Therapeutic Targeting of CD146/MCAM Reduces Bone Metastasis in Prostate Cancer

Prostate Cancer is the most common cancer and the second leading cause of cancer-related death in males. When prostate cancer acquires castration resistance, incurable metastases, primarily in the bone, occur. The aim of this study is to test the applicability of targeting melanoma cell adhesion molecule (MCAM; CD146) with a mAb for the treatment of lytic prostate cancer bone metastasis. We evaluated the effect of targeting MCAM using in vivo preclinical bone metastasis models and an in vitro bone niche coculture system. We utilized FACS, cell proliferation assays, and gene expression profiling to study the phenotype and function of MCAM knockdown in vitro and in vivo. To demonstrate the impact of MCAM targeting and therapeutic applicability, we employed an anti-MCAM mAb in vivo. MCAM is elevated in prostate cancer metastases resistant to androgen ablation. Treatment with DHT showed MCAM upregulation upon castration. We investigated the function of MCAM in a direct coculture model of human prostate cancer cells with human osteoblasts and found that there is a reduced influence of human osteoblasts on human prostate cancer cells in which MCAM has been knocked down. Furthermore, we observed a strongly reduced formation of osteolytic lesions upon bone inoculation of MCAM-depleted human prostate cancer cells in animal model of prostate cancer bone metastasis. This phenotype is supported by RNA sequencing (RNA-seq) analysis. Importantly, in vivo administration of an anti-MCAM human mAb reduced the tumor growth and lytic lesions. These results highlight the functional role for MCAM in the development of lytic bone metastasis and suggest that MCAM is a potential therapeutic target in prostate cancer bone metastasis. IMPLICATIONS: This study highlights the functional application of an anti-MCAM mAb to target prostate cancer bone metastasis.

Osteolytic cancer cells induce vascular/axon guidance processes in the bone/bone marrow stroma

Prostate and breast cancers frequently metastasize to bone. The physiological bone homeostasis is perturbed once cancer cells proliferate at the bone metastatic site. Tumors are complex structures consisting of cancer cells and numerous stroma cells.

In this study, we show that osteolytic cancer cells (PC-3 and MDA-MB231) induce transcriptome changes in the bone/bone marrow microenvironment (stroma). This stroma transcriptome differs from the previously reported stroma transcriptome of osteoinductive cancer cells (VCaP). While the biological process “angiogenesis/vasculogenesis” is enriched in both transcriptomes, the “vascular/axon guidance” process is a unique process that characterizes the osteolytic stroma. In osteolytic bone metastasis, angiogenesis is denoted by vessel morphology and marker expression specific for arteries/arterioles. Interestingly, intra-tumoral neurite-like structures were in proximity to arteries. Additionally, we found that increased numbers of mesenchymal stem cells and vascular smooth muscle cells, expressing osteolytic cytokines and inhibitors of bone formation, contribute to the osteolytic bone phenotype.

Osteoinductive and osteolytic cancer cells induce different types of vessels, representing functionally different hematopoietic stem cell niches. This finding suggests different growth requirements of osteolytic and osteoinductive cancer cells and the need for a differential anti-angiogenic strategy to inhibit tumor growth in osteolytic and osteoblastic bone metastasis.

Abstract 4344: Cd146 modulates the malignant phenotype in human prostate cancer

Prostate Cancer (PCa) is the most frequent cancer in males and the second leading cause of death from cancer in men. When PCa progress from androgen-responsive to castration resistance, the formation of incurable metastases, mainly in the bone, is almost inevitable. Therefore, understanding the factors that regulate homing and survival of metastatic cancer cells in the bone is important for the identification of new therapeutic targets. High CD146 expression has been measured in the stroma of lytic and blastic lesions in preclinical models of PCa bone metastasis. The objective of this study is to characterize the role of CD146 in the maintenance of the aggressive and invasive phenotype in human PCa. We used shRNAs to knockdown the expression of CD146 in the lytic PC-3M-Pro4Luc2dTomato and in the blastic C4-2BdTomato PCa cell lines. We validated the knockdown at protein level and tested the effect with functional assays such as migration, proliferation. We used RT-qPCR to test CD146 knockdown on EMT markers. We measured the effect of the knockdown on the maintenance of cancer stem/progenitor-like cells by ALDEFLUOR assay. CD146 knockdown reduced proliferation in PC-3M-Pro4Luc2dTomato PCa cells and resulted in increased E-Cadherin expression. Conversely, no effect on proliferation was measured on C4-2BdTomato cells. It has been described that metastatic human PCa cells target the hematopoietic stem cell (HSC) niche in the bone marrow at the level of an “endosteal/osteoblast” niche and a “vascular/perivascular” niche. We optimized an in vitro model of “osteoblast niche” to study the behavior of prostate cancer cells upon co-culture with osteoblasts and to measure the resulting effects on cancer stem/progenitor-like markers. Our results showed that CD146 is required for the osteoblast-mediated induction of ALDH activity on PCa cells and CD146 knockdown prevented the increase in the size of the ALDHhigh subpopulation in the tumor cells, mediated by human osteoblasts. Additionally, CD146 knockdown in PCa cells co-cultured with osteoblast, reduced the amount of CD146 expressed by osteoblasts compared to non-targeted control. Finally, we showed that CD146 is significantly increased in the highly metastatic ALDHhigh cells and identified a new subset of ALDHhigh / CD146high cells which could be depleted upon CD146 knockdown. In Conclusion, we detected a novel subset of ALDHhigh/CD146high cells and found that CD146 influences the maintenance of an aggressive-mesenchymal phenotype in human PCa. Therefore, CD146 represents a promising molecule to modulate the behavior of aggressive PCa cells.

Note: This abstract was not presented at the meeting.

