Why these two animals can resist cancer

Cancer-free existence.
Cancer-free existence.
Image: Flickr/Majyd/Bob Owen CC-BY
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Humans look to nature for inspiration. Fortunately, cancer researchers don’t have to look too hard. Elephants and naked mole rats do exceptionally well at resisting cancer, and we are starting to learn why.

Cancer is caused by mutations—a chance mistake in the genetic code. The greater the number of cells and the longer they live, the greater the chance of mutations.

Elephants don’t go through menopause

By that logic, however, elephants—which have perhaps 100 times as many cells as humans—should have gone extinct from the sheer number of cancer types they face. But only 5% of elephants die of cancer in comparison to more than 20% humans. So why the discrepancy?

A new study in the Journal of the American Medical Association has one answer. When researchers from a host of US universities studied the genome of elephants, they found 20 copies of TP53 gene, which is known to help resist cancers by repairing damaged DNA. Humans have only one copy of that gene.

Although the human lifespan has doubled in the last few centuries, it is only because of help from modern medicine. Elephants, on the other hand, have longer lifespans naturally and could not have that without the evolutionary advantage endowed by TP53.

Also, unlike humans, as far as we know, elephants don’t go through menopause. So to ensure that elephant babies born to older females weren’t riddled with badly mutated genes, evolutionary pressure would have created resistance to DNA damage via more copies of TP53.

The enigma of naked mole rats

The story of naked mole rats is even more inspiring. These weird creatures live underground, survive on little oxygen and food, are nearly blind, and, as far as we know, never develop cancer. Even if researchers try to induce cancer through artificial means.

Once the mutations set in, cancer cells proliferate by uncontrolled growth. This happens because the mechanisms inside the cell that usually regulate this process are broken. There are, however, external mechanisms that can help regulate this process. According to a 2013 study published in Nature, naked mole rats seem to exploit this mechanism to resist cancer.

The study found a polymer in between the cells of a naked mole rat, called hyaluronan, which was providing mechanical strength to the cells but also regulating cell growth. The thickness of the polymer determined whether cells grew or not.

When the researchers used an enzyme that degraded the polymer, they found that the rats’ cells started grow in clusters, just like normal rats’ cells do when they form a tumor. Even better, when they knocked out the genes responsible for producing the polymer and then injected cancer-causing virus, the rats’ cells became cancerous.

We may not yet have a cure for cancer, but such exceptional cases give hope. As Rochelle Buffenstein, a physiologist at the University of Texas Health Science Center, once told me, “As we learn more about these cancer-resistant mechanisms that are effective and can be directly pertinent to humans, we may find new cancer prevention strategies.”

Images from Bob Owen and Majyd have been used under CC-BY 2.0