Murine Double Minute 2 Inhibitor Research Articles

Radiosensitization of lung cancer by nutlin, an inhibitor of murine double minute 2

p53 plays a critical role in cell cycle arrest and induction of apoptosis. Certain malignancies carry wild-type p53, which is frequently down-regulated by murine double minute 2 (MDM2) overexpression. Availability of a small-molecule inhibitor against MDM2, nutlin, has made it feasible to evaluate the anti-MDM2-based therapeutic strategies. The rationale for the current study is that functional p53 has been linked with improved responses to radiation treatment. Hence, this study evaluates the use of nutlin, a small-molecule inhibitor that blocks the interaction of p53 and MDM2, in sensitizing cancer cells to radiation. Expression of MDM2, p53, and p21 in both p53 wild-type and p53-defective lung cancer cell lines was examined. Clonogenic and 7-amino-actinomycin D studies were used to determine possible mechanisms of cell death. The combined effect of MDM2 inhibition and radiation on cell cycle was also studied. We found that radiosensitization by nutlin occurs in lung cancer cells with wild-type p53. There were increased apoptosis and cell cycle arrest following administration of nutlin and radiation. Furthermore, the combination of nutlin and radiation decreased the ability of endothelial cells to form vasculature, as shown by Matrigel assays. Our data suggest that nutlin is an effective radiosensitizer of p53 wild-type cells. The radiosensitizing effect seems to be at least partially due to induction of apoptosis and cell cycle arrest. In addition, nutlin may be an effective radiosensitizer of tumor vasculature.

MDM2 antagonists induce p53-dependent apoptosis in AML: implications for leukemia therapy

AbstractAlthough TP53 mutations are rare in acute myeloid leukemia (AML), inactivation of wild-type p53 protein frequently occurs through overexpression of its negative regulator MDM2 (murine double minute 2). Recently, small-molecule antagonists of MDM2, Nutlins, have been developed that inhibit the p53-MDM2 interaction and activate p53 signaling. Here, we study the effects of p53 activation by Nutlin-3 in AML cells. Treatment with MDM2 inhibitor triggered several molecular events consistent with induction of apoptosis: loss of mitochondrial membrane potential, caspase activation, phosphatidylserine externalization, and DNA fragmentation. There was a positive correlation in primary AML samples with wild-type p53 between baseline MDM2 protein levels and apoptosis induced by MDM2 inhibition. No induction of apoptosis was observed in AML samples harboring mutant p53. Colony formation of AML progenitors was inhibited in a dose-dependent fashion, whereas normal CD34+ progenitor cells were less affected. Mechanistic studies suggested that Nutlin-induced apoptosis was mediated by both transcriptional activation of proapoptotic Bcl-2 family proteins, and transcription-independent mitochondrial permeabilization resulting from mitochondrial p53 translocation. MDM2 inhibition synergistically enhanced cytotoxicity of cytosine arabinoside and doxorubicin in AML blasts but not in normal hematopoietic progenitor cells. p53 activation by targeting the p53-MDM2 interaction might offer a novel therapeutic strategy for AML that retain wild-type p53.