Apoptosis resistance of neuroendocrine phenotypes in prostatic adenocarcinoma

STIM1 in tumor cell death: angel or devil?

Stromal interaction molecule 1 (STIM1) is involved in mediating the store-operated Ca2+ entry (SOCE), driving the influx of the intracellular second messenger calcium ion (Ca2+), which is closely associated with tumor cell proliferation, metastasis, apoptosis, autophagy, metabolism and immune processes. STIM1 is not only regulated at the transcriptional level by NF-κB and HIF-1, but also post-transcriptionally modified by miRNAs and degraded by ubiquitination. Recent studies have shown that STIM1 or Ca2+ signaling can regulate apoptosis, autophagy, pyroptosis, and ferroptosis in tumor cells and act discrepantly in different cancers. Furthermore, STIM1 contributes to resistance against antitumor therapy by influencing tumor cell death. Further investigation into the mechanisms through which STIM1 controls other forms of tumor cell death could aid in the discovery of novel therapeutic targets. Moreover, STIM1 has the ability to regulate immune cells within the tumor microenvironment. Here, we review the basic structure, function and regulation of STIM1, summarize the signaling pathways through which STIM1 regulates tumor cell death, and propose the prospects of antitumor therapy by targeting STIM1.

ZBTB7A as a novel vulnerability in neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is a highly aggressive subtype of prostate cancer. NEPC is characterized by the loss of androgen receptor (AR) signaling and transdifferentiation toward small-cell neuroendocrine (SCN) phenotypes, which results in resistance to AR-targeted therapy. NEPC resembles other SCN carcinomas clinically, histologically and in gene expression. Here, we leveraged SCN phenotype scores of various cancer cell lines and gene depletion screens from the Cancer Dependency Map (DepMap) to identify vulnerabilities in NEPC. We discovered ZBTB7A, a transcription factor, as a candidate promoting the progression of NEPC. Cancer cells with high SCN phenotype scores showed a strong dependency on RET kinase activity with a high correlation between RET and ZBTB7A dependencies in these cells. Utilizing informatic modeling of whole transcriptome sequencing data from patient samples, we identified distinct gene networking patterns of ZBTB7A in NEPC versus prostate adenocarcinoma. Specifically, we observed a robust association of ZBTB7A with genes promoting cell cycle progression, including apoptosis regulating genes. Silencing ZBTB7A in a NEPC cell line confirmed the dependency on ZBTB7A for cell growth via suppression of the G1/S transition in the cell cycle and induction of apoptosis. Collectively, our results highlight the oncogenic function of ZBTB7A in NEPC and emphasize the value of ZBTB7A as a promising therapeutic strategy for targeting NEPC tumors.

Targeting protein arginine methyltransferase 5 (PRMT5) suppresses radiation-induced neuroendocrine differentiation and sensitizes prostate cancer cells to radiation

Prostate cancer remains the second leading cause of cancer death among American men. Radiation therapy (RT) is a potentially curative treatment for localized prostate cancer, and failure to control localized disease contributes to the majority of prostate cancer deaths. Neuroendocrine differentiation (NED) in prostate cancer, a process by which prostate adenocarcinoma cells transdifferentiate into neuroendocrine-like (NE-like) cells, is an emerging mechanism of resistance to cancer therapies and contributes to disease progression. NED also occurs in response to treatment to promote the development of treatment-induced neuroendocrine prostate cancer (NEPC), a highly-aggressive and terminal stage disease. We previously demonstrated that by mimicking clinical RT protocol, fractionated ionizing radiation (FIR) induces prostate cancer cells to undergo NED in vitro and in vivo. Here, we performed transcriptomic analysis and confirmed that FIR-induced NE-like cells share some features of clinical NEPC, suggesting that FIR-induced NED represents a clinically-relevant model. Further, we demonstrated that protein arginine methyltransferase 5 (PRMT5), a master epigenetic regulator of the DNA damage response and a putative oncogene in prostate cancer, along with its cofactors pICln and MEP50, mediate FIR-induced NED. Knockdown of PRMT5, pICln, or MEP50 during FIR-inhibited NED sensitized prostate cancer cells to radiation. Significantly, PRMT5 knockdown in prostate cancer xenograft tumors in mice during FIR prevented NED, enhanced tumor killing, significantly reduced and delayed tumor recurrence, and prolonged overall survival. Collectively, our results demonstrate that PRMT5 promotes FIR-induced NED and suggests that targeting PRMT5 may be a novel and effective radiosensitization approach for prostate cancer RT.

ECTOPIC ADRENOCORTICOTROPIC HORMONE SYNDROME DUE TO METASTATIC PROSTATE CANCER WITH NEUROENDOCRINE DIFFERENTIATION

Objective

Neuroendocrine differentiation of prostate cancer can result in ectopic adrenocorticotropic hormone (ACTH) secretion (EAS) and Cushing syndrome. The aim of this report is to highlight this unusual mechanism of hypercortisolism and its management.

Methods

We report a 73-year-old patient with a history of prostate adenocarcinoma who presented with severe weakness, hyperglycemia, and hypokalemia caused by EAS.

Results

Diagnostic workup showed elevated 24-hour urine cortisol and ACTH levels consistent with EAS. Fluorodeoxyglucose positron emission tomography-computed tomography revealed a hypermetabolic mass in the prostate and metastatic lesions to the liver and bones. Liver biopsy was consistent with small cell carcinoma with positive immunostaining for ACTH. Pleural fluid analysis was consistent with high-grade neuroendocrine carcinoma. The patient underwent chemotherapy with carboplatin and etoposide. Hypercortisolism was treated with ketoconazole, metyrapone, mifepristone, and spironolactone. He suffered complications including opportunistic infections, deep venous thrombosis, and delirium. Given his poor prognosis and clinical decline, the patient opted for comfort measures only in a hospice facility.

Conclusion

Treatment-related neuroendocrine differentiation of prostate cancer is an emerging entity that may be associated with paraneoplastic syndromes including EAS.

Bag-1 Expression in Hyperplastic and Neoplastic Prostate Tissue: Is There Any Relationship with BCL-Related Proteins and Androgen Receptor Status?

Aims and Background

To evaluate the function and distribution of BAG-1 protein in hyperplastic and neoplastic prostate tissue and establish the relationship between this protein and BCL-related proteins (BCL-2 and BAX), androgen receptor (AR) expression and chromogranin A.

Methods

Twenty-eight prostatic adenocarcinomas and 16 prostate hyperplasias were included in this retrospective study. BAG-1, BCL-2, BAX, androgen receptor and chromogranin A immunostaining was performed by means of standard avidin-biotin peroxidase methods. The M30 antibody was used to identify preapoptotic and apoptotic cells. The immunohistochemical histological score (HSCORE) semi-quantative system was used to evaluate immunohistochemical staining.

Results

Statistical analysis showed a significant difference in HSCOREs of BAX, M30 and AR between the carcinoma and hyperplasia groups. Carcinomas expressed higher HSCOREs of these markers than hyperplasias. There were significant differences in nuclear and cytoplasmic BAG-1 positivity between high and low-grade carcinomas. BAG-1 expression was higher in low-grade carcinomas. In the carcinoma group there was a positive correlation (Pearson) between BCL-2 and cytoplasmic/nuclear BAG-1. In the hyperplasia group there was a negative correlation between BAX and BCL-2, and between AR and M30. We also detected a positive correlation between AR and nuclear/cytoplasmic BAG-1 and between nuclear and cytoplasmic BAG-1 in hyperplasias. BAG-1 showed the same specific basal cell localization as BCL-2 in hyperplastic and normal glands.

Conclusions

The BAG-1 protein showed a distinct distribution pattern in hyperplastic and neoplastic prostate. BAG-1 in association with BCL-2 inhibits apoptosis and may prolong the life of neoplastic cells and give them a chance to gain new oncogenic features in early carcinogenesis.

