Determining risk of biochemical recurrence in prostate cancer by immunohistochemical detection of PTEN expression and Akt activation

PURPOSE

A considerable fraction of patients who undergo radical prostatectomy as treatment for primary prostate cancer experience biochemical recurrence detected by elevated serum levels of prostate-specific antigen. In this study, we investigate whether loss of expression of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and the phosphorylated form of the cell survival protein Akt (pAkt) predicts biochemical recurrence.

EXPERIMENTAL DESIGN

Expression of PTEN and pAkt was detected by immunohistochemistry in paraffin-embedded prostate cancer tissue obtained from men undergoing radical prostatectomy. Outcome was determined by 60-month follow-up determining serum prostate-specific antigen levels.

RESULTS

By itself, PTEN was not a good predictor of biochemical recurrence; however, in combination with pAkt, it was a better predictor of the risk of biochemical recurrence compared with pAkt alone. Ninety percent of all cases with high pAkt and negative PTEN were recurrent whereas 88.2% of those with low pAkt and positive PTEN were nonrecurrent. In addition, high Gleason scores resulted in reduced protection from decreased pAkt and increased PTEN. By univariate logistic regression, pAkt alone gives an area under the receiver-operator characteristic curve of 0.82 whereas the area under the receiver-operator characteristic curve for the combination of PTEN, pAkt, and Gleason based on a stepwise selection model is 0.89, indicating excellent discrimination.

CONCLUSIONS

Our results indicate that loss of PTEN expression, together with increased Akt phosphorylation and Gleason score, is of significant predictive value for determining, at the time of prostatectomy, the risk of biochemical recurrence.

Direct and efficient cellular transformation of primary rat mesenchymal precursor cells by KSHV

Infections by viruses are associated with approximately 12% of human cancer. Kaposi's sarcoma-associated herpesvirus (KSHV) is causally linked to several malignancies commonly found in AIDS patients. The mechanism of KSHV-induced oncogenesis remains elusive, due in part to the lack of an adequate experimental system for cellular transformation of primary cells. Here, we report efficient infection and cellular transformation of primary rat embryonic metanephric mesenchymal precursor cells (MM cells) by KSHV. Cellular transformation occurred at as early as day 4 after infection and in nearly all infected cells. Transformed cells expressed hallmark vascular endothelial, lymphatic endothelial, and mesenchymal markers and efficiently induced tumors in nude mice. KSHV established latent infection in MM cells, and lytic induction resulted in low levels of detectable infectious virions despite robust expression of lytic genes. Most KSHV-induced tumor cells were in a latent state, although a few showed heterogeneous expression of lytic genes. This efficient system for KSHV cellular transformation of primary cells might facilitate the study of growth deregulation mechanisms resulting from KSHV infections.

KSHV microRNAs mediate cellular transformation and tumorigenesis by redundantly targeting cell growth and survival pathways

Kaposi's sarcoma-associated herpesvirus (KSHV) is causally linked to several human cancers, including Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease, malignancies commonly found in HIV-infected patients. While KSHV encodes diverse functional products, its mechanism of oncogenesis remains unknown. In this study, we determined the roles KSHV microRNAs (miRs) in cellular transformation and tumorigenesis using a recently developed KSHV-induced cellular transformation system of primary rat mesenchymal precursor cells. A mutant with a cluster of 10 precursor miRs (pre-miRs) deleted failed to transform primary cells, and instead, caused cell cycle arrest and apoptosis. Remarkably, the oncogenicity of the mutant virus was fully restored by genetic complementation with the miR cluster or several individual pre-miRs, which rescued cell cycle progression and inhibited apoptosis in part by redundantly targeting IκBα and the NF-κB pathway. Genomic analysis identified common targets of KSHV miRs in diverse pathways with several cancer-related pathways preferentially targeted. These works define for the first time an essential viral determinant for KSHV-induced oncogenesis and identify NF-κB as a critical pathway targeted by the viral miRs. Our results illustrate a common theme of shared functions with hierarchical order among the KSHV miRs.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causal agent of several human cancers. KSHV encodes over two dozen genes that regulate diverse cellular pathways. However, the molecular mechanism of KSHV-induced oncogenesis remains unknown. In this study, we determined the roles of KSHV microRNAs (miRs) in KSHV-induced oncogenesis using a recently developed KSHV cellular transformation system of primary rat mesenchymal precursor cells. A KSHV mutant with a cluster of 10 precursor miRs (pre-miRs) deleted failed to transform primary cells, and instead, caused cell cycle arrest and apoptosis. Expression of the miR cluster or several pre-miRs was sufficient to restore the oncogenicity of the mutant virus. KSHV miRs regulated cell cycle progression and inhibited apoptosis in part by redundantly targeting IκBα and the NF-κB pathway. By integrating gene expression profiling and target prediction, we identified common targets of KSHV miRs in diverse pathways. Importantly, several cancer-related pathways were preferentially targeted by KSHV miRs. These works have demonstrated for the first time the important roles of KSHV miRs in oncogenesis and identified NF-κB as a critical pathway targeted by the miRs. Our results reveal that shared function is a common theme of KSHV miRs, which manifest functional hierarchical order.

