Abstract C180: Novel small molecule inhibitors of signal transducer and activator of transcription (STAT3) for cancer treatment

Transcription factors (TFs) represent attractive targets for cancer therapy. However, very few direct TF inhibitors are currently in the clinic. STAT3 is overexpressed and activated in many human cancers promoting proliferation, survival and metabolic adaptation of cancer cells. In this study we investigated the mechanism of action of two new anticancer compounds, OPB-31121 and OPB-51602, currently evaluated in phase I clinical trials. Computational docking and molecular dynamic simulation (MDS) showed that the two compounds bound to the SH2 domain of STAT3 with an estimated binding affinity 2-3 orders of magnitude lower than other known STAT3 inhibitors (STAT3i). Furthermore, the compounds shared a common binding pocket that did not overlap with that of the other STAT3i. Binding assays using isothermal titration calorimetry (ITC) confirmed that OPB-31121 and OPB-51602 bound to recombinant STAT3-SH2 with Kd in the nM range. Binding of the two compounds was disrupted by mutations of amino acids in the predicted binding pocket. Interestingly, competition assays demonstrated that OPB-31121 and OPB-51602 did not prevent binding of other STAT3i, in agreement with the MDS predictions. OPB-51602 and OPB-31121 blocked both Tyr705 and Ser727 phosphorylation, which are required for full STAT3 activation, and inhibited the activity of STAT3 dependent luciferase reporter in human cancer cells. Both compounds strongly reduced anchorage-dependent growth and colony formation in soft-agar. Intriguingly, both compounds were more effective in conditions of metabolic stress (e.g., nutrient and glucose depletion), suggesting that they affected STAT3 functions relevant for metabolic adaptation of cancer cells. In vivo OPB-51602 (20-40 mg/kg PO daily for 2 weeks) arrested growth of DU145 prostate tumor xenografts and concomitantly reduced Tyr705 and Ser727 phosphorylation in tumor tissues. Interestingly, growth inhibition persisted after discontinuation of the treatment, suggesting a stable impairment of tumor-initiating capability and tumor regrowth. Altogether, this study identifies STAT3 as a relevant target of these new compounds. We show that both drugs interact directly with STAT3 and interfere with STAT3 functions in cells and tumor xenografts. Notably, the two compounds bind with high affinity to a unique pocket in the STAT3-SH2 domain that is not shared by other known STAT3i. These features might be relevant for their ability to block specific STAT3 functions and protein interactions resulting in distinctive biological activity and pharmacological properties of these novel compounds.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C180.

Citation Format: Lara Brambilla, Davide Genini, Erik Laurini, Gianluca Civenni, Sandra Pinton, Manuela Sarti, Laurent Perez, Sabrina Pricl, Giuseppina M. Carbone, Carlo V. Catapano. Novel small molecule inhibitors of signal transducer and activator of transcription (STAT3) for cancer treatment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C180.

RNAi-mediated silencing of Myc transcription inhibits stem-like cell maintenance and tumorigenicity in prostate cancer

Several studies link disease progression, recurrence, and treatment failures to the cancer stem-like cell (CSC) subpopulation within the heterogeneous tumor cell population. Myc is a transcription factor having a central function in stem cell biology and in human cancers. Hence, Myc represents an attractive target to develop CSC-specific therapies. Recent findings suggest that Myc transcription can be silenced using an RNA interference (RNAi)-based strategy that targets noncoding promoter-associated RNA (paRNA) overlapping the transcription start site. In this study, we investigated the effects of silencing Myc transcription on prostate CSC in cell culture and xenograft models of human prostate cancer. Treatment with an effective promoter-targeting siRNA reduced the fraction of CSCs, leading to reduced self-renewal, tumor-initiating, and metastatic capability. Combined analysis of stem-like cells and senescence markers indicated that Myc silencing triggered a phenotypic shift and senescence in the CSC subpopulation. Notably, systemic delivery of the promoter-targeting siRNA in the xenograft model produced a striking suppression in the development of prostate tumors. Our results support a pivotal role for Myc in CSC maintenance and show that Myc targeting via RNAi-based transcriptional silencing can trigger CSC senescence and loss of their tumor-initiating capability. More generally, our findings demonstrate the efficacy of RNAi-based transcriptional strategies and the potential to target regulatory noncoding paRNAs for therapeutic applications.

Differential expression of testin and survivin in breast cancer subtypes

Testin (TES) is a putative tumour-suppressor gene downregulated in various types of cancers. Survivin is a nodal protein involved in multiple signalling pathways, tumour maintenance and inhibition of apoptosis. Previous studies indicate that TES and survivin can functionally interact and modulate cell death and proliferation in breast cancer cells. The aim of the present study was to investigate the expression and prognostic relevance of TES and survivin in breast cancer subtypes examining a large cohort of breast cancer patients. We determined the expression of TES and survivin by immunohistochemistry (IHC) in tissue samples from 242 breast cancer patients diagnosed between 1981 and 2009. The expression of these proteins was compared with clinical and pathological data. There was a significant association of nuclear survivin overexpression and TES downregulation with triple-negative tumours [P=0.009; univariate odds ratio (OR), 3.20; 95% CI, 1.34-7.66] (P=0.018; multivariate OR, 2.90; 95% CI, 1.20‑6.97). A further significant correlation was observed between TES downregulation and the luminal B subtype (P=0.019, univariate OR: 2.90; 95% CI, 1.19‑7.06) (P=0.032, multivariate OR, 2.67; 95% CI, 1.09-6.65), independent of survivin expression. Our results demonstrated a statistically significant association between TES downregulation and highly aggressive breast tumour subtypes, such as triple-negative and luminal B tumours, along with the prognostic relevance of nuclear expression of survivin. To our knowledge, this is the first demonstration of such an association.

