Pre-clinical evaluation of the MDM2-p53 antagonist RG7388 alone and in combination with chemotherapy in neuroblastoma

Neuroblastoma is a predominantly p53 wild-type (wt) tumour and MDM2-p53 antagonists offer a novel therapeutic strategy for neuroblastoma patients. RG7388 (Roche) is currently undergoing early phase clinical evaluation in adults. This study assessed the efficacy of RG7388 as a single-agent and in combination with chemotherapies currently used to treat neuroblastoma in a panel of neuroblastoma cell lines. RG7388 GI₅₀ concentrations were determined in 21 p53-wt and mutant neuroblastoma cell lines of varying MYCN, MDM2 and p14^ARF status, together with MYCN-regulatable Tet21N cells. The primary determinant of response was the presence of wt p53, and overall there was a >200-fold difference in RG7388 GI₅₀ concentrations for p53-wt versus mutant cell lines. Tet21N MYCN+ cells were significantly more sensitive to RG7388 compared with MYCN− cells. Using median-effect analysis in 5 p53-wt neuroblastoma cell lines, selected combinations of RG7388 with cisplatin, doxorubicin, topotecan, temozolomide and busulfan were synergistic. Furthermore, combination treatments led to increased apoptosis, as evident by higher caspase-3/7 activity compared to either agent alone. These data show that RG7388 is highly potent against p53-wt neuroblastoma cells, and strongly supports its further evaluation as a novel therapy for patients with high-risk neuroblastoma and wt p53 to potentially improve survival and/or reduce toxicity.     

Structurally diverse MDM2–p53 antagonists act as modulators of MDR-1 function in neuroblastoma

Background:

A frequent mechanism of acquired multidrug resistance in human cancers is overexpression of ATP-binding cassette transporters such as the Multi-Drug Resistance Protein 1 (MDR-1). Nutlin-3, an MDM2–p53 antagonist, has previously been reported to be a competitive MDR-1 inhibitor.

Methods:

This study assessed whether the structurally diverse MDM2–p53 antagonists, MI-63, NDD0005, and RG7388 are also able to modulate MDR-1 function, particularly in p53 mutant neuroblastoma cells, using XTT-based cell viability assays, western blotting, and liquid chromatography–mass spectrometry analysis.

Results:

Verapamil and the MDM2–p53 antagonists potentiated vincristine-mediated growth inhibition in a concentration-dependent manner when used in combination with high MDR-1-expressing p53 mutant neuroblastoma cell lines at concentrations that did not affect the viability of cells when given alone. Liquid chromatography–mass spectrometry analyses showed that verapamil, Nutlin-3, MI-63 and NDD0005, but not RG7388, led to increased intracellular levels of vincristine in high MDR-1-expressing cell lines.

Conclusions:

These results show that in addition to Nutlin-3, other structurally unrelated MDM2–p53 antagonists can also act as MDR-1 inhibitors and reverse MDR-1-mediated multidrug resistance in neuroblastoma cell lines in a p53-independent manner. These findings are important for future clinical trial design with MDM2–p53 antagonists when used in combination with agents that are MDR-1 substrates.     

Augmented antitumor activity of 5‐fluorouracil by double knockdown of MDM4 and MDM2 in colon and gastric cancer cells

Inactivation of the TP53 tumor suppressor gene is essential during cancer development and progression. Mutations of TP53 are often missense and occur in various human cancers. In some fraction of wild‐type (wt) TP53 tumors, p53 is inactivated by upregulated murine double minute homolog 2 (MDM2) and MDM4. We previously reported that simultaneous knockdown of MDM4 and MDM2 using synthetic DNA‐modified siRNAs revived p53 activity and synergistically inhibited in vitro cell growth in cancer cells with wt TP53 and high MDM4 expression (wtTP53/highMDM4). In the present study, MDM4/MDM2 double knockdown with the siRNAs enhanced 5‐fluorouracil (5‐FU)‐induced p53 activation, arrested the cell cycle at G₁ phase, and potentiated the antitumor effect of 5‐FU in wtTP53/highMDM4 human colon (HCT116 and LoVo) and gastric (SNU‐1 and NUGC‐4) cancer cells. Exposure to 5‐FU alone induced MDM2 as well as p21 and PUMA by p53 activation. As p53‐MDM2 forms a negative feedback loop, enhancement of the antitumor effect of 5‐FU by MDM4/MDM2 double knockdown could be attributed to blocking of the feedback mechanism in addition to direct suppression of these p53 antagonists. Intratumor injection of the MDM4/MDM2 siRNAs suppressed in vivo tumor growth and boosted the antitumor effect of 5‐FU in an athymic mouse xenograft model using HCT116 cells. These results suggest that a combination of MDM4/MDM2 knockdown and conventional cytotoxic drugs could be a promising treatment strategy for wtTP53/highMDM4 gastrointestinal cancers.     

