Abstract P210: MDM2 gene amplification as a predictive biomarker for the MDM2 inhibitor milademetan
Authors: Tirunagaru Vijaya G. , Gounder Mrinal M. , Kumar Prasanna R. , Hong David S. , Doebele Robert C. 
Published: December 2021

Abstract
MDM2 is an E3 ubiquitin ligase that plays a critical role in the degradation of the tumor suppressor p53. Milademetan (RAIN-32) is an orally available, small molecule inhibitor of MDM2 that disrupts the MDM2-p53 protein complex thereby restoring p53 expression and activity. Milademetan has demonstrated anti-tumor activity in de-differentiated liposarcoma, a tumor type characterized by MDM2 gene amplification (amp) and WT TP53, in the phase I study of monotherapy milademetan (NCT01877382). Here we investigate the use of MDM2 gene amplification as a predictive biomarker for the selection of patients with advanced cancers who might benefit from milademetan. In this study we evaluated milademetan in MDM2 gene amp cancer models from a variety of tumor types using both in vitro assays, including 2D viability assays and organoid models, as well as in vivo patient-derived xenografts. We employed a mutual exclusivity analysis between MDM2 copy number (CN) and TP53 mutation status using publicly available next generation sequencing data to derive an optimal MDM2 CN threshold for patient selection and present clinical data from patients with MDM2 amp tumors treated with milademetan in the phase 1 study (NCT01877382). Three cell lines, CCFSTTG1 (astrocytoma), DKMG (glioblastoma), and SJSA1 (osteosarcoma), with MDM2 amp were identified and demonstrated inhibition of cell proliferation by milademetan with GI50 &lt;100 nM. Evidence of MDM2 target engagement and activation of p53 was demonstrated through induction of p21 and PUMA, transcriptional targets of p53. Four patient-derived organoid models from diverse cancers (2 lung adenocarcinoma, 1 cholangiocarcinoma, and 1 renall cell carcinoma) were identified with MDM2 amp and WT TP53 and demonstrated differential selectivity compared to non-MDM2 amp models also with WT TP53 (head and neck scquamous cell carcinoma, endometrial carcinoma). Xenograft models from tumor types including gastric, lung adenocarcinoma and osteosarcoma with MDM2 amp showed dose-dependent anti-tumor activity to milademetan in vivo. Induction of MIC-1, a p53 target gene, was observed in vivo following milademetan dosing. An MDM2 CN threshold of ≥ 12 was derived using mutual exclusivity analysis using the AACR Genie dataset across solid tumor types. Using TCGA Pan-Cancer Atlas dataset, we identified 1.1% of cancers that met the criteria of MDM2 CN ≥ 12 and WT TP53. Finally, 3 patients (breast cancer, synovial sarcoma, and small cell lung cancer) with MDM2 CN ≥ 12 were previously enrolled on the U101 study of milademetan, Schedule D (3 days on 11 days off), which was determined to be the dose schedule for future clinical trials, and all 3 patients experienced tumor reduction with 2 patients demonstrating a partial response and 1 confirmed partial response.
Milademetan shows evidence of preclinical and clinical anti-tumor activity in genetically selected tumors using MDM2 amp and WT TP53 as selection criteria. A basket study evaluating milademetan in solid tumors with MDM2 CN ≥ 12 and WT TP53 (MANTRA-2) is planned.
Citation Format: Vijaya G. Tirunagaru, Mrinal M. Gounder, Prasanna R. Kumar, David S. Hong, Robert C. Doebele. MDM2 gene amplification as a predictive biomarker for the MDM2 inhibitor milademetan [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P210.