ETS transcription factor ESE1/ELF3 orchestrates a positive feedback loop that constitutively activates NF-κB and drives prostate cancer progression

Chromosomal translocations leading to deregulated expression of ETS transcription factors are frequent in prostate tumors. Here, we report a novel mechanism leading to oncogenic activation of the ETS factor ESE1/ELF3 in prostate tumors. ESE1/ELF3 was overexpressed in human primary and metastatic tumors. It mediated transforming phenotypes in vitro and in vivo and induced an inflammatory transcriptome with changes in relevant oncogenic pathways. ESE1/ELF3 was induced by interleukin (IL)-1β through NF-κB and was a crucial mediator of the phenotypic and transcriptional changes induced by IL-1β in prostate cancer cells. This linkage was mediated by interaction of ESE1/ELF3 with the NF-κB subunits p65 and p50, acting by enhancing their nuclear translocation and transcriptional activity and by inducing p50 transcription. Supporting these findings, gene expression profiling revealed an enrichment of NF-κB effector functions in prostate cancer cells or tumors expressing high levels of ESE1/ELF3. We observed concordant upregulation of ESE1/ELF3 and NF-κB in human prostate tumors that was associated with adverse prognosis. Collectively, our results define an important new mechanistic link between inflammatory signaling and the progression of prostate cancer.

Abstract 3118: ESE1/ELF3 and constitutive activation of NF-kB in human prostate cancer: prognostic relevance and rationale for context-dependent therapeutic strategies

Activation of inflammatory circuits occurs frequently in human cancers. Here, we show that ESE1/ELF3 exerts oncogenic functions and is an important link between inflammatory signaling and prostate cancer progression. We found that ESE1/ELF3 is overexpressed in human primary and metastatic prostate tumors, mediates key transforming phenotypes in prostate cancer cells and induces transcriptional changes in relevant oncogenic pathways. Moreover, ESE1/ELF3 contributes to IL-1beta induced and constitutive activation of NF-kB by multiple transcriptional and post-transcriptional mechanisms. ESE1/ELF3 interacts with p65/RELA and p50/NFKB1, enhances nuclear localization and transcriptional activity of the NF-kB complex, and induces transcription of p50/NFKB1by binding to the gene promoter. This positive feedback loop leading to ESE1/ELF3 upregulation and NF-kB activation is also active in human prostate tumors. Bioinformatic analyses revealed that the ESE1/ELF3 transcriptional program converged with NF-kB and IL-1beta target genes in experimental models and human tumors. Furthermore, human prostate tumors with high ESE1/ELF3 expression were enriched of ESE1/ELF3 and NF-kB target genes. Evaluation of tumor tissue microarrays by immunohistochemistry and of multiple gene expression datasets revealed that combined upregulation of ESE1/ELF3 and p65/p50 was associated with significantly reduced overall survival and increased disease recurrence. Furthermore, we speculated that the positive feedback loop between ESE1/ELF3 and NF-kB could be selectively disrupted by NF-kB inhibitors. To test this hypothesis, we used BAY-117085, a known inhibitor of NF-kB, and a second compound, EC-70124, which was recently reported to potently inhibit NF-kB. Both compounds inhibited NF-kB reporter activity in prostate cancer cells and reduced phosphorylation of IkBα. Moreover, expression of genes induced by ESE1/ELF3, cell migration and proliferation were significantly reduced by NF-kB inhibitors selectively in ESE1/ELF3 expressing cells. Collectively, this study provides a mechanistic link between inflammation and prostate cancer progression and suggests new tools for patient stratification and design of context-dependent strategies for a subset of prostate cancer patients with clinically aggressive and high risk tumors marked by ESE1/ELF3 and NF-kB activation.

Citation Format: Nicole Longoni, Domenico Albino, Gianluca Civenni, Sandra Pinton, Maurizia Mello-Grand, Paola Ostano, Gioacchino D’ Ambrosio, Fausto Sessa, George N. Thalmann, Manuela Sarti, Ramon Garcia-Escudero, Francisco Morris, Giovanna Chiorino, Carlo V. Catapano, Giuseppina M. Carbone. ESE1/ELF3 and constitutive activation of NF-kB in human prostate cancer: prognostic relevance and rationale for context-dependent therapeutic strategies. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3118. doi:10.1158/1538-7445.AM2013-3118

Abstract 3307: Transcriptional silencing of c-Myc by promoter-directed siRNA efficiently target prostate cancer stem cells

Prostate cancer is the most frequent epithelial cancer in elderly men in Western countries. Depending on the stage, prostate cancer treatment requires surgery, hormone therapy, radio- and chemo-therapy. c-MYC is a transcription factor activated by mitogenic signaling pathways and playing a central function in stem cell biology. Over-activity of c-Myc plays a central role in tumorigenesis by affecting cell proliferation, metabolic adaptation and survival. Amplification of c-MYC is one of the most common genetic alterations occurring in cancer genomes. c-Myc expression is significantly elevated in invasive prostate adenocarcinomas compared to benign prostatic hyperplasia and normal prostate tissue. Particularly, c-Myc is highly expressed in prostate cancer cells having the CD44+/CD24- phenotype, which is described as a hallmark of cancer progenitor/stem cells (CSCs). Importantly, several studies link therapy resistance and disease progression to the CSC subpopulation within the highly heterogeneous cellular composition of the tumor. CSCs are likely the tumor initiating population that produces metastasis and disease recurrence. These lines of evidence suggest a central role of c-Myc in the maintenance of CSC compartment in human tumors and justify c-Myc as a therapeutic target.