Inhibition of mitochondrial translocase SLC25A5 and histone deacetylation is an effective combination therapy in neuroblastoma

The mitochondrion is a gatekeeper of apoptotic processes, and mediates drug resistance to several chemotherapy agents used to treat cancer. Neuroblastoma is a common solid cancer in young children with poor clinical outcomes following conventional chemotherapy. We sought druggable mitochondrial protein targets in neuroblastoma cells. Among mitochondria-associated gene targets, we found that high expression of the mitochondrial adenine nucleotide translocase 2 (SLC25A5/ANT2), was a strong predictor of poor neuroblastoma patient prognosis and contributed to a more malignant phenotype in pre-clinical models. Inhibiting this transporter with PENAO reduced cell viability in a panel of neuroblastoma cell lines in a TP53-status-dependant manner. We identified the histone deacetylase inhibitor, suberanilohydroxamic acid (SAHA), as the most effective drug in clinical use against mutant TP53 neuroblastoma cells. SAHA and PENAO synergistically reduced cell viability, and induced apoptosis, in neuroblastoma cells independent of TP53-status. The SAHA and PENAO drug combination significantly delayed tumour progression in pre-clinical neuroblastoma mouse models, suggesting that these clinically advanced inhibitors may be effective in treating the disease.     

The proline TP53 variant stimulates likely lymphangiogenesis in an orthotopic mouse model of pancreatic cancer

Background:

Pancreatic cancer is a deadly disease characterised by high incidence of TP53 mutations. Restoration of TP53 function is perceived as a highly attractive therapeutic strategy, whose effects are not well characterised.

Methods:

The current work adapted an inducible strategy of stage-specific reexpression of wild-type (wt) TP53 in an in vivo orthotopic mouse model of pancreatic cancer.

Results:

The reconstitution of wt TP53 function in TP53-mutant DanG and MiaPaCa-2 cells caused G1 cell cycle arrest but no evidence of apoptosis induction. Consistent with subcutaneous xenograft models, we found that wt TP53 reduced primary tumour growth. Wt TP53 reexpression during early tumour growth led to significant increase in vascularisation. This correlated with an unexpectedly high rate of micro-metastases in lymph nodes of animals with wt TP53 induction, despite the 90% decrease in median primary tumour weight. Reexpression of wt TP53 later in tumour development did not significantly affect the number of CD31-reactive vessels, but increased lymphatic vessel density.

Conclusion:

The increased number of lymphatic vessels and micro-metastases suggests that wt TP53 induction complexly affected the biology of different tumour constituents of pancreatic cancer. Our observation suggests that combination of the inducible system with an orthotopic model can yield important insights into in vivo pancreatic cancer biology.     

Prognostic and predictive value of changes in tumour cell proliferation in locally advanced breast cancer primarily treated with doxorubicin

