Iron overload augments 7,12-dimethylbenz(a)anthracene-initiated and 12-O-tetradecanoylphorbol-13-acetate-promoted skin tumorigenesis.

Reactive oxygen species and free radicals have been implicated in the multistep cutaneous chemical carcinogenesis. Much of the experimental evidence in this regard is indirect and is based on observations that prooxidant status usually enhances and antioxidant treatments generally inhibit tumor yield. Iron overload is known to enhance peroxidative damage and cause oxidative stress. In this study, we report that iron overload augments 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated cutaneous tumor promotion. Female Swiss mice were subjected to iron overload by injecting 1 mg iron/ mouse/day consecutively for 2 weeks. Tumors were initiated by applying a single dose of 7,12-dimethylbenz(a)anthracene and promoted with twice weekly applications of TPA for 20 weeks and the appearance of first tumor (latency period), percent incidence and number of tumors per mouse were recorded. It has been observed that the level of iron in involved (tumor-bearing) skin was about fourfold higher as compared to uninvolved (non-tumor) skin of iron overload animals and about tenfold higher as compared to the iron level in the skin of normal animals. When compared to the iron-unloaded control group, the iron overload mice showed an increased incidence of tumors. In iron overload animals, the tumors appeared 3 weeks earlier and also the number of tumors per mouse was significantly higher (2.5-fold). These data indicate that iron overload augments TPA-mediated tumor promotion. We propose that oxidative stress generated by iron overload may be responsible for the augmentation of cutaneous tumorigenesis.