Osteosclerotic prostate cancer metastasis to murine bone are enhanced with increased bone formation

Bone Health Issues in Patients with Prostate Cancer: An Evidence-Based Review

Bone health in prostate cancer patients represents a prerequisite for acceptable quality of life and optimal outcome of this disease. The major threat for bone health in prostate cancer displays cancer treatment induced bone loss as well as the development of bone metastases. In recent years, several new pharmaceuticals targeting bone metabolism such as denosumab or androgen pathway targeting drugs (abiraterone acetate and enzalutamide) have been approved for the treatment of progressive disease aiming to interrupt the vicious circle of bone metastasis and aberrant bone resorption. This development raised the awareness of the pivotal role of bone health in prostate cancer and introduced (symptomatic) skeletal related events as an important end point in recent clinical trials. Bone targeted drugs have become standard of care in patients with metastatic castration resistant prostate cancer, their role in metastatic hormone sensitive prostate cancer has been discussed controversely. In oligometastatic prostate cancer patients several promising approaches in metastasis directed therapy, including conventional surgery, stereotactic ablative radiation and image-guided single-fraction robotic stereotactic radiosurgery (CyberKnife®) were launched but are not in routine clinical use until now caused by sparse clinical evidence.

Metastatic prostate cancer with bone marrow infiltration mimicking multiple myeloma

Concomitant diagnosis of metastatic prostate cancer and a multiple myeloma in older male patients is challenging as both malignancies are usually associated with bone lesions. Exact knowledge, experience, and an interdisciplinary approach are required in order to differentiate between both malignancies and determine the exact treatment strategy.

Identification of Fibulin-1 as a Human Bone Marrow Stromal (HS-5) Cell-Derived Factor That Induces Human Prostate Cancer Cell Death

BACKGROUND

Previous studies showed that human bone marrow stromal HS-5 cells secreted unidentified factor(s) inducing PCa cell death. Herein, the HS-5-derived factor (HS-5 DF) was characterized and identified.

METHODS

Conditioned media from confluent HS-5 cells were collected and modified for biochemical characteristic testing of HS-5 DF. Cell survival was measured by apoptosis assay and live/dead assay. Fibulin-1 was identified from gel electrophoresis and mass spectrometry. The validation of Fibulin-1 as a HS-5 DF was done by immunoprecipitation (IP) and genetic knockdown by CRISPR/Cas9 system.

RESULTS

HS-5 DF was trypsin and heat sensitive, but pH stable. The tentative size of the factor fell between 30 kDa and 100 kDa. TGF-β1 treatment led to a suppression of HS-5 DF activity, a property consistent with bone metastasis in prostate cancer. Examination of TGF-β1 down regulated proteins led to identification of fibulin-1 as a candidate for the DF. IP of Fibulin-1 from HS-5 CM and CRISPR knockdown of Fibulin-1 showed a significant reduction of HS-5 CM-derived PCa cell death. These results strongly support a role for fibulin-1 in HS-5 bone marrow stromal cell induction of PCa cell death.

CONCLUSION

Our data indicate that Fibulin-1 functions as a HS-5 bone marrow stromal cell-derived factor inducing prostate cancer cell death. Prostate 77:729-742, 2017. © 2016 Wiley Periodicals, Inc.

Targeting bone metabolism in patients with advanced prostate cancer: current options and controversies

Maintaining bone health remains a clinical challenge in patients with prostate cancer (PC) who are at risk of developing metastatic bone disease and increased bone loss due to hormone ablation therapy. In patients with cancer-treatment induced bone loss (CTIBL), antiresorptive agents have been shown to improve bone mineral density (BMD) and to reduce the risk of fractures. For patients with bone metastases, both zoledronic acid and denosumab delay skeletal related events (SREs) in the castration resistant stage of disease. Novel agents targeting the Wnt inhibitors dickkopf-1 and sclerostin are currently under investigation for the treatment of osteoporosis and malignant bone disease. New antineoplastic drugs such as abiraterone, enzalutamide, and Radium-223 are capable of further delaying SREs in patients with advanced PC. The benefit of antiresorptive treatment for patients with castration sensitive PC appears to be limited. Recent trials on the use of zoledronic acid for the prevention of bone metastases failed to be successful, whereas denosumab delayed the occurrence of bone metastases by a median of 4.1 months. Currently, the use of antiresorptive drugs to prevent bone metastases still remains a field of controversies and further trials are needed to identify patient subgroups that may profit from early therapy.

