Establishment and characterization of a primary androgen-responsive African-American prostate cancer cell line, E006AA

PARP-ish: Gaps in Molecular Understanding and Clinical Trials Targeting PARP Exacerbate Racial Disparities in Prostate Cancer

PARP is a nuclear enzyme with a major function in the DNA damage response. PARP inhibitors (PARPi) have been developed for treating tumors harboring homologous recombination repair (HRR) defects that lead to a dependency on PARP. There are currently three PARPi approved for use in advanced prostate cancer (PCa), and several others are in clinical trials for this disease. Recent clinical trial results have reported differential efficacy based on the specific PARPi utilized as well as patient race. There is a racial disparity in PCa, where African American (AA) males are twice as likely to develop and die from the disease compared to European American (EA) males. Despite the disparity, there continues to be a lack of diversity in clinical trial cohorts for PCa. In this review, PARP nuclear functions, inhibition, and clinical relevance are explored through the lens of racial differences. This review will touch on the biological variations that have been explored thus far between AA and EA males with PCa to offer rationale for investigating PARPi response in the context of race at both the basic science and the clinical development levels.

Experimental in vitro, ex vivo and in vivo models in prostate cancer research

Androgen deprivation therapy has a central role in the treatment of advanced prostate cancer, often causing initial tumour remission before increasing independence from signal transduction mechanisms of the androgen receptor and then eventual disease progression. Novel treatment approaches are urgently needed, but only a fraction of promising drug candidates from the laboratory will eventually reach clinical approval, highlighting the demand for critical assessment of current preclinical models. Such models include standard, genetically modified and patient-derived cell lines, spheroid and organoid culture models, scaffold and hydrogel cultures, tissue slices, tumour xenograft models, patient-derived xenograft and circulating tumour cell eXplant models as well as transgenic and knockout mouse models. These models need to account for inter-patient and intra-patient heterogeneity, the acquisition of primary or secondary resistance, the interaction of tumour cells with their microenvironment, which make crucial contributions to tumour progression and resistance, as well as the effects of the 3D tissue network on drug penetration, bioavailability and efficacy.

Betulinic acid and its ionic derivatives impaired growth of prostate cancer cells without induction of GRP78 and CHOP

Prostate cancer (PCa) is the most common invasive malignancy for men in the USA. The incidence and mortality rates of PCa are significantly higher among African American men, as compared to those in Caucasian men. Betulinic acid (BA) is a penta-cyclic triterpenoid that is often found in the bark of several species of plants. It possesses a variety of biological activities, including anti-cancer activities. We examined the cytotoxic effects and endoplasmic reticulum (ER) stress induced by BA and its ionic derivatives with PCa cells derived from African Americans and Caucasian men. The viability of all PCa cells was reduced by the BA compounds, and the cytotoxicity of these BA compounds was independent of ethnicity and androgen dependency. The BA compounds induced modest effects on ER stress proteins when compared with ER stress inducers, tunicamycin and thapsigargin. The induction of glucose regulated protein 78 (GRP78) was largely correlated with the expression of C/EBP homologous protein (CHOP) and cleaved poly [ADP-ribose] polymerase (PARP)/caspase-3 in the PCa cells. In summary, our data demonstrated that BA compounds impaired the growth of PCa cells regardless of ethnicity – through GRP78- and CHOP-independent pathways.

Drosophila Accessory Gland: A Complementary In Vivo Model to Bring New Insight to Prostate Cancer

Prostate cancer is the most common cancer in aging men. Despite recent progress, there are still few effective treatments to cure its aggressive and metastatic stages. A better understanding of the molecular mechanisms driving disease initiation and progression appears essential to support the development of more efficient therapies and improve patient care. To do so, multiple research models, such as cell culture and mouse models, have been developed over the years and have improved our comprehension of the biology of the disease. Recently, a new model has been added with the use of the Drosophila accessory gland. With a high level of conservation of major signaling pathways implicated in human disease, this functional equivalent of the prostate represents a powerful, inexpensive, and rapid in vivo model to study epithelial carcinogenesis. The purpose of this review is to quickly overview the existing prostate cancer models, including their strengths and limitations. In particular, we discuss how the Drosophila accessory gland can be integrated as a convenient complementary model by bringing new understanding in the mechanisms driving prostate epithelial tumorigenesis, from initiation to metastatic formation.

Immunologic disparities in prostate cancer between American men of African and European descent

Health disparities between American men of African and European descent (AA and EA, respectively) can be attributed to multiple factors, including disparities in socioeconomic status, access to healthcare, lifestyle, ancestry, and molecular aberrations. Numerous clinical trials and research studies are being performed to identify new and better therapeutic approaches to detect and treat prostate cancer. Of potential concern is the fact that the majority of the patients enrolled on these trials are EA. This disproportionate enrollment of EA could have implications when disease management recommendations are proposed without regard to the existing disparities in prostate cancer between races. With increasing advancements in immunotherapies, the immunological disparities between men of diverse ethnicities will need to be fully explored to develop novel and effective therapeutic approaches for prostate cancer patients globally. To help address this need, this review fully describes inequalities in prostate cancer at the immunological level between AA and EA.

Should Grade Group 1 (GG1) be called cancer?

INTRODUCTION

ISUP Grade Group 1 prostate cancer is the lowest histologic grade of prostate cancer with a clinically indolent course. Removal of the term 'cancer' has been proposed and has historical precedent both in urothelial and thyroid carcinoma.

METHODS

Evidence-based review identifying arguments for and against Grade Group 1 being referred to as cancer.

RESULTS

Grade Group 1 has histologic evidence of tissue microinvasion and 0.3-3% rate of extraprostatic extension. Genomic evaluation suggests overlap of a minority of Grade Group 1 cancers with those of Grade Group 2. Conversely, Grade Group 1 tumors appear to have distinct genetic and genomic profiles from Grade Group 3 or higher tumors. Grade Group 1 has no documented ability for regional or distant metastasis and long-term follow up after treatment or active surveillance is safe with excellent oncologic outcomes.

DISCUSSION

Grade Group 1 prostate cancer, while showing evidence of neoplasia on histology has a remarkably indolent natural history more akin to non-neoplastic precursor lesions. Consideration should be given to renaming Grade Group 1 prostate cancer, which has the potential to minimize overtreatment, treatment-related side effects, patient anxiety, and financial burden on the healthcare system.

Disparities in prostate cancer incidence and mortality rates: Solvable or not?

Prostate cancer (PCa) is recognized as a disease possessing not only great variation in its geographic and racial distribution but also tremendous variation in its potential to cause morbidity and death and it, therefore, ought not to be considered a homogenous disease entity. Morbidity and death from PCa are disproportionately higher in men of African ancestry (MAA) who are generally observed to have more aggressive disease and worse outcomes following treatment compared to men of European ancestry (MEA). The higher rates of PCa among MAA relative to MEA appear to be multifactorial and related to inherent differences in biological aggressiveness; a continued lack of awareness of the disease and methods of prevention; a lower prevalence of screen-detected PCa; comparatively lower access to quality healthcare as well as systemic and institutionalized disparities in the administration of optimal care to MAA in developed countries such as the United States of America where high-quality care is available. Even when access to quality healthcare is assured in equal access settings, it appears that MAA still have worse outcomes after PCa treatment stage-for-stage and grade-for-grade compared to MEA, suggesting that, inherent racial, ethnic and biological differences are paramount in predicting poor outcomes. This review has explored the different contributing factors to the current disparities in PCa incidence and mortality rates with emphasis on the incongruence in how research has been conducted in understanding the disease towards developing therapies.

Xenoestrogen interference with nongenomic signaling actions of physiological estrogens in endocrine cancer cells

Rapid nongenomic signaling by estrogens (Es), initiated near the cell membrane, provides new explanations for the potent actions of environmental chemicals that imperfectly mimic physiological Es. These pathways can affect tumor growth, stabilization, or shrinkage via a number of signaling streams such as activation/inactivation of mitogen-activated protein kinases and caspases, generation of second messengers, and phospho-triggering of cyclin instability. Though prostate cancers are better known for their responsiveness to androgen deprivation, ∼17% of late stage tumors regress in response to high dose natural or pharmaceutical Es; however, the mechanisms at the cellular level are not understood. More accurate recent measurements show that estradiol (E₂) levels decline in aging men, leading to the hypothesis that maintaining young male levels of E₂ may prevent the growth of prostate cancers. Major contributions to reducing prostate cancer cell numbers included low E₂ concentrations producing sustained ERK phospho-activation correlated with generation of reactive oxygen species causing cancer cell death, and phospho-activation of cyclin D1 triggering its rapid degradation by interrupting cell cycle progression. These therapeutic actions were stronger in early stage tumor cells (with higher membrane estrogen receptor levels), and E₂ was far more effective compared to diethylstilbestrol (the most frequently prescribed E treatment). Xenoestrogens (XEs) exacerbated the growth of prostate cancer cells, and as we know from previous studies in pituitary cancer cells, can interfere with the nongenomic signaling actions of endogenous Es. Therefore, nongenomic actions of physiological levels of E₂ may be important deterrents to the growth of prostate cancers, which could be undermined by the actions of XEs.

