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Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of prostate cancer that most commonly evolves from preexisting prostate adenocarcinoma (PCA). Using Next Generation RNA-sequencing and oligonucleotide arrays, we profiled 7 NEPC, 30 PCA, and 5 benign prostate tissue (BEN), and validated findings on tumors from a large cohort of patients (37 NEPC, 169 PCA, 22 BEN) using IHC and FISH. We discovered significant overexpression and gene amplification of AURKA and MYCN in 40% of NEPC and 5% of PCA, respectively, and evidence that that they cooperate to induce a neuroendocrine phenotype in prostate cells. There was dramatic and enhanced sensitivity of NEPC (and MYCN overexpressing PCA) to Aurora kinase inhibitor therapy both in vitro and in vivo, with complete suppression of neuroendocrine marker expression following treatment. We propose that alterations in Aurora kinase A and N-myc are involved in the development of NEPC, and future clinical trials will help determine from the efficacy of Aurora kinase inhibitor therapy.We report on the largest in-depth molecular analysis of NEPC and provide new insight into molecular events involved in the progression of prostate cancer.

Androgen deprivation is the standard treatment for advanced prostate cancer (PCa), but most patients ultimately develop resistance and tumor recurrence. We found that MYB is transcriptionally activated by androgen deprivation therapy or genetic silencing of the androgen receptor (AR). MYB silencing inhibited PCa growth in culture and xenografts in mice. Microarray data revealed that c-Myb and AR shared a subset of target genes that encode DNA damage response (DDR) proteins, suggesting that c-Myb may supplant AR as the dominant regulator of their common DDR target genes in AR inhibition-resistant or AR-negative PCa. Gene signatures including AR, MYB, and their common DDR-associated target genes positively correlated with metastasis, castration resistance, tumor recurrence, and decreased survival in PCa patients. In culture and in xenograft-bearing mice, a combination strategy involving the knockdown of MYB, BRCA1, or TOPBP1 or the abrogation of cell cycle checkpoint arrest with AZD7762, an inhibitor of the checkpoint kinase Chk1, increased the cytotoxicity of the poly[adenosine 5'-diphosphate (ADP)-ribose] polymerase (PARP) inhibitor olaparib in PCa cells. Our results reveal new mechanism-based therapeutic approaches for PCa by targeting PARP and the DDR pathway involving c-Myb, TopBP1, ataxia telangiectasia mutated- and Rad3-related (ATR), and Chk1.

To understand the role of CCAAT-binding factor (CBF) in transcription in the context of chromatin-assembled DNA, we used regularly spaced nucleosomal DNA using topoisomerase IIα (topo IIα) and α2(1) collagen promoter templates, which were subsequently reconstituted in an in vitro transcription reaction. Binding of CBF to the nucleosomal wild-type topo IIα promoter containing four CBF-binding sites disrupted the regular nucleosomal structure not only in the promoter region containing the CBF-binding sites but also in the downstream region over the transcription start site. In contrast, no nucleosome disruption was observed in a mutant topo IIα promoter containing mutations in all CBF-binding sites. Interestingly, CBF also activated transcription from nucleosomal wild-type topo IIα promoter. In this experiment, a promoter containing one wild-type CBF-binding site was activated very weakly, whereas the promoter containing mutations in all sites was not activated by CBF. A truncated CBF that lacked the glutamine-rich domains did not activate transcription from nucleosomal wild-type topo IIα promoter but disrupted the nucleosomal structure about as much as did the binding of full-length CBF. Two nucleosomal mouse α2(1) collagen promoter DNAs, one containing a single and the other containing four CBF- binding sites, were also reconstituted in anin vitro transcription reaction. None of the nucleosomal collagen promoters was activated by CBF. However, both of these collagen promoters were activated by CBF when the transcription reaction was performed using naked DNA templates. Binding of CBF to the nucleosomal collagen promoter containing four binding sites disrupted the nucleosomal structure, similarly as observed in the topo IIα promoter. Altogether this study indicates that CBF-mediated nucleosomal disruption occurred independently of transcription activation. It also suggests that specific promoter structure may play a role in the CBF-mediated transcription activation of nucleosomal topo IIα promoter template.

The heterotrimeric CCAAT-binding factor CBF specifically interacts with the CCAAT motif present in the proximal promoters of numerous mammalian genes. To understand the in vivo function of CBF, a dominant negative mutant of CBF-B subunit that inhibits DNA binding of wild type CBF was stably expressed in mouse fibroblast cells under control of tetracycline-responsive promoter. Expression of the mutant CBF-B but not the wild-type CBF-B resulted in retardation of fibroblast cell growth. The analysis of cell growth using bromodeoxyuridine labeling showed that expression of the mutant CBF-B decreased the number of cells entering into S phase, and also delayed induction of S phase in the quiescent cells after serum stimulation, thus indicating that the inhibition of CBF binding prolonged the progression of S phase in fibroblasts. These results provide direct evidence for the first time that CBF is an important regulator of fibroblast growth. The inhibition of CBF binding reduced expression of various cellular genes including the alpha2(1) collagen, E2F1, and topoisomerase IIalpha genes which promoters contain the CBF-binding site. This result implied that expression of many other genes which promoters contain CBF-binding site was also decreased by the inhibition of CBF binding, and that the decreased expression of multiple cellular genes possibly caused the retardation of fibroblast cell growth.

We report that the heterotrimeric transcription factor NFY or “CAAT-binding factor” binds the −60 region of the human H ferritin promoter, the B site. DNA binding analysis with specific antibodies demonstrates that NFY/B/C subunits tightly bind this site and that NFY/C subunit is masked in vivo by binding with other protein(s). NFY binds the co-activator p300. Specifically, the NFY/B subunit interacts with the central segment of p300 in vivo and in vitro. cAMP substantially increases the formation of the NFY·p300 complex. Taken together these data provide a general model of cAMP induction of non-CRE-containing promoters and suggest that the NFY-B·p300 complex is located at the 5′ end of the promoter and the NFY-B·C·TFIIB on the 3′ end toward the transcription start site.

In this study, we used a photocross-linking method to identify specific contact of CCAAT-binding factor (CBF) subunits in a CBF-DNA complex. The analysis showed that all three subunits in the CBF-DNA complex were cross-linked to DNA and that CBF-B and CBF-C were cross-linked more strongly than CBF-A. None of the CBF-A and CBF-C subunits, which together formed a CBF-A/CBF-C heterodimer, were cross-linked without CBF-B; in contrast, CBF-B was cross-linked in the absence of CBF-A/CBF-C. No subunit of heterotrimeric CBF containing DNA-binding domain mutant of either CBF-B or CBF-C was cross-linked to DNA, and interestingly, cross-linking of CBF-B that occurred without CBF-A/CBF-C was inhibited in presence of mutant CBF-C/CBF-A heterodimer. Altogether, these results indicated that the specific DNA contact surface of each CBF subunit is generated as a result of interaction between CBF-B and CBF-A/CBF-C heterodimer and that the three CBF subunits interact interdependently with DNA to form a CBF-DNA complex. Equilibrium interactions among the three CBF subunits and between CBF subunits and DNA were studied by electrophoretic mobility shift assay. This showed that at equilibrium DNA-binding conditions, the CBF-A/CBF-C heterodimer is very stable, but association between CBF-B and CBF-A/CBF-C is very weak. The nature of the association of CBF-B with CBF-A/CBF-C was also revealed by studying the inhibition of CBF-DNA complex formation by the mutant CBF-B. This study indicated that the association between CBF-B and CBF-A/CBF-C is stabilized upon interaction with DNA, a process likely to favor formation of a high-affinity CBF-DNA complex.

Nuclear transcription factor-Y (NF-Y), a key regulator of cell-cycle progression, often loses its activity during differentiation into nonproliferative cells. In contrast, NF-Y is still active in mature, differentiated neurons, although its neuronal significance remains obscure. Here we show that conditional deletion of the subunit NF-YA in postmitotic mouse neurons induces progressive neurodegeneration with distinctive ubiquitin/p62 pathology; these proteins are not incorporated into filamentous inclusion but co-accumulated with insoluble membrane proteins broadly on endoplasmic reticulum (ER). The degeneration also accompanies drastic ER disorganization, that is, an aberrant increase in ribosome-free ER in the perinuclear region, without inducing ER stress response. We further perform chromatin immunoprecipitation and identify several NF-Y physiological targets including Grp94 potentially involved in ER disorganization. We propose that NF-Y is involved in a unique regulation mechanism of ER organization in mature neurons and its disruption causes previously undescribed novel neuropathology accompanying abnormal ubiquitin/p62 accumulation.

