The role of zinc in prostate cancer
AuthorWetherell, David Robert
AffiliationSurgery (Austin & Northern Health)
Access StatusOpen Access
© 2018 Dr. David Robert Wetherell
Prostate cancer (PCa) is the most common cancer amongst Australian men. Zinc is an essential metal and is vital for normal function of the prostate gland. Castrate-resistant prostate cancer (CRPC) is becoming increasingly resistant and treatment options are limited in number and often associated with poor clinical outcomes. Therefore a pertinent clinical issue is to develop more effective treatment regimes. Zinc appears to play a role in PCa, but a true understanding leading to therapeutic developments is yet to be achieved. In particular evidence regarding cell proliferation and zinc uptake and levels in PCa cells is conflicting. HIF1α is a well-known prognostic marker in PCa associated with poor prognosis, resistance to treatment and development of metastatic disease, however the cause over-expression in CRPC remains a mystery. Therefore the ability of PCa cells to uptake and store zinc, and the role of zinc in PCa cell proliferation, tumour growth and HIF1α mediated survival was investigated in this thesis. CRPC-like human PC3 cells are significantly resistant to docetaxel chemotherapy and overexpress HIF1α protein, compared to normal prostate epithelial control cells (PNT1A). Cell proliferation assays (MTT) demonstrated that physiological zinc administered to PC3 cells significantly slowed growth compared to normal PNT1A and androgen-sensitive PCa (LNCaP) cells. The effect of zinc supplementation or zinc chelation (by TPEN) does not affect macroscopic growth in PC3 xenograft tumours. There is no significant difference in baseline total zinc concentration (measured by ICP-MS) between cell lines normal (PNT1A), androgen sensitive (LNCaP) and CRPC (DU145 and PC3) cells. However, CRPC-like PC3 cells contain significantly higher unbound free Zn2+ and Immunofluorescence Microscopy (IFM) subcellular distribution of Zn2+ in PC3 cells is unlike that seen in normal prostate epithelial cells. PC3 cells are resistant to oxidative stress injury. Zinc strongly induces HIF1α protein expression in these cells in a time and dose dependent manner. Zinc mediated oxidative protection in PC3 cells is a HIF1α dependent as demonstrated in a PC3 HIF1α-KD model. No such zinc protection was seen PNT1A cells. Zinc could be essential in the resistant nature of CRPC cells as Zn2+ ions rescue HIF1α protein expression and are implicated in the normoxic stabilisation of the HIF1α protein by competing with Fe2+ ions at the PHD binding sites. Therefore zinc dysregulation in CRPC cells is an important factor in the development of resistance, as well as potentially progression to metastatic disease and poor prognosis in PCa.
Keywordsprostate; cancer; prostate cancer; castrate resistant; hypoxia inducible factor 1 alpha; prostate cancer; zinc; iron
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