MicroRNA-4719 and microRNA-6756-5p Correlate with Castration-Resistant Prostate Cancer Progression through Interleukin-24 Regulation

Prostate cancer (PCa) is the second leading cause of cancer death in the United States. The five-year survival rate for men diagnosed with localized PCa is nearly 100%, yet for those diagnosed with aggressive PCa, it is less than 30%. The pleiotropic cytokine Interleukin-24 (IL-24) has been shown to specifically kill PCa cells compared to normal cells when overexpressed in both in vitro and in vivo studies. Despite this, the mechanisms regulating IL-24 in PCa are not well understood. Since specific microRNAs (miRNAs) are dysregulated in PCa, we used miRNA target prediction algorithm tools to identify miR-4719 and miR-6556-5p as putative regulators of IL-24. This study elucidates the expression profile and role of miR-4719 and miR-6756-5p as regulators of IL-24 in PCa. qRT-PCR analysis shows miR-4719 and miR-6756-5p overexpression significantly decreases the expression of IL-24 in PCa cells compared to the negative control. Compared to the indolent PCa and normal prostate epithelial cells, miR-4719 and miR-6756-5p are significantly overexpressed in castration-resistant prostate cancer (CRPC) cell lines, indicating that their gain may be an early event in PCa progression. Moreover, miR-4719 and miR-6756-5p are significantly overexpressed in the CRPC cell line of African-American males (E006AA-hT) compared to CRPC cell lines of Caucasian males (PC-3 and DU-145), indicating that miR-4719 and miR-6756-5p may also play a role in racial disparity. Lastly, the inhibition of expression of miR-4719 and miR-6756-5p significantly increases IL-24 expression and inhibits proliferation and migration of CRPC cell lines. Our findings indicate that miR-4719 and miR-6756-5p may regulate CRPC progression through the targeting of IL-24 expression and may be biomarkers that differentiate between indolent and CRPC. Strategies to inhibit miR-4719 and miR-6756-5p expression to increase IL-24 in PCa may have therapeutic efficacy in aggressive PCa.

Application of Prostate Cancer Models for Preclinical Study: Advantages and Limitations of Cell Lines, Patient-Derived Xenografts, and Three-Dimensional Culture of Patient-Derived Cells

Various preclinical models have been developed to clarify the pathophysiology of prostate cancer (PCa). Traditional PCa cell lines from clinical metastatic lesions, as exemplified by DU-145, PC-3, and LNCaP cells, are useful tools to define mechanisms underlying tumorigenesis and drug resistance. Cell line-based experiments, however, have limitations for preclinical studies because those cells are basically adapted to 2-dimensional monolayer culture conditions, in which the majority of primary PCa cells cannot survive. Recent tissue engineering enables generation of PCa patient-derived xenografts (PDXs) from both primary and metastatic lesions. Compared with fresh PCa tissue transplantation in athymic mice, co-injection of PCa tissues with extracellular matrix in highly immunodeficient mice has remarkably improved the success rate of PDX generation. PDX models have advantages to appropriately recapitulate the molecular diversity, cellular heterogeneity, and histology of original patient tumors. In contrast to PDX models, patient-derived organoid and spheroid PCa models in 3-dimensional culture are more feasible tools for in vitro studies for retaining the characteristics of patient tumors. In this article, we review PCa preclinical model cell lines and their sublines, PDXs, and patient-derived organoid and spheroid models. These PCa models will be applied to the development of new strategies for cancer precision medicine.

Dysregulated gene expression predicts tumor aggressiveness in African-American prostate cancer patients

Molecular mechanisms underlying the health disparity of prostate cancer (PCa) have not been fully determined. In this study, we applied bioinformatic approach to identify and validate dysregulated genes associated with tumor aggressiveness in African American (AA) compared to Caucasian American (CA) men with PCa. We retrieved and analyzed microarray data from 619 PCa patients, 412 AA and 207 CA, and we validated these genes in tumor tissues and cell lines by Real-Time PCR, Western blot, immunocytochemistry (ICC) and immunohistochemistry (IHC) analyses. We identified 362 differentially expressed genes in AA men and involved in regulating signaling pathways associated with tumor aggressiveness. In PCa tissues and cells, NKX3.1, APPL2, TPD52, LTC4S, ALDH1A3 and AMD1 transcripts were significantly upregulated (p < 0.05) compared to normal cells. IHC confirmed the overexpression of TPD52 (p = 0.0098) and LTC4S (p < 0.0005) in AA compared to CA men. ICC and Western blot analyses additionally corroborated this observation in PCa cells. These findings suggest that dysregulation of transcripts in PCa may drive the disparity of PCa outcomes and provide new insights into development of new therapeutic agents against aggressive tumors. More studies are warranted to investigate the clinical significance of these dysregulated genes in promoting the oncogenic pathways in AA men.

Ethnic differences in TGFβ-signaling pathway may contribute to prostate cancer health disparity

Epidemiological studies show that the incidence and mortality rates of prostate cancer (PCa) are significantly higher in African-American (AA) men when compared with Caucasian (CA) men in the United States. Transforming growth factor β (TGFβ) signaling pathway is linked to health disparities in AAs. Recent studies suggest a role of TGFβ3 in cancer metastases and its effect on the migratory and invasive behavior; however, its role in PCa in AA men has not been studied. We determined the circulating levels of TGFβ3 in AA and CA men diagnosed with PCa using ELISA. We analyzed serum samples from both AA and CA men diagnosed with and without PCa. We show that AA PCa patients had higher levels of TGFβ3 protein compared with AA controls and CA patients. In fact, TGFβ3 protein levels in serum were higher in AA men without PCa compared with the CA population, which may correlate with more aggressive disease seen in AA men. Studies on AA-derived PCa cell lines revealed that TGFβ3 protein levels were also higher in these cells compared with CA-derived PCa cell lines. Our studies also reveal that TGFβ does not inhibit cell proliferation in AA-derived PCa cell lines, but it does induce migration and invasion through activation of PI3K pathway. We suggest that increased TGFβ3 levels are responsible for development of aggressive PCa in AA patients as a consequence of development of resistance to inhibitory effects of TGFβ on cell proliferation and induction of invasive metastatic behavior.

The identification of a novel antibody for CD133 using human antibody phage display

BACKGROUND

The transmembrane glycoprotein CD133 is believed to be a marker of adult prostate stem cells and cancer stem/initiating cells. Investigating the role of CD133 in the normal biology of the prostate and in cancer is complicated by the lack of a sensitive and accurate antibody for its detection. Here, we describe the characterization of a unique antibody identified using human antibody phage display that can recognize CD133 in both formalin-fixed tissues and cell lines.

METHODS

A human single-chain variable fragment (scFv) antibody phage display library possessing a diversity of 8 × 10⁹ was screened against fully glycosylated recombinant CD133. A counter screen was performed against deglycosylated CD133 to select for clones that preferentially recognized a glycosylation-independent epitope. The lead scFv was analyzed by flow cytometry and cloned into a rabbit immunoglobulin scaffold for immunohistochemistry (IHC).

RESULTS

The antibody designated HA10 was found to bind a glycosylation-independent epitope on the peptide backbone of CD133 with high affinity. As a reagent for flow cytometry, HA10 detected CD133 more accurately than a commonly used commercially available antibody. IHC analysis with HA10 documented the staining of basal cells and luminal cells in healthy prostate sections. Weak staining of luminal cells was observed in adenocarcinoma sections at a very low frequency. Examination of a LuCaP patient-derived xenograft tissue microarray found that only three of the LuCaP models were positive for CD133. The three CD133^pos LuCaP models all originated from non-AR driven metastatic prostate cancer with neuroendocrine differentiation. Subsequent interrogation of liver biopsies from a patient who failed second-generation anti-androgen therapy found high levels of CD133 staining. The original transurethral resection of the prostate from that patient was, however, absent of CD133.