A Testosterone Metabolite 19-Hydroxyandrostenedione Induces Neuroendocrine Trans-Differentiation of Prostate Cancer Cells via an Ectopic Olfactory Receptor

Olfactory receptor OR51E2, also known as a Prostate Specific G-Protein Receptor, is highly expressed in prostate cancer but its function is not well understood. Through in silico and in vitro analyses, we identified 24 agonists and 1 antagonist for this receptor. We detected that agonist 19-hydroxyandrostenedione, a product of the aromatase reaction, is endogenously produced upon receptor activation. We characterized the effects of receptor activation on metabolism using a prostate cancer cell line and demonstrated decreased intracellular anabolic signals and cell viability, induction of cell cycle arrest, and increased expression of neuronal markers. Furthermore, upregulation of neuron-specific enolase by agonist treatment was abolished in OR51E2-KO cells. The results of our study suggest that OR51E2 activation results in neuroendocrine trans-differentiation. These findings reveal a new role for OR51E2 and establish this G-protein coupled receptor as a novel therapeutic target in the treatment of prostate cancer.

MicroRNA-652 induces NED in LNCaP and EMT in PC3 prostate cancer cells

MicroRNAs (miRNAs) are small noncoding RNA molecules that post-transcriptionally regulate gene expression. Dysregulation of miRNAs is frequently associated with disease and, in particular, is involved in prostate cancer progression. Next generation miRNA sequencing identified a panel of five miRNAs associated with prostate cancer recurrence and metastasis. High expression of one of these five miRNAs, miR-652, correlated significantly with an increased rate of prostate cancer biochemical recurrence. Overexpression of miR-652 in prostate cancer cells, PC3 and LNCaP, resulted in increased growth, migration and invasion. Prostate cancer cell xenografts overexpressing miR-652 showed increased tumorigenicity and metastases. We found that miR-652 directly targets the B" regulatory subunit, PPP2R3A, of the tumor suppressor PP2A, inducing epithelial-mesenchymal transition (EMT) in PC3 cells and neuroendocrine-like differentiation (NED) in LNCaP cells. The mesenchymal marker N-cadherin increased and epithelial marker E-cadherin decreased in PC3 cells overexpressing miR-652. In LNCaP cells and xenografted tumors, overexpression of miR-652 increased markers of NED, including chromogranin A, neuron specific enolase, and synaptophysin. MiR-652 may contribute to prostate tumor progression by promoting NED through decreased PP2A function. MiR-652 expression could serve as a biomarker for aggressive prostate cancer, as well as provide an opportunity for novel therapy in prostate cancer.

The impact of finasteride and dutasteride treatments on proliferation, apoptosis, androgen receptor, 5α-reductase 1 and 5α-reductase 2 in TRAMP mouse prostates

BACKGROUND

Previously, we studied the effect of finasteride- or dutasteride-containing diets in male C57BL/6 TRAMP x FVB mice. Pre (6 weeks of age) and post (12 weeks of age) groups received finasteride or dutasteride to determine the efficacy of these pharmaceuticals on prostate cancer (PCa) development in male C57BL/6 TRAMP x FVB mice. Post-Dutasteride treatment was more effective than Pre-Dutasteride treatment, and dutasteride treatments were more effective than finasteride treatments in decreasing prostatic intraepithelial neoplasia (PIN) progression and PCa development. Finasteride and Pre-Dutasteride treatments significantly decreased high-grade PIN incidence, but increased poorly differentiated PCa incidence. In this study, molecular changes in prostates of these mice were characterized in an effort to elucidate the discordant response in Pre-Dutasteride and finasteride groups, and determine why Post-Dutasteride treatment was more effective.

METHOD/PRINCIPAL FINDINGS

Ki-67 (proliferation marker) and androgen receptor (AR) protein, apoptotic DNA fragmentation (TUNEL assay), 5α-reductase 1 (5αR1) and 5α-reductase 2 (5αR2) mRNA were quantified in male TRAMP mice prostate tissues with genitourinary weight < 1 and > 1 gram. Overall, proliferation and AR were decreased and apoptosis was increased in most tumors versus prostate epithelium and hyperplasia. Proliferation and AR were increased notably in hyperplasia versus prostate epithelium and tumor. There were no clear trends or differences in 5α-reductase 1 and 5α-reductase 2 levels between large and small tumors. The discordant response in Pre-Finasteride and Pre-Dutasteride groups may be due to upregulated 5αR1 levels in large versus small tumors. It is not clear what the mechanism is for the different response in the Post-Finasteride group. Post-Dutasteride treatment was more effective than Pre-Dutasteride treatment in decreasing 5αR1 in large tumors. Therefore, this may be why this treatment was more effective in decreasing PIN progression and PCa development.

CONCLUSION

The effect of finasteride and dutasteride on these biomarkers did not clearly elucidate their mechanism of action, but tumor 5αR1 levels were significantly positively correlated with adjusted prostate severe lesion score.

Neuroendocrine Cells of the Prostate Derive from the Neural Crest

The histogenesis of prostatic neuroendocrine cells is controversial: a stem cell hypothesis with a urogenital sinus-derived progeny of all prostatic epithelial cells is opposed by a dual origin hypothesis, favoring the derivation of neuroendocrine cells from the neural crest, with the secretory and basal cells being of urogenital sinus origin. A computer-assisted 3D reconstruction was used to analyze the distribution of chromogranin A immunoreactive cells in serial sections of human fetal prostate specimens (gestation weeks 18 and 25). Immunohistochemical double labeling studies with YFP and serotonin antisera combined with electron microscopy were carried out on double-transgenic Wnt1-Cre/ROSA26-YFP mice showing stable YFP expression in all neural crest-derived cell populations despite loss of Wnt1 expression. 3D reconstruction of the distribution pattern of neuroendocrine cells in the human fetal prostate indicates a migration of paraganglionic cells passing the stroma and reaching the prostate ducts. Double-transgenic mice showed 55% double labeling of periurethral neuroendocrine cells expressing both serotonin and YFP, whereas single serotonin labeling was observed in 36% and exclusive YFP labeling in 9%. The results favor the assumption of a major fraction of neural crest-derived neuroendocrine cells in both the human and murine prostates.

TRPV6 calcium channel translocates to the plasma membrane via Orai1-mediated mechanism and controls cancer cell survival

Transient receptor potential vanilloid subfamily member 6 (TRPV6) is a highly selective calcium channel that has been considered as a part of store-operated calcium entry (SOCE). Despite its first discovery in the early 2000s, the role of this channel in prostate cancer (PCa) remained, until now, obscure. Here we show that TRPV6 mediates calcium entry, which is highly increased in PCa due to the remodeling mechanism involving the translocation of the TRPV6 channel to the plasma membrane via the Orai1/TRPC1-mediated Ca(2+)/Annexin I/S100A11 pathway, partially contributing to SOCE. The TRPV6 calcium channel is expressed de novo by the PCa cell to increase its survival by enhancing proliferation and conferring apoptosis resistance. Xenografts in nude mice and bone metastasis models confirmed the remarkable aggressiveness of TRPV6-overexpressing tumors. Immunohistochemical analysis of these demonstrated the increased expression of clinical markers such as Ki-67, prostate specific antigen, synaptophysin, CD31, and CD56, which are strongly associated with a poor prognosis. Thus, the TRPV6 channel acquires its oncogenic potential in PCa due to the remodeling mechanism via the Orai1-mediated Ca(2+)/Annexin I/S100A11 pathway.

Chromogranin A staining as a prognostic variable in newly diagnosed Gleason score 7-10 prostate cancer treated with definitive radiotherapy

PURPOSE

To demonstrate the association of neuroendocrine differentiation, as identified by chromogranin A (CgA) staining, with clinical outcomes in newly diagnosed prostatic adenocarcinoma treated with definitive radiotherapy (RT).

