Abstract C060: Broad spectrum activity of the MDM2 inhibitor MI-773 in hematologic and solid cancer cell lines in-vitro and determination of predictive biomarkers
Authors: Fiebig Heinz-Herbert , Kelter Gerhard , Hendriks Hans R , Hasani Hoor Al , Vuaroqueaux Vincent 
Published: March 2020

Abstract
The Mouse Double Minute 2 (MDM2) proto-oncogene is a primary cellular inhibitor of p53 tumor suppressor protein. MDM2 encodes for a nuclear-localized E3 ubiquitin-protein ligase via direct interaction responsible for proteasomal degradation of p53. Its overexpression in TP53 wild type tumors leads to the loss of apoptotic function and cell survival. MDM2 inhibitors were envisioned to restore p53 activity in p53 wild type tumors, several are currently being evaluated in the clinic. MI-773 is a small molecule, that inhibits the p53-MDM2 protein-protein interaction. It has been evaluated in Phase I. We aimed to pursue characterization of MI-773’s anti-tumor activity by performing a large pharmacogenomic study to identify tumor candidates for such treatment. MI-773 was tested in vitro in a 2D monolayer assay in 274 human tumor cell lines (50 hematologic and 224 solid cancer cell lines) belonging to 36 tumor types. Drug sensitivity results in vitro were correlated with molecular data of the cell lines, including whole exome mutations, gene copy number variations and gene expression profiles, to study molecular determinants for a response. MI-773 showed a moderate anti-tumor potency (median IC50 13,5 µM, range 0.1 to up to30 µM) and pronounced selectivity was observed in several hematologic and solid cancer cell lines. Fifty tumor cell lines (18,5%) were 10 times more sensitive compared to the median IC50 of all cell lines. Among the solid cell lines, melanomas, kidney, stomach, breast and pleural mesotheliomas were the most sensitive tumor types, whereas ALL, AML, and multiple myelomas were the most sensitive hematological tumors. Confirmatory in vivo studies of MI-773 in the most sensitive tumors are planned. The Compare analysis of MI-773 with 44 targeted agents and 250 cytotoxic agents in 40 to 117 tumor cell lines showed the highest similarity with p53/MDM2 inhibitors Nutlin-3a and YH239-EE with Spearman correlation coefficients of 0,71 and 0,56, a clear indication that biological testing’s in cell line panels allows identification of the mechanism of action of novel compounds. As expected, TP53 mutation was the major determinant of tumor sensitivity to MI-773 (Wilcoxon test, adjusted p value= 2;28E-12). Sixty one out of 88 (69%) tumor cell lines wild type TP53 showed a high sensitivity to MI-773 whereas 141 out of 162 (87%) cell lines mutated for the gene were resistant. Transcriptome analysis revealed that the expression levels of 355 genes were significantly associated with sensitivity to MI-773 (LIMMA and Spearman test adjusted p values both p&lt;0.05). MDM2, CDKN1A, SPATA18 and ZMAT3 were the strongest predictors positively associated with both TP53 integrity and sensitivity toward MI-773. Pathway analysis confirmed that overall the genes upregulated in tumor cell lines sensitive to MI-773 to be dominantly involved in negative regulation of mitotic cell cycle, regulation of cell cycle phase transition or signal transduction by p53 class mediator. The present study demonstrated that the MDM2 inhibitor MI-773 could be used in a broad range of hematological and solid tumor types, however, with the determination of TP53 as a prerequisite. MDM2 inhibitors should be evaluated in p53 wild type melanomas, mesotheliomas, kidney, stomach, and breast cancers as well as in ALL, AML, and multiple myelomas.
Citation Format: Heinz-Herbert Fiebig, Gerhard Kelter, Hans R Hendriks, Hoor Al Hasani, Vincent Vuaroqueaux. Broad spectrum activity of the MDM2 inhibitor MI-773 in hematologic and solid cancer cell lines in-vitro and determination of predictive biomarkers [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C060. doi:10.1158/1535-7163.TARG-19-C060