The molecular mechanisms by which mesenchymal cells differentiate into chondrocytes are still poorly understood. We have used the gene for a chondrocyte marker, the proalpha1(II) collagen gene (Col2a1), as a model to delineate a minimal sequence needed for chondrocyte expression and identify chondrocyte-specific proteins binding to this sequence. We previously localized a cartilage-specific enhancer to 156 bp of the mouse Col2a1 intron 1. We show here that four copies of a 48-bp subsegment strongly increased promoter activity in transiently transfected rat chondrosarcoma (RCS) cells and mouse primary chondrocytes but not in 10T1/2 fibroblasts. They also directed cartilage specificity in transgenic mouse embryos. These 48 bp include two 11-bp inverted repeats with only one mismatch. Tandem copies of an 18-bp element containing the 3' repeat strongly enhanced promoter activity in RCS cells and chondrocytes but not in fibroblasts. Transgenic mice harboring 12 copies of this 18-mer expressed luciferase in ribs and vertebrae and in isolated chondrocytes but not in noncartilaginous tissues except skin and brain. In gel retardation assays, an RCS cell-specific protein and another closely related protein expressed only in RCS cells and primary chondrocytes bound to a 10-bp sequence within the 18-mer. Mutations in these 10 bp abolished activity of the multimerized 18-bp enhancer, and deletion of these 10 bp abolished enhancer activity of 465- and 231-bp intron 1 segments. This sequence contains a low-affinity binding site for POU domain proteins, and competition experiments with a high-affinity POU domain binding site strongly suggested that the chondrocyte proteins belong to this family. Together, our results indicate that an 18-bp sequence in Col2a1 intron 1 controls chondrocyte expression and suggest that RCS cells and chondrocytes contain specific POU domain proteins involved in enhancer activity.

The CCAAT binding factor CBF is a heteromeric transcription factor, which binds to functional CCAAT motifs in many eukaryotic promoters. cDNAs for the A and B subunits of CBF (CBF-A and CBF-B) and for their yeast homologues HAP3 and HAP2 have been previously isolated, but the purified recombinant CBF-A and CBF-B together are unable to bind to CCAAT motifs in DNA. Here we report the isolation of a cDNA coding for rat CBF-C, demonstrate that recombinant CBF-C is required together with CBF-A and CBF-B to form a CBF-DNA complex, and show that CBF-C is present in this protein-DNA complex together with the other two subunits. We further show that CBF-C allows formation of a complex between the purified recombinant yeast HAP2 and HAP3 polypeptides and a CCAAT-containing DNA and is present in this complex, implying the existence of a CBF-C homologue in yeast. We show that CBF-A and CBF-C interact with each other to form a CBF-A-CBF-C complex and that CBF-B does not interact with CBF-A or CBF-C individually but that it associates with the CBF-A-CBF-C complex. Our results indicate that CBF is a unique evolutionarily conserved DNA binding protein.

Purpose: To study Wnt/β-catenin in castrate-resistant prostate cancer (CRPC) and understand its function independently of the β-catenin-androgen receptor (AR) interaction. Experimental Design: We carried out β-catenin immunocytochemical analysis, evaluated TOP-flash reporter activity (a reporter of β-catenin-mediated transcription), and sequenced the β-catenin gene inMDA prostate cancer 118a, MDA prostate cancer 118b, MDA prostate cancer 2b, and PC-3 prostate cancer cells. We knocked down β-catenin in AR-negative MDA prostate cancer 118b cells and carried out comparative gene-array analysis. We also immunohistochemically analyzed β-catenin and AR in 27 bone metastases of human CRPCs. Results: β-Catenin nuclear accumulation and TOP-flash reporter activity were high in MDA prostate cancer 118b but not in MDA prostate cancer 2b or PC-3 cells. MDA prostate cancer 118a and MDA prostate cancer 118b cells carry a mutated β-catenin at codon 32 (D32G). Ten genes were expressed differently (false discovery rate, 0.05) in MDA prostate cancer 118b cells with downregulated β-catenin. One such gene, hyaluronan synthase 2 (HAS2), synthesizes hyaluronan, a core component of the extracellular matrix. We confirmed HAS2 upregulation in PC-3 cells transfected with D32G-mutant β-catenin. Finally, we found nuclear localization of β-catenin in 10 of 27 human tissue specimens; this localization was inversely associated with AR expression (P=0.056, Fisher's exact test), suggesting that reduced AR expression enables Wnt/β-catenin signaling. Conclusion: We identified a previously unknown downstream target of β-catenin, HAS2, in prostate cancer, and found that high β-catenin nuclear localization and low or no AR expression may define a subpopulation of men with bone metastatic prostate cancer. These findings may guide physicians in managing these patients. Fil: Wan, Xinhai. University of Texas; Estados Unidos Fil: Liu, Jie. University of Texas; Estados Unidos Fil: Lu, Jing-Fang. University of Texas; Estados Unidos Fil: Tzelepi, Vassiliki. University of Texas; Estados Unidos Fil: Yang, Jun. University of Texas; Estados Unidos Fil: Starbuck, Michael W.. University of Texas; Estados Unidos Fil: Diao, Lixia. University of Texas; Estados Unidos Fil: Wang, Jing. University of Texas; Estados Unidos Fil: Efstathiou, Eleni. University of Texas; Estados Unidos Fil: Vazquez, Elba Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Troncoso, Silvana Patricia. University of Texas; Estados Unidos Fil: Maity, Sankar N.. University of Texas; Estados Unidos Fil: Navone, Nora. University of Texas; Estados Unidos

CCAAT-binding factor (CBF), a heteromeric transcription factor that binds to sequences containing a CCAAT motif, is composed of three subunits. A, B and C, which are all required for DNA binding. The mouse CBF-A gene contains seven coding exons, which span 12 kb. Evidence is also presented for an additional 5′ untranslated exon. The 90-aminoacid (aa) segment of CBF-A, which shows a high degree of sequence identity with the yeast transcription factor, HAP3, is split into exons 3 and 4. An alternatively spliced RNA that lacks exon 3 was identified by polymerase chain reaction. Although removal of exon 3 interrupts the CBF-A reading frame, a potential start codon at the 3′ end of exon 2 is in the same reading frame as the reading frame encoding CBF-A in exons 4 to 7. A CBF-A polypeptide of the predicted 17-kDa, size, was indeed identified after in vitro transcription and translation of the DNA complementary to RNA (cDNA) corresponding to the alternatively spliced CBF-A mRNA. In contrast to full-length CBF-A, this truncated CBFA did not bind to a DNA sequence containing the CCAAT motif in the presence of the other two components of CBF. This result indicates that the segment corresponding to the exons missing in the truncated isoform of CBF-A is essential for the binding of CBF to DNA.

Purpose: Small-cell prostate carcinoma (SCPC) morphology predicts for a distinct clinical behavior, resistance to androgen ablation, and frequent but short responses to chemotherapy. We sought to develop model systems that reflect human SCPC and can improve our understanding of its biology. Experimental Design: We developed a set of castration-resistant prostate carcinomas xenografts and examined their fidelity to their human tumors of origin. We compared the expression and genomic profiles of SCPC and large-cell neuroendocrine carcinoma (LCNEC) xenografts to those of typical prostate adenocarcinoma xenografts. Results were validated immunohistochemically in a panel of 60 human tumors. Results: The reported SCPC and LCNEC xenografts retain high fidelity to their human tumors of origin and are characterized by a marked upregulation of UBE2C and other mitotic genes in the absence of androgen receptor (AR), retinoblastoma (RB1), and cyclin D1 (CCND1) expression. We confirmed these findings in a panel of samples of CRPC patients. In addition, array comparative genomic hybridization of the xenografts showed that the SCPC/LCNEC tumors display more copy number variations than the adenocarcinoma counterparts. Amplification of the UBE2C locus and microdeletions of RB1 were present in a subset, but none displayed AR nor CCND1 deletions. The AR, RB1, and CCND1 promoters showed no CpG methylation in the SCPC xenografts. Conclusion: Modeling human prostate carcinoma with xenografts allows in-depth and detailed studies of its underlying biology. The detailed clinical annotation of the donor tumors enables associations of anticipated relevance to be made. Future studies in the xenografts will address the functional significance of the findings. Clin Cancer Res; 18(3); 666–77. ©2011 AACR.

BACKGROUND Hedgehog signaling is a stromal-mesenchymal pathway central to the development and homeostasis of both the prostate and the bone. Aberrant Hedgehog signaling activation has been associated with prostate cancer aggressiveness. We hypothesize that Hedgehog pathway is a candidate therapeutic target in advanced prostate cancer. We confirm increased Hedgehog signaling in advanced and bone metastatic castrate resistant prostate cancer and examine the pharmacodynamic effect of Smoothened inhibition by the novel reagent GDC-0449 in an experimental prostate cancer model. METHODS Hedgehog signaling component expression was assessed in tissue microarrays of high grade locally advanced and bone metastatic disease. Male SCID mice subcutaneously injected with the bone forming xenograft MDA PCa 118b were treated with GDC-0449. Hedgehog signaling in the tumor microenvironment was assessed by proteomic and species specific RNA expression and compared between GDC-0449 treated and untreated animals. RESULTS We observe Hedgehog signaling in high grade locally advanced and bone marrow infiltrating disease. Evidence of paracrine activation of Hedgehog signaling in the tumor xenograft, was provided by increased Sonic Hedgehog expression in human tumor epithelial cells, coupled with increased Gli1 and Patched1 expression in the murine stromal compartment, while normal murine stroma did not exhibit Hh signaling expression. GDC-0449 treatment attenuated Hh signaling as evidenced by reduced expression of Gli1 and Ptch1. Reduction in proliferation (Ki67) was observed with no change in tumor volume. CONCLUSIONS GDC-0449 treatment is pharmacodynamically effective as evidenced by paracrine Hedgehog signaling inhibition and results in tumor cell proliferation reduction. Understanding these observations will inform the clinical development of therapy based on Hedgehog signaling inhibition. Prostate 72:1638–1647, 2012. © 2012 Wiley Periodicals, Inc.