Citation Format: Eugenio Zoni, Letizia Astrologo, Janine Melsen, Sofia Karkampouna, Irena Klima, Joël Grosjean, Peter C. Gray, Gabri van der Pluijm, Marco G. Cecchini, Marianna Kruithof-de Julio, George N. Thalmann. Cd146 modulates the malignant phenotype in human prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4344. doi:10.1158/1538-7445.AM2017-4344

The molecular signature of the stroma response in prostate cancer-induced osteoblastic bone metastasis highlights expansion of hematopoietic and prostate epithelial stem cell niches

The reciprocal interaction between cancer cells and the tissue-specific stroma is critical for primary and metastatic tumor growth progression. Prostate cancer cells colonize preferentially bone (osteotropism), where they alter the physiological balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption, and elicit prevalently an osteoblastic response (osteoinduction). The molecular cues provided by osteoblasts for the survival and growth of bone metastatic prostate cancer cells are largely unknown. We exploited the sufficient divergence between human and mouse RNA sequences together with redefinition of highly species-specific gene arrays by computer-aided and experimental exclusion of cross-hybridizing oligonucleotide probes. This strategy allowed the dissection of the stroma (mouse) from the cancer cell (human) transcriptome in bone metastasis xenograft models of human osteoinductive prostate cancer cells (VCaP and C4-2B). As a result, we generated the osteoblastic bone metastasis-associated stroma transcriptome (OB-BMST). Subtraction of genes shared by inflammation, wound healing and desmoplastic responses, and by the tissue type-independent stroma responses to a variety of non-osteotropic and osteotropic primary cancers generated a curated gene signature ("Core" OB-BMST) putatively representing the bone marrow/bone-specific stroma response to prostate cancer-induced, osteoblastic bone metastasis. The expression pattern of three representative Core OB-BMST genes (PTN, EPHA3 and FSCN1) seems to confirm the bone specificity of this response. A robust induction of genes involved in osteogenesis and angiogenesis dominates both the OB-BMST and Core OB-BMST. This translates in an amplification of hematopoietic and, remarkably, prostate epithelial stem cell niche components that may function as a self-reinforcing bone metastatic niche providing a growth support specific for osteoinductive prostate cancer cells. The induction of this combinatorial stem cell niche is a novel mechanism that may also explain cancer cell osteotropism and local interference with hematopoiesis (myelophthisis). Accordingly, these stem cell niche components may represent innovative therapeutic targets and/or serum biomarkers in osteoblastic bone metastasis.

Characterization and clinical relevance of ALDHbright populations in prostate cancer

PURPOSE

High aldehyde dehydrogenase (ALDH) has been suggested to selectively mark cells with high tumorigenic potential in established prostate cancer cell lines. However, the existence of cells with high ALDH activity (ALDH(bright)) in primary prostate cancer specimens has not been shown so far. We investigated the presence, phenotype, and clinical significance of ALDH(bright) populations in clinical prostate cancer specimens.

EXPERIMENTAL DESIGN

We used ALDEFLUOR technology and fluorescence-activated cell-sorting (FACS) staining to identify and characterize ALDH(bright) populations in cells freshly isolated from clinical prostate cancer specimens. Expression of genes encoding ALDH-specific isoforms was evaluated by quantitative real-time PCR in normal prostate, benign prostatic hyperplasia (BPH), and prostate cancer tissues. ALDH1A1-specific expression and prognostic significance were assessed by staining two tissue microarrays that included more than 500 samples of BPH, prostatic intraepithelial neoplasia (PIN), and multistage prostate cancer.

RESULTS

ALDH(bright) cells were detectable in freshly excised prostate cancer specimens (n = 39) and were mainly included within the EpCAM((+)) and Trop2((+)) cell populations. Although several ALDH isoforms were expressed to high extents in prostate cancer, only ALDH1A1 gene expression significantly correlated with ALDH activity (P < 0.01) and was increased in cancers with high Gleason scores (P = 0.03). Most importantly, ALDH1A1 protein was expressed significantly more frequently and at higher levels in advanced-stage than in low-stage prostate cancer and BPH. Notably, ALDH1A1 positivity was associated with poor survival (P = 0.02) in hormone-naïve patients.

CONCLUSIONS

Our data indicate that ALDH contributes to the identification of subsets of prostate cancer cells of potentially high clinical relevance.

Stem-like cells with luminal progenitor phenotype survive castration in human prostate cancer

Castration is the standard therapy for advanced prostate cancer (PC). Although this treatment is initially effective, tumors invariably relapse as incurable, castration-resistant PC (CRPC). Adaptation of androgen-dependent PC cells to an androgen-depleted environment or selection of pre-existing, CRPC cells have been proposed as mechanisms of CRPC development. Stem cell (SC)-like PC cells have been implicated not only as tumor initiating/maintaining in PC but also as tumor-reinitiating cells in CRPC. Recently, castration-resistant cells expressing the NK3 homeobox 1 (Nkx3-1) (CARNs), the other luminal markers cytokeratin 18 (CK18) and androgen receptor (AR), and possessing SC properties, have been found in castrated mouse prostate and proposed as the cell-of-origin of CRPC. However, the human counterpart of CARNs has not been identified yet. Here, we demonstrate that in the human PC xenograft BM18, pre-existing SC-like and neuroendocrine (NE) PC cells are selected by castration and survive as totally quiescent. SC-like BM18 cells, displaying the SC markers aldehyde dehydrogenase 1A1 or NANOG, coexpress the luminal markers NKX3-1, CK18, and a low level of AR (AR(low)) but not basal or NE markers. These CR luminal SC-like cells, but not NE cells, reinitiate BM18 tumor growth after androgen replacement. The AR(low) seems to mediate directly both castration survival and tumor reinitiation. This study identifies for the first time in human PC SC-/CARN-like cells that may represent the cell-of-origin of tumor reinitiation as CRPC. This finding will be fundamental for refining the hierarchy among human PC cancer cells and may have important clinical implications.

