The MDM2 Antagonist Nutlin-3 Is Lethal to Mantle Cell Lymphoma with Wild Type p53.

Mantle cell lymphoma (MCL) has one of the poorest overall prognoses of the non-Hodgkin lymphomas, and is resistant to standard chemotherapy. P53 mutations are rare in typical mantle cell lymphoma and occur in only about 1/3 of the less common blastoid variant. The relatively low overall rate of p53 mutation in MCL suggests that this lymphoma may be a good candidate for biologic therapies that upregulate p53 and lead to cell death. Nutlin-3 is a novel small-molecule antagonist of MDM2 that efficiently activates p53 by blocking the MDM2-p53 interaction. In this study, we investigated the effects of nutlin-3 in 5 MCL cell lines with known p53 mutation status (wt-p53: REC-1, Z138, Granta-519, JVM-2; mt-p53: Jeko-1). IC₅₀s for all cell lines were determined, and the activation of p53 and multiple p53 target genes were studied by western blot analysis. Cell proliferation and apoptosis were assessed using the MTT test and flow cytometry. Treatment with Nutlin-3 resulted in a marked reduction in cell proliferation/viability, and an increase in the apoptotic fraction, in a time and concentration-dependent manner in wt-p53 cells (IC₅₀ at 48 hrs; 7.5 uM for Granta-519, 9.2 uM for REC-1, 0.5 uM for Z138, and 5.7 uM for JVM-2), while mt-p53 Jeko was resistant to nutlin-3 treatment (IC₅₀>60 uM), and showed no increase in the apoptotic cell fraction. In the wt-p53 MCL cell lines, nutlin-3 treatment increased the cellular levels of p53, and several p53 dependent proteins including p21, MDM2 itself and the proapoptotic BH3-only protein Puma, while there was no change in the levels of these proteins in Jeko-1. Recently, attention has been focused on novel p53 target genes that function to inhibit cell growth and proliferation, rather than by inducing apoptosis. These include the AKT-mTOR regulators PTEN, TSC2 and AMPKβ1. We saw no increase in these novel p53 targets in any of the cell lines analyzed, suggesting that nutlin-3-activated p53 activates only a subset of its possible targets. These findings demonstrate that nutlin-3 successfully activates wt-p53 in mantle cell lymphoma leading to the upregulation of traditional targets such as p21 and proapoptotic proteins including Puma, and result in apoptotic cell death. The data suggest that p53 activators such as nutlin-3 may be effective agents in the treatment of mantle cell lymphoma.