The enzyme 5α-reductase, which converts testosterone to dihydrotestosterone (DHT), performs key functions in the androgen receptor (AR) signaling pathway. The three isoenzymes of 5α-reductase identified to date are encoded by different genes: SRD5A1, SRD5A2, and SRD5A3. In this study, we investigated mechanisms underlying androgen regulation of 5α-reductase isoenzyme expression in human prostate cells. We found that androgen regulates the mRNA level of 5α-reductase isoenzymes in a cell type–specific manner, that such regulation occurs at the transcriptional level, and that AR is necessary for this regulation. In addition, our results suggest that AR is recruited to a negative androgen response element (nARE) on the promoter of SRD5A3 in vivo and directly binds to the nARE in vitro. The different expression levels of 5α-reductase isoenzymes may confer response or resistance to 5α-reductase inhibitors and thus may have importance in prostate cancer prevention.

BACKGROUND Small-cell carcinoma (SCC) of the prostate is an AR-negative variant of prostate cancer found at progression in 10–20% of castrate-resistant disease. Its finding predicts a distinct clinical course and a poor prognosis. Large-cell neuroendocrine carcinoma (LCNEC) is a much rarer variant that behaves similarly to SCC. The biological mechanisms that drive these disease variants are poorly understood. METHODS Eight tumor fragments from the salvage pelvic exenteration specimen of a patient with castrate-resistant prostate carcinoma were subcutaneously implanted into 6- to 8-week-old male CB17 SCID mice. Serial tissue sections and tissue microarrays of the resulting MDA PCa 144 xenograft lines were used for histopathologic and immunohistochemical characterization of the xenografts and their tissue of origin. RNA from two representative xenograft sublines was used for gene-expression profiling. RESULTS All eight fragments formed tumors: four of the MDA PCa 144 xenograft sublines had morphologic characteristics of SCC and four, of LCNEC. All retained high fidelity to their parent tumor tissue, which remained stable through serial passages. Morphological transitions in the specimen of origin suggested LCNEC represents an intermediate step between adenocarcinoma and SCC. Over 2,500 genes were differentially expressed between the SCC (MDA PCa 144-13) and the LCNEC (MDA PCa 144-4) sublines and enriched in “Nervous System Development” Gene Ontology subtree. CONCLUSION The eight xenograft models described represent the spectrum of neuroendocrine carcinomas in prostate cancer and will be valuable preclinical tools to study the pathogenesis of and therapy targets for this increasingly recognized subset of lethal prostate cancer. Prostate 71:846–856, 2011. © 2010 Wiley-Liss, Inc.

Mutations in SOX9, a gene essential for chondrocyte differentiation cause the human disease campomelic dysplasia (CD). To understand how SOX9 activates transcription, we characterized the DNA binding and cell-free transcription ability of wild-type SOX9 and a dimerization domain SOX9 mutant. Whereas formation of monomeric mutant SOX9–DNA complex increased linearly with increasing SOX9 concentrations, formation of a wild-type SOX9–DNA dimeric complex increased more slowly suggesting a more sigmoidal-type progression. Stability of SOX9–DNA complexes, however, was unaffected by the dimerization mutation. Both wild-type and mutant SOX9 activated transcription of a naked Col2a1 DNA template. However, after nucleosomal assembly, only wild-type and not the mutant was able to remodel chromatin and activate transcription of this template. Using a cell line, in which the Col2a1 vector was stably integrated, no differences were seen in the interactions of wild-type and mutant SOX9 with the chromatin of the Col2a1 vector using ChIP. However, the mutant was unable to activate transcription in agreement with in vitro results. We hypothesize that the SOX9 dimerization domain is necessary to remodel the Col2a1 chromatin in order to allow transcription to take place. These results further clarify the mechanism that accounts for CD in patients harboring SOX9 dimerization domain mutations.

We sought to determine the cis-acting elements responsible for the pattern of tissue specific expression of the mouse alpha 2(I) collagen gene. Using an RNase protection assay we first verified that expression of the alpha 2(I) collagen gene is mainly confined to tendons, bone, and skin in mice. Both transgenic mice and DNA transfection of tissue culture cells were used as experimental approaches. Transgenic mice lines were generated harboring chloramphenicol acetyltransferase (CAT) chimeric genes that contained either (a) 2000 base pairs (bp) of 5'-flanking sequences of the mouse alpha 2(I) collagen gene plus additional sequences between +418 and +1524 of the first intron of this gene or (b) the same promoter sequences without intron sequences or (c) the 350-bp proximal promoter sequences. Transgenic mice containing both types of 2000-bp promoters showed a pattern of CAT expression that was tissue specific. The presence of sequences of the first intron in the transgene did not increase the level of promoter activity. Transgenic mice harboring the 350-bp alpha 2(I) collagen promoter also showed a pattern that was tissue-specific except that high level expression also occurred in the brain. This suggests that negative regulation is an important component of tissue-specific expression. In order to analyze the first 350 bases in detail, we performed transient expression experiments, using promoter fragments attached to the luciferase reporter gene. Fibroblasts, which show a high level expression of the endogenous alpha 2(I) collagen gene, and B cells, in which the gene is silent, were transfected with a series of deletions and substitution mutations within the proximal 350-bp promoter. These experiments were unable to define unique cell-specific cis-acting elements. However, when the sequence between -315 and -284 was tandemly repeated upstream of a minimal alpha 2(I) collagen promoter (-41 to +54), the activity of this construction was considerably higher in fibroblasts than in B cells when compared with the minimal promoter itself. In gel retardation assays, the levels of complexes that bind to this sequence were higher in fibroblast nuclear extracts than in myeloma nuclear extracts. Our results are consistent with the hypothesis that the -315 to -284 DNA sequence participates in the cell-specific control of the alpha 2(I) collagen gene in fibroblasts.

Full-length cDNA clones for the CBF-A and CBF-B subunits of the CCAAT binding mammalian heteromeric transcription factor (CBF) have previously been isolated from both rat and mouse. Whereas recombinant CBF-B binds to DNA after complementation with a highly purified CBF-A fraction, recombinant CBF-A was unable to bind to DNA after complementation with either purified CBF-B or recombinant CBF-B. However, when recombinant CBF-A, synthesized as a fusion protein with glutathione S-transferase was denatured together with a highly purified fraction containing CBF-A in the presence of 5.5 M guanidine hydrochloride and subsequently renatured, the recombinant CBF-A bound to DNA after complementation with CBF-B. This binding of recombinant CBF-A could not be detected if recombinant CBF-A was not mixed during the denaturation-renaturation process together with the purified fraction containing the 32-kDa CBF-A. Using a Southwestern blot we demonstrated that a polypeptide of approximately 40 kDa, present in the purified CBF-A fraction, bound to DNA after complementation with both recombinant CBF-A and CBF-B. After fractionation of the purified CBF-A preparation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a species of approximately 40 kDa was eluted from the gel and shown to have DNA binding activity after complementation with both recombinant CBF-A and CBF-B. Our results indicate that a third polypeptide, designated CBF-C, forms a tight complex with CBF-A. Together with CBF-A and CBF-B, CBF-C is required for the DNA binding activity of CBF.

CCAAT-binding factors A (CBF-A) and B (CBF-B) are two subunits of the heteromeric CCAAT-binding factor. Portions of CBF-A and CBF-B have a high degree of amino acid sequence identity to segments of the HAP3 and HAP2 subunits of a yeast multimeric transcription factor. We show here that the subunits of CBF interact with each other in the absence of DNA binding. This interaction was revealed by cross-linking and coimmunoprecipitation studies. Both the DNA binding and subunit interaction functions of CBF-B have been examined by mutational analysis. A segment of 83 amino acids from residues 252 to 334, which corresponds to the evolutionarily conserved portion of CBF-B, is necessary and sufficient for CBF-A-dependent DNA binding. Carboxyl-terminal deletions of this segment (or mutations in arginine residues in this carboxyl-terminal part) abolish DNA binding, but do not alter subunit interactions between CBF-A and CBF-B. Mutations in hydrophobic amino acids within the amino-terminal part of the evolutionarily conserved sequence at positions 252-334 result in loss of both DNA binding and subunit interaction activities. Our results indicate that the evolutionarily conserved segment of CBF-B contains both DNA-binding and subunit interaction domains and that the integrity of both domains is essential for DNA binding.