Akt in Prostate Cancer: Possible Role in Androgen-Independence

Akt, a downstream effector of phosphatidylinositol 3-kinase (PI3K), has often been implicated in prostate cancer. Studies in prostate tumor cell lines revealed that Akt activation is probably important for the progression of prostate cancer to an androgen-independent state. Investigations of human prostate cancer tissues show that although there is neither Akt gene amplification nor enhanced protein expression in prostate cancer compared to normal tissue, poorly differentiated tumors exhibit increased expression of a phosphorylated (activated) form of Akt compared to normal tissue, prostatic intraepithelial neoplasia (PIN) or well-differentiated prostate cancer. Akt phosphorylation is accompanied by the inactivation of ERK, a member of the mitogen activated protein kinase (MAPK) family. In this article, we postulate that Akt promotes androgen-independent survival of prostate tumor cells by modulating the expression and activation of the androgen receptor (AR).

Combined targeting of STAT3/NF-κB/COX-2/EP4 for effective management of pancreatic cancer

PURPOSE

Near equal rates of incidence and mortality emphasize the need for novel targeted approaches for better management of patients with pancreatic cancer. Inflammatory molecules NF-κB and STAT3 are overexpressed in pancreatic tumors. Inhibition of one protein allows cancer cells to survive using the other. The goal of this study is to determine whether targeting STAT3/NF-κB crosstalk with a natural product Nexrutine can inhibit inflammatory signaling in pancreatic cancer.

EXPERIMENTAL DESIGN

HPNE, HPNE-Ras, BxPC3, Capan-2, MIA PaCa-2, and AsPC-1 cells were tested for growth, apoptosis, cyclooxygenase-2 (COX-2), NF-κB, and STAT3 level in response to Nexrutine treatment. Transient expression, gel shift, chromatin immunoprecipitation assay was used to examine transcriptional regulation of COX-2. STAT3 knockdown was used to decipher STAT3/NF-κB crosstalk. Histopathologic and immunoblotting evaluation was performed on BK5-COX-2 transgenic mice treated with Nexrutine. In vivo expression of prostaglandin receptor E-prostanoid 4 (EP4) was analyzed in a retrospective cohort of pancreatic tumors using a tissue microarray.

RESULTS

Nexrutine treatment inhibited growth of pancreatic cancer cells through induction of apoptosis. Reduced levels and activity of STAT3, NF-κB, and their crosstalk led to transcriptional suppression of COX-2 and subsequent decreased levels of prostaglandin E2 (PGE2) and PGF2. STAT3 knockdown studies suggest STAT3 as negative regulator of NF-κB activation. Nexrutine intervention reduced the levels of NF-κB, STAT3, and fibrosis in vivo. Expression of prostaglandin receptor EP4 that is known to play a role in fibrosis was significantly elevated in human pancreatic tumors.

CONCLUSIONS

Dual inhibition of STAT3-NF-κB by Nexrutine may overcome problems associated with inhibition of either pathway.

Dietary resveratrol prevents development of high-grade prostatic intraepithelial neoplastic lesions: involvement of SIRT1/S6K axis

SIRT1 (mammalian ortholog of the yeast silent information regulator 2) is a NAD-dependent histone deacetylase belonging to the multigene family of sirtuins. Anecdotal and epidemiologic observations provide evidence for beneficial effects of the calorie restriction mimetic resveratrol (RES), a SIRT1 activator in preventing cardiovascular diseases and cancer. Although SIRT1 possesses both tumorigenic and antitumorigenic potential, the molecular mechanisms underlying SIRT1-mediated tumor progression or inhibition are poorly understood. In this study, we investigated the role of SIRT1 in multiple human prostate cancer cell lines and prostate-specific PTEN knockout mouse model using resveratrol. Androgen-independent prostate cancer cell lines (C42B, PC3, and DU145) express higher levels of SIRT1 than androgen-responsive (LNCaP) and nontumorigenic prostate cells (RWPE-1). Resveratrol enhanced this expression without any significant effect on SIRT1 enzymatic activity. Inhibition of SIRT1 expression using shRNA enhanced cell proliferation and inhibited autophagy by repressing phosphorylation of S6K and 4E-BP1. These biologic correlates were reversed in the presence of resveratrol. Analysis of prostates from dietary intervention with resveratrol showed a significant reduction in prostate weight and reduction in the incidence of high-grade prostatic intraepithelial neoplastic (HGPIN) lesions by approximately 54% with no significant change in body weight. Consistent with the in vitro findings, resveratrol intervention in the PTEN knockout mouse model was associated with reduction in the prostatic levels of mTOR complex 1 (mTORC1) activity and increased expression of SIRT1. These data suggest that SIRT1/S6K-mediated inhibition of autophagy drives prostate tumorigenesis. Therefore, modulation of SIRT1/S6K signaling represents an effective strategy for prostate cancer prevention.