MATERIALS/METHODS

Patients with Gleason score ≥7 adenocarcinoma were identified from our outcomes database. RT consisted of external beam, brachytherapy, or external beam with brachytherapy boost. Biopsy specimens were stained for neuroendocrine differentiation with CgA. Results were interpreted by a single pathologist. CgA staining was quantified as 0%, <1%, 1-10%, or >10% of tumor cells. Clinical outcomes were blinded at the time of pathologic evaluation.

RESULTS

CgA staining was performed on 289 patients. 149 patients had Gleason score 7, and 140 were Gleason score 8-10. Median follow-up was 6.5 years. For patients with <1% versus >1% CgA staining, pretreatment characteristics were well-balanced. CgA staining was detected in 90 cases (31%). 58 patients had focal positive (<1%) CgA staining, and 32 cases had >1% of tumor cells CgA positive. Patients with >1% CgA staining had inferior biochemical control, clinical failure, distant metastases (DM), and cause-specific survival (CSS) rates. Ten-year rates of DM were 8% versus 48% for patients with <1% versus >1% CgA positive cells, respectively (P < 0.001). CSS at 10 years was 95% versus 76%, respectively (P < 0.001). Local control was equivalent in the two patient cohorts. Patients with <1% CgA staining had similar outcomes to those patients with 0% staining.

CONCLUSIONS

Neuroendocrine differentiation involving >1% of tumor cells on prostate cancer biopsies is a predictor of DM and CSS in patients treated with primary RT.

T-type calcium channels blockers as new tools in cancer therapies

T-type calcium channels are involved in a multitude of cellular processes, both physiological and pathological, including cancer. T-type channels are also often aberrantly expressed in different human cancers and participate in the regulation of cell cycle progression, proliferation, migration, and survival. Here, we review the recent literature and discuss the controversies, supporting the role of T-type Ca(2+) channels in cancer cells and the proposed use of channels blockers as anticancer agents. A growing number of reports show that pharmacological inhibition or RNAi-mediated downregulation of T-type channels leads to inhibition of cancer cell proliferation and increased cancer cell death. In addition to a single agent activity, experimental results demonstrate that T-type channel blockers enhance the anticancer effects of conventional radio- and chemotherapy. At present, the detailed biological mechanism(s) underlying the anticancer activity of these channel blockers is not fully understood. Recent findings and ideas summarized here identify T-type Ca(2+) channels as a molecular target for anticancer therapy and offer new directions for the design of novel therapeutic strategies employing channels blockers. Physiological relevance: T-type calcium channels are often aberrantly expressed or deregulated in cancer cells, supporting their proliferation, survival, and resistance to treatment; therefore, T-type Ca(2+) channels could be attractive molecular targets for anticancer therapy.

Linking inflammation and neuroendocrine differentiation: the role of macrophage migration inhibitory factor-mediated signaling in prostate cancer

A new paper by Tawadros et al. in Endocrine-Related Cancer demonstrates a link between macrophage migration inhibitory factor and neuroendocrine differentiation in prostate cancer. This paper may have implications in explaining the effect of prostatitis and chronic inflammation on the development of aggressive prostate cancer.

Germline genetic variation modulates tumor progression and metastasis in a mouse model of neuroendocrine prostate carcinoma

Neuroendocrine (NE) differentiation has gained increased attention as a prostate cancer (PC) prognostic marker. The aim of this study is to determine whether host germline genetic variation influences tumor progression and metastasis in C57BL/6-Tg(TRAMP)8247Ng/J (TRAMP) mouse model of aggressive NEPC. TRAMP mice were crossed to the eight progenitor strains of the Collaborative Cross recombinant inbred panel to address this. Tumor growth and metastasis burden were quantified in heterozygous transgene positive F1 male mice at 30 weeks of age. Compared to wild-type C57BL/6J-Tg(TRAMP)824Ng/J males, TRAMP x CAST/EiJ, TRAMP x NOD/ShiLtJ and TRAMP x NZO/HlLtJ F1 males displayed significant increases in tumor growth. Conversely, TRAMP x WSB/EiJ and TRAMP x PWK/PhJ F1 males displayed significant reductions in tumor growth. Interestingly, despite reduced tumor burden, TRAMP x WSB/EiJ males had an increased nodal metastasis burden. Patterns of distant pulmonary metastasis tended to follow the same patterns as that of local dissemination in each of the strains. All tumors and metastases displayed positive staining for NE markers, synaptophysin, and FOXA2. These experiments conclusively demonstrate that the introduction of germline variation by breeding modulates tumor growth, local metastasis burden, and distant metastasis frequency in this model of NEPC. These strains will be useful as model systems to facilitate the identification of germline modifier genes that promote the development of aggressive forms of PC.

Cytoskeleton reorganization as an alternative mechanism of store-operated calcium entry control in neuroendocrine-differentiated cells

Neuroendocrine differentiation (NED) is a hallmark of advanced androgen-independent prostate cancer, for which no successful therapy exists. NED tumour cells escape apoptotic cell death by alterations of Ca(2+) homeostasis where the store-operated Ca(2+) entry (SOCE) is known to be a key event. We have previously shown that the downregulation of Orai1 protein representing the major molecular component of endogenous SOCE in human prostate cancer cells, and constituting the principal source of Ca(2+) influx used by the cell to trigger apoptosis, contributes to the establishment of an apoptosis-resistant phenotype (Cell Death Dis. 2010 Sep 16;1:e75.). Here, we report for the first time that the decrease of SOCE during NED may be caused by alternative NED-induced mechanism involving cytoskeleton reorganisation. NED induced by androgen deprivation resulted in a decrease of SOCE due to cortical F-actin over-polymerization which inhibits thapsigargin-induced SOCE. The disruption of F-actin polymerization by Cytochalasin D in NED cells restored SOCE, while the induction of F-actin polymerization by jasplakinolide or calyculin A diminished SOCE without changing the expression of key SOCE players: Orai1, STIM1, and TRPC1. Our data suggest that targeting cytoskeleton-induced pathways of malignant cells together with SOCE-involved channels may prove a useful strategy in the treatment of advanced prostate cancer.

Biology of castration-recurrent prostate cancer

Although androgen-deprivation therapy is the standard therapy for advanced and metastatic prostate cancer, this treatment is only palliative. Prostate cancer recurs then grows despite low circulating testicular androgens, using several mechanisms that remain dependent on androgen-receptor signaling in most cases. This article reviews the diversity of mechanisms used for growth by castration-recurrent prostate cancer.

Neuroendocrine differentiation in castration-resistant prostate cancer: a systematic diagnostic attempt

BACKGROUND

Assessing the neuroendocrine (NE) pattern in castration-resistant prostate cancer (CRPC) may prove useful in selecting potential responders to target therapies such as somatostatin analogues. The aim of this study was to define a panel of markers or examinations appropriate to characterize NE differentiation (NED).

METHODS

Forty-seven patients with CRPC underwent a systematic diagnostic attempt to characterize the NE phenotype using a plasma blood test for chromogranin A (CgA) and immunohistochemical staining of needle biopsy-obtained specimens (CgA, somatostatin receptor 2 [SSTR2], Ki-67, and androgen receptors). In a subgroup of 26 patients, somatostatin receptor scintigraphy using (111)In-DTPA-d-Phe octreotide (octreotide scintigraphy; Octreoscan, Covidien, Hazelwood, MO) was also performed.

RESULTS

NED was found in 85.1% of patients (if serum CgA, tissular CgA, and tissular SSTR2 were considered separately: 54%, 67%, and 58%, respectively). Only 15% of the 26-patient subgroup had an abnormal octreotide scintigraphy result. Although p-CgA and t-CgA were associated with more aggressive disease with a worse prognosis, patients with positive tissular SSTR2 staining had longer overall survival (OS).

