Vitamin D receptor agonist EB1089 is a potent regulator of prostatic "intracrine" metabolism.
BACKGROUND
A contributing factor to the emergence of castrate resistant prostate cancer (CRPC) is the ability of the tumor to circumvent low circulating levels of testosterone during androgen deprivation therapy (ADT), through the production of "intracrine" tumoral androgens from precursors including cholesterol and dehydroepiandrosterone (DHEA). As these processes promote AR signaling and prostate cancer progression their modulation is required for disease prevention and treatment.


METHODS
We evaluated the involvement of the vitamin D receptor ligand EB1089 in the regulation of genes with a role in androgen metabolism using the androgen dependent cell lines LNCaP and LAPC-4. EB1089 regulation of androgen metabolism was assessed using QRT-PCR, luciferase promoter assays, western blotting, enzyme activity assays, and LC-MS analyses.


RESULTS
EB1089 induced significant expression of genes involved in androgen metabolism in prostate cancer cells. Real-Time PCR analysis revealed that VDR mediated significant regulation of CYP3A4, CYP3A5, CYP3A43, AKR1C1-3, UGT2B15/17, and HSD17B2. Data revealed potent regulation of CYP3A4 at the level of mRNA, protein expression and enzymatic activity, with VDR identified as the predominant regulator. Inhibition of CYP3A activity using the specific inhibitor ritonavir resulted in alleviation of the anti-proliferative response of VDR ligands in prostate cancer cells. Mass spectrometry revealed that overexpression of CYP3A protein in prostate cancer cells resulted in a significant increase in the oxidative inactivation of testosterone and DHEA to their 6-β-hydroxy-testosterone and 16-α-hydroxy-DHEA metabolites, respectively.


CONCLUSIONS
These data highlight a potential application of VDR-based therapies for the reduction of growth-promoting androgens within the tumor micro-environment.
School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, United Kingdom.
Declan
D
Doherty
Scarlett Anne
SA
Dvorkin
Edna Patricia
EP
Rodriguez
Paul Daniel
PD
Thompson
D000728:Androgens / Q000235:genetics / Q000378:metabolism*; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D051544:Cytochrome P-450 CYP3A / Q000032:analysis / Q000235:genetics; D065692:Cytochrome P-450 CYP3A Inhibitors; D003687:Dehydroepiandrosterone / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D011467:Prostate / Q000187:drug effects* / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism*; D064129:Prostatic Neoplasms, Castration-Resistant / Q000378:metabolism / Q000517:prevention & control; D012333:RNA, Messenger / Q000032:analysis; D018167:Receptors, Calcitriol / Q000819:agonists / Q000502:physiology*; D019438:Ritonavir / Q000494:pharmacology; D013739:Testosterone / Q000378:metabolism
D000728:Androgens; D065692:Cytochrome P-450 CYP3A Inhibitors; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D013739:Testosterone; D003687:Dehydroepiandrosterone; D051544:Cytochrome P-450 CYP3A; D002117:Calcitriol; D019438:Ritonavir; C078903:seocalcitol
AKR1C; CYP3A; metabolism; prostate cancer; vitamin D receptor