Inducible FGFR-1 activation leads to irreversible prostate adenocarcinoma and an epithelial-to-mesenchymal transition.

Fibroblast Growth Factor Receptor-1 (FGFR1) is commonly overexpressed in advanced prostate cancer (PCa). To investigate causality, we utilized an inducible FGFR1 (iFGFR1) prostate mouse model. Activation of iFGFR1 with chemical inducers of dimerization (CID) led to highly synchronous, step-wise progression to adenocarcinoma that is linked to an epithelial-to-mesenchymal transition (EMT). iFGFR1 inactivation by CID withdrawal led to full reversion of prostatic intraepithelial neoplasia, whereas PCa lesions became iFGFR1-independent. Gene expression profiling at distinct stages of tumor progression revealed an increase in EMT-associated Sox9 and changes in the Wnt signaling pathway, including Fzd4, which was validated in human PCa. The iFGFR1 model clearly implicates FGFR1 in PCa progression and demonstrates how CID-inducible models can help evaluate candidate molecules in tumor progression and maintenance.

Histone lysine demethylase 4 family proteins maintain the transcriptional program and adrenergic cellular state of MYCN-amplified neuroblastoma.

Neuroblastoma with MYCN amplification (MNA) is a high-risk disease that has a poor survival rate. Neuroblastoma displays cellular heterogeneity, including more differentiated (adrenergic) and more primitive (mesenchymal) cellular states. Here, we demonstrate that MYCN oncoprotein promotes a cellular state switch in mesenchymal cells to an adrenergic state, accompanied by induction of histone lysine demethylase 4 family members (KDM4A-C) that act in concert to control the expression of MYCN and adrenergic core regulatory circulatory (CRC) transcription factors. Pharmacologic inhibition of KDM4 blocks expression of MYCN and the adrenergic CRC transcriptome with genome-wide induction of transcriptionally repressive H3K9me3, resulting in potent anticancer activity against neuroblastomas with MNA by inducing neuroblastic differentiation and apoptosis. Furthermore, a short-term KDM4 inhibition in combination with conventional, cytotoxic chemotherapy results in complete tumor responses of xenografts with MNA. Thus, KDM4 blockade may serve as a transformative strategy to target the adrenergic CRC dependencies in MNA neuroblastomas.

Regenerative protein thymosin beta-4 is a novel regulator of purinergic signaling.

By an unknown mechanism, ß-thymosins are extracellular modulators of angiogenesis, inflammation, wound healing, and development. We were interested in identifying ß-thymosin interactors and determining their importance in ß-thymosins signaling in human vein endothelial cells (HUVECs). We performed pulldown experiments with biotinylated thymosin ß-4 (Tß4) in comparison to neutravidin beads alone and used mass spectrometric analysis to identify differentially interacting proteins. By this method, we identified F1-F0 ATP synthase, a known target of antiangiogenic angiostatin. By surface plasmon resonance, we determined for Tß4 binding to the ß subunit of ATP synthase a K(D) of 12 nM. Blocking antibodies and antagonists (oligomycin, IC(50) ∼1.8 µM; piceatannol, IC(50) ∼1.05 µM; and angiostatin, IC(50) ∼2.9 µg/ml) of ATP synthase inhibited the Tß4-induced increase in cell surface ATP levels, as measured by luciferase assay, and the Tß4-induced increase in HUVEC migration, as measured by transwell migration assay. Silencing of the ATP-responsive purinergic receptor P2X4 with siRNA also blocked Tß4-induced HUVEC migration in a transwell assay. Furthermore, in silico we identified common amphiphilic α-helical structural similarities between ß-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis. In summary, we have identified an extracellular signaling pathway where Tß4 increases cell surface ATP levels via ATP synthase and have shown further that ATP-responsive P2X4 receptor is required for Tß4-induced HUVEC migration.

Therapeutically targeting oncogenic CRCs facilitates induced differentiation of NB by RA and the BET bromodomain inhibitor.