We previously reported that high tumour cell proliferation evaluated by Ki-67 expression, high mitotic frequency and high histological grade were associated with resistance to primary doxorubicin monotherapy in locally advanced breast cancer harbouring wild-type (wt) TP53. The aim of our present study was to evaluate the predictive and prognostic impact of proliferation parameters assessed in tumour tissue obtained after chemotherapy, and alterations induced in tumour cell proliferation. While we found a significant reduction in Ki-67 expression and mitotic frequency in tumours with wtTP53 (p=0.001 and p=0.008, respectively), no significant change was recorded in tumours expressing mutant TP53. For histological grade there was no significant change in either group. There was a direct correlation between pre- and post-treatment values for Ki-67 and mitotic frequency in tumours harbouring wtTP53 (p=0.0001 for both), but no correlation in tumours harbouring mutated TP53. High post-treatment Ki-67 expression and mitotic frequency were found to predict doxorubicin resistance only in patients with wtTP53 (p=0.04 and p=0.03, respectively). The prognostic importance of proliferation markers and histological grade was found to be similar whether they were determined in the pre- or post-treatment samples (Ki-67; pre: p=0.02; post: p=0.03; mitotic frequency; p=0.002 and p=0.01, respectively; histological grade; p=0.0001 and p=0.002, respectively). While the reduction in mitotic frequency was associated with improved survival (p=0.03), no significant associations between changes in other parameters and outcome were recorded.     

Antitumor effect of WEE1 blockade as monotherapy or in combination with cisplatin in urothelial cancer

Overcoming cisplatin (CDDP) resistance is a major issue in urothelial cancer (UC), in which CDDP-based chemotherapy is the first-line treatment. WEE1, a G₂/M checkpoint kinase, confers chemoresistance in response to genotoxic agents. However, the efficacy of WEE1 blockade in UC has not been reported. MK-1775, a WEE1 inhibitor also known as AZD-1775, blocked proliferation of UC cell lines in a dose-dependent manner irrespective of TP53 status. MK-1775 synergized with CDDP to block proliferation, inducing apoptosis and mitotic catastrophe in TP53-mutant UC cells but not in TP53-WT cells. Knocking down TP53 in TP53-WT cells induced synergism of MK-1775 and CDDP. In UMUC3 cell xenografts and two patient-derived xenograft lines with MDM2 overexpression, in which the p53/cell cycle pathway was inactivated, AZD-1775 combined with CDDP suppressed tumor growth inducing both M-phase entry and apoptosis, whereas AZD-1775 alone was as effective as the combination in RT4 cell xenografts. Drug susceptibility assay using an ex vivo cancer tissue-originated spheroid system showed correlations with the in vivo efficacy of AZD-1775 alone or combined with CDDP. We determined the feasibility of the drug susceptibility assay using spheroids established from UC surgical specimens obtained by transurethral resection. In conclusion, WEE1 is a promising therapeutic target in the treatment of UC, and a highly specific small molecule inhibitor is currently in early phase clinical trials for cancer. Differential antitumor efficacy of WEE1 blockade alone or combined with CDDP could exist according to p53/cell cycle pathway activity, which might be predictable using an ex vivo 3D primary culture system.     

High resolution melting for mutation scanning of <Emphasis Type="Italic">TP53</Emphasis>exons 5–8

Background  

p53 is commonly inactivated by mutations in the DNA-binding domain in a wide range of cancers. As mutant p53 often influences response to therapy, effective and rapid methods to scan for mutations in TP53 are likely to be of clinical value. We therefore evaluated the use of high resolution melting (HRM) as a rapid mutation scanning tool for TP53 in tumour samples.     

Mdm2 antagonists induce apoptosis and synergize with cisplatin overcoming chemoresistance in TP53 wild‐type ovarian cancer cells

Ovarian cancer (OVCa) is the leading cause of death from gynecological malignancies. Although treatment for advanced OVCa has improved with the introduction of taxane–platinum chemotherapy, the majority of patients will develop resistance to the treatment, leading to poor prognosis. One of the causes of chemoresistance is the reduced ability to undergo apoptosis. Cisplatin is a genotoxic drug that leads cells to apoptosis through the activation of the p53 pathway. Defective signaling in this pathway compromises p53 function, and thus cisplatin does not induce apoptosis. A new group of nongenotoxic small molecules called Nutlins have been developed to inhibit p53‐Mdm2 binding, inducing apoptosis in chemoresistant tumors through the activation of the p53 pathway. The wild‐type p53 cisplatin‐resistant ovarian cancer cell‐line A2780cis was used to test the effect of Nutlin‐3a (Nut3a) on apoptosis response. The results showed that Nut3a synergized with cisplatin, inducing cell‐cycle arrest in G2/M and potentiating apoptotic cell death. Increased apoptosis was also induced in wild‐type TP53 primary OVCa cultures by double cisplatin–Nut3a treatment. In conclusion, Nut3a appears to sensitize chemoresistant OVCa cells to cisplatin, inducing apoptosis. As increased response was generalized in primary tumors, this cisplatin–Nut3a combination could be useful for the treatment of patients harboring wild‐type TP53 who do not respond to standard chemotherapy.     

