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

Osteoclasts directly influence castration-resistant prostate cancer cells

Metastasis to bone is the leading cause of death from prostate cancer. Interaction between tumor cells and bone cells can promote progression and influence tumor phenotype. It is known that prostate cancer cells support osteoclast differentiation, and degradation of bone matrix by osteoclasts releases growth factors stimulating tumor cell proliferation and invasion. In the present study osteolytic (PC-3) and osteoblastic (LNCaP-19) castration-resistant prostate cancer (CRPC) cells were co-cultured with mature osteoclasts or their precursor cells (RAW 264.7) to characterize direct effects of mature osteoclasts on CRPC cells. Osteoclasts increased proliferation and decrease apoptosis of CRPC cells as assessed with flow cytometry. RNA sequencing revealed that osteolytic CRPC cells were more responsive to osteoclast stimulation regarding gene expression, but the overall induced expression patterns were similar between the prostate cancer cell lines. Genes related to DNA repair were upregulated by osteoclasts, while genes related to endoplasmic reticulum stress-induced apoptosis and cholesterol synthesis were downregulated. The results of this study shows that osteoclasts directly influence CRPC cells, increasing proliferation, decreasing apoptosis, and affecting gene expression pathways that can affect sensitivity to DNA damage and endoplasmic reticulum function. This suggests targeting of osteoclasts to be a possible way to affect efficacy of other drugs by combination regimens in treating prostate cancer metastases.

Prostate cancer addiction to oxidative stress defines sensitivity to anti-tumor neutrophils

Bone metastatic prostate cancer (BM-PCa) remains one of the most difficult cancers to treat due to the complex interactions of cancer and stromal cells. We previously showed that bone marrow neutrophils elicit an anti-tumor immune response against BM-PCa. Further, we demonstrated that BM-PCa induces neutrophil oxidative burst, which has previously been identified to promote primary tumor growth of other cancers, and a goal of this study was to define the importance of neutrophil oxidative burst in BM-PCa. To do this, we first examined the impact of depletion of reactive oxygen species (ROS), via systemic deletion of the main source of ROS in phagocytes, NADPH oxidase (Nox)2, which we found to suppress prostate tumor growth in bone. Further, using pharmacologic ROS inhibitors and Nox2-null neutrophils, we found that ROS depletion specifically suppresses growth of androgen-insensitive prostate cancer cells. Upon closer examination using bulk RNA sequencing analysis, we identified that metastatic prostate cancer induces neutrophil transcriptomic changes that activates pathways associated with response to oxidative stress. In tandem, prostate cancer cells resist neutrophil anti-tumor response via extracellular (i.e., regulation of neutrophils) and intracellular alterations of glutathione synthesis, the most potent cellular antioxidant. These findings demonstrate that BM-PCa thrive under oxidative stress conditions and such that regulation of ROS and glutathione programming could be leveraged for targeting of BM-PCa progression.

The roles of RUNX2 and osteoclasts in regulating expression of steroidogenic enzymes in castration-resistant prostate cancer cells

Intratumoral steroidogenesis is involved in development of castration-resistant prostate cancer (CRPC) as bone metastases. The osteoblast transcription factor RUNX2 influences steroidogenesis and is induced in CRPC cells by osteoblasts. This study investigates osteoclastic influence on RUNX2 in intratumoral steroidogenesis. Steroidogenic enzymes and steroid receptors were detected with immunohistochemistry in xenograft intratibial tumors from CRPC cells. In vitro, expression of RUNX2 was increased by osteoclasts in osteoblastic LNCaP-19 cells, but not in osteolytic PC-3. Silencing of RUNX2 downregulates expression of CYP11A1, CYP17A1 and HSD3B1 in LNCaP-19 cells co-cultured with osteoclasts, leading to inhibition of KLK3 expression. Osteoclasts promoted CYP11A1 and RUNX2 promoted AKR1C3, HSD17B3 and CYP19A1, but suppressed ESR2 in PC-3 cells. This study shows that osteoclasts promote RUNX2 regulated induction of key steroidogenic enzymes, influencing activation of androgen receptor in CRPC cells. The potential of RUNX2 as a target to inhibit progression of skeletal metastases of CRPC needs further investigation.

The nonreceptor protein tyrosine kinase Src participates in every step of cancer-induced bone pain

Cancer-induced bone pain (CIBP) is a refractory form of pain that has a high incidence in advanced tumors. Src protein tyrosine kinase is mainly composed of six domains, with two states of automatic inhibition and activation. The modular domain allows Src to conveniently regulate by and communicate with a variety of proteins, directly or indirectly participate in each step of the CIBP process. Src is beneficial to the growth and proliferation of tumor cells, and it can promote the metastases of primary tumors to bone. In the microenvironment of bone metastasis, it mainly mediates bone resorption, activates related peripheral receptors to participate in the formation of pain signals, and may promote the generation of pathological sensory nerve fibers. In the process of pain signal transmission, it mainly mediates NMDAR and central glial cells to regulate pain signal intensity and central sensitization, but it is not limited to these two aspects. Both basic experimentation and clinical research have shown encouraging potential, providing new ideas and inspiration for the prevention and treatment of CIBP.

Progress in Targeted Alpha-Particle-Emitting Radiopharmaceuticals as Treatments for Prostate Cancer Patients with Bone Metastases

Bone metastasis remains a major cause of death in cancer patients, and current therapies for bone metastatic disease are mainly palliative. Bone metastases arise after cancer cells have colonized the bone and co-opted the normal bone remodeling process. In addition to bone-targeted therapies (e.g., bisphosphonate and denosumab), hormone therapy, chemotherapy, external beam radiation therapy, and surgical intervention, attempts have been made to use systemic radiotherapy as a means of delivering cytocidal radiation to every bone metastatic lesion. Initially, several bone-seeking beta-minus-particle-emitting radiopharmaceuticals were incorporated into the treatment for bone metastases, but they failed to extend the overall survival in patients. However, recent clinical trials indicate that radium-223 dichloride (223RaCl2), an alpha-particle-emitting radiopharmaceutical, improves the overall survival of prostate cancer patients with bone metastases. This success has renewed interest in targeted alpha-particle therapy development for visceral and bone metastasis. This review will discuss (i) the biology of bone metastasis, especially focusing on the vicious cycle of bone metastasis, (ii) how bone remodeling has been exploited to administer systemic radiotherapies, and (iii) targeted radiotherapy development and progress in the development of targeted alpha-particle therapy for the treatment of prostate cancer bone metastasis.

Comparison of PET/CT and MRI in the Diagnosis of Bone Metastasis in Prostate Cancer Patients: A Network Analysis of Diagnostic Studies

BACKGROUND

Accurate diagnosis of bone metastasis status of prostate cancer (PCa) is becoming increasingly more important in guiding local and systemic treatment. Positron emission tomography/computed tomography (PET/CT) and magnetic resonance imaging (MRI) have increasingly been utilized globally to assess the bone metastases in PCa. Our meta-analysis was a high-volume series in which the utility of PET/CT with different radioligands was compared to MRI with different parameters in this setting.