In prostate cancer, androgen blockade strategies are commonly used to treat osteoblastic bone metastases. However, responses to these therapies are typically brief, and the mechanism underlying androgen-independent progression is not clear. Here, we established what we believe to be the first human androgen receptor-negative prostate cancer xenografts whose cells induced an osteoblastic reaction in bone and in the subcutis of immunodeficient mice. Accordingly, these cells grew in castrated as well as intact male mice. We identified FGF9 as being overexpressed in the xenografts relative to other bone-derived prostate cancer cells and discovered that FGF9 induced osteoblast proliferation and new bone formation in a bone organ assay. Mice treated with FGF9-neutralizing antibody developed smaller bone tumors and reduced bone formation. Finally, we found positive FGF9 immunostaining in prostate cancer cells in 24 of 56 primary tumors derived from human organ-confined prostate cancer and in 25 of 25 bone metastasis cases studied. Collectively, these results suggest that FGF9 contributes to prostate cancer-induced new bone formation and may participate in the osteoblastic progression of prostate cancer in bone. Androgen receptor-null cells may contribute to the castration-resistant osteoblastic progression of prostate cancer cells in bone and provide a preclinical model for studying therapies that target these cells. Fil: Zhi, Gang Li. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Mathew, Paul. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Yang, Jun. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Starbuck, Michael W.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Zurita, Amado J.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Liu, Jie. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Sikes, Charles. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Multani, Asha S.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Efstathiou, Eleni. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Lopez, Adriana. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Wang, Jing. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Fanning, Tina V.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Prieto, Victor G.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Kundra, Vikas. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Vazquez, Elba Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Troncoso, Patricia. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Raymond, Austin K.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Logothetis, Christopher J.. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Lin, Sue-Hwa. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Maity, Sankar. University Of Texas Md Anderson Cancer Center; Estados Unidos Fil: Navone, Nora M.. University Of Texas Md Anderson Cancer Center; Estados Unidos

CCAAT-binding factor (CBF) is a heteromeric mammalian transcription factor which binds to sequences containing a CCAAT motif in a number of promoters such as those for type I collagen, albumin, MHC Class II, beta-actin, and others. It consists of two different components that are both needed for DNA binding. We have purified the "A" chain of CBF to apparent homogeneity by sequence-specific DNA affinity chromatography followed by Mono S and Mono Q ion-exchange chromatography and obtained the amino acid sequences of tryptic peptides of this polypeptide. Amino acid sequences of two of these tryptic peptides were used to synthesize oligonucleotide primers. The primers served to obtain a small cDNA by the polymerase chain reaction method, which was then further used to obtain larger cDNA clones. DNA sequence analysis of a representative cDNA clone revealed the presence of an open reading frame of 207 amino acids coding for a putative polypeptide of 25 kDa. Transcription of these cDNAs in vitro followed by translation in a reticulocyte lysate produced a polypeptide that migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the same mobility as the native A chain. The deduced amino acid sequence of the A chain showed a remarkable identity over a length of 90-amino acid residues with a sequence of the Hap3 polypeptide, a component of a heteromeric multisubunit yeast transcription factor.

CBF is a heteromeric mammalian transcription factor that binds to CCAAT sequences in a number of promoters such as the two type I collagen promoters, the albumin promoter, the major histocompatibility complex class II promoter, and others. It is composed of two components, A and B, that are both needed for DNA binding. We have isolated a rat cDNA containing the complete 341-amino acid coding sequence of the B component of CBF. Expression of this cDNA in vitro generates a polypeptide that shows the same dependency on the A component as the native B component in the formation of a complex with a CCAAT-containing DNA. The C-terminal portion of the B component from residue 260 to residue 312 shows a 75% sequence identity with a portion of the Hap2 protein, a component of a heteromeric CCAAT-binding protein in yeast. In contrast, the rest of the protein shows little sequence homology with Hap2, although both proteins contain glutamine-rich domains. In the B component of CBF this domain spans the amino-terminal 60% of the protein, whereas in Hap2 this domain is much smaller. Hence, only a few changes in one domain of this protein were tolerated during evolution between yeast and mammals, whereas the rest of the protein diverged much more extensively.

5055 Background: AVPCa shares clinical features with small cell carcinoma (SCC) such as resistance to androgen signaling inhibition and frequent visceral metastases. A prospective clinical trial of...

149 Background: Unusually aggressive PC behavior is linked to small cell carcinoma (SCC) morphology. We observed SCC clinical features in association with morphologically heterogeneous PC and, in a prospective clinical trial (NCT00514540), also with chemotherapy responsiveness. Our previous studies in patient derived xenografts (PDX) revealed a distinct molecular profile for SCC. Here we sought to support the hypothesis that clinically defined aggressive variant PCs also share relevant biology with SCC. Methods: 59 PC samples, and 8 PDX, from 42 men registered to NCT00514540 were stained for RB, p53, AR, NKX3-1, ASCL1, AURKA, UBE2C and Ki67. Labeling indices (LI) were calculated as the ratio of positive epithelial cells to total of epithelial cells, at 200x. We determined copy number alterations (CNA) by Onco Scan® in 36 of 59 samples and 8 PDX lines. We used Western Blot and qRT-PCR to expand pathway analyses and their associations in PDX models. Results: Donor patients were similar to non-donor patients except for higher ECOG PS and LDH values. Strong positive correlations between nuclear AR (AR-N) and NKX3.1, AR-N and RB, AR-N and nuclear AURKA (AURKA-N), NKX3.1 and RB, p53 and nuclear UBE2C (UBE2C-N), Ki67 and UBE2C-N, Ki67 and cytoplasmic UBE2C (UBE2C-C) as well as a strong negative correlation between NKX3.1 and Ki 67 were observed. Frequent copy number losses were found for PTEN (largely gene-specific) and RB1 (often associated with regional-CNA). Gene-specific AURKA amplifications were not observed. Only RB1 CNA showed a positive correlation with its LI. Samples were segregated by quantity of CNA. PDX models shared these features and showed that only AR-negative tumors expressed pro-neural transcription factors, albeit heterogeneously. Conclusions: Our results support the hypothesis that clinically defined aggressive variant PC (including SCC and non-SCC morphologies) are characterized by frequent Rb, p53 and PTEN alterations, aberrant expression of mitotic, neural development and AR-signaling pathways, and high rates of CNA. Ongoing studies will confirm whether these molecular features distinguish this variant from the more common bone-homing, bone-forming, AR-driven adenocarcinomas of the prostate.

277 Background: Androgen deprivation, anti-androgen and androgen biosynthesis inhibitor treatment can initially control the metastatic prostate cancer (PCa), but treatment-refractory progression frequently follows, with the loss of tumor suppressors (TSPs) and increased expression of cell cycle proteins. Inhibition of the nuclear export protein, Exportin 1 (XPO1) leads to nuclear accumulation of cargo proteins such as TSPs & cell-cycle regulators implicated in castration-resistant PCa (CRPC) progression. XPO1 and specific cargo genes are overexpressed in metastatic CRPC relative to benign & primary prostate tumors, implicating XPO1 activity as playing a role in disease progression. Selinexor (KPT-330), a novel, oral SINE currently in Phase 1/2 for both hematological and solid tumors, has potent activity against CRPC. We hypothesized this activity is due selinexor induced nuclear expression of TSPs. Methods: To test this hypothesis, we treated selected PCa cell lines and patient-derived xenografts (PDXs, two adenocarcinomas and one small cell carcinonoma) with selinexor to determine the effect on survival and cargo protein localization. Results: Treatment with selinexor markedly inhibited PCa cell proliferation in vitro, activated the tumor suppressor TP53 & inhibited cell-cycle regulators. Also, treatment of the PDXs with selinexor for at least 3 weeks significantly inhibited tumor growth & reduced the prostate-specific antigen level in the adenocarcinomas. Selinexor increased cell death in all three PDX tumors and reduced cell proliferation in the adenocarcinomas, but not in the small-cell tumor. Expression analyses demonstrated that selinexor induced nuclear accumulation of different cargo proteins unique to the PCa model, accounting for PDX-specific regression. Conclusions: These results point to an anti-tumorigenic effect of selinexor treatment across a spectrum of hormone-refractory PCa that may provide insight into the drivers of PCa treatment resistance and heterogeneity.

To understand the physiological function of the mammalian heterotrimeric CCAAT binding factor CBF, also known as NF-Y, we have generated a conditional Cbf-b mouse mutant by introducing loxP sites in the murine Cbf-b/Nf-ya gene. Controlled expression of Cre recombinase deletes the gene in vivo, which leads to a loss of DNA binding by the CBF complex and hence CBF-mediated transcription. Deletion of both Cbf-b alleles causes early embryo lethality, indicating that CBF activity is essential for early mouse development. In primary cultures of mouse embryonic fibroblasts, conditional inactivation of CBF results in a block in cell proliferation and inhibition of S phase or DNA synthesis, which is followed by induction of apoptosis. We conclude that the CBF transcription factor complex is essential for cell proliferation and viability.

Transcriptional enhancers are short stretches of DNA that function to achieve highly specific patterns of gene expression. To identify the mechanisms by which enhancers achieve their specificity, we made use of an enhancer from the aboral ectoderm-specific spec2a gene of the sea urchin Strongylocentrotus purpuratus. The spec2a enhancer contains five cis-regulatory elements within 78 base pairs that interact with five distinct DNA-binding proteins to confer aboral ectoderm expression. Here, we present an analysis of the sea urchin CCAAT binding factor (CBF), which binds to a CCAAT motif within the spec2a enhancer. S. purpuratus CBF and SpOtx, a ubiquitously expressed factor, act together at closely placed cis-regulatory elements to mediate spec2a transcription in the ectoderm. SpCBF was the sole factor that bound to the spec2a CCAAT element, and two of the three subunits that make up the CBF holoprotein were cloned and shown to have high sequence conservation with their vertebrate orthologs. Based on its involvement in the regulation of several other sea urchin genes, SpCBF appears to be a major transcription factor in the sea urchin embryo for positive regulation of ectoderm gene expression. In addition to its role in vertebrate cell growth and proliferation, our results indicate that CBF also functions at the early stages of germ layer formation, namely ectoderm differentiation.

