Abstract 2786: Potent inhibition of human liposarcoma cell growth and survival by novel modulators of the MDM2-p53 interaction

Abstract

Abstract The tumor suppressor p53 is commonly inactivated in human malignancies. One mechanism is by genomic amplification and consequent overexpression of the ubiquitin E3 ligase MDM2, which targets p53 for proteosome-mediated degradation. The MDM2 gene is amplified in >95% of human liposarcomas, a disease for which the efficacy of systemic therapies is limited. Here, we compared the effects of two novel highly potent and selective inhibitors of the MDM2-p53 interaction, with the classic MDM2 inhibitor Nutlin-3 on the expression and activity of p53 and the resulting changes in human liposarcoma cell proliferation and survival. We determined MDM2 copy number, p53 mutational status, and relative expression levels of MDM2 and p53 proteins in 8 human liposarcoma cell lines and normal human preadipocytes/adipocytes. TP53 status was wild type in 7 of 8 liposarcoma cell lines, which also had genomic amplification of MDM2. MDM2 protein expression correlated with the degree of amplification and was highly expressed in comparison to normal preadipocytes/adipocytes. The two spiro-oxindole derivatives - Compounds A and B- (1) and Nutlin-3 were applied to liposarcoma cell lines with or without p53 siRNA and the biological consequences were determined by immunoblot, cell viability, cell cycle and apoptosis assays. Treatment with MDM2 inhibitors led to increased p53 protein levels and induction of its transcriptional targets MDM2 and p21. Cell viability was markedly decreased in a dose-dependent manner in liposarcoma cells with wild-type p53, with IC50 values of 0.40-4.23 μM, 0.37-1.88 μM and 2.72-9.83 μM for Compound A, Compound B, and Nutlin-3, respectively. These effects were markedly abrogated by siRNA-mediated p53 knockdown and in a cell line harboring a de novo p53 mutation. Compound A and Compound B also induced cell cycle arrest and apoptosis at approximately 5 fold lower concentrations than Nutlin-3. At low concentrations, G0/G1 cell arrest occurred, whereas higher concentrations resulted in G2/M arrest and induction of apoptosis. Cell line and tumor xenograft experiments are ongoing. These data demonstrate that Compounds A and B are highly potent and specific inhibitors of MDM2 with activity in genetically characterized liposarcoma cells. Further study and clinical development in this disease is warranted. 1. Wang S. et al., AACR, Orlando FL, 2011, Abstract LB-204 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2786. doi:1538-7445.AM2012-2786