High NRBP1 expression in prostate cancer is linked with poor clinical outcomes and increased cancer cell growth

BACKGROUND

We recently established the rationale that NRBP1 (nuclear receptor binding protein 1) has a potential growth-promoting role in cell biology. NRBP1 interacts directly with TSC-22, a potential tumor suppressor gene that is differently expressed in prostate cancer. Consequently, we analyzed the role of NRBP1 expression in prostate cancer cell lines and its expression on prostate cancer tissue microarrays (TMA).

METHODS

The effect of NRBP1 expression on tumor cell growth was analyzed by using RNAi. NRBP1 protein expression was evaluated on two TMAs containing prostate samples from more than 1,000 patients. Associations with clinico-pathological features, the proliferation marker Ki67 and survival data were analyzed.

RESULTS

RNAi mediated silencing of NRBP1 expression in prostate cancer cell lines resulted in reduced cell growth (P < 0.05). TMA analysis revealed NRBP1 protein expression in benign prostate hyperplasia in 6% as compared to 60% in both, high-grade intraepithelial neoplasia and prostate cancer samples. Strong NRBP1 protein expression was restricted to prostate cancer and correlated with higher expression of the proliferation marker Ki67 (P < 0.05). Further, patients with strong NRBP1 protein expression showed poor clinical outcomes (P < 0.05). Analysis of matched localized cancer tissues before and after castration revealed that post-therapy-related repression of NRBP1 expression was significantly associated with better overall survival.

CONCLUSIONS

We demonstrate that expression of NRBP1 is up-regulated during the progression of prostate cancer and that high NRBP1 expression is linked with poor prognosis and enhanced tumor cell growth.

Diagnostic microchip to assay 3D colony-growth potential of captured circulating tumor cells

Microfluidic technology has been successfully applied to isolate very rare tumor-derived epithelial cells (circulating tumor cells, CTCs) from blood with relatively high yield and purity, opening up exciting prospects for early detection of cancer. However, a major limitation of state-of-the-art CTC-chips is their inability to characterize the behavior and function of captured CTCs, for example to obtain information on proliferative and invasive properties or, ultimately, tumor re-initiating potential. Although CTCs can be efficiently immunostained with markers reporting phenotype or fate (e.g. apoptosis, proliferation), it has not yet been possible to reliably grow captured CTCs over long periods of time and at single cell level. It is challenging to remove CTCs from a microchip after capture, therefore such analyses should ideally be performed directly on-chip. To address this challenge, we merged CTC capture with three-dimensional (3D) tumor cell culture on the same microfluidic platform. PC3 prostate cancer cells were isolated from spiked blood on a transparent PDMS CTC-chip, encapsulated on-chip in a biomimetic hydrogel matrix (QGel™) that was formed in situ, and their clonal 3D spheroid growth potential was assessed by microscopy over one week in culture. The possibility to clonally expand a subset of captured CTCs in a near-physiological in vitro model adds an important element to the expanding CTC-chip toolbox that ultimately should improve prediction of treatment responses and disease progression.

Antagonistic TSC22D1 variants control BRAF(E600)-induced senescence

Oncogene-induced cellular senescence (OIS) is an increasingly recognized tumour suppressor mechanism that confines the outgrowth of neoplastic cells in vivo. It relies on a complex signalling network, but only few components have been identified so far. Gene-expression profiling revealed a >100-fold increase in the levels of the transcription factor and putative tumour suppressor gene TGFβ-stimulated clone 22 (TSC22D1) in BRAF(E600)-induced senescence, in both human fibroblasts and melanocytes. Only the short TSC22D1 transcript was upregulated, whereas the abundance of the large protein variant was suppressed by proteasomal degradation. The TSC22D1 protein variants, in complex with their dimerization partner TSC22 homologue gene 1 (THG1), exerted opposing functions, as selective depletion of the short form, or conversely, overexpression of the large variant, resulted in abrogation of OIS. This was accompanied by the suppression of several inflammatory factors and p15(INK4B), with TSC22D1 acting as a critical effector of C/EBPβ. Our results demonstrate that the differential regulation of antagonistic TSC22D1 variants is required for the establishment of OIS and suggest distinct contributions of TSC22 family members to the progression of BRAF(E600)-driven neoplasia.

The role of the BMP signaling antagonist noggin in the development of prostate cancer osteolytic bone metastasis

Members of the BMP and Wnt protein families play a relevant role in physiologic and pathologic bone turnover. Extracellular antagonists are crucial for the modulation of their activity. Lack of expression of the BMP antagonist noggin by osteoinductive, carcinoma-derived cell lines is a determinant of the osteoblast response induced by their bone metastases. In contrast, osteolytic, carcinoma-derived cell lines express noggin constitutively. We hypothesized that cancer cell-derived noggin may contribute to the pathogenesis of osteolytic bone metastasis of solid cancers by repressing bone formation. Intra-osseous xenografts of PC-3 prostate cancer cells induced osteolytic lesions characterized not only by enhanced osteoclast-mediated bone resorption, but also by decreased osteoblast-mediated bone formation. Therefore, in this model, uncoupling of the bone remodeling process contributes to osteolysis. Bone formation was preserved in the osteolytic lesions induced by noggin-silenced PC-3 cells, suggesting that cancer cell-derived noggin interferes with physiologic bone coupling. Furthermore, intra-osseous tumor growth of noggin-silenced PC-3 cells was limited, most probably as a result of the persisting osteoblast activity. This investigation provides new evidence for a model of osteolytic bone metastasis where constitutive secretion of noggin by cancer cells mediates inhibition of bone formation, thereby preventing repair of osteolytic lesions generated by an excess of osteoclast-mediated bone resorption. Therefore, noggin suppression may be a novel strategy for the treatment of osteolytic bone metastases.