CONCLUSION

This systematic approach to explore the NED in a quite homogeneous group of patients with CRPC seems reproducible and appropriate. Further investigations are required to validate this panel and better characterize potential responders to targeted therapy.

Prognostic significance of neuroendocrine differentiation in prostate adenocarcinoma

Much progress has been made toward an understanding of the development and progression of prostate cancer (PC) and the factors that drive the development of androgen independence. Neuroendocrine (NE) cells may provide an intriguing link between NE cell differentiation (NED) and tumor progression in PC. NED in PC generally confers a more aggressive clinical behavior and less favorable prognosis than conventional PC. In this article, we review the known functions of NE cells in PC and discuss the current knowledge on stimulation of cancer proliferation, invasion, apoptosis resistance, serum and immunohistochemical markers, and the prognostic significance of NED in human PC.

Regulation of neuroendocrine differentiation by AKT/hnRNPK/AR/β-catenin signaling in prostate cancer cells

Current diagnostic tools cannot predict clinical failure and androgen-independent disease progression for patients with prostate cancer (PC). The survival signaling pathways of prostate cells play a central role in the progression of tumors to a neuroendocrine (NE) phenotype. NE cells demonstrate attributes that suggest that they are an integral part of the signaling cascade leading to castration-resistant PC. In this study, making use of in vitro neuroendocrine differentiation (NED) of human LNCaP and mouse TRAMP-C2 cells after androgen withdrawal, and of the transgenic adenocarcinoma of mouse prostate (TRAMP) model, we characterized a sequence of molecular events leading to NED and identified a number of markers that could be detectable by routine analyses not only in castration resistant PC but also in hormone naïve PC at the time of initial diagnosis. We found that NED associates with AKT activation that in turn regulates heterogeneous nuclear ribonucleoprotein K (hnRNP K), androgen receptor (AR) and β-catenin levels. Addition of molecules targeting membrane-bound receptors and protein kinases blocks NE differentiation in LNCaP and TRAMP-C2 cells. The extent of AKT phosphorylation and hnRNP K, AR and β-catenin levels may have a potential value as prognostic indicators discriminating between androgen-responsive and unresponsive cells and could be used as molecular targets to monitor the anti-tumor action of new therapeutic protocols based on antireceptor agents and/or neuroendocrine hormone antagonists.

Ion channnels and transporters in cancer. 5. Ion channels in control of cancer and cell apoptosis

Ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. The involvement of ion channels in regulation of programmed cell death, or apoptosis, has been known for at least three decades based on observation that classical blockers of ion channels can influence cell death rates, prolonging or shortening cell survival. Identification of the central role of these channels in regulation of cell cycle and apoptosis as well as the recent discovery that the expression of ion channels is not limited solely to the plasma membrane, but may also include membranes of internal compartments, has led researchers to appreciate the pivotal role of ion channels plays in development of cancer. This review focuses on the aspects of programmed cell death influenced by various ion channels and how dysfunctions and misregulations of these channels may affect the development and progression of different cancers.

Factors implicated in radiation therapy failure and radiosensitization of prostate cancer

Tissue markers may be helpful in enhancing prediction of radiation therapy (RT) failure of prostate cancer (PCa). Among the various biomarkers tested in Phase III randomized trials conducted by the Radiation Therapy Oncology Group, p16, Ki-67, MDM2, COX-2, and PKA yielded the most robust data in predicting RT failure. Other pathways involved in RT failure are also implicated in the development of castration-resistant PCa, including the hypersensitive androgen receptor, EGFR, VEGF-R, and PI3K/Akt. Most of them are detectable in PCa tissue even at the time of initial diagnosis. Emerging evidence suggests that RT failure of PCa results from a multifactorial and heterogeneous disease process. A number of tissue markers are available to identify patients at high risk to fail RT. Some of these markers have the promise to be targeted by drugs currently available to enhance the efficacy of RT and delay disease progression.

Prognostic significance of focal neuroendocrine differentiation in prostate cancer: cases with autopsy-verified cause of death

AIMS

This study was designed to evaluate the prognostic significance of focal chromogranin A (cgA) expression in prostate cancer in a series of cases with autopsy-verified cause of death.

METHODS AND RESULTS

Seventy seven autopsy-verified cases of prostate cancer were identified, 41 cases with metastatic disease and 36 with nonmetastatic disease at autopsy. Immunohistochemical analysis for cgA was performed in 40 cases on the archived diagnostic biopsies taken during the patients' lifetime. After exclusion of a single case of carcinoid tumor, 14 of the 18 (78%) metastatic and none of the 21 (0%) nonmetastatic tumors showed focal neuroendocrine differentiation (NED). The Gleason score and focal cgA expression further increased the accuracy of the prediction of the outcome, as all the cases with focal NED associated with high Gleason score had metastatic disease in contrast to cases without cgA-expression and low Gleason score, all of which were non-metastatic.

CONCLUSIONS

Focal NED seems to be a powerful negative prognostic parameter in prostate adenocarcinomas. The outcome of the disease in prostate cancer can be accurately predicted based on focal NED of the tumor cells either alone or in combination with Gleason score.

Androgen-responsive and -unresponsive prostate cancer cell lines respond differently to stimuli inducing neuroendocrine differentiation

The treatment of advanced prostate cancer (CaP) with androgen deprivation therapy inevitably renders the tumours castration resistant and incurable. Under these conditions, neuroendocrine differentiation (NED) of CaP cells occurs and neuropeptides released by neuroendocrine cells facilitate tumour progression. Pharmacological strategies aiming to prevent or delay NED during androgen ablation could, therefore, increase the effectiveness of the therapy. Mechanisms and pathways inducing NED in CaP are poorly understood and data are often discordant. In the present study, we used several CaP cell lines (androgen-responsive: LNCaP, PC3-AR, 22RV1 and -irresponsive: DU145 and PC3) to evaluate NED after androgen deprivation or treatment with epidermal growth factor (EGF). NED was determined by neuron-specific enolase and chromogranin A expression and by the occurrence of morphological changes in the cells. Androgen-deprivation conditions induced NED in LNCaP and PC3-AR, but not in 22Rv1, PC3 and DU145 cells. LNCaP and PC3-AR cells also became resistant to thapsigargin-induced apoptosis. In all the AR-positive cell lines, androgen deprivation caused a decrease in androgen receptor expression indicating that it is downregulated irrespective of NED induction. Treatment with EGF induced NED in DU145 cells and the EGF receptor inhibitor gefinitib prevented the process. On the contrary, no effect of EGF was demonstrated in LNCaP or 22Rv1 cells. CaP cell lines did not respond univocally to treatments inducing NED, suggesting that studies on this topic should be performed in a wide spectrum of cell models which can be more indicative of the tumour variability in vivo.

Paracrine factors produced by bone marrow stromal cells induce apoptosis and neuroendocrine differentiation in prostate cancer cells

BACKGROUND

Preferential bony metastasis of human prostate cancer (PCa) cells contributes to disease mortality and morbidity. Local factors in bone stromal extracellular matrix microenvironment affect tumor growth through paracrine interactions between tumor and stromal cells.

METHODS

Using co-culture and medium transfer, we used several methods to assess interactions between PCa and bone stromal cells using three PCa cell lines: PC3, LNCaP, and the LNCaP derivative, C4-2B.

RESULTS

Co-culture of LNCaP and C4-2B cells with bone marrow stromal cell lines, HS27a and HS5, decreased cell number, as did culture with conditioned medium (CM) harvested from these two cell lines suggesting a soluble paracrine factor was responsible. PC3 cell growth was unaffected. CM harvested from bone stromal cell lines triggered apoptosis in LNCaP and C4-2B cell lines, but not in PC3 cells. Surviving C4-2B cells grown in bone stromal cell CM over several days were growth arrested, suggesting presence of a growth inhibitor. Apoptosis induced by CM was dose-dependent. Flow cytometry demonstrated that over a 5-day culture period in stromal cell CM, LNCaP, and C4-2B cell lines, but not PC3 cells, underwent greater apoptosis than parallel cultures in SF medium. The LNCaP and C4-2B cells showed morphology and biomarker expression consistent with transdifferentiation towards a neuroendocrine phenotype after exposure to stromal cell CM.