Platelets govern pre-metastatic tumor communication to bone

Although the survival rate for early detected cancers is high, once a cancer metastasizes to bone, it is incurable. Interestingly, patients without visible metastases display abnormal bone formation and resorption, suggesting a link between primary cancers and the bone microenvironment prior to metastasis, and this link likely facilitates preparation of the pre-metastatic niche. We hypothesized that communication with the primary tumor would result in bone remodeling alterations, and that platelets could facilitate this communication. By using three tumor models, we demonstrate that primary tumor growth stimulates bone formation measured by microcomputed tomography. Further, platelet depletion prevented tumor-induced bone formation, highlighting the importance of platelets in the communication between tumors and the bone microenvironment. Finally, we determine that platelets sequester a variety of tumor-derived proteins, TGF-β1 and MMP-1 in particular, which regulate bone formation. Thus, our data reveal that platelets function as mediators of tumor-bone communication prior to metastasis.

The role of tumour-stromal interactions in modifying drug response: challenges and opportunities

The role of stromal cells and the tumour microenvironment in general in modulating tumour sensitivity is increasingly becoming a key consideration for the development of active anticancer therapeutics. Here, we discuss how these tumour-stromal interactions affect tumour cell signalling, survival, proliferation and drug sensitivity. Particular emphasis is placed on the ability of stromal cells to confer - to tumour cells - resistance or sensitization to different classes of therapeutics, depending on the specific microenvironmental context. The mechanistic understanding of these microenvironmental interactions can influence the evaluation and selection of candidate agents for various cancers, in both the primary site as well as the metastatic setting. Progress in in vitro screening platforms as well as orthotopic and 'orthometastatic' xenograft mouse models has enabled comprehensive characterization of the impact of the tumour microenvironment on therapeutic efficacy. These recent advances can hopefully bridge the gap between preclinical studies and clinical trials of anticancer agents.

Optimal management of bone metastases in prostate cancer

The biological basis of the selective outgrowth of disseminated prostate cancer cells within the hematopoietic bone microenvironment remains a compelling biological mystery. A major proportion of the morbidity and mortality related to prostate cancer can be traced to the burden of bone metastases. The optimal management of bone health in men with prostate cancer requires control of the underlying epithelial neoplasm, attenuation of the subverted bone remodeling process that accompanies disease progression, reduction in the bone complications of disease-directed therapy, and management of co-existing comorbidities that enhance bone fragility. While bone-homing radioisotopes, bisphosphonates, and RANK ligand inhibitors have demonstrated reduction in bone pain and/or other skeletal-related events, further advances into definitive improvements in survival and/or global quality of life are required. A deeper understanding of the biology of bone metastases will likely facilitate a bone-directed therapeutic approach toward a major impact on the survival of men with this important disease.

Effect of parathyroid hormone on hypogonadism induced bone loss of proximal femur of orchiectomized rat

Purpose

Management of hypogonadism-induced osteoporosis in elderly men is still a challenge. We investigated the short-term effects of parathyroid hormone (PTH) treatments on strength, micro-architecture, and mineral density of trochanteric region of orchiectomized rat femur.

Methods

Eight-month-old male Sprague–Dawley rats (n = 44) were divided into two groups: (1) orchiectomized (ORX) and (2) sham group. Twelve weeks after orchiectomy, half of the orchiectomized animals were treated with daily subcutaneously injected PTH (0.040 mg/kg/BW) (ORX-PTH) for 5 weeks. The other half remained untreated (ORX). The sham-operated group was divided and treated in the same way (sham, sham-PTH). After 5 weeks, both femurs were excised for biomechanical and histomorphometric analysis, trabecular measurements, mineral content assessment, and immunofluorescence analysis.

Results

The femoral trochanteric strength after PTH treatment was enhanced in the breaking test (ORX-F_max = 158.7 N vs. ORX + PTH-F_max = 202 N). Stiffness of treated ORX animals reached nearly the levels observed in untreated sham rats. PTH therapy improved the trabecular connectivity, width, and area (ORX-Tb.Ar = 47.79% vs. ORX + PTH-Tb.Ar = 68.47%, P < 0.05) in the proximal femur. The treated rats showed significantly improved mineral content in ashed femurs (ORX-mineral content = 43.73% vs. ORX + PTH-mineral content = 49.49%) when compared to the untreated animals. A comparison of widths of fluorescence bands in cortical bone of the subtrochanteric cross-sections showed a significant increase in oppositions after the PTH therapy.

