"It is not a sun-screening effect, but it's something more than that - it's a biological effect," said Allan Conney, William M. and Myrle W. Garbe Professor of Cancer and Leukemia Research at Rutgers' Ernest Mario School of Pharmacy. "We may have found a safe and effective way of preventing skin cancer," he said of the discovery, described in the Proceedings of the National Academy of Sciences early online edition, available the week of Aug. 26.
It has been known for a long time that skin cancer is caused predominantly by sunlight. The authors, a group that included Conney and a team of other researchers in the laboratory, explained that sunscreen use has decreased the risk of skin cancers, but there is a need to identify additional approaches for skin-cancer prevention in individuals previously exposed to high-dose levels of sunlight.
The research team, all members of the school's department of chemical biology, studied a special strain of hairless mice that had been exposed to ultraviolet B light twice weekly for 20 weeks. This put the mice at risk for tumor formation and skin cancer. After stopping the exposures, the researchers applied caffeine and epigallocatechin gallate (EGCG), two components of green tea, topically to the skin. Both caffeine and EGCG significantly inhibited cancer formation in the mice.
Although the study showed that most of the positive effects were true for both of these substances, caffeine has the advantage over EGCG. EGCG is chemically less stable, so there could be a problem in applying it topically, Conney said A previous study conducted in the laboratory dealt with caffeine taken orally. The caffeine was provided in the drinking fluid for the mice and the researchers found it inhibited ultraviolet light-induced tumors and cancers in this case, as well. Conney cites advantages to using the direct skin application over oral administration, pointing to the ability to provide more highly concentrated doses and larger overall dosages. "Whether you can give enough orally to be effective in humans is not known," said Conney. "Whether people could ingest that amount without becoming hyperactive is also a real question mark."
The newly published study also reported the highly selective action of both caffeine and EGCG in killing cancer cells. Adjacent normal skin cells were not affected. "The discovery of this selectivity was very exciting to us," said Conney. "Also, in our study it didn't matter if the tumors were benign or malignant; cells in both were killed while leaving the normal cells alone."
The study suggests further research is needed to determine whether or not the skin application of these agents would be effective in people. The researchers anticipate human clinical trials in the near future. "For now," said Conney, "if you are a mouse, it would be terrific. In people we just don't know yet."
EDITOR'S NOTE: Professor Conney is available for interviews at (732) 445-4940. He may also be contacted at email@example.com. Text of Conney's paper is available from www.eurekalert.org or by contacting the PNAS news office at firstname.lastname@example.org.