If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Sunlight And Melanin Implicated In Cancerous Chemistry

Photochemistry: Skin pigments participate in DNA-damaging reactions hours after exposure to UV light

by Matt Davenport
February 19, 2015 | A version of this story appeared in Volume 93, Issue 8

The sun can induce cancerous DNA damage in skin cells even after it sets, according to a new study (Science 2015, DOI: 10.1126/science.1256022).

Credit: National Cancer Institute
Melanomas, such as this one, are often caused by exposure to UV light.
Photo of a skin melanoma lesion.
Credit: National Cancer Institute
Melanomas, such as this one, are often caused by exposure to UV light.

An international team of scientists has found that radical species generated by ultraviolet light can cause damage to DNA long after irradiation stops. They do this with the aid of compounds derived from melanin, a pigment known to shield mammals from burns and other harmful UV effects. The melanin-assisted process creates lesions known as cyclobutane pyrimidine dimers in DNA, which can lead to mutations that cause melanoma, a type of skin cancer.

These lesions are identical to the well-known genetic alterations caused when UV light directly strikes DNA. “But at least half of the dimers you get come in the dark, rather than during your trip to the beach,” says Douglas E. Brash of Yale University, who led the new study.

These chemically mediated lesions can take hours to evolve, Brash explains, whereas direct DNA damage occurs within picoseconds of exposure. Using techniques including mass spectrometry and high-performance liquid chromatography, the researchers identified a previously unrecognized process that could play a significant role in melanomas.

UV light stimulates enzymes that produce superoxide and nitric oxide, Brash says. These radicals react to create peroxynitrite, which can oxidize and fragment melanin polymers. Peroxynitrite further reacts with these fragments, creating unstable compounds. These molecules degrade into electrically excited species able to dump their energy into DNA and damage it.

“There’s no other way to explain how you get the damage after you turn the light off,” says John-Stephen Taylor, a chemist at the University of Washington in St. Louis, who was not involved in the study. In a written perspective, Taylor calls the new report a “brilliant piece of detective work” (Science 2015, DOI: 10.1126/science.aaa6578).

The researchers hope their work will help create topical treatments or “evening after” sunscreens to block this chemical damage, Brash says. In the meantime, people can protect themselves by wearing sunscreen and staying out of tanning beds.

“Basically, don’t fry yourself,” he suggests.

Melanoma schematic.
Credit: Shutterstock
If melanomas are caught early, doctors can excise cancer cells before they spread.


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.