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High serum levels of Dickkopf-1 are associated with a poor prognosis in prostate cancer patients
© Rachner et al.; licensee BioMed Central Ltd. 2014
Received: 21 May 2014
Accepted: 30 August 2014
Published: 2 September 2014
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.
Prostate cancer is the most common cancer in men, and patients with advanced disease frequently develop bone metastases . In bone, osteoblast functions are dependent on canonical Wnt signalling . This process is controlled by Wnt inhibitors, including sclerostin and dickkopf-1 (DKK-1) . Elevated levels of DKK-1 promote bone lesions in multiple myeloma and breast cancer by inhibiting osteoblast activity [4–6]. The clinical efficacy of DKK-1 inhibition is currently tested in patients with multiple myeloma . The role of DKK-1 in prostate cancer, however, is less clear. DKK-1 tissue expression has been described to increase in primary prostate cancer lesions compared to normal tissue, and high DKK-1 levels within prostate cancer metastases were associated with poor survival . Furthermore, in a murine model of prostate cancer, DKK-1 stimulated subcutaneous tumour growth and bone metastasis . By contrast, knock-down of DKK-1 delayed the development of both soft tissue and osseous prostate cancer lesions . These findings suggest that DKK-1 may have an impact on cancer biology beyond its role in malignant bone disease. Here, we assessed the role of DKK-1 expression in tissues and sera from patients with prostate cancer and evaluated its prognostic value in affected patients.
Patient characteristics of TMA
Median (IQR) or Frequency (%)
Age at diagnosis (years)
65 (61, 68)
Preoperative PSA (ng/ml)
8.6 (5.54, 15.71)
Tumor staging (n = 400)
Lymph node involvement
All tissue samples were obtained, stored and assessed under the same conditions as approved by the Institutional Review Board (institutional review board of the TU Dresden). Written informed consent was obtained from all patients. Histological processing was performed in the accredited Department of Pathology and conducted using a standardized procedure to assure reproducibility.
DKK-1 tissue protein levels were assessed using IHC as previously described . Briefly, 2 μm-thick paraffin sections were dewaxed, rehydrated using an alcohol gradient, and heat-treated for antigen retrieval. Endogenous peroxidase activity was blocked using 0.3% H2O2/PBS for 10 min at room temperature and non-specific binding sites using the blocking buffer of the VECTASTAIN Elite ABC Kit (VECTOR Laboratories, Peterborough, UK) for 45 min. Sections were incubated with an anti-DKK-1 antibody (ab22827; Abcam, Milton, UK) overnight at 4°C. Subsequently, slides were treated with an anti-goat secondary antibody conjugated to biotin and developed utilizing avidin-conjugated HRP with diaminiobenzidine (DAKO). Specificity of the antibody has been previously validated . TMAs were assessed by two experienced scientists. Staining intensity was scored as either absent (0), weak (1), moderate (2) or strong (3). Unless otherwise specified staining score is presented as the mean value of the 4 tumour or 2 adjacent normal samples from each patient.
Clinical features of patients following division into groups according to DKK-1 serum levels (low vs. high)
Low DKK-1 (n = 40)
High DKK-1 (n = 40)
Mean ± SD
Mean ± SD
16.18 ± 7.5
38.44 ± 7.24
Follow up (years)
8.56 ± 2.77
8.26 ± 3.29
65.03 ± 4.40
65.27 ± 5.66
14.35 ± 13.27
9.86 ± 8.98
All human samples used in this project (serum and tissue) were obtained following informed patient consent and approval of the institutional review board of the TU Dresden (EK195092004).
DKK-1 protein expression in prostatic tissues is presented as the mean score of all available tissue spots from each individual. Groups of two were assessed by the Mann–Whitney-U-Test, groups of three or more were assessed by ANOVA. Correlation was determined by using the Spearman's rank correlation coefficient. Serum and TMA samples were divided into two groups at the DKK-1 median and classified as high or low DKK-1. Kaplan Meier curves were assessed using the log-rank (Mantel-Cox) test. Disease-specific survival (DSS) was defined as time between surgery of the primary tumour and death of disease or time of last follow-up. For overall survival (OS), death of any cause or time of last follow-up was considered as endpoint. Univariate Cox regression was performed on each clinical covariate to examine its impact on survival. Multivariate analyses were performed in a step-wise addition of covariates significant in the univariate analyses. P values < 0.05 were considered statistically significant.
