Abstract 3730: The PPM1D inhibitor GSK2830371 has p53-dependent anti-lymphoma effects and enhances bortezomib-induced apoptosis in mantle cell lymphoma

Abstract

Abstract p53 mutations are relatively rare (∼15%) in mantle cell lymphoma (MCL). Chemotherapeutic agents induce DNA damage, p53 phosphorylation and pro-apoptotic wild-type (WT) p53 signaling, resulting in lymphoma cell death. However, DNA damaging agents may have severe acute toxicities, accelerate clonal evolution and cause therapy-related neoplasms by adding new mutations to the original clones. PPM1D is a serine/threonine phosphatase that negatively regulates key DNA damage response proteins including p53, CHK2, Histone H2AX, and ATM. PPM1D has been thought to be an oncogenic protein. It has been reported that PPM1D is overexpressed or amplified in breast and ovarian cancers. GSK2830371 (GSK) is a PPM1D inhibitor, which binds to a flap subdomain that regulates enzymatic activity of PPM1D and substrate recognition (Nat Chem Biol 2014). Treatment of tumor cells with the inhibitor GSK has been found to increase phosphorylation of PPM1D substrates and cause growth inhibition in tumor cells harboring wild-type p53. We investigated the clinical significance of PPM1D and anti-lymphoma effects of GSK in MCL. The mRNA expression levels in patient samples were determined using Oncomine. Our gene expression analyses showed an increase in PPM1D mRNA expression in MCL samples versus normal naïve B lymphocytes (P = 0.044) that are the normal counterparts of MCL. PPM1D mRNA levels were positively correlated with CCND1 (encoding Cyclin D1) mRNA levels (r = 0.33, P = 0.0014) and proliferation signature averages (r = 0.54, P < 0.0001). Higher PPM1D expression at diagnosis was associated with a poorer prognosis in MCL patients (i.e., a median overall survival of 3.9 years for cases with PPM1D expression in the lowest third and 1.4 years in the highest third, P = 0.0047). These results indicate that PPM1D overexpression has a negative prognostic impact on MCL overall disease survival and that PPM1D is a potential therapeutic target in MCL. A total of 8 MCL (3 p53 WT and 5 mutant) cell lines were treated with GSK. 10 μM GSK inhibited cell growth of p53 WT Z-138, JVM-2 and Granta-519 cells by 68%, 38% and 39%, respectively. p53 mutant cells were relatively resistant to GSK (14.8 ± 4.7% growth inhibition). p53 knockdown de-sensitized Z-138 and JVM-2 cells to GSK-induced apoptosis. GSK increased total and Ser15-phosphorylated p53 levels and p53 targets p21 and PUMA in p53 WT cells. Basal levels of PPM1D and its substrates were not associated with GSK sensitivity among MCL cell lines. Interestingly, GSK enhanced bortezomib-induced apoptosis in a p53-independent manner, partially through activation of p38 signaling; p38 inhibition attenuated the combination effect. Collectively, PPM1D inhibition may offer a novel therapeutic strategy for MCL. Citation Format: Kensuke Kojima, Mariko Yoshimura, Aya Maeda, Hiroaki Kitamura, Yuki Nishida, Shinya Kimura. The PPM1D inhibitor GSK2830371 has p53-dependent anti-lymphoma effects and enhances bortezomib-induced apoptosis in mantle cell lymphoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3730.