Established Prostate Tumors Research Articles

TP53 loss-of-function causes vulnerability to autophagy inhibition in aggressive prostate cancer.

TP53 loss-of-function is commonly found in aggressive prostate cancer. However, a highly-efficient therapy for this tumor subtype is still lacking. In this study, we investigated the relationship between TP53 mutation status and autophagy in prostate cancer and assessed the efficacy of autophagy inhibitors on TP53-deficient tumors. We first evaluated the expression patterns of p53 and autophagy-related proteins, namely LC3B, ULK1 and BECLIN1, as well as their relationship in treatment-naïve and castration-resistant prostate cancer specimens through immunohistochemistry. Subsequently, we generated a Trp53-deleted genetically-engineered mouse model, established prostate tumor organoid lines from the mice and assessed the efficacy of autophagy inhibitors in overcoming Enzalutamide resistance in the tumor organoid model. We also investigated the impact of TP53 re-expression in modulating responses to autophagy inhibitors using LNCaP cell line, which harbored a TP53 missense mutation. Lastly, we attempted to identify potential autophagy-related genes that were crucial for TP53-deficient tumor maintenance. TP53 loss-of-function was associated with increased levels of autophagy-related proteins in aggressive prostate cancers and Trp53-deleted genetically-engineered mouse-derived tumors. Moreover, the generated androgen receptor-independent tumor organoids were highly vulnerable to autophagy inhibition. Upon TP53 re-expression, not only did the surviving LNCaP cells demonstrate resistance, but they also showed growth advantage in response to autophagy inhibition. Lastly, PEX14, an important peroxisomal regulator was differentially upregulated in aggressive tumors with TP53 loss-of-function mutations, thus implying the importance of peroxisome turnover in this tumor subtype. Our results support the potential use of autophagy inhibitors in prostate cancers that contain TP53 loss-of-function mutations.

Pyruvate Kinase M1 Suppresses Development and Progression of Prostate Adenocarcinoma.

Differential expression of PKM1 and PKM2 impacts prostate tumorigenesis and suggests a potential therapeutic vulnerability in prostate cancer.

Formulation of the bivalent prostate cancer vaccine with surgifoam elicits antigen-specific effector T cells in PSA-transgenic mice.

We previously developed and characterized an adenoviral-based prostate cancer vaccine for simultaneous targeting of prostate-specific antigen (PSA) and prostate stem cell antigen (PSCA). We also demonstrated that immunization of mice with the bivalent vaccine (Ad5-PSA+PSCA) inhibited the growth of established prostate tumors. However, there are multiple challenges hindering the success of immunological therapies in the clinic. One of the prime concerns has been to overcome the immunological tolerance and maintenance of long-term effector T cells. In this study, we further characterized the use of the bivalent vaccine (Ad5-PSA+PSCA) in a transgenic mouse model expressing human PSA in the mouse prostate. We demonstrated the expression of PSA analyzed at the mRNA level (by RT-PCR) and protein level (by immunohistochemistry) in the prostate lobes harvested from the PSA-transgenic (PSA-Tg) mice. We established that the administration of the bivalent vaccine in surgifoam to the PSA-Tg mice induces strong PSA-specific effector CD8+ T cells as measured by IFN-γ secretion and in vitro cytotoxic T-cell assay. Furthermore, the use of surgifoam with Ad5-PSA+PSCA vaccine allows multiple boosting vaccinations with a significant increase in antigen-specific CD8+ T cells. These observations suggest that the formulation of the bivalent prostate cancer vaccine (Ad5-PSA+PSCA) with surgifoam bypasses the neutralizing antibody response, thus allowing multiple boosting. This formulation is also helpful for inducing an antigen-specific immune response in the presence of self-antigen, and maintains long-term effector CD8+ T cells.

Novel tumor suppressor microRNA at frequently deleted chromosomal region 8p21 regulates epidermal growth factor receptor in prostate cancer.

