ESR1 and p53 interactome alteration defines mechanisms of tamoxifen response in luminal breast cancer.

The canonical mechanism behind tamoxifen's therapeutic effect on estrogen receptor α/ESR1+ breast cancers is inhibition of ESR1-dependent estrogen signaling. Although ESR1+ tumors expressing wild-type p53 were reported to be more responsive to tamoxifen (Tam) therapy, p53 has not been factored into choice of this therapy and the mechanism underlying the role of p53 in Tam response remains unclear. In a window-of-opportunity trial on patients with newly diagnosed stage I-III ESR1+/HER2/wild-type p53 breast cancer who were randomized to arms with or without Tam prior to surgery, we reveal that the ESR1-p53 interaction in tumors was inhibited by Tam. This resulted in functional reactivation of p53 leading to transcriptional reprogramming that favors tumor-suppressive signaling, as well as downregulation of oncogenic pathways. These findings illustrating the convergence of ESR1 and p53 signaling during Tam therapy enrich mechanistic understanding of the impact of p53 on the response to Tam therapy.

Efficacy and safety of tivozanib in recurrent, platinum-resistant ovarian, fallopian tube or primary peritoneal cancer, an NCCN phase II trial.

OBJECTIVE: Tivozanib is a potent selective pan-vascular endothelial growth factor receptor tyrosine kinase inhibitor with a long half-life. This study assessed its activity in patients with recurrent, platinum-resistant ovarian, fallopian tube or primary peritoneal cancer (OC). METHODS: This open-label phase II study used a Simon's two-stage design. Eligible patients had recurrent, platinum-resistant OC and measurable or detectable disease. There was no limit on the number of prior regimens. Treatment consisted of tivozanib 1.5 mg orally once daily for 21 days in a 28-day cycle. The primary endpoint was objective response rate (ORR). Secondary endpoints were progression-free survival (PFS), overall survival (OS), and toxicity assessment. RESULTS: Thirty-one patients were enrolled, and 30 were treated. The median age was 59.5 years, and median number of prior regimens was 4 (range 1-9). Twenty-four patients were evaluable for response, and four (16.7%) achieved a partial response (PR; ORR = 16.7%). An additional fourteen (58.3%) patients had stable disease (SD). The clinical benefit rate (PR + SD) was 75.0%, and the median duration of objective response was 5.7 months. For all patients on trial, the median PFS was 4.1 months (95% confidence interval (CI): 1.7-5.8) and OS 8.6 months (95% CI: 5.4-12.5). There were no treatment-related deaths. Serious adverse events occurred in 13.3% of patients and included small intestinal perforation or obstruction and stroke. Grade 3-4 adverse events occurred in 60% of patients, including hypertension (26.7%) and fatigue (10%). CONCLUSIONS: Tivozanib is effective in patients with recurrent OC, with moderate toxicity and no treatment-related deaths, supporting its further development.

Intracellular optical doppler phenotypes of chemosensitivity in human epithelial ovarian cancer.

Development of an assay to predict response to chemotherapy has remained an elusive goal in cancer research. We report a phenotypic chemosensitivity assay for epithelial ovarian cancer based on Doppler spectroscopy of infrared light scattered from intracellular motions in living three-dimensional tumor biopsy tissue measured in vitro. The study analyzed biospecimens from 20 human patients with epithelial ovarian cancer. Matched primary and metastatic tumor tissues were collected for 3 patients, and an additional 3 patients provided only metastatic tissues. Doppler fluctuation spectra were obtained using full-field optical coherence tomography through off-axis digital holography. Frequencies in the range from 10 mHz to 10 Hz are sensitive to changes in intracellular dynamics caused by platinum-based chemotherapy. Metastatic tumor tissues were found to display a biodynamic phenotype that was similar to primary tissue from patients who had poor clinical outcomes. The biodynamic phenotypic profile correctly classified 90% [88-91% c.i.] of the patients when the metastatic samples were characterized as having a chemoresistant phenotype. This work suggests that Doppler profiling of tissue response to chemotherapy has the potential to predict patient clinical outcomes based on primary, but not metastatic, tumor tissue.