MATERIALS AND METHODS

Three databases, including Medline, Embase, and Cochrane Library, were searched to retrieve original trials from their inception to August 31, 2019 according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) statement. The methodological quality of the included studies was assessed by two independent investigators utilizing Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2). A Bayesian network meta-analysis was performed using an arm-based model. Absolute sensitivity and specificity, relative sensitivity and specificity, diagnostic odds ratio (DOR), and superiority index, and their associated 95% confidence intervals (CI) were used to assess the diagnostic value.

RESULTS

Forty-five studies with 2,843 patients and 4,263 lesions were identified. Network meta-analysis reveals that 68Ga-labeled prostate membrane antigen (68Ga-PSMA) PET/CT has the highest superiority index (7.30) with the sensitivity of 0.91 and specificity of 0.99, followed by 18F-NaF, 11C-choline, 18F-choline, 18F-fludeoxyglucose (FDG), and 18F-fluciclovine PET/CT. The use of high magnetic field strength, multisequence, diffusion-weighted imaging (DWI), and more imaging planes will increase the diagnostic value of MRI for the detection of bone metastasis in prostate cancer patients. Where available, 3.0-T high-quality MRI approaches 68Ga-PSMA PET/CT was performed in the detection of bone metastasis on patient-based level (sensitivity, 0.94 vs. 0.91; specificity, 0.94 vs. 0.96; superiority index, 4.43 vs. 4.56).

CONCLUSIONS

68Ga-PSMA PET/CT is recommended for the diagnosis of bone metastasis in prostate cancer patients. Where available, 3.0-T high-quality MRI approaches 68Ga-PSMA PET/CT should be performed in the detection of bone metastasis.

Exosomes derived from osteogenic tumor activate osteoclast differentiation and concurrently inhibit osteogenesis by transferring COL1A1-targeting miRNA-92a-1-5p

In patients with prostate cancer (PCa), bone lesions appear osteoblastic in radiographs; however, pathological fractures frequently occur in PCa patients, and bone resorption is observed in all metastatic lesions under histopathologic assessment. The mechanisms that balance the activities of osteoblasts and osteoclasts in PCa patients remain unclear. We unexpectedly discovered that PCa exosomes are critical mediators in the regulation of bone homeostasis that results in osteoclastic lesions and thereby promotes tumor growth in bone. We evaluated how exosomes derived from osteoblastic, osteoclastic, and mixed PCa cell lines affect osteoblast and osteoclast differentiation, revealing that all three types of PCa exosomes promoted osteoclastogenesis in vitro and induced osteolysis in vivo. Mechanistically, microRNAs (miRNAs) delivered by PCa exosomes were found to play several key roles in bone homeostasis. Among the delivered miRNAs, miR-92a-1-5p, the most abundant miRNA, downregulated type I collagen expression by directly targeting COL1A1, and thus promoting osteoclast differentiation and inhibiting osteoblastogenesis. Furthermore, PCa exosomes also markedly reduced type I collagen expression in vivo. Our findings not only offer a novel perspective on tumor bone metastasis, where-contrary to our initial hypothesis-exosomes derived from an osteoblastic tumor induce osteoclast differentiation, but also suggest potential therapeutic targets for PCa bone metastasis.

ROR2 suppresses metastasis of prostate cancer via regulation of miR-199a-5p-PIAS3-AKT2 signaling axis

Bones are the most common metastatic sites for prostate cancer (PCa). Receptor tyrosine kinase-like orphan receptor 2 (ROR2), a noncanonical Wnt receptor, plays crucial roles in skeletal morphogenesis, osteoblast differentiation, and bone formation. The role of ROR2 in PCa metastasis is unclear. We analyzed online datasets from Oncomine as well as using IHC staining on tissue array to determine the relationship between ROR2 expression level and disease outcome of PCa. To investigate how ROR2 regulates migration and invasion of PCa cells, we performed transwell assay and orthotopic xenograft model in nude mice. We then applied the Micro-Western Array (MWA), a high-throughput western blotting platform to analyze the downstream signaling pathways being regulated by ROR2. Compared with nonmalignant PZ-HPV-7 and RWPE-1 cells, PCa cell lines express lower level of ROR2 protein. Constitutive expression of ROR2 in PC-3, DU-145, or C4-2B PCa cells significantly suppressed the cell migration, invasion, and epithelial-mesenchymal transition (EMT) proteins. MWA, western blotting, and microRNA analysis showed that elevation of ROR2 suppressed the expression of miR-199a-5p, which in turn increased the expression of PIAS3. The upregulation of PIAS3 then decreased AKT2 and the phosphorylation of AKT, resulting in the inhibition of migration and invasion of PCa cells both in vitro and in orthotopic xenograft mice model. IHC staining of tissue array and Oncomine datasets analysis indicated that the gene and protein level of ROR2 is much lower in metastatic prostate tumors as compared with primary tumors or adjacent normal prostate tissues. Low level of ROR2 correlated to poor survival and high recurrent frequency in PCa patients. In conclusion, we discovered that ROR2 suppresses PCa metastasis via regulation of PIAS3-PI3K-AKT2 signaling axis.

A multi-targeted approach to treating bone metastases

The treatment of bone-metastatic cancer now takes advantage of the unique biology of this clinical state. The complex interplay between the cancer cells and the bone microenvironment leads to a host of therapeutic targets, with agents in various stages of clinical use or study. Targets include interactions between the cancer cells and osteoclasts, osteoblasts, endothelial cells, stromal cells, hematopoietic progenitor cells, cells of the immune system, and the bone matrix. Efforts at understanding specific mechanisms of drug resistance in the bone are also ongoing. Successful clinical outcomes will be the result of co-targeting and interrupting the various tumor-supportive elements and cooperating pathways at the level of the tumor cell, the primary and metastatic microenvironments, and systemic cancer effects, leading to a "scaled network disruption" to undermine the disease state.

A randomized phase II study of cediranib alone versus cediranib in combination with dasatinib in docetaxel resistant, castration resistant prostate cancer patients

BACKGROUND

Activation of the vascular endothelial growth factor receptor (VEGFR) and the oncogenic Src pathway has been implicated in the development of castration-resistant prostate cancer (CRPC) in preclinical models. Cediranib and dasatinib are multi-kinase inhibitors targeting VEGFR and Src respectively. Phase II studies of cediranib and dasatinib in CRPC have shown single agent activity.

METHODS

Docetaxel-pretreated CRPC patients were randomized to arm A: cediranib alone (20 mg/day) versus arm B: cediranib (20 mg/day) plus dasatinib (100 mg/day) given orally on 4-week cycles. Primary endpoint was 12-week progression-free survival (PFS) as per the Prostate Cancer Clinical Trials Working Group (PCWG2). Patient reported outcomes were evaluated using Functional Assessment of Cancer Therapy-Prostate (FACT-P) and Present Pain Intensity (PPI) scales. Correlative studies of bone turnover markers (BTM), including bone alkaline phosphate (BAP) and serum beta-C telopeptide (B-CTx) were serially assayed. Results A total of 22 patients, 11 per arm, were enrolled. Baseline demographics were similar in both arms. Median number of cycles =4 in arm A (range 1-12) and 2 in arm B (range 1-9). Twelve-week PFS was 73 % in arm A versus 18 % in arm B (p = 0.03). Median PFS in months (arm A versus B) was: 5.2 versus 2.6 (95 % CI: 1.9-6.5 versus 1.4-not reached). Most common grade 3 toxicities were hypertension, anemia and thrombocytopenia in arm A and hypertension, diarrhea and fatigue in arm B. One treatment-related death (retroperitoneal hemorrhage) was seen in arm A. FACT-P and PPI scores did not significantly change in either arm. No correlation between BTM and PFS was seen in either arm.