High aldehyde dehydrogenase activity identifies tumor-initiating and metastasis-initiating cells in human prostate cancer

Metastatic progression of advanced prostate cancer is a major clinical problem. Identifying the cell(s) of origin in prostate cancer and its distant metastases may permit the development of more effective treatment and preventive therapies. In this study, aldehyde dehydrogenase (ALDH) activity was used as a basis to isolate and compare subpopulations of primary human prostate cancer cells and cell lines. ALDH-high prostate cancer cells displayed strongly elevated clonogenicity and migratory behavior in vitro. More strikingly, ALDH-high cells readily formed distant metastases with strongly enhanced tumor progression at both orthotopic and metastatic sites in preclinical models. Several ALDH isoforms were expressed in human prostate cancer cells and clinical specimens of primary prostate tumors with matched bone metastases. Our findings suggest that ALDH-based viable cell sorting can be used to identify and characterize tumor-initiating and, more importantly perhaps, metastasis-initiating cells in human prostate cancer.

Abstract 470: The homing of prostate cancer to bone in vivo is modulated by Zoledronic acid

Cancer metastasis to the skeleton is a major problem with prostate cancer and requires the development of specialised approaches to treatment. Zoledronic acid, a bone resorptive agent, is currently the only bisphosphonate with proven benefit in prostate cancer. However, there is minimal research investigating whether Zoledronic acid modulates the early mechanisms involved in metastasis. The aim of this study is to determine whether different treatment regimes using Zoledronic acid modulate the early events in tumour/bone interactions.

Metatarsals from newborn mice (1-3 day old) are engrafted into a Dorsal Skinfold Chamber (DSC) implanted on a SCID mouse (5-6 weeks old). Prostate (PC3-GFP) cancer cells (1 × 105) are then injected via the heart (i.c) to simulate micrometastatic spread (n=20/group). Animals are treated with either i) weekly s.c injection of Zoledronic acid (25µg/kg/inection=100μg/kg in total) or saline or ii) single s.c injection of Zoledronic acid (100μg/kg) or saline for the 4 week study duration. The groups are further subdivided, so half of the animals receive treatment either before or after injection of tumour cells. Recordings of the chamber tissue and metatarsal are made at 48hr intervals for the duration of the experiment for the presence of PC3-GFP cells within the metatarsal. At the end of the study, tissue is harvested and processed for microCT, multi-photon analysis and histology.TreatmentNumber of PC3-GFP cells homing to metatarsalDay 3Day 9Day 15 Weekly treatment before PC3-GFP cells1.1 ± 0.1*1.3 ± 0.2*2.1 ± 0.3*Weekly treatment after PC3-GFP cells3.2 ± 0.5*3.4 ± 0.8*4.4 ± 0.7*Single treatment before PC3-GFP cells1.7 ± 0.3*8.9 ± 0.9*13.6 ± 0.8Control3.2 ± 0.714.7 ± 1.015.9 ± 1.4

Table 1. Number of PC3-GFP cells present in metatarsal after i.c. injection (*p&lt;0.05 compared to control).

Treatment with Zoledronic acid reduces tumour cell homing to bone. Weekly treatment of Zoledronic acid prior to prostate cancer cell administration reduces homing to bone to a greater extent than the other treatment regimes test.

Funded by Sixth European Framework Programme (PROMET).

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 470.

In vitro propagation and characterization of neoplastic stem/progenitor-like cells from human prostate cancer tissue

BACKGROUND

According to the cancer stem cell hypothesis, tumor growth is sustained by a subpopulation of cancer stem/progenitor-like cells. Self-renewal and high clonogenic potential are characteristics shared by normal stem and neoplastic stem/progenitor-like cells. We investigated whether human prostate cancer specimens contain cells with these properties.

METHODS

Self-renewal and clonogenic potential were assessed by serial passaging of spheres and colony formation, respectively. Gene expression was analyzed by real time PCR. Protein expression was detected by immunocytochemistry. The neoplastic nature of the cells was verified by detection of the TMPRSS2/ERG gene fusion expression.

RESULTS

The epithelial fraction isolated from surgical specimens generated colonies in 68% (19/28) of the patients. Laminin adhesion selected for cells with high clonogenic potential. The epithelial fraction from 85% (42/49) of the patients generated primary prostaspheres. Serial passaging of prostaspheres demonstrated their self-renewal capacity, which is also supported by their expression of the stem cell markers Oct-4, Nanog, Bmi-1, and Jagged-1 mRNA. Cells derived from prostaspheres were more clonogenic than the parental epithelial fraction. The pattern of mRNA expression in prostaspheres resembled that of the basal compartment of the prostate (CK5(+)/CK14(+)/CK19(high)/CK18(-/low)/c-met(+)/AR(-/low)/PSA(-/low)), but also included stem cell markers (CD49b(+)/CD49f(+)/CD44(+)/DeltaNp63(+)/Nestin(+)/CD133(+)). The distribution of marker expression in prostaspheres suggests their heterogeneous cell composition. Prostaspheres expressed significantly higher PSCA mRNA levels than the epithelial fraction.

CONCLUSION

Human prostate cancer specimens contain neoplastic cells with self-renewal and clonogenic potential, which can be enriched and perpetuated in prostaspheres. Prostaspheres should prove valuable for the identification of prostate cancer stem/progenitor-like cells.

Potential role of pre-existing blood vessels for vascularization and mineralization of osteochondral graftsAn intravital microscopic study in mice

BACKGROUND

The aim of this study was to develop an experimental model that allows to elude the potential role of the preexisting graft microvasculature for vascularization and mineralization of osteochondral grafts.

ANIMALS AND METHODS

For that purpose, the II-IV metatarsals of fetal DDY-mice known to be nonvascularized at day 16 of gestation (M16) but vascularized at day 18 (M18) were freshly transplanted into dorsal skin fold chambers of adult DDY mice. Using intravital microscopy angiogenesis, leukocyte-endothelium interaction and mineralization were assessed for 12 days.