158 Background: CRPC typically responds to anti-androgen therapy but resistance is common. CYP17 inhibitors that block lyase (L) and not hydroxylase (H), do not require prednisone, and may delay tumor resistance are needed. VT-464 is an oral, non-steroidal inhibitor of CYP17 L in clinical development for CRPC. The present studies characterized: 1) the kinetic mechanism of VT-464 inhibition of h-CYP17 L and H, and 2) VT-464 effects compared to abiraterone acetate (AA) in CRPC models. Methods: CYP17 Enzyme Assays: r-h-CYP17 inhibition studies were conducted using substrates pregnenolone (for H) or 17-a-hydroxypregnenolone (for L). Product rates (17-a-hydroxypregnenolone (H) and DHEA (L)) were assessed by LC/MS/MS. Data were fit to inhibition models using SigmaPlot 11.2. In vitro CRPC studies: VT-464 and AA effects on AR transcription (luciferase) and PSA and NKX3.1 gene expression (QRT-PCR) were compared in C4-2B cells. Mouse xenograft model: Effects of oral VT-464 or AA on tumor growth and tumoral steroids (T, DHT, P) were compared in the MDA-PCa-133 castrate mouse model. Results: VT-464 was a reversible uncompetitive inhibitor of CYP17 L (Ki = 84 nM, K’i=200 nM) and a competitive inhibitor of H (Ki = 620 nM). VT-464 CYP17 L/H selectivity was 7.4 at low [S] but selectivity increased with increasing [S]. VT-464 L/H selectivity was 60-x greater than AA. In C4-2B cells VT-464 and AA inhibited AR transactivation but VT-464 suppressed PSA and NKX3.1 more potently than AA. In the xenograft model, VT-464 decreased tumor volume as effectively as AA. VT-464 more potently decreased T and DHT, while AA increased P. Conclusions: VT-464 demonstrated much greater CYP17 L selectivity than AA and equivalent or superior activity in several CRPC models. Less tumor resistance may arise from treatment with the CYP17 lyase-selective inhibitor VT-464 than with AA, since it more effectively blocked androgen biosynthesis, did not cause an accumulation of progesterone, and should not require co-administration of prednisone.

Scaffold molecules interact with multiple effectors to elicit specific signal transduction pathways. CIITA, a non-DNA-binding regulator of class II major histocompatibility complex (MHC) gene transcription, may serve as a transcriptional scaffold. Regulation of the class II MHC promoter by CIITA requires strict spatial-helical arrangements of the X and Y promoter elements. The X element binds RFX (RFX5/RFXANK-RFXB/RFXAP) and CREB, while Y binds NF-Y/CBF (NF-YA, NF-YB, and NF-YC). CIITA interacts with all three. In vivo analysis using both N-terminal and C-terminal deletion constructs identified critical domains of CIITA that are required for interaction with NF-YB, NF-YC, RFX5, RFXANK/RFXB, and CREB. We propose that binding of NF-Y/CBF, RFX, and CREB by CIITA results in a macromolecular complex which allows transcription factors to interact with the class II MHC promoter in a spatially and helically constrained fashion.

The CCAAT motif is one of the common promoter elements present in the proximal promoter of numerous mammalian genes transcribed by RNA polymerase II. CBF (also called NF-Y and CP1) consists of three different subunits and interacts specifically with the CCAAT motif. In each CBF subunit, the segment needed for formation of the CBF-DNA complex is conserved from yeast to human and, interestingly, the conserved segment of two CBF subunits, CBF-A and CBF-C, are homologous to the histone-fold motif of eukaryotic histones and archaebacterial histone-like protein HMf-2. The histone fold motifs of CBF-A and CBF-C interact with each other to form a heterodimer that associates with CBF-B to form a heterotrimeric CBF molecule, which then binds to DNA.

CBF is a heterotrimeric protein that binds to DNA containing CCAAT motifs. Here we have analyzed interactions of recombinant CBF with DNA using hydroxyl radical footprinting and methylation interference assays. In the CBF-DNA complex, three separate DNA regions are protected from hydroxyl radical cleavage, one located over and immediately adjacent to the CCAAT motif itself and the other two located on both sides of the CCAAT motif. The methylation interference assay showed, however, that only in the CCAAT motif region methylation of bases was able to interfere with the formation of a CBF-DNA complex, suggesting that CBF makes sequence-specific contacts only in the CCAAT motif region. To further determine the specific DNA sequences necessary for CBF binding, we employed a polymerase chain reaction-mediated random binding site selection method. This analysis showed that CBF binding to DNA requires the CCAAT sequence and other specific sequences immediately flanking both ends of the CCAAT motif. We also showed that the nature of the flanking nucleotide sequences affects the affinity of CBF for DNA. Interestingly, most of the CCAAT motifs present in various higher eukaryotic promoters correspond to the CBF binding sites that were selected, consistent with the hypothesis that these motifs are binding sites for CBF and, hence, that CBF could regulate transcription of numerous eukaryotic genes.

We performed in vivo dimethylsulfate footprinting of the 220 bp mouse proximal proalpha1(I) collagen promoter and the 350 bp mouse proximal proalpha2(I) collagen promoter in BALB/3T3 fibroblasts, primary mouse skin fibroblasts, S-194 B cells, NMuLi liver epithelial cells and RAG renal adenocarcinoma cells and in vitro DNase I footprinting of these promoters using nuclear extracts of these different cell types. Whereas proalpha1(I) and proalpha2(I) collagen RNAs were present in BALB/3T3 fibroblasts and primary fibroblasts, these RNAs could not be detected in the three other cell lines. Comparison of in vitro DNase I footprints for each of the two proximal collagen promoters indicated that the patterns of protection were very similar with the different nuclear extracts, suggesting that the DNA binding proteins binding to these promoters were present in all cell types tested. In contrast, in vivo footprints over these proximal promoters were cell-specific, occurring only in fibroblast cells and not in the other three cell types. The in vivo footprints were generally located within the in vitro footprinted regions. Our results suggest that although all cell types tested contained nuclear proteins that can bind to the proximal proalpha1(I) and proalpha2(I) collagen promoters in vitro , it is only in fibroblasts that these proteins bind to their cognate sites in vivo . We discuss possible regulatory mechanisms in type I collagen genes that can contribute to the cell-specific in vivo protein-DNA interactions at the proximal promoters.

Molecular markers that identify clinically meaningful, biologically based, subsets of PC are lacking. This results in inefficient clinical trial designs and suboptimal therapy selection off-protocol. The androgen receptor (AR)-negative small cell PC (SCPC) is an often-unrecognized morphological variant of the disease found on repeat biopsies during the castrate-resistant (CR) progression of PC. Its presence predicts for a poor response to hormonal therapies, a distinct clinical behavior and a short survival. Characteristic clinical features of SCPC are frequently present in patients with CRPC, constituting a clinical syndrome termed anaplastic PC. We hypothesized that the anaplastic PC share underlying biology with SCPC, irrespective of morphology. Preclinical studies show that SCPC are characterized by loss of tumor suppressors and AR signaling, as well as overexpression of mitotic genes and proneural transcription factors. To test our hypothesis we used immunohistochemistry to analyze the expression of markers in these pathways, in tumor biopsies from chemotherapy-naïve men with anaplastic PC participating in a prospective phase II clinical trial. To date we have analyzed 6 markers in 25 samples (6 with pure or mixed SCPC morphology) from prostate biopsies (n=10), transurethral resections of prostate tumors (n=4), bone marrow or bone biopsies (n=9), lymph node (n=1) or brain (n=1). Results are shown in Table 1. Table 1. Immunohistochemistry Anaplastic PC % Positive Cells AR RB1 p53 UBE2C Ki67 CYP17A1 0 8 11 11 5 1 0 < or = 10% 3 6 9 9 8 1 > 10% 14 8 5 11 16 24 Of the 17 samples that had ≤10% RB1+ cells, 10 had ≤10% AR+ cells and 9 had >10% UBE2C+ cells. Of the 11 samples that had ≤10% AR+ cells, 10 also had ≤10% RB1+ cells and 6 had >10% UBE2C+ cells. These data support our hypothesis that the anaplastic prostate carcinomas are characterized by loss of tumor suppressors and overexpression of mitotic genes. Updated results in additional samples and of additional markers will be presented. Citation Format: Ana M. Aparicio, Sankar Maity, Xuemei Wang, Anh G. Hoang, Eleni Efstathiou, Patricia Troncoso, Christopher J. Logothetis. A molecular characterization of the anaplastic prostate carcinomas. [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 1195. doi:10.1158/1538-7445.AM2013-1195

