Who you gonna call? Pt. 2

The last entry of this blog tried to answer the question why calling microbes for help is a good idea to protect you from sunburns. Sunburns are not only painful, they also make your skin age faster and increase your risk for skin cancer [1].

Recently, another bacterial hero emerged that might not you protect you from sunburns but it produces a compound that stops skin cancer. "Where can one find this heroic bacterium?", you ask. Thermal vents in the deep sea? The guts of exotic animals? Well, look no further than your own skin and you'll find it! Staphylococcus epidermidis is often outshone by its notorious cousin Staphylococcus aureus, but it's a bit of a Dr. Jekyll & Mr. Hyde itself. With its Jekyll-personality it's a normal bacterium found in the skin flora - but beware of the Hyde: S. epidermidis can make nasty-to-treat biofilms and cause severe infections in immuno-compromised patients.

Now, researchers have added another personality to S. epidermidis' psychographic: that of a melanoma (skin cancer) -fighting hero! Certain strains of S. epidermidis produce a small compound called 6-N-hydroxyaminopurine (6-HAP) [2]. Chemically, 6-HAP resembles adenine - a DNA building block (theme-alert!) - and that's also the secret behind the anti-cancer effect. DNA building block look-alikes are used to treat viral infections and certain cancers because they inhibit the synthesis of new DNA. These molecules are similar enough to the proper DNA building blocks to be built into the DNA but different enough from them to terminate the DNA synthesis because the chemical bonds can not form properly.
Structural similarity between 6-HAP (left) and adenine (right). Source: PubChem

The isolated compound was effective in reducing the growth of cancer cell lines and reduced tumor formation in mice that were injected with rapidly growing melanoma cells. Importantly, mice that had the 6-HAP-producing S. epidermidis in their skin flora developed less tumors after UV-radiation than mice with 6-HAP-negative S. epidermidis. Hence, the bacteria not only produce a tumor-inhibiting substance but they can also produce it at (mouse-)clinically relevant concentrations [2].

The bacteria living in and on our body have been associated with a plethora of diseases: metabolic diseases, gastrointestinal cancer, respiratory diseases, mental illnesses, obesity, you name it...[3] Many of these findings still need to pass the test of time, but if it holds true that carrying certain strains of S. epidermidis can protect from skin cancer, it should be added to that list! Yet another reason to appreciate the bacteria on your body and wish them a happy #WorldMicrobiomeDay!

Sources:
[1] Polefka et al. Effect of solar radiation on the skin. J Cosmet Dermatol. June 2012
[2] Nakatsuji et al. A commensal strain of Staphylococcus epidermidis protects against skin neoplasia. Science Advances, 28 February 2018
[3] Wang et al. The Human Microbiota in Health and Disease. Engineering, February 2017

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