High-throughput screens identify HSP90 inhibitors as potent therapeutics that target inter-related growth and survival pathways in advanced prostate cancer.

The development of new treatments for castrate resistant prostate cancer (CRPC) must address such challenges as intrinsic tumor heterogeneity and phenotypic plasticity. Combined PTEN/TP53 alterations represent a major genotype of CRPC (25-30%) and are associated with poor outcomes. Using tumor-derived, castration-resistant Pten/Tp53 null luminal prostate cells for comprehensive, high-throughput, mechanism-based screening, we identified several vulnerabilities among >1900 compounds, including inhibitors of: PI3K/AKT/mTOR, the proteasome, the cell cycle, heat shock proteins, DNA repair, NFκB, MAPK, and epigenetic modifiers. HSP90 inhibitors were one of the most active compound classes in the screen and have clinical potential for use in drug combinations to enhance efficacy and delay the development of resistance. To inform future design of rational drug combinations, we tested ganetespib, a potent second-generation HSP90 inhibitor, as a single agent in multiple CRPC genotypes and phenotypes. Ganetespib decreased growth of endogenous Pten/Tp53 null tumors, confirming therapeutic activity in situ. Fifteen human CRPC LuCaP PDX-derived organoid models were assayed for responses to 110 drugs, and HSP90 inhibitors (ganetespib and onalespib) were among the select group of drugs (<10%) that demonstrated broad activity (>75% of models) at high potency (IC50 <1 µM). Ganetespib inhibits multiple targets, including AR and PI3K pathways, which regulate mutually compensatory growth and survival signals in some forms of CRPC. Combined with castration, ganetespib displayed deeper PDX tumor regressions and delayed castration resistance relative to either monotherapy. In all, comprehensive data from near-patient models presents novel contexts for HSP90 inhibition in multiple CRPC genotypes and phenotypes, expands upon HSP90 inhibitors as simultaneous inhibitors of oncogenic signaling and resistance mechanisms, and suggests utility for combined HSP90/AR inhibition in CRPC.

Correction: Loss of EGFR signaling-regulated miR-203 promotes prostate cancer bone metastasis and tyrosine kinase inhibitors resistance.

[This corrects the article DOI: 10.18632/oncotarget.1994.].

Identification of Different Classes of Luminal Progenitor Cells within Prostate Tumors.

Primary prostate cancer almost always has a luminal phenotype. However, little is known about the stem/progenitor properties of transformed cells within tumors. Using the aggressive Pten/Tp53-null mouse model of prostate cancer, we show that two classes of luminal progenitors exist within a tumor. Not only did tumors contain previously described multipotent progenitors, but also a major population of committed luminal progenitors. Luminal cells, sorted directly from tumors or grown as organoids, initiated tumors of adenocarcinoma or multilineage histological phenotypes, which is consistent with luminal and multipotent differentiation potentials, respectively. Moreover, using organoids we show that the ability of luminal-committed progenitors to self-renew is a tumor-specific property, absent in benign luminal cells. Finally, a significant fraction of luminal progenitors survived in vivo castration. In all, these data reveal two luminal tumor populations with different stem/progenitor cell capacities, providing insight into prostate cancer cells that initiate tumors and can influence treatment response.

Loss of Androgen-Regulated MicroRNA 1 Activates SRC and Promotes Prostate Cancer Bone Metastasis.

Bone metastasis is the hallmark of progressive and castration-resistant prostate cancers. MicroRNA 1 (miR-1) levels are decreased in clinical samples of primary prostate cancer and further reduced in metastases. SRC has been implicated as a critical factor in bone metastasis, and here we show that SRC is a direct target of miR-1. In prostate cancer patient samples, miR-1 levels are inversely correlated with SRC expression and a SRC-dependent gene signature. Ectopic miR-1 expression inhibited extracellular signal-regulated kinase (ERK) signaling and bone metastasis in a xenograft model. In contrast, SRC overexpression was sufficient to reconstitute bone metastasis and ERK signaling in cells expressing high levels of miR-1. Androgen receptor (AR) activity, defined by an AR output signature, is low in a portion of castration-resistant prostate cancer. We show that AR binds to the miR-1-2 regulatory region and regulates miR-1 transcription. Patients with low miR-1 levels displayed correlated low canonical AR gene signatures. Our data support the existence of an AR-miR-1-SRC regulatory network. We propose that loss of miR-1 is one mechanistic link between low canonical AR output and SRC-promoted metastatic phenotypes.