p53 Reactivation by PRIMA-1Met (APR-246) sensitises V600E/KBRAF melanoma to vemurafenib

Intrinsic and acquired resistance of metastatic melanoma to ^V600E/KBRAF and/or MEK inhibitors, which is often caused by activation of the PI3K/AKT survival pathway, represents a major clinical challenge. Given that p53 is capable of antagonising PI3K/AKT activation we hypothesised that pharmacological restoration of p53 activity may increase the sensitivity of BRAF-mutant melanoma to MAPK-targeted therapy and eventually delay and/or prevent acquisition of drug resistance. To test this possibility we exposed a panel of vemurafenib-sensitive and resistant (innate and acquired) ^V600E/KBRAF melanomas to a ^V600E/KBRAF inhibitor (vemurafenib) alone or in combination with a direct p53 activator (PRIMA-1^Met/APR-246). Strikingly, PRIMA-1^Met synergised with vemurafenib to induce apoptosis and suppress proliferation of ^V600E/KBRAF melanoma cells in vitro and to inhibit tumour growth in vivo. Importantly, this drug combination decreased the viability of both vemurafenib-sensitive and resistant melanoma cells irrespectively of the TP53 status. Notably, p53 reactivation was invariably accompanied by PI3K/AKT pathway inhibition, the activity of which was found as a dominant resistance mechanism to BRAF inhibition in our lines. From all various combinatorial modalities tested, targeting the MAPK and PI3K signalling pathways through p53 reactivation or not, the PRIMA-1^Met/vemurafenib combination was the most cytotoxic. We conclude that PRIMA-1^Met through its ability to directly reactivate p53 regardless of the mechanism causing its deactivation, and thereby dampen PI3K signalling, sensitises ^V600E/KBRAF-positive melanoma to BRAF inhibitors.     

Alterations of the p53 and PIK3CA/AKT/mTOR pathways in angiosarcomas

BACKGROUND:

The p53 and phosphoinositide‐3‐kinase, catalytic, alpha polypeptide/v‐akt murine thymoma viral oncogene homolog/mechanistic target of rapamycin (PIK3CA/AKT/mTOR) pathways frequently are altered in sarcoma with complex genomics, such as leiomyosarcoma (LMS) or undifferentiated pleomorphic sarcoma (UPS). The scale of genetic abnormalities in these pathways remains unknown in angiosarcoma (AS).

METHODS:

The authors investigated the status of critical genes involved in the p53 and PIK3CA/AKT/mTOR pathways in a series of 62 AS.

RESULTS:

The mutation and deletion rates of tumor protein 53 (TP53) were 4% and 0%, respectively. Overexpression of p53 was detected by immunohistochemistry in 49% of patients and was associated with inferior disease‐free survival. Although p14 inactivation or overexpression of the human murine double minute homolog (HDM2) were frequent in LMS and UPS and could substitute for TP53 mutation or deletion, such alterations were rare in angiosarcomas. Phosphorylated ribosomal protein S6 kinase (p‐S6K) and/or phosphorylated eukaryotic translation initiation factor 4E binding protein 1 (p‐4eBP1) overexpression was observed in 42% of patients, suggesting frequent activation of the PIK3CA/AKT/mTOR pathway in angiosarcomas. Activation was not related to intragenic deletion of phosphatase and tensin homolog (PTEN), an aberration that is frequent in LMS and UPS but absent in angiosarcomas.