A Novel ALDH1A1 Inhibitor Targets Cells with Stem Cell Characteristics in Ovarian Cancer.

A small of population of slow cycling and chemo-resistant cells referred to as cancer stem cells (CSC) have been implicated in cancer recurrence. There is emerging interest in developing targeted therapeutics to eradicate CSCs. Aldehyde-dehydrogenase (ALDH) activity was shown to be a functional marker of CSCs in ovarian cancer (OC). ALDH activity is increased in cells grown as spheres versus monolayer cultures under differentiating conditions and in OC cells after treatment with platinum. Here, we describe the activity of CM37, a newly identified small molecule with inhibitory activity against ALDH1A1, in OC models enriched in CSCs. Treatment with CM37 reduced OC cells' proliferation as spheroids under low attachment growth conditions and the expression of stemness-associated markers (OCT4 and SOX2) in ALDH+ cells fluorescence-activated cell sorting (FACS)-sorted from cell lines and malignant OC ascites. Likewise, siRNA-mediated ALDH1A1 knockdown reduced OC cells' proliferation as spheres, expression of stemness markers, and delayed tumor initiation capacity in vivo. Treatment with CM37 promoted DNA damage in OC cells, as evidenced by induction of γH2AX. This corresponded to increased expression of genes involved in DNA damage response, such as NEIL3, as measured in ALDH+ cells treated with CM37 or in cells where ALDH1A1 was knocked down. By inhibiting ALDH1A1, CM37 augmented intracellular ROS accumulation, which in turn led to increased DNA damage and reduced OC cell viability. Cumulatively, our findings demonstrate that a novel ALDH1A1 small molecule inhibitor is active in OC models enriched in CSCs. Further optimization of this new class of small molecules could provide a novel strategy for targeting treatment-resistant OC.

TP53 Status as a Determinant of Pro- vs Anti-Tumorigenic Effects of Estrogen Receptor-Beta in Breast Cancer.

BACKGROUND: Anti-tumorigenic vs pro-tumorigenic roles of estrogen receptor-beta (ESR2) in breast cancer remain unsettled. We investigated the potential of TP53 status to be a determinant of the bi-faceted role of ESR2 and associated therapeutic implications for triple negative breast cancer (TNBC). METHODS: ESR2-TP53 interaction was analyzed with multiple assays including the in situ proximity ligation assay. Transcriptional effects on TP53-target genes and cell proliferation in response to knocking down or overexpressing ESR2 were determined. Patient survival according to ESR2 expression levels and TP53 mutation status was analyzed in the basal-like TNBC subgroup in the Molecular Taxonomy of Breast Cancer International Consortium (n = 308) and Roswell Park Comprehensive Cancer Center (n = 46) patient cohorts by univariate Cox regression and log-rank test. All statistical tests are two-sided. RESULTS: ESR2 interaction with wild-type and mutant TP53 caused pro-proliferative and anti-proliferative effects, respectively. Depleting ESR2 in cells expressing wild-type TP53 resulted in increased expression of TP53-target genes CDKN1A (control group mean [SD] = 1 [0.13] vs ESR2 depletion group mean [SD] = 2.08 [0.24], P = .003) and BBC3 (control group mean [SD] = 1 [0.06] vs ESR2 depleted group mean [SD] = 1.92 [0.25], P = .003); however, expression of CDKN1A (control group mean [SD] = 1 [0.21] vs ESR2 depleted group mean [SD] = 0.56 [0.12], P = .02) and BBC3 (control group mean [SD] = 1 [0.03] vs ESR2 depleted group mean [SD] = 0.55 [0.09], P = .008) was decreased in cells expressing mutant TP53. Overexpressing ESR2 had opposite effects. Tamoxifen increased ESR2-mutant TP53 interaction, leading to reactivation of TP73 and apoptosis. High levels of ESR2 expression in mutant TP53-expressing basal-like tumors is associated with better prognosis (Molecular Taxonomy of Breast Cancer International Consortium cohort: log-rank P = .001; hazard ratio = 0.26, 95% confidence interval = 0.08 to 0.84, univariate Cox P = .02). CONCLUSIONS: TP53 status is a determinant of the functional duality of ESR2. Our study suggests that ESR2-mutant TP53 combination prognosticates survival in TNBC revealing a novel strategy to stratify TNBC for therapeutic intervention potentially by repurposing tamoxifen.

