Histological, immunophenotypic and histomorphometric characterization of prostate cancer bone metastases

Abscisic acid signaling through LANCL2 and PPARγ induces activation of p38MAPK resulting in dormancy of prostate cancer metastatic cells

Prostate cancer (PCa) is one the most common malignancies in men. The high incidence of bone metastasis years after primary therapy suggests that disseminated tumor cells must become dormant, but maintain their ability to proliferate in the bone marrow. Abscisic acid (ABA) is a stress response molecule best known for its regulation of seed germination, stomal opening, root shoot growth and other stress responses in plants. ABA is also synthesized by mammalian cells and has been linked to human disease. The aim of the present study was to examine the role of ABA in regulating tumor dormancy via signaling through lanthionine synthetase C‑like protein 2 (LANCL2) and peroxisome proliferator activated receptor γ (PPARγ) receptors. ABA signaling in human PCa cell lines was studied using targeted gene knockdown (KD), western blotting, quantitative PCR, cell proliferation, migration, invasion and soft agar assays, as well as co‑culture assays with bone marrow stromal cells. The data demonstrated that ABA signaling increased the expression of p21, p27 and p16, while inhibiting viability, migration, invasion and colony size in a reversable manner without toxicity. ABA also induced p38MAPK activation and NR2F1 signaling. Targeted gene KD of LANCL2 and PPARγ abrogated the cellular responses to ABA. Taken together, these data demonstrate that ABA may induce dormancy in PCa cell lines through LANCL2 and PPARγ signaling, and suggest novel targets to manage metastatic PCa growth.

Mechanosensitive Ion Channels: Their Physiological Importance and Potential Key Role in Cancer

Mechanosensitive ion channels comprise a broad group of proteins that sense mechanical extracellular and intracellular changes, translating them into cation influx to adapt and respond to these physical cues. All cells in the organism are mechanosensitive, and these physical cues have proven to have an important role in regulating proliferation, cell fate and differentiation, migration and cellular stress, among other processes. Indeed, the mechanical properties of the extracellular matrix in cancer change drastically due to high cell proliferation and modification of extracellular protein secretion, suggesting an important contribution to tumor cell regulation. In this review, we describe the physiological significance of mechanosensitive ion channels, emphasizing their role in cancer and immunity, and providing compelling proof of the importance of continuing to explore their potential as new therapeutic targets in cancer research.

Exploring the role of differentially expressed metabolic genes and their mechanisms in bone metastatic prostate cancer

Background

Approximately 10-20% of patients diagnosed with prostate cancer (PCa) evolve into castration-resistant prostate cancer (CRPC), while nearly 90% of patients with metastatic CRPC (mCRPC) exhibit osseous metastases (BM). These BM are intimately correlated with the stability of the tumour microenvironment.

Purpose

This study aspires to uncover the metabolism-related genes and the underlying mechanisms responsible for bone metastatic prostate cancer (BMPCa).

Methods

Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets of PCa and BM were analyzed through R Studio software to identify differentially expressed genes (DEGs). The DEGs underwent functional enrichment via Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO), with key factors screened by a random forest utilized to establish a prognostic model for PCa. The study explored the relationship between DEGs and the stability of the immune microenvironment. The action and specificity of CRISP3 in PCa was validated through western blot analysis, CCK-8 assay, scratch assay, and cellular assay.

Results

The screening of GEO and TCGA datasets resulted in the identification of 199 co-differential genes. Three DEGs, including DES, HBB, and SLPI, were selected by random forest classification model and cox regression model. Immuno-infiltration analysis disclosed that a higher infiltration of naïve B cells and resting CD4 memory T cells occurred in the high-expression group of DES, whereas infiltration of resting M1 macrophages and NK cells was greater in the low-expression group of DES. A significant infiltration of neutrophils was observed in the high-expression group of HBB, while greater infiltration of gamma delta T cells and M1 macrophages was noted in the low-expression group of HBB. Resting dendritic cells, CD8 T cells, and resting T regulatory cells (Tregs) infiltrated significantly in the high-expression group of SLPI, while only resting mast cells infiltrated significantly in the low-expression group of SLPI. CRISP3 was established as a critical gene in BMPCa linked to DES expression. Targeting CRISP3, d-glucopyranose may impact tumour prognosis. During the mechanistic experiments, it was established that CRISP3 can advance the proliferation and metastatic potential of PCa by advancing epithelial-to-mesenchymal transition (EMT).

Conclusion

By modulating lipid metabolism and maintaining immunological and microenvironmental balance, DES, HBB, and SLPI suppress prostate cancer cell growth. The presence of DES-associated CRISP3 is a harbinger of unfavorable outcomes in prostate cancer and may escalate tumor proliferation and metastatic capabilities by inducing epithelial-mesenchymal transition.

PECAM1 plays a role in the pathogenesis and treatment of bone metastases

Bone is the third most common metastatic site for all primary tumors, the common primary focus of bone metastases include breast cancer, prostate cancer, and so on. And the median survival time of patients with bone metastases is only 2–3 years. Therefore, it is urgent to develop new targets to diagnose and treat bone metastases. Based on two data sets GSE146661 and GSE77930 associated with bone metastases, it was found that 209 genes differentially expressed in bone metastases group and control group. PECAM1 was selected as hub-gene for the follow-up research after constructing protein-protein interaction (PPI) network and enrichment analysis. Moreover, q-PCR analysis verified that the expression of PECAM1 decreased in bone metastatic tumor tissues. PECAM1 was believed to be possibly related to the function of osteoclasts, we knocked down the expression of PECAM1 with shRNA in lymphocytes extracted from bone marrow nailed blood. The results indicated that sh-PECAM1 treatment could promote osteoclast differentiation, and the sh-PECAM1-treated osteoclast culture medium could significantly promote the proliferation and migration of tumor cells. These results suggested that PECAM1 may be a potential biomarker for the diagnosis and treatment of bone metastases of tumor.