Arginine vasopressin stimulates mesangial cell proliferation by activating the epidermal growth factor receptor

The potent vasoconstrictor arginine vasopressin (AVP) is also a mitogen for mesangial cells. Treatment with AVP decreased transit time through the cell cycle. AVP-stimulated mesangial cell growth by activating both the Ras mitogen-activated protein kinase (MAPK) and the phosphatidylinositol 3-kinase (PI3K) cell signaling pathways. Both the selective PI3K inhibitor LY-294002 and the MAPK kinase (MEK) inhibitor PD-98059 inhibited AVP-stimulated mesangial cell proliferation. However, LY-294002 was more potent, indicating an important role for PI3K activation in AVP-stimulated mesangial cell proliferation. AVP appeared to exert its effect on MAPK and PI3K activation, as well as on cell proliferation, by activating the epidermal growth factor receptor (EGF-R). Pretreatment with the tyrphostin-derived EGF-R antagonist AG-1478 inhibited mesangial cell proliferation as well as the activation of extracellular signal-regulated kinase 1/2 (ERK1/2 or p42/p44MAPK), and p70S6 kinase, a downstream effector of PI3K, providing evidence that MAPK and PI3K activation, respectively, occurred downstream of EGF-R activation. Treatment with rapamycin, an inhibitor of the p70S6 kinase activator mTOR, also resulted in growth inhibition, further suggesting the importance of the PI3K signaling pathway in AVP-induced proliferation. AVP treatment appeared to transactivate EGF-R by inducing tyrosine phosphorylation of the Ca2+/protein kinase C (PKC)-dependent nonreceptor tyrosine kinase, Pyk2, leading to Pyk2/c-Src association and c-Src activation. This was followed by association of c-Src with EGF-R and EGF-R activation. These data suggested that AVP-stimulated Pyk2 tyrosine phosphorylation to activate c-Src, thereby leading to EGF-R transactivation.

Viral cyclin promotes KSHV-induced cellular transformation and tumorigenesis by overriding contact inhibition

Kaposi sarcoma-associated herpesvirus (KSHV) is a tumor virus encoding several proto-oncogenes. However, the roles of these viral genes in KSHV-induced tumorigenesis have not been defined. In this study, we used a recently developed model of KSHV-induced cellular transformation and tumorigenesis combining with a reverse genetic system to examine the role of a KSHV latent gene vCyclin (ORF72), a cellular Cyclin D2 homolog, in KSHV-induced oncogenesis. Deletion of vCyclin did not affect cell proliferation and cell cycle progression at a low-density condition, when cells were at an active proliferation state. However, vCyclin mutant cells were contact-inhibited and arrested at G 1 phase at a high-density condition. As a result, vCyclin mutant cells formed less and smaller colonies in soft agar assay. Nude mice inoculated with vCyclin mutant cells had reduced tumor incidence and extended tumor latency and survival compared with mice inoculated with wild-type (WT) virus-infected cells. WT but not mutant virus effectively induced Cyclin-dependent kinase inhibitor p27/Kip1 Ser10 phosphorylation and cytoplasmic relocalization. shRNA knockdown of p27 released the blockage of the mutant cells from cell cycle arrest at G 1 phase at a high-density condition. Together, these results indicate that vCyclin primarily functions to enhance cellular transformation and tumorigenesis by promoting cell cycle progression and cell proliferation at a contact-inhibited condition.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

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.

EXPERIMENTAL DESIGN

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.

RESULTS

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.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

SETD6 regulates NF-κB signaling in urothelial cell survival: Implications for bladder cancer

Non-muscle invasive bladder cancer has a high recurrence rate of 45-70%, progressing to muscle invasive disease in about 15% of those patients over a 5-year period. Administration of the mycobacterium, Bacillus Calmette-Guerin (BCG) that induces local inflammation resulting in tumor remission in responsive patients is frequently used for treatment. BCG-treated patients with NF-κB del/del genotype have an increased risk of recurrence suggesting an important role of NF-κB in bladder cancer. Since protein methyltransferases play critical roles in modulating chromatin structure and gene expression, we screened a focused array of epigenetic modification genes to identify differential expression between normal urothelial and bladder cancer cells. We found and validated high expression of the SET-domain-containing protein methyltransferase, SETD6. SETD6 monomethylates NF-κB-p65 at lysine 310. Our results show that primary urothelial cells and normal bladder tissue have nearly undetectable message and protein level of SETD6 that increases in transformed urothelial cells and is further increased in bladder cancer cells and tissues. Overexpression of SETD6 in transformed urothelial cells increased cell survival and colony formation while knockdown in cancer cells decreased both parameters. Luciferase reporter assays showed that SETD6 induced the canonical NF-κB signaling pathway. Further, the use of catalytic SETD6 and IκBα mutant shows that SETD6 positively regulates survival by affecting p65 message, protein level and its function as determined by increased expression of NF-κB target genes. Our findings suggest that SETD6 plays an important role in NF-κB regulation and may have an important role in NF-κB-mediated local inflammatory response following BCG treatment.