Genomic loss of chromosome (chr) 8p21 region, containing prostate-specific NKX3.1 gene, is a frequent alteration of the prostate cancer (PCa) oncogenome. We propose a novel, paradigm shifting hypothesis that this frequently deleted locus is also associated with a cluster of microRNA genes- miR-3622a/b- that are lost in PCa and play an important mechanistic role in progression and metastasis. In this study, we demonstrate the role of miR-3622b in prostate cancer. Expression analyses in a cohort of PCa clinical specimens and cell lines show that miR-3622b expression is frequently lost in prostate cancer. Low miR-3622b expression was found to be associated with tumor progression and poor biochemical recurrence-free survival. Further, our analyses suggest that miR-3622b expression is a promising prostate cancer diagnostic biomarker that exhibits 100% specificity and 66% sensitivity. Restoration of miR-3622b expression in PCa cell lines led to reduced cellular viability, proliferation, invasiveness, migration and increased apoptosis. miR-3622b overexpression in vivo induced regression of established prostate tumor xenografts pointing to its therapeutic potential. Further, we found that miR-3622b directly represses Epidermal Growth Factor Receptor (EGFR). In conclusion, our study suggests that miR-3622b plays a tumor suppressive role and is frequently downregulated in prostate cancer, leading to EGFR upregulation. Importantly, miR-3622b has associated diagnostic, prognostic and therapeutic potential. Considering the association of chr8p21 loss with poor prognosis, our findings are highly significant and support a novel concept that associates a long standing observation of frequent loss of a chromosomal region with a novel miRNA in prostate cancer.

Abstract 1103: Tumor suppressive role of a novel microRNA at frequently deleted chromosomal locus 8p21 in prostate cancer

Abstract Background: A frequent genomic alteration in prostate cancer (PCa) is the loss of chromosome (chr) 8p21 in approximately 30%-50% of cases. Genomic deletions of this region increase significantly with tumor grade and are associated with tumor progression and poor prognosis suggesting its role in PCa progression. A common region of loss of heterozygosity (LOH) has been mapped to the chr8p21 locus that harbors prostate-specific NKX3.1 homeobox gene. Recent genomic studies suggest that this region harbors alternative tumor suppressor genes apart from NKX3.1 that have largely remained elusive. We propose a novel, paradigm shifting hypothesis that this frequently deleted locus is associated with a cluster of microRNA genes- miR-3622a/b- that are lost in prostate cancer and play an important mechanistic role in PCa progression and metastasis. We previously demonstrated that miR-3622a plays a crucial role in PCa epithelial-to-mesenchymal transition by direct targeting of ZEB1 and SNAI2. Here we demonstrate the role of miR-3622b in prostate cancer. Methods: miRNA expression profiling was performed in microdissected prostate cancer tissues and matched adjacent normal regions by real-time PCR. To assess the functional significance of miR-3622b in PCa, we overexpressed miR-3622b/ control miRNA (miR-CON) in PCa cell lines (Du145, PC3, LNCaP) followed by functional assays.We also examined the therapeutic potential of synthetic miR-3622b mimics in vivo in a prostate cancer xenograft mouse model. Results: Expression analyses in a cohort of prostate cancer clinical specimens showed that miR-3622b expression is frequently lost in prostate cancer. Further, loss of miR-3622b expression significantly correlated with poor survival outcome and tumor progression. miR-3622b overexpression significantly decreased cellular viability and clonogenicity in PCa cell lines supporting an anti-proliferative role for this microRNA. miR-3622b overexpression also led to significant reduction of invasiveness and migration in PCa cell lines. In vivo studies demonstrated that miR-3622b overexpression induced regression of established prostate tumor xenografts. Conclusions: Collectively, these data suggest that miR-3622b plays a tumor suppressive role in PCa. We propose that frequent loss of miR-3622a/b at chr8p21 region by genetic and epigenetic mechanisms promotes prostate cancer progression and metastasis. This study supports a novel concept that connects a long standing observation of frequent loss of a chromosomal region with a novel miRNA cluster in prostate cancer. Citation Format: Nathan Bucay, Kiran Sekhon, Shahana Majid, Varahram Shahryari, Soichiro Yamamura, Z. Laura Tabatabai, Kirsten Greene, Yuichiro Tanaka, Rajvir Dahiya, Guoren Deng, Sharanjot Saini. Tumor suppressive role of a novel microRNA at frequently deleted chromosomal locus 8p21 in prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1103.