RESULTS

Angiogenesis occurred at 32 hours in M18, but not before 57 hours in M16 (p = 0.002), with perfusion of these vessels at 42 hours (p = 0.005) and 65 hours (p = 0.1), respectively. Vessels reached a density three times as high as that of the recipient site at day 6, remaining constant until day 12 in M18, whereas in M16 vascular density increased from day 6 and reached that of M18 at day 12 (p = 0.04). Leukocyte-endothelium interaction showed sticker counts elevated by a factor of 4-5 in M18 as compared to M16. Mineralization of osteochondral grafts did not differ between M16 and M18, which significantly increased in both groups throughout the observation period.

INTERPRETATION

We propose the faster kinetics in the angiogenic response to M18 and the elevated counts of sticking leukocytes to rest on the potential of establishing end-to-end anastomoses (inosculation) of the vascularized graft with recipient vessels.

Loss of inhibition over master pathways of bone mass regulation results in osteosclerotic bone metastases in prostate cancer

Prostate cancer is the most common cancer among men in industrialised countries. Most patients with prostate cancer, however, will not die of it. As a result, many of them will experience symptomatic metastasis during the course of the disease. Prostate cancer has a high propensity to metastasize to bone. Unlike many other cancers prostate cancer cells induce a rather osteosclerotic than osteolytic reaction in the bone marrow by interfering with physiological bone remodelling. A proper understanding of the mechanisms of tumour cell-induced bone alterations and exaggerated bone deposition in prostate cancer may open new and urgently needed therapeutic approaches in the field of palliative care for affected patients. In this review we focus on the central role of two major regulators of bone mass, the wingless type integration site family members (WNTs) and the bone morphogenetic proteins (BMPs), in the development of osteosclerotic bone metastases.

Agents used for chemoprevention of prostate cancer may influence PSA secretion independently of cell growth in the LNCaP model of human prostate cancer progression

BACKGROUND

The aim of this study was to evaluate the inhibitory growth effects of different potential chemopreventive agents in vitro and to determine their influence on PSA mRNA and protein expression with an established screening platform.

METHODS

LNCaP and C4-2 cells were incubated with genistein, seleno-L-methionine, lycopene, DL-alpha-tocopherol, and trans-beta-carotene at three different concentrations and cell growth was determined by the MTT assay. PSA mRNA expression was assessed by quantitative real-time RT-PCR and secreted PSA protein levels were quantified by the microparticle enzyme immunoassay.

RESULTS

Genistein, seleno-l-methionine and lycopene inhibited LNCaP cell growth, and the proliferation of C4-2 cells was suppressed by seleno-L-methionine and lycopene. PSA mRNA expression was downregulated by genistein in LNCaP but not C4-2 cells. No other compound tested altered PSA mRNA expression. PSA protein expression was downregulated by genistein, seleno-L-methionine, DL-alpha-tocopherol in LNCaP cells. In C4-2 cells only genistein significantly reduced the secretion of PSA protein.

CONCLUSIONS

In the LNCaP progression model PSA expression depends on the compound, its concentration and on the hormonal dependence of the cell line used and does not necessarily reflect cell growth or death. Before potential substances are evaluated in clinical trials using PSA as a surrogate end point marker, their effect on PSA mRNA and protein expression has to be considered to correctly assess treatment response by PSA.

Bone Morphogenetic Protein 7 in the Development and Treatment of Bone Metastases from Breast Cancer

Bone morphogenetic protein 7 (BMP7) counteracts the physiological epithelial-to-mesenchymal transition (EMT), a process that is indicative of epithelial plasticity. Because EMT is involved in cancer, we investigated whether BMP7 plays a role in breast cancer growth and metastasis. In this study, we show that decreased BMP7 expression in primary breast cancer is significantly associated with the formation of clinically overt bone metastases in patients with > or = 10 years of follow-up. In line with these clinical observations, BMP7 expression is inversely related to tumorigenicity and invasive behavior of human breast cancer cell lines. Moreover, BMP7 decreased the expression of vimentin, a mesenchymal marker associated with invasiveness and poor prognosis, in human MDA-MB-231 (MDA-231)-B/Luc(+) breast cancer cells under basal and transforming growth factor-beta (TGF-beta)-stimulated conditions. In addition, exogenous addition of BMP7 to TGF-beta-stimulated MDA-231 cells inhibited Smad-mediated TGF-beta signaling. Furthermore, in a well-established bone metastasis model using whole-body bioluminescent reporter imaging, stable overexpression of BMP7 in MDA-231 cells inhibited de novo formation and progression of osteolytic bone metastases and, hence, their metastatic capability. In line with these observations, daily i.v. administration of BMP7 (100 mug/kg/d) significantly inhibited orthotopic and intrabone growth of MDA-231-B/Luc(+) cells in nude mice. Our data suggest that decreased BMP7 expression during carcinogenesis in the human breast contributes to the acquisition of a bone metastatic phenotype. Because exogenous BMP7 can still counteract the breast cancer growth at the primary site and in bone, BMP7 may represent a novel therapeutic molecule for repression of local and bone metastatic growth of breast cancer.

