Abstract 5136: HDACi inhibits liposarcoma via targeting of the MDM2-p53 signaling axis and PTEN, irrespective of p53 mutational status
Authors: Ou Wen-bin , Li Hailong , Liu Li , Zhou Shengmei , Kuang Ye , Yan Ziqin , Jiang Zhe , Shi Si , Meng Fanguo , Sheng Qing , Zhou Haimeng , Fletcher Jonathan A. 
Published: May 2015

Abstract
Liposarcoma (LPS) is the most common sarcoma of humans. There are no systemic therapeutic regimens known to improve survival when complete surgical resection is not feasible, underscoring the need for an improved molecular understanding of LPS to stimulate the development of effective targeted therapies. The MDM2-p53 pathway plays a prominent role in WDLPS pathogenesis, with the vast majority of human tumors harboring either MDM2 amplifications or p53 mutations. Nutlin-3, a small-molecular antagonist of MDM2, inhibits cell proliferation via blocking the interaction of MDM2-p53 in LPS with wild-type p53. We wonder whether MDM2 overexpression due to amplification or/and mutant p53 still plays a crucial oncogenic role in LPS containing p53 mutation. Herein, we developed isogenic liposarcoma lines in which the parental forms were MDM2 amplification and p53 wild-type, whereas sublines had mutation p53 expression, showed Nutlin-3 resistance. mRNA sequencing and immunoblotting showed that MDM2 and CDK4 were overexpression in the parental lines and sublines, whereas MDM2 and CDK4 expression was low in mesothelioma and GIST cell lines. HDAC inhibitor (HDACi, SAHA and LBH589) treatment resulted in the dephosphorylation and degradation of MDM2 and p53, but little affected CDK4 and JUN expression, irrespective of p53 mutational status in LPS with MDM2 amplification, and in a mesothelioma cell line JMN1B with p53 mutation, but not two mesothelioma lines containing normal MDM2 level and wild-type p53. Our findings indicate that regulation of wild-type 53 degradation by HDACi is MDM2 amplification-dependent. HDAC inhibition by SAHA and LBH589 had a substantially effect on LPS and mesothelioma proliferation and survival associated with upregulation of the PTEN and p21, inhibition of cell proliferation marker cyclin A and PCNA expression, induction of G1 or G2 phase arrest; induction of apoptosis showing an increase of caspase 3/7 activity and expression, PARP cleavage, and the sub-G1 apoptotic population. Moreover, we characterize biological functions of MDM2-p53 axis in nutlin-3-sensitive and nutlin-3-resistant LPS, showing MDM2 knockdown in the four LPS lines and p53 knockdown in the three mutant-p53 LPS lines resulted in anti-proliferative effects. Additive effects were obtained through a coordinated attack on MDM2 and p53, as demonstrated by immunoblots, cell viability and cell cycle analyses, showing that MDM2 and p53 knockdown, in LPS cell lines containing the p53 mutation, induced greater cell apoptosis and anti-proliferative effects, compared to either intervention alone, which is comparable to the effects seen after HDAC inhibition by SAHA and LBH589. These compelling pro-apoptotic and anti-proliferative responses indicate that HDAC inhibition warrants clinical evaluation as a novel therapeutic strategy in LPS, including nutlin-3 resistant sublines with the p53 mutation.
Note: This abstract was not presented at the meeting.
Citation Format: Wen-bin Ou, Hailong Li, Li Liu, Shengmei Zhou, Ye Kuang, Ziqin Yan, Zhe Jiang, Si Shi, Fanguo Meng, Qing Sheng, Haimeng Zhou, Jonathan A. Fletcher. HDACi inhibits liposarcoma via targeting of the MDM2-p53 signaling axis and PTEN, irrespective of p53 mutational status. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5136. doi:10.1158/1538-7445.AM2014-5136