CONCLUSIONS

We have developed a novel antibody that was able to detect CD133 by both IHC and flow cytometry. Using HA10 as an IHC reagent, we found that CD133 is a marker for a very rare cell type in both healthy prostate and adenocarcinoma sections. Our preliminary investigation also suggests that there may be an association between CD133 and non-AR driven prostate cancer with neuroendocrine differentiation.

Novel role of Giα2 in cell migration: Downstream of PI3-kinase-AKT and Rac1 in prostate cancer cells

Tumor cell motility is the essential step in cancer metastasis. Previously, we showed that oxytocin and epidermal growth factor (EGF) effects on cell migration in prostate cancer cells require Giα2 protein. In the current study, we investigated the interactions among G-protein coupled receptor (GPCR), Giα2, PI3-kinase, and Rac1 activation in the induction of migratory and invasive behavior by diverse stimuli. Knockdown and knockout of endogenous Giα2 in PC3 cells resulted in attenuation of transforming growth factor β1 (TGFβ1), oxytocin, SDF-1α, and EGF effects on cell migration and invasion. In addition, knockdown of Giα2 in E006AA cells attenuated cell migration and overexpression of Giα2 in LNCaP cells caused significant increase in basal and EGF-stimulated cell migration. Pretreatment of PC3 cells with Pertussis toxin resulted in attenuation of TGFβ1- and oxytocin-induced migratory behavior and PI3-kinase activation without affecting EGF-induced PI3-kinase activation and cell migration. Basal- and EGF-induced activation of Rac1 in PC3 and DU145 cells were not affected in cells after Giα2 knockdown. On the other hand, Giα2 knockdown abolished the migratory capability of PC3 cells overexpressing constitutively active Rac1. The knockdown or knockout of Giα2 resulted in impaired formation of lamellipodia at the leading edge of the migrating cells. We conclude that Giα2 protein acts at two different levels which are both dependent and independent of GPCR signaling to induce cell migration and invasion in prostate cancer cells and its action is downstream of PI3-kinase-AKT-Rac1 axis.

Hypoxia-induced exosome secretion promotes survival of African-American and Caucasian prostate cancer cells

African American men in the United States have higher mortality due to prostate cancer (PCa) compared to other races. One reason for this disparity is the lack of in-depth understanding of the PCa biology in African Americans. For example, hypoxia in prostate tumor microenvironment is associated with adverse prognosis; still, no hypoxia-related studies have been reported in African Americans. Here, we compared African-American and Caucasian PCa cells for exosome secretion under normoxic (21% O2) and hypoxic (1% O2) conditions. All cell lines showed higher exosome secretion under hypoxia but it was clearly more prominent in African-American PCa cells. Further, under hypoxia, Rab5 (a biomarker for early endosome) was clustered in perinuclear region; and CD63 (a biomarker for exosomes and multivesicular endosomes) showed greater co-localization with actin cytoskeleton especially in African American PCa cells. Importantly, exosome biogenesis inhibitors GW4869 (10-20 µM) or DMA (10-20 µg/ml) significantly decreased cell viability and clonogenicity in PCa cells. Interestingly, we also observed higher level of lactic acid loaded in exosomes secreted under hypoxia. Overall, under chronic hypoxia, PCa cells secrete more exosomes as a survival mechanism to remove metabolic waste.

Supraphysiologic Testosterone Therapy in the Treatment of Prostate Cancer: Models, Mechanisms and Questions

Since Huggins defined the androgen-sensitive nature of prostate cancer (PCa), suppression of systemic testosterone (T) has remained the most effective initial therapy for advanced disease although progression inevitably occurs. From the inception of clinical efforts to suppress androgen receptor (AR) signaling by reducing AR ligands, it was also recognized that administration of T in men with castration-resistant prostate cancer (CRPC) could result in substantial clinical responses. Data from preclinical models have reproducibly shown biphasic responses to T administration, with proliferation at low androgen concentrations and growth inhibition at supraphysiological T concentrations. Many questions regarding the biphasic response of PCa to androgen treatment remain, primarily regarding the mechanisms driving these responses and how best to exploit the biphasic phenomenon clinically. Here we review the preclinical and clinical data on high dose androgen growth repression and discuss cellular pathways and mechanisms likely to be involved in mediating this response. Although meaningful clinical responses have now been observed in men with PCa treated with high dose T, not all men respond, leading to questions regarding which tumor characteristics promote response or resistance, and highlighting the need for studies designed to determine the molecular mechanism(s) driving these responses and identify predictive biomarkers.

Proteomic characterization of paired non-malignant and malignant African-American prostate epithelial cell lines distinguishes them by structural proteins

Background

While many factors may contribute to the higher prostate cancer incidence and mortality experienced by African-American men compared to their counterparts, the contribution of tumor biology is underexplored due to inadequate availability of African-American patient-derived cell lines and specimens. Here, we characterize the proteomes of non-malignant RC-77 N/E and malignant RC-77 T/E prostate epithelial cell lines previously established from prostate specimens from the same African-American patient with early stage primary prostate cancer.

Methods

In this comparative proteomic analysis of RC-77 N/E and RC-77 T/E cells, differentially expressed proteins were identified and analyzed for overrepresentation of PANTHER protein classes, Gene Ontology annotations, and pathways. The enrichment of gene sets and pathway significance were assessed using Gene Set Enrichment Analysis and Signaling Pathway Impact Analysis, respectively. The gene and protein expression data of age- and stage-matched prostate cancer specimens from The Cancer Genome Atlas were analyzed.

Results

Structural and cytoskeletal proteins were differentially expressed and statistically overrepresented between RC-77 N/E and RC-77 T/E cells. Beta-catenin, alpha-actinin-1, and filamin-A were upregulated in the tumorigenic RC-77 T/E cells, while integrin beta-1, integrin alpha-6, caveolin-1, laminin subunit gamma-2, and CD44 antigen were downregulated. The increased protein level of beta-catenin and the reduction of caveolin-1 protein level in the tumorigenic RC-77 T/E cells mirrored the upregulation of beta-catenin mRNA and downregulation of caveolin-1 mRNA in African-American prostate cancer specimens compared to non-malignant controls. After subtracting race-specific non-malignant RNA expression, beta-catenin and caveolin-1 mRNA expression levels were higher in African-American prostate cancer specimens than in Caucasian-American specimens. The “ECM-Receptor Interaction” and “Cell Adhesion Molecules”, and the “Tight Junction” and “Adherens Junction” pathways contained proteins are associated with RC-77 N/E and RC-77 T/E cells, respectively.

Conclusions

Our results suggest RC-77 T/E and RC-77 N/E cell lines can be distinguished by differentially expressed structural and cytoskeletal proteins, which appeared in several pathways across multiple analyses. Our results indicate that the expression of beta-catenin and caveolin-1 may be prostate cancer- and race-specific. Although the RC-77 cell model may not be representative of all African-American prostate cancer due to tumor heterogeneity, it is a unique resource for studying prostate cancer initiation and progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3462-7) contains supplementary material, which is available to authorized users.

Mitochondrial dysfunction-mediated apoptosis resistance associates with defective heat shock protein response in African-American men with prostate cancer

BACKGROUND

African-American (AA) patients with prostate cancer (PCa) respond poorly to current therapy compared with Caucasian American (CA) PCa patients. Although underlying mechanisms are not defined, mitochondrial dysfunction is a key reason for this disparity.

METHODS

Cell death, cell cycle, and mitochondrial function/stress were analysed by flow cytometry or by Seahorse XF24 analyzer. Expression of cellular proteins was determined using immunoblotting and real-time PCR analyses. Cell survival/motility was evaluated by clonogenic, cell migration, and gelatin zymography assays.

RESULTS

Glycolytic pathway inhibitor dichloroacetate (DCA) inhibited cell proliferation in both AA PCa cells (AA cells) and CA PCa cells (CA cells). AA cells possess reduced endogenous reactive oxygen species, mitochondrial membrane potential (mtMP), and mitochondrial mass compared with CA cells. DCA upregulated mtMP in both cell types, whereas mitochondrial mass was significantly increased in CA cells. DCA enhanced taxol-induced cell death in CA cells while sensitising AA cells to doxorubicin. Reduced expression of heat shock proteins (HSPs) was observed in AA cells, whereas DCA induced expression of CHOP, C/EBP, HSP60, and HSP90 in CA cells. AA cells are more aggressive and metastatic than CA cells.

