Layman summary with societal impact Almost half of the primary malignant brain tumours are GBs. The diagnosis of GB is a hard verdict for patients because GB is associated with a low survival rate and many clinical symptoms, including epileptic seizures and intracranial pressure. The current treatment strategy consists of surgical resection, radiotherapy and chemotherapy, but fails to significantly increase the survival rate due to the overall resistance to this therapy. Therefore, development of new therapies is necessary for GB. The results of this preclinical study using the F98 GB rat model show that Tonabersat may add value to the standard of care. In particular, the patient's life span after diagnosis could feasibly be prolonged by the addition of Tonabersat. On top of this, the results seem to indicate that omitting chemotherapy does not affect the survival time significantly. In the future, this could lead to a strategy consisting of a combination of radiotherapy and Tonabersat, which would be an advantage for the patient because the toxic side-effects of chemotherapy on the body (e.g. hair loss and nausea) could be cleared. The application of Tonabersat in humans showed no serious side-effects when evaluated in phase II clinical trials for migraine prevention. This may increase the patient's quality of life. Besides GB, Tonabersat might serve as a therapy for other cancer types (e.g. breast cancer and prostate cancer) where Cx43 seems to be involved in therapy resistance and tumour invasion.