CONCLUSIONS

Although limited by small numbers, this randomized study showed that the combination of VEGFR and Src targeted therapy did not result in improved efficacy and may be associated with a worse outcome than VEGFR targeted therapy alone in patients with CRPC. ClinicalTrials.gov number: NCT01260688.

Osteoblasts stimulate the osteogenic and metastatic progression of castration-resistant prostate cancer in a novel model for in vitro and in vivo studies

Castration-resistant prostate cancer (CRPC) is strongly associated with sclerotic bone metastases and poor prognosis. Models that mimic human CRPC are needed to identify the mechanisms for prostate cancer (PC) growth in bone and to develop new therapeutic strategies. We characterize a new model, LNCaP-19, and investigate the interaction between tumor cells and osteoblasts in the sclerotic tumor response of CRPC. Osteogenic profiling of PC cell lines (LNCaP-19, LNCaP, C4-2B₄, and PC-3) was performed by gene expression arrays and mineral staining. Conditioned medium from MC3T3-E1 was used for osteoblast stimulation of CRPC cells. The capacity of LNCaP-19 cells to induce sclerotic lesions was assessed in intratibial xenografts and verified by serum markers, histological analysis and bone mineral density (BMD) measurements. The CRPC cell line LNCaP-19 expresses a pronounced osteogenic profile compared to its parental androgen-dependent cell line LNCaP. Osteoblast-derived factors further increase the expression of genes known to enhance metastatic progression of PC. LNCaP-19 forms sclerotic tumors in tibia of castrated mice as evident by increased total BMD (P < 0.01). There was a strong correlation between serum osteocalcin and BMD (total: R² 0.811, P < 0.01, trabecular: R² 0.673, P < 0.05). For the first time we demonstrate that a CRPC cell line generated in vitro has osteogenic capacity and that osteomimicry can be an inherent feature of these cells. Osteoblast-derived factors further promote the osteogenic and metastatic phenotype in CRPC cells. Altogether, our model demonstrates that both tumor cells and osteoblasts are mediators of the bone forming process of CRPC.

The hurdle of antiandrogen drug resistance: drug design strategies

INTRODUCTION

Prostate cancer is the second most common cancer death in men after lung cancer, due to distant metastases. While distant prostate cancer is typically castrate resistant, it is not necessarily androgen independent. For this reason, a review of the literature regarding the pathways involved in androgen signaling and therapeutic regimens to treat distant metastases is beneficial to increasing the survival rate of prostate cancer patients.

AREAS COVERED

In this article, the author reviews the literature from the past decade covering metastatic hormone refractory prostate cancer with the aim to examine and identify pathways, therapeutic targets and current therapies for treating castrate-resistant disease. As this area is lacking, the author aims to provide the reader with knowledge of the molecular consequences of castrate resistant prostate cancer, the current treatment paradigms and future directions.

EXPERT OPINION

While there have been advances in the treatment of castrate resistant prostate cancer, only minimal advances have been made in overall survival rate. Due to aberrant mutations and activation in the androgen receptor gene, and the complexity of cell signaling within prostate cancer, the androgen receptor should remain a main target for drug discovery efforts. This author believes that designing compounds that will reduce the activation of the androgen receptor may hold the key to a cure in the future.

The role of the bone microenvironment in skeletal metastasis

The bone microenvironment provides a fertile soil for cancer cells. It is therefore not surprising that the skeleton is a frequent site of cancer metastasis. It is believed that reciprocal interactions between tumour and bone cells, known as the “vicious cycle of bone metastasis” support the establishment and orchestrate the expansion of malignant cancers in bone. While the full range of molecular mechanisms of cancer metastasis to bone remain to be elucidated, recent research has deepened our understanding of the cell-mediated processes that may be involved in cancer cell survival and growth in bone. This review aims to address the importance of the bone microenvironment in skeletal cancer metastasis and discusses potential therapeutic implications of novel insights.

Targeting bone remodeling by isoflavone and 3,3'-diindolylmethane in the context of prostate cancer bone metastasis

Prostate cancer (PCa) bone metastases have long been believed to be osteoblastic because of bone remodeling leading to the formation of new bone. However, recent studies have shown increased osteolytic activity in the beginning stages of PCa bone metastases, suggesting that targeting both osteolytic and osteoblastic mediators would likely inhibit bone remodeling and PCa bone metastasis. In this study, we found that PCa cells could stimulate differentiation of osteoclasts and osteoblasts through the up-regulation of RANKL, RUNX2 and osteopontin, promoting bone remodeling. Interestingly, we found that formulated isoflavone and 3,3′-diindolylmethane (BR-DIM) were able to inhibit the differentiation of osteoclasts and osteoblasts through the inhibition of cell signal transduction in RANKL, osteoblastic, and PCa cell signaling. Moreover, we found that isoflavone and BR-DIM down-regulated the expression of miR-92a, which is known to be associated with RANKL signaling, EMT and cancer progression. By pathway and network analysis, we also observed the regulatory effects of isoflavone and BR-DIM on multiple signaling pathways such as AR/PSA, NKX3-1/Akt/p27, MITF, etc. Therefore, isoflavone and BR-DIM with their multi-targeted effects could be useful for the prevention of PCa progression, especially by attenuating bone metastasis mechanisms.

Role of E-cadherin in antimigratory and antiinvasive efficacy of silibinin in prostate cancer cells

The epithelial-to-mesenchymal transition (EMT) in prostate cancer (PCA) cells is considered prerequisite for acquiring migratory/invasive phenotype, and subsequent metastasis. We hypothesized that promoting the E-cadherin expression in PCA cells by using nontoxic phytochemicals, like silibinin, would prevent EMT and consequently invasiveness. Our results showed that silibinin treatment (5-90 μmol/L) significantly inhibits migratory and invasive potential of advance human PCA PC3, PC3MM2, and C4-2B cells in in vitro assays. Importantly, the antimigratory/antiinvasive efficacy of silibinin was not due to its cytotoxicity toward PCA cells. Molecular analyses showed that silibinin increases E-cadherin level that was localized mainly at cellular membrane as evidenced by subcellular fractional and confocal analyses in PC3 cells, which might be responsible for morphologically observed shift toward epithelial character. Silibinin also decreased the levels of Slug, Snail, phospho-Akt(ser(473)), nuclear β-catenin, phospho-Src(tyr(419)) and Hakai; together they play an important role in regulating E-cadherin expression/function and EMT. Similar silibinin effects on E-cadherin, β-catenin, phospho-Src(tyr(419)), and Hakai levels were also observed in PC3MM2 and C4-2B PCA cells. Selective Src inhibition by dasatinib also showed increased E-cadherin expression in PC3 cells suggesting a possible involvement of Src inhibition in silibinin-caused increase in E-cadherin level. Additional studies in PC3 cells with stable knock-down of E-cadherin expression revealed that antimigratory/antiinvasive efficacy of silibinin is in-part dependent on E-cadherin expression. Together, our results showing antimigratory/antiinvasive effects of silibinin and associated mechanisms suggest that silibinin should be tested further in clinically relevant animal models toward exploiting its potential benefits against metastatic PCA.