Bone Health Management in the Continuum of Prostate Cancer Disease

Prostate cancer (PCa) is the second-leading cause of cancer-related deaths in men. PCa cells require androgen receptor (AR) signaling for their growth and survival. Androgen deprivation therapy (ADT) is the preferred treatment for patients with locally advanced and metastatic PCa disease. Despite their initial response to androgen blockade, most patients eventually will develop metastatic castration-resistant prostate cancer (mCRPC). Bone metastases are common in men with mCRPC, occurring in 30% of patients within 2 years of castration resistance and in >90% of patients over the course of the disease. Patients with mCRPC-induced bone metastasis develop lesions throughout their skeleton; the 5-year survival rate for these patients is 47%. Bone-metastasis-induced early changes in the bone that proceed the osteoblastic response in the bone matrix are monitored and detected via modern magnetic resonance and PET/CT imaging technologies. Various treatment options, such as targeting osteolytic metastasis with bisphosphonates, prednisone, dexamethasone, denosumab, immunotherapy, external beam radiation therapy, radiopharmaceuticals, surgery, and pain medications are employed to treat prostate-cancer-induced bone metastasis and manage bone health. However, these diagnostics and treatment options are not very accurate nor efficient enough to treat bone metastases and manage bone health. In this review, we present the pathogenesis of PCa-induced bone metastasis, its deleterious impacts on vital organs, the impact of metastatic PCa on bone health, treatment interventions for bone metastasis and management of bone- and skeletal-related events, and possible current and future therapeutic options for bone management in the continuum of prostate cancer disease.

Evolving cancer-niche interactions and therapeutic targets during bone metastasis

Many cancer types metastasize to bone. This propensity may be a product of genetic traits of the primary tumour in some cancers. Upon arrival, cancer cells establish interactions with various bone-resident cells during the process of colonization. These interactions, to a large degree, dictate cancer cell fates at multiple steps of the metastatic cascade, from single cells to overt metastases. The bone microenvironment may even influence cancer cells to subsequently spread to multiple other organs. Therefore, it is imperative to spatiotemporally delineate the evolving cancer-bone crosstalk during bone colonization. In this Review, we provide a summary of the bone microenvironment and its impact on bone metastasis. On the basis of the microscopic anatomy, we tentatively define a roadmap of the journey of cancer cells through bone relative to various microenvironment components, including the potential of bone to function as a launch pad for secondary metastasis. Finally, we examine common and distinct features of bone metastasis from various cancer types. Our goal is to stimulate future studies leading to the development of a broader scope of potent therapies.

Clinical Characteristics, Treatment Modalities, and Potential Contributing and Prognostic Factors in Patients with Bone Metastases from Gynecological Cancers: A Systematic Review

The purpose of this study is to review the clinical characteristics, treatment modalities, and potential contributing and prognostic factors of bone metastases from gynecological cancers (GCs). A systematic literature search on PubMed, Scopus, Web of Science Core Collection and Cochrane Central Register of Controlled Trials databases was conducted. Thirty-one studies, all retrospective, were included in this review, for a total of 2880 patients with GC bone metastases. Primary tumors leading to bone metastases included endometrial cancer (EC), cervical cancer (CC), ovarian cancer (OC), uterine sarcoma (US) and vulvar cancer (VuC), mainly with an International Federation of Gynecology and Obstetrics (FIGO) Stage of III and IV. The main bone metastatic lesion site was the vertebral column, followed by the pelvic bone and lower extremity bones. The median survival rate after bone metastases diagnosis ranged from 3.0 to 45 months. The most frequent treatments were palliative and included radiotherapy and chemotherapy, followed by surgery. The findings of this review give a first dataset for a greater understanding of GC bone metastases that could help clinicians move toward a more “personalized” and thus more effective patient management.

Prostate Cancer Dormancy and Reactivation in Bone Marrow

Prostate cancer has a variable clinical course, ranging from curable local disease to lethal metastatic spread. Eradicating metastatic cells is a unique challenge that is rarely met with the available therapies. Thus, targeting prostate cancer cells in earlier disease states is a crucial window of opportunity. Interestingly, cancer cells migrate from their primary site during pre-cancerous and malignant phases to seed secondary organs. These cells, known as disseminated cancer cells (DCCs), may remain dormant for months or decades before activating to form metastases. Bone marrow, a dormancy-permissive site, is the major organ for housed DCCs and eventual metastases in prostate cancer. The dynamic interplay between DCCs and the primary tumor microenvironment (TME), as well as that between DCCs and the secondary organ niche, controls the conversion between states of dormancy and activation. Here, we discuss recent discoveries that have improved our understanding of dormancy signaling and the role of the TME in modulating the epigenetic reprogramming of DCCs. We offer potential strategies to target DCCs in prostate cancer.

Prostate Cancer Cell Extracellular Vesicles Increase Mineralisation of Bone Osteoblast Precursor Cells in an In Vitro Model

Simple Summary

Prostate cancer frequently metastasizes to the bone, where it forms primarily osteoblastic lesions. Currently there is no real therapeutic option for this late stage of disease, and understanding prostate cancer-bone interaction and communication is vital. Using a simple in vitro model of os-teoblast differentiation and mineralization, we studied this interaction and observed that prostate cancer cells secreted large quantities of extracellular vesicles containing microRNAs. When ex-posed to the extracellular vesicles, increased osteoblast differentiation and mineralization could be observed, and upon RNA-seq several of these microRNAs were implicated as upstream regulators of the mineralization process. These microRNAs also correlated with poor survival in online analysis of patient datasets. We characterized and validated four genes known to be targeted by microRNA-16, and found that extracellular vesicles could deliver miR-16, and increase minerali-zation.