Small cell prostate cancer (SCPC) is an androgen receptor (AR) negative variant that often emerges in the castration-resistant progression of typical AR-positive prostate adenocarcinomas. Its presence predicts for an aggressive clinical course with poor response to hormonal therapies and a short median survival. Evidence suggests that the emergence of (SCPC) occurs through cellular transdifferentiation. Therefore, we hypothesized that loss of AR gene transcription may depend on epigenetic events. Given the central role of AR in prostate cancer, we reasoned that identifying the mechanisms involved in its downregulation could improve our understanding of how the lethal SCPC subtype arises. Here we investigated the DNA methylation and histone modifications of AR in a group of six prostate tumor xenografts developed from men with CRPC (two AR-positive [MDA PCa 170.4 and MDA PCa 180.30] and four AR-negative SCPC [MDA PCa 144.13, MDA PCa 144.4, MDA PCa 155 and MDA PCa 146.10]) and three established prostate cancer cell lines (one AR-positive [LNCaP] and two AR-negative [PC3 and DU145]). We first evaluated the methylation status of selected CpG sites in the AR promoter-associated CpG island using bisulfite-sequencing followed by pyrosequencing analysis. Except for the cancer cell lines PC-3 and DU145, all other cell lines and xenografts were unmethylated regardless of the AR expression status. Next, we used chromatin immunoprecipitation (ChIP) to evaluate marking of the AR promoter and a putative proximal enhancer by active (H3K4me3 and H3K9ac) and repressive (H3K9me2 and H3K27me3) histone modifications. Marking of the constitutively expressed genes (ACTB and GAPDH) and a repressed gene (HBB) served as control for these experiments. As expected, the only samples with AR marking by H3K4me3 and H3K9ac were the two AR-positive xenografts and LNCaP. Marking by repressive histone modifications was more variable: H3K27me3 was a universal finding in AR-negative samples except for Du-145, and was accompanied by H3K9me2 in two out of four xenografts. H3K27me3 and H3K9me2 also marked the putative enhancer region when AR was repressed. Altogether, these data indicate that promoter DNA methylation of AR is an infrequent finding in prostate cancer, while polycomb protein-based silencing is nearly universal in AR-negative variants. Also, it shows that H3K9me2 promotes reinforcement of silencing. Thus, we propose that reactivation of AR may by achieved in selected cases by inhibiting H3K27me3 alone, while concomitant inhibition of both polycomb and SET domain proteins may be necessary for double-positive H3K27/K9 methylation cases. Given the purported differentiating and tumor suppressor effects of AR, its reactivation in SCPC may be of therapeutic benefit. Citation Format: Brittany N. Kleb, Marcos RH Estecio, Guanglin Wu, Jing-Fang Lu, Christopher J. Logothetis, Sankar Maity, Ana M. Aparicio. Mechanism of androgen receptor (AR) silencing in small cell prostate carcinoma. [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 2986. doi:10.1158/1538-7445.AM2013-2986

Cytochrome P450 17α-hydroxylase /17,20-lyase (CYP17) is a validated treatment target for metastatic castrate-resistant prostate cancer (mCRPC). Abiraterone acetate (AA; Zytiga) inhibits 17α-hydroxylase and 17,20-lyase reactions catalyzed by CYP17 and thus reduces androgen biosynthesis. However, co-administration of prednisone is required to suppress the mineralocorticoid excess from 17α-hydroxylase inhibitions. VT-464, a non-steroidal small molecule inhibits androgen production without mineralocorticoid excess or cortisol depletion by selective inhibition of CYP17 17,20-lyase. We determined the impact of VT-464 on tumor growth of a mCRPC xenograft, MDA-PCa-133, in vivo, and on androgen signaling in C4-2B prostate cancer cells in vitro. The MDA-PCa-133 xenograft is derived from a clinical CRPC bone metastasis. Subcutaneous MDA-PCa-133 tumor expresses PSA, full-length androgen receptor (AR) and AR-V7 isoform. We determined the effect of VT464 and AA on MDA-PCa-133 growing in tumor-bearing castrated male mice: randomization into three groups; oral treatment with vehicle only, VT-464, (100 mg/kg bid), or AA (100 mg/kg bid) for 25 days. Both VT-464 and AA reduced tumor volume (>two fold compared to vehicle; p We determined the effects of VT-464 on AR-dependent luciferase reporter activity and expression of AR signaling genes, PSA and NKX3.1, in cultured C4-2B prostate cancer cells with or without VT-464 or AA treatment. VT-464 or AA highly reduced AR-dependent reporter activity and specific expression of PSA and NKX3.1. AR-dependent signaling in the presence of VT-464 or AA was restored however by 10 nM DHT, consistent with VT-464- or AA-mediated depletion of androgen in C4-2B cells. The AR-dependent reporter activity was also measured following overexpression of full-length AR or AR-V7 isoform in C4-2B cells. Full-length AR-dependent reporter activity was (>80%) inhibited; AR-V7-dependent reporter activity was inhibited by 50% by 1 μM VT-464 or AA. We conclude that VT-464 inhibited AR signaling as effectively as AA in C4-2B prostate cancer cells. The findings suggest that AR signaling in cells, which express high levels of AR isoform (AR-V7) are more resistant to androgen biosynthesis inhibitors than those with wild type AR. Preliminary observations suggest C4-2B cells with AR-V7 are less sensitive to AA than VT- 464. Ongoing clinical and co-clinical studies will determine if the observed differences in steroid profile and relative efficacy of VT-464 compared to AA are clinically and biologically meaningful. Citation Format: Sankar N. Maity, Guanglin Wu, Jing-fang Lu, Joel R. Eisner, Stephen W. Rafferty, Robert J. Schotzinger, William R. Moore, Christopher J. Logothetis, John C. Araujo, Eleni Efstathiou. Efficacy of VT-464, a novel selective inhibitor of cytochrome P450 17,20-lyase, in castrate-resistant prostate cancer models. [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 4772. doi:10.1158/1538-7445.AM2013-4772

Circulating markers that inform of the adaptive biology and the clinical virulence of prostate cancer do not exist. Small cell carcinoma of the prostate (SCPC) is an aggressive, androgen receptor (AR)-negative, morphological variant that arises often during the castration-resistant progression of typical adenocarcinoma. Its presence is associated with a poor response to hormonal therapies and predicts for a short survival. Micro-RNAs (miRNAs) regulate a range of processes, including establishment and maintenance of tissue differentiation, and are well-preserved in serum. Based on the observation that SCPC are characterized by a loss of prostate epithelial marker expression (such as AR and HOXB13) and an increase in the expression of proneural transcription factors (such as MYCN and ASCL1) we formulated the hypothesis that the SCPC display a miRNA profile distinct from that of typical AR-driven prostate carcinomas. We profiled the miR extracted from the serum samples of 13 men with biopsy-proven SCPC, and of 9 men with bone-predominant metastatic CRPC. Because SCPC is associated with large tumor burdens, we selected patients with bone-predominant CRPC that had abnormally high alkaline phosphatase levels and PSA > 20ng/mL. 322 miR were detected in at least one of the 22 samples. We identified two miR that were present in 10 and 11 of 13 (77% and 85%) patients with SCPC and 3 and 1 of 9 (33% and 11%) of men with unselected typical bone-predominant CRPC. Both of these miRs have been shown to control multiple genes regulating neuronal differentiation and to induce the conversion of human fibroblasts into neurons, a mechanism which may be shared by prostate adenocarcinoma cells in their transdifferentiation to small cell prostate cancer cells. Moreover, one of them was recently shown to silence AR expression. Therefore we conclude that two circulating miRs may serve to monitor adaptive responses and identify virulent subsets of prostate cancer, thus serving to guide therapy and selection of patients for clinical trials. Validation of these findings is ongoing in a larger cohort of patients. Citation Format: Ana M. Aparicio, Emily Gallichotte, Heather Cheng, Suk-Young Yoo, Sankar Maity, Christopher Logothetis, Muneesh Tewari. Circulating micro-RNAs can detect adaptive response to therapy and aggressive subset of prostate cancer. [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 1205. doi:10.1158/1538-7445.AM2013-1205

The mammalian CCAAT-binding factor (CBF; also called NF-Y and CP1) is a heterotrimeric protein consisting of three subunits, CBF-A, CBF-B, and CBF-C, all of which are required for DNA binding and all of which are present in the CBF-DNA complex. In this study using cross-linking and immunoprecipitation methods, we first established that CBF-B interacts simultaneously with both subunits of the CBF-A-CBF-C heterodimer to form a heterotrimeric CBF molecule. We then performed a mutational analysis of CBF-C to define functional interactions with the other two CBF subunits and with DNA using several in vitro assays and an in vivo yeast two-hybrid system. Our experiments established that the evolutionarily conserved segment of CBF-C, which shows similarities with the histone-fold motif of histone H2A, was necessary for formation of the CBF-DNA complex. The domain of CBF-C which interacts with CBF-A included a large portion of this segment, one that corresponds to the segment of the histone-fold motif in H2A used for interaction with H2B. Two classes of interactions involved in formation of the CBF-A-CBF-C heterodimer were detected; one class, provided by residues in the middle of the interaction domain, was needed for formation of the CBF-A-CBF-C heterodimer. The other, provided by sequences flanking those of the first class was needed for stabilization of the heterodimer. Two separate domains were identified in the conserved segment of CBF-C for interaction with CBF-B; these were located on each side of the CBF-A interaction domain. Since our previous experiments identified a single CBF-B interaction domain in the histone-fold motif of CBF-A, we propose that a tridentate interaction domain in the CBF-A-CBF-C heterodimer interacts with the 21-amino-acid-long subunit interaction domain of CBF-B. Together with our previous mutational analysis of CBF-A (S. Sinha, I.-S. Kim, K.-Y. Sohn, B. de Crombrugghe, and S. N. Maity, Mol. Cell. Biol. 16:328-337, 1996), this study demonstrates that the histone fold-motifs of CBF-A and CBF-C interact with each other to form the CBF-A-CBF-C heterodimer and generate a hybrid surface which then interacts with CBF-B to form the heterotrimeric CBF molecule.