CONCLUSIONS:

The current results indicated that angiosarcomas constitute a distinct subgroup among sarcomas with complex genomics. Although TP53 mutation and PTEN deletion are frequent in LMS and UPS, these aberrations are rarely involved in the pathogenesis of angiosarcoma. Cancer 2012. © 2012 American Cancer Society.     

Effects of the VEGFR inhibitor ZD6474 in combination with radiotherapy and temozolomide in an orthotopic glioma model

Aim of the study The extensive neovascularisation of malignant glioma is mainly influenced by vascular endothelial growth factor (VEGF). The effect of ZD6474, a potent inhibitor of VEGF-receptor-2, was evaluated in combination with either radiotherapy or temozolomide. Methods The effects on glioma growth were investigated in the intracerebral BT4C rat glioma model. ZD6474 30 mg/kg was given alone or in combination with radiotherapy 12 Gy × 1 or with temozolomide 100 mg/kg for 3 days. Two different experiments were performed comparing ZD6474 to radiotherapy or temozolomide. For each experiment 28 animals were randomized into four groups. Results ZD6474 in combination with radiotherapy significantly decreased tumour area by 66% compared with controls whereas the combination with temozolomide decreased tumour area by 74%. Conclusions ZD6474 in combination with two standard modalities in the treatment of malignant glioma, radiotherapy and chemotherapy, markedly decreased the growth of an intracerebral experimental glioma. These results justify further investigations of these therapies in combination. Preliminary parts of this study were presented on EANO, Edinburgh, May 2005 and on ECCO, Paris, October 2005.     

TP53 mutations increase radioresistance in rhabdomyosarcoma and Ewing sarcoma

Background p53 plays a key role in the DNA repair process and response to ionising radiation. We sought to determine the clinical phenotype of TP53 mutations and p53 pathway alterations in patients with rhabdomyosarcoma (RMS) and Ewing sarcoma (ES) treated with radiation.Methods Of patients with available genomic sequencing, we identified 109 patients with RMS and ES treated to a total of 286 radiation sites. We compared irradiated tumour control among tumours with TP53 mutations (n = 40) to those that were TP53 wild-type (n = 246). We additionally compared irradiated tumour control among tumours with any p53 pathway alteration (defined as tumours with TP53 mutations or TP53 wild-type tumours identified to have MDM2/4 amplification and/or CDKN2A/B deletion, n = 78) to those without such alterations (n = 208).Results The median follow-up was 26 months from radiation. TP53 mutations were associated with worse irradiated tumour control among the entire cohort (hazard ratio, HR = 2.8, P < 0.0001). Tumours with any p53 pathway alteration also had inferior irradiated tumour control (HR = 2.0, P = 0.003). On multivariable analysis, after controlling for tumour histology, intent of radiation, presence of gross disease, and biologically effective dose, TP53 mutations continued to be associated with a radioresistant phenotype (HR = 7.1, P < 0.0001).Conclusions Our results show that TP53 mutations are associated with increased radioresistance in RMS and ES. Novel strategies to overcome this radioresistance are important for improved outcomes in p53 disruptive RMS and ES.Subject terms: Paediatric cancer, Cancer genomics, Cancer genomics, Tumour-suppressor proteins     

Individualizing antimetabolic treatment strategies for head and neck squamous cell carcinoma based on TP53 mutational status

BACKGROUND:

Mutations in the tumor protein 53 (TP53) tumor suppressor gene are common in head and neck squamous cell carcinoma (HNSCC) and correlate with radioresistance. Currently, there are no clinically available therapeutic approaches targeting p53 in HNSCC. In this report, the authors propose a strategy that uses TP53 mutational status to individualize antimetabolic strategies for the potentiation of radiation toxicity in HNSCC cells.

METHODS:

Glycolytic flux and mitochondrial respiration were evaluated in wild‐type (wt) and mutant (mut) TP53 HNSCC cell lines. Sensitivity to external‐beam radiation (XRT) was measured using a clonogenic assay.

