Targeting Mdmx to treat breast cancers with wild-type p53.

The function of the tumor suppressor p53 is universally compromised in cancers. It is the most frequently mutated gene in human cancers (reviewed). In cases where p53 is not mutated, alternative regulatory pathways inactivate its tumor suppressive functions. This is primarily achieved through elevation in the expression of the key inhibitors of p53: Mdm2 or Mdmx (also called Mdm4) (reviewed). In breast cancer (BrCa), the frequency of p53 mutations varies markedly between the different subtypes, with basal-like BrCas bearing a high frequency of p53 mutations, whereas luminal BrCas generally express wild-type (wt) p53. Here we show that Mdmx is unexpectedly highly expressed in normal breast epithelial cells and its expression is further elevated in most luminal BrCas, whereas p53 expression is generally low, consistent with wt p53 status. Inducible knockdown (KD) of Mdmx in luminal BrCa MCF-7 cells impedes the growth of these cells in culture, in a p53-dependent manner. Importantly, KD of Mdmx in orthotopic xenograft transplants resulted in growth inhibition associated with prolonged survival, both in a preventative model and also in a treatment model. Growth impediment in response to Mdmx KD was associated with cellular senescence. The growth inhibitory capacity of Mdmx KD was recapitulated in an additional luminal BrCa cell line MPE600, which expresses wt p53. Further, the growth inhibitory capacity of Mdmx KD was also demonstrated in the wt p53 basal-like cell line SKBR7 line. These results identify Mdmx growth dependency in wt p53 expressing BrCas, across a range of subtypes. Based on our findings, we propose that Mdmx targeting is an attractive strategy for treating BrCas harboring wt p53.

The Hippo pathway transcriptional co-activator, YAP, is an ovarian cancer oncogene.

The Salvador-Warts-Hippo (SWH) pathway was first discovered in Drosophila melanogaster as a potent inhibitor of tissue growth. The SWH pathway is highly conserved between D. melanogaster and mammals, both in function and in the mechanism of signal transduction. The mammalian SWH pathway limits tissue growth by inhibiting the nuclear access and expression of the transcriptional co-activator, Yes-associated protein (YAP). Mutation and altered expression of SWH pathway proteins has been observed in several types of human cancer, but the contribution of these events to tumorigenesis has been unclear. Here we show that YAP can enhance the transformed phenotype of ovarian cancer cell lines and that YAP confers resistance to chemotherapeutic agents that are commonly used to treat ovarian cancer. We find that high nuclear YAP expression correlates with poor patient prognosis in a cohort of 268 invasive epithelial ovarian cancer samples. Segregation by histotype shows that the correlation between nuclear YAP and poor survival is predominantly associated with clear cell tumors, independent of stage. Collectively our findings suggest that YAP derepression contributes to the genesis of ovarian clear cell carcinoma and that the SWH pathway is an attractive therapeutic target.

BRCA1 tumours correlate with a HIF-1alpha phenotype and have a poor prognosis through modulation of hydroxylase enzyme profile expression.

BACKGROUND: There are limited data regarding the hypoxia pathway in familial breast cancers. We therefore performed a study of hypoxic factors in BRCA1, BRCA2 and BRCAX breast cancers. METHODS: Immunoperoxidase staining for HIF-1alpha, PHD1, PHD2, PHD3, VEGF and FIH was carried out in 125 (38 BRCA1, 33 BRCA2 and 54 BRCAX) breast carcinomas. These were correlated with clinicopathological parameters and the intrinsic breast cancer phenotypes. RESULTS: BRCA1 tumours correlated with positivity for HIF-1alpha (P=0.008) and negativity for PHD3 (P=0.037). HIF-1alpha positivity (P=0.001), PHD3 negativity (P=0.037) and nuclear FIH negativity (P=0.011) was associated with basal phenotype. HIF-1alpha expression correlated with high tumour grade (P=0.009), negative oestrogen receptor (ER) status (P=0.001) and the absence of lymph node metastasis (P=0.028). Nuclear FIH expression and PHD3 correlated with positive ER expression (P=0.024 and P=0.035, respectively). BRCA1 cancers with positive HIF-1alpha or cytoplasmic FIH had a significantly shorter relapse-free survival (P=0.007 and P=0.049, respectively). CONCLUSIONS: The aggressive nature of BRCA1 and basal-type tumours may be partly explained by an enhanced hypoxic drive and hypoxia driven ER degradation because of suppressed PHD and aberrantly located FIH expression. This may have important implications, as these tumours may respond to compounds directed against HIF-1alpha or its downstream targets.

Expression of the forkhead box transcription factor FOXP1 is associated with oestrogen receptor alpha, oestrogen receptor beta and improved survival in familial breast cancers.

BACKGROUND: The role of FOXP1 in sporadic breast cancers has been widely studied but its role in familial breast cancers is yet unexplored. AIMS: To investigate FOXP1 expression in different molecular subtypes of familial breast cancers and to correlate its expression with clinicopathological parameters, oestrogen receptors (ER) and survival. METHODS: Immunohistochemical staining for FOXP1 was performed in 126 familial breast carcinomas comprising 35 BRCA1, 34 BRCA2 and 57 BRCAX. RESULTS: Nuclear FOXP1 expression ranged from focal weak to widespread strong expression. Expression of FOXP1 was higher in familial breast cancers (54%) compared with sporadic cancers (46%) (p<0.001). There was a significant correlation between FOXP1 with ERalpha (p = 0.038) and ERbeta (p = 0.007) in familial breast cancers. FOXP1 was more highly expressed in familial breast cancers compared with sporadic cancers for luminal (p = 0.021) and basal (p<0.001), but not HER2 and null phenotypes (both p>0.05). The absence of FOXP1 expression was associated with a shorter relapse-free (p = 0.025) and overall survival (p = 0.009) in familial breast cancer. Negativity for FOXP1 was associated with a significantly worse overall survival in BRCA2 cancers (p = 0.021) and there was a non-significant separation of the survival curves for BRCA1 cancers (p = 0.183). No differences in survival were seen for BRCAX cancers (p = 0.762). CONCLUSION: Results suggest that FOXP1 demonstrates different expression patterns in familial breast cancers than sporadic tumours, even in tumours showing similar phenotypes. They also suggest a different role of FOXP1 as a tumour suppressor in familial tumours, which is unrelated to ER expression and may impact on therapeutic options.