Common fruits not only contain a number of vitamins and minerals that help fight everyday illnesses but could also harbour agents that can reduce the risk for skin cancer, suggests new research presented this week at the Frontiers in Cancer Prevention Research meeting.

Researchers from the University of Wisconsin reported that a pomegranate extract inhibited skin tumours in mice, while the red wine compound reseveratrol, applied topically, inhibited the expression of a cancer-causing protein normally caused by exposure to UVB rays.

"We are pleased to see numerous studies exploring the therapeutic value of topically-applied natural ingredients that people can begin incorporating into everyday life and may enhance the activity of standard sunscreens," said Dr David Alberts from the University of Arizona.

Incidence of skin cancer, which is the most frequently diagnosed malignancy in the United States, is also growing rapidly in Europe. In the UK, melanoma accounts for 2 per cent of all newly diagnosed cancers each year. Among people under 35, it is the third most common cancer in women and fifth most common in men.

Pomegranate fruit extract (PFE), from the tree Punica granatum, contains several polyphenols and anthocyanidins (pigment that gives certain fruits their dark red colour), which demonstrates a higher antioxidant activity than that of red wine and green tea, according to the Wisconsin researchers.

The team evaluated pomegranate's anti-skin tumour effects by comparing topical application of pomegranate extract on neonatal mice (CD-1) against TPA-induced markers (12-0-tetradecanoylphorbol-13-acetate), a strong promoter of chemically induced skin cancer. Applying pomegranate extract (2 mg/mouse) onto the skin of neonatal mice 30 minutes prior to TPA (3.2 µmole/mouse) application significantly inhibited TPA-mediated increases in skin edema and hyperplasia, they said.

They also tested the pomegranate extract on TPA-induced skin tumour promotion. The animals pretreated with pomegranate extract showed substantially reduced tumour incidence and lower tumour body burden. In the TPA treated group, all mice developed tumours at 16 weeks, whereas only 30 per cent of the mice treated with pomegranate extract exhibited tumours at that point.

"For the first time, we have clear evidence that pomegranate extract possesses anti-skin-tumour-promoting effects," said Dr Farrukh Afaq, lead investigator of the study.

He added: "With such a variety of pathways inhibited by the topical application of the natural supplement, we are confident of its therapeutic value and hope it will translate to other models."

According to the researchers, because pomegranate is capable of inhibiting conventional as well as novel biomarkers of TPA-induced tumours, it may possess chemopreventive activity in a wide range of tumour models. The researchers plan to carry out an in-depth study to define its active agents.

A second study presented at the conference (abstract 1489) examined the effect of resveratrol, an antioxidant found in grapes and red wines, on UVB-related skin damage. Researchers evaluated the effect of topical application of resveratrol (10 µmole/mouse/0.2 ml acetone) on multiple UVB (seven consecutive exposures in seven days) exposure-mediated damages in the skin of SKH-1 hairless mice.

The study evaluated resveratrol's influence on survivin, involved in the control of cell division, and a structurally unique member of the apoptosis inhibitors protein family. Survivin is overexpressed in most human cancers, but absent in normal adult tissues, and is considered a promising therapeutic target for novel anticancer therapies. Results of the study showed that resveratrol treatment significantly decreased UVB exposure-mediated up-regulation in the mRNA levels and protein expression of survivin.

"We're pleased to see that resveratrol is able to modulate multiple signaling in the cells, which actually protects the skin cells from damages that may lead to the development of cancer," said Dr Nihal Ahmad, of the University of Wisconsin, and lead author of the study. "Further study should continue to support the argument to incorporate this agent into skin care products and regular diets, through the moderate consumption of grapes and red wine."

Resveratrol significantly inhibited UVB-mediated increases in skin thickness and edema; epidermal cyclooxygenase (COX-2); ornithine decarboxylase (ODC) enzyme and protein levels; and protein levels of proliferating cell nuclear antigen (PCNA), all of which are established markers of tumor promotion. Resveratrol also further stimulated a UVB-mediated increase in p53 protein levels and was found to inhibit UVB exposure-mediated increases in cell cycle promoting signals including the activation of cell division.

Dr Alberts noted the need for promotion of such research. "The incidence of skin cancer is rising faster than any other solid tumour in the United States. It is critical that we develop novel approaches to both primary and secondary prevention of what appears to be becoming an epidemic."

The conference , taking place in Phoenix, Arizona, ends today.