Abstract

Skeletal metastases are the most common form of secondary tumour associated with prostate cancer (PCa). The aberrant function of bone cells neighbouring these tumours leads to the devel-opment of osteoblastic lesions. Communication between PCa cells and bone cells in bone envi-ronments governs both the formation/development of the associated lesion, and growth of the secondary tumour. Using osteoblasts as a model system, we observed that PCa cells and their conditioned medium could stimulate and increase mineralisation and osteoblasts’ differentiation. Secreted factors within PCa-conditioned medium responsible for osteoblastic changes included small extracellular vesicles (sEVs), which were sufficient to drive osteoblastogenesis. Using MiR-seq, we profiled the miRNA content of PCa sEVs, showing that miR-16-5p was highly ex-pressed. MiR-16 was subsequently higher in EV-treated 7F2 cells and a miR-16 mimic could also stimulate mineralisation. Next, using RNA-seq of extracellular vesicle (EV)-treated 7F2 cells, we observed a large degree of gene downregulation and an increased mineralisation. Ingenuity® Pathway Analysis (IPA^®) revealed that miR-16-5p (and other miRs) was a likely upstream effec-tor. MiR-16-5p targets in 7F2 cells, possibly involved in osteoblastogenesis, were included for val-idation, namely AXIN2, PLSCR4, ADRB2 and DLL1. We then confirmed the targeting and dow-regulation of these genes by sEV miR-16-5p using luciferase UTR (untranslated region) reporters. Conversely, the overexpression of PLSCR4, ADRB2 and DLL1 lead to decreased osteoblastogene-sis. These results indicate that miR-16 is an inducer of osteoblastogenesis and is transmitted through prostate cancer-derived sEVs. The mechanism is a likely contributor towards the for-mation of osteoblastic lesions in metastatic PCa.

Metastatic Spread in Prostate Cancer Patients Influencing Radiotherapy Response

Radiotherapy and surgery are curative treatment options for localized prostate cancer (PCa) with a 5-year survival rate of nearly 100%. Once PCa cells spread into distant organs, such as bone, the overall survival rate of patients drops dramatically. The metastatic cascade and organotropism of PCa cells are regulated by different cellular subtypes, organ microenvironment, and their interactions. This cross-talk leads to pre-metastatic niche formation that releases chemo-attractive factors enforcing the formation of distant metastasis. Biological characteristics of PCa metastasis impacting on metastatic sites, burden, and latency is of clinical relevance. Therefore, the implementation of modern hybrid imaging technologies into clinical routine increased the sensitivity to detect metastases at earlier stages. This enlarged the number of PCa patients diagnosed with a limited number of metastases, summarized as oligometastatic disease. These patients can be treated with androgen deprivation in combination with local-ablative radiotherapy or radiopharmaceuticals directed to metastatic sites. Unfortunately, the number of patients with disease recurrence is high due to the enormous heterogeneity within the oligometastatic patient population and the lack of available biomarkers with predictive potential for metastasis-directed radiotherapy. Another, so far unmet clinical need is the diagnosis of minimal residual disease before onset of clinical manifestation and/or early relapse after initial therapy. Here, monitoring of circulating and disseminating tumor cells in PCa patients during the course of radiotherapy may give us novel insight into how metastatic spread is influenced by radiotherapy and vice versa. In summary, this review critically compares current clinical concepts for metastatic PCa patients and discuss the implementation of recent preclinical findings improving our understanding of metastatic dissemination and radiotherapy resistance into standard of care.

Emerging Players in Prostate Cancer-Bone Niche Communication

Patients with advanced prostate cancer (PCa) frequently develop skeletal metastases that are associated with fractures, disability, and increased mortality. Within the bone metastatic niche, mutual interactions between tumor cells and osteoblasts have been proposed as major contributors of osteotropism by PCa. Here, we highlight the emerging role of PCa-derived extracellular vesicles (EVs) in reprogramming osteoblasts and support of premetastatic niche formation. We also develop the concept of cancer-associated osteoblasts (CAOs) and outline the potential of PCa cells to acquire an osteoblastic phenotype, termed osteomimicry, as two strategies that PCa utilizes to create a favorable protected niche. Finally, we delineate future research that may help to deconstruct the complexity of PCa osteotropism.

Bone metastases

Bone is the most frequent site for metastasis for many cancers, notably for tumours originating in the breast and the prostate. Tumour cells can escape from the primary tumour site and colonize the bone microenvironment. Within the bone, these disseminated tumour cells, as well as those arising in the context of multiple myeloma, may assume a state of dormancy, remaining quiescent for years before resuming proliferation and causing overt metastasis, which causes bone destruction via activation of osteoclast-mediated osteolysis. This structural damage can lead to considerable morbidity, including pain, fractures and impaired quality of life. Although treatment of bone metastases and myeloma bone disease is rarely curative, disease control is often possible for many years through the use of systemic anticancer treatments on a background of multidisciplinary supportive care. This care should include bone-targeted agents to inhibit tumour-associated osteolysis and prevent skeletal morbidity as well as use of appropriate local treatments such as radiation therapy, orthopaedic surgery and specialist palliative care to minimize the impact of metastatic bone disease on physical functioning. In this Primer, we provide an overview of the clinical features, the pathophysiology and the specific treatment approaches to prevent and treat bone metastases from solid tumours as well as myeloma bone disease.