Characterization of PacMetUT1, a recently isolated human prostate cancer cell line

BACKGROUND

Existing prostate cancer cell lines have limitations.

METHODS

Cells were characterized using Western blotting, immunohistochemistry, invasion into Matrigel, and by studying xenograft tumors.

RESULTS

We describe a cell line (PacMetUT1) isolated from a lymph node of a 57-year-old male with prostate cancer. Compared to existing prostate cancer cell lines, the growth rate of PacMetUT1 xenograft tumors is slower with tumors occurring at injection sites and with metastases to lung and liver. Androgen receptor (AR) was detected in vivo by Western blotting and the cells responded to methyltrienolone (R1881). PacMetUT1 cells are more invasive in Matrigel than DU-145, PC-3, and LNCaP cells, and showed greater anchorage-independent growth in soft agar. The cells do not express prostate specific antigen (PSA) in vitro or in xenografts. However, the green fluorescent protein (GFP) gene was introduced and stably expressed in PacMetUT1 cells, allowing tumor imaging in vivo. Xenograft tumors show epithelial features and are positive for keratin, epithelial membrane antigen, EGF receptor, and E cadherin. In contrast, fibroblast markers vimentin, desmin, and Factor VIII, were negative. Karyotyping showed losses of 6p, 7q, 8p, 18q, and 22q, and gains of 8q and 9q; additional genetic material was observed at 2q and 12p.

CONCLUSION

The PacMetUT1 cell line allows metastases to be assessed using a single animal model. Because of its slower growth, PacMetUT1 more closely mimics the human disease. Studies of tumor progression or metastasis can be conducted over a longer period of time.

Role of protein kinase C in arginine vasopressin-stimulated ERK and p70S6 kinase phosphorylation

We previously showed in rat renal glomerular mesangial cells, that arginine vasopressin (AVP)-stimulated cell proliferation was mediated by epidermal growth factor receptor (EGF-R) transactivation, and activation (phosphorylation) of ERK1/2 and p70S6 kinase (Ghosh et al. [2001]: Am J Physiol Renal Physiol 280:F972-F979]. In this paper, we extend these observations and show that different protein kinase C (PKC) isoforms play different roles in mediating AVP-stimulated ERK1/2 and p70S6 kinase phosphorylation and cell proliferation. AVP treatment for 0-60 min stimulated the serine/threonine phosphorylation of PKC isoforms alpha, delta, epsilon, and zeta. The activation of PKC was dependent on EGF-R and phosphatidylinositol 3-kinase (PI3K) activation. In addition, inhibition of conventional and novel PKC isoforms by chronic (24 h) exposure to phorbol 12-myristate 13-acetate (PMA) inhibited AVP-induced activation of ERK and p70S6 kinase as well as EGF-R phosphorylation. Rottlerin, a specific inhibitor of PKCdelta, inhibited both ERK and p70S6 kinase phosphorylation and cell proliferation. In contrast, a PKCepsilon translocation inhibitor decreased ERK1/2 activation without affecting p70S6 kinase or cell proliferation, while a dominant negative PKCzeta (K281W) cDNA delayed p70S6 kinase activation without affecting ERK1/2. On the other hand, Gö6976, an inhibitor of conventional PKC isoforms, did not affect p70S6 kinase, but stimulated ERK1/2 phosphorylation without affecting cell proliferation. Our results indicate that PKCdelta plays an important role in AVP-stimulated ERK and p70S6 kinase activation and cell proliferation.

GLI3 Is Stabilized by SPOP Mutations and Promotes Castration Resistance via Functional Cooperation with Androgen Receptor in Prostate Cancer

Although the Sonic hedgehog (SHH) signaling pathway has been implicated in promoting malignant phenotypes of prostate cancer, details on how it is activated and exerts its oncogenic role during prostate cancer development and progression is less clear. Here, we show that GLI3, a key SHH pathway effector, is transcriptionally upregulated during androgen deprivation and posttranslationally stabilized in prostate cancer cells by mutation of speckle-type POZ protein (SPOP). GLI3 is a substrate of SPOP-mediated proteasomal degradation in prostate cancer cells and prostate cancer driver mutations in SPOP abrogate GLI3 degradation. Functionally, GLI3 is necessary and sufficient for the growth and migration of androgen receptor (AR)-positive prostate cancer cells, particularly under androgen-depleted conditions. Importantly, we demonstrate that GLI3 physically interacts and functionally cooperates with AR to enrich an AR-dependent gene expression program leading to castration-resistant growth of xenografted prostate tumors. Finally, we identify an AR/GLI3 coregulated gene signature that is highly correlated with castration-resistant metastatic prostate cancer and predictive of disease recurrence. Together, these findings reveal that hyperactivated GLI3 promotes castration-resistant growth of prostate cancer and provide a rationale for therapeutic targeting of GLI3 in patients with castration-resistant prostate cancer (CRPC). IMPLICATIONS: We describe two clinically relevant mechanisms leading to hyperactivated GLI3 signaling and enhanced AR/GLI3 cross-talk, suggesting that GLI3-specific inhibitors might prove effective to block prostate cancer development or delay CRPC.