Bone metastasis: mechanisms and therapeutic opportunities

The skeleton is one of the most common sites for metastatic cancer, and tumors arising from the breast or prostate possess an increased propensity to spread to this site. The growth of disseminated tumor cells in the skeleton requires tumor cells to inhabit the bone marrow, from which they stimulate local bone cell activity. Crosstalk between tumor cells and resident bone and bone marrow cells disrupts normal bone homeostasis, which leads to tumor growth in bone. The metastatic tumor cells have the ability to elicit responses that stimulate bone resorption, bone formation or both. The net result of these activities is profound skeletal destruction that can have dire consequences for patients. The molecular mechanisms that underlie these painful and often incurable consequences of tumor metastasis to bone are beginning to be recognized, and they represent promising new molecular targets for therapy.

Combined inhibition of the BMP pathway and the RANK-RANKL axis in a mixed lytic/blastic prostate cancer lesion

The purpose of this study was to investigate the influence of combined inhibition of receptor activator of nuclear factor kappa-B ligand (RANKL) and bone morphogenetic protein (BMP) activity in a mixed lytic/blastic prostate cancer lesion in bone. Human prostate cancer cells (C4 2b) were injected into immunocompromised mice using an intratibial injection model to create mixed lytic/blastic lesions. RANK-Fc, a recombinant RANKL antagonist, was injected subcutaneously three times a week (10mg/kg) to inhibit RANKL and subsequent formation, function and survival of osteoclasts. Inhibition of BMP activity was achieved by transducing prostate cancer cells ex vivo with a retroviral vector expressing noggin (retronoggin; RN). There were three treatment groups (RANK-Fc treatment, RN treatment and combined RN and RANK-Fc treatment) and two control groups (untreated control and empty vector control for the RN treatment group). The progression of bone lesion and tumor growth was evaluated using plain radiographs, hindlimb tumor size, (18)F-Fluorodeoxyglucose and (18)F-fluoride micro PET-CT, histology and histomorphometry. Treatment with RANK-Fc alone inhibited osteolysis and transformed a mixed lytic/blastic lesion into an osteoblastic phenotype. Treatment with RN alone inhibited the osteoblastic component in a mixed lytic/blastic lesion and resulted in formation of smaller osteolytic bone lesion with smaller soft tissue size. The animals treated with both RN and RANK-Fc demonstrated delayed development of bone lesions, inhibition of osteolysis, small soft tissue tumors and preservation of bone architecture with less tumor induced new bone formation. This study suggests that combined inhibition of the RANKL and the BMP pathway may be an effective biologic therapy to inhibit the progression of established mixed lytic/blastic prostate cancer lesions in bone.

Inhibition of prostate cancer osteoblastic progression with VEGF121/rGel, a single agent targeting osteoblasts, osteoclasts, and tumor neovasculature

PURPOSE

A hallmark of prostate cancer (PCa) progression is the development of osteoblastic bone metastases, which respond poorly to available therapies. We previously reported that VEGF(121)/rGel targets osteoclast precursors and tumor neovasculature. Here we tested the hypothesis that targeting nontumor cells expressing these receptors can inhibit tumor progression in a clinically relevant model of osteoblastic PCa.

EXPERIMENTAL DESIGN

Cells from MDA PCa 118b, a PCa xenograft obtained from a bone metastasis in a patient with castrate-resistant PCa, were injected into the femurs of mice. Osteoblastic progression was monitored following systemic administration of VEGF(121)/rGel.

RESULTS

VEGF(121)/rGel was cytotoxic in vitro to osteoblast precursor cells. This cytotoxicity was specific as VEGF(121)/rGel internalization into osteoblasts was VEGF(121) receptor driven. Furthermore, VEGF(121)/rGel significantly inhibited PCa-induced bone formation in a mouse calvaria culture assay. In vivo, VEGF(121)/rGel significantly inhibited the osteoblastic progression of PCa cells in the femurs of nude mice. Microcomputed tomographic analysis revealed that VEGF(121)/rGel restored the bone volume fraction of tumor-bearing femurs to values similar to those of the contralateral (non-tumor-bearing) femurs. VEGF(121)/rGel significantly reduced the number of tumor-associated osteoclasts but did not change the numbers of peritumoral osteoblasts. Importantly, VEGF(121)/rGel-treated mice had significantly less tumor burden than control mice. Our results thus indicate that VEGF(121)/rGel inhibits osteoblastic tumor progression by targeting angiogenesis, osteoclastogenesis, and bone formation.

CONCLUSIONS

Targeting VEGF receptor (VEGFR)-1- or VEGFR-2-expressing cells is effective in controlling the osteoblastic progression of PCa in bone. These findings provide the basis for an effective multitargeted approach for metastatic PCa.

Computed microtomography of bone specimens for rapid analysis of bone changes associated with malignancy

Breast and prostate cancers are specially metastasizing to bone. Metastases from breast cancer usually exhibit a mixed osteolytic/osteosclerotic aspect, with osteolysis predominating. Osteosclerosis is a common finding in prostatic cancer although osteolysis occurs within the sclerotic lesions. B-cell malignancies (lymphoma, myeloma) are also associated with marked osteolysis. Histopathological examination of bone biopsies was used for the diagnosis of malignancies and, prior to embedding, microcomputed tomography (microCT) was done on the bone specimens. Patients (247) who presented either a bone metastasis, an overt myeloma, a lymphoma or a monoclonal gammopathy of undetermined significance were studied. All patients had a bone biopsy studied by 2D histomorphometry for the histopathology. During the fixation time, the bone cores were analyzed by microCT. On the 3D reconstructed models provided by microCT, signs of osteolysis/osteosclerosis were searched: excess of bone resorption, focal disorganization of microarchitecture, bone metaplasia, osteosclerosis. A strong agreement was obtained between histomorphometry and microCT results using Cohen's kappa test (kappa = 0.713). MicroCT identified excess bone resorption on trabecular surfaces when eroded surfaces were >10.5% by histomorphometry. MicroCT failed to identify some patients with smoldering myeloma or some lymphomas with microresorption. MicroCT data are obtained within 4 hr and suggest the malignant invasion of bone marrow when excess of bone resorption/formation is obtained. MicroCT can be used in the immediate postbiopsy period making possible a fast identification of malignancy. However these signs are not specific and must be confirmed by histopathological analysis.

The use of F-18 choline PET in the assessment of bone metastases in prostate cancer: correlation with morphological changes on CT

AIM

F-18 fluor choline-positron emission tomography/computed tomography (FCH-PET/CT) has emerged as a new diagnostic tool for the imaging of prostate cancer. In this study, we have evaluated the potential role of FCH-PET/CT for the assessment of bone metastases in patients with prostate cancer. Furthermore, we assessed the pattern of metabolic uptake by FCH in relation to morphologic changes on CT.

METHODS

Seventy men with biopsy-proven prostate cancer underwent FCH-PET/CT for preoperative staging or follow-up evaluation. Thirty-two patients were evaluated preoperatively, and 38 patients were referred for post operative evaluation of suspected recurrence or progression based on clinical algorithms. PET imaging consisted of a dynamic PET/CT acquisition of the pelvic region during 8 min (1-min frames) starting 1 min after i.v. injection of 4.07 MBq/kg/bw FCH which was followed immediately by a semi whole body acquisition.