Retinoic acids (RAs) are the most successful therapeutics for cancer differentiation therapy used in high-risk neuroblastoma (NB) maintenance therapy but are limited in effectiveness. This study identifies a strategy for improving efficacy through disruption of cancer cell identity via BET inhibitors. Mutations that block development are theorized to cause NB through retention of immature cell identities contributing to oncogenesis. NB has two interchangeable cell identities, maintained by two different core transcriptional regulatory circuitries (CRCs): a therapy-resistant mesenchymal/stem cell state and a proliferative adrenergic cell state. MYCN amplification is a common mutation of high-risk NB and recently found to block differentiation by driving high expression of the adrenergic CRC transcription factor ASCL1. We investigated whether disruption of immature CRCs can promote RA-induced differentiation since only a subset of NB patients responds to RA. We found that silencing ASCL1, a critical member of the adrenergic CRC, or global disruption of CRCs with the BET inhibitor JQ1, suppresses gene expression of multiple CRC factors, improving RA-mediated differentiation. Further, JQ1 and RA synergistically decrease proliferation and induce differentiation in NB cell lines. Our findings support preclinical studies of RA and BET inhibitors as a combination therapy in treating NB.

XPO1 inhibition with selinexor synergizes with proteasome inhibition in neuroblastoma by targeting nuclear export of IkB.

Across many cancer types in adults, upregulation of the nuclear-to-cytoplasmic transport protein Exportin-1 (XPO1) correlates with poor outcome and responsiveness to selinexor, an FDA-approved XPO1 inhibitor. Similar data are emerging in childhood cancers, for which selinexor is being evaluated in early phase clinical studies. Using proteomic profiling of primary tumor material from patients with high-risk neuroblastoma, as well as gene expression profiling from independent cohorts, we have demonstrated that XPO1 overexpression correlates with poor patient prognosis. Neuroblastoma cell lines are also sensitive to selinexor in the low nanomolar range. Based on these findings and knowledge that bortezomib, a proteasome inhibitor, blocks degradation of XPO1 cargo proteins, we hypothesized that combination treatment with selinexor and bortezomib would synergistically inhibit neuroblastoma cellular proliferation. We observed that selinexor promoted nuclear retention of IkB and that bortezomib augmented the ability of selinexor to induce cell-cycle arrest and cell death by apoptosis. This synergy was abrogated through siRNA knockdown of IkB. The synergistic effect of combining selinexor and bortezomib in vitro provides rationale for further investigation of this combination treatment for patients with high-risk neuroblastoma.

Large 1p36 Deletions Affecting Arid1a Locus Facilitate Mycn-Driven Oncogenesis in Neuroblastoma.

Loss of heterozygosity (LOH) at 1p36 occurs in multiple cancers, including neuroblastoma (NBL). MYCN amplification and 1p36 deletions tightly correlate with markers of tumor aggressiveness in NBL. Although distal 1p36 losses associate with single-copy MYCN tumors, larger deletions correlate with MYCN amplification, indicating two tumor suppressor regions in 1p36, only one of which facilitates MYCN oncogenesis. To better define this region, we genome-edited the syntenic 1p36 locus in primary mouse neural crest cells (NCCs), a putative NBL cell of origin. In in vitro cell transformation assays, we show that Chd5 loss confers most of the MYCN-independent tumor suppressor effects of 1p36 LOH. In contrast, MYCN-driven tumorigenesis selects for NCCs with Arid1a deletions from a pool of NCCs with randomly sized 1p36 deletions, establishing Arid1a as the MYCN-associated tumor suppressor. Our findings reveal that Arid1a loss collaborates with oncogenic MYCN and better define the tumor suppressor functions of 1p36 LOH in NBL.

Bromodomain-Selective BET Inhibitors Are Potent Antitumor Agents against MYC-Driven Pediatric Cancer.

Inhibition of members of the bromodomain and extraterminal (BET) family of proteins has proven a valid strategy for cancer chemotherapy. All BET identified to date contain two bromodomains (BD; BD1 and BD2) that are necessary for recognition of acetylated lysine residues in the N-terminal regions of histones. Chemical matter that targets BET (BETi) also interact via these domains. Molecular and cellular data indicate that BD1 and BD2 have different biological roles depending upon their cellular context, with BD2 particularly associated with cancer. We have therefore pursued the development of BD2-selective molecules both as chemical probes and as potential leads for drug development. Here we report the structure-based generation of a novel series of tetrahydroquinoline analogs that exhibit >50-fold selectivity for BD2 versus BD1. This selective targeting resulted in engagement with BD-containing proteins in cells, resulting in modulation of MYC proteins and downstream targets. These compounds were potent cytotoxins toward numerous pediatric cancer cell lines and were minimally toxic to nontumorigenic cells. In addition, unlike the pan BETi (+)-JQ1, these BD2-selective inhibitors demonstrated no rebound expression effects. Finally, we report a pharmacokinetic-optimized, metabolically stable derivative that induced growth delay in a neuroblastoma xenograft model with minimal toxicity. We conclude that BD2-selective agents are valid candidates for antitumor drug design for pediatric malignancies driven by the MYC oncogene. SIGNIFICANCE: This study presents bromodomain-selective BET inhibitors that act as antitumor agents and demonstrates that these molecules have in vivo activity towards neuroblastoma, with essentially no toxicity.

