Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027819 (neuroblastoma)
 27,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

p53 mutations have been reported in cell lines derived from relapsed neuroblastoma tumors. We hypothesize that functional inactivation of p53 by mutation or other mechanisms is common in relapsed neuroblastoma and can contribute to chemoresistance. Our aim was to determine the frequency of p53 mutations, p14(ARF) methylation, or deletion and MDM2 amplification in 23 neuroblastoma cell lines (6 derived at diagnosis and 17 derived at relapse). One cell line was p53 mutant (BE2c) and two cell lines were deleted for p14(ARF) (LAN-6 and SHEP). Two cell lines were methylated for p14(ARF) (GIMEN and PER-108), one of which had low levels of p14(ARF) mRNA expression which increased following demethylation with 5-aza-2/deoxycytidine treatment (GIMEN), and four cell lines were confirmed to be MDM2-amplified. All these cell lines were derived from neuroblastomas at relapse. Inactivation of the p53 pathway was observed in 9 out of 17 neuroblastoma cell lines (53%) established at relapse and in none of the cell lines established from pretreatment tumors. If these data are confirmed in neuroblastoma tumors, this suggests that p53-independent therapy and reactivation of inactive p53 approaches would be useful in the management of relapsed neuroblastoma.
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PMID:Increased frequency of aberrations in the p53/MDM2/p14(ARF) pathway in neuroblastoma cell lines established at relapse. 1648 14

Novel therapeutic approaches are urgently needed for high-stage neuroblastoma, a major therapeutic challenge in pediatric oncology. The majority of neuroblastoma tumors are p53 wild type with intact downstream p53 signaling pathways. We hypothesize that stabilization of p53 would sensitize this aggressive tumor to genotoxic chemotherapy via inhibition of MDM2, the primary negative upstream regulator of p53. We used pharmacologic inhibition of the MDM2-p53 interaction with the small-molecule inhibitor Nutlin and studied the subsequent response to chemotherapy in neuroblastoma cell lines. We did 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and terminal deoxynucleotidyl transferase assays to measure proliferation and apoptosis in several cell lines (IMR32, MYCN3, and JF) treated with combinations of cisplatin, etoposide, and Nutlin. We found consistent and robust decreases in proliferation and increases in apoptosis with the addition of Nutlin 3a to etoposide or cisplatin in all cell lines tested and no response to the inactive Nutlin 3b enantiomer. We also show a rapid and robust accumulation of p53 protein by Western blot in these cells within 1 to 2 hours of treatment. We conclude that MDM2 inhibition dramatically enhances the activity of genotoxic drugs in neuroblastoma and should be considered as an adjuvant to chemotherapy for this aggressive pediatric cancer and for possibly other p53 wild-type solid tumors.
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PMID:MDM2 inhibition sensitizes neuroblastoma to chemotherapy-induced apoptotic cell death. 1698 70

Circumvention of the p53 tumor suppressor barrier in neuroblastoma is rarely caused by TP53 mutation but might arise from inappropriately increased activity of its principal negative regulator MDM2. We show here that targeted disruption of the p53-MDM2 interaction by the small-molecule MDM2 antagonist nutlin-3 stabilizes p53 and selectively activates the p53 pathway in neuroblastoma cells with wild-type p53, resulting in a pronounced antiproliferative and cytotoxic effect through induction of G(1) cell cycle arrest and apoptosis. A nutlin-3 response was observed regardless of MYCN amplification status. Remarkably, surviving SK-N-SH cells adopted a senescence-like phenotype, whereas CLB-GA and NGP cells underwent neuronal differentiation. p53 dependence of these alternative outcomes of nutlin-3 treatment was evidenced by abrogation of the effects when p53 was knocked down by lentiviral-mediated short hairpin RNA interference. The diversity of cellular responses reveals pleiotropic mechanisms of nutlins to disable neuroblastoma cells and exemplifies the feasibility of exploiting, by a single targeted intervention, the multiplicity of anticancer activities exerted by a key tumor suppressor as p53. The observed treatment effects without the need of imposing a genotoxic burden suggest that selective MDM2 antagonists might be beneficial for treatment of neuroblastoma patients with and without MYCN amplification.
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PMID:Small-molecule MDM2 antagonists as a new therapy concept for neuroblastoma. 1701 22

We previously reported that 3 p53 wild type (wt) MYCN amplified (MNA) neuroblastoma cell lines failed to G1 arrest after DNA damage despite induction of p53, p21(WAF1) and MDM2. We hypothesised that this was due to high MYCN expression. p53 responses to DNA damage were examined in an additional 13 p53 wt neuroblastoma cell lines. MNA was significantly associated with a failure to G1 arrest after DNA damage (p < 0.001) and higher levels of apoptosis after irradiation (p < 0.05). p21(WAF1) and hypophosphorylated (hypo) RB accumulation post irradiation were significantly lower in cell lines that failed to G1 arrest (p < 0.05). Conditional MYCN expression in non-MNA SHEP Tet21N cells did not affect the G1 arrest after irradiation. MYCN knockdown using siRNA in 3 p53 wt MNA cell lines did not restore a G1 arrest after irradiation, but increased the baseline G1 population, p21(WAF1) and hypo RB expression. MYCN siRNA also caused a G1 arrest in a p53 mutant MNA cell line. This study is the first to determine that MNA correlates with a failure to G1 arrest and attenuated p21(WAF1) induction; however MYCN expression alone is not causally responsible.
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PMID:The role of MYCN in the failure of MYCN amplified neuroblastoma cell lines to G1 arrest after DNA damage. 1717 27