TLR9 signaling through NF-κB/RELA and STAT3 promotes tumor-propagating potential of prostate cancer cells.

Prostate cancer progression was associated with tumorigenic signaling activated by proinflammatory mediators. However, the etiology of these events remains elusive. Here, we demonstrate that triggering of the innate immune receptor, Toll-like Receptor 9 (TLR9), in androgen-independent prostate cancer cells initiates signaling cascade leading to increased tumor growth and progression. Using limited dilution/serial transplantation experiments, we show that TLR9 is essential for prostate cancer cells' potential to propagate and self-renew in vivo. Furthermore, low expression or silencing of TLR9 limits the clonogenic potential and mesenchymal stem cell-like properties of LNCaP- and PC3-derived prostate cancer cell variants. Genome-wide transcriptional analysis of prostate cancer cells isolated from xenotransplanted TLR9-positive and -negative tumors revealed a unique gene expression signature, with prominent upregulation of inflammation- and stem cell-related markers. TLR9 signaling orchestrated expression of critical stem cell-related genes such as NKX3.1, KLF-4, BMI-1 and COL1A1, at both mRNA and protein levels. Our further analysis identified that TLR9-induced NF-κB/RELA and STAT3 transcription factors co-regulated NKX3.1 and KLF4 gene expression by directly binding to both promoters. Finally, we demonstrated the feasibility of using TLR9-targeted siRNA delivery to block RELA- and STAT3-dependent prostate cancer cell self-renewal in vivo. The intratumoral administration of CpG-RELAsiRNA or CpG-STAT3siRNA but not control conjugates inhibited growth of established prostate tumors and reduced clonogenic potential of cancer cells. Overcoming cancer cell self-renewal and tumor-propagating potential by targeted inhibition of TLR9 signaling can provide therapeutic strategy for late-stage prostate cancer patients.

TLR4 activation by lipopolysaccharide confers survival advantage to growth factor deprived prostate cancer cells.

Prostate cancer (PCa) cells express Toll-like receptor-4 (TLR4), a known pro-tumorigenic molecule for different cancer cells. The cancer cells residing in the avascular region of the tumor confront various metabolic stresses and continuously adapt mechanisms to overcome them. We hypothesized that TLR4 activation might provide direct survival advantage to metabolically stressed PCa cells. We first investigated the effect of LPS on survival of serum deprived PCa cells. To understand the molecular mechanisms involved in TLR4 mediated PCa survival, we next investigated change in expression of markers for apoptosis, senescence and autophagy. Ultimately, the effect of LPS on established prostate tumors was confirmed in vivo using a syngeneic rat model for PCa. Lipopolysaccharide (LPS)-mediated TLR4 activation significantly enhanced survival of serum deprived (SD) PC3, DU145 and MAT-LyLu PCa cells. TLR4 inhibition by a specific inhibitor resulted in rapid death of SD-PC3 cells, which was significantly suppressed by LPS. Interestingly, LPS treatment suppressed macroautophagy in SD-PC3 cells and increased expression of CCL2 (C-C motif ligand-2), a known autophagy inhibitor and pro-survival factor. Intra-tumor LPS injection resulted in increased tumor mass, induced TLR4 activation, suppressed autophagy, and increased the macrophage population in MAT-LyLu-tumors. Our study reveals that bacterial LPS enhance survival of PCa cells under conditions of nutrient stress through TLR4 activation. Moreover, LPS induces overexpression of CCL2 involved in the suppression of starvation-induced macroautophagy in PCa cells, and enhanced macrophage population in prostate tumors in vivo. Taken together, the current study suggests the importance of bacterial infection or TLR4-activation in prostate cancer pathogenesis.