Conclusions

Our finding supports the hypothesis that PTH therapy seems to be a rational therapy in patients with hypogonadism induced bone loss and improves the bone strength of trochanteric region of rat femur.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Targeting the {alpha} receptor for platelet-derived growth factor as a primary or combination therapy in a preclinical model of prostate cancer skeletal metastasis

PURPOSE

Platelet-derived growth factor α (PDGFRα) is highly expressed in primary prostate cancer and associated skeletal metastases. Here, we tested whether targeting this receptor could impair metastatic colonization and progression, as well as prolong survival, either as primary or as combination therapy.

EXPERIMENTAL DESIGN

We used a preclinical animal model of metastasis in which PC3-ML human prostate cancer cells are inoculated directly in the blood circulation. First, the humanized, monoclonal antibody IMC-3G3 was administered to mice bearing established skeletal metastases. Second, we targeted the stromal PDGFRα with IMC-1E10, an antibody specific for the murine receptor. Third, IMC-3G3 and the bisphosphonate zoledronic acid (ZA), administered separately or in combination, were tested on the progression of skeletal lesions and overall survival. In addition, the ability of IMC-3G3 and ZA to impair initial colonization of the bone marrow by prostate cancer cells was investigated.

RESULTS

The blockade of PDGFRα on prostate cancer cells by IMC-3G3 reduces the size of established skeletal metastases, whereas the IMC-1E10 antibody directed against the stromal PDGFRα fails to inhibit metastatic progression. IMC-3G3 and ZA, either separately or in combination, significantly slow tumor growth and seem to prolong survival. Lastly, the blockade of PDGFRα by IMC-3G3 inhibits the initial phase of bone colonization, whereas ZA is ineffective at this stage.

CONCLUSION

This study presents compelling evidence that targeting PDGFRα with IMC-3G3 delays the progression of early metastatic foci and reduces the size of more established lesions. In addition, IMC-3G3, either alone or in combination with ZA, prolongs survival in animal models.

Short-term intermittent PTH 1-34 administration enhances bone formation in SCID/Beige mice

The anabolic effect of intermittent PTH on bone is variable depending on the species studied, duration/mode of administration, and location of skeletal response investigated. We tested the hypothesis low dose, short term, intermittent PTH 1-34 administration is sufficient to enhance bone formation without altering bone resorption. To test our hypothesis, mice were treated intermittently with one of three concentrations of PTH 1-34 (1 microg/kg; low, 10 microg/kg, or 20 microg/kg; high) for three weeks. The skeletal response was identified by quantifying: serum markers of bone turnover, cancellous bone parameters in distal femur, proximal tibia, and lumbar vertebrae by microCT, and number of osteoblasts and osteoclasts in distal femur. Mice receiving 20 microg/kg of PTH 1-34 demonstrated a 30% increase in serum osteocalcin, but no differences in serum calcium, type I collagen teleopeptides, or TRACP 5b. For all bones, microCT analysis suggested mice receiving 20 microg/kg of PTH 1-34 had increased cancellous bone mineral density, trabecular thickness and spacing, but decreased trabecular number. A 60% increase in the number of alkaline phosphatase positive osteoblasts in the distal femur was also observed in tissue sections; however, the number of TRAP positive osteoclasts was not different between test and control groups. While animals administered 10 microg/kg demonstrated similar trends for all bone turnover indices, such alterations were not observed in animals administered PTH 1-34 at 1 microg/kg per day. Thus, PTH 1-34, administered intermittently for three weeks at 20 microg/kg is sufficient to enhance bone formation without enhancing resorption.

The relation of serum parathyroid hormone and serum calcium to serum levels of prostate-specific antigen: a population-based study

Experimental and clinical data implicate calcium and parathyroid hormone (PTH) in the development of prostate cancer. However, epidemiologic data on the role of these variables in prostate health are sparse. We examined the relationship between serum levels of calcium, PTH, and prostate-specific antigen (PSA), an established marker of prostate growth, in a large, population-based study using multivariate linear regression. We studied 1,273 men in National Health and Nutrition Survey 2005 to 2006 who were >or=40 years of age and who were without clinical prostate cancer. Adjusted for age, race, body mass index, and serum levels of 25-hydroxyvitamin D, serum levels of PTH were significantly positively correlated with serum PSA (P = 0.01). Serum levels of PTH and calcium each were correlated significantly with free PSA (P = 0.05 and 0.008, respectively). The percentage of men who had elevated serum levels of PTH (PTH, >or=66 pg/mL) was significantly greater among African American men (19.2 versus 9.6%, P = 0.04). Compared with men whose PTH was at the lower end of the reference range, the predicted PSA for men with a PTH of 66 pg/mL was increased 43%. These findings support the hypothesis that serum calcium and serum PTH stimulate prostate growth in men without clinical prostate cancer and have implications for the use of PSA as a screening tool for prostate cancer.