RESULTS

Overall, 262 lesions showed increased uptake on FCH-PET. Two hundred ten lesions (210/262) were interpreted as bone metastases. The mean standardized uptake values (SUV) in all malignant lesions was 8.1 +/- 3.9. Forty-nine lesions (24%) had no detectable morphological changes on CT-probably due to bone marrow metastases. Fifty-six sclerotic lesions (having a Hounsfield unit (HU) level of more than 825) were interpreted as highly suspicious for metastatic bone disease on CT and/or other imaging modalities such as the bone scan but showed no FCH uptake. There was a significant correlation between tracer uptake as assessed by SUV and the density of sclerotic lesions by HU (r = -0.52, p < 0.001). The sensitivity, specificity, and accuracy of FCH-PET/CT in detecting bone metastases from prostate cancer was 79%, 97%, and 84%, respectively.

CONCLUSION

FCH-PET/CT showed promising results for the early detection of bone metastases in prostate cancer patients. We have found that a HU level of above 825 is associated with an absence of FCH uptake. Almost all of the FCH-negative sclerotic lesions were detected in patients who were under hormone therapy, which raises the possibility that these lesions might no longer be viable. However, clarification and the prognostic value of such lesions require further research.

Prostate cancer cells modulate osteoblast mineralisation and osteoclast differentiation through Id-1

Background:

Id-1 is overexpressed in and correlated with metastatic potential of prostate cancer. The role of Id-1 in this metastatic process was further analysed.

Methods:

Conditioned media from prostate cancer cells, expressing various levels of Id-1, were used to stimulate pre-osteoclast differentiation and osteoblast mineralisation. Downstream effectors of Id-1 were identified. Expressions of Id-1 and its downstream effectors in prostate cancers were studied using immunohistochemistry in a prostate cancer patient cohort (N=110).

Results:

We found that conditioned media from LNCaP prostate cancer cells overexpressing Id-1 had a higher ability to drive osteoclast differentiation and a lower ability to stimulate osteoblast mineralisation than control, whereas conditioned media from PC3 prostate cancer cells with Id-1 knockdown were less able to stimulate osteoclast differentiation. Id-1 was found to negatively regulate TNF-β and this correlation was confirmed in human prostate cancer specimens (P=0.03). Furthermore, addition of recombinant TNF-β to LNCaP Id-1 cell-derived media blocked the effect of Id-1 overexpression on osteoblast mineralisation.

Conclusion:

In prostate cancer cells, the ability of Id-1 to modulate bone cell differentiation favouring metastatic bone disease is partially mediated by TNF-β, and Id-1 could be a potential therapeutic target for prostate cancer to bone metastasis.

The critical role of the bone microenvironment in cancer metastases

Bone metastatic disease is a late-stage event of many common cancers, such as those of prostate and breast. It is incurable and causes severe morbidity. Tumor and bone interact in a vicious cycle, where tumor-secreted factors stimulate bone cells, which in turn release growth factors and cytokines that act back on the tumor cells. Within the vicious cycle are many potential therapeutic targets for novel treatment of bone metastatic disease. Therapeutic strategies can be oriented to inhibit bone cells (osteoclasts and osteoblasts) or tumor responses to factors enriched in the bone microenvironment. Many publications, especially from pre-clinical animal models, show that this approach, especially combination treatments, can reduce tumor burden and tumor-derived bone lesions. This supports a novel paradigm: tumor growth can be effectively inhibited by targeting the bone and its microenvironment rather than the tumor itself alone.

Metastasis mechanisms

Metastasis, the spread of malignant cells from a primary tumor to distant sites, poses the biggest problem to cancer treatment and is the main cause of death of cancer patients. It occurs in a series of discrete steps, which have been modeled into a "metastatic cascade". In this review, we comprehensively describe the molecular and cellular mechanisms underlying the different steps, including Epithelial-Mesenchymal Transition (EMT), invasion, anoikis, angiogenesis, transport through vessels and outgrowth of secondary tumors. Furthermore, we implement recent findings that have broadened and challenged the classical view on the metastatic cascade, for example the establishment of a "premetastatic niche", the requirement of stem cell-like properties, the role of the tumor stroma and paracrine interactions of the tumor with cells in distant anatomical sites. A better understanding of the molecular processes underlying metastasis will conceivably present us with novel targets for therapeutic intervention.

Using surrogate biomarkers to predict clinical benefit in men with castration-resistant prostate cancer: an update and review of the literature

Recurrent prostate cancer has a complex molecular etiology and a prolonged disease course. Although initially responsive to androgen ablation, many men eventually become castration resistant, develop skeletal metastases, and are palliatively treated with docetaxel-based chemotherapy, radiation therapy, bisphosphonates, and best supportive care. Given the modest success rates of the current standard of care, clinical trial enrollment is encouraged. Castration-resistant prostate cancer (CRPC) is a heterogeneous disease, both in clinical manifestations and outcomes, requiring an individualized approach to both patient care and trial design. Herein, we review surrogate markers of disease progression and treatment efficacy in advanced prostate cancer in light of recently published guidelines that have redefined eligibility, response criteria, and suitable endpoints in prostate cancer drug development. The guidelines have refined outcome measures to potentially better capture clinical benefit and the ability of novel targeted molecular and biologic agents to impact favorably on this disease. We consider prostate-specific antigen changes, circulating tumor cells, bone scan alterations, markers of bone metabolism (urinary N-telopeptide and bone-specific alkaline phosphatase), pain improvements, and progression-free survival. To illustrate the role and challenges of these potential biomarkers and endpoints in drug development, we discuss a class of novel molecularly targeted agents, the src kinase inhibitors. Given that there are currently no validated surrogate markers of overall survival for assessing early clinical benefit from systemic therapy in metastatic CRPC, incorporation of relevant biomarkers into all phases of clinical development is essential to accelerate drug development in this field.

The use of F-18 choline PET in the assessment of bone metastases in prostate cancer: correlation with morphological changes on CT

AIM

F-18 fluor choline-positron emission tomography/computed tomography (FCH-PET/CT) has emerged as a new diagnostic tool for the imaging of prostate cancer. In this study, we have evaluated the potential role of FCH-PET/CT for the assessment of bone metastases in patients with prostate cancer. Furthermore, we assessed the pattern of metabolic uptake by FCH in relation to morphologic changes on CT.

METHODS

Seventy men with biopsy-proven prostate cancer underwent FCH-PET/CT for preoperative staging or follow-up evaluation. Thirty-two patients were evaluated preoperatively, and 38 patients were referred for postoperative evaluation of suspected recurrence or progression based on clinical algorithms. PET imaging consisted of a dynamic PET/CT acquisition of the pelvic region during 8 min (1 min frames) starting 1 min after i.v. injection of 4.07 MBq/kg/bw FCH, which was followed immediately by a semi-whole body acquisition.