Previously, we showed that the c-Myc gene could be silenced with small interfering RNAs (siRNA) targeting its promoter. Interestingly, single transfection with myc targeting siRNA (myc-siRNA) induced long lasting effects on cell proliferation and clonogenicity, indicative of a persistent loss of proliferative and clonogenic potential. In this study, we investigated the effects of transcriptional silencing of c-Myc on the CSC subpopulation in human prostate cancer cell lines in vitro and in vivo. We found that treatment with myc-siRNA significantly reduced the fraction of CSCs defined by expression of stem cell surface markers CD44 and CD24, in vitro sphere forming ability and self-renewal. Furthermore, combined analysis of senescence and cell surface markers showed that senescence occurred prevalently in the CD44+/CD24- cell subpopulation leading to its depletion, and reduced self renewal capability, in vivo tumorigenicity and metastatic potential. Moreover, repeated intraperitoneal administration of myc-siRNA over a 4-week period reduced tumor growth in a xenogeneic prostate cancer model. These results are consistent with the role of c-Myc in the maintenance of the CSC subpopulation in human prostate tumors and suggest that c-Myc downregulation induces an irreversible loss of clonogenic and tumor-initiating capability linked to the induction of cell senescence in CSCs. Our findings show also that an RNAi-based transcriptional therapy directed to genes directly involved in the maintenance of the cancer stem cells could be an efficient approach to block progression and relapse of prostate cancer.

Citation Format: Gianluca Civenni, Anastasia Malek, Domenico Albino, Manuela Sarti, Sandra Pinton, Stefano Di Marco, Giuseppina M. Carbone, Carlo V. Catapano. Transcriptional silencing of c-Myc by promoter-directed siRNA efficiently target prostate cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3307. doi:10.1158/1538-7445.AM2013-3307

Transcriptional and Non-Transcriptional Functions of PPARβ/δ in Non-Small Cell Lung Cancer

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a nuclear receptor involved in regulation of lipid and glucose metabolism, wound healing and inflammation. PPARβ/δ has been associated also with cancer. Here we investigated the expression of PPARβ/δ and components of the prostaglandin biosynthetic pathway in non-small cell lung cancer (NSCLC). We found increased expression of PPARβ/δ, Cox-2, cPLA₂, PGES and VEGF in human NSCLC compared to normal lung. In NSCLC cell lines PPARβ/δ activation increased proliferation and survival, while PPARβ/δ knock-down reduced viability and increased apoptosis. PPARβ/δ agonists induced Cox-2 and VEGF transcription, suggesting the existence of feed-forward loops promoting cell survival, inflammation and angiogenesis. These effects were seen only in high PPARβ/δ expressing cells, while low expressing cells were less or not affected. The effects were also abolished by PPARβ/δ knock-down or incubation with a PPARβ/δ antagonist. Induction of VEGF was due to both binding of PPARβ/δ to the VEGF promoter and PI3K activation through a non-genomic mechanism. We found that PPARβ/δ interacted with the PI3K regulatory subunit p85α leading to PI3K activation and Akt phosphorylation. Collectively, these data indicate that PPARβ/δ might be a central element in lung carcinogenesis controlling multiple pathways and representing a potential target for NSCLC treatment.

Active-targeted nanotherapy strategies for prostate cancer

Castration-resistant prostate cancer remains incurable and a major cause of mortality worldwide. The absence of effective therapeutic approaches for advanced prostate cancer has led to an intensive search for novel treatments. Emerging nanomedical approaches have shown promising results, in vitro and in vivo, in improving drug distribution and bioavailability, tumor penetration and in limiting toxicity. Nanoscaled carriers bearing finely controlled size and surface properties such as liposomes, dendrimers and nanoparticles have been developed for successful passive and active tumortargeting. Enhanced pharmacokinetics of nanotherapeutics, through improved target delivery and prolonged tissue halflife provides optimal drug delivery that is tumor-specific. Tumor-targeting may be improved through ligand directed delivery systems binding to tumor-specific surface receptors improving cellular uptake through receptor-mediated endocytosis. Recently published data have provided pre-clinical evidence showing the potential of active-targeted nanotherapeutics in prostate cancer therapy; unfortunately, only a few of these therapies have translated into early phase clinical trials development. Hence, progress of active-targeted nanotherapy improving efficiency of site-specific drug delivery is a critical challenge in future clinical treatment of prostate cancer. Exploring specific prostate cell-surface antigens or receptor overexpression may elaborate promising strategies for future therapeutic design. This review presents an overview of some new strategies for prostate cancer active-targeting nanotherapeutics.

Modulation of the activity of Sp transcription factors by mithramycin analogues as a new strategy for treatment of metastatic prostate cancer

Deregulated activity of transcription factors (TFs) of the Sp/KLF family, like Sp1, Sp3 and Sp4, and consequent over-expression of Sp-regulated genes occur frequently in human cancers. This provides the rationale for development of inhibitors of Sp TFs as cancer therapeutics. Mithramycin A (MTM-A) is a natural polyketide that binds GC-rich DNA sequences, inhibits activity of Sp TFs and exhibits potent antitumor activity in experimental systems. However, clinical use of MTM-A is limited by the severe toxicity of the compound. Here, we studied two MTM-A analogues, which had been generated by genetically engineering of the MTM-A biosynthetic pathway, and evaluated their activity in human prostate cancer in cell cultures and mouse models. The compounds, named MTM-SDK and MTM-SK, were highly effective in vitro inhibiting proliferation of prostate cancer cells and transcription of Sp-regulated genes by blocking binding of Sp proteins to the gene promoters When administered to mice, both compounds were well tolerated with maximum tolerated doses of MTM-SDK and MTM-SK, respectively, 4- and 32- fold higher than MTM-A. After systemic administration, both compounds were cleared rapidly from the bloodstream but maintained plasma levels well above the active concentrations required in vitro for inhibition of Sp TF activity and cell proliferation. Consistently, MTM-SDK and MTM-SK inhibited transcription of Sp-regulated genes in prostate tumor xenografts and exhibited potent antitumor activity in subcutaneous and metastatic tumor xenograft models with no or minimal toxicity. Taken together, these data indicate that MTM-SDK and MTM-SK possess significantly improved pharmacological and toxicological properties compared to MTM-A and represent promising drugs for treatment of advanced prostate cancer.