Elimination of Progressive Mammary Cancer by Repeated Administrations of Chimeric Antigen Receptor-Modified T Cells

Continuous oncogenic processes that generate cancer require an on-going treatment approach to eliminate the transformed cells, and prevent their further development. Here, we studied the ability of T cells expressing a chimeric antibody-based receptor (CAR) to offer a therapeutic benefit for breast cancer induced by erbB-2. We tested CAR-modified T cells (T-bodies) specific to erbB-2 for their antitumor potential in a mouse model overexpressing a human erbB-2 transgene that develops mammary tumors. Comparing the antitumor reactivity of CAR-modified T cells under various therapeutic settings, either prophylactic, prior to tumor development, or therapeutically. We found that repeated administration of CAR-modified T cells is required to eliminate spontaneously developing mammary cancer. Systemic, as well as intratumoral administered CAR-modified T cells accumulated at tumor sites and eventually eliminated the malignant cells. Interestingly, within a few weeks after a single CAR T cells' administration, and rejection of primary lesion, tumors usually relapsed both in treated mammary gland and at remote sites; however, repeated injections of CAR-modified T cells were able to control the secondary tumors. Since spontaneous tumors can arise repeatedly, especially in the case of syndromes characterized by specific susceptibility to cancer, multiple administrations of CAR-modified T cells can serve to control relapsing disease.

Immunotherapy Exposes Cancer Stem Cell Resistance and a New Synthetic Lethality

Development of resistance to targeted drugs and immunotherapy limits improvement in response rates and disease-free survival of cancer patients. In advanced melanoma, for example, multiple mechanisms of resistance emerge during BRAF inhibitor drug therapy that affect both tumor cell properties and microenvironment.1 In addition, just as immunoediting during the de novo immune response against cancer selects for immune-resistant tumor variants,2 active and passive immunotherapies can create selective pressures that lead to outgrowth of resistant tumor cells or new metastases (Figure 1). Understanding the mechanisms of resistance is critical to developing therapeutic strategies to counteract them as well as preventive measures to avoid their onset. In this issue of Molecular Therapy, Boisgerault and colleagues3 nicely elucidate these points using a tumor vaccination model to induce a T-cell response that places a selective pressure on the tumor facilitating the emergence or selective survival of resistant cancer stem cells or cells undergoing epithelial–mesenchymal transition (EMT). The study further shows how acquired or intrinsic mechanisms of resistance can reveal molecular vulnerabilities that may allow responses even to chemotherapy drugs that would have been considered ineffectual.

Abstract 3960: Whole body irradiation extends the duration of antitumor immunity toward established prostate tumors by adoptively transferred CD8+ T cells in TRAMP mice.

Abstract Adoptive T cell transfer following whole body irradiation (WBI) can induce dramatic tumor regression in a subset of metastatic melanoma patients. We previously found that this approach also eliminates established autochthonous SV40 T-antigen induced murine brain tumors. However, the broader utility of this immunotherapy approach has not been systematically evaluated in solid tumors of different tissue origin. Here, we assessed the efficacy of applying WBI with adoptive T cell transfer to an SV40 T-antigen driven murine model of prostate cancer (TRAMP) previously shown to rapidly tolerize tumor-specific CD8+ T cells. TRAMP mice bearing established prostate tumors were treated with 475cGy WBI followed by adoptive transfer of T-antigen-specific T cell receptor transgenic CD8+ T cells. Accumulation, phenotype and function of the transferred T cells were monitored by flow cytometry, while therapeutic impact on mouse prostate tumors was assessed by histological scoring. Transferred T cells proliferated in both irradiated and non-irradiated TRAMP mice, but accumulated to significantly higher levels and persisted longer in the secondary lymphoid organs and prostate of irradiated mice. WBI also significantly increased the proportion of T cells that produced the effector molecule granzyme B. Prostate-infiltrating T cells in both treatment groups exhibited an effector differentiated phenotype, although neither developed a significant population of IFNγ-producing cells. Gross observations revealed that the urogenital tract in irradiated TRAMP mice was significantly smaller than that of non-irradiated mice two weeks after transfer, corresponding with a modest but statistically significant drop in pathological score. By three weeks after transfer, when prostate-infiltrating T cells had dramatically contracted in irradiated TRAMP mice, cumulative histological scores were generally equivalent although only mice in the non-irradiated treatment group had progressed to adenocarcinoma. Our results suggest that the addition of irradiation extends the persistence of functional tumor-specific T cells in the highly tolerogenic microenvironment of the TRAMP prostate. T cell accumulation was associated with a short-term delay in progression of established tumors. Citation Format: Lindsay Ward-Kavanagh, Timothy Cooper, Todd D. Schell. Whole body irradiation extends the duration of antitumor immunity toward established prostate tumors by adoptively transferred CD8+ T cells in TRAMP mice. [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 3960. doi:10.1158/1538-7445.AM2013-3960

