The Wnt inhibitor Dickkopf-1 (DKK-1) has been linked to the progression of malignant bone disease by impairing osteoblast activity. In addition, there is increasing data to suggest direct tumor promoting effects of DKK-1. The prognostic role of DKK-1 expression in prostate cancer remains unclear. A prostate cancer tissue microarray (n = 400) was stained for DKK-1 and DKK-1 serum levels were measured in 80 patients with prostate cancer. The independent prognostic value of DKK-1 expression was assessed using multivariate analyses. DKK-1 tissue expression was significantly increased in prostate cancer compared to benign disease, but was not correlated with survival. However, high DKK-1 serum levels at the time of the diagnosis were associated with a significantly shorter overall and disease-specific survival. Multivariate analyses defined high serum levels of DKK-1 as an independent prognostic marker in prostate cancer (HR 3.73; 95%CI 1.44-9.66, p = 0.007). High DKK-1 serum levels are associated with a poor survival in patients with prostate cancer. In light of current clinical trials evaluating the efficacy of anti-DKK-1 antibody therapies in multiple myeloma and solid malignancies, the measurement of DKK-1 in prostate cancer may gain clinical relevance.

Recent evidence suggests that the prostate cancer (PCa)-specific up-regulation of certain genes such as AMACR, EZH2, PSGR, PSMA and TRPM8 could be associated with an aberrant expression of non-coding microRNAs (miRNA). In silico analyses were used to search for miRNAs being putative regulators of PCa-associated genes. The expression of nine selected miRNAs (hsa-miR-101, -138, -186, -224, -26a, -26b, -374a, -410, -660) as well as of the aforementioned PCa-associated genes was analyzed by quantitative PCR using 50 malignant (Tu) and matched non-malignant (Tf) tissue samples from prostatectomy specimens as well as 30 samples from patients with benign prostatic hyperplasia (BPH). Then, correlations between paired miRNA and target gene expression levels were analyzed. Furthermore, the effect of exogenously administered miR-26a on selected target genes was determined by quantitative PCR and Western Blot in various PCa cell lines. A luciferase reporter assay was used for target validation. The expression of all selected miRNAs was decreased in PCa tissue samples compared to either control group (Tu vs Tf: -1.35 to -5.61-fold; Tu vs BPH: -1.17 to -5.49-fold). The down-regulation of most miRNAs inversely correlated with an up-regulation of their putative target genes with Spearman correlation coefficients ranging from -0.107 to -0.551. MiR-186 showed a significantly diminished expression in patients with non-organ confined PCa and initial metastases. Furthermore, over-expression of miR-26a reduced the mRNA and protein expression of its potential target gene AMACR in vitro. Using the luciferase reporter assay AMACR was validated as new target for miR-26a. The findings of this study indicate that the expression of specific miRNAs is decreased in PCa and inversely correlates with the up-regulation of their putative target genes. Consequently, miRNAs could contribute to oncogenesis and progression of PCa via an altered miRNA-target gene-interaction.

Background: We assessed serum concentrations of the receptor activator of nuclear factor kappa-B ligand (RANKL) and its decoy receptor osteoprotegerin (OPG), two proteins implicated in the development and progression of breast cancer (BC), in 509 patients with primary, non-metastatic BC. Then the results were evaluated with regards to the occurrence of bone metastases, the presence of disseminated tumor cells (DTC) in the bone marrow, survival and risk of developing metastatic disease. Patients and Methods: Before surgery, two bone marrow aspirates were analyzed for DTC using density centrifugation followed by immunocytochemistry (pan-cytokeratin antibody A45-B/B3). RANKL and OPG levels in the serum were measured by ELISA. Results: RANKL levels were significantly lower in women >60 years (p<0.0001) and RANKL/OPG ratios higher in lymph node-positive patients (p<0.05). High OPG serum levels were associated with a higher risk of death from BC (HR 1.94 95%CI 1.23-3.07; p=0.005) and OPG was an independent prognostic marker for BC specific survival (multivariate analyses, p=0.035). RANKL levels were 33% higher (p<0.0001) in DTC^pos patients (41%) whereas high levels were associated with a significantly better BC specific survival in DTC^neg patients as compared to low levels (HR 0.524; 95%CI 0.30-0.95; p=0.04). RANKL serum levels were significantly increased in patients who developed bone metastases (p=0.01) and patients within the highest quartile of RANKL had a significantly increased risk of developing bone metastases compared to those in the lowest (HR 4.62, 95%CI 1.49-14.34, p=0.03). Conclusion: These findings warrant further investigation as they provide a rationale for novel diagnostic or therapeutic approaches.

Docetaxel (DTX) is a mainstay in the treatment of metastatic prostate cancer. Failure of DTX therapy is often associated with multidrug resistance caused by overexpression of efflux membrane transporters of the ABC family such as the glycoprotein ABCB1. This study investigated multiple approaches targeting ABCB1 to resensitize DTX-resistant (DTXR) prostate cancer cell lines. In DU145 DTXR and PC-3 DTXR cells as well as age-matched parental controls, the expression of selected ABC transporters was analyzed by quantitative PCR, Western blot, flow cytometry and immunofluorescence. ABCB1 effluxing activity was studied using the fluorescent ABCB1 substrate rhodamine 123. The influence of ABCB1 inhibitors (elacridar, tariquidar), ABCB1-specific siRNA and inhibition of post-translational glycosylation on DTX tolerance was assessed by cell viability and colony formation assays. In DTXR cells, only ABCB1 was highly upregulated, which was accompanied by a strong effluxing activity and additional post-translational glycosylation of ABCB1. Pharmacological inhibition and siRNA-mediated knockdown of ABCB1 completely resensitized DTXR cells to DTX. Inhibition of glycosylation with tunicamycin affected DTX resistance partially in DU145 DTXR cells, which was accompanied by a slight intracellular accumulation and decreased effluxing activity of ABCB1. In conclusion, DTX resistance can be reversed by various strategies with small molecule inhibitors representing the most promising and feasible approach.