ESE3/EHF controls epithelial cell differentiation and its loss leads to prostate tumors with mesenchymal and stem-like features

Cancer stem cells (CSC) play a significant role in tumor progression, disease recurrence, and treatment failure. Here, we show that the endogenously expressed ETS transcription factor ESE3/EHF controls prostate epithelial cell differentiation and stem-like potential. We found that loss of ESE3/EHF induced epithelial-to-mesenchymal transition (EMT), stem-like features, and tumor-initiating and metastatic properties in prostate epithelial cells, and reexpression of ESE3/EHF inhibited the stem-like properties and tumorigenic potential of prostate cancer cells. Mechanistically, ESE3/EHF repressed the expression of key EMT and CSC genes, including TWIST1, ZEB2, BMI1, and POU5F1. Analysis of human tissue microarrays showed that reduced ESE3/EHF expression is an early event in tumorigenesis, frequently occurring independently of other ETS gene alterations. Additional analyses linked loss of ESE3/EHF expression to a distinct group of prostate tumors with distinctive molecular and biologic characteristics, including increased expression of EMT and CSC genes. Low ESE3/EHF expression was also associated with increased biochemical recurrence of prostate cancer and reduced overall survival after prostatectomy. Collectively, our findings define a key role for ESE3/EHF in the development of a subset of prostate tumors and highlight the clinical importance of identifying molecularly defined tumor subgroups.

Abstract B24: Loss of expression of the endogenous ETS factor ESE3/EHF is associated with a distinct tumor subtype with stem-like and basal cell features

Gene fusions leading to ectopic expression of ETS transcription factors are frequent in prostate tumors. However, the impact of endogenously expressed ETS factors on prostate tumorigenesis has not been deeply investigated. A comprehensive analysis of the ETS transcriptional network in normal and prostate tumor samples revealed frequent deregulation of multiple ETS factors, including endogenously expressed ETS like ESE3/EHF. We found that ETS gene expression patterns could be used to classify prostate tumors in subgroups characterized by partially distinct transcriptional and biological features. To further explore this concept we analyzed in greater details the properties of the group of ETS fusion negative tumors characterized by exclusive loss of ESE3/EHF expression without other ETS gene alterations (ESE3low tumors). ESE3low tumors represented approximately 25% of all tumors in multiple patient cohorts. Loss of ESE3/EHF expression determined by IHC on tissue microarray (TMAs) was an early event occurring at the level of HGPINs and tumors. Furthermore, reduced or absent ESE3/EHF stain in TMAs was associated with significantly increased biochemical relapse and reduced 10-year survival following prostatectomy for primary prostate cancer, independently of ERG status. Consistent with a role in tumor initiation and progression, ESE3/EHF knockdown in immortalized prostate epithelial cells induced epithelial-to-mesenchymal transition (EMT), in vitro stem-like properties and in vivo tumour-initiating and metastatic capability. Conversely, re-expression of ESE3/EHF in prostate cancer cells reduced stem-like potential and tumorigenicity. Analysis of gene expression profiling (GEP) data from three independent studies showed that the ESE3low tumours shared unique characteristics and displayed transcriptional features strikingly similar to transformed ESE3/EHF-knockdown prostate epithelial cells. Functional annotation and gene set enrichment analysis (GSEA) showed that ESE3low tumors were enriched of EMT and stem cell features. Furthermore, GSEA and unsupervised clustering indicated that ESE3low tumors retained prevalently expression of basal cell markers over luminal markers and displayed significant attenuation of androgen-induced genes compared to all other tumors. Interestingly, most of the ERG expressing tumors displayed opposite characteristics with expression of luminal markers. MicroRNA and lincRNA expression profiling also showed distinctive patterns between ESE3low tumors and the other tumors, while confirming the similarity with ESE3/EHF-knockdown cells. Collectively, these findings support a direct role of loss of ESE3/EHF expression in the pathogenesis of a subset of prostate tumors. Moreover, these data imply that distinct tumor subtypes can be indentified based on the expression of specific molecular marker that could reflect intrinsic differences in tumour biology and clinical evolution.

Citation Format: Maurizia Mello-Grand, Manuela Sarti, Gioacchino D'Ambrosio, Fausto Sessa, George Thalmann, Giovanna Chiorino, Carlo V. Catapano, Giuseppina MR Carbone, Domenico Albino, Vijay Kumar Singh, Gianluca Civenni, Nicole Longoni, Chiara Ghimenti, Paola Ostano, Sandra Pinton. Loss of expression of the endogenous ETS factor ESE3/EHF is associated with a distinct tumor subtype with stem-like and basal cell features [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B24.

Abstract B25: The ETS transcription factor ESE1 promotes activation of the NFKB pathway in prostate tumors