Inducible dimerization of FGFR1: development of a mouse model to analyze progressive transformation of the mammary gland.

To develop an inducible and progressive model of mammary gland tumorigenesis, transgenic mice were generated with a mouse mammary tumor virus-long terminal repeat-driven, conditional, fibroblast growth factor (FGF)-independent FGF receptor (FGFR)1 (iFGFR1) that can be induced to dimerize with the drug AP20187. Treatment of transgenic mice with AP20187 resulted in iFGFR1 tyrosine phosphorylation, increased proliferation, activation of mitogen-activated protein kinase and Akt, and lateral budding. Lateral buds appeared as early as 3 d after AP20187 treatment and initially consisted of bilayered epithelial cells and displayed apical and basolateral polarity appeared after 13 d of AP20187 treatment. Invasive lesions characterized by multicell-layered lateral buds, decreased myoepithelium, increased vascular branching, and loss of cell polarity were observed after 2-4 wk of treatment. These data indicate that acute iFGFR1 signaling results in increased lateral budding of the mammary ductal epithelium, and that sustained activation induces alveolar hyperplasia and invasive lesions.

Inducible prostate intraepithelial neoplasia with reversible hyperplasia in conditional FGFR1-expressing mice.

Accurate determination of the contributions of oncogenes toward tumor progression requires their regulation. Herein, we created transgenic mice with prostate-specific expression of ligand-inducible FGFR1 or FGFR2, based on lipid-permeable dimerizing molecules, called chemical inducers of dimerization. Despite extensive homology and equivalent expression by both chimeric receptors in the ventral prostate gland, only FGFR1 triggers detectable nuclear translocation of Erk and progression to prostatic intraepithelial neoplasia (PIN). Induction of PIN grade I-II, indicated by multiple layers of atypical cells, is seen consistently by 12 weeks of chemical inducers of dimerization treatment. By 6 months, more extensive nuclear atypia, thickened "reactive" stroma, and basement membrane herniation occurs, corresponding to PIN IV. By timed removal of FGFR1 signaling, we show that induced hyperplasia is reversible until extensive intraductal vascularization occurs, but continued progression requires prolonged FGFR1 signaling. Additionally, by highlighting differences between the two receptors and creating the foundation for controlling FGFR1 signaling during prostate cancer progression, a model of early stage prostate cancer is established for developing targeted intervention directed toward the FGFR signaling axis.

Conditional activation of fibroblast growth factor receptor (FGFR) 1, but not FGFR2, in prostate cancer cells leads to increased osteopontin induction, extracellular signal-regulated kinase activation, and in vivo proliferation.

Changes in the fibroblast growth factor receptor (FGFR) axis are often associated with prostate cancer (CaP) progression. We have used chemically induced dimerization (CID) to elucidate the individual contributions of FGFR1 and FGFR2 to tumor etiology. Novel CaP cell lines stably expressing CID/AP20187-inducible FGFR1 (iFGFR1) and iFGFR2 were made using the tumorigenic transgenic adenocarcinoma of the murine prostate (TRAMP)-derived clone, TRAMP-C2N (C2N), to generate C2N.iFGFR1 or C2N.iFGFR2 cells. To test the effects of iFGFR activation on tumor growth, mice bearing s.c. C2N.iFGFR1- or C2N.iFGFR2-derived tumors were treated biweekly with CID. Activation of iFGFR1 led to rapid tumor growth as a result of increased proliferation. In contrast, expression of iFGFR2 inhibited tumor growth. Furthermore, we have ascertained that FGFR1 activation appears to be most important during the early stages of tumor development, but once established, tumors become rapidly CID independent. In these C2N-based lines, quantitative signaling differences were seen between the two receptors, with iFGFR1 leading to more robust extracellular signal-regulated kinase activation. Additionally, activation of iFGFR1, but not iFGFR2, led to strong up-regulation of osteopontin, a secreted glycoprotein involved in integrin activation and associated with CaP progression and metastasis. These studies support the hypothesis that observed changes in the FGFR axis in mammals during CaP progression are causally important.

