Applying sun protection factor 30 (SPF30) sunscreen prior to exposure to ultraviolet-B (UVB) light delayed melanoma onset in a mouse model, report researchers from The Ohio State University Comprehensive Cancer Center Comprehensive Cancer Center -- Arthur G. James Cancer Hospital and Richard J. Solove Research Institute in Columbus.

The findings were presented at the American Association for Cancer Research Annual Meeting 2016 in New Orleans.

"Over the past 40 years, the melanoma incidence rate has consistently increased in the United States," says principal investigator Christin Burd, PhD an assistant professor in the Department of Molecular Genetics and the Department of Molecular Virology, Immunology & Medical Genetics at The OSUCCC -- James. "Sunscreens are known to prevent skin from burning when exposed to UV sunlight, which is a major risk factor for melanoma. However, it has not been possible to test whether sunscreens prevent melanoma, because these are generally manufactured as cosmetics and tested in human volunteers or synthetic skin models.

"We have developed a mouse model that allows us to test the ability of a sunscreen to not only prevent burns but also to prevent melanoma," Dr. Burd says. "This is a remarkable accomplishment. We hope that this model will lead to breakthroughs in melanoma prevention."

These genetically engineered mice spontaneously develop melanoma about 26 weeks after the chemical 4-hydroxytamoxifen (4OHT) is applied to the skin.

In the new study, researchers found that if they exposed these mice to a single dose of UVB light one day after applying 4OHT to the skin, melanomas appeared much more rapidly, and there were many more tumors.

The researchers then used the mouse model to test the ability of a number of sunscreens labeled SPF30 to prevent melanoma. The sunscreens, which contained a range of UV-blocking agents, were applied to the mice prior to exposure to the UVB light. All the sunscreens delayed melanoma onset and reduced tumor incidence.

"There were some minor differences in melanoma prevention amongst the different SPF30-labeled sunscreens," says Burd. "However, we later discovered that even though the sunscreens were all marketed as SPF30, some were actually predicted to have a higher rating. For this reason, it is hard to compare the melanoma-preventing capacity of the different sunscreens at this time."

A major limitation of the study is that the short dose of UVB used in these experiments is equivalent to the amount of UVB exposure a person might experience in a week's long beach vacation. In addition, researchers used only UVB light, which means that the mice were exposed to only a portion of the entire UV spectrum present in sunlight.

The OSUCCC -- James team will continue research aimed at isolating which specific sunscreen ingredients that provide the strongest protection against melanoma to develop smarter sunscreens that are both safe to use and proven effective in reducing skin cancer risk.

This study was funded by Pelotonia, a grassroots cycling event based in Columbus, Ohio, which has raised more than $106 million for cancer research at Ohio State.

PHOTO CAPTION: SPF-30 rating can prevent the formation of melanoma

Credit: The Ohio State University Comprehensive Cancer Center - Arthur G. James Cancer Hospital and Richard J. Solove Research Institute