Generation of Prostate Cancer Patient-Derived Xenografts to Investigate Mechanisms of Novel Treatments and Treatment Resistance

Treatment advances lead to survival benefits of patients with advanced prostate cancer. These treatments are highly efficacious in a subset of patients; however, similarly to other cancers, after initial responses the tumors develop resistance (acquired resistance) and the patients succumb to the disease. Furthermore, there is a subset of patients who do not respond to the treatment at all (de novo resistance). Preclinical testing using patient-derived xenografts (PDXs) has led to successful drug development, and PDXs will continue to provide valuable resources to generate clinically relevant data with translational potential. PDXs demonstrate tumor heterogeneity observed in patients, preserve tumor-microenvironment architecture, and provide clinically relevant treatment responses. In view of the evolving biology of the advanced prostate cancer associated with new treatments, PDXs representing these new tumor phenotypes are urgently needed for the study of treatment responses and resistance. In this chapter, we describe methodologies used to establish prostate cancer PDXs and use of these PDXs to study de novo and acquired resistance.

Bladder cancer cells secrete while normal bladder cells express but do not secrete AGR2

Anterior gradient 2 (AGR2) is a cancer-associated secreted protein found predominantly in adenocarcinomas. Given its ubiquity in solid tumors, cancer-secreted AGR2 could be a useful biomarker in urine or blood for early detection. However, normal organs express and might also secrete AGR2, which would impact its utility as a cancer biomarker. Uniform AGR2 expression is found in the normal bladder urothelium. Little AGR2 is secreted by the urothelial cells as no measurable amounts could be detected in urine. The urinary proteomes of healthy people contain no listing for AGR2. Likewise, the blood proteomes of healthy people also contain no significant peptide counts for AGR2 suggesting little urothelial secretion into capillaries of the lamina propria. Expression of AGR2 is lost in urothelial carcinoma, with only 25% of primary tumors observed to retain AGR2 expression in a cohort of lymph node-positive cases. AGR2 is secreted by the urothelial carcinoma cells as urinary AGR2 was measured in the voided urine of 25% of the cases analyzed in a cohort of cancer vs. non-cancer patients. The fraction of AGR2-positive urine samples was consistent with the fraction of urothelial carcinoma that stained positive for AGR2. Since cancer cells secrete AGR2 while normal cells do not, its measurement in body fluids could be used to indicate tumor presence. Furthermore, AGR2 has also been found on the cell surface of cancer cells. Taken together, secretion and cell surface localization of AGR2 are characteristic of cancer, while expression of AGR2 by itself is not.

The role of the microenvironment-dormant prostate disseminated tumor cells in the bone marrow

Disseminated tumor cells (DTC) leave the primary tumor and reside in distant sites (e.g. bone) early in prostate cancer. Patients may harbor dormant DTC which develop into clinically overt metastasis years after radical prostatectomy. We will describe recent evidence suggesting high p38/ERK ratio, bone morphogenetic proteins, and tumor growth factor-beta 2 promote dormancy in solid tumors. Furthermore, we will discuss the possible regulation of dormancy by hematopoietic stem cell and vascular niches, and describe novel models recapitulating bone marrow metastatic latency and out- growth, 3D microvascular networks, and 3D biomatrix supportive niches in the studies of tumor cell dormancy.

AFM-based dual nano-mechanical phenotypes for cancer metastasis

An enhanced mechanical compliance is considered to be a mechanical indicator for metastatic cancer cells. Our study using atomic force microscopy (AFM) revealed that breast cancer cells agreed well with this hypothesis. However, prostate cancer cells displayed a reverse correlation; less metastatic prostate cancer cells were more mechanically compliant. Two-dimensional AFM force spectroscopy was performed to characterize dual mechanical properties-the cell-substrate adhesion as well as the mechanical compliance. Interestingly, prostate cancer cells displayed a strong positive correlation between the cell-substrate adhesion and metastatic potential. However, there was no clearly observable correlation between the cell-substrate adhesion and the metastatic potential despite variations in mechanical compliance of breast cancer cells. These results suggest that the correlation between the dual mechanical signatures and metastatic potential be uniquely identified for cancer cells originating from different organs. We postulate that this correlation could reveal which step of cancer progression is favorable in terms of physical interaction between cancer cells and micro-environments. We expect that based on the "seed and soil hypothesis", the identification of the dual mechanical phenotypes, could provide a new insight for understanding how a dominant metastatic site is determined for cancer cells originating from specific organs.

Cavin-1/PTRF alters prostate cancer cell-derived extracellular vesicle content and internalization to attenuate extracellular vesicle-mediated osteoclastogenesis and osteoblast proliferation

Background

Tumour-derived extracellular vesicles (EVs) play a role in tumour progression; however, the spectrum of molecular mechanisms regulating EV secretion and cargo selection remain to be fully elucidated. We have reported that cavin-1 expression in prostate cancer PC3 cells reduced the abundance of a subset of EV proteins, concomitant with reduced xenograft tumour growth and metastasis.

Methods

We examined the functional outcomes and mechanisms of cavin-1 expression on PC3-derived EVs (PC3-EVs).