RESULTS:

HNSCC cells that expressed mutTP53 demonstrated radioresistance compared with HNSCC cells that expressed wtTP53. Glycolytic inhibition potentiated radiation toxicity in mutTP53‐expressing, but not wtTP53‐expressing, HNSCC cells. The relative sensitivity of mutTP53 HNSCC cells to glycolytic inhibition was caused by a glycolytic dependence associated with decreased mitochondrial complex II and IV activity. The wtTP53‐expressing cells maintained mitochondrial reserves and were relatively insensitive to glycolytic inhibition. Inhibition of respiration using metformin increased glycolytic dependence in wtTP53‐expressing cells and potentiated the effects of glycolyic inhibition on radiation toxicity.

CONCLUSIONS:

TP53 mutation in HNSCC cells was correlated with a metabolic shift away from mitochondrial respiration toward glycolysis, resulting in increased sensitivity to the potentiating effects of glycolytic inhibition on radiation toxicity. In contrast, wtTP53‐expressing cells required inhibition of both mitochondrial respiration and glycolysis to become sensitized to radiation. Therefore, the authors concluded that TP53 mutational status may be used as a marker of altered tumor cell metabolism to individualize HNSCC treatment selection of specific, targeted metabolic agents that can overcome cellular resistance to radiation therapy. Cancer 2012;. © 2011 American Cancer Society.     

Correlation of TP53 and MDM2 genotypes with response to therapy in sarcoma

BACKGROUND:

Relatively few sarcomas harbor TP53 (tumor protein p53) mutations, but in many cases, amplification of MDM2 (murine double minute 2) effectively inactivate p53. The p53 pathway activity can also be affected by normal genetic variation.

METHODS:

The mutation status of TP53 and expression of MDM2, TP53, and their genetic variants SNP309 and R72P (Arg72Pro) were investigated in 125 sarcoma patient samples and 18 sarcoma cell lines. Association of the different genotypes and gene aberrations with chemotherapy response and survival, as well as response to MDM2 antagonists in vitro was evaluated.

RESULTS:

Twenty‐two percent of the tumors had mutant TP53 and 20% MDM2 gene amplification. Patients with wild‐type TP53 (TP53^Wt) tumors had improved survival (P < .001) and TP53^Wt was an independent prognostic factor (hazard ratio = 0.41; 95% confidence interval = 0.23‐0.74; P = .03). Interestingly, there was a trend toward longer time to progression after chemotherapy for tumors with the apoptosis‐prone p53 variant R72 (P = .07), which was strongest with doxorubicin/ifosfamide‐based regimens (P = .01). Liposarcomas had low R72 frequency (33% versus 56%), but increased levels of MDM2 and MDM4 (51% and 11%, P < .001). MDM2 overexpression on a TP53^Wt background predicted better response to MDM2 antagonist Nutlin‐3a, irrespective of R72P or SNP309 status.

CONCLUSIONS:

Improved survival after chemotherapy was found in patients with TP53^Wt tumors harboring the R72 variant. MDM2 overexpression in TP53^Wt tumors predicted good response to MDM2 antagonists, irrespective of R72P or SNP309 status. Thus, detailed TP53 and MDM2 genotype analyses prior to systemic therapy are recommended. Cancer 2013. © 2012 American Cancer Society.     

Nutlin‐3a selects for cells harbouring TP53 mutations

TP53 mutations occur in half of all human tumours. Mutagen‐induced or spontaneous TP53 mutagenesis can be studied in vitro using the human TP53 knock‐in (Hupki) mouse embryo fibroblast (HUF) immortalisation assay (HIMA). TP53 mutations arise in up to 30% of mutagen‐treated, immortalised HUFs; however, mutants are not identified until TP53 sequence analysis following immortalisation (2–5 months) and much effort is expended maintaining TP53‐WT cultures. In order to improve the selectivity of the HIMA for HUFs harbouring TP53 mutations, we explored the use of Nutlin‐3a, an MDM2 inhibitor that leads to stabilisation and activation of wild‐type (WT) p53. First, we treated previously established immortal HUF lines carrying WT or mutated TP53 with Nutlin‐3a to examine the effect on cell growth and p53 activation. Nutlin‐3a induced the p53 pathway in TP53‐WT HUFs and inhibited cell growth, whereas most TP53‐mutated HUFs were resistant to Nutlin‐3a. We then assessed whether Nutlin‐3a treatment could discriminate between TP53‐WT and TP53‐mutated cells during the HIMA (n = 72 cultures). As immortal clones emerged from senescent cultures, each was treated with 10 µM Nutlin‐3a for 5 days and observed for sensitivity or resistance. TP53 was subsequently sequenced from all immortalised clones. We found that all Nutlin‐3a‐resistant clones harboured TP53 mutations, which were diverse in position and functional impact, while all but one of the Nutlin‐3a‐sensitive clones were TP53‐WT. These data suggest that including a Nutlin‐3a counter‐screen significantly improves the specificity and efficiency of the HIMA, whereby TP53‐mutated clones are selected prior to sequencing and TP53‐WT clones can be discarded.     