RESULTS

Overall, 262 lesions showed increased uptake on FCH-PET. Two hundred ten lesions (210 of 262) were interpreted as bone metastases. The mean of maximum standardized uptake value (SUV(max)) in all malignant lesions was 8.1 +/- 3.9. Forty-nine lesions (24%) had no detectable morphological changes on CT-probably due to bone marrow metastases. Fifty-six sclerotic lesions (having a Hounsfield unit (HU) level of more than 825) were interpreted as highly suspicious for metastatic bone disease on CT and/or other imaging modalities such as the bone scan, but showed no FCH uptake. There was a significant correlation between tracer uptake as assessed by SUV and the density of sclerotic lesions by HU (r = -0.52, p < 0.001). The sensitivity, specificity, and accuracy of FCH-PET/CT in detecting bone metastases from prostate cancer was 79%, 97%, and 84%, respectively.

CONCLUSION

FCH-PET/CT showed promising results for the early detection of bone metastases in prostate cancer patients. We have found that a HU level of above 825 is associated with an absence of FCH uptake. Almost all of the FCH-negative sclerotic lesions were detected in patients who were under hormone therapy, which raises the possibility that these lesions might no longer be viable. However, clarification and the prognostic value of such lesions require further research.

Butanol fraction containing berberine or related compound from nexrutine inhibits NFkappaB signaling and induces apoptosis in prostate cancer cells

BACKGROUND

Epidemiological and laboratory studies support the hypothesis that several plant components influence prostate carcinogenesis and holds promise for disease prevention. Previously we reported that Nexrutine (bark extract from Phellodendron amurense) inhibits proliferation of prostate cancer cells and prostate tumor development in the transgenic adenocarcinoma of mouse prostate (TRAMP) model through modulation of Akt signaling pathway. In the present investigation we conducted studies to further define the mechanism of action of Nexrutine and to identify the active component associated with its biological activity.

METHODS

Androgen-responsive, androgen-independent human prostate cancer cell lines and tissues from TRAMP mice fed Nexrutine(R) were used in these studies. Activity guided fractionation identified butanol fraction recapitulating the activities of Nexrutine assessed by proliferation assays, apoptotic assays (DAPI and TUNEL staining), transient transfections, gel shift assays and Western blotting. In addition ultra-performance liquid chromatography (UPLC) of butanol fraction was used to identify active component of Nexrutine.

RESULTS

Butanol fraction recapitulated the activities of Nexrutine in (i) inhibiting proliferation; (ii) inducing apoptosis; and (iii) modulating transcriptional activity of NFkappaB in prostate cancer cells. Our data also indicates that both Nexrutine and butanol fraction modulates NFkappaB transcriptional activity by inhibiting IkappaBalpha phosphorylation. Expression of p65 and phosphorylated IkappaBalpha are high in tumors from TRAMP mice. In contrast dietary administration of Nexrutine reduced expression of p65 and phosphorylated IkappaBalpha in prostate from TRAMP mice. In addition using UPLC, we have identified berberine or closely related compound in the butanol fraction.

CONCLUSION

The results suggest that berberine or closely related component of butanol fraction may be responsible for the observed biological activities and induce apoptosis in prostate cancer cells by targeting critical cell survival signaling pathways both in vitro and in vivo.

Current and future treatments of bone metastases

Bone metastases contribute to a significant degree of morbidity in patients with common cancers through the development of skeletal related events (SRE) such as bone pain and pathological fracture. Traditional therapy has relied on surgical removal of lesions and, with the advent of adjuvant therapies, has been combined with radiotherapy, chemotherapy, and more recently osteoclast inhibiting agents like bisphosphonates. Although these therapeutic combinations can achieve a degree of local control, and rarely cure, across the vast majority of metastatic cancers they provide only palliation. Newer molecular agents currently under investigation, combined with innovations in surgery and radiation therapy offer a more targeted approach to bone metastasis. These utilise our understanding of key steps in the metastatic cascade including chemotactic attraction to bone, secretion of proteases, the cancer supporting microenvironment of bone matrix and the RANK-RANKL interaction for osteoclast activation. Direct inhibition of metastasis progression and osteolysis with less reliance on cytotoxic agents and invasive therapy should result in improved metastatic control, longer survival and less overall morbidity.

Influence of simultaneous targeting of the bone morphogenetic protein pathway and RANK/RANKL axis in osteolytic prostate cancer lesion in bone

Metastasis to bone is the leading cause of morbidity and mortality in advanced prostate cancer patients. Considering the complex reciprocal interactions between the tumor cells and the bone microenvironment, there is increasing interest in developing combination therapies targeting both the tumor growth and the bone microenvironment. In this study, we investigated the effect of simultaneous blockade of BMP pathway and RANK/RANKL axis in an osteolytic prostate cancer lesion in bone. We used a retroviral vector encoding noggin (RetroNoggin) to antagonize the effect of BMPs and RANK:Fc, which is a recombinant RANKL antagonist was used to inhibit RANK/RANKL axis. The tumor growth and bone loss were evaluated using plain radiographs, hind limb tumor measurements, micro PET/CT ((18)FDG and (18)F-fluoride tracer), and histology. Tibias implanted with PC-3 cells developed pure osteolytic lesions at 2-weeks with progressive increase in cortical bone destruction at successive time points. Tibias implanted with PC-3 cells over expressing noggin (RetroNoggin) resulted in reduced tumor size and decreased bone loss compared to the implanted tibias in untreated control animals. RANK:Fc administration inhibited the formation of osteoclasts, delayed the development of osteolytic lesions, decreased bone loss and reduced tumor size in tibias implanted with PC-3 cells. The combination therapy with RANK:Fc and noggin over expression effectively delayed the radiographic development of osteolytic lesions, and decreased the bone loss and tumor burden compared to implanted tibias treated with noggin over expression alone. Furthermore, the animals treated with the combination strategy exhibited decreased bone loss (micro CT) and lower tumor burden (FDG micro PET) compared to animals treated with RANK:Fc alone. Combined blockade of RANK/RANKL axis and BMP pathway resulted in reduced tumor burden and decreased bone loss compared to inhibition of either individual pathway alone in osteolytic prostate cancer lesion in bone. These results suggest that simultaneous targeting of tumor cells and osteoclasts may be the most effective method of inhibiting the progression of established osteolytic metastatic lesions in vivo.

Src as a therapeutic target in men with prostate cancer and bone metastases

While responsive to androgen ablation in its early stages, prostate cancer eventually becomes castration-resistant and metastasizes preferentially to bone. Once this happens, the disease carries considerable morbidity and is incurable. The process of bone metastasis involves a complex interplay between tumour and bone tissue. The eventual characteristic clinical presentation of disorganized osteoblastic bone lesions is preceded by a facilitatory osteoblastic phase; an osteoblastic component then continues to underlie the process. Increasing evidence has shown a ubiquitous role for Src (a proto-oncogene tyrosine-protein kinase) in multiple tumour and bone-signalling processes involved in prostate tumour progression, driving proliferation, survival, migration and transition to androgen-independent growth. It is also intimately involved in positively regulating osteoclast physiology. As such, this molecule represents an attractive target for managing progressing prostate cancer. Encouraging results have been obtained in preclinical and clinical studies using Src inhibitors like AZD0530 and dasatinib. Both compounds reduced markers of bone resorption, in patients with cancer and those with advanced castration-resistant prostate cancer, respectively. Moreover, because Src is central to many mechanisms thought to be responsible for the development of castration resistance, adding Src inhibitors to a treatment regimen might reverse this phenomenon. As a result, many Src inhibitors are in preclinical development. This review explores Src inhibition as a strategy for managing bone metastasis in prostate cancer, with a particular focus on targeting the critical osteoclastic response. Other emerging and novel approaches are also considered.