CONCLUSIONS

The reactive bone stromal microenvironment initially is hostile to PCa cells producing widespread apoptosis. Activation of transdifferentiation in a subset of apoptotic resistant cells may support phenotypic adaptation during disease progression in bone, eventually favoring lethal disease.

Incidence of high chromogranin A serum levels in patients with non metastatic prostate adenocarcinoma

Background

ChromograninA in prostate carcinoma (PC) indicate NE differentiation. This tumour is more aggressive and resistant to hormone therapy.

Patients and methods

We analyzed the incidence of pre-operative ChromograninA serum levels in non metastatic PC patients. Serum PSA and ChromograninA were analyzed before treatment. Clinicopathological parameters were evaluated in relation to serum ChromograninA. 486 patients were enrolled.

Results

We found 352 pT2 and 134 pT3. 21 patients were N+. 278 patients had Gleason score levels <7; 173 patients had levels = 7 (122 were 3+4 and 51 4+3); and 35 patients with levels >7. Median PSA pre-operative level was 7.61 ng/ml. PSA was significantly associated with pT stage (pT2 with PSA abnormal 23.6% vs pT3 48.5%, p < 0.0001) and with a Gleason score (PSA abnormal 60% in the Gleason score was >7 vs 29.5% in the Gleason score = 7 vs 27.3% in the Gleason score <7, p < 0.0001). In 114 patients pre-operative ChromograninA levels were elevated (23.5%). Serum ChromograninA levels had no significant association with PSA (p = 0.44) and pT stage (p = 0.89). abnormal ChromograninA levels increased from a Gleason score of <7 (25.5%) to >7 (31.4%) (p = 0.12). The serum ChromograninA levels in the two groups of patients were subdivided before and after 2005 on the basis of different used assays, showing no correlation with serum ChromograninA and other parameters.

Conclusions

This study showed that ChromograninA levels correlated to NE differentiation and possible aggressiveness of PC. Pre-operative circulating ChromograninA could complement PSA in selecting more aggressive PC cases, particularly in the presence of a higher Gleason score. Complementary information is provided by the absence of a correlation between serum ChromograninA and PSA levels.

Orai1 contributes to the establishment of an apoptosis-resistant phenotype in prostate cancer cells

The molecular nature of calcium (Ca²⁺)-dependent mechanisms and the ion channels having a major role in the apoptosis of cancer cells remain a subject of debate. Here, we show that the recently identified Orai1 protein represents the major molecular component of endogenous store-operated Ca²⁺ entry (SOCE) in human prostate cancer (PCa) cells, and constitutes the principal source of Ca²⁺ influx used by the cell to trigger apoptosis. The downregulation of Orai1, and consequently SOCE, protects the cells from diverse apoptosis-inducing pathways, such as those induced by thapsigargin (Tg), tumor necrosis factor α, and cisplatin/oxaliplatin. The transfection of functional Orai1 mutants, such as R91W, a selectivity mutant, and L273S, a coiled-coil mutant, into the cells significantly decreased both SOCE and the rate of Tg-induced apoptosis. This suggests that the functional coupling of STIM1 to Orai1, as well as Orai1 Ca²⁺-selectivity as a channel, is required for its pro-apoptotic effects. We have also shown that the apoptosis resistance of androgen-independent PCa cells is associated with the downregulation of Orai1 expression as well as SOCE. Orai1 rescue, following Orai1 transfection of steroid-deprived cells, re-established the store-operated channel current and restored the normal rate of apoptosis. Thus, Orai1 has a pivotal role in the triggering of apoptosis, irrespective of apoptosis-inducing stimuli, and in the establishment of an apoptosis-resistant phenotype in PCa cells.

Molecular processes leading to aberrant androgen receptor signaling and castration resistance in prostate cancer

Hormone therapies targeting androgen receptor signaling are the mainstay of treatment for patients with advanced prostate cancer. The length of clinical remission induced by hormone therapies varies substantially among treated patients. Why some patients progress rapidly after treatment while others benefit with prolonged remission is a question that remains unsolved. The androgen receptor signaling pathway is the key molecular determinant of castration resistance, and a key target for prostate cancer drug design. Recent advances in characterizing molecular processes leading to the development of castration-resistant prostate cancer, including the discovery of multiple androgen receptor splicing variants, offer opportunities for rational development of new clinical tools or approaches to predict, monitor or control/prevent prostate cancer progression in the castrate setting.

From pathogenesis to prevention of castration resistant prostate cancer

BACKGROUND

Significant progress in understanding the molecular basis of castration resistant prostate cancer (CRPCa) has been achieved in recent years. Despite this progress, CRPCa still remains a lethal disease. Early detection and prevention of CRPCa may provide a new strategy to improve survival of patients diagnosed with PCa at risk to fail standard androgen deprivation therapy (ADT).

METHODS

Herein, we review pathogenetic mechanisms implicated in PCa progression toward castration resistant disease that are detectable in hormone naive PCa to define relevant therapeutic targets for prevention.

RESULTS

Upregulation of androgen receptor (AR) expression has been recognized a major determinant for the development of CRPCa. This hypersensitive pathway is further boosted by the increase of intratumoral androgen synthesis. AR mutants bind promiscuous steroids, and may convert AR antagonists to agonists. Various non-hormonal growth factor receptors transactivate the AR, even in absence of androgens (outlaw pathway). Finally, PCa cells can bypass the AR through various mechanisms, including BCL-2, COX-2, neuroendocrine differentiation. Most of these pathogenetic factors involved in the development of CRPCa are detectable in hormone naive PCa tissue even at the time of initial diagnosis, and could be targeted by drugs currently available.

CONCLUSIONS

CRPCa is the end-stage of a multifactorial and heterogeneous disease process. Pathogenetic factors responsible for the development of the CRPCa phenotype are detectable in the patient's PCa tissue long before the clinical onset of the disease. This approach provides opportunity for early detection and prevention by targeting pathways relevant for the individual disease process.

Ionizing radiation induces prostate cancer neuroendocrine differentiation through interplay of CREB and ATF2: implications for disease progression

Radiation therapy is a first-line treatment for prostate cancer patients with localized tumors. Although some patients respond well to the treatment, approximately 10% of low-risk and up to 60% of high-risk prostate cancer patients experience recurrent tumors. However, the molecular mechanisms underlying tumor recurrence remain largely unknown. Here we show that fractionated ionizing radiation (IR) induces differentiation of LNCaP prostate cancer cells into neuroendocrine (NE)-like cells, which are known to be implicated in prostate cancer progression, androgen-independent growth, and poor prognosis. Further analyses revealed that two cyclic AMP-responsive element binding transcription factors, cyclic AMP-response element binding protein (CREB) and activating transcription factor 2 (ATF2), function as a transcriptional activator and a repressor, respectively, of NE-like differentiation and that IR induces NE-like differentiation by increasing the nuclear content of phospho-CREB and cytoplasmic accumulation of ATF2. Consistent with this notion, stable expression of a nonphosphorylatable CREB or a constitutively nuclear-localized ATF2 in LNCaP cells inhibits IR-induced NE-like differentiation. IR-induced NE-like morphologies are reversible, and three IR-resistant clones isolated from dedifferentiated cells have acquired the ability to proliferate and lost the NE-like cell properties. In addition, these three IR-resistant clones exhibit differential responses to IR- and androgen depletion-induced NE-like differentiation. However, they are all resistant to cell death induced by IR and the chemotherapeutic agent docetaxel and to androgen depletion-induced growth inhibition. These results suggest that radiation therapy-induced NE-like differentiation may represent a novel pathway by which prostate cancer cells survive the treatment and contribute to tumor recurrence.