BMP7, a putative regulator of epithelial homeostasis in the human prostate, is a potent inhibitor of prostate cancer bone metastasis in vivo

Bone morphogenic protein 7 (BMP7) counteracts physiological epithelial-to-mesenchymal transition, a process that is indicative of epithelial plasticity. Because epithelial-to-mesenchymal transition is involved in cancer, we investigated whether BMP7 plays a role in prostate cancer growth and metastasis. BMP7 expression in laser-microdissected primary human prostate cancer tissue was strongly down-regulated compared with normal prostate luminal epithelium. Furthermore, BMP7 expression in prostate cancer cell lines was inversely related to tumorigenic and metastatic potential in vivo and significantly correlated to E-cadherin/vimentin ratios. Exogenous addition of BMP7 to human prostate cancer cells dose-dependently inhibited transforming growth factor beta-induced activation of nuclear Smad3/4 complexes via ALK5 and induced E-cadherin expression. Moreover, BMP7-induced activation of nuclear Smad1/4/5 signaling transduced via BMP type I receptors was synergistically stimulated in the presence of transforming growth factor beta, a growth factor that is enriched in the bone microenvironment. Daily BMP7 administration to nude mice inhibited the growth of cancer cells in bone. In contrast, no significant growth inhibitory effect of BMP7 was observed in intraprostatic xenografts. Collectively, our observations suggest that BMP7 controls and preserves the epithelial phenotype in the human prostate and underscore a decisive role of the tumor microenvironment in mediating the therapeutic response of BMP7. Thus, BMP7 can still counteract the epithelial-to-mesenchymal transition process in the metastatic tumor, positioning BMP7 as a novel therapeutic molecule for treatment of metastatic bone disease.

Lack of noggin expression by cancer cells is a determinant of the osteoblast response in bone metastases

Prostate and mammary cancer bone metastases can be osteoblastic or osteolytic, but the mechanisms determining these features are unclear. Bone morphogenetic and Wnt proteins are osteoinductive molecules. Their activity is modulated by antagonists such as noggin and dickkopf-1. Differential expression analysis of bone morphogenetic and Wnt protein antagonists in human prostate and mammary cancer cell lines showed that osteolytic cell lines constitutively express in vitro noggin and dickkopf-1 and at least one of the osteolytic cytokines parathyroid hormone-related protein, colony-stimulating factor-1, and interleukin-8. In contrast, osteoinductive cell lines express neither noggin nor dickkopf-1 nor osteolytic cytokines in vitro. The noggin differential expression profile observed in vitro was confirmed in vivo in prostate cancer cell lines xenografted into bone and in clinical samples of bone metastasis. Forced noggin expression in an osteoinductive prostate cancer cell line abolished the osteoblast response induced in vivo by its intraosseous xenografts. Basal bone resorption and tumor growth kinetics were marginally affected. Lack of noggin and possibly dickkopf-1 expression by cancer cells may be a relevant mechanism contributing to the osteoblast response in bone metastases. Concomitant lack of osteolytic cytokines may be permissive of this effect. Noggin is a candidate drug for the adjuvant therapy of bone metastasis.

Prostate specific antigen expression does not necessarily correlate with prostate cancer cell growth

PURPOSE

The antiproliferative effects of pharmacological agents used for androgen ablative therapy in prostate cancer, including goserelin, bicalutamide and cyproterone acetate (Fluka Chemie, Buchs, Switzerland), were tested in vitro. It was determined whether they affected prostate specific antigen mRNA and protein expression independent of growth inhibition.

MATERIALS AND METHODS

Goserelin, bicalutamide (AstraZeneca, Zug, Switzerland) and cyproterone acetate were added to prostate specific antigen expressing, androgen dependent LNCaP and androgen independent C4-2 cell line (Urocor, Oklahoma City, Oklahoma) cultures. Proliferation was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay (Roche, Mannheim, Germany). Prostate specific antigen mRNA expression was assessed by quantitative real-time polymerase chain reaction. Secreted prostate specific antigen protein levels were quantified by microparticle enzyme-immunoassay.

RESULTS

Goserelin inhibited cell growth and prostate specific antigen protein secretion in LNCaP and C4-2 cells. Prostate specific antigen mRNA expression was not decreased. Bicalutamide did not affect cell growth or prostate specific antigen mRNA expression in LNCaP or C4-2 cells, although it significantly decreased prostate specific antigen protein secretion in LNCaP and to a lesser extent in C4-2 cells. Cyproterone acetate decreased the growth of C4-2 but not of LNCaP cells. It did not affect prostate specific antigen mRNA or protein expression in either cell line.

CONCLUSIONS

Prostate specific antigen expression does not necessarily correlate with cell growth. Without a substantial effect on cell growth bicalutamide lowers prostate specific antigen synthesis, whereas cyproterone acetate decreases cell growth with no effect on prostate specific antigen secretion. Prostate specific antigen expression may be influenced by growth inhibition but also by altered mRNA and protein levels depending on the agent, its concentration and the cell line evaluated. For interpreting clinical trials prostate specific antigen is not necessarily a surrogate end point marker for a treatment effect on prostate cancer cell growth.

Differential expression of TGFbeta-stimulated clone 22 in normal prostate and prostate cancer

The transforming growth factor-beta (TGFbeta) superfamily and its downstream effector genes are key regulators of epithelial homeostasis. Altered expression of these genes may be associated with malignant transformation of the prostate gland. The cDNA array analysis of differential expression of the TGFbeta superfamily and functionally related genes between patient-matched noncancerous prostate (NP) and prostate cancer (PC) bulk tissue specimens highlighted two genes, namely TGFbeta-stimulated clone-22 (TSC-22) and Id4. Verification of their mRNA expression by real-time PCR in patient-matched NP and PC bulk tissue, in laser-captured pure epithelial and cancer cells and in NP and PC cell lines confirmed TSC-22 underexpression, but not Id4 overexpression, in PC and in human PC cell lines. Immunohistochemical analysis showed that TSC-22 protein expression in NP is restricted to the basal cells and colocalizes with the basal cell marker cytokeratin 5. In contrast, all matched PC samples lack TSC-22 immunoreactivity. Likewise, PC cell lines do not show detectable TSC-22 protein expression as shown by immunoblotting. TSC-22 should be considered as a novel basal cell marker, potentially useful for studying lineage determination within the epithelial compartment of the prostate. Conversely, lack of TSC-22 seems to be a hallmark of malignant transformation of the prostate epithelium. Accordingly, TSC-22 immunohistochemistry may prove to be a diagnostic tool for discriminating benign lesions from malignant ones of the prostate. The suggested tumour suppressor function of TSC-22 warrants further investigation on its role in prostate carcinogenesis and on the TSC-22 pathway as a candidate therapeutic target in PC.

