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Cancer resistance in elephants

Elephants almost never get cancer. For decades scientists could not understand why elephants don’t have cancer – their remarkable resistance to cancer was a subject of many discussions and publications.

In general, big animals like elephants live longer and their cells have to divide more, so we would expect them to be more susceptible to cancer. But actually it is not the case and this exceptional phenomenon called “Peto’s paradox”.

Richard Peto is a statistical epidemiologist from University of Oxford – he formulated the paradox in 1977. Meaning of the paradox is that “at the species level, the incidence of cancer does not appear to correlate with the number of cells in an organism”. Biologically every cell has the risk to become cancerous – big/large long living species theoretically should have an increased risk of developing cancer compared to small and shorter living organisms. Richard Peto noted lack of correlation between body size and cancer risks. In scientific society this phenomena is known as “Peto’s Paradox”.

Elephant is the best example of described paradox. Thousands of blood and tissue samples taken from elephants were tested by several scientists. And the explanation was found – elephants have extra copies of very specific gene that spots trouble in cells and this gene called “P53”.

P53 is well known ancient gene found in all so called “multicellular” animals. P53 has two important responsibilities:

1. to detect stress or any damage in the cell, and
2. to stop the cell from dividing until the stress has passed or until the DNA is repaired.

African elephants

Humans inherit one copy of P53 from each parent – both copies are crucial as they are protecting us from cancer. Some people are born with defective gene and this condition known as “Li-Fraumeni syndrome”. In most cases people with this syndrome get cancer in childhood because they are not protected from cancer and their lifetime risk is close to 100%. This is the short explanation how important is gene P53.

Now about elephants – scientists discovered that elephants have many copies of mentioned powerful cancer preventive and tumor suppressing gene P53. Most elephants carry 40 copies of P53, which causes cells with damaged DNA to self-destruct, while humans have just two copies. It was noted that African elephants have at least 20 copies of P53 gene from each parent.

Laboratory tests show that cells of elephants respond to the damage of their DNA very specifically – the elephant cells were ready to commit suicide (apoptosis) instead of trying to repair damaged cells (as human body is doing). Once damaged cell is “killed”, cancer cannot develop anymore – it is gone and cannot turn into cancer. This could be more effective approach to cancer prevention than trying to stop a mutated cell from dividing and not being able to completely repair itself.

According to researchers, in the majority of human cancers, the gene P53 is mutated, leading to increased cell reproduction (a hallmark of cancer) and genomic instability (mutations in the genome). Actually human cells are not protected as well as elephant’s cells are.

Elephants are good examples for many scientists to learn how during evolution some species “learn” cancer prevention.

“Evolution has had 55 million years to figure out how to avoid cancer. Now I think it’s up to us to take a page out of nature’s playbook and learn how to take this information and apply it to those who need it most. Nature has already figured out how to prevent cancer. It’s up to us to learn how different animals tackle the problem so we can adapt those strategies to prevent cancer in people”.
Dr Joshua Schiffman, University of Utah

Presently scientists are looking for molecules that might mimic the effect of extra copies of gene P53 in elephants – it could help damaged human body cells instead of trying to repair DNA, condemn damaged cells to commit suicide (apoptosis). Modern nanotechnologies could be able to deliver elephant’s gene P53 into human cells which could be considered not only as cancer prevention but also as cancer treatment new technology.

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