A comprehensive analysis of coregulator recruitment, androgen receptor function and gene expression in prostate cancer.

Standard treatment for metastatic prostate cancer (CaP) prevents ligand-activation of androgen receptor (AR). Despite initial remission, CaP progresses while relying on AR. AR transcriptional output controls CaP behavior and is an alternative therapeutic target, but its molecular regulation is poorly understood. Here, we show that action of activated AR partitions into fractions that are controlled preferentially by different coregulators. In a 452-AR-target gene panel, each of 18 clinically relevant coregulators mediates androgen-responsiveness of 0-57% genes and acts as a coactivator or corepressor in a gene-specific manner. Selectivity in coregulator-dependent AR action is reflected in differential AR binding site composition and involvement with CaP biology and progression. Isolation of a novel transcriptional mechanism in which WDR77 unites the actions of AR and p53, the major genomic drivers of lethal CaP, to control cell cycle progression provides proof-of-principle for treatment via selective interference with AR action by exploiting AR dependence on coregulators.

Estrogen receptor alpha (ERα/ESR1) mediates the p53-independent overexpression of MDM4/MDMX and MDM2 in human breast cancer.

MDM2 and MDM4 are heterodimeric, non-redundant oncoproteins that potently inhibit the p53 tumor suppressor protein. MDM2 and MDM4 also enhance the tumorigenicity of breast cancer cells in in vitro and in vivo models and are overexpressed in primary human breast cancers. Prior studies have characterized Estrogen Receptor Alpha (ERα/ESR1) as a regulator of MDM2 expression and an MDM2- and p53-interacting protein. However, similar crosstalk between ERα and MDM4 has not been investigated. Moreover, signaling pathways that mediate the overexpression of MDM4 in human breast cancer remain to be elucidated. Using the Cancer Genome Atlas (TCGA) breast invasive carcinoma patient cohort, we have analyzed correlations between ERα status and MDM4 and MDM2 expression in primary, treatment-naïve, invasive breast carcinoma samples. We report that the expression of MDM4 and MDM2 is elevated in primary human breast cancers of luminal A/B subtypes and associates with ERα-positive disease, independently of p53 mutation status. Furthermore, in cell culture models, ERα positively regulates MDM4 and MDM2 expression via p53-independent mechanisms, and these effects can be blocked by the clinically-relevant endocrine therapies fulvestrant and tamoxifen. Additionally, ERα also positively regulates p53 expression. Lastly, we report that endogenous MDM4 negatively regulates ERα expression and forms a protein complex with ERα in breast cancer cell lines and primary human breast tumor tissue. This suggests direct signaling crosstalk and negative feedback loops between ERα and MDM4 expression in breast cancer cells. Collectively, these novel findings implicate ERα as a central component of the p53-MDM2-MDM4 signaling axis in human breast cancer.

Differential regulation of cyclin D1 expression by protein kinase C α and ϵ signaling in intestinal epithelial cells.

Cellular accumulation of cyclin D1, a key regulator of cell proliferation and tumorigenesis, is subject to tight control. Our previous studies have identified PKCα as a negative regulator of cyclin D1 in the intestinal epithelium. However, treatment of non-transformed IEC-18 ileal crypt cells with PKC agonists has a biphasic effect on cyclin D1 expression. Initial PKCα-mediated down-regulation is followed by recovery and subsequent accumulation of the cyclin to levels markedly higher than those seen in untreated cells. Using protein overexpression strategies, siRNA, and pharmacological inhibitors, we now demonstrate that the recovery and hyperinduction of cyclin D1 reflect the combined effects of (a) loss of negative signals from PKCα due to agonist-induced PKCα down-regulation and (b) positive effects of PKCϵ. PKCϵ-mediated up-regulation of cyclin D1 requires sustained ERK stimulation and transcriptional activation of the proximal cyclin D1 (CCDN1) promoter, without apparent involvement of changes in protein stability or translation. PKCϵ also up-regulates cyclin D1 expression in colon cancer cells, through mechanisms that parallel those in IEC-18 cells. Although induction of cyclin D1 by PKCϵ is dependent on non-canonical NF-κB activation, the NF-κB site in the proximal promoter is not required. Instead, cyclin D1 promoter activity is regulated by a novel interaction between NF-κB and factors that associate with the cyclic AMP-response element adjacent to the NF-κB site. The differential effects of PKCα and PKCϵ on cyclin D1 accumulation are likely to contribute to the opposing tumor-suppressive and tumor-promoting activities of these PKC family members in the intestinal epithelium.