Cushing's syndrome due to ectopic ACTH production by (neuroendocrine) prostate carcinoma

Ectopic adrenocorticotropin (ACTH) secretion accounts for less than 10% of all causes of endogenous Cushing's syndrome (CS) and is usually associated with neuroendocrine tumors and small cell carcinoma of the lung. We report the case of a 62-year-old man with CS due to ectopic ACTH production by small cell carcinoma of the prostate. He presented with severe hypercortisolism and associated symptoms. Plasma neuron specific enolase (NSE) was grossly elevated. Despite performing a laparoscopic bilateral adrenalectomy, the patient died as a result of sepsis with multi-organ failure. Post-mortem immunohistochemical staining of prostate tumor tissue showed ACTH expression. ACTH staining was also performed in four additional patients with small cell carcinoma of the urinary tract without CS. None of these additional cases showed a positive staining for ACTH. Although a rare cause of ectopic ACTH production, neuroendocrine prostate carcinoma should be considered in male patients with Cushing's syndrome, in particular in those with an occult source of ACTH overproduction.

Neuroendocrine transdifferentiation induced by VPA is mediated by PPARgamma activation and confers resistance to antiblastic therapy in prostate carcinoma

BACKGROUND

Prostate cancer (PCa) is the most commonly diagnosed cancer in men in the Western Countries. When prostatectomy fails to eradicate the primary tumor, PCa is generally refractory to all therapeutic approaches. Valproic acid (VPA) is a promising anticancer agent recently assigned to the class of histone deacetylase (HDAC) inhibitors. However molecular mechanisms underlying VPA action in PCa cells are largely unknown and further experimental validation to prove its potential application in clinic practice is needed.

RESULTS

In our study we show that VPA is a potent inducer of neuro-endocrine transdifferentiation (NET) in androgen receptor null PCa cells, both in vitro and in vivo. NET was an early event detectable through the expression of neuro-endocrine (NE) markers within 72 hr after VPA treatment and it was associated to a reduction in the overall cell proliferation. When we interrupted VPA treatment we observed the recovery in residual cells of the basal proliferation rate both in vitro and in a xenograft model. The NET process was related to Bcl-2 over-expression in non-NE PCa cells and to the activation of PPARgamma in NE cells. The use of specific PPARgamma antagonist was able to reduce significantly the expression of NE markers induced by VPA.

CONCLUSIONS

Our data indicate that the use of VPA as monotherapy in PCa has to be considered with extreme caution, since it may induce an unfavorable NET. In order to counteract the VPA-induced NET, the inhibition of PPARgamma may represent a suitable adjuvant treatment strategy and awaits further experimental validation.

Irradiation enhances the metastatic potential of prostatic small cell carcinoma xenografts

BACKGROUND

Small cell carcinoma of the prostate (SCCP) is a rare subset of prostate cancer (0.5-2% of all prostatic carcinomas), predominantly composed of neuroendocrine (NE) cells, with a very poor prognosis. Irradiation is one of the mainstay options for SCCP local treatment, yet, little is known about the clinical response of these aggressive tumors to radiotherapy.

METHODS

Using SCID mice, the response to fractionated ionizing radiation (IR) of two unique human NE xenografts of SCCP (WISH-PC2 and WM-4A) was investigated.

RESULTS

Fractionated irradiation of WISH-PC2 xenografts using total doses of >24 Gy induced a delay in tumor growth, while total doses of >36 Gy led to local tumor eradication. However, most of the irradiated mice suffered from disseminated metastases. Similarly, in the WM-4A xenograft, a total dose of 20 Gy led to tumor growth delay and some of the mice also developed metastases. Non-irradiated local xenografts failed to disseminate, even following surgical excision of the main tumor mass; however, tumor cells administered intravenously did form metastases. Metastases of both xenografts were located in the adrenal/kidney and inter-scapular regions, areas rich in brown adipose tissue. A correlation was found between the appearance of irradiation-induced metastases and activation of the gelatinase activity of matrix metalloproteinase-9.

CONCLUSIONS

Clinically, this study raises the possibility that radiation to SCCP may promote metastatic disease. For patients in whom prostate biopsy shows a predominance of small cell cancer, it may be necessary to deliver systemic therapy together with the radiotherapy in order to prevent the development of metastases.

Neuroendocrine differentiation in prostate cancer: from lab to bedside

OBJECTIVES

To discuss the current knowledge on induction, production, sustenance and promotion of neuroendocrine differentiation in human prostate cancer.

METHODS

Review of the literature using PubMed search and scientific journal publications.

RESULTS

Morphological evidence explains some functional relationship between neuroendocrine and neoplastic surrounding cells. Transdifferentiation phenomenon and new biochemical pathways could be included in the development of androgen independence and prostate cancer progression.

CONCLUSION

Multiple evidence seems to confirm that a synergistic functional network between epithelial PSA secretory cells and neuroendocrine intraprostatic system is the main trigger for the induction and sustenance of neuroendocrine differentiation. The development of new antineoplastic molecules should consider the multiple interference of the intercellular network.

EGF prevents the neuroendocrine differentiation of LNCaP cells induced by serum deprivation: the modulator role of PI3K/Akt

The primary focus of this investigation was to study the relationship between neuroendocrine (NE) differentiation and epidermal growth factor (EGF) because both have been implicated in the progression of prostate cancer. For this purpose, we used gefitinib and trastuzumab, which are inhibitors of EGF receptor (EGFR) and ErbB2, respectively. EGF prevents NE differentiation induced by androgen depletion. This effect is prevented by gefitinib, which blocks the activation of EGFR and ErbB2, stimulation of mitogen-activated protein kinase (MAPK), and cell proliferation induced by EGF. Conversely, trastuzumab does not inhibit the effect of EGF on EGFR phosphorylation, MAPK activity, cell proliferation, and NE differentiation, although it reduces ErbB2 levels specifically, suggesting that ErbB2 is not necessary to inhibit NE differentiation. Prevention of NE differentiation by EGF is mediated by a MAPK-dependent mechanism and requires constitutive Akt activation. The abrogation of the PI3K/Akt pathway changes the role of EGF from inhibitor to inductor of NE differentiation. We show that EGFR tyrosine kinase, MAPK, and PI3K inhibitors inhibit the cell proliferation stimulated by EGF but induce the acquisition of NE phenotype. Altogether, the present data should be borne in mind when designing new clinical schedules for the treatment of prostate cancer, including the use of ErbB receptors and associated signaling pathway inhibitors.

Increased expression of cyclin B1 sensitizes prostate cancer cells to apoptosis induced by chemotherapy

Chemotherapeutic drugs ideally should take advantage of the differences between transformed and normal cells and induce apoptosis only in cancer cells. One such difference may be the overexpression of cyclin B1 protein in cancer cells, which is required for the proper progression through mitosis. Previously, we showed that treatment of human prostate cancer cells with 2-methoxyestradiol (2-ME) or docetaxel results in an accumulation of cyclin B1 protein and an increase in cyclin B1 kinase activity, followed by induction of apoptotic cell death. Inhibition of cyclin B1 kinase lowers apoptosis induced by 2-ME and docetaxel. In this study, we established a positive correlation between cyclin B1 protein and apoptosis induced by chemotherapy in prostate cancer cells. There is minimal cyclin B1 and induction of apoptosis by chemotherapy in nontransformed cells. LNCaP and PC-3 prostate cancer cells stably overexpressing cyclin B1 are more sensitive to apoptosis induced by chemotherapy. LNCaP cells expressing cyclin B1 small interfering RNA to lower cyclin B1 protein or dominant negative cyclin-dependent kinase 1 to inhibit cyclin B1 kinase show a decrease in apoptosis. Increased sensitivity to apoptosis by overexpression of cyclin B1 may be due to lower Bcl-2, higher p53, and decreased neuroendocrine differentiation. We suggest that a cancer-specific mechanism whereby 2-ME and docetaxel may exert anti-prostate cancer activity is the deregulated activation of cyclin B1 kinase, leading to the induction of apoptotic cell death. Our results also suggest that higher levels of cyclin B1 in prostate cancer cells may be a good prognostic marker for chemotherapy.