Tyrosine phosphorylation of focal adhesion kinase (p125FAK): regulation by cAMP and thrombin in mesangial cells

Stress fibers, composed of actin filaments, converge upon and associate with a number of proteins, including focal adhesion kinase (p125FAK), and integrin receptors to form areas of close contact between cells and the extracellular matrix referred to as focal adhesions. Treatment of mesangial cells with cAMP-elevating agents causes a loss of focal adhesions, fragmentation of stress fibers, and decreased tyrosine phosphorylation of p125FAK. Thrombin reverses these effects of cAMP, and this model can be used to address some of the cellular mechanisms involved in regulating the loss and formation of focal adhesions. This study reports the effects of cAMP and thrombin on mesangial cell shape, distribution of actin, formation of stress fibers, and tyrosine phosphorylation of p125FAK. cAMP-treated cells display a condensed cell body with slender processes that traverse the area formerly covered by the cell. Addition of thrombin to these cells restores actin filaments (stress fibers) and increases tyrosine phosphorylation of p125FAK, and the cells resume a flattened morphology, even in the continued presence of cAMP-elevating agents. Peptides that mimic the tethered ligand portion of the thrombin receptor have the same effects on cell morphology and stress fiber formation as thrombin. In selected experiments, agents that disrupt either stress fibers (cytochalasin D) or microtubules (nocodazole; Sigma Chemical, St. Louis, MO) were used to examine the role of these cytoskeletal elements in thrombin-induced restoration of focal adhesions. Cytochalasin D blocked the ability of thrombin to restore focal adhesions and phosphorylate p125FAK. The effects of nocodazole, an agent that destabilizes microtubules (but which has no known receptor), are very similar to those of thrombin. The findings discussed in this study indicate that thrombin can modulate the formation of focal adhesions. The organization of stress fibers and microtubules is apparently intimately related to the phosphorylation of p125FAK and can be modulated by soluble receptor agonists such as thrombin or via altered polymerization of microtubules.

Crosstalk between RON and androgen receptor signaling in the development of castration resistant prostate cancer

Castrate-resistant prostate cancer (CRPC) is the fatal form of prostate cancer. Although reactivation of androgen receptor (AR) occurs following androgen deprivation, the precise mechanism involved is unclear. Here we show that the receptor tyrosine kinase, RON alters mechanical properties of cells to influence epithelial to mesenchymal transition and functions as a transcription factor to differentially regulate AR signaling. RON inhibits AR activation and subset of AR-regulated transcripts in androgen responsive LNCaP cells. However in C4-2B, a castrate-resistant sub-line of LNCaP and AR-negative androgen independent DU145 cells, RON activates subset of AR-regulated transcripts. Expression of AR in PC-3 cells leads to activation of RON under androgen deprivation but not under androgen proficient conditions implicating a role for RON in androgen independence. Consistently, RON expression is significantly elevated in castrate resistant prostate tumors. Taken together our results suggest that RON activation could aid in promoting androgen independence and that inhibition of RON in combination with AR antagonist(s) merits serious consideration as a therapeutic option during hormone deprivation therapy.

Evidence for 2-Methoxyestradiol-Mediated Inhibition of Receptor Tyrosine Kinase RON in the Management of Prostate Cancer

2-Methoxyestradiol (2-ME₂) possesses anti-tumorigenic activities in multiple tumor models with acceptable tolerability profile in humans. Incomplete understanding of the mechanism has hindered its development as an anti-tumorigenic compound. We have identified for the first-time macrophage stimulatory protein 1 receptor (MST1R) as a potential target of 2-ME₂ in prostate cancer cells. Human tissue validation studies show that MST1R (a.k.a RON) protein levels are significantly elevated in prostate cancer tissues compared to adjacent normal/benign glands. Serum levels of macrophage stimulatory protein (MSP), a ligand for RON, is not only associated with the risk of disease recurrence, but also significantly elevated in samples from African American patients. 2-ME₂ treatment inhibited mechanical properties such as adhesion and elasticity that are associated with epithelial mesenchymal transition by downregulating mRNA expression and protein levels of MST1R in prostate cancer cell lines. Intervention with 2-ME₂ significantly reduced tumor burden in mice. Notably, global metabolomic profiling studies identified significantly higher circulating levels of bile acids in castrated animals that were decreased with 2-ME₂ intervention. In summary, findings presented in this manuscript identified MSP as a potential marker for predicting biochemical recurrence and suggest repurposing 2-ME₂ to target RON signaling may be a potential therapeutic modality for prostate cancer.

Immunohistochemical demonstration of phospho-Akt in high Gleason grade prostate cancer

PURPOSE

Whereas the early stage of prostate cancer is marked by excessive proliferation, in advanced stages of the disease, a decreased apoptotic death rate (increased cell survival) also contributes to net tumor growth. Altered regulation of the mitogen-activated protein kinase (MAPK)-regulated cell proliferation and Akt-regulated cell survival pathways are suspected causes. In this study, we wanted to determine: (a) whether the degree of Akt activation can be assessed by immunohistochemical staining of paraffin- embedded human prostate cancer biopsies with an antibody to phospho-Akt (Ser473); and (b) whether phospho-MAPK/Erk1/2 and phospho-Akt expression are altered in prostate cancer.