Results

PC3-EVs were internalized by osteoclast precursor RAW264.7 cells and primary human osteoblasts (hOBs) in vitro, stimulating osteoclastogenesis 37-fold and hOB proliferation 1.5-fold, respectively. Strikin gly, EVs derived from cavin-1-expressing PC3 cells (cavin-1-PC3-EVs) failed to induce multinucleate osteoblasts or hOB proliferation. Cavin-1 was not detected in EVs, indicating an indirect mechanism of action. EV morphology, size and quantity were also not affected by cavin-1 expression, suggesting that cavin-1 modulated EV cargo recruitment rather than release. While cavin-1-EVs had no osteoclastogenic function, they were internalized by RAW264.7 cells but at a reduced efficiency compared to control EVs. EV surface proteins are required for internalization of PC3-EVs by RAW264.7 cells, as proteinase K treatment abolished uptake of both control and cavin-1-PC3-EVs. Removal of sialic acid modifications by neuraminidase treatment increased the amount of control PC3-EVs internalized by RAW264.7 cells, without affecting cavin-1-PC3-EVs. This suggests that cavin-1 expression altered the glycosylation modifications on PC3-EV surface. Finally, cavin-1 expression did not affect EV in vivo tissue targeting as both control and cavin-1-PC3-EVs were predominantly retained in the lung and bone 24 hours after injection into mice.

Discussion

Taken together, our results reveal a novel pathway for EV cargo sorting, and highlight the potential of utilizing cavin-1-mediated pathways to attenuate metastatic prostate cancer.

Interleukin-27 gene delivery for modifying malignant interactions between prostate tumor and bone

We have examined the role of a novel cytokine, interleukin-27 (IL-27), in mediating interactions between prostate cancer and bone. IL-27 is the most recently characterized member of the family of heterodimeric IL-12-related cytokines and has shown promise in halting tumor growth and mediating tumor regression in several cancer models, including prostate cancer. Prostate cancer is frequently associated with metastases to the bone, where the tumor induces a vicious cycle of communication with osteoblasts and osteoclasts to induce bone lesions, which are a significant cause of pain and skeletal-related events for patients, including a high fracture risk. We describe our findings in the effects of IL-27 gene delivery on prostate cancer cells, osteoblasts, and osteoclasts at different stages of differentiation. We applied the IL-27 gene delivery protocol in vivo utilizing sonoporation (sonodelivery) with the goal of treating and reducing the growth of prostate cancer at a bone metastatic site in vivo. We used a new model of immune-competent prostate adenocarcinoma and characterized the tumor growth reduction, gene expression, and effector cellular profiles. Our results suggest that IL-27 can be effective in reducing tumor growth, can help normalize bone structure, and can promote enhanced accumulation of effector cells in prostate tumors. These results are promising, because they are relevant to developing a novel IL-27-based strategy that can treat both the tumor and the bone, by using this simple and effective sonodelivery method for treating prostate tumor bone metastases.

Non-invasive microCT imaging characterization and in vivo targeting of BB2 receptor expression of a PC-3 bone metastasis model

PURPOSE

A devastating progression of human prostate cancer is the development of bone metastasis. Animal models of bone metastasis induced by inoculating human prostate cell lines into mice are well established. Here, we report the characterization of a mouse model of prostatic bone metastasis using non-invasive microCT and targeted microSPECT imaging of bone tumors using the bombesin receptor (BB2r)-avid radiolabeled peptide, (111)In-DOTA-8-Aoc-BBN[7–14]NH(2).

PROCEDURES

Immunocompromised mice were inoculated with human prostate cancer cells by intracardiac injection. Metastatic lesion development was monitored by serially imaging mice weekly with microCT. Mice with CT imaging-confirmed bone lesions were administered (111)In-DOTA-8-Aoc-BBN[7–14]NH(2) for microSPECT imaging of BB2r expressing lesions.

RESULTS

Metastatic bone lesions as small as 0.3 mm in diameter were detected by microCT image analysis as early as 21 days after tumor cell inoculation and had wide anatomical distribution. MicroSPECT imaging using (111)In-DOTA-8-Aoc-BBN[7–14]NH(2) successfully targeted BB2r expressing metastatic bone lesions of the tibia at day 29.

CONCLUSIONS

MicroCT imaging can accurately and non-invasively follow the onset and progression of metastatic bone lesions in mouse models of prostate cancer. Micro-CT coupled with BB2r Micro-SPECT imaging affords the opportunity to obtain a combined receptor/anatomic map of metastatic bone lesion status in this mouse model.

AFM nano-mechanics and calcium dynamics of prostate cancer cells with distinct metastatic potential

BACKGROUND

Despite recent advances, it is not clear to correlate the mechanical compliances and the metastatic potential of cancer cells. In this study, we investigated combined signatures of mechanical compliances, adhesions, and calcium dynamics correlated with the metastatic potential of cancer cells.

SCOPE OF REVIEW

We used the lowly (LNCaP) and highly (CL-1, CL-2) metastatic human prostate cancer cells. The AFM-based nanomechanics was performed to determine the elastic moduli and the cell-to-substrate adhesion. The intracellular calcium dynamics was evaluated by fluorescence spectroscopy. Cell migration and the distribution of cytoskeleton were evaluated using the wounded monolayer model and immunofluorescence, respectively. The elastic moduli, the calcium dynamics, and the migratory ability are greater in CL-1 and CL-2 than LNCaP. CL-1 and CL-2 also display a significantly larger area of cell-to-substrate adhesions while the LNCaP displays a limited adhesion. These properties were slightly reduced in CL-2 compared with CL-1 cells. The enhanced elastic moduli and calcium dynamics found in CL-1 and CL-2 can be consistently explained by the intensified tensile stress generated by actin cytoskeletons anchored at more focal adhesion sites.