DN‐R175H p53 mutation is more effective than p53 interference in inducing epithelial disorganization and activation of proliferation signals in human carcinoma cells: Role of E‐cadherin

One of the hallmarks of carcinomas is epithelial disorganization, linked to overexpression of matrix metalloproteases (MMP) like MMP‐9, loss of intercellular E‐cadherin and activation of epidermal growth receptor (EGFR/erbB1). Since the p53 tumor suppressor pathway is inactivated in most human cancers due to gene mutations or defective wt p53 signaling, we now investigated in human wt p53 breast carcinoma MCF‐7 cells, whether single treatment with the p53 transactivation pharmacological inhibitor pifithrin‐α, transient p53 siRNA interference or stable insertion of a dominant‐negative (DN) R175H p53 mutant increase: (i) EGFR/erbB1 activation, (ii) MMP‐9 expression and (iii) loss of surface E‐cadherin. Transient abrogation of wt p53 function increased phosphorylation of EGFR/erbB1 and MMP‐9 expression. However, all these effects were much more pronounced in cells stably transduced with the dominant negative–Arg‐175His mutant p53 (DN‐R175H mutant p53), which also showed loss of epithelial cytoarchitecture and extensive E‐cadherin downregulation. Collectively, these results support the notion that the DN‐R175H mutant p53 exerts a gain of oncogenic function by promoting disruption of E‐cadherin intercellular contacts and activation of proliferation signals. Our data suggests that epithelial shape and growth control are unequally affected depending on how wt p53 function is impaired and whether partial or full tumor suppressor activity is lost. © 2009 UICC     

Immunohistochemical detection of Polo-like kinase-1 (PLK1) in primary breast cancer is associated with TP53 mutation and poor clinical outcom

Introduction

Polo-like kinase-1 (PLK1) is a crucial driver of cell cycle progression and its down-regulation plays an important checkpoint role in response to DNA damage. Mechanistically, this is mediated by p53 which represses PLK1 expression through chromatin remodelling. Consistent with this model, cultured cells lacking p53 fail to repress PLK1 expression. This study examined PLK1 expression, p53 mutation and clinical outcome in breast cancer.

Methods

Immunohistochemistry was performed using antibodies to PLK1, MDM2 and Ki67 on Tissue Micro-Array (TMA) slides of a cohort of 215 primary breast cancers. The TP53 gene (encoding p53) was sequenced in all tumour samples. Protein expression scored using the "Quickscore" method was compared with clinical and pathological data, including survival.

Results

Staining of PLK1 was observed in 11% of primary breast tumours and was significantly associated with the presence of TP53 mutation (P = 0.0063). Moreover, patients with both PLK1 expression and TP53 mutation showed a significantly worse survival than those with either PLK1 expression or TP53 mutation alone. There was also a close association of elevated PLK1 with triple negative tumours, considered to be poor prognosis breast cancers that generally harbour TP53 mutation. Further association was observed between elevated PLK1 levels and the major p53 negative regulator, MDM2.

Conclusions

The significant association between elevated PLK1 and TP53 mutation in women with breast cancer is consistent with escape from repression of PLK1 expression by mutant p53. Tumours expressing elevated PLK1, but lacking functional p53, may be potential targets for novel anti-PLK1-targeted drugs.