CONCLUSIONS

Restoration of mitochondrial function may provide new option for reducing PCa health disparity among American men.

Combination therapy induces unfolded protein response and cytoskeletal rearrangement leading to mitochondrial apoptosis in prostate cancer

Development of therapeutic resistance is responsible for most prostate cancer (PCa) related mortality. Resistance has been attributed to an acquired or selected cancer stem cell phenotype. Here we report the histone deacetylase inhibitor apicidin (APC) or ER stressor thapsigargin (TG) potentiate paclitaxel (TXL)-induced apoptosis in PCa cells and limit accumulation of cancer stem cells. TXL-induced responses were modulated in the presence of TG with increased accumulation of cells at G1-phase, rearrangement of the cytoskeleton, and changes in cytokine release. Cytoskeletal rearrangement was associated with modulation of the cytoplasmic and mitochondrial unfolded protein response leading to mitochondrial dysfunction and release of proapoptotic proteins from mitochondria. TXL in combination with APC or TG enhanced caspase activation. Importantly, TXL in combination with TG induced caspase activation and apoptosis in X-ray resistant LNCaP cells. Increased release of transforming growth factor-beta (TGF-β) was observed while phosphorylated β-catenin level was suppressed with TXL combination treatments. This was accompanied by a decrease in the CD44(+)CD133(+) cancer stem cell-like population, suggesting treatment affects cancer stem cell properties. Taken together, combination treatment with TXL and either APC or TG induces efficient apoptosis in both proliferating and cancer stem cells, suggesting this therapeutic combination may overcome drug resistance and recurrence in PCa.

Cell line modeling to study biomarker panel in prostate cancer

BACKGROUND

African-American men with prostate cancer (PCa) present with higher-grade and -stage tumors compared to Caucasians. While the disparity may result from multiple factors, a biological basis is often strongly suspected. Currently, few well-characterized experimental model systems are available to study the biological basis of racial disparity in PCa. We report a validated in vitro cell line model system that could be used for the purpose.

METHODS

We assembled a PCa cell line model that included currently available African-American PCa cell lines and LNCaP (androgen-dependent) and C4-2 (castration-resistant) Caucasian PCa cells. The utility of the cell lines in studying the biological basis of variance in a malignant phenotype was explored using a multiplex biomarker panel consisting of proteins that have been proven to play a role in the progression of PCa. The panel expression was evaluated by Western blot and RT-PCR in cell lines and validated in human PCa tissues by RT-PCR. As proof-of-principle to demonstrate the utility of our model in functional studies, we performed MTS viability assays and molecular studies.

RESULTS

The dysregulation of the multiplex biomarker panel in primary African-American cell line (E006AA) was similar to metastatic Caucasian cell lines, which would suggest that the cell line model could be used to study an inherent aggressive phenotype in African-American men with PCa. We had previously demonstrated that Protein kinase D1 (PKD1) is a novel kinase that is down regulated in advanced prostate cancer. We established the functional relevance by over expressing PKD1, which resulted in decreased proliferation and epithelial mesenchymal transition (EMT) in PCa cells. Moreover, we established the feasibility of studying the expression of the multiplex biomarker panel in archived human PCa tissue from African-Americans and Caucasians as a prelude to future translational studies.

CONCLUSION

We have characterized a novel in vitro cell line model that could be used to study the biological basis of disparity in PCa between African-Americans and Caucasians.

PVT1 Exon 9: A Potential Biomarker of Aggressive Prostate Cancer?

Prostate cancer (PCa) is the most commonly diagnosed cancer as well as the greatest source of cancer-related mortality in males of African ancestry (MoAA). Interestingly, this has been shown to be associated with single nucleotide polymorphisms around regions 2 and 3 of the 8q24 human chromosomal region. The non-protein coding gene locus Plasmacytoma Variant Translocation 1 (PVT1) is located at 8q24 and is overexpressed in PCa and, therefore, is also a candidate biomarker to explain the well-known disparity in this group. PVT1 has at least 12 exons that make separate transcripts which may have different functions, all of which are at present unknown in PCa. Our aim was to determine if any PVT1 transcripts play a role in aggressiveness and racial disparity in PCa. We used a panel of seven PCa cell lines including three derived from MoAA. Ribonucleic acid extraction, complementary deoxyribonucleic acid synthesis, and quantitative polymerase chain reaction (qPCR) were performed to evaluate expression of all 12 PVT1 exons. Each qPCR was performed in quadruplicates. At least four separate qPCR experiments were performed. Expression of PVT1 exons was inconsistent except for exon 9. There was no significant difference in exon 9 expression between cell lines derived from Caucasian males (CM), and an indolent cell line derived from MoAA. However, exon 9 expression in the aggressive MDA PCa 2b and E006AA-hT cell lines derived from MoAA was significantly higher than in other cell lines. Consequently, we observed differential expression of exon 9 of PVT1 in a manner that suggests that PVT1 exon 9 may be associated with aggressive PCa in MoAA.

Paucity of PD-L1 expression in prostate cancer: innate and adaptive immune resistance

BACKGROUND

Primary prostate cancers are infiltrated with programmed death-1 (PD-1) expressing CD8+ T-cells. However, in early clinical trials, men with metastatic castrate-resistant prostate cancer did not respond to PD-1 blockade as a monotherapy. One explanation for this unresponsiveness could be that prostate tumors generally do not express programmed death ligand-1 (PD-L1), the primary ligand for PD-1. However, lack of PD-L1 expression in prostate cancer would be surprising, given that phosphatase and tensin homolog (PTEN) loss is relatively common in prostate cancer and several studies have shown that PTEN loss correlates with PD-L1 upregulation--constituting a mechanism of innate immune resistance. This study tested whether prostate cancer cells were capable of expressing PD-L1, and whether the rare PD-L1 expression that occurs in human specimens correlates with PTEN loss.

METHODS

Human prostate cancer cell lines were evaluated for PD-L1 expression and loss of PTEN by flow cytometry and western blotting, respectively. Immunohistochemical (IHC) staining for PTEN was correlated with PD-L1 IHC using a series of resected human prostate cancer samples.

RESULTS

In vitro, many prostate cancer cell lines upregulated PD-L1 expression in response to inflammatory cytokines, consistent with adaptive immune resistance. In these cell lines, no association between PTEN loss and PD-L1 expression was apparent. In primary prostate tumors, PD-L1 expression was rare, and was not associated with PTEN loss.

CONCLUSIONS

These studies show that some prostate cancer cell lines are capable of expressing PD-L1. However, in human prostate cancer, PTEN loss is not associated with PD-L1 expression, arguing against innate immune resistance as a mechanism that mitigates antitumor immune responses in this disease.

Paucity of PD-L1 expression in prostate cancer: innate and adaptive immune resistance

Background

Primary prostate cancers are infiltrated with PD-1 expressing CD8+ T cells. However, in early clinical trials, men with mCRPC did not respond to PD-1 blockade as a monotherapy. One explanation for this unresponsiveness could be that prostate tumors generally do not express PD-L1, the primary ligand for PD-1. However, lack of PD-L1 expression in prostate cancer would be surprising, given that PTEN loss is relatively common in prostate cancer and several studies have shown that PTEN loss correlates with PD-L1 up-regulation - constituting a mechanism of innate immune resistance. This study tested whether prostate cancer cells were capable of expressing PD-L1, and whether the rare PD-L1 expression that occurs in human specimens correlates with PTEN loss.

Methods

Human prostate cancer cell lines were evaluated for PD-L1 expression and loss of PTEN by flow cytometry and western blotting, respectively. Immunohistochemical (IHC) staining for PTEN was correlated with PD-L1 IHC using a series of resected human prostate cancer samples.

Results

In vitro, many prostate cancer cell lines up-regulated PD-L1 expression in response to inflammatory cytokines, consistent with adaptive immune resistance. In these cell lines, no association between PTEN loss and PD-L1 expression was apparent. In primary prostate tumors, PD-L1 expression was rare, and was not associated with PTEN loss.

Conclusions

These studies show that some prostate cancer cell lines are capable of expressing PD-L1. However, in human prostate cancer, PTEN loss is not associated with PD-L1 expression, arguing against innate immune resistance as a mechanism that mitigates anti-tumor immune responses in this disease.