Ion channels in death and differentiation of prostate cancer cells

Plasma membrane ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. Enhanced proliferation, aberrant differentiation, and impaired ability to die are the prime reasons for abnormal tissue growth, which can eventually turn into uncontrolled expansion and invasion, characteristic of cancer. Prostate cancer (PCa) cells express a variety of plasma membrane ion channels. By providing the influx of essential signaling ions, perturbing intracellular ion concentrations, regulating cell volume, and maintaining membrane potential, PCa cells are critically involved in proliferation, differentiation, and apoptosis. PCa cells of varying metastatic ability can be distinguished by their ion channel characteristics. Increased malignancy and invasiveness of androgen-independent PCa cells is generally associated with the shift to a 'more excitable' phenotype of their plasma membrane. This shift is manifested by the appearance of voltage-gated Na(+) and Ca(2+) channels which contribute to their enhanced apoptotic resistance together with downregulated store-operated Ca(2+) influx, altered expression of different K(+) channels and members of the Transient Receptor Potential (TRP) channel family, and strengthened capability for maintaining volume constancy. The present review examines channel types expressed by PCa cells and their involvement in metastatic behaviors.

Molecular markers of prostate cancer

Although prostate-specific antigen (PSA) has evolved as a very useful tool for detection of prostate cancer, there remains an urgent need for more accurate biomarkers to diagnose prostate cancer and predict cancer-related outcomes. Recent advances in the study of proteomics and high throughput techniques have led to the discovery of many potential biomarkers for prostate cancer. This article briefly reviews the current status of PSA testing and discusses several candidate protein biomarkers for prostate cancer, as well as highlighting some recent proteomic discoveries with the potential to supplement or even replace PSA for the diagnosis and prognosis of prostate cancer.

Prostate androgen-regulated gene: a novel potential target for androgen-independent prostate cancer therapy

AIM

To investigate the involvement of the prostate androgen-regulated (PAR) gene in the androgen receptor (AR) signaling pathway and the malignant phenotype of androgen-independent prostate cancer (PCa) cells.

METHODS

The difference in PAR expression between LNCaP and PC3 cells was detected by reverse transcription-polymerase chain reaction (RT-PCR). Androgen and anti-androgen effects on PAR expression were evaluated by RT-PCR in LNCaP, PC3 cells and PC3 cells stably transfected with vector containing wild-type AR. To determine the importance of PAR in the malignant proliferation of androgen-independent PCa cells, we used small interfering RNA (siRNA) transfection to knock down the expression of the gene in PC3 cells. The changes in the malignant phenotype of PCa cells after transfection were analyzed by cell count, colony formation in soft agar and flow cytometry.

RESULTS

PAR expression was 3-fold higher in PC3 cells than that in LNCaP cells. Dihydrotestosterone (DHT) regulated PAR mRNA expression in LNCaP cells and the effect was inhibited by the AR antagonist, flutamide. By contrast, DHT did not affect PAR expression in PC3 cells. The reintroduction of AR into PC3 cells by stable transfection restored the androgen effect on PAR upregulation. After the knockdown of the PAR gene by siRNA, PC3 cells exhibited a reversal of the malignant phenotype.

CONCLUSION

Because of the possibility that PAR is downstream from the AR, and because of its contribution to malignant proliferation in androgen-independent PCa cells, the gene could be a potential therapeutic target for androgen-independent PCa with AR signaling pathway alteration.

[Neuroendocrine differentiation in prostate cancer: an unrecognized and therapy resistant phenotype]

Neuroendocrine (NE) differentiation frequently occurs in common prostatic malignancies but usually escapes pathological and clinical detection. The present review focuses on biological properties of NE tumor cells making them resistant to androgen deprivation and radiation therapy. Recent data have shown that NE prostate cancer cells (as defined by the most commonly used endocrine marker chromogranin A) are arrested in the G0-phase of the cell cycle and do not undergo apoptosis. This particular phenotype consistently lacks the nuclear androgen receptor in both benign and malignant conditions but produces a series of hormonal growth factors exerting mitogenic stimuli on adjacent, exocrine tumor cells. Neoplastic NE cells devoid of the nuclear androgen receptor constitute an androgen-insensitive cell population in prostate cancer. The absence of proliferative and apoptotic activity makes NE tumor cells particularly resistant towards cytotoxic drugs and radiation therapy. Pathological and clinical detection of NE features is recommended for all prostate cancer patients for whom radiation therapy and androgen deprivation is being considered.

Immunohistochemical and ultrastructural features of neuroendocrine differentiated carcinomas of the prostate: an immunoelectron microscopic study

The purpose of this study was to further define the immunohistochemical and ultrastructural characteristics of neuroendocrine (NE) differentiated prostatic carcinomas. Seventy-seven specimens were obtained from prostatic carcinoma tumors during prostatectomy, transurethral resection of prostate or biopsy in 77 prostate cancer patients, and analyzed by immunohistochemical staining for chromogranin A (CgA). Nine of these tumors were also studied by elctron microscopy and 4 were examined by pre-embedding immunoelectron microscopy. CgA-stained cells were detected in 36 tumors (47%). Clinically advanced tumors or tumors with higher histological grades were associated with increased NE differentiation. Three of the tumors studied by electron microscopy contained cells showing unequivocal NE differentiation revealed by the presence of neurosecretory granules, while the poorly NE-differentiated malignant cells contained pleomorphic granules, which were lysosomal-like rather than NE-type granules. Immunoelectron microscopy demonstrated the presence of CgA immunoreactivity on the pleomorphic granules in the poorly differentiated malignant glands. This study suggests that NE-differentiated malignant cells in prostate cancer tissues may induce aggressive behavior in adjacent proliferating neoplastic cells via a paracrine mechanism.

Prognostic significance of plasma chromogranin a levels in patients with hormone-refractory prostate cancer treated in Cancer and Leukemia Group B 9480 study

OBJECTIVES

To test the hypothesis that chromogranin A (CgA) levels are prognostic in patients with metastatic hormone-refractory prostate cancer (HRPC). The extent of neuroendocrine differentiation in prostate cancer correlates with aggressive disease and with progression to HRPC. Plasma CgA levels in patients with prostate cancer may reflect the extent of the tumor neuroendocrine phenotype.

METHODS

Pretreatment plasma was collected from 390 patients with metastatic HRPC enrolled in the Cancer and Leukemia Group B (CALGB) 9480 trial, a study of three different doses of suramin. Plasma CgA levels were determined in 321 samples in duplicate using a quantitative sandwich immunoassay. The proportional hazards model was used to assess the prognostic significance of CgA in predicting overall survival.

RESULTS

The median plasma CgA level was 12 U/L (interquartile range 7.7 to 19.3). In univariate analysis, plasma CgA correlated inversely with survival times, with a survival time of 17 months for low CgA (less than 12 U/L, 95% CI 14 to 19) compared with 11 months for high CgA (95% CI 8 to 14, P = 0.014) and at all exploratory cutpoints, including CgA of 9.5 U/L or less versus greater than 9.5 U/L, with survival of 19 months compared with 12 months (P = 0.0015). In multivariate models (adjusting for performance status, prostate-specific antigen, and lactate dehydrogenase), the plasma CgA levels remained predictive of overall survival.

CONCLUSIONS

These results support the hypothesis that serum CgA levels correlate with outcome in patients with HRPC, although the clinical significance needs to be established in confirmatory studies before incorporation of CgA measurements in clinical practice.