MAJOR CONCLUSIONS

Although the suppressed mechanical compliance of highly metastatic cells may not support the enhanced cancer metastasis, the enhanced adhesion and calcium dynamics are favorable for invasion and extra-vasation required for malignant progression.

GENERAL SIGNIFICANCE

Our results suggest that the mechanical compliance alone may fail to indicate the metastatic progression, but the combined biomechanical signatures of mechanical compliance, adhesion, and calcium dynamics can provide critical clues to determine the metastatic potential of cells.

Molecular targets for radiation oncology in prostate cancer

Recent selected developments of the molecular science of prostate cancer (PrCa) biology and radiation oncology are reviewed. We present potential targets for molecular integration treatment strategies with radiation therapy (RT), and highlight potential strategies for molecular treatment in combination with RT for patient care. We provide a synopsis of the information to date regarding molecular biology of PrCa, and potential integrated research strategy for improved treatment of PrCa. Many patients with early-stage disease at presentation can be treated effectively with androgen ablation treatment, surgery, or RT. However, a significant portion of men are diagnosed with advanced stage/high-risk disease and these patients progress despite curative therapeutic intervention. Unfortunately, management options for these patients are limited and are not always successful including treatment for hormone refractory disease. In this review, we focus on molecules of extracellular matrix component, apoptosis, androgen receptor, RUNX, and DNA methylation. Expanding our knowledge of the molecular biology of PrCa will permit the development of novel treatment strategies integrated with RT to improve patient outcome.

Mouse models of prostate cancer

The development and optimization of high-throughput screening methods has identified a multitude of genetic changes associated with human disease. The use of immunodeficient and genetically engineered mouse models that mimic the human disease has been crucial in validating the importance of these genetic pathways in prostate cancer. These models provide a platform for finding novel therapies to treat human patients afflicted with prostate cancer as well as those who have debilitating bone metastases. In this paper, we focus on the historical development and phenotypic descriptions of mouse models used to study prostate cancer. We also comment on how closely each model recapitulates human prostate cancer.

Methodology to investigate androgen-sensitive and castration-resistant human prostate cancer xenografts in preclinical setting

Understanding the biology of prostate cancer and the roles of androgen receptor in prostate cancer progression is essential to the development of novel therapeutic strategies to effectively attack and eradicate this disease. Preclinical, in vivo, studies are critical to further evaluate potential clinical relevance of in vitro findings. Ideally, in vivo studies should employ models that mimic characteristics of prostate cancer from early diagnosis through the period of castration-resistant metastases. In this chapter we describe methodologies used to grow human prostate cancer xenografts in mice. In this setting, roles of androgen receptor signaling in prostate cancer progression and efficacy of novel treatment modalities, including those affecting androgen receptor signaling, can be investigated.

p21CIP-1/WAF-1 induction is required to inhibit prostate cancer growth elicited by deficient expression of the Wnt inhibitor Dickkopf-1

Osteoblastic bone metastases are the most common metastases produced by human prostate cancers (PCa). Deregulated activity of Wnt growth factors resulting from overexpression of the Wnt inhibitor Dickkopf-1 (DKK-1) is known to contribute to formation of the osteoblastic component of PCa skeletal bone metastases. In this study, we report that DKK-1 knockdown in osteolytic human PCa cells unexpectedly delays the development of both soft tissue and osseous lesions. PCa cells deficient in DKK-1 expression did not increase canonical Wnt signaling in target osteoblast cell lines; however, DKK-1 knockdown PCa cells exhibited increased expression of the CDK inhibitor p21(CIP1/WAF1) and a 32% increase in G(1) arrest compared with control cells. Ablating p21(CIP1/WAF1) in PCa cells deficient in DKK-1 was sufficient to rescue tumor growth. Collectively, our findings demonstrate that DKK-1 overexpression supports tumor growth in part by restricting expression of p21(CIP1/WAF1) through a mechanism independent of canonical Wnt signaling.

Snail transcription factor regulates neuroendocrine differentiation in LNCaP prostate cancer cells

BACKGROUND

Snail transcription factor induces epithelial-mesenchymal transition (EMT) via decreased cell adhesion-associated molecules like E-cadherin, and increased mesenchymal markers like vimentin. We previously established Snail-mediated EMT model utilizing androgen-dependent LNCaP cells. These cells express increased vimentin protein and relocalization of E-cadherin from the cell membrane to the cytosol. Interestingly, Snail transfection in LNCaP cells resulted in cells acquiring a neuroendocrine (NE)-like morphology with long neurite-like processes.

METHODS

We tested for expression of NE markers neuron-specific enolase (NSE) and chromogranin A (CgA) by Western blot analysis, and performed proliferation assays to test for paracrine cell proliferation.

RESULTS

LNCaP cells transfected with Snail displayed increase in the NE markers, NSE and CgA as well as translocation of androgen receptor (AR) to the nucleus. LNCaP C-33 cells that have been previously published as a neuroendocrine differentiation (NED) model exhibited increased expression levels of Snail protein as compared to LNCaP parental cells. Functionally, conditioned medium from the LNCaP-Snail transfected cells increased proliferation of parental LNCaP and PC-3 cells, which could be abrogated by NSE/CgA siRNA. Additionally, NED in LNCaP-C33 cells or that induced in parental LNCaP cells by serum starvation could be inhibited by knockdown of Snail with siRNA.

CONCLUSION

Overall our data provide evidence that Snail transcription factor may promote tumor aggressiveness in the LNCaP cells through multiple processes; induction of EMT may be required to promote migration, while NED may promote tumor proliferation by a paracrine mechanism. Therefore, therapeutic targeting of Snail may prove beneficial in not only abrogating EMT but also NED.