The role of alpha 6 integrin in prostate cancer migration and bone pain in a novel xenograft model

Of the estimated 565,650 people in the U.S. who will die of cancer in 2008, almost all will have metastasis. Breast, prostate, kidney, thyroid and lung cancers metastasize to the bone. Tumor cells reside within the bone using integrin type cell adhesion receptors and elicit incapacitating bone pain and fractures. In particular, metastatic human prostate tumors express and cleave the integrin A6, a receptor for extracellular matrix components of the bone, i.e., laminin 332 and laminin 511. More than 50% of all prostate cancer patients develop severe bone pain during their remaining lifetime. One major goal is to prevent or delay cancer induced bone pain. We used a novel xenograft mouse model to directly determine if bone pain could be prevented by blocking the known cleavage of the A6 integrin adhesion receptor. Human tumor cells expressing either the wildtype or mutated A6 integrin were placed within the living bone matrix and 21 days later, integrin expression was confirmed by RT-PCR, radiographs were collected and behavioral measurements of spontaneous and evoked pain performed. All animals independent of integrin status had indistinguishable tumor burden and developed bone loss 21 days after surgery. A comparison of animals containing the wild type or mutated integrin revealed that tumor cells expressing the mutated integrin resulted in a dramatic decrease in bone loss, unicortical or bicortical fractures and a decrease in the ability of tumor cells to reach the epiphyseal plate of the bone. Further, tumor cells within the bone expressing the integrin mutation prevented cancer induced spontaneous flinching, tactile allodynia, and movement evoked pain. Preventing A6 integrin cleavage on the prostate tumor cell surface decreased the migration of tumor cells within the bone and the onset and degree of bone pain and fractures. These results suggest that strategies for blocking the cleavage of the adhesion receptors on the tumor cell surface can significantly prevent cancer induced bone pain and slow disease progression within the bone. Since integrin cleavage is mediated by Urokinase-type Plasminogen Activator (uPA), further work is warranted to test the efficacy of uPA inhibitors for prevention or delay of cancer induced bone pain.

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

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

Histopathological assessment of prostate cancer bone osteoblastic metastases

PURPOSE

Many patients with prostate cancer have bone metastases that appear osteoblastic on radiography, and yet these patients are at increased risk for fracture. The discrepancy between the radiological and clinical aspects of those events is not well understood. We better characterized the histopathology of bone processes in prostate cancer bone metastases.

MATERIALS AND METHODS

Histomorphometry was used to evaluate multisite bone biopsies in 12 patients who died with multiple bone metastases, of whom 7 had received bisphosphonate therapy.

RESULTS

Bone histomorphometry revealed a wide spectrum of cancer induced bone changes in different metastatic sites in individual patients, ranging from a pronounced osteodense to a pronounced osteopenic type. Each metastatic lesion was associated with various amounts of resorption. Decreased bone volume was seen in half of all biopsies. Osteodense lesions were largely composed of under mineralized woven bone, which increases the frailty of new bone. Interestingly woven bone was produced by alkaline phosphatase spindle-shaped cells arising from the connective stroma surrounding tumor cells. The bone response generally was similar in bisphosphonate treated patients and those who did not receive bisphosphonate.

CONCLUSIONS

Despite the osteoblastic nature of bone metastases in prostate cancer, the osteolytic-osteopenic bone lesions found in each clinically osteoblastic case may explain the frequent fractures observed in these cases. In addition, the finding that woven bone formed directly from the tumor stroma and not from the adjacent bone surface supports further research into the mechanisms of abnormal bone formation in prostate cancer bone metastases.

RANK ligand inhibition plus docetaxel improves survival and reduces tumor burden in a murine model of prostate cancer bone metastasis

Tumor cells induce excessive osteoclastogenesis, mediating pathologic bone resorption and subsequent release of growth factors and calcium from bone matrix, resulting in a "vicious cycle" of bone breakdown and tumor proliferation. RANK ligand (RANKL) is an essential mediator of osteoclast formation, function, and survival. In metastatic prostate cancer models, RANKL inhibition directly prevents osteolysis via blockade of osteoclastogenesis and indirectly reduces progression of skeletal tumor burden by reducing local growth factor and calcium concentrations. Docetaxel, a well-established chemotherapy for metastatic hormone-refractory prostate cancer, arrests the cell cycle and induces apoptosis of tumor cells. Suppression of osteoclastogenesis through RANKL inhibition may enhance the effects of docetaxel on skeletal tumors. We evaluated the combination of the RANKL inhibitor osteoprotegerin-Fc (OPG-Fc) with docetaxel in a murine model of prostate cancer bone metastasis. Tumor progression, tumor area, and tumor proliferation and apoptosis were assessed. OPG-Fc alone reduced bone resorption (P < 0.001 versus PBS), inhibited progression of established osteolytic lesions, and reduced tumor area (P < 0.0001 versus PBS). Docetaxel alone reduced tumor burden (P < 0.0001 versus PBS) and delayed the development of osteolytic lesions. OPG-Fc in combination with docetaxel suppressed skeletal tumor burden (P = 0.0005) and increased median survival time by 16.7% (P = 0.0385) compared with docetaxel alone. RANKL inhibition may enhance docetaxel effects by increasing tumor cell apoptosis as evident by increased active caspase-3. These studies show that inhibition of RANKL provides an additive benefit to docetaxel treatment in a murine model of prostate cancer bone metastasis and supports clinical evaluation of this treatment option in patients.

Prostate cancer, serum parathyroid hormone, and the progression of skeletal metastases

Bony metastases from prostate cancer are a significant cause of morbidity and mortality. These metastases are predominantly blastic (bone-forming) and commonly cause increased serum levels of parathyroid hormone (PTH) as calcium ions are transferred from serum into blastic bone. The epidemiologic and clinical significance of secondary hyperparathyroidism in advanced prostate cancer have not been widely appreciated. Prostate cancer bony metastases show increased expression of the PTH receptor (PTH-IR) and PTH promotes the growth and invasiveness of prostate cancer cells in bone. Thus, blastic metastases appear to induce a "vicious cycle" in which PTH resorbs normal bone to support the growth of blastic bone. Recognition of the potential role of PTH in the progression of skeletal metastases suggests novel opportunities for prostate cancer secondary prevention. In particular, we propose that suppressing serum PTH in advanced prostate cancer may reduce morbidity by decreasing fractures and pain caused by bone resorption and may reduce mortality by retarding the progression of metastatic disease.