Serum microRNA expression patterns that predict early treatment failure in prostate cancer patients

We aimed to identify microRNA (miRNA) expression patterns in the serum of prostate cancer (CaP) patients that predict the risk of early treatment failure following radical prostatectomy (RP). Microarray and Q-RT-PCR analyses identified 43 miRNAs as differentiating disease stages within 14 prostate cell lines and reflectedpublically available patient data. 34 of these miRNA were detectable in the serum of CaP patients. Association with time to biochemical progression was examined in a cohort of CaP patients following RP. A greater than two-fold increase in hazard of biochemical progression associated with altered expression of miR-103, miR-125b and miR-222 (p <.0008) in the serum of CaP patients. Prediction models based on penalized regression analyses showed that the levels of the miRNAs and PSA together were better at detecting false positives than models without miRNAs, for similar level of sensitivity. Analyses of publically available data revealed significant and reciprocal relationships between changes in CpG methylation and miRNA expression patterns suggesting a role for CpG methylation to regulate miRNA. Exploratory validation supported roles for miR-222 and miR-125b to predict progression risk in CaP. The current study established that expression patterns of serum-detectable miRNAs taken at the time of RP are prognostic for men who are at risk of experiencing subsequent early biochemical progression. These non-invasive approaches could be used to augment treatment decisions.

ROBO1, a tumor suppressor and critical molecular barrier for localized tumor cells to acquire invasive phenotype: study in African-American and Caucasian prostate cancer models

High-risk populations exhibit early transformation of localized prostate cancer (CaP) disease to metastasis which results in the mortality of such patients. The paucity of knowledge about the molecular mechanism involved in acquiring of metastatic behavior by primary tumor cells and non-availability of reliable phenotype-discriminating biomarkers are stumbling blocks in the management of CaP disease. Here, we determine the role and translational relevance of ROBO1 (an organogenesis-associated gene) in human CaP. Employing CaP-progression models and prostatic tissues of Caucasian and African-American patients, we show that ROBO1 expression is localized to cell-membrane and significantly lost in primary and metastatic tumors. While Caucasians exhibited similar ROBO1 levels in primary and metastatic phenotype, a significant difference was observed between tumor phenotypes in African-Americans. Epigenetic assays identified promoter methylation of ROBO1 specific to African-American metastatic CaP cells. Using African-American CaP models for further studies, we show that ROBO1 negatively regulates motility and invasiveness of primary CaP cells, and its loss causes these cells to acquire invasive trait. To understand the underlying mechanism, we employed ROBO1-expressing/ROBO1-C2C3-mutant constructs, immunoprecipitation, confocal-microscopy and luciferase-reporter techniques. We show that ROBO1 through its interaction with DOCK1 (at SH3-SH2-domain) controls the Rac-activation. However, loss of ROBO1 results in Rac1-activation which in turn causes E-Cadherin/β-catenin cytoskeleton destabilization and induction of cell migration. We suggest that ROBO1 is a predictive biomarker that has potential to discriminate among CaP types, and could be exploited as a molecular target to inhibit the progression of disease as well as treat metastasis in high-risk populations such as African-Americans.

Establishment and characterization of a highly tumorigenic African American prostate cancer cell line, E006AA-hT

Genuine racial differences in prostate cancer (PCa) biology have been considered among the potential reasons to explain PCa disparities. There is no animal model to represent all aspects of human PCa and, more specifically, to be used for PCa disparity research. The lack of a spontaneously transformed in vitro cell-based model system has been a significant impediment to investigating and understanding potential molecular mechanisms, and the hormonal, genetic, and epigenetic factors underlying the biological and clinical aggressiveness of PCa in African American (AA) men.

In this study, we established and characterized the E006AA-hT cell line as a highly tumorigenic subline of the previously characterized primary AA-PCa cell line, E006AA. Extensive characterization of the E006AA-hT cell line was accomplished using cytodifferentiation and prostate-specific markers, spectral karyotyping, cell line authentication assays, cell proliferation and migration assays, and in vitro tumorigenesis assays.

Spectral karyotyping of E006AA-hT showed a hypertriploid chromosome complement and shared cytogenetic changes similar to its parental cells such as diploid X, absence of Y-chromosomes, numerical gains in chromosomes 5,6,8,10,17,20,21, and marker chromosomes of unknown origin. In addition, E006AA-hT also presented numerous clonal and structural aberrations such as insertion, deletion, duplication, and translocations in chromosomes 1-5, 8, 9, 11, 13, 14, 17, and 18. The E006AA-hT cell line was shown to be highly tumorigenic and produced tumors at an accelerated growth rate in both athymic nude and triple-deficient SCID mice.

Silencing the mutated androgen receptor (AR-599 Ser>Gly) did not affect proliferation (loss-of-function), but decreased migration (gain-of-function) in E006AA-hT and its parental cell type. These data support that AR-point mutations may lead simultaneously to different “loss-of-function” and “gain-of-function” phenotypes in PCa cells. E006AA-Par and its subline as the only available spontaneously transformed low- and highly-tumorigenic primary AA-PCa cell lines could be used for basic and translational research aimed in supporting prostate cancer disparity research.

Identification of novel GRM1 mutations and single nucleotide polymorphisms in prostate cancer cell lines and tissues

Metabotropic glutamate receptor 1 (GRM1) signaling has been implicated in benign and malignant disorders including prostate cancer (PCa). To further explore the role of genetic alterations of GRM1 in PCa, we screened the entire human GRM1 gene including coding sequence, exon-intron junctions, and flanking untranslated regions (UTRs) for the presence of mutations and single nucleotide polymorphisms (SNPs) in several PCa cell lines and matched tumor-normal tissues from Caucasian Americans (CAs) and African Americans (AAs). We used bidirectional sequencing, allele-specific PCR, and bioinformatics to identify the genetic changes in GRM1 and to predict their functional role. A novel missense mutation identified at C1744T (582 Pro > Ser) position of GRM1 gene in a primary AA-PCa cell line (E006AA) was predicted to affect the protein stability and functions. Another novel mutation identified at exon-intron junction of exon-8 in C4-2B cell line resulted in alteration of the GRM1 splicing donor site. In addition, we found missense SNP at T2977C (993 Ser > Pro) position and multiple non-coding mutations and SNPs in 3'-UTR of GRM1 gene in PCa cell lines and tissues. These novel mutations may contribute to the disease by alterations in GRM1 gene splicing, receptor activation, and post-receptor downstream signaling.

Conversion of androgen receptor signaling from a growth suppressor in normal prostate epithelial cells to an oncogene in prostate cancer cells involves a gain of function in c-Myc regulation

In normal prostate, androgen-dependent androgen receptor (AR) signaling within prostate stromal cells induces their secretion of paracrine factors, termed “andromedins” which stimulate growth of the epithelial cells. The present studies demonstrate that androgen-dependent andromedin-driven growth stimulation is counter-balanced by androgen-induced AR signaling within normal adult prostate epithelial cells resulting in terminal G₀ growth arrest coupled with terminal differentiation into ΔNp63-negative, PSA-expressing secretory luminal cells. This cell autonomous AR-driven terminal differentiation requires DNA-binding of the AR protein, is associated with decreases in c-Myc m-RNA and protein, are coupled with increases in p21, p27, and SKP-2 protein expression, and does not require functional p53. These changes result in down-regulation of Cyclin D₁ protein and RB phosphoryation. shRNA knockdown documents that neither RB, p21, p27 alone or in combination are required for such AR-induced G₀ growth arrest. Transgenic expression of a constitutive vector to prevent c-Myc down-regulation overrides AR-mediated growth arrest in normal prostate epithelial cells, which documents that AR-induced c-Myc down-regulation is critical in terminal growth arrest of normal prostate epithelial cells. In contrast, in prostate cancer cells, androgen-induced AR signaling paradoxically up-regulates c-Myc expression and stimulates growth as documented by inhibition of both of these responses following exposure to the AR antagonist, bicalutamide. These data document that AR signaling is converted from a growth suppressor in normal prostate epithelial cells to an oncogene in prostate cancer cells during prostatic carcinogenesis and that this conversion involves a gain of function for regulation of c-Myc expression.