Evaluation of neuroendocrine staining and androgen receptor expression in incidental prostatic adenocarcinoma: Prognostic implications

OBJECTIVES

To identify neuroendocrine cells and androgen receptors (ARs), possible predictors of cancer progression, in a series of untreated patients with incidental Stage T1a prostate cancer (PCa). Neuroendocrine cells may exert a dynamic role in the microenvironment of PCa. The AR is thought to have a central role in the propagation of prostate carcinogenesis.

METHODS

Prostatectomy specimens from 81 patients with Stage T1a PCa were available for analysis. Neuroendocrine cells were detected by immunohistochemistry using antibodies to chromogranin A (CgA) and neuron-specific enolase, and the antibody against AR enabled the evaluation of the nuclear AR status. Tumor cell proliferation was assessed with the Ki-67 labeling index using MIB-1 antibody. The patients were followed up for a mean of 63.9 months, and a subsequent rise in prostate-specific antigen or positive digital rectal examination findings confirmed by biopsy was considered disease progression.

RESULTS

Of the 81 specimens, 62 (76.54%) were positive for CgA and/or neuron-specific enolase and 19 (23.46%) were negative. A statistically significant correlation was found between CgA positivity and tumor dedifferentiation (P = 0.002). Well-differentiated tumors revealed an overexpression of ARs (P < 0.005). On multivariate analysis, worsening tumor differentiation emerged as the only independent predictor of progression-free survival (P = 0.041); however, only CgA positivity was an independent predictor of tumor progression in well and moderately differentiated tumors (P = 0.038).

CONCLUSIONS

The results of this study suggest that CgA may represent a useful marker for subsequent aggressive behavior and progression in incidental well and moderately differentiated Stage T1a PCa.

Neuroendocrine differentiation in prostate cancer: implications for new treatment modalities

OBJECTIVES

This review aims to provide practising clinicians with the most recent knowledge of the biological nature of prostate cancer (PC) to facilitate investigation of new treatment modalities for patients with PC, especially the hormone-refractory state of the disease.

METHODS

Review of the literature using PubMed search and scientific journal publications.

RESULTS

Much progress has been made towards an understanding of the development and progression of PC, and the factors which drive the development of androgen independence. Neuroendocrine (NE) cells may provide an intriguing link between NE cell differentiation and tumour progression in PC with the genetically supported formation of androgen-independent clones which regulate the proliferation of neighbouring non-NE-phenotype cancer cells in a paracrine manner by secretion of NE products. Various NE peptides stimulate proliferation of androgen-independent PC through transactivation of the androgen receptors (AR). Therefore, cancerous epithelial cells that increase their responsiveness to NE factors or induce NE cells to release trophic factors may have a survival advantage over their siblings.

CONCLUSION

This review shows the need to improve our understanding of the biological nature of PC, especially cancer cells of the NE phenotype and their regulatory products to develop new therapeutic protocols and trials based on NE hormones and their agonists/antagonists.

Evidence for downregulation of calcium signaling proteins in advanced mouse adenocarcinoma

BACKGROUND

Prostate cancer (PCa) is the leading cancer related death in America. Gleason grading is currently the predominant method for prediction, with only few biomarkers available. More biomarkers, especially as they relate to cancer progression are desirable.

METHODS

The abundance of several important proteins in prostate tissue was compared between wild-type mouse dorsal prostate and well-differentiated transgenic adenocarcinoma mouse prostate (TRAMP) mouse dorsal prostates, and between wild-type mouse dorsal prostate and poorly-differentiated TRAMP mouse tumor tissue. 2DIGE method in conjunction with MALDI-ToF and Western blots was used to determine differential expression.

RESULTS

In TRAMP dorsal prostates with well-differentiated adenocarcinoma, there were few significant changes in the protein abundances compared to wild-type dorsal prostates, with the exception of increases in proliferating cell nuclear antigen (PCNA) and beta tubulin, two proteins implicated in cell proliferation, and a more than 2-fold increase in Hsp60, a protein involved in the suppression of apoptosis. In the poorly-differentiated tumors, the changes in protein abundance were substantial. While some of those changes could be related to the disappearance of stromal tissue or the appearance of epithelial tissue, other changes in protein abundance were more significant to the cancer development itself. Most notable was the overall decrease in calcium homeostasis proteins with a 10-fold decrease in calreticulin and Hsp70 and a 40-fold decrease in creatine kinase bb in the cancerous tissue.

CONCLUSIONS

Proteomics of TRAMP mice provide an excellent method to observe changes in protein abundance, revealing changes in pathways during cancer progression.

IB1/JIP-1 controls JNK activation and increased during prostatic LNCaP cells neuroendocrine differentiation

The scaffold protein Islet-Brain1/c-Jun amino-terminal kinase Interacting Protein-1 (IB1/JIP-1) is a modulator of the c-Jun N-terminal kinase (JNK) activity, which has been implicated in pleiotrophic cellular functions including cell differentiation, division, and death. In this study, we described the presence of IB1/JIP-1 in epithelium of the rat prostate as well as in the human prostatic LNCaP cells. We investigated the functional role of IB1/JIP-1 in LNCaP cells exposed to the proapoptotic agent N-(4-hydroxyphenyl)retinamide (4-HPR) which induced a reduction of IB1/JIP-1 content and a concomittant increase in JNK activity. Conversely, IB1/JIP-1 overexpression using a viral gene transfer prevented the JNK activation and the 4-HPR-induced apoptosis was blunted. In prostatic adenocarcinoma cells, the neuroendocrine (NE) phenotype acquisition is associated with tumor progression and androgen independence. During NE transdifferentiation of LNCaP cells, IB1/JIP-1 levels were increased. This regulated expression of IB1/JIP-1 is secondary to a loss of the neuronal transcriptional repressor neuron restrictive silencing factor (NRSF/REST) function which is known to repress IB1/JIP-1. Together, these results indicated that IB1/JIP-1 participates to the neuronal phenotype of the human LNCaP cells and is a regulator of JNK signaling pathway.

[Neuroendocrine differentiation in prostate cancer. An unrecognized and therapy-resistant phenotype]

Neuroendocrine (NE) differentiation frequently occurs in common prostatic malignancies and has attracted increasing attention in contemporary prostate cancer research. This particular phenotype, however, usually escapes pathological and clinical detection in routine practice. The present review focuses on the biological properties of NE tumor cells that make them resistant to androgen deprivation and radiation therapy. NE cells produce a number of hormonal growth factors (e.g., serotonin) that may act through endocrine, paracrine, and autocrine mechanisms. Morphogenetic studies have identified intermediate phenotypes between the three basic cell types of the prostatic epithelium indicating their common origin from stem cells located in the basal cell layer. Virtually all prostatic adenocarcinomas show NE differentiation as defined by the most commonly used endocrine marker chromogranin A. Clinical studies suggest that the extent of NE differentiation increases with tumor progression and the development of androgen insensitivity. NE differentiation exclusively occurs in the G0 phase of the cell cycle in which tumor cells are usually resistant to radiation therapy and cytotoxic drugs. In addition, NE tumor cells also escape programmed cell death. Even under androgen deprivation, only 0.16% of NE tumor cells show apoptotic activity. This indicates that the vast majority of NE tumor cells represent an immortal cell population in prostate cancer. Although NE tumor cells do not proliferate, they produce a number of NE growth factors with mitogenic properties that maintain cell proliferation in adjacent (exocrine) tumor cells through a paracrine mechanism. NE tumor cells consistently lack the androgen receptor and are androgen insensitive in all stages of the disease. They derive through a process of intermediate differentiation from exocrine tumor cells, the most prevalent phenotype in common prostatic adenocarcinoma. Elevated serum levels of chromogranin A in prostate cancer patients correlate with poor prognosis and are scarcely influenced by either androgen deprivation or chemotherapy. Looking for NE differentiation is recommended in the pathological and clinical evaluation of prostate cancer patients for whom radiation and androgen deprivation are therapeutic options.