The goal of this 1:1 randomized, multi-center, open-label phase Ib/II clinical trial is to explore the efficacy of the add-on of the anti-glutamatergic drugs gabapentin, sulfasalazine and memantine to standard chemoradiotherapy with temozolomide compared to chemoradiotherapy alone in patients with newly diagnosed glioblastoma.
Inclusion criteria * Diagnosis: Newly diagnosed supratentorial glioblastoma according to the 2021 World Health Organization (WHO) Classification of Central Nervous System Tumors * Signed informed consent * Age \>18 years * Eligible for standard chemoradiotherapy with temozolomide (TMZ/RT-\>TMZ, hypofractionated RT regimen not allowed) * KPS 70 or more * Ability to judge per local investigator estimate (at least oriented to time, place and situation) * Paraffin-embedded tissue for central pathology review * Adequate heamatological, liver and renal function Exclusion criteria * Scheduled for hypofractionated radiotherapy * Women who are pregnant or breast feeding, * Intention to become pregnant during the course of the study or intention to father a child, * Lack of safe contraception, defined as: Female participants of childbearing potential, not using and not willing to continue using a medically reliable method of contraception for the entire study duration, such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices, or who are not using any other method considered sufficiently reliable by the investigator in individual cases. Female participants who are surgically sterilised / hysterectomised or post-menopausal for longer than 2 years are not considered as being of child bearing potential. * Other clinically significant concomitant disease states (e.g., renal failure, hepatic dysfunction, cardiovascular disease), * Known or suspected non-compliance, drug or alcohol abuse, * Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant, * Participation in another study with investigational drug within the 30 days preceding and during the present study, * Previous enrolment into the current study, * Being an investigator, his/her family members, employees and other dependent persons, * Any prior radiotherapy of the brain or radiotherapy with potential overlap of the irradiation fields, * Active malignancy that may interfere with the study treatment, * Abnormal ECG with QTc \>450 ms, * Contraindication for Gadolinium-enhanced MRI, * Previous intolerance reactions to one of the study drugs, * Intolerance reactions to sulfonamides or salicylates, * Acute intermittend porphyria, * Known glucose-6-phosphate dehydrogenase deficiency, * Concomitant therapy with digoxin, cyclosporin, methotrexate, * History of exfoliative dermatitis, Stevens-Johnson-Syndrome, toxic epidermal necrolysis, DRESS (Drug Rash with Eosinophilia and Systemic Symptoms) syndrome or renal tubular acidosis.