Androgen receptor mutations and polymorphisms in African American prostate cancer

The Androgen receptor (AR) plays a central role in the normal development of the prostate gland, in prostate carcinogenesis, and in the progression of prostate cancer (PCa) to advanced metastatic disease. African American (AA) men with PCa present with higher tumor volume, more advanced tumor stage, and higher Gleason score. This could be in part related to the AR expression or activity in the prostate tissue of AA men, or to unique mutations or polymorphisms of the AR. In Caucasian Americans (CAs), AR mutations are rare or infrequent in organ-confined tumors, but occur at a higher rate in advanced, metastatic, or castrate-recurrent disease. In AAs, the prevalence, clinical, and biological significance of AR mutations in PCa are unknown. In this study, we investigated the occurrence of somatic and germline AR mutations in patients with primary PCa in AAs compared with CAs. Due to very limited data available on allelic distribution of E213 (G/A) single nucleotide polymorphism (SNP), we also assessed this in patients with sporadic PCa and in unrelated healthy individuals from both ethnic populations. Somatic missense AR mutations were detected at a higher rate in AAs (17 out of 200 cases) than in CAs (2 out of 100 cases). In AAs, the majority of these mutations (41.1%) were from Gleason 7 tumors, a small portion (23.5%) from Gleason 8 tumors, and the rest (35.2%) from Gleason 6 tumors. Analysis of genomic DNAs extracted from white blood cells of patients with sporadic PCa revealed that the rate of germline AR mutations were also higher (~4 times) in AAs than in CAs. With respect to E213 (G/A) SNP, the E213 A-allele expression was 5.85 times higher in healthy unrelated AA men than in CA men. However, in AAs with somatic AR mutation, the E213 G-allele distribution was almost equal to the A-allele. Silencing of one of the somatic AR mutations (i.e., 597 Ser>Gly) in a primary AA-PCa cell line (e.g., E006AA) revealed that similar AR mutation can be associated simultaneously with both "gain-of-function" phenotype (cell migration and invasion) and a "loss-of-function" phenotype (proliferation). Our data demonstrated a higher susceptibility for genetic alterations in the AR in the form of somatic mutations in sporadic PCa or in the form of germline mutations in AAs as compared with CAs. These data may support the idea that AR-specific hypermutator phenotype in combination with other genes, might serve as a contributing factor to ethnic differences in PCa and potentially different clinical outcome in AAs as a high-risk population.

Ericifolin: a novel antitumor compound from allspice that silences androgen receptor in prostate cancer

Silencing of androgen receptor (AR) signaling is a specific and effective mechanism to cure cancer of the prostate (CaP). In this study, the isolation and characterization of a compound from the aromatic berries of Pimenta dioica (allspice) that silences AR is presented. Potential antitumor activities of an aqueous allspice extract (AAE) and a compound purified from the extract were tested on CaP cells. AAE inhibited tumor cell proliferation and colony formation (50% growth inhibition ∼40-85 µg/ml) but not the viability of quiescent normal fibroblasts or non-tumorigenic prostate cells. In tumor cells, AAE inhibited cell cycle progression at G1/S, induced apoptosis or autophagy. Apoptosis was by caspase-dependent poly (ADP ribose) polymerase cleavage. A caspase-independent, apoptosis-inducing factor-mediated mechanism of apoptosis caused cell death in castration-resistant AR-positive or AR-negative CaP cells, such as CWR22RV1, PC-3 or DU145 cells. Treatment with AAE decreased the levels of AR messenger RNA (mRNA), protein and silenced AR activity in AR-positive cells. AR depletion was due to inhibition of AR promoter activity and mRNA stability. Delayed tumor growth (~55%) without measurable systemic toxicity was observed in LNCaP tumor-bearing mice treated with AAE by oral or intraperitoneal routes. LNCaP tumor tissues from AAE-treated mice revealed increased apoptosis as a potential mechanism of antitumor activity of AAE. The chemical identity of bioactive compound in AAE was established through multistep high-performance liquid chromatography fractionation, mass and Nuclear Magnetic Resonance spectroscopies. The compound, eugenol 5-O-β-(6'-galloylglucopyranoside) or ericifolin (EF), showed antiproliferative, pro-apoptosis and anti-AR transcription activities. These results demonstrate a potential use of AAE and EF against prostate cancer.

In vitro model systems to study androgen receptor signaling in prostate cancer

Prostate cancer (PCa) is one of the most common causes of male cancer-related death in Western nations. The cellular response to androgens is mediated via the androgen receptor (AR), a ligand-inducible transcription factor whose dysregulation plays a key role during PCa development and progression following androgen deprivation therapy, the current mainstay systemic treatment for advanced PCa. Thus, a better understanding of AR signaling and new strategies to abrogate AR activity are essential for improved therapeutic intervention. Consequently, a large number of experimental cell culture models have been established to facilitate in vitro investigations into the role of AR signaling in PCa development and progression. These different model systems mimic distinct stages of this heterogeneous disease and exhibit differences with respect to AR expression/status and androgen responsiveness. Technological advances have facilitated the development of in vitro systems that more closely reflect the physiological setting, for example via the use of three-dimensional coculture to study the interaction of prostate epithelial cells with the stroma, endothelium, immune system and tissue matrix environment. This review provides an overview of the most commonly used in vitro cell models currently available to study AR signaling with particular focus on their use in addressing key questions relating to the development and progression of PCa. It is hoped that the continued development of in vitro models will provide more biologically relevant platforms for mechanistic studies, drug discovery and design ensuring a more rapid transfer of knowledge from the laboratory to the clinic.

Androgen receptor-target genes in african american prostate cancer disparities

The incidence and mortality rates of prostate cancer (PCa) are higher in African American (AA) compared to Caucasian American (CA) men. To elucidate the molecular mechanisms underlying PCa disparities, we employed an integrative approach combining gene expression profiling and pathway and promoter analyses to investigate differential transcriptomes and deregulated signaling pathways in AA versus CA cancers. A comparison of AA and CA PCa specimens identified 1,188 differentially expressed genes. Interestingly, these transcriptional differences were overrepresented in signaling pathways that converged on the androgen receptor (AR), suggesting that the AR may be a unifying oncogenic theme in AA PCa. Gene promoter analysis revealed that 382 out of 1,188 genes contained cis-acting AR-binding sequences. Chromatin immunoprecipitation confirmed STAT1, RHOA, ITGB5, MAPKAPK2, CSNK2A,1 and PIK3CB genes as novel AR targets in PCa disparities. Moreover, functional screens revealed that androgen-stimulated AR binding and upregulation of RHOA, ITGB5, and PIK3CB genes were associated with increased invasive activity of AA PCa cells, as siRNA-mediated knockdown of each gene caused a loss of androgen-stimulated invasion. In summation, our findings demonstrate that transcriptional changes have preferentially occurred in multiple signaling pathways converging (“transcriptional convergence”) on AR signaling, thereby contributing to AR-target gene activation and PCa aggressiveness in AAs.

BMI1, stem cell factor acting as novel serum-biomarker for Caucasian and African-American prostate cancer

BACKGROUND

Lack of reliable predictive biomarkers is a stumbling block in the management of prostate cancer (CaP). Prostate-specific antigen (PSA) widely used in clinics has several caveats as a CaP biomarker. African-American CaP patients have poor prognosis than Caucasians, and notably the serum-PSA does not perform well in this group. Further, some men with low serum-PSA remain unnoticed for CaP until they develop disease. Thus, there is a need to identify a reliable diagnostic and predictive biomarker of CaP. Here, we show that BMI1 stem-cell protein is secretory and could be explored for biomarker use in CaP patients.

METHODOLOGY/PRINCIPAL FINDINGS

Semi-quantitative analysis of BMI1 was performed in prostatic tissues of TRAMP (autochthonous transgenic mouse model), human CaP patients, and in cell-based models representing normal and different CaP phenotypes in African-American and Caucasian men, by employing immunohistochemistry, immunoblotting and Slot-blotting. Quantitative analysis of BMI1 and PSA were performed in blood and culture-media of siRNA-transfected and non-transfected cells by employing ELISA. BMI1 protein is (i) secreted by CaP cells, (ii) increased in the apical region of epithelial cells and stromal region in prostatic tumors, and (iii) detected in human blood. BMI1 is detectable in blood of CaP patients in an order of increasing tumor stage, exhibit a positive correlation with serum-PSA and importantly is detectable in patients which exhibit low serum-PSA. The clinical significance of BMI1 as a biomarker could be ascertained from observation that CaP cells secrete this protein in higher levels than cells representative of benign prostatic hyperplasia (BPH).

CONCLUSIONS/SIGNIFICANCE

BMI1 could be developed as a dual bio-marker (serum and biopsy) for the diagnosis and prognosis of CaP in Caucasian and African-American men. Though compelling these data warrant further investigation in a cohort of African-American patients.