ETS transcription factors are important elements in the pathogenesis of prostate cancer. Here, we report that the ETS factor ESE1, which is expressed in normal prostate epithelial cells, is frequently upregulated in prostate tumors and functionally linked to activation of the NFkB pathway and inflammation. Immunohistochemistry and QRT-PCR in normal prostate and primary prostate tumor samples showed increased expression of ESE1 in about 35% of tumors. Over-expression of ESE1 was observed both in the presence and absence of ERG over-expression, indicating that activation of ESE1 could have an independent role in a subset of prostate tumors. Furthermore, elevated levels of ESE1 were significantly associated with higher rates of biochemical relapses in patients with primary tumors treated with radical prostatectomy (Log Rank (Mantel-Cox)=0.018). Overexpression of ESE1 in prostate cancer cells, like LNCaP and 22RV1, promoted a more aggressive phenotype with increased growth in soft-agar, resistance to anoikis and cell migration. When injected in nude mice, ESE1 over-expressing prostate cancer cells exhibited greater ability to form lung metastasis compared to control cells. ESE1 affected transcription of many genes and ChIP showed binding of ESE1 to ETS binding sites in the promoter of key genes involved in cell adhesion, metastasis and inflammation. Relevantly, we observed that mRNA and protein level of the NFkB subunit NFKB1 (p50) was increased in stable ESE1 expressing cells. Analysis of NFKB1 promoter revealed the presence of a previously unknown ETS binding site and ChIP demonstrated binding of ESE1 to this site, consistent with transcriptional activation of the gene by ESE1. Immunofluorescence microscopy showed a marked intranuclear localization of the NFkB p50/p65 complex, indicating that ESE1 promoted also NFkB activation. Consistently, the activity of the NFkB-responsive luciferase reporter was increased in ESE1 expressing cells compared to control cells. Furthermore, we found that the pro-inflammatory cytokine IL-1beta increased ESE1 mRNA and protein level in LNCaP cells while promoting intranuclear localization of the NFkB complex. This was associated with the induction of anoikis resistance and cell migration. All these effects were rescued by siRNA mediated knockdown of ESE1 indicating that ESE1 had a key role in mediating the effects of IL-1beta in these cells. We propose that the production of pro-inflammatory cytokines like IL-1beta within the tumor microenvironment results in the upregulation of ESE1 and establishment of a feed-forward loop leading to the constitutive activation of the NFkB linked to the ability of ESE1 to induce p50 transcription and NFkB nuclear translocation. These data show an important oncogenic role of ESE1 in prostate tumors and reveal a previously unidentified link between this ETS factor and the NFkB pathway.

Citation Format: Nicole Longoni, Maurizia Mello-Grand, Manuela Sarti, Sandra Pinton, Cecilia Dallavalle, Giovanna Chiorino, Carlo V. Catapano, Giuseppina M. Carbone. The ETS transcription factor ESE1 promotes activation of the NFKB pathway in prostate tumors [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B25.

Abstract C21: LincRNA expression data analysis identifies prostate tumor subtypes with distinct biological processes

Prostate cancer (PCa) shows tremendous heterogeneity which makes it difficult to identify patients with an increased risk of disease recurrence. A better understanding of the biological mechanism of prostate cancer formation and progression is crucial for the discovery of new markers for this disease. In recent years it has become apparent that different non-coding RNAs are also implicated in prostate cancer. Several microRNAs are now associated with progression and classification of prostate cancer and other malignancies. The role played in progression and differentiation of distinct PCa subtypes by a recently discovered class of non-coding RNAs, called large intergenic non-coding RNAs (lincRNAs), has remained unexplored. LincRNAs are believed to have major consequences on gene expression patterns through epigenetic mechanisms. Thousands of lincRNAs have been identified in human tissues, but only few have been functionally characterized. To assess the role of lincRNAs in PCa, we analysed the expression pattern of nearly 28000 Entrez genes and 7500 unique lincRNAs in 56 primary PCas and 5 normal prostate tissues, using Agilent 8x60k arrays. Unsupervised clustering over 1610 lincRNAs, selected after filtering out non informative probes, classified 61 samples into 5 distinct classes. Anova analysis was done to identify genes specifically over or under expressed in each cluster and was followed by functional annotation analysis. Normal samples were separated into a cluster characterized by the down regulation of genes involved in chemotaxis and intracellular signaling cascade. The four tumor clusters showed up regulation of distinct biological processes, like cell cycle, chromatin organization and immune response, together with deregulation of MAP-kinase signaling through EGFR and members of the RAS family oncogene. These results show that sample classification based on lincRNA profiling is able to separate tumors into subgroups with distinct biological processes.

Citation Format: Maurizia Mello-Grand, Vijay K. Singh, Chiara Ghimenti, Maria Scatolini, Nicole Longoni, Laura Curti, Andrea Zitella, Paolo Gontero, Carlo V. Catapano, Giuseppina M. Carbone, Giovanna Chiorino. LincRNA expression data analysis identifies prostate tumor subtypes with distinct biological processes [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C21.

PAMAM dendrimers for siRNA delivery: computational and experimental insights

Short double-stranded RNAs, which are known as short interfering RNA (siRNA), can be used to specifically down-regulate the expression of the targeted gene in a process known as RNA interference (RNAi). However, the success of gene silencing applications based on the use of synthetic siRNA critically depends on efficient intracellular delivery. Polycationic branched macromolecules such as poly(amidoamine) (PAMAM) dendrimers show a strong binding affinity for RNA molecules and, hence, can provide an effective, reproducible, and relatively nontoxic method for transferring siRNAs into animal cells. Notwithstanding these perspectives, relatively few attempts have been made so far along these lines to study in detail the molecular mechanisms underlying the complexation process between PAMAMs and siRNAs. In this work we combine molecular simulation and experimental approaches to study the molecular requirements of the interaction of RNA-based therapeutics and PAMAM dendrimers of different generations. The dendrimers and their siRNA complexes were structurally characterized, and the free energy of binding between each dendrimer and a model siRNA was quantified by using the well-known MM/PBSA approach. DOSY NMR experiments confirmed the structural in silico prediction and yielded further information on both the complex structure and stoichiometry at low N/P ratio values. siRNA/PAMAM complex formation was monitored at different N/P ratios using gel retardation assays, and a simple model was proposed, which related the amount of siRNA complexed to the entropy variation upon complex formation obtained from the computer simulations.

