2017 Background: MDM2 inhibits tumor suppressor p53. Brigimadlin, a potent MDM2–p53 antagonist, restores wild-type (wt) p53 function and has shown early efficacy in pts with solid tumors (LoRusso et al Cancer Disc 2023). GBM is an area of unmet need with 5-year survival &lt;10%. In p53 wt GBM pt-derived xenograft models, brigimadlin promotes tumor cell apoptosis and extends survival in combination with RT. Methods: NCT05376800 is a Ph 0/Ia open-label, single-arm trial that aims to measure brigimadlin concentration in brain tumor tissue in pts with histologically or radiologically newly diagnosed GBM eligible for resection (Ph 0) and determine the maximum tolerated dose of brigimadlin plus RT in pts with TP53wt, IDH wt, MGMT promoter unmethylated GBM (Ph Ia). In Ph 0, pts received one brigimadlin dose (30 mg or 45 mg) ~12–24 h before resection. Ph 0 primary endpoints are the measured total concentration and the calculated unbound concentration of brigimadlin in brain tissue homogenate from non-contrast enhancing (NCE) and contrast enhancing (CE) regions. The predefined threshold for trial continuation is 0.5 nmol/L (corresponding to IC 50 in GBM cell lines) unbound brigimadlin in CE samples in ≥50% of pts. Brigimadlin concentration was measured using LC/MS and corrected for amount of brigimadlin in residual blood. Unbound concentration was calculated using an in vitro estimate of unbound fraction (f u ): 0.654% (rat brain slice). f u in human plasma was 0.22%. K p,uu (ratio of unbound concentration in brain vs plasma) was calculated. Biomarker testing was performed. Results: Data are available for 11 pts (brigimadlin 30 mg: n=6; 45 mg: n=5). In the 30 mg group, median total brigimadlin concentration in NCE samples was 267 nmol/L (4 samples, range 86–316 nmol/L) and 332 nmol/L (6 samples, range 272–952 nmol/L) in CE samples. In the 45 mg group, median total brigimadlin concentration in NCE samples was 197 nmol/L (5 samples, range 140–347 nmol/L) and 603 nmol/L (5 samples, range 441–905 nmol/L) in CE samples. Unbound concentration exceeded the 0.5 nmol/L threshold in most cases (Table). Post-brigimadlin, an increase in selected p53 target gene expression was observed in CE vs NCE tissue. Conclusions: Unbound brigimadlin concentrations in CE regions in all pts receiving the low dose of 30 mg brigimadlin exceeded the 0.5 nmol/L threshold. K p,uu in most patients was close to 1 in CE regions. Biomarker data support target engagement in brain tissue. Our findings support continued investigation of brigimadlin in GBM. Recruitment is ongoing. Updated data will be presented. Clinical trial information: NCT05376800 . [Table: see text]

A phase (Ph) 0/Ia study of brigimadlin concentration in brain tissue and a non-randomized, open-label, dose escalation study of brigimadlin in combination with radiotherapy (RT) in patients (pts) with newly diagnosed glioblastoma (GBM).