The MYC family oncogenes cause transformation and tumor progression by corrupting multiple cellular pathways, altering cell cycle progression, apoptosis, and genomic instability. Several recent studies show that MYCC (c-Myc) expression alters DNA repair mechanisms, cell cycle checkpoints, and karyotypic stability, and this is likely partially due to alterations in centrosome replication control. In neuroblastoma cell lines, MYCN (N-Myc) expression induces centrosome amplification in response to ionizing radiation. Centrosomes are cytoplasmic domains that critically regulate cytokinesis, and aberrations in their number or structure are linked to mitotic defects and karyotypic instability. Whereas centrosome replication is linked to p53 and Rb/E2F-mediated cell cycle progression, the mechanisms downstream of MYCN that generate centrosome amplification are incompletely characterized. We hypothesized that MDM2, a direct transcriptional target of MYCN with central inhibitory effects on p53, plays a role in MYC-mediated genomic instability by altering p53 responses to DNA damage, facilitating centrosome amplification. Herein we show that MYCN mediates centrosome amplification in a p53-dependent manner. Accordingly, inhibition of the p53-MDM2 interaction with Nutlin 3A (which activates p53) completely ablates the MYCN-dependent contribution to centrosome amplification after ionizing radiation. We further show that modulating MDM2 expression levels by overexpression or RNA interference-mediated posttranscriptional inhibition dramatically affects centrosome amplification in MYCN-induced cells, indicating that MDM2 is a necessary and sufficient mediator of MYCN-mediated centrosome amplification. Finally, we show a significant correlation between centrosome amplification and MYCN amplification in primary neuroblastoma tumors. These data support the hypothesis that elevated MDM2 levels contribute to MYCN-induced genomic instability through altered regulation of centrosome replication in neuroblastoma.
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PMID:MYCN-directed centrosome amplification requires MDM2-mediated suppression of p53 activity in neuroblastoma cells. 1736 62

Aberrant cytoplasmic sequestration has been reported as an alternative mechanism of p53 inactivation to mutation in neuroblastoma. We hypothesized that p53 localization and function in neuroblastoma is related to differentiation status. Eighty-two untreated and 24 paired pre and post-chemotherapy neuroblastomas were studied by immunocytochemistry for p53, p21(WAF1), BAX, Bcl2 and Ki67. Predominantly nuclear p53 was detected in undifferentiated neuroblastoma, and both nuclear and cytoplasmic p53 in differentiating neuroblastoma. The nuclear p53 labeling index (LI) correlated with the Ki67 LI (r = 0.51, p <0.001), and weakly with p21(WAF1) (r = 0.37), but not with BAX or Bcl2. There was a significant reduction in p53, p21(WAF1) and Ki67 LI after chemotherapy (p < 0.01), an increase in BAX (p <0.05), but no change in Bcl2. p53 localization and function were examined in two p53 wild-type undifferentiated and 9-cis retinoic acid differentiated neuroblastoma cell lines. Using immunocytochemistry, immunofluorescence and cell fractionation, p53 was found to be predominantly nuclear in both undifferentiated and differentiated cells. Following irradiation, there was upregulation of p53, p21(WAF1) and MDM2, but less induced PARP and caspase 3 cleavage in differentiated cells, suggesting intact p53 transcriptional function, but resistance to apoptosis. p53 function in undifferentiated and differentiated cells was confirmed by upregulation of p21(WAF1) and MDM2 following Nutlin-3 treatment. In conclusion, p53 is predominantly nuclear and functional in neuroblastoma regardless of differentiation status.
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PMID:p53 is nuclear and functional in both undifferentiated and differentiated neuroblastoma. 1791 39

Circumvention of the p53 checkpoint in neuroblastoma (NB) might arise from increased expression of its main negative regulator MDM2. The SNP309, a T-to-G substitution in the MDM2 promoter, was associated with higher levels of MDM2 mRNA and protein, with consequent attenuation of the p53 pathway. The association between MDM2 SNP309 and disease progression and survival was evaluated in a cohort of 142 children with stage 4 NB. The SNP309 GG patients had a worse overall survival and a worse survival after relapse than the TT ones, whereas the heterozygotes showed an intermediate behaviour (p=0.043 and p=0.049, respectively, log-rank test for trend). No evident association between SNP309 and event free survival was found. The lack of association between SNP309 and MYCN status indicates that MDM2 SNP309 may be a new independent prognostic factor for stage 4 NB.
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PMID:Impact of MDM2 SNP309 genotype on progression and survival of stage 4 neuroblastoma. 1883 71

