mitoBKCa, helps govern mitochondrial function and oxidative stress, and previous work by the same group showed that its loss elevates mitochondrial reactive oxygen species in U87MG cells. Because ionizing radiation acts largely through oxidative chemistry, the team hypothesized that BKCa deletion might reshape the cellular response to ultra-high dose rate beams.

To test this, the researchers used CRISPR-Cas9 genome editing to generate U87MG cells lacking the pore-forming alpha subunit encoded by KCNMA1, then exposed both wild-type and knockout cells to a 9 MeV electron beam delivered by a modified intraoperative linear accelerator operating in FLASH mode at an average dose rate of 150 Gy per second, with total irradiation times under 40 milliseconds. Doses of approximately 2, 3 and 5 Gy were verified with radiochromic film and a real-time inductive dosimetry system, with flasks positioned in a slab phantom under ambient oxygen conditions. The team then interrogated the cells with a comprehensive battery of assays: clonogenic survival, fluorescence-based ROS measurement, BrdU-DAPI cell-cycle analysis, Annexin V and propidium iodide staining, PARP1 cleavage detection, the alkaline comet assay, gamma-H2AX flow cytometry, 53BP1 immunofluorescence, quantitative PCR for fourteen DNA repair genes, and Western blotting.

The first surprise was what did not change. Clonogenic survival, the gold-standard endpoint of radiobiology, declined dose-dependently in both cell lines, from full survival in untreated controls to roughly 27 percent at 5 Gy in wild-type cells and about 35 percent in knockout cells, but the differences between genotypes were not statistically significant at any dose. Deleting BKCa, in other words, did not make the cells more resistant or more sensitive in terms of long-term colony-forming capacity. Yet beneath this deceptively calm surface, the molecular machinery was behaving very differently. Knockout cells accumulated significantly more reactive oxygen species after 3 Gy, reaching levels of 4.66 relative units compared with 2.21 in wild-type cells, consistent with the idea that the channel helps maintain mitochondrial redox homeostasis and that its absence leaves cells more vulnerable to radiation-induced oxidative stress.

The cell-cycle response also diverged sharply. Thirty minutes after irradiation, wild-type cells distributed themselves across G0/G1, S and G2/M phases, whereas the knockout cells piled up dramatically in G0/G1, reaching nearly 75 percent of the population compared with about 48 percent in irradiated wild-type cells. Notably, the genotoxic chemotherapeutic etoposide produced a classic G2/M arrest in both lines, showing that the two cell lines respond differently to distinct forms of DNA damage and that the G0/G1 accumulation is a specific feature of the ultra-high dose rate response in channel-deficient cells. The authors caution that their data do not establish a direct causal mechanism linking BKCa deletion to this checkpoint redistribution, and that future work on specific checkpoint regulators will be needed.

Cell death signaling told a subtler story. Both cell lines showed reduced viability and increased early apoptosis after irradiation, but without significant differences between genotypes. Cleaved PARP1, a caspase-generated marker of apoptotic signaling, rose significantly in knockout cells but not in wild-type cells, although the between-genotype comparison did not reach significance and Western blotting of the cleaved-to-full-length PARP1 ratio showed no genotype-dependent difference. The most striking finding, however, concerned DNA damage signaling itself. Despite suffering comparable or greater DNA strand damage, as confirmed by the alkaline comet assay with tail DNA rising to more than 80 percent in irradiated knockout cells, the knockout cells accumulated far less gamma-H2AX, the phosphorylated histone that marks double-strand breaks, reaching only about 24 percent positive cells versus nearly 70 percent in irradiated wild-type cells. Formation of 53BP1 foci, which recruit repair complexes to damaged chromatin and bias repair toward non-homologous end joining, was likewise significantly reduced in the knockout cells.

The authors are careful to stress that reduced gamma-H2AX and 53BP1 should not be read as an absence of DNA damage. The comet assay proves the damage is there. Rather, the findings point to impaired damage recognition and altered assembly of repair complexes, a dysregulation of the early DNA damage response rather than a reduction in the insult itself. This interpretation is reinforced by the transcriptional data. Irradiated knockout cells upregulated double-strand break repair genes including ATM, BRCA1 and RAD51 relative to irradiated wild-type cells, while simultaneously downregulating single-strand break repair genes dependent on PARP enzymes, including PARP1, PARP2, PARP3 and XRCC1. The team had previously implicated BKCa as a regulator of the DNA damage response under oxidative stress caused by particulate matter exposure, and the new results extend that concept to ionizing radiation delivered at ultra-high dose rates.

The study has clear limitations that the authors acknowledge candidly. All experiments used a single isogenic U87MG model in vitro, so validation in additional cell lines and patient-derived glioblastoma models is essential, and no conventional dose-rate control was included, meaning the observed effects cannot be attributed specifically to the FLASH effect as opposed to the irradiation conditions used. Nevertheless, the work identifies BKCa as a genuine modulator of the early molecular response of glioblastoma cells to ultra-high dose rate irradiation, spanning redox balance, cell-cycle distribution, DNA damage signaling, apoptotic markers and repair gene transcription. Given that potassium channels can be targeted pharmacologically or genetically, the findings open a plausible path toward combining channel modulation with FLASH radiotherapy and temozolomide, although the authors emphasize that the present data provide no evidence yet of BKCa-dependent radiosensitization. As clinical FLASH trials accelerate, understanding which molecular levers distinguish tumor from normal tissue responses may prove decisive, and this study suggests that an ion channel once studied mainly for its role in cell migration may be one of those levers.

Subject of Research: How BKCa potassium channel deletion modulates the DNA damage response of glioblastoma cells to electron ultra-high dose rate irradiation

Article Title: BKCa channel deletion modulates the DNA damage response to electron ultra-high dose rate irradiation in glioblastoma cells

Article References: Maliszewska-Olejniczak, K., Fryc, M., Kustra, A., Wiktorska, K., Lenartowicz-Gasik, A., Soroka, W., Rzadkiewicz, J., Żochowska, M., Kulawiak, B., & Bednarczyk, P. (2026). BKCa channel deletion modulates the DNA damage response to electron ultra-high dose rate irradiation in glioblastoma cells. Journal of Neuro-Oncology, 179(3), Article 95. https://doi.org/10.1007/s11060-026-05804-z

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05804-z

Keywords: glioblastoma, BKCa channel, FLASH radiotherapy, ultra-high dose rate irradiation, DNA damage response, gamma-H2AX, 53BP1, reactive oxygen species, U87MG cells, apoptosis, DNA repair, ion channels