Inhibition of the p53 E3 Ligase HDM-2 Induces Apoptosis and DNA Damage–Independent p53 Phosphorylation in Mantle Cell Lymphoma

• Published in: Clinical cancer research 2008-09, Vol.14 (17), p.5416-5425
• Main Authors: Jones, Richard J, Chen, Qing, Voorhees, Peter M, Young, Ken H, Bruey-Sedano, Nathalie, Yang, Dajun, Orlowski, Robert Z
• Format: Article
• Language: English
• Subjects: Antineoplastic agents; Apoptosis - drug effects; Biological and medical sciences; Cell Line, Tumor; DNA Damage; Drug Evaluation, Preclinical; HDM-2; Hematologic and hematopoietic diseases; Humans; Leukemias. Malignant lymphomas. Malignant reticulosis. Myelofibrosis; Lymphoma, Mantle-Cell - genetics; Lymphoma, Mantle-Cell - pathology; mantle cell lymphoma; MDM-2; Medical sciences; MI-63; nutlin; p53; Pharmacology. Drug treatments; Phosphorylation; Proto-Oncogene Proteins c-mdm2 - antagonists & inhibitors; Tumor Suppressor Protein p53 - metabolism; Ubiquitin-Protein Ligases - antagonists & inhibitors
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.CCR-08-0150

Purpose: The ubiquitin-proteasome pathway has been validated as a target in non–Hodgkin's lymphoma through demonstration of the activity of the proteasome inhibitor bortezomib. Experimental Design: Another potentially attractive target is the human homologue of the murine double minute-2 protein, HDM-2, which serves as the major p53 E3 ubiquitin ligase; we therefore evaluated the activity of a novel agent, MI-63, which disrupts the HDM-2/p53 interaction. Results: Treatment of wild-type p53 mantle cell lymphoma (MCL) cell lines with MI-63 resulted in a dose- and time-dependent inhibition of proliferation, with an IC 50 in the 0.5 to 5.0 μmol/L range. MI-63 induced p53 and HDM-2 accumulation, as well as other downstream p53 targets such as p53 up-regulated modulator of apoptosis and p21 Cip1 . This was associated with cell cycle arrest at G 1 -S; activation of caspase-3, caspase-8, and caspase-9; cleavage of poly-(ADP-ribose) polymerase; and loss of E2F1. HDM-2 inhibition caused phosphorylation of p53 at multiple serine residues, including 15, 37, and 392, which coincided with low levels of DNA strand breaks. DNA damage occurred in a small percentage of cells and did not induce phosphorylation of the DNA damage marker H2A.X Ser139 . Combinations of MI-63 with the molecularly targeted agents bortezomib and rapamycin showed synergistic, sequence-dependent antiproliferative effects. Treatment of primary MCL patient samples resulted in apoptosis and induction of p53 and p21, which was not seen in normal controls. Conclusions: These findings support the hypothesis that inhibition of the HDM-2/p53 interaction may be a promising approach both by itself and in combination with currently used chemotherapeutics against lymphoid malignancies.