Bone morphogenetic protein 7 is expressed in prostate cancer metastases and its effects on prostate tumor cells depend on cell phenotype and the tumor microenvironment

Bone morphogenetic protein (BMP) signaling is important in prostate development and prostate cancer (PCa) progression. However, because of the multiple effects of different BMPs, no final conclusions have been made as to the role of BMPs in PCa. In our studies, we have focused on BMP-7 because it is involved in prostate morphogenesis, and its expression is regulated by androgens. The objective of our study was to determine BMP-7 expression in PCa metastases and investigate the effects of BMP-7 on PCa cells. Our results show that BMP-7 is expressed in metastatic PCa and its levels are increased in castration-resistant PCa versus androgen-dependent PCa, whereas the expression of BMP-7 is decreased in primary PCa versus normal prostate. Our in vitro results show that BMP-7 inhibits proliferation of androgen-sensitive LNCaP cells, stimulates androgen receptor signaling, increases the expression of differentiation-associated genes, and decreases the levels of some wingless-regulated transcripts. Interestingly, these effects were not detected in C4-2 castration-resistant PCa cells. In vivo expression of BMP-7 in castration-resistant C4-2 cells did not alter proliferation when these cells were grown subcutaneously, but their growth was inhibited in the bone environment. In summary, our results show that BMP-7 is expressed at the highest level in advanced castration-resistant PCa cells and that the inhibitory effects of BMP-7 are dependent on the differentiation status of PCa cells and the tumor microenvironment. Further studies are needed to identify changes in BMP-7 signaling that lead to the loss of its control of proliferation during PCa progression.

Osteolytic prostate cancer cells induce the expression of specific cytokines in bone-forming osteoblasts through a Stat3/5-dependent mechanism

Prostate cancer primarily metastasizes to bone, and the interaction of cancer cells with bone cells results in a local activation of bone formation and/or bone resorption. Since the cellular and molecular mechanisms underlying the development of these tumor-induced osteoblastic or osteolytic lesions are still poorly understood, we have compared the effects of two prostate cancer cell lines, osteoblastic MDA-PCa-2b cells and osteolytic PC-3 cells, on bone-forming osteoblasts. Using Affymetrix Gene Chip hybridization followed by qRT-PCR confirmation we were able to identify specific genes, including Smpd3 and Dmp1, whose expression is significantly reduced upon treatment with PC-3-conditioned medium. Moreover, we observed that PC-3-conditioned medium led to a marked induction of several cytokine genes, including Cxcl5, Cxcl12 and Tnfsf11, the latter one encoding for the osteoclast differentiation factor Rankl. Likewise, when we analyzed the effects of MDA-PCa-2b- and PC-3-conditioned medium on signal transduction in osteoblasts we did not only observe opposite effects on the canonical Wnt signalling pathway, but also a specific induction of Erk and Stat phosphorylation by PC-3-conditioned medium. Most importantly, the induction of Cxcl5, Cxcl12 and Tnfsf11 in osteoblasts by PC-3-conditioned medium was abrogated by the Stat3/5 inhibitor piceatannol, whereas the selective blockade of Stat1 and Erk activation had no effect. Together with the finding, that activated Stat3 in osteoblasts was detectable in bone biopsies from patients with osteolytic metastases, our data suggest that the Stat3/5-dependent activation of cytokine expression in osteoblasts may have a significant impact on cancer cell migration and proliferation, but also on osteoclast activation.

PTHrP contributes to the anti-proliferative and integrin alpha6beta4-regulating effects of 1,25-dihydroxyvitamin D(3)

Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. 1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] suppresses PTHrP expression and exerts an anti-proliferative effect in prostate carcinoma cells. We used the human prostate cancer cell line C4-2 as a model system to ask whether down-regulation of PTHrP expression by 1,25(OH)(2)D(3) plays a role in the anti-proliferative effects of 1,25(OH)(2)D(3). Since PTHrP increases the expression of the pro-invasive integrin alpha6beta4, we also asked whether 1,25(OH)(2)D(3) decreases integrin alpha6beta4 expression in C4-2 cells, and whether modulation of PTHrP expression by 1,25(OH)(2)D(3) plays a role in the effects of 1,25(OH)(2)D(3) on integrin alpha6beta4 expression. Two strategies were utilized to modulate PTHrP levels: overexpression of PTHrP (-36 to +139) and suppression of endogenous PTHrP expression using siRNAs. We report a direct correlation between PTHrP expression, C4-2 cell proliferation and integrin alpha6beta4 expression at the mRNA and cell surface protein level. Treatment of parental C4-2 cells with 1,25(OH)(2)D(3) decreased cell proliferation and integrin alpha6 and beta4 expression. These 1,25(OH)(2)D(3) effects were significantly attenuated in cells with suppressed PTHrP expression. 1,25(OH)(2)D(3) regulates PTHrP expression via a negative vitamin D response element (nVDRE) within the noncoding region of the PTHrP gene. The effects of 1,25(OH)(2)D(3) on cell proliferation and integrin alpha6beta4 expression were significantly attenuated in cells overexpressing PTHrP (-36 to +139), which lacks the nVDRE. These findings suggest that one of the pathways via which 1,25(OH)(2)D(3) exerts its anti-proliferative effects is through down-regulation of PTHrP expression.

Proteases as modulators of tumor-stromal interaction: primary tumors to bone metastases

As cells undergo oncogenic transformation and as malignant cells arrive at metastatic sites, a complex interplay occurs with the surrounding stroma. This dialogue between the tumor and stroma ultimately dictates the success of the tumor cells in the given microenvironment. As a result, understanding the molecular mechanisms at work is important for developing new therapeutic modalities. Proteases are major players in the interaction between tumor and stroma. This review will focus on the role of proteases in modulating tumor-stromal interactions of both primary breast and prostate tumors as well as at bone metastatic sites in a way that favors tumor growth.