CBF-A, CBF-B, and CBF-C together form the heterotrimeric mammalian CCAAT-binding factor, CBF, which binds to DNA to form a CBF-DNA complex. Here we examined the transcription activation function of CBF in an in vitro reconstituted system using the three purified recombinant CBF subunits expressed in Escherichia coli. Two of the subunits, CBF-A and CBF-C, were coexpressed and purified as a CBF-A/CBF-C complex. Addition of the three wild-type recombinant CBF subunits to EL4 cell nuclear extracts depleted of CBF stimulated transcription 5-20-fold from proalpha2(1) collagen promoters and 10-fold from the Rous sarcoma virus long terminal repeat. Two CBF deletion mutants, one containing full-length CBF-A and CBF-C and a CBF-B lacking the NH2-terminal residues 1-224, and the other containing full- length CBF-A and CBF-B and a CBF-C lacking the COOH-terminal residues 114-309, also stimulated transcription from these promoters, but the level of activation was reduced to half that obtained with the full-length CBF subunits. In contrast, a CBF deletion mutant protein containing full-length CBF-A and deleted forms of both CBF-B and CBF-C showed very little transcription activation from these promoters. Hence, this study demonstrates that the heterotrimeric CBF protein consists of two transcription activation domains, one present in CBF-B and the other in CBF-C, and that the two domains act additively in the in vitro assay. The activation domains of both CBF-B and CBF-C, which are rich in glutamine and hydrophobic residues, showed amino acid sequence similarities with each other and with the glutamine-rich activation domain of transcription factor Sp1.

The mammalian CCAAT-binding factor CBF (also called NF-Y or CP1) consists of three subunits, CBF-A, CBF-B, and CBF-C, all of which are required for DNA binding and present in the CBF-DNA complex. In this study we first established the stoichiometries of the CBF subunits, both in the CBF molecule and in the CBF-DNA complex, and showed that one molecule of each subunit is present in the complex. To begin to understand the interactions between the CBF subunits and DNA, we performed a mutational analysis of the CBF-A subunit. This analysis identified three classes of mutations in the segment of CBF-A that is conserved in Saccharomyces cerevisiae and mammals. Analysis of the first class of mutants revealed that a major part of the conserved segment was essential for interactions with CBF-C to form a heterodimeric CBF-A/CBF-C complex. The second class of mutants identified a segment of CBF-A that is necessary for interactions between the CBF-A/CBF-C heterodimer and CBF-B to form a CBF heterotrimer. The third class defined a domain of CBF-A involved in binding the CBF heterotrimer to DNA. The second and third classes of mutants acted as dominant negative mutants inhibiting the formation of a complex between the wild-type CBF subunits and DNA. The segment of CBF-A necessary for DNA binding showed sequence homology to a segment of CBF-C. Interestingly, these sequences in CBF-A and CBF-C were also homologous to the sequences in the histone-fold motifs of histones H2B and H2A, respectively, and to the archaebacterial histone-like protein HMf-2. We discuss the functional domains of CBF-A and the properties of CBF in light of these sequence homologies and propose that an ancient histone-like motif in two CBF subunits controls the formation of a heterodimer between these subunits and the assembly of a sequence-specific DNA-protein complex.

Publisher Summary Several proteins have been isolated that bind to CCAAT motifs. The CCAAT-binding factor (CBF; also designated NF-Y and CP1) is one of these and is capable of forming a specific complex with a number of promoter DNAs containing a CCAAT motif. Point mutations in each base of the CCAAT motif of these DNAs resulted in either loss or decrease in formation of the DNA-CBF complex, indicating that DNA binding of CBF requires a high degree of conservation of the CCAAT sequence. Moreover, mutations in the CCAAT motif that inhibit formation of the CBF-DNA complex also resulted in reduced transcription activity. These and other results indicated that CBF is a transcription factor that can activate various eukaryotic genes. Other CCAAT-binding polypeptides include CTF/NF1 and C/EBP, but the DNA sequences in the binding sites for these two proteins often do not contain a complete CCAAT motif. Hence, CBF can be distinguished from these two proteins on the basis of the sequence requirements in the DNA-binding sites.

Background: Treatment of metastatic prostate cancer (PCa) with single agents has shown only modest efficacy. We hypothesized dual inhibition of different pathways in PCa results in improved tumor inhibition. The Src family kinases (SFK) and insulin-like growth factor-1 (IGF-1) signaling axes are aberrantly activated in both primary PCa and bone metastases and regulate distinct and overlapping functions in PCa progression. We examined the antitumor effects of combined inhibition of these pathways. Materials and Methods: Src andIGF-1 receptor (IGF-1R) inhibition was achieved in vitro by short hairpin (sh)RNA and in vitro and in vivo by small molecule inhibitors (dasatinib and BMS-754807, against SFK and IGF-1R/Insulin Receptor(IR), respectively). Results: In vitro, inhibition of IGF-1 signaling affected cell survival and proliferation. SFK blockade alone had modest effects on proliferation, but significantly enhanced the IGF-1R blockade. These findings correlated with a robust inhibition of IGF-1induced Akt1 phophorylation by dasatinib, whereas Akt2 phosphorylation was SFK independent and only inhibited by BMS754807. Thus, complete inhibition of both Akt genes, not seen by either drug alone, is likely a major mechanism for the decreased survival of PCa cells. Furthermore, dasatinib and BMS-754807 inhibited in vivo growth of the primary human xenograft MDA PCa 133, with corresponding inhibition of Akt in tumors. Also, both orthotopic and intratibial tumor growth of PC-3 cells were more potently inhibited by dual SFK and IGF-1R/IR blockade compared to either pathway alone, with a corresponding decrease in bone turnover markers. Conclusions: Dual IGF-1R/IR and SFK inhibition may be a rational therapeutic approach in PCa by blocking both independent and complementary processes critical to tumor growth.

The CCAAT-binding factor CBF is a heteromeric transcription factor that specifically binds to CCAAT sequences in many eukaryotic genes. CBF consists of three subunits, CBF-A, CBF-B, and CBF-C, all three of which are necessary for DNA binding. In this study we examined the transcription activation function of CBF by two different approaches. We first used a heterologous system in which a series of deletion mutations of CBF-B, fused to the bacterial LexA DNA binding domain, were transfected into HeLa cells together with a reporter gene driven by a minimal promoter containing LexA binding sites. These experiments showed that CBF-B needed both a glutamine-rich domain and an adjacent serine/threonine-rich domain to activate the reporter gene optimally. The glutamine-rich domain by itself activated transcription only modestly. We also set up an in vitro transcription reconstituted system in which trans-activation by CBF occurred through a physiological CCAAT motif. Nuclear extracts from NIH 3T3 cells were first depleted of CBF and then complemented with recombinant CBF-B and a highly purified fraction containing native CBF-A and CBF-C. Recombinant full-length CBF-B together with CBF-A and CBF-C activated transcription of several alpha 2(I) collagen gene promoter constructs. We then tested whether in this system the glutamine- and serine/threonine-rich domains of CBF-B were needed for trans-activation by CBF. We generated a truncated form of CBF-B that was still able to bind DNA in the presence of CBF-A and CBF-C. Even in the absence of the glutamine- and serine/threonine-rich domains of CBF-B, reconstituted CBF did activate transcription, suggesting that CBF transcriptional activation can also be mediated by the other subunits of CBF or by another transcription factor present in the nuclear extracts that interacts with CBF. Taken together our results suggest a model in which CBF has the potential to activate transcription either through the glutamine- and serine/threonine-rich domains of CBF-B or through the other subunits of CBF or through another component recruited by CBF.