DKK-1 protein levels are increased in prostate cancer tissue
High DKK-1 serum levels are associated with a poor survival in prostate cancer
Uni- and multivariate Cox regression analyses for clinical characteristics and DKK-1 serum levels on overall survival in patients with prostate cancer
pT (pT3/4 vs. pT2)
pN (pN1 vs. pN0)
DKK-1 (high vs. low)
High levels of DKK-1 expression in metastatic prostate cancer tissue have been previously associated with a poorer survival . The role of serum DKK-1 levels in localised prostate cancer patients has not been previously investigated. In line with earlier reports in prostate cancer, we show an increased DKK-1 expression in prostate cancer tissue compared to BPH . In our TMA analyses, no correlation between DKK-1 tissue expression in the primary tumour and patient survival was observed. However, DKK-1 expression within the tumour was very heterogeneous. Heterogeneity is a known finding within prostate cancer lesions [11, 12]. The heterogeneity of DKK-1 protein expression within the tumour may limit the diagnostic value of DKK-1 assessment from biopsies of the primary cancer and also explains the lack of correlation between tumour and serum DKK-1 levels. Assessment of circulating DKK-1 levels in patients at the time of diagnosis, prior to any therapy, revealed that patients with low levels of DKK-1 had a significantly better DSS and OS than those with high DKK-1 levels. A limiting factor of our study is its descriptive nature and the relatively small number of patients available for serum assessment. Larger prospective trials should be performed to further validate the findings presented here. However, there is increasing data from preclinical studies suggesting that DKK-1 may have direct effects on tumour proliferation and cell cycle. High levels of DKK-1 promoted tumour progression , and inhibition of DKK-1 decreased tumour burden in prostate cancer . A decreased tumour burden, following DKK-1 inhibition has also been observed in multiple myeloma . Interestingly, when assessing DKK-1 serum levels in patients with prostate cancer (n = 80) compared to benign prostate hyperplasia (n = 23), we did not see a significant increase (25.3 ± 6.0 vs. 27.9 ± 12.9) in DKK-1 values. This finding, together with the lacking correlation between prostate cancer DKK-1 and DKK-1 serum levels could be explained by the hypothesis that prostate cancer derived DKK-1 only modestly influences DKK-1 serum levels. If this is the case, increased DKK-1 expression in non-tumour derived tissue, as seen in our TMA, may have direct tumour promoting effects. There are an increasing number of reports that suggest different mechanisms by which DKK-1 may affect tumour biology. These anti-tumour effects appear to be, at least in part, independent of Wnt signaling and a role of p21CIP-1/WAF-1 has been suggested . Recently, DKK-1 was reported to mediate tumour survival in osteosarcoma cells, via the stress response enzyme ALDH1 . In addition, a negative correlation between DKK-1 serum levels and prognosis has been suggested in non-small cell lung cancer as well as cervical carcinoma [15, 16]. These observations support the role of DKK-1 as a potential tumour promoter and are fully consistent with our finding that high circulating DKK-1 levels are associated with a worse disease-specific and overall survival in prostate cancer patients. However, it remains unclear to what extent DKK-1 serum levels are tumour derived, or if high levels of circulating DKK-1 from other sites promote tumour growth and/or resistance to therapy.
In conclusion, high levels of serum DKK-1 were associated with a poorer overall survival in prostate cancer patient. In light of anti-DKK-1-antibodies currently under clinical evaluation for patients with advanced multiple myeloma, these data warrant further research on the role of DKK-1 in solid malignancies, including prostate cancer.
This work was supported by the DAdorW/Amgen Bone Fellowship and the MedDrive start-up grant from the TU Dresden to TDR, and grants RA 2151/2-1 (to TDR and LCH) and Forschergruppe-1586 SKELMET to SF, MK and LCH from the Deutsche Forschungsgemeinschaft. We thank Josefa Hötzel, Sandra Hippauf and Jörg Hofmann for technical assistance.
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