New testing model underlines how SPF30 sunscreen can delay melanoma
The research was conducted on a mouse model with similar skin characteristic to humans, which the research team says can be used to identify new, more effective melanoma-preventing agents.
The research was carried out by the Ohio State University Comprehensive Cancer Center - Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, and the resulting data was presented at the American Association for Cancer Research (AACR) annual meeting, earlier this month.
Focusing on melanoma prevention rather than sunburn
The primary objectives of the research were to discover how to veer away from current research that focuses on sunscreens preventing sunburn towards the discovery of how they can reduce the risk of melanomas.
"Over the past 40 years, the melanoma incidence rate has consistently increased in the United States," said Burd, an assistant professor in the Department of Molecular Genetics and the Department of Molecular Virology, Immunology & Medical Genetics at The OSUCCC.
"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.”
A mouse model developed for the study
To look deeper into the effects of sunscreen on melanomas, the scientists developed a mouse model that tests for both burns and melanomas after exposure to UV rays, an invention that was previously reported on in the in the AACR journal Cancer Discovery
According to the scientists, these genetically engineered mice spontaneously develop melanoma about 26 weeks after the chemical 4-hydroxytamoxifen (4OHT) is applied to the skin.
According to Burd, the study on the mice found that, if they exposed the genetically engineered 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. "Melanoma-free survival was reduced by 80 percent, to about five weeks,"
The SPF30 test
The scientists then applied a number of sunscreens with a number of UV-blocking agents to the mice prior to exposing them to UVB light. The results were impressive, determining that all delayed melanoma onset and reduced tumor incidence.
"There were some minor differences in melanoma prevention amongst the different SPF30-labeled sunscreens," said 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."
Study limitations and what’s next
The team of scientists says it is now working to adapt the testing method to more realistic conditions, given that the dose of UVB exposure used in the experiment was the equivalent of the average exposure any individual might get in week-long beach holiday.
As a result, the scientists are now working to reduce the level of UVB exposure in the experiment, while also increasing the UV spectrum to represent typical exposure from sunlight.
The next stage of the experiment will also look at how different sunscreen ingredients act on both burns and melanomas, although Burd does also point out that experimenting on animals means funding from cosmetics companies committed to non-animal testing is not possible.