Pharmacological manipulation of protein acetylation levels by histone deacetylase (HDAC) inhibitors represents a novel therapeutic strategy to treat neurodegeneration as well as cancer. However, the molecular mechanisms that determine how HDAC inhibition exerts a protective effect in neurons as opposed to a cytotoxic action in tumor cells has not been elucidated. We addressed this issue in cultured postnatal mouse cortical neurons whose p53-dependent and p53-independent intrinsic apoptotic programs require the proapoptotic multidomain protein, Bax. Despite promoting nuclear p53 accumulation, Class I/II HDAC inhibitors (HDACIs) protected neurons from p53-dependent cell death induced by camptothecin, etoposide, heterologous p53 expression or the MDM2 inhibitor, nutlin-3a. HDACIs suppressed p53-dependent PUMA expression, a critical signaling intermediate linking p53 to Bax activation, thus preventing postmitochondrial events including cleavage of caspase-9 and caspase-3. In human SH-SY5Y neuroblastoma cells, however, HDACIs were not able to prevent p53-dependent cell death. Moreover, HDACIs also prevented caspase-3 cleavage in postnatal cortical neurons treated with staurosporine, 3-nitropropionic acid and a Bcl-2 inhibitor, all of which require the presence of Bax but not p53 to promote apoptosis. Although these three toxic agents displayed a requirement for Bax, they did not promote PUMA induction. These results demonstrate that HDACIs block Bax-dependent cell death by two distinct mechanisms to prevent neuronal apoptosis, thus identifying for the first time a defined molecular target for their neuroprotective actions.
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PMID:Histone deacetylase inhibitors prevent p53-dependent and p53-independent Bax-mediated neuronal apoptosis through two distinct mechanisms. 1926 78

Neuroblastoma (NB) is a primitive neuroectodermal tumor and the second most common solid tumor in children. NB exhibits heterogeneous behavior and spontaneous regression can occur in patients under 12 months of age. Response to treatment is both age- and stage-specific; however, patients over 1 year of age are generally considered high risk. NB tumors from these patients are often characterized by alterations in p53 expression and murine double minute (MDM2) activity with concomitant resistance to chemotherapy. We evaluated the ability of nutlin-3 to sensitize a p53-null and doxorubicin-resistant NB cell line, LA155N, to doxorubicin. Nutlin-3 treatment upregulated TAp73 and E2F1 protein levels. It potentiated the ability of doxorubicin to block cell proliferation and activate apoptosis and TAp73 knockdown resulted in a reduction of this sensitization. Additionally, PUMA expression was induced by the combination treatment, but reduced by knockdown of either TAp73 or E2F1. We conclude that, following nutlin-3 treatment, TAp73 and E2F1 are released from MDM2 and activated by doxorubicin to induce PUMA and apoptosis. This study addresses p53-independent mechanisms of nutlin-3 action in chemoresistant NB, especially in combination with chemotherapeutics. We believe that this model has strong clinical relevance for chemoresistant and p53 dysfunctional NB.
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PMID:The MDM2 antagonist nutlin-3 sensitizes p53-null neuroblastoma cells to doxorubicin via E2F1 and TAp73. 1936 Mar 52

Neuroblastoma is derived from neural crest precursor components of the peripheral sympathetic nervous system and accounts for more than 15% of all pediatric cancer deaths. A clearer understanding of the molecular basis of neuroblastoma is required for novel therapeutic approaches to improve morbidity and mortality. Neuroblastoma is uniformly p53 wild type at diagnosis and must overcome p53-mediated tumor suppression during pathogenesis. Amplification of the MYCN oncogene correlates with the most clinically aggressive form of the cancer, and MDM2, a primary inhibitor of the p53 tumor suppressor, is a direct transcriptional target of, and positively regulated by, both MYCN and MYCC. We hypothesize that MDM2 contributes to MYCN-driven tumorigenesis helping to ameliorate p53-dependent apoptotic oncogenic stress during tumor initiation and progression. To study the interaction of MYCN and MDM2, we generated an Mdm2 haploinsufficient transgenic animal model of neuroblastoma. In Mdm2(+/-)MYCN transgenics, tumor latency and animal survival are remarkably extended, whereas tumor incidence and growth are reduced. Analysis of the Mdm2/p53 pathway reveals remarkable p53 stabilization counter-balanced by epigenetic silencing of the p19(Arf) gene in the Mdm2 haploinsufficient tumors. In human neuroblastoma xenograft models, conditional small interfering RNA-mediated knockdown of MDM2 in cells expressing wild-type p53 dramatically suppresses tumor growth in a p53-dependent manner. In summary, we provided evidence for a crucial role for direct inhibition of p53 by MDM2 and suppression of the p19(ARF)/p53 axis in neuroblastoma tumorigenesis, supporting the development of therapies targeting these pathways.
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PMID:Mdm2 deficiency suppresses MYCN-Driven neuroblastoma tumorigenesis in vivo. 1964 5


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