Window of opportunity trial reveals mechanisms of response and resistance to navtemadlin in patients with recurrent glioblastoma [patients]
To investigate the effectiveness of p53 reactivation in treating glioblastoma, we conducted a surgical window-of-opportunity trial (NCT03107780) of the MDM2 inhibitor navtemadlin (KRT-232) on 21 patients and determined achievable drug concentrations within tumor tissue and biological mechanisms of response and resistance. Both 120 mg and 240 mg daily dosing achieved a pharmacodynamic impact, but patient relapse was observed. Sequencing of three recurrent tumors revealed an absence of TP53-inactivating mutations, indicating alternative mechanisms of resistance. To understand the mechanisms of response and resistance associated with navtemadlin, we conducted functional and spatial analyses of human tissue and patient-derived glioblastoma (GBM) models. Navtemadlin induced partial tumor cell death as monotherapy, but combination with temozolomide enhanced apoptosis while sparing normal bone marrow cells in vitro. We additionally report upregulation of oligodendrocyte differentiation genes as an unexplored mechanism of navtemadlin tolerance in GBM. Overall, these results indicate that clinically achievable doses of navtemadlin exert pharmacodynamic effects and suggest that combined treatment with standard-of-care DNA damaging chemotherapy may be a route to more durable survival benefits. Overall design: To detect whether navtemadlin activates the p53 pathway in patient tumor tissue, we conducted bulk RNA sequencing (RNAseq) of formalin-fixed paraffin-embedded (FFPE) biopsies obtained at diagnosis (pre-treatment) and after 30 hours of drug exposure (on-treatment).