Loss of EGFR signaling regulated miR-203 promotes prostate cancer bone metastasis and tyrosine kinase inhibitors resistance.

Activation of EGFR signaling pathway leads to prostate cancer bone metastasis; however, therapies targeting EGFR have demonstrated limited effectiveness and led to drug resistance. miR-203 levels are down-regulated in clinical samples of primary prostate cancer and further reduced in metastatic prostate cancer. Here we show that ectopic miR-203 expression displayed reduced bone metastasis and induced sensitivity to tyrosine kinase inhibitors (TKIs) treatment in a xenograft model. Our results demonstrate that the induction of bone metastasis and TKI resistance require miR-203 down regulation, activation of the EGFR pathway via altered expression of EGFR ligands (EREG and TGFA) and anti-apoptotic proteins (API5, BIRC2, and TRIAP1). Importantly, a sufficient reconstitution of invasiveness and resistance to TKIs treatment was observed in cells transfected with anti-miR-203. In prostate cancer patients, our data showed that miR-203 levels were inversely correlated with the expression of two EGFR ligands, EREG and TGFA, and an EGFR dependent gene signature. Our results support the existence of a miR-203, EGFR, TKIs resistance regulatory network in prostate cancer progression. We propose that the loss of miR-203 is a molecular link in the progression of prostate cancer metastasis and TKIs resistance characterized by high EGFR ligands output and anti-apoptotic proteins activation.

TMPRSS2- driven ERG expression in vivo increases self-renewal and maintains expression in a castration resistant subpopulation.

Genomic rearrangements commonly occur in many types of cancers and often initiate or alter the progression of disease. Here we describe an in vivo mouse model that recapitulates the most frequent rearrangement in prostate cancer, the fusion of the promoter region of TMPRSS2 with the coding region of the transcription factor, ERG. A recombinant bacterial artificial chromosome including an extended TMPRSS2 promoter driving genomic ERG was constructed and used for transgenesis in mice. TMPRSS2-ERG expression was evaluated in tissue sections and FACS-fractionated prostate cell populations. In addition to the anticipated expression in luminal cells, TMPRSS2-ERG was similarly expressed in the Sca-1(hi)/EpCAM(+) basal/progenitor fraction, where expanded numbers of clonogenic self-renewing progenitors were found, as assayed by in vitro sphere formation. These clonogenic cells increased intrinsic self renewal in subsequent generations. In addition, ERG dependent self-renewal and invasion in vitro was demonstrated in prostate cell lines derived from the model. Clinical studies have suggested that the TMPRSS2-ERG translocation occurs early in prostate cancer development. In the model described here, the presence of the TMPRSS2-ERG fusion alone was not transforming but synergized with heterozygous Pten deletion to promote PIN. Taken together, these data suggest that one function of TMPRSS2-ERG is the expansion of self-renewing cells, which may serve as targets for subsequent mutations. Primary prostate epithelial cells demonstrated increased post transcriptional turnover of ERG compared to the TMPRSS2-ERG positive VCaP cell line, originally isolated from a prostate cancer metastasis. Finally, we determined that TMPRSS2-ERG expression occurred in both castration-sensitive and resistant prostate epithelial subpopulations, suggesting the existence of androgen-independent mechanisms of TMPRSS2 expression in prostate epithelium.

Prostate cancer stem cells: The case for model systems.

Advanced prostate cancers are treated with androgen deprivation therapy, which usually leads to a rapid and significant reduction in tumor burden but subsequent development of castration-resistant and metastatic disease almost always occurs. The source of tumor heterogeneity and the accompanying mechanisms leading to treatment resistance are major areas of prostate cancer research. Although our understanding of tumor heterogeneity is evolving, the functional isolation of tumor propagating populations, also known as cancer stem cells (CSCs), is fundamental to the identification and molecular characterization of castration-resistant prostate cancer cells. Of clinical importance, knowledge of prostate CSCs has implications for design of next generation-targeted therapies aimed at both eradicating primary tumor mass and preventing castration-resistant disease. The inability to routinely transplant fractionated primary human prostate tumors has prevented progress in analyzing the source of heterogeneous and treatment-resistant populations in prostate cancer. Here, we briefly overview the mechanisms of castration resistance, including the hypothesis for the existence of androgen-independent prostate CSCs. Finally, we discuss the interpretation of preclinical models and their utility for characterizing prostate CSCs in androgen-replete and androgen-deprived conditions.