Tissue microarray analysis of hMSH2 expression predicts outcome in men with prostate cancer

PURPOSE

Mismatch repair genes are responsible for the coordinated correction of misincorporated nucleotides formed during DNA replication. Mismatch repair expression is altered in a subset of prostate cancers (PCs) and a recent study suggested that time to biochemical recurrence following prostatectomy correlated with the degree of hMSH2 immunohistochemical staining. We compared hMSH2 expression and survival in clinically organ confined PC.

MATERIALS AND METHODS

A prostate tissue microarray was constructed using 243 specimens from patients who underwent radical prostatectomy with extended lymph node dissection for clinically organ confined PC with up to 12 years of followup. Immunohistochemistry was performed with anti-human MSH2 monoclonal antibody. Three independent observers evaluated hMSH2 expression on a scale of 0 to 4. Low expression was defined as a score of less than 2 and high expression was defined as a score of 2 or higher. Statistical analysis used the Fisher exact test, and Goodman and Kruskal gamma coefficient.

RESULTS

Higher Gleason score significantly correlated with higher hMSH2 expression (p < 0.0002). Low hMSH2 expression correlated with increased overall, disease-free and biochemical disease-free survival (all p < 0.01). Analysis comparing low vs high hMSH2 expression was significant with respect to overall (p = 0.0004), disease-free (p = 0.005) and biochemical disease-free (p = 0.0177) survival.

CONCLUSIONS

hMSH2 is differentially expressed in malignant prostate tissue and hMSH2 immunohistochemical staining intensity correlates with Gleason score, overall and disease-free survival. Taken together our results suggest that hMSH2 expression may be a useful prognostic biomarker for outcome in men with clinically organ confined PC.

Interference with the Microenvironmental Support Impairs the De novo Formation of Bone Metastases In vivo

Interference with the microenvironmental growth support is an attractive therapeutic strategy for repressing metastatic tumor growth. Bone is a highly dynamic tissue that is continuously remodeled by bone resorption and subsequent bone formation. Growth factors supporting bone metastatic growth are released especially during bone resorption. Differently from most other tissues, drugs that can limit local turnover, such as bisphosphonates, are available for bone. In the present study, we tested the hypothesis that inhibition of bone turnover can affect development and growth progression of experimental bone metastasis. Whole-body bioluminescent reporter imaging was used for the detection, monitoring, and quantification in vivo of the growth progression of bone metastases induced by intracardiac or intraosseous injection of luciferase-transfected breast cancer cells (MDA-231-B/luc+) to nude mice. Suppression of bone turnover by bisphosphonates, before bone colonization by cancer cells, inhibited by a great extent the number of developing bone metastasis. Tumor growth in the few, but still developing, bone metastases was affected only transiently. Reduction of bone turnover had no effect on growth progression of bone metastases, which were already established when bisphosphonate treatment was initiated, despite a substantial reduction in osteolysis. Therefore, cancer cells metastatic to bone, after an initial growth phase that depends on the interaction with the local stroma, become independent of microenvironmental growth factor support and progress autonomously. Inhibition of bone turnover may represent a useful adjuvant therapy especially for cancer patients at risk to develop bone metastasis.

Electroporation enhances transfection efficiency in murine cutaneous wounds

Transfection of wounds with DNA-encoding growth factors has the potential to improve healing, but current means of nonviral gene delivery are inefficient. Repeated high doses of DNA, necessary to achieve reliable gene expression, are detrimental to healing. We assessed the ability of in vivo electroporation to enhance gene expression. Full-thickness cutaneous excisional wounds were created on the dorsum of female mice. A luciferase- encoding plasmid driven by a CMV promoter was injected at the wound border. Following plasmid administration, electroporative pulses were applied to injection sites. Pulse parameters were varied over a range of voltage, duration, and number. Animals were euthanized at intervals after transfection and the luciferase activity measured. Application of electric pulses consistently increased luciferase expression. The electroporative effect was most marked at a plasmid dose of 50 micro g, where an approximate tenfold increase was seen. Six 100- micro s-duration pulses of 1750 V/cm were found to be the most effective in increasing luciferase activity. High numbers of pulses tended to be less effective than smaller numbers. This optimal electroporation regimen had no detrimental effect on wound healing. We conclude that electroporation increases the efficiency of transgene expression and may have a role in gene therapy to enhance wound healing.

