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Open Access Research

HDM2 antagonist MI-219 (spiro-oxindole), but not Nutlin-3 (cis-imidazoline), regulates p53 through enhanced HDM2 autoubiquitination and degradation in human malignant B-cell lymphomas

Angela M Sosin1, Angelika M Burger2, Aisha Siddiqi1, Judith Abrams3, Ramzi M Mohammad1 and Ayad M Al-Katib45*

Author Affiliations

1 Department of Oncology, Barbara Ann Karmanos Cancer Institute (KCI), Detroit, MI, 48201, USA

2 Department of Pharmacology, Wayne State University School of Medicine (WSU-SOM), Detroit, MI, 48201, USA

3 Biostatistics Core Facility (KCI), Detroit, USA

4 Department of Internal Medicine, Hematology-Oncology, WSU-SOM and the Lymphoma Clinic, Van Elslander Cancer Center, St John Hospital and Medical Center, Grosse Pointe Woods, MI, 48236, USA

5 Division of Hematology and Oncology Department of Internal Medicine, Wayne State University School of Medicine, 540 E. Canfield, 8229 Scott Hall, Detroit, MI, 48201, USA

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Journal of Hematology & Oncology 2012, 5:57  doi:10.1186/1756-8722-5-57

Published: 18 September 2012

Abstract

Background

Lymphomas frequently retain wild-type (wt) p53 function but overexpress HDM2, thereby compromising p53 activity. Therefore, lymphoma is a suitable model for studying the therapeutic value of disrupting the HDM2-p53 interaction by small-molecule inhibitors (SMIs). HDM2 have been developed and are under various stages of preclinical and clinical investigation. Previously, we examined the anti-lymphoma activity of MI-319, the laboratory grade of a new class of HDM2 SMI, the spiro-oxindole, in follicular lymphoma. Since then, MI-219, the clinical grade has become readily available. This study further examines the preclinical effects and mechanisms of MI-219 in a panel of human lymphoma cell lines as well as a cohort of patient-derived B-lymphcytes for its potential clinical use.

Results

Preclinical assessment of MI-219 was evaluated by means of an in vitro and ex vivo approach and compared to Nutlin-3, the gold standard. Characterization of p53 activity and stability were assessed by quantitative PCR, Western blot, and immunoprecipitation. Biological outcome was measured using Trypan blue exclusion assay, Annexin V/PI, PARP and caspase-3 cleavage. Surprisingly, the overall biological effects of Nutlin-3 were more delayed (48 h) while MI-219 triggered an earlier response (12-24 h), predominantly in the form of apoptotic cell death. Using a cell free autoubiquitination assay, neither agent interfered with HDM2 E3 ligase function. MI-219 was more effective in upregulating wt-p53 stabilization compared to Nutlin-3. MI-219, but not Nutlin-3, enhanced the autoubiquitination and degradation of HDM2.

Conclusions

Our data reveals unexpected differences between MI-219 and the well-studied Nutlin-3 in lymphoma cell lines and patient samples. We suggest a novel mechanism for MI-219 that alters the functional activity of HDM2 through enhanced autoubiquitination and degradation. Additionally, this mechanism appears to correspond to biological outcome. Our results provide evidence that different classes of HDM2 SMIs elicit molecular events that extend beyond HDM2-p53 dissociation which may be of biological and potentially therapeutic importance.

Keywords:
HDM2; p53; Apoptosis; MI-219; Nutlin-3; B-cell lymphoma; Small-molecule inhibitor; Autoubiquitination