CD73-Deficient Mice Are Resistant to Carcinogenesis

CD73 is a cell surface 5'-nucleotidase that converts AMP to adenosine, an immune suppressive molecule. CD73 may promote immune escape in cancer by contributing to the degradation of extracellular ATP released by dying cancer cells in hypoxic tumors or following chemotherapy. However, whether CD73 exerts a critical oncogenic function during tumorigenesis is unknown. In this study, we used genetically deficient mice to investigate its contribution to autochthonous tumor formation. CD73 deficiency suppressed the development of 3-methylcholanthrene (MCA)-induced fibrosarcomas through a mechanism relying upon IFN-γ, natural killer (NK) cells, and CD8(+) T cells. Similarly, CD73 deficiency also suppressed prostate tumorigenesis in TRAMP transgenic mice. Importantly, treatment with an anti-CD73 monoclonal antibody effectively suppressed growth of established MCA-induced tumors or TRAMP-C1 prostate tumors and inhibited the development of TRAMP-C1 lung metastases. The therapeutic activity of anti-CD73 monoclonal antibody against primary tumors was dependent on CD8(+) T cells, whereas its antimetastatic activity was dependent on host CD73 expression independent of T cells or NK cells. Taken together, our findings indicate that CD73 is a critical factor in tumorigenesis and that anti-CD73 antibodies may offer a novel generalized strategy to blunt immune escape and treat cancer.

Abstract 851: Interactions among transcription factors as a potential mechanism for inhibiting castrate-resistant prostate cancer (CRPCa) in transgenic adenocarcinoma of mouse prostate (TRAMP) through regulation of FLIP

Abstract Androgens are critical regulators of prostate differentiation and function as well as prostate cancer growth and survival. Prostate tumors initially regress in response to androgen-ablation therapy. However, most cancers eventually relapse with an androgen-depletion-independent phenotype that is often more aggressive than the original androgen-dependent tumor. Studies from our laboratory demonstrated that intervention with 2-ME2[2-methoxyestradiol] prevents early stage prostate cancer development and causes regression of established prostate tumors in the transgenic adenocarcinoma of mouse prostate model. Although 2-ME2 was found to be safe, well tolerated, reduce or stabilize PSA levels when given to hormone refractory prostate cancer patients who had failed other treatments including hormone therapy, it was found to be less bioavailable. Accordingly second generation 2-ME2 was developed using nanocrystal colloidal dispersion technology and has increased its bioavailability by 5-10 fold (EntreMed, Inc, Rockville, MD). In the current study we tested the ability of this newly formulated 2-ME2 on the development and progression of castrate-resistant prostate cancer in TRAMP mice. 10-12 week old TRAMP mice were castrated and fed water containing different amounts of 2-ME2 for 6 weeks. Efficacy was evaluated by magnetic resonance imaging, determining the prostate seminal vesicle complex volume and histological analysis of prostate tumor or tissue. Our results also show that 2-ME2 inhibited development of CRPCa in these mice. Further molecular analysis using cell lines demonstrated 2-ME2 treatment significantly inhibited DHT-stimulated cell proliferation in androgen-responsive LNCaP cells (p<0.001). Further DHT-induced FLIP, PSA and AR transcriptional activity (as measured by promoter activities) were also reduced by 2-ME2 (p<0.001). Transient expression assays coupled with gel-shift and ChIP assays show binding of multiple transcription factors including Sp1, Sp3, NFκB and AR to the FLIP promoter. 2-ME2 treatment reduced such binding to the FLIP promoter as evidenced by ChIP. 2-ME2 treatment also modulated the interactions among these transcription factors as evidenced by Re-ChIP assays. Interestingly transcription factor CREB but not Sp1 seems to play a predominant role in androgen regulation of FLIP expression. Our findings suggest that 2-ME2 affects androgen induced survival of prostate cancer cells through regulation of FLIP involving potential interactions between multiple transcription factors. Supported by ACS RSG-04-169 and NIH CA 135451 (APK). 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 851. doi:10.1158/1538-7445.AM2011-851