Small RNA-directed transcriptional control: new insights into mechanisms and therapeutic applications

The discovery of RNA interference (RNAi) has opened new avenues in biology and medicine. In addition to post-transcriptional gene silencing, new findings are expanding the range of action of small duplex RNAs and broadening the spectrum of the potential applications of RNAi-based therapeutics. In recent years a complex and heterogeneous network of non-protein coding RNAs (ncRNAs) with potential regulatory functions has come into the spotlight providing an unexpected perspective on the mechanisms of transcriptional and epigenetic control of gene expression in human cells. The spread and complexity of these RNA-based transcriptional regulatory networks are still to be explored. However, they are likely to be important mechanisms controlling gene expression in human cells. As we will learn more about these processes, endogenous small RNAs and ncRNAs participating in these transcriptional regulatory networks might become valuable targets to modulate expression of genes involved in human diseases. Thus, understanding these basic processes of gene regulation might be translated in the near future into innovative therapeutic strategies to treat human diseases.

ETS transcription factors control transcription of EZH2 and epigenetic silencing of the tumor suppressor gene Nkx3.1 in prostate cancer

Background

ETS transcription factors regulate important signaling pathways involved in cell differentiation and development in many tissues and have emerged as important players in prostate cancer. However, the biological impact of ETS factors in prostate tumorigenesis is still debated.

Methodology/Principal Findings

We performed an analysis of the ETS gene family using microarray data and real-time PCR in normal and tumor tissues along with functional studies in normal and cancer cell lines to understand the impact in prostate tumorigenesis and identify key targets of these transcription factors. We found frequent dysregulation of ETS genes with oncogenic (i.e., ERG and ESE1) and tumor suppressor (i.e., ESE3) properties in prostate tumors compared to normal prostate. Tumor subgroups (i.e., ERG^high, ESE1^high, ESE3^low and NoETS tumors) were identified on the basis of their ETS expression status and showed distinct transcriptional and biological features. ERG^high and ESE3^low tumors had the most robust gene signatures with both distinct and overlapping features. Integrating genomic data with functional studies in multiple cell lines, we demonstrated that ERG and ESE3 controlled in opposite direction transcription of the Polycomb Group protein EZH2, a key gene in development, differentiation, stem cell biology and tumorigenesis. We further demonstrated that the prostate-specific tumor suppressor gene Nkx3.1 was controlled by ERG and ESE3 both directly and through induction of EZH2.

Conclusions/Significance

These findings provide new insights into the role of the ETS transcriptional network in prostate tumorigenesis and uncover previously unrecognized links between aberrant expression of ETS factors, deregulation of epigenetic effectors and silencing of tumor suppressor genes. The link between aberrant ETS activity and epigenetic gene silencing may be relevant for the clinical management of prostate cancer and design of new therapeutic strategies.

Inhibition of Sp1-dependent transcription and antitumor activity of the new aureolic acid analogues mithramycin SDK and SK in human ovarian cancer xenografts

OBJECTIVE

Increased activity of Sp family of transcription factors is a frequent and critical event in cancer development and progression. Genes governing tumor growth, invasion and angiogenesis are regulated by Sp factors, like Sp1, Sp3 or Sp4, and are frequently over-expressed in tumors. Targeting Sp factors has been explored as a therapeutic approach. Mithramycin (MTM) is a natural antibiotic that binds DNA and inhibit Sp1-dependent transcription. New analogues, named MTM-SDK and MTM-SK, were recently obtained by genetic engineering of the MTM biosynthetic pathway and have demonstrated improved transcriptional and antiproliferative activity in ovarian cancer cell lines in vitro. In the present study we evaluated the activity of the new compounds in human ovarian cancer xenografts.

METHODS

Expression of Sp1 and target proteins in ovarian cancer specimens and tumor xenografts was assessed by immunohistochemistry. Drug-induced silencing of Sp1-regulated genes in cells and tumor xenograft samples was assessed by quantitative RT-PCR. Toxicity and antitumor activity of the compounds were investigated in healthy and tumor-bearing immunocompromised mice, respectively.

RESULTS

Expression of Sp1 was frequently increased in human epithelial ovarian cancers. MTM-SDK and MTM-SK acted as potent inhibitors of Sp1-dependent transcription both in vitro and in tumor xenografts. Both compounds were well tolerated even after prolonged administration and delayed growth of ovarian tumor xenografts. MTM-SDK was particularly effective against orthotopic tumors leading to a significant increase of survival and delay of tumor progression.

CONCLUSIONS

MTM-SDK and MTM-SK show relevant activity in vivo and represent interesting candidates for treatment of ovarian cancers.

Abstract 4965: The epithelial-specific ETS transcription factor ESE1 links inflammation with prostate cancer transformation and progression

Altered expression of ETS transcription factors by chromosomal translocation is a frequent event in prostate cancers. However, deregulated expression of other oncogenic ETS factors can be important for the pathogenesis of this disease. By analyzing the expression of multiple ETS genes in prostate cancer and normal prostate by genomic profiling and quantitative real-time PCR we found that the epithelial-specific ETS factor ESE1 was highly expressed (>4 fold) in 44% of prostate tumors compared to normal prostate. ESE1 has been previously shown to be induced by pro-inflammatory stimuli and to regulate the expression of genes involved in inflammation. Treatment of immortalized prostate epithelial cells (LHS) and prostate cancer cells 22RV1 with the pro-inflammatory cytokine IL-1beta induced ESE1 at RNA and protein levels. Concomitantly we observed that cells acquired ability to grow in poly-hema coated plates and an EMT phenotype. To define the role of ESE1 in prostate cancer progression we established 22RV1 prostate cancer cells stably expressing ESE1 (22RV1-ESE1). ESE1 expressing cells were capable to grow in poly-hema coated plates and when injected in nude mice formed larger subcutaneous tumors compared to control cells. Global gene expression profiles indicate robust changes with many genes differentially expressed in 22RV1-ESE1 cells compared to control cells, including key genes involved in cell invasion and metastasis such as COX2 and MMP-10. Consistently, 22RV1-ESE1 cells had greater ability to migrate compared to parental cells in Boyden Chamber and wound-healing assays. Furthermore, when implanted in mice via tail vein injection, 22RV1-ESE1 cells displayed greater ability to form lung metastasis compared to control cells. These results suggest that ESE1 contribute to the acquisition of transforming properties such as the ability to invade and metastasize. Induction of ESE1 during chronic inflammation could be an essential step for prostate cancer initiation and may co-operate with other ETS alterations for prostate cancer progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4965.

