Effects of hypoxia and iron on ascorbic acid-mediated cytotoxicity in prostate cancer cell lines

Ascorbic acid (ASC) has long been proposed as a potential cancer co-treatment due to its specific toxicity towards cancer cells, but discrepancies between in vitro and in vivo studies suggest that external factors may modulate its cytotoxicity. Here, we investigate the impact of hypoxia and iron on the therapeutic effectiveness of ASC on prostate cancer cell lines. Hypoxia-induced increases in the EC₅₀ of ASC in the prostate cancer cell lines PC-3, DU 145, LNCaP, and CWR22Rv1 but not in the prostate non-cancer cell lines RWPE-1 and TERT-PrECs. The synthetic androgen dihydrotestosterone did not modify ASC's effectiveness in either normoxia or hypoxia, which was tested because both early and advanced prostate cancer maintain the androgen receptor pathway. The effects of hypoxia on cytotoxicity depend on the drug. Hypoxia did not affect the EC₅₀ for the DNA-damaging agent etoposide but decreased the sensitivity for the anti-microtubule agent paclitaxel in PC-3 and DU 145 cells. Although hypoxic cells were iron deficient, adding iron back to cells did not reverse the effects of the hypoxic atmosphere. Interestingly, the EC₅₀ for ASC was approximately two-fold higher in iron-treated cells than non‑iron-treated cells for the PC-3 line. The higher EC50 was not observed by knocking down ferritin heavy chain mRNA. In summary, both hypoxia and iron attenuate the effectiveness of high concentrations of ASC in prostate cancer cell lines, which may affect the therapeutic benefit of ASC for prostate cancer patients.