Involvement of FLIP in 2-Methoxyestradiol–Induced Tumor Regression in Transgenic Adenocarcinoma of Mouse Prostate Model

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression. Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice. High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1. Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

BRAF Activation Initiates but Does Not Maintain Invasive Prostate Adenocarcinoma

Prostate cancer is the second leading cause of cancer-related deaths in men. Activation of MAP kinase signaling pathway has been implicated in advanced and androgen-independent prostate cancers, although formal genetic proof has been lacking. In the course of modeling malignant melanoma in a tyrosinase promoter transgenic system, we developed a genetically-engineered mouse (GEM) model of invasive prostate cancers, whereby an activating mutation of BRAFV600E–a mutation found in ∼10% of human prostate tumors–was targeted to the epithelial compartment of the prostate gland on the background of Ink4a/Arf deficiency. These GEM mice developed prostate gland hyperplasia with progression to rapidly growing invasive adenocarcinoma without evidence of AKT activation, providing genetic proof that activation of MAP kinase signaling is sufficient to drive prostate tumorigenesis. Importantly, genetic extinction of BRAFV600E in established prostate tumors did not lead to tumor regression, indicating that while sufficient to initiate development of invasive prostate adenocarcinoma, BRAFV600E is not required for its maintenance.

Silibinin Inhibits Established Prostate Tumor Growth, Progression, Invasion, and Metastasis and Suppresses Tumor Angiogenesis and Epithelial-Mesenchymal Transition in Transgenic Adenocarcinoma of the Mouse Prostate Model Mice

The chronic nature of prostate cancer growth and progression leading to metastasis provides a large window for intervention. Herein, for the first time, we investigated the effect and associated mechanisms of silibinin phosphatidylcholine (silybin-phytosome) on established prostate tumors in transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Twenty-week-old TRAMP male mice having palpable prostate tumor were fed with control or 0.5% and 1%, w/w, silybin-phytosome diets for 11 weeks and then sacrificed. Dietary silibinin inhibited the growth of prostate tumors (up to 60%, P < 0.001) and suppressed tumor progression from prostatic intraepithelial neoplasia to differentiated adenocarcinoma and poorly differentiated adenocarcinoma, with a complete absence of poorly differentiated adenocarcinoma at higher doses. It also inhibited the incidence of tumor invasion of seminal vesicle (up to 81%, P < 0.001) with complete absence of distant metastasis. Silibinin moderately inhibited tumor cell proliferation and induced apoptosis, but strongly suppressed tumor microvessel density (up to 60%, P < 0.001), vascular endothelial growth factor, and vascular endothelial growth factor receptor-2 expression. Antibody array analysis of plasma showed a decrease in the circulatory levels of vascular endothelial growth factor and basic fibroblast growth factor. Decreased levels of matrix metalloproteinases (MMP), snail-1, and vimentin, and an increased level of E-cadherin were also observed, indicating the anti-epithelial-mesenchymal transition effect of silibinin in tumors. Overall, silibinin treatment of TRAMP mice bearing prostate tumor inhibited tumor growth, progression, local invasion, and distant metastasis involving suppression of tumor angiogenesis and epithelial-mesenchymal transition. These findings would have greater relevance for the ongoing phase II clinical trial with silibinin-phytosome in prostate cancer patients.