Abstract 196: UHRF1 is upregulated in prostate cancer and induces epigenetic silencing of tumor suppressor genes

Cancer of the prostate is the most common cancer and a leading cause of cancer death in Europe and North America. At the present there is a need to understand the mechanisms involved in the pathogenesis of this disease and discover alternative therapeutic targets. UHRF1 (ubiquitin-like protein containing PHD and RING domains 1), a nuclear RING finger protein, has been previously reported to acts as a dominant negative effectors of cell growth. UHRF1 is involved in epigenetic mechanisms by virtue of its interaction with DNMTs and HMTs. In this study, analysis of gene expression profiles of prostate tumors and normal prostate showed that UHRF1 is frequently over-expressed in tumors compared to normal tissues. UHRF1 expression was very low in immortalized prostate epithelial cells (LH) while it was higher in the Ras transformed counterpart LHSR cells. Furthermore, we observed low level of UHRF1 in the androgen-dependent prostate cancer cell lines LNCaP and 22Rv1, while higher levels were present in the androgen-independent cell lines PC3 and DU145. These data suggested that over-expression of UHRF1 is associated with malignant transformation and prostate cancer progression. To understand the role of UHRF1 we performed knockdown experiments with UHRF1 specific siRNA. Transient transfection in PC3 cells reduced UHRF1 mRNA and protein level. UHRF1 knock-down resulted in reversion of the transformed phenotype with significant inhibition of clonogenic growth in anchorage dependent and independent condition. Reversion of the transformed phenotype occurred concomitantly with restoration of the expression of several tumor suppressor genes relevant for prostate differentiation, proliferation and epithelial-mesenchymal transition such as CDH1 and RARB2. Moreover, chromatin immunoprecipitation showed binding of UHRF1 to these gene promoter and UHRF1 knockdown resulted in significant reduction of repressive histone marks on gene promoters. These studies suggest that deregulated UHRF1 expression results in epigenetic silencing of relevant tumor suppressor genes, contributing to prostate cancer progression. Targeting UHRF1 may result in re-expression of tumor suppressor genes and thus may be a valid strategy for therapeutic intervention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 196.

Abstract 5019: Loss of the ETS transcription factor ESE3 induces epithelial-mesenchimal transition and generates cells with stem cell-like properties

ETS transcription factors have emerged as important elements in the pathogenesis of prostate cancer. Most ETS factors promote cell proliferation, survival and transformation, while few others act as tumor suppressors. We have recently reported that the epithelial-specific ETS factor ESE3 is frequently down-regulated in prostate cancer, affects negatively cell proliferation and survival, and acts as tumor suppressor in prostate epithelial cells. ESE3 signatures extracted from prostate cancer clinical samples indicated a broad dedifferentiation program. Thus, we hypothesized that ESE3 maintains the differentiation state of prostate epithelial cells and that its loss leads to cell transformation. In this study, we report that stable knock-down of ESE3 in immortalized human prostate epithelial LHS cells (LHS-ESE3kd) resulted in the induction of epithelial-mesenchymal transition (EMT) with the acquisition of a fibroblast-like appearance. Concomitantly, LHS-ESE3kd cells acquired also ability to grow in anchorage-independent conditions in soft-agar and to form prostatosheres in sphere-forming assays. Expression of various stem-cell markers was also increased in LHS-ESE3kd compared to LHS cells. In a panel of prostate cell lines the ability to form prostatospheres was inversely correlated with ESE3 expression level, providing further support to the idea that the gene is an important regulator of the stem cell compartment. Consistently, re-expression of ESE3 in DU145 cells, which do not express ESE3, induced morphological changes consistent with a mesenchymal-epithelial transition, reduced the ability of the cells to migrate and to form prostatospheres. Cancer stem cells are reportedly to be drug resistant and drugs like taxol can select for drug-resistant cells with stem cell properties. We observed that resistance to taxol was inversely correlated with ESE3 expression in prostate cell lines. Furthermore, treatment of LHS-ESE3kd cells with taxol increased sphere formation, consistent with an enlargement of the stem-cell compartment by the ESE3 knock-down and increased selection by the drug. Collectively, these findings implicate that ESE3 controls the differentiation state and stem cell properties of prostate epithelial cells and that loss of ESE3 can be an important event in prostate tumorigenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5019.

Abstract 3145: Non-coding promoter-associated RNAs (PARs) orchestrate the epigenetic control of CDH1 transcription in cancer cells

