Purpose: p53 pathway alterations are key molecular events in glioblastoma (GBM). MDM2 inhibitors increase expression and stability of p53 and are presumed to be most efficacious in patients with TP53 wild-type and MDM2-amplified cancers. However, this biomarker hypothesis has not been tested in patients or patient-derived models for GBM.

Experimental Design: We performed a preclinical evaluation of RG7112 MDM2 inhibitor, across a panel of 36 patient-derived GBM cell lines (PDCL), each genetically characterized according to their P53 pathway status. We then performed a pharmacokinetic (PK) profiling of RG7112 distribution in mice and evaluated the therapeutic activity of RG7112 in orthotopic and subcutaneous GBM models.

Results: MDM2-amplified PDCLs were 44 times more sensitive than TP53-mutated lines that showed complete resistance at therapeutically attainable concentrations (avg. IC₅₀ of 0.52 μmol/L vs. 21.9 μmol/L). MDM4-amplified PDCLs were highly sensitive but showed intermediate response (avg. IC₅₀ of 1.2 μmol/L), whereas response was heterogeneous in TP53 wild-type PDCLs with normal MDM2/4 levels (avg. IC₅₀ of 7.7 μmol/L). In MDM2-amplified lines, RG7112 restored p53 activity inducing robust p21 expression and apoptosis. PK profiling of RG7112-treated PDCL intracranial xenografts demonstrated that the compound significantly crosses the blood–brain and the blood–tumor barriers. Most importantly, treatment of MDM2-amplified/TP53 wild-type PDCL-derived model (subcutaneous and orthotopic) reduced tumor growth, was cytotoxic, and significantly increased survival.

Conclusions: These data strongly support development of MDM2 inhibitors for clinical testing in MDM2-amplified GBM patients. Moreover, significant efficacy in a subset of non–MDM2-amplified models suggests that additional markers of response to MDM2 inhibitors must be identified. Clin Cancer Res; 22(5); 1185–96. ©2015 AACR.