Estrogen-mediated upregulation of Noxa is associated with cell cycle progression in estrogen receptor-positive breast cancer cells.

Noxa is a Bcl-2-homology domain (BH3)-only protein reported to be a proapoptotic member of the Bcl-2 family. Estrogen has been well documented to stimulate cell growth and inhibit apoptosis in estrogen receptor (ER)-positive breast cancer cells. Intriguingly, recent reports have shown that 17ß-estradiol (E2) induces Noxa expression, although the mechanisms underlying E2-mediated induction of Noxa and its functional significance are unknown. Using MCF7 human breast cancer cells as an experimental model, we show that Noxa is upregulated by E2 via p53-independent processes that involve c-Myc and ERα. Experiments using small interfering ribonucleic acids (siRNA) to specifically knock down p53, c-Myc, and ERα demonstrated that c-Myc and ERα, but not p53, are involved in the transcriptional upregulation of Noxa following E2 treatment. Furthermore, while E2 promoted the recruitment of c-Myc and ERα to the NOXA promoter in chromatin immunoprecipitation (ChIP) assays, E2 did not induce p53 recruitment. Interestingly, E2-mediated upregulation of Noxa was not associated with apoptosis. However, siRNA-mediated knockdown of Noxa resulted in cell cycle arrest in G(0)/G(1)-phase and significantly delayed the G(1)-to-S-phase transition following E2 treatment, indicating that Noxa expression is required for cell cycle progression in ER-positive breast cancer cells.

Mechanisms of estrogen receptor antagonism toward p53 and its implications in breast cancer therapeutic response and stem cell regulation.

Estrogen receptor alpha (ERalpha) plays an important role in the onset and progression of breast cancer, whereas p53 functions as a major tumor suppressor. We previously reported that ERalpha binds to p53, resulting in inhibition of transcriptional regulation by p53. Here, we report on the molecular mechanisms by which ERalpha suppresses p53's transactivation function. Sequential ChIP assays demonstrated that ERalpha represses p53-mediated transcriptional activation in human breast cancer cells by recruiting nuclear receptor corepressors (NCoR and SMRT) and histone deacetylase 1 (HDAC1). RNAi-mediated down-regulation of NCoR resulted in increased endogenous expression of the cyclin-dependent kinase (CDK)-inhibitor p21(Waf1/Cip1) (CDKN1A) gene, a prototypic transcriptional target of p53. While 17beta-estradiol (E2) enhanced ERalpha binding to p53 and inhibited p21 transcription, antiestrogens decreased ERalpha recruitment and induced transcription. The effects of estrogen and antiestrogens on p21 transcription were diametrically opposite to their known effects on the conventional ERE-containing ERalpha target gene, pS2/TFF1. These results suggest that ERalpha uses dual strategies to promote abnormal cellular proliferation: enhancing the transcription of ERE-containing proproliferative genes and repressing the transcription of p53-responsive antiproliferative genes. Importantly, ERalpha binds to p53 and inhibits transcriptional activation by p53 in stem/progenitor cell-containing murine mammospheres, suggesting a potential role for the ER-p53 interaction in mammary tissue homeostasis and cancer formation. Furthermore, retrospective studies analyzing response to tamoxifen therapy in a subset of patients with ER-positive breast cancer expressing either wild-type or mutant p53 suggest that the presence of wild-type p53 is an important determinant of positive therapeutic response.