Lethal prostate cancer is predominantly a castrate-resistant disease. However, castrate-resistant prostate cancer (CRPC) is clinically heterogeneous and a classification that is predictive of outcome and response to therapies is lacking. Previous epigenetic profiling studies in CRPC have been limited to a small number of genes or sequences and therefore we explored the DNA methylome of CRPC and its capacity to classify the disease. We performed methylated CpG island amplification microarrays (MCAMs) using a panel of xenografts derived from 24 patients with CRPC tumors, 8 prostate tumors, 1 local recurrence, 5 liver metastases, 3 pleural fluid samples, 2 adrenal gland metastases and 1 each of the following: bone, subcutaneous tissue, retroperitoneal lymph node, ascitic fluid and brain. The xenograft morphology consisted of 15 adenocarcinomas, 11 small cell carcinomas, 3 large cell neuroendocrine carcinomas, 1 squamous cell carcinoma, 2 mixed morphologies and 2 unknown. The Lowess-normalized M values were used for analysis and the MCAM results were validated by pyrosequencing of 20 sequences associated with 12 genes with a sensitivity of 61.9%, a specificity of 84.3%, a positive predictive value of 73.6% and a negative predictive value of 75.7%. An unsupervised hierarchal clustering analysis using M values for probes located in CpG islands was performed and these results were compared with the clinicopathological features of the tissues. We observed that, different xenograft sublines derived from the same donor tumor clustered together suggesting that the DNA methylome is homogenous throughout a given tumor mass, despite the presence of histological heterogeneity, and that it is maintained through serial passages in mice. Unsupervised hierarchal clustering classified the xenografts into 3 groups, which showed trend towards distinct clinicopathological features including overall survival and androgen receptor (AR) status. In summary, we found that DNA methylation is a frequent event in CRPC and well preserved in xenograft tumors. Furthermore, the methylation profile of CRPC may represent a marker of clinicopathological subgroups with differential survival and AR status. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 991. doi:1538-7445.AM2012-991

Small cell and large cell neuroendocrine carcinoma belong to the spectrum of poorly differentiated neuroendocrine carcinomas (NECa) of the prostate, characterized by a distinct clinical course. Often unrecognized, they can emerge either de novo or in the castrate-resistant progression of typical acinar adenocarcinoma (AdCa) and are found in 10-20% of men who die of the disease. Although sensitive to chemotherapy, responses are short lived and prognosis is dismal. An understanding of the biology underlying NECa and identification of novel therapeutic targets for this variant are urgently needed. In this study we used xenograft models and tissue specimens obtained from castrate-resistant prostate carcinomas (CRPC) to gain insight into the pathways implicated in the development of the highly aggressive NECa. Xenograft models with features of typical AdCa (n=3) and NECa (n=4) were subjected to gene-expression profiling using Affymetrix HGU133 Plus 2.0. One-way ANOVA was applied to identify differentially expressed probes (DEPs). The Web-based Gene Ontology (GO) Tree Machine was used to examine GO hierarchies. Selected genes were validated by quantitative real-time PCR (qRT-PCR) and Western blotting in the xenografts and by immunohistochemistry in the xenografts, and the tumor specimens of 62 patients with CRPC. Unsupervised hierarchal clustering of the raw data classified the xenografts correctly according to their morphology. Using stringent FDR 0.05, we identified 140 DEPs (0.3%) between the two groups. GO analysis revealed significant enrichment in the “M phase of mitotic cell cycle” biological process subtree (adjP=7.04e-08). Amongst the genes differentially expressed between the two groups, UBE2C, (E2 ubiquitin-conjugating enzyme UBCH10), a member of the anaphase promoting complex (APC), was significantly upregulated in NECa relative to AdCa by qRT-PCR (P=0.003) and immunohistochemistry (P=0.007) in xenografts, and by immunohistochemistry in the CRPC specimens (P Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 36. doi:10.1158/1538-7445.AM2011-36

Background Our previous work has provided strong evidence that the transcription factor SOX9 is completely needed for chondrogenic differentiation and cartilage formation acting as a “master switch” in this differentiation. Heterozygous mutations in SOX9 cause campomelic dysplasia, a severe skeletal dysmorphology syndrome in humans characterized by a generalized hypoplasia of endochondral bones. To obtain insights into the logic used by SOX9 to control a network of target genes in chondrocytes, we performed a ChIP-on-chip experiment using SOX9 antibodies. Methodology/Principal Findings The ChIP DNA was hybridized to a microarray, which covered 80 genes, many of which are involved in chondrocyte differentiation. Hybridization peaks were detected in a series of cartilage extracellular matrix (ECM) genes including Col2a1, Col11a2, Aggrecan and Cdrap as well as in genes for specific transcription factors and signaling molecules. Our results also showed SOX9 interaction sites in genes that code for proteins that enhance the transcriptional activity of SOX9. Interestingly, a strong SOX9 signal was also observed in genes such as Col1a1 and Osx, whose expression is strongly down regulated in chondrocytes but is high in osteoblasts. In the Col2a1 gene, in addition to an interaction site on a previously identified enhancer in intron 1, another strong interaction site was seen in intron 6. This site is free of nucleosomes specifically in chondrocytes suggesting an important role of this site on Col2a1 transcription regulation by SOX9. Conclusions/Significance Our results provide a broad understanding of the strategies used by a “master” transcription factor of differentiation in control of the genetic program of chondrocytes.

Currently no therapy effectively controls the progression of advanced human prostate cancer. We previously reported that fibroblast growth factor 9 (FGF9) contributes to the osteoblastic progression of human prostate cancer in bone (J Clin Invest 2008;118:2697). We examined the effect of TKI258 (a receptor tyrosine kinase inhibitor [TKI] with strong activity against FGF receptor 1-3 [FGFR1-3; IC50 < 40 nM]; [Novartis Pharma Corp.]) on primary mouse osteoblasts treated with and without FGF9 and TKI258. TKI258 blocked FGF9's induction of p-FRS2α (a gatekeeper that mediates FGFR downstream signals) an indication that TKI258 specifically blocks FGF signaling in osteoblasts. These observations provide strong evidence implicating FGF signaling in the osteoblastic progression of prostate cancer in bone. We hypothesized that pharmacologic blockade of the FGFR signaling has an antitumor effect in prostate cancer. To test our hypothesis, we studied the antitumor efficacy of TKI258 in the osteoblastic growth of MDA PCa 118b, a prostate cancer tumor graft that depends on FGF9 for growth. We assessed the effect of TKI258 on the growth of MDA PCa 118b prostate cancer cells in the femurs of male SCID mice. Ten mice were treated with TKI258 (20 and 60 mg/kg body weight daily by oral gavage), and another 10 mice were treated with vehicle only. Treatment started the day after we identified tumor on MRI scanning at the site of tumor cell injection and continued for 3 weeks, when we used MRI to assess tumor volumes in the femurs and microCT to assess bone mass. Femurs bearing MDA PCa 118b in mice treated with TKI258 had significantly smaller tumors (P = 0.019) and less prostate cancer-induced cortical bone (P = 0.034) than did control mice. Histopathologic analysis indicated that tumors in the treated mice were smaller than in the controls. Initial analysis of tumor-associated osteoclasts (assessed by their expression of tartrate-resistant acidic phosphatase) shows no difference between the treated and control mice. The femurs bearing MDA PCa 118b tumors were then analyzed by Western blotting to measure signaling; we found that TKI258 specifically inhibited p-ERK1/2 (an FGF signaling target gene) but not p-AKT. Taken together, these results suggest that TKI258 inhibits the growth of prostate cancer cells in bone by targeting both those cells and osteoblasts (but not osteoclasts), possibly by blocking FGF signaling. Subsequent molecular analysis of FGF downstream target genes will help elucidate the mechanism underlying TKI258's inhibition of prostate cancer growth in bone. Results from these studies will also help identify markers of response to TKI258 that will be used to interpret an ongoing clinical study with TKI258 in selected men with castrate-resistant prostate cancer with bone marrow infiltration. The results will serve as the foundation for the development of candidate predictive markers and further therapies based on targeting the FGF pathway. 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 344.

Background: The tumor microenvironment is involved in prostate cancer progression. Several stromal-epithelial-interacting pathways associated with prostate cancer (PCa) progression in the bone, are also considered candidates of resistance to current therapeutic strategies applied. Hedgehog (Hh) signaling has been associated with PCa aggressiveness. Therefore Hh pathway could be a novel diagnostic and therapeutic target, also contributing to therapy against prostate carcinoma metastasis in bone. Experimental work on specific chemical inhibitors of Hh signaling suggests that they may represent an entirely new class of therapeutic agents. In this study we tested the efficacy of Hh pathway inhibition with Smoothened inhibitor GDC-0449 in 118b prostate cancer xenograft model. Experimental Design: We employed the xenograft MDA PCa 118b, derived from the bone metastasis of a patient with castrate-resistant prostatic adenocarcinoma. This is characterized by unique bone producing feature when injected subcutaneously in SCID mice. Bone is the most common site for metastasis of prostate carcinoma, therefore a model with the new bone formation distinctive characteristic is really informative. Following MDA PCa 118b sc injection, animals were treated with Smoothened inhibitor GDC-0449 (oral administration, for 21 days). Hh pathway components expression was measured both in the tumor cells and stromal compartment using species specific primers for real-time PCR, western blot analysis and immunohistochemistry. Results: Paracrine Hedgehog signaling was confirmed in the tumor xenograft microenvironment. Baseline Shh expression was present in human tumor cells and significantly higher compared to stromal compartment, while nuclear Gli1 (a hallmark of pathway activation) and Ptch1 expression in the stromal compartment were present and significantly higher compared to human tumor cells. Smoothened inhibition resulted in attenuation of stromal expression of Gli1 and Ptch1, in the treated group compared to the control thus confirming the pharmacodynamic effect of the agent. A trend for slower tumor growth at the treated group was observed, while a decline in proliferation rate was noted when Hh pathway was suppressed in the stromal compartment. Conclusion: Hh signaling pathway demonstrates paracrine activation in the 118b prostate cancer bone producing xenograft model. GDC-0449 is effective in blocking Hh signaling in PCa. Future directions: A combination of Hedgehog signaling inhibition and cytotoxic therapies, such as androgen ablation would likely increase efficacy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C253.