EXPERIMENTAL DESIGN

To examine the activation status of MAPK/Erk1/2 and Akt, archival paraffin-embedded sections from 74 cases of resected prostate cancer were immunostained with antibodies to phospho-MAPK/Erk1/2 (Thr202/ Tyr204) and phospho-Akt (Ser473).

RESULTS

The staining intensity for phospho-Akt was significantly greater in Gleason grades 8-10 (92% of such cases staining strongly) compared with prostatic intraepithelial neoplasia and all other grades of prostate cancer (only 10% of these cases staining strongly; P < or = 0.001). The staining intensity for phospho-MAPK/Erk, on the other hand, was significantly greater for normal, hyperplastic, and prostatic intraepithelial neoplasia lesions but declined with disease progression, reaching its lowest level of expression in high Gleason grades 8-10 (P < 0.0001).

CONCLUSION

The activation state of the cell survival protein Akt can be analyzed in human prostate cancer by immunohistochemical staining of paraffin-embedded tissue with a phospho-specific Akt (Ser473) antibody. Advanced disease is accompanied by activation of Akt and inactivation of Erk.

Abstract 2582: 2-ME2-induced biological effects in prostate cancer: Role for miR127-3p/SET8

Prostate cancer is the second most common cause of death related to cancer in Western societies. 2-Methoxyestradiol (2-ME2), an endogenous metabolite of 17-α estradiol inhibits tumor cell proliferation in various cancer cells, including the prostate. Previous studies from our laboratory showed that 2-ME2 (i) inhibits proliferation of both androgen responsive and independent cells through induction of apoptosis involving G2/M check point block; (ii) prevents the development of prostate tumors in transgenic adenocarcinoma of mouse prostate (TRAMP) model. Although various molecular targets have been proposed, the mechanism of action behind its antiproliferative activity is still uncertain. Here we investigated the possible role for 2-ME2 induced antiproliferative activity by examining the altered regulation of microRNA (miRNAs). MicroRNA expression profiling identified miR127-3p as most significantly up regulated in response to 2-ME2 treatment in androgen independent (PC-3) cells. We have also identified histone methylase SET8 as a potential target of miR 127-3p. We have validated these data using Q-PCR. Further 2-ME2 treatment reduced binding of multiple transcription factors including Sp1, Sp3 and NFκB to the FLIP promoter as evidenced by transient expression assays, ChIP and gel-shift assays. Our findings indicate that 2-ME2 suppresses proliferation and induces apoptosis in prostate cancer cells possibly through miR127-3p/SET8 mediated regulation of FLIP. Supported by NIH CA 135451 (APK).

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 2582. doi:1538-7445.AM2012-2582

Abstract 3315: RON-mediated hijacking of AR signaling in androgen-independent prostate cancer

Despite significant progress in developing effective strategies for management of localized prostate cancer, the 5-year survival for metastatic castrate-resistant disease is less than 30%. Previous studies from our own and other laboratories showed the anti-tumorigenic potential of 2-Methoxyestradiol (2-ME2) in various tumor models. Although variety of mechanisms including anti-angiogenic, pro-apoptotic, cell cycle deregulation has been reported to contribute to 2-ME2-mediated biological effects, the precise mechanism is unclear. To explore the role of 2-ME2, we carried out gene expression array analysis and discovered Recepteur d’Origine Nantais (RON) as one of the most significantly down regulated gene in response to 2-ME2 treatment. Subsequently, RON was found to be significantly upregulated in advanced-stage PCA cell lines, which do not express androgen receptor (AR); and high-grade human prostate tumors. Stable silencing of RON in androgen independent, PTEN-/- PC3 cells showed noticeable changes in cell morphology, actin filament organization, as well as markers of epithelial-to-mesenchymal transition (EMT). In PTEN wild type DU145 cells, RON knockdown caused an increase in AR expression and promoter activity but decreased the transcriptional activation and expression of AR target genes such as PSA. In contrast, RON overexpression in androgen-responsive LNCAP cells leads to a suppression of the transcriptional activation of both AR and its downstream targets, including PSA. Furthermore, we found that RON silencing decreases expression and promoter activity of the anti-apoptotic protein FLICE-like inhibitory protein (FLIP) that is accompanied by the induction of apoptosis. In addition, intervention with 2-ME2 reduced tumor growth that is accompanied with decreased RON expression in the prostate in transgenic adenocarcinoma of mouse prostate (TRAMP) model. These observations implicate RON as a hijacker of AR signaling that contributes in part to PCA growth. Therefore, restoration of native AR signaling via RON targeting could possibly be exploited in combination with antiandrogenic therapy to prevent recurrence of castrate-resistant prostate cancer. Supported by CA135451 (APK).