Critical and reciprocal regulation of KLF4 and SLUG in transforming growth factor ß-initiated prostate cancer epithelial-mesenchymal transition.

Epithelial-mesenchymal transition (EMT) is implicated in various pathological processes within the prostate, including benign prostate hyperplasia (BPH) and prostate cancer progression. However, an ordered sequence of signaling events initiating carcinoma-associated EMT has not been established. In a model of transforming growth factor ß (TGFß)-induced prostatic EMT, SLUG is the dominant regulator of EMT initiation in vitro and in vivo, as demonstrated by the inhibition of EMT following Slug depletion. In contrast, SNAIL depletion was significantly less rate limiting. TGFß-stimulated KLF4 degradation is required for SLUG induction. Expression of a degradation-resistant KLF4 mutant inhibited EMT, and furthermore, depletion of Klf4 was sufficient to initiate SLUG-dependent EMT. We show that KLF4 and another epithelial determinant, FOXA1, are direct transcriptional inhibitors of SLUG expression in mouse and human prostate cancer cells. Furthermore, self-reinforcing regulatory loops for SLUG-KLF4 and SLUG-FOXA1 lead to SLUG-dependent binding of polycomb repressive complexes to the Klf4 and Foxa1 promoters, silencing transcription and consolidating mesenchymal commitment. Analysis of tissue arrays demonstrated decreased KLF4 and increased SLUG expression in advanced-stage primary prostate cancer, substantiating the involvement of the EMT signaling events described in model systems.

Self-renewing Pten-/- TP53-/- protospheres produce metastatic adenocarcinoma cell lines with multipotent progenitor activity.

Prostate cancers of luminal adenocarcinoma histology display a range of clinical behaviors. Although most prostate cancers are slow-growing and indolent, a proportion is aggressive, developing metastasis and resistance to androgen deprivation treatment. One hypothesis is that a portion of aggressive cancers initiate from stem-like, androgen-independent tumor-propagating cells. Here we demonstrate the in vitro creation of a mouse cell line, selected for growth as self-renewing stem/progenitor cells, which manifests many in vivo properties of aggressive prostate cancer. Normal mouse prostate epithelium containing floxed Pten and TP53 alleles was subjected to CRE-mediated deletion in vitro followed by serial propagation as protospheres. A polyclonal cell line was established from dissociated protospheres and subsequently a clonal daughter line was derived. Both lines demonstrate a mature luminal phenotype in vitro. The established lines contain a stable minor population of progenitor cells with protosphere-forming ability and multi-lineage differentiation capacity. Both lines formed orthotopic adenocarcinoma tumors with metastatic potential to lung. Intracardiac inoculation resulted in brain and lung metastasis, while intra-tibial injection induced osteoblastic bone formation, recapitulating the bone metastatic phenotype of human prostate cancer. The cells showed androgen receptor dependent growth in vitro. Importantly, in vivo, the deprivation of androgens from established orthotopic tumors resulted in tumor regression and eventually castration-resistant growth. These data suggest that transformed prostate progenitor cells preferentially differentiate toward luminal cells and recapitulate many characteristics of the human disease.

Characterizing the contribution of stem/progenitor cells to tumorigenesis in the Pten-/-TP53-/- prostate cancer model.

Loss of PTEN is one of the most common mutations in prostate cancer, and loss of wild-type TP53 is associated with prostate cancer progression and castrate resistance. Modeling prostate cancer in the mouse has shown that while Pten deletion in prostate epithelial cells leads to adenocarcinoma, combined loss of Pten and TP53 results in rapidly developing disease with greater tumor burden and early death. TP53 contributes significantly to the regulation of stem cell self-renewal, and we hypothesized that loss of Pten/TP53 would result in measurable changes in prostate cancer stem/progenitor cell properties. Clonogenic assays that isolate progenitor function in primary prostate epithelial cells were used to measure self-renewal, differentiation, and tumorigenic potential. Pten/TP53 null as compared with wild-type protospheres showed increased self-renewal activity and modified lineage commitment. Orthotopic transplantation of Pten/TP53 null cells derived from protospheres produced invasive Prostatic Intraepithelial Neoplasia (PIN)/adenocarcinoma, recapitulating the pathology seen in primary tumors. Pten/TP53 null progenitors relative to wild type also demonstrated increased dependence on the AKT/mammalian target of rapamycin complex 1 (mTORC1) and androgen receptor (AR) pathways for clonogenic and tumorigenic growth. These data demonstrate roles for Pten/TP53 in prostate epithelial stem/progenitor cell function, and moreover, as seen in patients with castrate-resistant prostate cancer, suggest for the involvement of an AR-dependent axis in the clonogenic expansion of prostate cancer stem cells.

