Abstract 594: MDM2 inhibition by MI-219 elicits differential molecular effects in wild-type p53 lymphoma cells

Abstract

Abstract Mutations in TP53 occur in 50% of all cancers but are far less common in hematological malignancies. The activity of wild-type p53 (wt-p53) is frequently compromised in lymphomas by overexpression of MDM2. Small-molecule inhibitors (SMIs) that can disrupt the MDM2-p53 interaction and restore p53 function may be an attractive therapeutic strategy. Although response to MDM2 inhibition has previously been determined to greatly depend on p53 status, p53 functional consequences are not fully understood in the presence of MDM2 SMIs. We recently demonstrated striking growth inhibition of two different classes of MDM2 SMIs: Nutlin-3; a cis-imadiazole and MI-219; a spiro-oxindole. Growth inhibition was seen in wt-, but not mutant-, p53 lymphoma cells and did not affect MDM2 E3 ligase activity. In this study, we report that MDM2 inhibition exerts differential molecular effects in wt-p53 lymphoma cells. We found that wt-p53 cell lines, FSCCL and KM-H2, are sensitive to MDM2 inhibition in a time- and dose-dependent manner. Moreover, MI-219 showed greater potency compared to analogous concentrations of Nutlin-3. MI-219 caused more pronounced cell cycle arrest of both cell lines in G0/G1 over a 72 hour time period. Treatment stabilized and activated p53 as well as upregulated p21 and MDM2 protein levels. MG132 and cycloheximide treatments were performed in the presence or absence of MI-219 to determine whether the increase in p53 was due to dissociation from MDM2 and not increased degradation or stabilization. Co-immunoprecipitation confirmed MDM2 SMI disruption of the MDM2-p53 interaction. There was clear evidence of apoptosis in FSCCL, but surprisingly not in KM-H2, as indicated by TUNEL/PI staining (54.39% ± 4.78 vs. 1.32% ± 0.52 after 24 hours). Additionally, apoptosis markers were induced at both mRNA (p53AIP1) and protein levels (caspase-3 and PARP cleavage) after exposure to MI-219 in FSCCL compared to KM-H2. The molecular mechanisms by which MDM2 SMIs exert this differential effect are currently under investigation. Our data presents the preclinical structure for further exploration of MI-219 as a therapeutic approach in the treatment of wt-p53 lymphomas. However, based on our findings, we conclude that additional insights to p53 biology are necessary to maximize their therapeutic potential from preclinical to clinical development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 594. doi:10.1158/1538-7445.AM2011-594