Citation Format: Izhar Singh Batth, Peng Meng, Roble Bedolla, Robert E. Reddick, Addanki Pratap Kumar. RON-mediated hijacking of AR signaling in androgen-independent prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3315. doi:10.1158/1538-7445.AM2014-3315

Abstract 3673: AMPK-SIRT1 axis: a potential therapeutic target for prostate cancer management

Recently we have shown that resveratrol (RES) intervention prevents development of high-grade prostatic intraepithelial neoplastic (HGPIN) lesions in prostate-specific PTEN knockout mouse model targeting SIRT1/mTORC1 axis. It is known that insufficient nutrient supply combined with high proliferation keeps solid tumors including prostate under hypoxic and metabolic stress. Tumor cells adapt to survive under such conditions through activation of AMP-activated kinase (AMPK). AMPK has been reported to be activated in prostate tumors. Therefore targeting AMPK and associated signaling pathways will be a promising approach for prostate cancer management. Accordingly we investigated the role of AMPK in RES-induced growth inhibitory effects using multiple human prostate cancer cell lines and preclinical animal model. These data show that RES treatment (50 μM, 24 h) results in activation of SIRT1, significant inhibition of AMPK phosphorylation and cell survival in human prostate cancer cells (RWPE-1, LNCaP, C42B and DU145). The observed molecular changes were associated with induction of apoptosis and autophagy following treatment with RES. Further dietary administration of RES (0.1 and 2%) to 4-5 week old prostate-specific PTEN knockout mice for 11 and 14 weeks showed prevention of HGPIN development. Interestingly intervention for 7 weeks showed prevention of HGPIN development at lower dose but not at high dose. On the other hand, 28-week intervention had no significant effect on the development of HGPIN lesions. Immunohistochemical evaluation showed modulation of AMPK, pS6K and SIRT1 in the prostate. Overall these data provide novel insights into RES-induced prevention of HGPIN development via AMPK/SIRT1/mTORC1 axis. Supported in part by NIH (CA 137518 and 135451 APK).

Citation Format: Guiming Li, Paul Rivas, Roble Bedolla, Robert L. Reddick, Rita Ghosh, Addanki P. Kumar. AMPK-SIRT1 axis: a potential therapeutic target for prostate cancer management. [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 3673. doi:10.1158/1538-7445.AM2013-3673

Abstract A12: Identification of Nrdp1 as a novel androgen receptor transcription target differentially regulated in androgen-dependent and independent prostate cancer

Background: The ErbB receptor tyrosine kinase family regulates proliferation and survival in prostate cancer (PCa). We recently showed that ErbB3 plays a significant role in increasing androgen receptor (AR) transcriptional activity and in causing castration-resistant PCa (CRPC). Reciprocally, AR maintained castration sensitivity by suppressing ErbB3 levels through transcriptional regulation of E3 ubiquitin ligase Nrdp1, while loss of AR regulation of Nrdp1 resulted in an unrestricted surge in ErbB3 levels, and cell growth. Here, we investigate whether Nrdp1 is a transcriptional target of the AR in PCa cells.

Results: The promoter region of Nrdp1 contains three androgen response elements (AREs) - one located 215 aa upstream of the transcriptional start site (ARE.03), and two within an internal promoter (ARE.01 and ARE.02). Chromatin immunoprecipitation (ChIP) studies revealed AR binding in PCa cells to ARE.03. AR binding to ARE.03 was found to be androgen regulated in androgen-dependent LNCaP cells, whereas no AR binding to ARE.01 or ARE.02 has been detected in this cell line. Luciferase assay to determine AR transcriptional activity on ARE.03 showed significant response to androgens, whereas full mutation of ARE.03 abolished AR transcriptional activity. However, the AR failed to bind to ARE.03 in C4-2 and LNCaP-AI cell lines, CRPC sublines of LNCaP cells, although no mutations in these regions were identified, while AR continued to bind the AR to PSA ARE in these cells, indicating that the AR was still active. Thus the AR binds to PSA ARE in both androgen-dependent and –independent cells, but to ARE.03 only in androgen-dependent but not –independent cells. Luciferase assay in LNCaP-AI cells showed decreased AR transcriptional activity on ARE.03 when compared to LNCaP, supporting decreased AR binding to this region. Hence we investigated the cause for the differential binding of the AR in these two areas. The structural protein Filamin A (FlnA) was earlier shown to cleave to a 90 kDa fragment (FlnA16-24) whose nuclear localization maintained androgen dependence. We investigated whether this protein played a role in regulation of AR binding to ARE.03 in PCa cells. Transfection of FlnA16-24 in C4-2 cells resulted in localization of FlnA 16-24 to the nucleus, and restored AR binding to ARE.03. FlnA 16-24 significantly increased luciferase activity on ARE.03, while suppressing AR activity on PSA indicating that this AR binding protein is required for AR-mediated transcription of Nrdp1.

