The potential cancer preventive roles of calcitriol, the dihydroxylated metabolite of vitamin D3, as well as 20(S)-protopanaxadiol (aPPD), the aglycone of the protopanaxadiol family of ginsenosides, have gained much attention in recent years for the prevention/treatment of prostate cancer (PCa).
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In the present study, we evaluated the anticancer and chemosensitization effects of calcitriol at clinically relevant concentrations and aPPD, either alone or in combination, in two well-characterized human PCa cell lines: androgen-sensitive non-metastatic LNCaP cells and androgen-independent metastatic C4-2 cells. The effects of the treatments on PCa cell viability and proliferation rates were evaluated by MTS and Brdu assays, respectively. Combination Indices (CI) and Dose Reduction Indices (DRI) were estimated to assess synergistic anticancer activity using Calcusyn software (Biosoft, Cambridge, UK). Then, we determined the potential Pharmacodynamic interaction mechanisms as follows: The protein expression levels of the genes those are known to control cell cycle (cyclin D1 and cdk2); apoptosis (Bcl-2, Bax, and Capspases 3), androgen receptor and vitamin D receptors were examined upon combinational treatment. The cell viability assay data show that addition of 10nM calcitriol to aPPD significantly lowered its IC50 values from the range of 41-53μM to 13-23μM, in LNCaP and C4-2 prostate cancer cells. The cell proliferation rate was significantly lower for combination treatments compared to the cells treated with aPPD alone. Similarly, Western blot results indicate that aPPD significantly upregulated vitamin D receptor (VDR) expression, while calcitriol further enhanced the ability of aPPD to induce pro-apoptotic BAX, increased cleaved caspase-3 and downregulate cdk2 protein levels. Thus, the pharmacodynamic interaction between aPPD and calcitriol in impacting growth inhibition and apoptosis appears to be synergistic in nature. In conclusion, calcitriol sensitizes PCa cells to aPPD-mediated anticancer effects by enhancing its ability to induce apoptosis and reduce cell proliferation, and this synergism may limit calcitriol toxicity by facilitating the use of lower calcitriol doses. The associated increase in VDR expression and calcitriol half-life may be mechanistically associated with this sensitization effect.
The Journal of steroid biochemistry and molecular biology. 2015 Dec 17 [Epub ahead of print]
Mohamed Ben-Eltriki, Subrata Deb, Hans Adomat, Emma S Tomlinson Guns
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The Vancouver Prostate Centre at Vancouver General Hospital, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada; Department of Experimental Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada. , Department of Biopharmaceutical Sciences, College of Pharmacy at Roosevelt University, Schaumburg, IL, USA. , The Vancouver Prostate Centre at Vancouver General Hospital, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada. , The Vancouver Prostate Centre at Vancouver General Hospital, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada; Department of Urologic Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.