DNA in eukaryotic cells is wrapped around histones to form chromatin fibers. Chromatin can assume different conformations that dictate its biological activity. The equilibrium between distinct chromatin states is achieved via a cascade of epigenetic events involving DNA and histone modifications. However, the underlying mechanisms determining the timing and selectivity of these epigenetic events are not fully understood. Alterations in epigenetic patterns are common in cancer leading to the aberrant silencing of tumor suppressor genes. The CDH1 gene encodes the epithelial cell adhesion molecule E-cadherin and is frequently silenced in epithelial tumors. CDH1 silencing is associated with cell transformation, tumor invasiveness and metastatic dissemination along with epithelial-mesenchymal transition and acquisition of stem cell properties. Recently, non-protein coding RNAs (ncRNAs) and components of the RNA interference machinery have been proposed as important elements in epigenetic mechanisms that might assist in targeting epigenetic effectors to specific genomic loci. In this study, we investigated the role of non-coding promoter-associated RNA (PARs) in the transcriptional regulation of the CDH1 gene. PARs with both sense and antisense orientation relative to the protein-coding RNA were found in the CDH1 gene using strand-specific RT-PCR and 5’RACE. Sense and antisense PARs were positively and negatively correlated, respectively, to the level of CDH1 RNA in different cell lines, suggesting a functional link between coding and non-coding RNAs. RNA immunoprecipitation showed binding of the Argonaute protein Ago1 to the sense PAR in PC3 cells, in which the CDH1 gene was silenced. Knock-down of Ago1 led to re-expression of CDH1 along with increased histone H3 acetylation and decreased histone H3K9 methylation in the CDH1 promoter. Similar changes in the histone code and re-expression of CDH1 were induced by knocking down the H3K9 histone methyltransferase SUV39H1 and HDAC1. Moreover, Ago1 knock-down reduced binding of both SUV39H1 and HDAC1 to the CDH1 promoter, indicating a critical role of Ago1 in establishing their association with the promoter. Consistent with a role of the PARs in CDH1 transcriptional control, targeting the sense PAR with small interfering RNAs induced chromatin remodeling and CDH1 re-expression, supporting the hypothesis that PARs can direct epigenetic effectors to gene promoters through their interaction with Ago1. These findings suggest the existence of endogenous ncRNA-based mechanisms of transcriptional control that cooperate with and complement DNA and protein based epigenetic pathways in human cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3145.

A sensitive polymerase chain reaction-based method for detection and quantification of metastasis in human xenograft mouse models

Tumor cell dissemination to distant organs accounts for the majority of cancer related deaths. Analysis of the stepwise process of metastasis formation and progression might provide novel therapeutic strategies for the treatment of disseminated cancer. However, studies with both biological and therapeutic endpoints would require highly sensitive and specific methods for precise quantification of the metastatic tumor burden in vivo. We have developed a quantitative real-time PCR-based assay for the detection and quantification of human tumor cells disseminated in mouse organs. The method relies on the parallel amplification of unique, species-specific, conserved and non-transcribed sequences in the mouse and human genomes. We tested the method in xenograft models to assess the metastatic potential of various cancer cell lines, the impact of injection modality and cell type on organ distribution, and the early stages of metastasis implantation and progression. With this method, we observed clear quantitative differences among colon cancer cell lines in terms of metastasis formation in the lung, consistent with the different in vitro growth properties. The mode of cell implantation and cell intrinsic properties strongly affected the metastatic pattern of prostate and breast cancer cell lines in mouse organs. The qPCR assay accurately determined the malignant cell burden even at early stages of metastasis progression in the lung. We describe a very sensitive assay for the highly reproducible detection and accurate quantification of human metastatic cells in mouse tissues and demonstrate its broad applicability to various experimental settings.

Impact of genomic methylation on radiation sensitivity of colorectal carcinoma

PURPOSE

To investigate the influence of demethylation with 5-aza-cytidine (AZA) on radiation sensitivity and to define the intrinsic radiation sensitivity of methylation deficient colorectal carcinoma cells.

METHODS AND MATERIALS

Radiation sensitizing effects of AZA were investigated in four colorectal carcinoma cell lines (HCT116, SW480, L174 T, Co115), defining influence of AZA on proliferation, clonogenic survival, and cell cycling with or without ionizing radiation. The methylation status for cancer or DNA damage response-related genes silenced by promoter methylation was determined. The effect of deletion of the potential target genes (DNMT1, DNMT3b, and double mutants) on radiation sensitivity was analyzed.

RESULTS

AZA showed radiation sensitizing properties at >or=1 micromol/l, a concentration that does not interfere with the cell cycle by itself, in all four tested cell lines with a sensitivity-enhancing ratio (SER) of 1.6 to 2.1 (confidence interval [CI] 0.9-3.3). AZA successfully demethylated promoters of p16 and hMLH1, genes associated with ionizing radiation response. Prolonged exposure to low-dose AZA resulted in sustained radiosensitivity if associated with persistent genomic hypomethylation after recovery from AZA. Compared with maternal HCT116 cells, DNMT3b-defcient deficient cells were more sensitive to radiation with a SER of 2.0 (CI 0.9-2.1; p = 0.03), and DNMT3b/DNMT1-/- double-deficient cells showed a SER of 1.6 (CI 0.5-2.7; p = 0.09).

CONCLUSIONS

AZA-induced genomic hypomethylation results in enhanced radiation sensitivity in colorectal carcinoma. The mediators leading to sensitization remain unknown. Defining the specific factors associated with radiation sensitization after genomic demethylation may open the way to better targeting for the purpose of radiation sensitization.

Mechanisms of triplex DNA-mediated inhibition of transcription initiation in cells

Triplex-forming oligonucleotides (TFOs) are attractive tools to control gene expression at the transcriptional level. This anti-gene approach has proven to be successful in various experimental settings. However, the mechanisms leading to transcriptional repression in cells have not been fully investigated yet. Here, we examined the consequence of triplex DNA formation on the binding of transcriptional activators, co-activators and RNA Polymerase II to the ets2 gene promoter using chromatin immunoprecipitation assays. The triplex target sequence was located approximately 40-bp upstream of the transcription start site (TSS) and overlapped an Sp1 binding site relevant for ets2 transcription. We found that the ets2-TFO prevented binding of Sp1, TAF(II)130 and TAF(II)250 to the ets2 promoter, while binding of RNA polymerase II and TBP were not affected. The effects were both sequence and target specific, since the TFO had no effect on the c-myc promoter and a mutated ets2 promoter construct. Thus, triplex DNA formation near a TSS leads to formation of a non-functional pre-initiation complex (PIC) by blocking binding of transcriptional activators and co-activator molecules. This is the first direct demonstration of interference with PIC assembly at the TSS by oligonucleotide-triplex DNA formation in cells.