Conclusions: Our results indicated that Nrdp1 is regulated in androgen sensitive cells, but not in CRPC cells, by AR binding to ARE.03, whereas no such difference in AR binding to PSA ARE exists. We show that AR binding to ARE.03 is abolished in CRPC cells because of a decreased expression of nuclear FlnA, and that restoration of nuclear FlnA will restore androgen-sensitive cell growth. Our data indicate that the AR-coregulator FlnA is required for AR binding to the Nrdp1 promoter and that loss of this protein results in the failure of AR to regulate Nrdp1 transcription, resulting in unrestricted increase in ErbB3. These data identified Nrdp1 as a novel target of AR transcriptional activity in androgen-dependent but not in CRPC cells.

RhoA-dependent murine prostate cancer cell proliferation and apoptosis: role of protein kinase Czeta

We previously showed that RhoA played an important role in the proliferation of murine We prostate cancer (TRAMP) cells (P. M. Ghosh et al., Oncogene, 18: 4120-4130, 1999). Untransfected TRAMP cells as well as those expressing constitutively active RhoA (Q63L) mutant protein (Q63L cells) were highly proliferative. In contrast, TRAMP cells expressing dominant-negative RhoA (T19N) mutant protein (T19N cells) were slow growing. In this study, we showed, in addition, that T19N cells displayed reduced rates of apoptotic cell death in response to serum deprivation, compared with TRAMP and Q63L cells, and we studied the mechanisms of the effects of RhoA on TRAMP cell proliferation and apoptosis. Both proliferation and apoptosis of TRAMP and Q63L cells were dependent on the activation of phosphatidylinositol 3-kinase (PI3K). The ubiquitous mitogen-activated Ser/Thr kinase, p70S6 kinase, a downstream effector of PI3K, was overexpressed in TRAMP and Q63L cells. Another PI3K effector, the cell survival protein Akt, displayed increased activity in T19N cells, which did not express active RhoA, compared with TRAMP and Q63L cells. The atypical protein kinase C (PKC) isoform PKCzeta, which is downstream of PI3K, was activated in cells expressing active RhoA. In addition, expression of constitutively activated PKCzeta in TRAMP cells enhanced proliferation and p70S6 kinase phosphorylation, whereas the inhibition of PKCzeta activation resulted in activation of Akt and enhanced cell survival. Thus, the effects of RhoA on TRAMP cell proliferation and apoptosis may be mediated by PKCzeta.

Abstract 5823: Palmatine as a potential pancreatic cancer therapeutic agent

Over the last 30 years, little improvement has been made to the 5 year survival rate of pancreatic cancer (PanCA) patients. While survival has increase by 2% over the last several years, the current rate is still less than 8%. This depressing fact demonstrates the importance of developing or improving therapies to more effectively manage this disease. Along these lines, published studies from our laboratory demonstrated the anti-tumorigenic potential of the cork tree bark extract, Nexrutine® (Nx). Nx suppressed growth of pancreatic cancer cells through downregulation of STAT3/NF-κB activation. Subsequent biochemical and molecular investigations revealed palmatine (PMT) (i) as an active constituent of Nx able to suppress the growth of pancreatic cancer cells; (ii) synergizes with gemcitabine (GEM); and (iii) downregulates GLI1, COL1A1 and Survivin. Despite such promising in vitro observations however, the in vivo relevance of PMT is undefined. Furthermore, it is unclear if PMT can recapitulate the biological activities of Nx in vivo. In this investigation, we tested the hypothesis that PMT recapitulates the biological activities of Nx and enhances GEM activity. This hypothesis was tested by comparing the efficacy of Nx and PMT using (i) athymic mice implanted with Capan-2 cells; (ii) a syngenic mouse model using C57BL/6 mice implanted with KPC-GFP-Luc cells; and (iii) a short term ex vivo model utilizing cells isolated from primary pancreatic tumors following surgical resection. Additionally, in vitro experiments were also done to assess the underlying molecular mechanism. Analysis of these data show that both Nx and PMT are well tolerated in vivo and a significant reduction in the levels of serum inflammatory cytokines including IL-6, granulocyte-colony stimulating factor (G-CSF), and CXCL1. Interestingly, animals receiving PMT, but not Nx, showed a trend towards decreased pancreatic tumor weight that was associated with histopathological changes. Investigation into the potential mechanism revealed that Nx and PMT mediated inhibition of STAT3, EP4, Src, TrkA, and RPS6 activities may contribute to the observed growth inhibitory and anti-inflammatory effects. Incredibly, our ex vivo analysis of patient derived PanCA cells demonstrated that both Nx and PMT could inhibit the growth of these cells. Collectively, our data demonstrates PMT recapitulates biological activities of Nx and that there is potential for developing PMT as an agent for clinical management of PanCA. Supported by NCCIH (R01 AT007448; APK) and VA-MERIT Award (I01 BX 000766; APK).

Citation Format: Amanda R. Muñoz, Roble Bedolla, Shih-Bo Huang, Xiaou Yang, Paul Rivas, Robert Reddick, Martha Hanes, Glenn Halff, Rita Ghosh, Addanki P. Kumar. Palmatine as a potential pancreatic cancer therapeutic agent [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5823.