Cellular interactions in the tropism of prostate cancer to bone

At autopsy >or=80% of prostate cancers have established macrometastases in marrow containing bone. The mechanism(s) to explain this remarkable level of bone involvement remain to be elucidated. We examined the adhesive and invasive behavior of prostate cancer cells to osteoblastic and human bone marrow endothelial cells (HBME-1) in an attempt to explain the tropism of prostate cells for bone. We found an inverse relationship between adhesion and prostate cell tumorigenicity and metastatic potential. Relative cell adhesion of P69 between cell lines was 1.74-fold (95% confidence interval [CI] = 1.15-2.64) and 1.58-fold (95% CI = 0.94-2.68) greater at 1 hr and 2 hr, respectively, than LNCaP that was essentially equivalent to C4-2 cells when using an osteoblastic cell line, D1 as the substrate. Similar results were acquired when HBME-1 were used as substratum. There was a marked increase in adhesion of the poorly tumorigenic cell line P69 as compared to the cancer cells to HBME-1. P69 adhesion was 2.78-fold (95% CI = 1.87-4.84) and 2.0-fold (95% CI = 1.43-2.80) greater at 1 hr and 2 hr, respectively when compared to LNCaP or C4-2 cells. D1 cells, a bone homing osteoblastic precursor, behaved contrary to the metastatic, bone-colonizing C4-2 cell line and bound best to other bone cells but not as well as a non-homing fetal bone marrow-derived cell line, D2. Invasion of prostate cancer cells through HBME-1 lawns was examined at 8 hr and 16 hr. In contrast to the adhesion studies, the invasion of the more aggressive C4-2 cells was 3.46-fold (95% CI = 1.18-10.17) and 2.65-fold (95% CI = 1.26-5.56) greater at 8 hr and 16 hr, respectively than LNCaP cells. Similarly, LNCaP cell invasion was 1.73-fold (95% CI = 0.69-4.37) and 2.35-fold (95% CI = 1.41-3.93) greater at 8 hr and 16 hr, respectively than P69 cells at the invasion of HBME-1 monolayers. At 8 hr, C4-2 cells had 6.0-fold (95% CI = 2.63,13.65) higher invasive potential than P69 cells. Phage display biopanning of LNCaP cells versus C4-2 cells in vitro using 4 separate techniques repeatedly identified the same peptide in support of minimal cell surface changes associated with the ability of C4-2 cells to metastasize to bone. As integrins are vital to cell adhesion and migration, we examined the integrin subunit expression in the prostate cell lines. The expression of integrin subunits is much higher in the nontumorigenic cell line, P69, whereas the differences in integrin expression between LNCaP and C4-2 are negligible. Only alpha(2) and beta(5) integrin subunits increase from LNCaP to C4-2. Given that C4-2 cells spontaneously metastasize to bone in vivo and LNCaP cells do not, these studies imply that the ability of a metastatic prostate cancer cell to colonize the bone is not completely dependent upon the ability of the cancer cell to adhere to either osteoblastic cells or to the bone marrow endothelial cell lining. Therefore, the initial interaction between the bone endothelium or stroma and prostate cells is not accurately referred to as a tropic or homing response. The invasion assay results indicate that the invasive potential of the cell more accurately reflects the bone colonizing potential of a prostate cancer cell. It is likely that bidirectional paracrine interactions, subsequent to marrow adhesion, between prostate cancer cells and the bone microenvironment are what determine the successful colonization of the bone by prostate cancer cells. Further, functional changes in surface proteins that are involved in invasion are likely to occur without major changes in levels of cell surface protein expression. Functional integrin association, substratum usage and outside in signaling are more likely to predict metastatic behavior.

Peptabodies as tools to test ligands isolated from phage-displayed peptide libraries

We have previously isolated filamentous bacteriophages, expressing linear hexa-peptides and homing to bone marrow endothelium (BME), by panning in vivo of a phage-displayed peptide library in mice. Here, we used peptabody fusion proteins to test the binding capacity of the hexa-peptide SSLTTG to BME cells in vitro. To display this motif in a multimeric form, as originally presented on the bacteriophage, we expressed it N-terminally as a fusion with the peptabody cartilage oligomeric matrix assembly protein (COMP) pentamerization domain, either alone or followed by the N1 domain of the pIII phage coat protein. Binding of the peptabody constructs to the mouse BME cell line STR-10 was investigated by immunofluorescence using anti-COMP antibodies. Only peptabody fusion proteins co-expressing pIII-N1 exhibited binding to STR-10, regardless of the presence or absence of SSLTTG. These results indicate that the phage coat protein pIII-N1 domain is the principle determinant responsible for the binding of filamentous bacteriophages to cells of the reticulo-endothelial system (RES). Peptabodies expressing pIII-N1 did not bind to the osteoblast-like cell line MC3T3-E1, indicating that binding is mediated by receptors specifically expressed by BME cells in vivo. Polyinosinic acid (poly-I) was able to inhibit binding of bacteriophages and pIII-N1 expressing peptabodies to STR-10, confirming our previous studies showing that bacteriophages bind to scavenger receptors (SR) expressed by BME cells. In summary, the present study shows the usefulness of peptabodies as a general tool to test the binding capacity of peptide ligands identified by phage display.

Insulin-like growth factor binding protein-3 is overexpressed in endothelial cells of mouse breast tumor vessels

Angiogenesis is a key process in a variety of human diseases, including cancer. The ability to target selectively the tumor vasculature is potentially useful for the diagnosis and treatment of cancer. Still, little information is available regarding markers that are restricted to the ECs of tumor vessels. cDNA array technology allows simultaneous analysis of relative expression levels of a broad spectrum of genes in 2 related cell populations. We used this technology with the aim of identifying markers specific for TECs. TECs were isolated by CD31-mediated immunomagnetic separation from tumors induced by s.c. injection of NF9006 breast carcinoma cells into syngeneic mice. NECs were isolated from lactating mammary glands. The endothelial nature of isolated cells was confirmed by RT-PCR using CD31-specific primers and by uptake of DiI-Ac-LDL. Macrophage contamination in the EC isolations could be reasonably ruled out by assessing the expression of the macrophage marker c-fms. (32)P-labeled cDNA probes generated by reverse transcription from total RNA were hybridized to mouse-specific gene arrays. Several genes consistently showed differential expression between TECs and NECs. However, expression of only 1 of these genes, IGFBP-3, was restricted exclusively to ECs. Semiquantitative RT-PCR revealed 22- to 33-fold differential expression of IGFBP-3 in the TEC fraction. IGFBP-3 was overexpressed by a factor of 5 in an additional mouse model of breast carcinoma induced by 4T1.2 tumor cells. These results indicate that IGFBP-3 is a potential novel marker of angiogenesis. Elucidation of its role in tumor neovascularization may open the possibility of IGFBP-3 as a therapeutic target for antiangiogenesis.