Adaptive auto-regulation of androgen receptor provides a paradigm shifting rationale for bipolar androgen therapy (BAT) for castrate resistant human prostate cancer

Cell culture/xenograft and gene arrays of clinical material document that development of castration resistant prostate cancer (CRPC) cells involves acquisition of adaptive auto-regulation resulting in >25-fold increase in Androgen Receptor (AR) protein expression in a low androgen environment. Such adaptive AR increase paradoxically is a liability in castrated hosts, however, when supraphysiologic androgen is acutely replaced. Cell synchronization/anti-androgen response is due to AR binding to replication complexes (RC) at origin of replication sites (ORS) in early G1 associated with licensing/restricting DNA for single round of duplication during S-phase. When CRPC cells are acutely exposed to supraphysiologic androgen, adaptively increased nuclear AR is over-stabilized, preventing sufficient degradation in mitosis, inhibiting DNA re-licensing, and thus death in the subsequent cell cycle. These mechanistic results and the fact that AR/RC binding occurs in metastatic CRPCs directly from patients provides a paradigm shifting rationale for bipolar androgen therapy (BAT) in patient progressing on chronic androgen ablation. BAT involves giving sequential cycles alternating between periods of acute supraphysiologic androgen followed by acute ablation to take advantage of vulnerability produced by adaptive auto-regulation and binding of AR to RC in CRPC cells. BAT therapy is effective in xenografts and based upon positive results has entered clinical testing.

Establishment and characterization of a pair of non-malignant and malignant tumor derived cell lines from an African American prostate cancer patient

Research into molecular and genetic mechanisms underlying prostate carcinogenesis in high-risk African American men would be greatly advanced by in vitro models of African American prostate tumors representing primary tumors. However, the generation of immortalized primary African American prostate cancer cells that will accurately reflect the in situ characteristics of malignant epithelium is currently limited but is greatly needed. We have successfully established immortalized cell lines of a pair of non-malignant and malignant tumors derived from an African American prostate cancer patient with HPV-16E6E7 (RC-77N/E and RC-77T/E). RC-77N/E and RC-77T/E cells are currently growing well at passage 40. Both cells exhibit epithelial morphology and are androgen sensitive. The RC-77T/E cells produced tumors in SCID mice whereas the RC-77N/E cells produced no tumor in SCID mice. These cells expressed androgen-regulated prostate-specific homobox gene, NKX 3.1, epithelial cell specific cytokeratn 8, androgen receptor (AR), prostate specific antigen (PSA), and p16. Chromosome analysis showed that both cell lines are similar; near diploid human male (XY) with most chromosome counts in the 45-48 range. However, RC-77T/E cell line has new marker chromosomes: M1B=del/t(4;?)(q28;?), M5=16q+ in addition to those observed in the RC-77N/E cell line (M1=del(4)(q28q34)+hsr in some, M1A=t(4q;?),M2=der(9?),M2A=del(M2p-),M3=iso(?), M4=der(22?)). This is the first documented case of the establishment of pair of non-malignant and malignant tumors derived from an African American prostate cancer patient. These models will provide novel tools to study the molecular and genetic mechanisms of prostate carcinogenesis, especially for high-risk African American men.

Stemness markers characterize IGR-CaP1, a new cell line derived from primary epithelial prostate cancer

Deciphering molecular pathways involved in the early steps of prostate oncogenesis requires both in vitro and in vivo models derived from human primary tumors. However the few recognized models of human prostate epithelial cancer originate from metastases. To date, very few models are proposed from primary tumors and immortalizing normal human prostate cells does not recapitulate the natural history of the disease. By culturing human prostate primary tumor cells onto human epithelial extra-cellular matrix, we successfully selected a new prostate cancer cell line, IGR-CaP1, and clonally-derived subclones. IGR-CaP1 cells, that harbor a tetraploid karyotype, high telomerase activity and mutated TP53, rapidly induced subcutaneous xenografts in nude mice. Furthermore, IGR-CaP1 cell lines, all exhibiting negativity for the androgen receptor and PSA, express the specific prostate markers alpha-methylacyl-CoA racemase and a low level of the prostate-specific membrane antigen PSMA, along with the prostate basal epithelial markers CK5 and CK14. More importantly, these clones express high CD44, CD133, and CXCR4 levels associated with high expression of α2β1-integrin and Oct4 which are reported to be prostate cancer stemness markers. RT-PCR data also revealed high activation of the Sonic Hedgehog signalling pathway in these cells. Additionally, the IGR-CaP1 cells possess a 3D sphere-forming ability and a renewal capacity by maintaining their CSC potential after xenografting in mice. As a result, the hormone-independent IGR-CaP1 cellular clones exhibit the original features of both basal prostate tissue and cancer stemness. Tumorigenic IGR-CaP1 clones constitute invaluable human models for studying prostate cancer progression and drug assessment in vitro as well as in animals specifically for developing new therapeutic approaches targeting prostate cancer stem cells.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

Loss of androgen receptor-dependent growth suppression by prostate cancer cells can occur independently from acquiring oncogenic addiction to androgen receptor signaling

The conversion of androgen receptor (AR) signaling as a mechanism of growth suppression of normal prostate epithelial cells to that of growth stimulation in prostate cancer cells is often associated with AR mutation, amplification and over-expression. Thus, down-regulation of AR signaling is commonly therapeutic for prostate cancer. The E006AA cell line was established from a hormone naïve, localized prostate cancer. E006AA cells are genetically aneuploid and grow equally well when xenografted into either intact or castrated male NOG but not nude mice. These cells exhibit: 1) X chromosome duplication and AR gene amplification, although paradoxically not coupled with increased AR expression, and 2) somatic, dominant-negative Serine-599-Glycine loss-of-function mutation within the dimerization surface of the DNA binding domain of the AR gene. No effect on the growth of E006AA cells is observed using targeted knockdown of endogenous mutant AR, ectopic expression of wild-type AR, or treatment with androgens or anti-androgens. E006AA cells represent a prototype for a newly identified subtype of prostate cancer cells that exhibit a dominant-negative AR loss-of-function in a hormonally naïve patient. Such loss-of-function eliminates AR-mediated growth suppression normally induced by normal physiological levels of androgens, thus producing a selective growth advantage for these malignant cells in hormonally naïve patients. These data highlight that loss of AR-mediated growth suppression is an independent process, and that, without additional changes, is insufficient for acquiring oncogene addiction to AR signaling. Thus, patients with prostate cancer cells harboring such AR loss-of-function mutations will not benefit from aggressive hormone or anti-AR therapies even though they express AR protein.

Homozygous deletions and recurrent amplifications implicate new genes involved in prostate cancer

Prostate cancer cell lines provide ideal in vitro systems for the identification and analysis of prostate tumor suppressors and oncogenes. A detailed characterization of the architecture of prostate cancer cell line genomes would facilitate the study of precise roles of various genes in prostate tumorigenesis in general. To contribute to such a characterization, we used the GeneChip 500K single nucleotide polymorphic (SNP) array for analysis of genotypes and relative DNA copy number changes across the genome of 11 cell lines derived from both normal and cancerous prostate tissues. For comparison purposes, we also examined the alterations observed in the cell lines in tumor/normal pairs of clinical samples from 72 patients. Along with genome-wide maps of DNA copy number changes and loss of heterozygosity for these cell lines, we report previously unreported homozygous deletions and recurrent amplifications in prostate cancers in this study. The homozygous deletions affected a number of biologically important genes, including PPP2R2A and BNIP3L identified in this study and CDKN2A/CDKN2B reported previously. Although most amplified genomic regions tended to be large, amplifications at 8q24.21 were of particular interest because the affected regions are relatively small, are found in multiple cell lines, are located near MYC, an oncogene strongly implicated in prostate tumorigenesis, and are known to harbor SNPs that are associated with inherited susceptibility for prostate cancer. The genomic alterations revealed in this study provide an important catalog of positional information relevant to efforts aimed at deciphering the molecular genetic basis of prostate cancer.