The role of tumor microenvironment in prostate cancer bone metastasis

Prostate cancer (PCa) epithelial cells require a number of factors to facilitate their establishment and growth at a distant site of metastasis. Their ability to adapt to their microenvironment, proliferate and recruit an underlying stroma is integral to the survival and growth of the metastasis. PCa predominantly metastasizes to the bone, and bone metastases are the main cause of morbidity. The bone marrow provides a permissive environment for the formation of a metastasis. In some cases, the cells may remain dormant for some time, eventually proliferating in response to an unknown "trigger." The marrow is rich in progenitor cells that differentiate into numerous cell types, producing new blood vessels, supporting fibroblasts, and an underlying extracellular matrix (ECM) that form the reactive stroma. By secreting a number of cytokines, growth factors and proteases they recruit auxiliary cells required to produce a functional stroma. These components are involved in a reciprocal interaction between the stroma and the PCa cells, allowing for the growth and survival of the tumor. Left unchecked, once a PCa tumor has established itself in the bone marrow it will eventually replace the marrow, interrupting bone homeostasis and typically promoting an osteoblastic response in the bone including osteoclastic events. The abundant deposition of new woven bone results in nerve compression, bone pain and an increase in fractures in patients with PCa bone metastases. This review will examine the tumor microenvironment, its role in facilitating tumor dissemination, growth and the resultant pathologies associated with PCa bone metastasis.

Targeting factors involved in bone remodeling as treatment strategies in prostate cancer bone metastasis

Prostate cancer is the most commonly diagnosed cancer in men within the western world and the third leading cause of cancer-related deaths. Even if the cancer is considered localized to the prostate, there is a 15% to 20% incidence of subsequent metastatic disease. Prostate cancer has a very high proclivity for metastasizing to bone, with approximately 90% of men with advanced disease having skeletal lesions. The prostate cancer metastases are characteristically osteoblastic, with extensive new bone deposition, unlike other tumors that metastasize to bone and cause an osteolytic response reflective of bone degradation. There are a considerable number of studies relating to inhibition of the osteoblastic response, including interference with endothelin-1, bone morphogenetic proteins, and Wnt signaling pathways. Within the past few years, several studies showed that increased osteolytic activity also occurs in the background of the prostate cancer skeletal metastases. Because growth factors are being released from the bone matrix during degradation, it suggests that inhibition of osteolysis might be effective in slowing tumor growth. Several strategies are being developed and applied to affect directly the osteolytic events, including use of bisphosphonates and targeting the critical biological regulators of osteoclastogenesis, receptor activator of nuclear factor-kappaB and receptor activator of nuclear factor-kappaB ligand. This review focuses on several of the clinical and preclinical strategies to inhibit the growth of prostate cancer cells in bone and to alleviate the multitude of associated skeletal-related events.

Mechanisms of disease: roles of OPG, RANKL and RANK in the pathophysiology of skeletal metastasis

The discovery of osteoprotegerin, receptor activator of nuclear factor kappa B (RANK) and RANK ligand as critical molecular determinants of osteoclastogenesis and regulators of bone resorption, has revolutionized our understanding of the processes of normal and pathological bone biology. Altering the relative biological availabilities of these molecules has direct consequences for the regulation of both bone resorption and bone remodeling. Importantly, recent research suggests a pivotal role for these molecules in mediating cancer-induced bone destruction. This review summarizes the current evidence of osteoprotegerin, RANK ligand and RANK involvement in the pathophysiology of skeletal metastasis, and of therapeutic targeting of this process.

Prostate cancer cells promote osteoblastic bone metastases through Wnts

Prostate cancer produces painful osteoblastic bone metastases. Although prostate cancer cells produce numerous osteogenic factors, to date, none have been shown to mediate osteoblastic bone metastases in an in vivo model of prostate cancer. Wnts are a large family of proteins that promote bone growth. Wnt activity is antagonized by endogenous proteins including dickkopf-1 (DKK-1). We explored if prostate cancer cells mediate osteoblastic activity through Wnts using DKK-1 as a tool to modify Wnt activity. A variety of Wnt mRNAs were found to be expressed in prostate cancer cell lines and Wnt mRNA expression was increased in primary prostate cancer compared with nonneoplastic prostate tissue. In addition to expressing Wnts, PC-3 prostate cancer cells expressed the Wnt inhibitor DKK-1. To determine if DKK-1 masked Wnt-mediated osteoblastic activity in osteolytic PC-3 cells, the cells were stably transfected with DKK-1 short hairpin RNA. Decreasing DKK-1 enabled PC-3 cells to induce osteoblastic activity, including alkaline phosphatase production and mineralization, in murine bone marrow stromal cells indicating that DKK-1 blocked Wnt-mediated osteoblastic activity in PC-3 cells. Another prostate cancer cell line, C4-2B, induces mixed osteoblastic/osteolytic lesions. To determine if Wnts contribute to C4-2B's ability to induce mixed osteoblastic/osteolytic lesions, C4-2B cells were stably transfected with either empty vector or DKK-1 expression vector to block Wnt activity. The cells were then injected in the tibiae of mice and allowed to grow for 12 weeks. Blocking Wnt activity converted the C4-2B cells to a highly osteolytic tumor. Taken together, these data show that Wnts contribute to the mechanism through which prostate cancer induces osteoblastic activity.