Antagonizing Bcl-2 family members sensitizes neuroblastoma and Ewing's sarcoma to an inhibitor of glutamine metabolism.

Neuroblastomas (NBL) and Ewing's sarcomas (EWS) together cause 18% of all pediatric cancer deaths. Though there is growing interest in targeting the dysregulated metabolism of cancer as a therapeutic strategy, this approach has not been fully examined in NBL and EWS. In this study, we first tested a panel of metabolic inhibitors and identified the glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON) as the most potent chemotherapeutic across all NBL and EWS cell lines tested. Myc, a master regulator of metabolism, is commonly overexpressed in both of these pediatric malignancies and recent studies have established that Myc causes cancer cells to become "addicted" to glutamine. We found DON strongly inhibited tumor growth of multiple tumor lines in mouse xenograft models. In vitro, inhibition of caspases partially reversed the effects of DON in high Myc expressing cell lines, but not in low Myc expressing lines. We further showed that induction of apoptosis by DON in Myc-overexpressing cancers is via the pro-apoptotic factor Bax. To relieve inhibition of Bax, we tested DON in combination with the Bcl-2 family antagonist navitoclax (ABT-263). In vitro, this combination caused an increase in DON activity across the entire panel of cell lines tested, with synergistic effects in two of the N-Myc amplified neuroblastoma cell lines. Our study supports targeting glutamine metabolism to treat Myc overexpressing cancers, such as NBL and EWS, particularly in combination with Bcl-2 family antagonists.

A cell motility screen reveals role for MARCKS-related protein in adherens junction formation and tumorigenesis.

Invasion through the extracellular matrix (ECM) is important for wound healing, immunological responses and metastasis. We established an invasion-based cell motility screen using Boyden chambers overlaid with Matrigel to select for pro-invasive genes. By this method we identified antisense to MARCKS related protein (MRP), whose family member MARCKS is a target of miR-21, a microRNA involved in tumor growth, invasion and metastasis in multiple human cancers. We confirmed that targeted knockdown of MRP, in both EpRas mammary epithelial cells and PC3 prostate cancer cells, promoted in vitro cell migration that was blocked by trifluoperazine. Additionally, we observed increased immunofluoresence of E-cadherin, beta-catenin and APC at sites of cell-cell contact in EpRas cells with MRP knockdown suggesting formation of adherens junctions. By wound healing assay we observed that reduced MRP supported collective cell migration, a type of cell movement where adherens junctions are maintained. However, destabilized adherens junctions, like those seen in EpRas cells, are frequently important for oncogenic signaling. Consequently, knockdown of MRP in EpRas caused loss of tumorigenesis in vivo, and reduced Wnt3a induced TCF reporter signaling in vitro. Together our data suggest that reducing MRP expression promotes formation of adherens junctions in EpRas cells, allowing collective cell migration, but interferes with oncogenic beta-catenin signaling and tumorigenesis.

An inducible system for the study of FGF signalling in early amphibian development.

The use of a novel inducible FGF signalling system in the frog Xenopus laevis is reported. We show that the lipophilic, synthetic, dimerizing agent AP20187 is able to rapidly activate signalling through an ectopically expressed mutant form of FGFR1 (iFGFR1) in Xenopus embryos. iFGFR1 lacks an extracellular ligand binding domain and contains an AP20187 binding domain fused to the intracellular domain of mouse FGFR1. Induction of signalling by AP20187 is possible until at least early neurula stages, and we demonstrate that ectopically expressed iFGFR1 protein persists until late neurula stages. We show that activation of signalling through iFGFR1 can mimic a number of previously reported FGF activities, including mesoderm induction, repression of anterior development, and neural posteriorization. We show that competence to morphological posteriorization of the anteroposterior axis by FGF signalling only extends until about stage 10.5. We demonstrate that the competence of neural tissue to express the posterior markers Hoxa7 and Xcad3, in response to FGF signalling, is lost by the end of gastrula stages. We also show that activation of FGF signalling stimulates morphogenetic movements in neural tissue until at least the end of the gastrula stage.