Prosaposin is an AR-target gene and its neurotrophic domain upregulates AR expression and activity in prostate stromal cells

Recent studies have introduced prosaposin (PSAP) as a pleiotrophic growth factor for prostate cancer (PCa). We have previously reported that PSAP or one of its known active molecular derivatives, saposin C functions as an androgen-agonist and androgen-regulated gene (ARG) for androgen-sensitive (AS) PCa cell lines. Due to the potential significance of androgen receptor (AR)-expressing stroma in PCa, we evaluated a possible bi-directional paracrine regulatory interactions between DHT and PSAP in AR-positive prostate stromal (PrSt) cells. We report that saposin C in a ligand-independent manner increased AR expression, its nuclear content, and tyrosine phosphorylation. DHT treatment of PrSt cells increased PSAP expression. We also demonstrated both serum- and androgen-inducibility of a previously characterized hormone-responsive element (HRE) located in the proximal region of PSAP promoter. In addition, conditioned-media derived from PrSt cells and bone fibroblasts (i.e., MSF) differentially increased PSAP-promoter activity in androgen-independent (AI) PC-3 and AS LNCaP cells. Our data for the first time demonstrate that not only saposin C or PSAP regulates AR expression/activity, but also function as an ARG in PrSt. Ligand-independent activation of AR by PSAP or saposin C in PCa and stromal cells may contribute not only to prostate carcinogenesis at an early stage, but also in AI progression of the disease in an androgen-deprived tumor microenvironment.

Low-calcium serum-free defined medium selects for growth of normal prostatic epithelial stem cells

Stage-specific differentiation markers were used to evaluate the cellular composition and the origin of nonimmortalized (PrEC) and immortalized (PZ-HPV7, CA-HPV10, RWPE-1, and 957E/hTERT) human prostate cell lines. These studies documented that immortalized and nonimmortalized prostate epithelial cells established and maintained in low (i.e., <300 micromol/L) Ca(2+) serum-free defined (SFD) medium were all derived from normal nonmalignant prostate tissues and contain CD133(+)/ABCG2(+)/alpha(2)beta(1)(Hi)/p63(-)/PSCA(-)/AR(-)/PSA(-) prostate stem cells. In these cultures, prostate stem cells are able to self-renew and generate two distinct cell lineages: the minor proliferatively quiescent neuroendocrine lineage and the major transit-amplifying cell lineage. Subsequently, CD133(-)/ABCG2(-)/alpha(2)beta(1)(Hi)/p63(+)/PSCA(-)/AR(-)/PSA(-) transit-amplifying cells proliferate frequently and eventually mature into proliferatively quiescent CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(+)/AR(-)/PSA(-) intermediate cells. Such proliferatively quiescent intermediate cells, however, do not complete their full maturation into CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(-)/AR(+)/PSA(+) luminal-secretory cells in low Ca(2+) SFD medium. Addition of universal type I IFN and synthetic androgen (R1881) to culture medium resulted in up-regulation of androgen receptor protein expression. However, it failed to induce full differentiation of intermediate cells into AR(+)/PSA(+) luminal-secretory cells. Our results indicate that such inability of prostate epithelial cells to complete their differentiation is due to continuous expression of Notch-1 receptor and its downstream effector, Hey-1 protein, which actively suppresses differentiation via its ability to transcriptionally repress a series of genes, including the GATA family of transcription factors.

Prosaposin is a novel androgen-regulated gene in prostate cancer cell line LNCaP

Androgen-regulated genes (ARG) are implicated in normal and neoplastic growth of the prostate. Recently, we reported genomic amplification and/or overexpression of a previously known neurotrophic factor, prosaposin, in androgen-independent (AI) or metastatic prostate cancer (PCa) cells and tissues. Prosaposin and/or its known active molecular derivatives (e.g., saposin C) function as a pluripotent growth factor with diverse biological activities that favor malignant phenotypes in PCa cells. In addition, prosaposin or saposin C upregulates androgen receptor (AR) and AR-target genes (i.e., prostate-specific antigen, Probasin) expression and activity in LNCaP cells. Here, we examined prosaposin as an ARG. We report that DHT treatment of LNCaP cells increases prosaposin expression. In addition, we demonstrate androgen-responsiveness of prosaposin promoter and AR occupancy to a hormone-responsive element located in the proximal region of the prosaposin promoter. Our data for the first time identify prosaposin as an ARG. This observation, together with the pleiotropic growth factor activity of prosaposin, might suggest a role for this molecule in AR-dependent progression of prostate cancer at its early or late AI-state.

Prosaposin upregulates AR and PSA expression and activity in prostate cancer cells (LNCaP)

BACKGROUND

Prosaposin overexpression and/or genomic amplification have been demonstrated in androgen-independent (AI) prostate cancer cell lines and tissues. Here, we explored the possibility for a functional relationship between prosaposin and androgen receptor (AR) in LNCaP cells.

METHODS

The effect of prosaposin or its active molecular derivatives (e.g., saposin C) on expression and activity of androgen receptor (AR) and prostate-specific antigen (PSA) was examined by using immunoblotting, RT-PCR, transfection, and reporter gene assays, immunofluorescence staining, and inhibitors of signal transduction pathways.

RESULTS

Prosaposin or saposin C, in an AI-manner, (a) increased AR mRNA and protein expression and nuclear AR content and its phosphorylation state; (b) increased PSA mRNA and protein expression; and (c) upregulated PSA- and an androgen-inducible probasin (PB)-reporter gene activity in LNCaP and AR-transfected PC-3 cells. Induction of PSA expression and reporter activity was substantially blocked or prevented with the antiandrogen bicalutamide, pertussis toxin, or inhibitors of MAPK- and PI3K/Akt-signaling pathways, indicating an androgen-agonistic effect for saposin C that involves AR and multiple signaling pathways.

CONCLUSIONS

The results for the first time introduce prosaposin as an androgen-agonist in prostate cancer cells. This finding, together with the growth-promoting effect and overexpression of prosaposin, may support a growth advantage to AI prostate cancer cells.

Characterization of the androgen receptor in a benign prostate tissue-derived human prostate epithelial cell line: RC-165N/human telomerase reverse transcriptase

The majority of prostate epithelial cell lines stably expressing wild-type (wt) or mutant (mt) androgen receptor (AR) are derived from metastatic prostate cancers. Therefore, the wt AR-expressing RC-165N/human telomerase reverse transcriptase (hTERT) cell line derived from the benign prostate tissue of an African-American patient provides a unique opportunity to assess the functional status of AR in a cellular context not studied before. Although androgen-induced expression of known androgen responsive genes such as PMEPA1, and NDRG1 was observed in RC-165N/hTERT, this cell line expresses prostate-specific antigen (PSA) at significantly lower levels. Chromatin immunoprecipitation assay revealed androgen-dependent binding of AR to androgen response elements of PSA, PMEPA1 and NDRG1 genes. Similarities, as well as differences were noted in the expression of androgen responsive genes between RC-165N/hTERT and LNCaP cells. Comprehensive evaluations of AR functions in RC-165N/hTERT cells suggest that whereas some features of known AR functions are maintained in this benign prostatic tissue-derived cell line, other AR functions are not retained. Objective evaluations of similar cell lines will lead to the understanding of AR functions in prostate growth and differentiation.

Amplification and overexpression of prosaposin in prostate cancer

We identified prosaposin (PSAP) as a secreted protein expressed in androgen-independent (AI) prostate cancer cells by cloning/sequencing, after probing a PC-3 cDNA library expressed in the lambdaTriplEx phagemid expression vector with a polyclonal rabbit antibody generated against pooled human seminal plasma. PSAP is a neurotrophic molecule; its deficiency or inactivation has proved to be lethal in man and mice, and in mice, it leads to abnormal development and atrophy of the prostate gland, despite normal testosterone levels. We used Southern hybridization, quantitative real-time polymerase chain reaction, and/or single nucleotide polymorphism (SNP) array analysis, and we now report the genomic amplification of PSAP in the metastatic AI prostate cancer cell lines, PC-3, DU-145, MDA-PCa 2b, M-12, and NCI-H660. In addition, by using SNP arrays and a set of 25 punch biopsy samples of human prostate cancer xenografts (LAPC3, LuCaP 23.1, 35, 49, 58, 73, 77, 81, 86.2, 92.1, 93, 96, 105, and 115), lymph nodes, and visceral-organ metastases, we detected amplification of the PSAP locus (10q22.1) in LuCaP 58 and 96 xenografts and two lymph node metastases. In addition, AI metastatic prostate cancer cell lines C4-2B and IA8-ARCaP over-expressed PSAP mRNA without evidence of genomic amplification. Taken together with prior data that demonstrated the growth-, migration-, and invasion-promoting activities, the activation of multiple signal transduction pathways, and the antiapoptotic effect of PSAP (or one of its active domains, saposin C) in prostate cancer cells, our current observation of PSAP amplification or overexpression in prostate cancer suggests, for the first time, a role for this molecule in the process of carcinogenesis or cancer progression in the prostate.