PTEN Knockout Prostate Cancer as a Model for Experimental Immunotherapy

Testing immunotherapeutic strategies for prostate cancer has been impeded by the lack of relevant tumor models in immunocompetent animals. This opportunity is now provided by the recent development of prostate specific PTEN knockout mice, which show spontaneous development of true adenocarcinoma arising from prostate epithelium and more faithfully recapitulate the human disease than any previous model. We investigated the feasibility of using tumor cells derived from this model to test tumor vaccination and adoptive immunotherapeutic strategies for prostate cancer. PTEN-CaP8 adenocarcinoma cells derived from the biallelic PTEN knockout prostate cancer model were used to vaccinate nontumor bearing litter mates. Tumor specific effector cells were generated from splenocytes of vaccinated mice by mixed lymphocyte-tumor reactions, and antiproliferative effects and cytokine generation were examined in vitro. The effect of vaccination or adoptive immunotherapy on luciferase marked PTEN-CaP8 subcutaneous tumors was monitored by tumor volumetric measurements and noninvasive bioluminescence imaging. Vaccination of litter mate mice with irradiated PTEN-CaP8 cells showed a significant prophylactic effect against the subsequent tumor challenge. Effector cells harvested from vaccinated litter mates showed significant interferon-gamma secretion upon co-incubation with PTEN-CaP8 target cells and they were capable of efficient target cell growth inhibition in vitro. Intratumor adoptive transfer of effector cells resulted in significant growth inhibition of preestablished prostate tumors in vivo. The PTEN knockout model serves as a highly useful model in which to investigate tumor cell vaccination and adoptive immunotherapeutic strategies in the context of true adenocarcinoma of the prostate. This model should accelerate efforts to develop effective immunotherapies for human prostate cancer.

Human Adrenomedullin Up-regulates Interleukin-13 Receptor α2 Chain in Prostate CancerIn vitroandIn vivo: A Novel Approach to Sensitize Prostate Cancer to Anticancer Therapy

Interleukin-13 (IL-13) receptor alpha2 (IL-13Ralpha2), a high-affinity IL-13 binding subunit and a tumor antigen, is amplified in a variety of human tumor cell lines and tumors in vivo. By cDNA microarray, we have shown that gene transfer of human and rat adrenomedullin (AM) up-regulates IL-13Ralpha2 in a human prostate tumor cell line. Here, we show that IL-13Ralpha2 mRNA and protein are also up-regulated in PC-3 prostate tumor cells by recombinant AM (rAM) and human synthetic AM peptide in a dose-dependent manner in vitro and in vivo in mouse prostate tumor model. The 8- to 10-fold up-regulation of IL-13Ralpha2 by rAM or AM peptide in prostate tumor cells in vitro and in vivo increased their sensitivity to IL-13PE cytotoxin consisting of IL-13 and a truncated form of Pseudomonas exotoxin. Immunodeficient mice with established prostate tumors transfected with AM or treated with AM peptide showed reduction in tumor size by intratumoral administration of IL-13PE in a dose-dependent manner. At the highest dose (three 100 mug/kg/d every alternate day), >70% reduction of tumor size was observed compared with controls (P <or= 0.01). These results indicate that two completely unrelated hormones (AM and IL-13) are closely related to each other and that we have identified a novel role of AM in sensitizing certain types of prostate tumors to IL-13R-directed therapeutic agent.

