Anti-proliferative effects of vitamin D on prostate cancer cells in vitro
There is evidence that vitamin D is active against prostate cancer (Schwartz & Hulka, 1990). Epidemiological studies have found that men with low serum levels of vitamin D have an increased risk of this disease (Ahonen et al., 2000). There is a lack of evidence of the effect of 1,25-dihydroxy vitamin D3 (1,25(OH)D), the active metabolite of vitamin D, on various stages of prostate cancer in vitro. The initial aim of this study was to investigate the effect of 1,25(OH)D on proliferation of three prostate carcinoma cell lines: DU145, LNCaP, and PC-3. The second part of the study aimed to assess possible mechanisms of anti-proliferative action. The effects of 1,25(OH)D were examined on the synthesis of the vitamin D receptor (VDR), the p21 tumour suppressor protein, and the CYP24 cytochrome P450. Methods:
The active metabolite of vitamin D, 1,25(OH)D, was added to each cell line in concentrations up to 100 nM. Cells were incubated for 72 h and proliferation was assessed using an MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Cell viability data from this assay were statistically analysed using a statistical computer software package (SPSS version 11). Treated and untreated control cells were compared using one-way ANOVA with LSD post-hoc analysis. Results are expressed as mean ± SD. Significance was taken as P < 0.05. The most responsive cell line, DU145, was further analysed by reverse transcription-polymerase chain reaction (RT-PCR). Additions of 1,25(OH)D were made to DU145 cells and incubated for 72 h. RNA was extracted and reverse transcribed into cDNA. The cDNA was amplified, electrophoresed and compared against a control to determine the expression levels of VDR, p21 and CYP24. Results:
The cells most responsive to 1,25(OH)D were DU145 cells and exhibited 54 ± 10.3% growth inhibition at the highest concentration tested, 100 nM. Treatment of LNCaP cells with 1,25(OH)D revealed a trend towards growth inhibition (90.0 ± 13.8%) whereas PC-3 cells were not affected. Transcription of the genes for VDR, p21 and CYP24 was investigated in DU145 cells only. Transcription of the genes for VDR and p21 was undetectable in both control and treated DU145 cells. Transcription of CYP24 did not occur in untreated cells but was induced by addition of 100 nM1,25(OH)D. Discussion:
The addition of 1,25(OH)D significantly attenuated proliferation of DU145 cells but not LNCaP or PC-3 cells. This suggests that 1,25(OH)D is a potent inhibitor of DU145 prostate cancer cells but not the other two cell lines. DU145 cells are androgen insensitive and are representative of prostate cancer with moderate metastatic potential. This study suggests that 1,25(OH)D may be chemoprotective in more advanced stages of prostate cancer. Previous studies suggested that effects on DU145 cells might result from 1,25(OH)D enabling the VDR to activate transcription of genes that have appropriate response elements in their promoters (Skowronski et al., 1993). These include the gene for the tumour suppressor protein p21. However, RT-PCR analysis indicated that mRNAs for VDR and p21 were not present in DU145 cells and that transcription was not induced by 1,25(OH)D. Transcription of the gene for CYP24 was activated by 100 nM1,25(OH)D. CYP24 is known to metabolise 1,25(OH)D. It is possible that a derivative of 1,25(OH)D acts against DU145 cells. Conclusion:
This study shows that 1,25(OH)D is active against the DU145 prostate cancer cell line. This effect does not involve the VDR transcriptional activator but may be associated with CYP24 cytochrome P450-catalysed modification of 1,25(OH)D. References:
Ahonen, M.H., Tenkanen, L., Teppo, L., Hakama, M. & Tuohimaa, P. (2000) Prostate cancer risk and prediagnostic serum 25-hydroxyvitamin D levels (Finland). Cancer Causes Control, 11, 847–852.
Schwartz, G.G. & Hulka, B.S. (1990) Is vitamin D deficiency a risk factor for prostate cancer? (Hypothesis). Anticancer Res. 10, 1307–1311.
Skowronski, R.J., Peehl, D.M. & Feldman, D. (1993) Vitamin D and prostate cancer: 1,25 dihydroxyvitamin D3 receptors and actions in human prostate cancer cell lines. Endocrinology132, 1952–1960.
Document Type: Research Article
Publication date: 2011-06-01