Epithelial to mesenchymal transition (EMT) in human prostate cancer: lessons learned from ARCaP model

Androgen refractory cancer of the prostate (ARCaP) cells contain androgen receptor (AR) and synthesize and secrete prostate specific antigen (PSA). We isolated epithelia-like ARCaP(E) from parental ARCaP cells and induced them to undergo epithelial-mesenchymal transition (EMT) by exposing these cells to soluble factors including TGFbeta1 plus EGF, IGF-1, beta2-microglobulin (beta2-m), or a bone microenvironment. The molecular and behavioral characteristics of the resultant ARCaP(M) were characterized extensively in comparison to the parental ARCaP(E) cells. In addition to expressing mesenchymal biomarkers, ARCaP(M) gained 100% incidence of bone metastasis. ARCaP(M) cells express receptor activator of NF-kappaB ligand (RANKL), which was shown to increase tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in culture, and when metastatic to bone in vivo. We provide evidence that RANKL expression was promoted by increased cell signaling mediated by the activation of Stat3-Snail-LIV-1. RANKL expressed by ARCaP(M) cells is functional both in vitro and in vivo. The lesson we learned from the ARCaP model of EMT is that activation of a specific cell signaling pathway by soluble factors can lead to increased bone turnover, mediated by enhanced RANKL expression by tumor cells, which is implicated in the high incidence of prostate cancer bone colonization. The ARCaP EMT model is highly attractive for developing new therapeutic agents to treat prostate cancer bone metastasis.

Identifying the differential effects of silymarin constituents on cell growth and cell cycle regulatory molecules in human prostate cancer cells

Prostate cancer (PCa) is the leading cause of cancer-related deaths in men; urgent measures are warranted to lower this deadly malignancy. Silymarin is a known cancer chemopreventive agent, but the relative anticancer efficacy of its constituents is still unknown. Here, we compared the efficacy of 7 pure flavonolignan compounds isolated from silymarin, namely silybin A, silybin B, isosilybin A, isosilybin B, silydianin, isosilydianin, silychristin and isosilychristin, in advanced human PCa PC3 cells. Silybin A, silybin B, isosilybin A, isosilybin B, silibinin and silymarin strongly inhibited the colony formation by PC3 cells (p < 0.001), while silydianin, silychristin and isosilychristin had marginal effect (p < 0.05). Using cell growth and death assays, we identified isosilybin B as the most effective isomer. FACS analysis for cell cycle also showed that silybin A, silybin B, isosilybin A, isosilybin B, silibinin and silymarin treatment resulted in strong cell cycle arrest in PC3 cells after 72 hr of treatment, while the effect of silydianin, silychristin and isosilychristin was marginal (if any). Western blot analysis also showed the differential effect of these compounds on the levels of cell cycle regulators-cyclins (D, E, A and B), CDKs (Cdk2, 4 and Cdc2), CDKIs (p21 and p27) and other cell cycle regulators (Skp2, Cdc25A, B, C and Chk2). This study provided further evidence for differential anticancer potential among each silymarin constituent, which would have potential implications in devising better formulations of silymarin against prostate and other cancers.

RANKL inhibition is an effective adjuvant for docetaxel in a prostate cancer bone metastases model

BACKGROUND

Docetaxel induces an anti-tumor response in men with advanced prostate cancer (PCa); however, the side effects associated with docetaxel treatment can be severe, resulting in discontinuation of therapy. Thus, identification of an effective adjuvant therapy to allow lower doses of docetaxel is needed. Advanced PCa is typically accompanied by skeletal metastasis. Receptor activator of NFkB ligand (RANKL) is a key pro-osteoclastic factor. Targeting RANKL decreases establishment and progression of PCa growth in bone in murine models.

METHODS

The efficacy of inhibiting RANKL, using a recombinant soluble RANK extracellular domain fused with the immunoglobulin Fc domain (RANK-Fc), was tested as an adjuvant therapy with docetaxel for PCa bone metastasis in a murine intra-tibial model.

RESULT

The combination of RANK-Fc and docetaxel reduced tumor burden in bone greater than either treatment alone.

CONCLUSION

The combination of docetaxel with a RANKL-inhibiting agent merits further investigation for treatment of advance PCa.

Skeletal metastases: decreasing tumor burden by targeting the bone microenvironment

Several common cancers often metastasize to the skeleton in advanced disease. Bone metastases are incurable and cause protracted, severe symptoms. Growth of tumor in bone is driven by a vicious cycle: tumor-secreted factors stimulate bone cells, which in turn release growth factors and cytokines. The bone-derived factors fuel the vicious cycle by acting back on the tumor cells. The vicious cycle offers novel targets for the treatment of advanced cancers. Treatments can inhibit bone cells (osteoclasts and osteoblasts) that are stimulated by tumor-secreted factors. Drugs can also inhibit tumor responses to factors enriched in the bone microenvironment, such as transforming growth factor-beta. Animal models show that these approaches, especially combination treatments, can reduce tumor burden. The results suggest a novel paradigm in which tumor growth can be effectively inhibited by drugs that target cells in the bone microenvironment and not the tumor cells themselves.

Angiogenesis in implantation

PROBLEM

Implantation failure and early pregnancy loss are common following natural conceptions and they are particularly important clinical hurdles to overcome following assisted reproduction attempts. The importance of adequate vascular development and maintenance during implantation has recently become a major focus of investigation.

MATERIALS AND METHODS

Review of current published literature was undertaken to summerize the cells and cell products that regulate tissue vascularity during implantation.

RESULTS

Vascular development at the maternal fetal interface can be regulated by a number of different cell types; two principal candidates are trophoblast and natural killer cells. A wide range of soluble factors, some with well established angiogenic functions as well as other more novel factors, can contribute to vascular development and maintenance at the maternal-fetal interface.

CONCLUSIONS

Robust vascular development occurs during implantation and early placentation of normal pregnancies. Studies to define the extent and mechanisms by which defects in vascularity contribute to human implantation failure and early miscarriage need to be undertaken.

Bone morphogenetic protein 7 expression associates with bone metastasis in breast carcinomas

BACKGROUND

We recently showed that bone morphogenetic protein 7 (BMP7) is overexpressed in primary breast tumors. Here we explored the clinical significance of BMP7 expression in breast cancer.

MATERIALS AND METHODS

This study included 483 breast cancer patients with complete clinicopathological information and up to 15 years of follow-up. Samples contained 241 lobular carcinomas, 242 ductal carcinomas, and 40 local recurrences. BMP7 protein expression was determined using immunohistochemistry.

RESULTS

BMP7 was expressed in 47% of the primary tumor samples and 13% of the local recurrences. The primary tumors expressed BMP7 more often than the corresponding local recurrences (P = 0.004). BMP7 expression was dependent on the tumor subtype; 57% of the lobular carcinomas but only 37% of the ductal carcinomas were BMP7 positive (P = 0.0001). BMP7 expression was associated with accelerated bone metastasis formation (P = 0.040), especially in ductal carcinomas (P = 0.033), and multivariate analysis confirmed that BMP7 is an independent prognostic indicator for early bone metastasis development (P = 0.032).

CONCLUSION

BMP7 is clearly associated with bone metastasis formation and thus might have clinical utility in identification of patients with increased risk of bone metastasis. This is the first time that bone inducing factor BMP7 has been linked to the bone metastasis process in breast cancer.

[Pathophysiology of bone metastases in urologic carcinomas]

The skeletal system is the most frequent metastatic site of hematogenous spread of urologic carcinomas. Osseus metastases are classified as osteoneutral, osteolytic, osteoblastic and combinations thereof. Osteolytic metastases lead to bone resorption by activating osteoclasts, while osteoblastic metastases stimulate osteoblasts by paracrine mechanisms. The local osteoblastic effect is associated with secondary systemic bone resorption. The use of bisphosphonates is now an established supportive therapy and newer treatment strategies including targeted intervention in the pathophysiology of bone metastases and radioimmunotherapy are being applied or will be coming soon.