Partially circumventing peripheral tolerance for oncogene‐specific prostate cancer immunotherapy

Failure of cancer immunotherapy is essentially due to immunological tolerance to tumor-associated antigens (TAAs), as these antigens are also expressed in healthy tissues. Here, we used transgenic adenocarcinoma of mouse prostate (TRAMP) mice, which develop lethal prostate cancer due to prostate-specific expression of SV40 T antigen (Tag), to evaluate effects of prostatic transformation on oncogene TAA-specific tolerance and to test the possibility of breaking such tolerance using a modified recombinant vaccinia virus. We showed that Tag expression in TRAMP mice is uniquely extra-thymic, and levels of prostatic Tag expression positively correlate with malignant transformation of the prostate. Yet, young tumor-free TRAMP mice were tolerant to Tag antigen. We therefore attempted overcoming such peripheral oncogene-specific T cell tolerance through immunization with a vaccinia construct encoding Tag immunogenic epitopes. This vaccination modality showed that oncogene-specific tolerance was successfully overcome by effective in vivo priming of Tag-specific cytotoxic T cells (CTLs). However, this was restricted to young TRAMP mice. Tag-specific CTL from "tumor naïve" young TRAMP mice showed significant anti-tumor efficacy in vivo by eliminating established heterotopic prostate tumors and prolonging survival in SCID mice harboring Tag-expressing tumors. In contrast, older TRAMP mice with established prostate tumors exhibited oncogene-specific tolerance as evidenced by failure to generate Tag-specific CTL following Tag-specific immunization. Peripheral tolerance can be overcome for effective anti-tumor therapy following oncogene-specific immunization. However, this ability to elicit oncogene-specific CTL is impeded in the tumor-bearing host, in the context of increased oncogene expression associated with tumor progression.

Induction of hsp70-Mediated Th17 Autoimmunity Can Be Exploited as Immunotherapy for Metastatic Prostate Cancer

A close connectivity between autoimmune and tumor rejection responses is known to exist in the case of melanoma immunotherapy. However, relatively little is known about self-antigens on other types of normal cells, their relation to the development of autoimmune disease, and their possible coexistence as potential tumor rejection antigens on associated tumors. In the current study, we induced inflammatory killing of normal prostate tissue in situ using a fusogenic membrane glycoprotein along with the immune adjuvant hsp70. We show here that, in the prostate, hsp70 induces interleukin (IL)-6, which triggers a CD4- and CD8-dependent progressive autoimmune reactivity, associated with IL-17 expression. This autoimmune response was also able to induce the rejection of established prostate tumors, but not other histologic types of tumors, growing elsewhere in the animal. These data show that the intimate connectivity between autoimmune and tumor rejection responses extends beyond the classic melanoma paradigm and may be clinically valuable for the treatment of established metastatic disease of the prostate.

Defects in the Acquisition of CD8 T Cell Effector Function after Priming with Tumor or Soluble Antigen Can Be Overcome by the Addition of an OX40 Agonist

Several members of the TNFR superfamily, including OX40 (CD134), 4-1BB (CD137), and CD27 provide critical costimulatory signals that promote T cell survival and differentiation in vivo. Although several studies have demonstrated that OX40 engagement can enhance CD4 T cell responses, the mechanisms by which OX40-mediated signals augment CD8 T cell responses are still unclear. Previously, we and others have shown that OX40 engagement on Ag-specific CD8 T cells led to increased CD8 T cell expansion, survival, and the generation of greater numbers of long-lived memory cells. Currently, we demonstrate that provision of an OX40 agonist during the activation of naive CD8 T cells primed in vivo with either soluble or tumor-associated Ag significantly augments granzyme B expression and CD8 T cell cytolytic function through an IL-2-dependent mechanism. Furthermore, augmented CTL function required direct engagement of OX40 on the responding CD8 T cells and was associated with increased antitumor activity against established prostate tumors and enhanced the survival of tumor-bearing hosts. Thus, in the absence of danger signals, as is often the case in a tumor-bearing host, provision of an OX40 agonist can overcome defective CD8 T cell priming and lead to a functional antitumor response in vivo.