Parathyroid hormone-related protein inhibits DKK1 expression through c-Jun-mediated inhibition of ß-catenin activation of the DKK1 promoter in prostate cancer.

Prostate cancer (PCa)bone metastases are unique in that majority of them induce excessive mineralized bone matrix, through undefined mechanisms, as opposed to most other cancers that induce bone resorption. Parathyroid hormone-related protein (PTHrP) is produced by PCa cells and intermittent PTHrP exposure has bone anabolic effects, suggesting that PTHrP could contribute to the excess bone mineralization. Wnts are bone-productive factors produced by PCa cells, and the Wnt inhibitor Dickkopfs-1 (DKK1) has been shown to promote PCa progression. These findings, in conjunction with the observation that PTHrP expression increases and DKK1 expression decreases as PCa progresses, led to the hypothesis that PTHrP could be a negative regulator of DKK1 expression in PCa cells and, hence, allow the osteoblastic activity of Wnts to be realized. To test this, we first demonstrated that PTHrP downregulated DKK1 mRNA and protein expression. We then found through multiple mutated DKK1 promoter assays that PTHrP, through c-Jun activation, downregulated the DKK1 promoter through a transcription factor (TCF) response element site. Furthermore, chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that PTHrP mediated this effect through inducing c-Jun to bind to a transcriptional activator complex consisting of ß-catenin, which binds the most proximal DKK1 promoter, the TCF response element. Together, these results demonstrate a novel signaling linkage between PTHrP and Wnt signaling pathways that results in downregulation of a Wnt inhibitor allowing for Wnt activity that could contribute the osteoblastic nature of PCa.

Understanding and targeting osteoclastic activity in prostate cancer bone metastases.

Bone metastasis is a debilitating side effect of advanced prostatic carcinoma impacting nearly all of the men developing this disease. Even though a majority of these lesions are considered osteoblastic, it is believed that there is an underlying osteolytic component. Lytic processes are governed primarily by osteoclasts, the primary bone resorptive cell. Osteolysis has been implicated in tumor cell seeding and nourishment of tumor growth via development of pro-tumorigenic changes in the microenvironment. Herein, we provide a current view of the processes involved in regulating osteolysis in the presence of prostate cancer bone metastases. Several factors have been implicated in the division, differentiation, and activation of osteoclasts, including, but not limited to, interleukin-6, receptor activator of nuclear factor kappa B ligand (RANKL), osteoprotegerin (OPG), and parathyroid hormone-related protein (PTHrP). Effector molecules in bone resorption play a significant role, such as matrix metalloproteinases (MMPs), cathepsins, and acid secretion. The primary method for treating skeletal events associated with prostate cancer bone metastases has been bisphosphonates. However, a new therapeutic, denosumab, a monoclonal antibody that inhibits RANKL in a mechanism similar to that attributed to the endogenous mediator OPG, has received approval for treatment of skeletally associated metastases. Additional novel targets are continuously being developed for bone metastases. In this review, we describe the processes involved in osteolysis of the prostate cancer bone microenvironment, and introduce therapeutics that may play a role in inhibiting tumor growth leading to increased survival and quality of life.

Induction of VEGF by tepoxalin does not lead to increased tumour growth in a canine osteosarcoma xenograft.

The purpose of this study was to determine the impact of the non-steroidal anti-inflammatory drug tepoxalin on canine tumour cell growth and describe the changes associated with tepoxalin treatment. In vitro experiments were performed to assess tepoxalin-associated alterations in tumour cell growth. Clinically achievable tepoxalin concentrations did not significantly alter tumour cell growth in vitro. Vascular endothelial growth factor (VEGF) production and hypoxia-inducible factor-1α dose-dependently increased in vitro in the presence of tepoxalin. A canine osteosarcoma xenograft was used to determine in vivo effects of tepoxalin on tumour growth and angiogenesis. Despite increased VEGF in vitro, there was a significant growth delay associated with tepoxalin treatment. Normal dogs were administered tepoxalin to assess effects on systemic VEGF production, but not found to have significantly increased VEGF. These data suggest that tepoxalin may moderately inhibit tumour growth and may be administered as an analgesic to tumour-bearing dogs.

Association of blood monocyte and lymphocyte count and disease-free interval in dogs with osteosarcoma.

BACKGROUND: Identification of biomarkers that predict outcomes in dogs with osteosarcoma (OSA) would be valuable to veterinarians and owners. Leukocyte numbers in peripheral blood are associated with outcomes in some types of cancer in humans. HYPOTHESIS/OBJECTIVES: We hypothesized that increased numbers of monocytes would be associated with reduced disease-free interval (DFI) in dogs with OSA. ANIMALS: Medical data from 69 dogs with appendicular OSA treated with amputation and chemotherapy were selected for study. METHODS: Retrospective study. Statistical associations were assessed by univariate and multivariate analysis. Information about DFI and leukogram values, tumor location, and serum alkaline phosphatase was abstracted from the medical record. RESULTS: Higher numbers of circulating monocytes (>0.4×10(3) cells/µL) and lymphocytes (>1.0×10(3) cells/µL) before treatment were found to be significantly (P<.05) associated with shorter DFI in dogs with OSA. Other parameters associated with poor outcomes were increased alkaline phosphatase, primary tumor location, and age. CONCLUSION AND CLINICAL IMPORTANCE: These results indicated that pretreatment evaluation of monocyte and lymphocyte counts provided prognostic information for dogs with appendicular OSA. Notably, most animals in this study had monocyte counts within the normal reference range, indicating that variations within the reference range of leukocyte values might also have prognostic significance.

Interleukin-11 receptor alpha is expressed on canine osteosarcoma.

Osteosarcoma (OSA) is the most common bone tumour in humans and companion animals, and has a poor long-term prognosis. The identification of new markers and targeted therapies may help increase long-term survival of these patients. Previous studies have demonstrated that interleukin-11 receptor alpha (IL-11Ralpha) is expressed in human and murine OSA but not in normal bone. The current study demonstrated via western analysis, immunoflourescence and immunohistochemistry that IL-11Ralpha was expressed in primary canine OSA tissues as well as in a number of canine OSA cell lines, but not in normal canine bone. Cytotoxin-conjugated antibodies targeting IL-11Ralpha-mediated canine OSA cytotoxicity. Thus, canine OSA may be a valuable model for the evaluation of IL-11Ralpha directed therapies.