Beta-adrenoceptor subtype expression in human placenta and umbilical arteries in normal and preeclamptic pregnancies.

OBJECTIVES: Preeclampsia is characterised by an abnormal vascular response to placentation and is associated with increased systemic vascular resistance and endothelial cell dysfunction. This study investigated the mRNA and protein expression of the beta(2) and beta(3)-adrenoceptors (beta-ARs) in placenta, and umbilical arteries, from preeclamptic and normotensive patients, to determine if the presence of preeclampsia altered the expression of either receptor. METHODS: RT-PCR was used to identify beta(2)-AR and beta(3)-AR mRNA transcripts in the human placenta and in human umbilical arteries. Real-time RT-PCR was performed on total RNA from normal and preeclamptic placentae and umbilical arteries. Western blotting using antibodies for beta(2)-AR, beta(3)-AR, and beta-actin was performed on total protein isolated from preeclamptic and normotensive placentae. RESULTS: There was no significant difference in mRNA expression levels of beta(2)-AR and beta(3)-AR between normal and preeclamptic tissues (p > 0.05). No significant difference was observed in protein levels of beta(2)-AR and beta(3)-AR between placentae from normal and preeclamptic patients (p > 0.05). CONCLUSIONS: Aberrations in the beta-adrenoceptor signalling systems, rather than in the regulation of expression of these receptors may occur in preeclampsia, as is the case in other hypertensive disorders.

Expression levels of mRNA for Rho A/Rho kinase and its role in isoprostane-induced vasoconstriction of human placental and maternal vessels.

Preeclampsia is characterized by intense and prolonged vasoconstriction. Rho A-mediated calcium sensitization is central to prolonged contractility of vascular smooth muscle. The aims of this study are (1) to investigate mRNA expression levels of Rho A/Rho kinases in placental tissues from normotensive and preeclamptic women and (2) to investigate the effects of 2 isoprostanes, 8-iso prostaglandin F(2)( alpha) (8-iso PGF(2 alpha) ) and 8-iso prostaglandin E(2) (8-iso PGE(2)), on small placental and myometrial vessel resistance and to determine if their effects were mediated via the Rho kinase pathway. Real-time reverse transcription polymerase chain reaction for Rho A, ROCK I, and ROCK II was performed on total RNA from normotensive and preeclamptic placentae. The effects of 8- iso PGF(2 alpha) and 8-iso PGE(2) (alone and with the specific Rho kinase inhibitor Y-27632) on placental and myometrial vessels (<400 microm) were measured and compared with control recordings. Rho A mRNA expression levels were significantly higher in placentae from preeclamptic women than in placentae from normotensive women (P < .01). There was no significant difference in expression levels of ROCK I and ROCK II between both tissue types (P > .05). Both isoprostanes exerted a significant concentration-dependent vasocontractile effect on both vessel types (P < .001). This effect was antagonized by Y-27632 in placental arteries but not in myometrial arteries. Increased Rho A mRNA expression in placentae from preeclamptic women is suggestive of a role for the Rho kinase pathway in the modulation of the placental vasculature in this condition. Isoprostanes exert their vasocontractile effect, in placental vasculature, in part via the Rho kinase pathway.

Acute myeloid leukemia with basophilic differentiation (AML, M-2B) in a cat.

A 4-year-old, neutered male Domestic Shorthair cat with a history of depression, anorexia, and weight loss was diagnosed with acute myelogenous leukemia (AML). The cat tested positive by both the feline immunodeficiency virus antibody test and feline leukemia virus enzyme-linked immunosorbent assay test. Results of cytochemical stains on peripheral blood and bone marrow specimens indicated acute myeloid leukemia with unusual basophilic differentiation (AML, M-2B).