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It seems like every time scientists learn something new about sharks, people wonder whether this new information will finally show us how sharks will cure cancer. There’s no doubt about it, sharks are awesome, but is there a magic cure hidden in their genes?

Hosted by: Hank Green

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Sources:
Sources:
https://www.livescience.com/41655-great-white-shark-cancer.html
https://ocean.si.edu/ocean-life/sharks-rays/sharks
https://www.livescience.com/5921-hammerhead-sharks-360-degrees-stereo.html
https://www.nationalgeographic.com/animals/2005/07/shark-attack-threats-bull-sharks-location/
http://www.bbc.com/earth/story/20151005-the-truth-about-great-white-sharks
https://www.floridamuseum.ufl.edu/discover-fish/sharks/shark-biology/#blooded
https://www.eurekalert.org/pub_releases/2019-02/nsu-gws021319.php
https://www.ncbi.nlm.nih.gov/pubmed/11181991
https://www.cancer.org/cancer/cancer-basics/what-is-cancer.html
https://usa.oceana.org/fun-facts-about-great-white-sharks
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3060950/
https://www.scientificamerican.com/article/how-big-animals-deter-cancer/
https://www.nationalgeographic.com/science/2018/08/news-cancer-elephants-genes-dna-new-research/
https://www.nature.com/articles/nrc.2017.35
https://www.popsci.com/zombie-gene-elephants-cancer
https://www.nature.com/scitable/topicpage/transposons-the-jumping-genes-518
https://blogs.scientificamerican.com/science-sushi/mythbusting-101-sharks-will-cure-cancer/
http://cancerres.aacrjournals.org/content/64/23/8485.short
https://www.ncbi.nlm.nih.gov/pubmed/20553753
https://www.sciencedirect.com/science/article/pii/S0163725816000322
https://www.yalemedicine.org/stories/blocking-dna-repair-to-fight-cancer/
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image Sources:
https://commons.wikimedia.org/wiki/File:Basking_Shark.jpg
https://visualsonline.cancer.gov/details.cfm?imageid=9962
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Go to CuriosityStream.com/SciShow to learn more { ♪INTRO }. It seems like every time scientists learn something about sharks— like, a new genome is published— everyone suddenly starts going on about whether this new bit of information will finally show us how sharks will cure cancer.

And there’s no doubt about it— sharks are awesome. And they can do some pretty incredible things. But wiping human cancers off the face of the Earth is not ever going to be one of them.

Sharks are not invincible. They still get old. They get sick.

And just like the rest of us, they can get cancer. There’s no magic cure hidden in their genes— just like there wasn’t one in their cartilage. So let us kill this zombie of a myth once and for all.

The idea that sharks are swimming cancer cures all started in the 1970s. Back then, researchers observed that cartilage— a flexible but firm kind of connective tissue— inhibited blood vessels from developing into different kinds of tissues. Since tumors tend to need a lot of blood to survive and grow, blocking this kind of blood vessel formation could help treat cancers.

And a shark’s skeleton is primarily made up of cartilage. Lo and behold, when researchers stuck shark cartilage near tumors, it turned out it, too, restricts blood vessels from developing into them. Lo and behold, when researchers stuck shark cartilage near tumors, it restricted the growth of new blood vessels.

Somehow, that led people to think that sharks never get cancer and ingesting shark cartilage in pill form could be used to treat cancer in humans. This turned out to be flat-out wrong— multiple studies have proved that shark cartilage is not an effective treatment for cancer. And sharks definitely get cancer.

Scientists have even found ones with tumors in their cartilage. So countless sharks around the world were slaughtered for nothing, and to make matters worse, this myth pulled desperate cancer patients away from actually helpful treatments. Now, the myth is back once again, but this time, the secret cancer cure is supposedly hidden in their genes.

This all came up in 2019 because scientists were finally able to figure out what the genome great white sharks looks like— and they found some interesting things. Like, the animals have unique adaptations in genes associated with fighting infections and aspects of wound healing like blood clotting, which could explain how they mend their tissues so quickly. And their whole genome is one-and-a-half times larger than the human genome!

A lot of that extra bulk is thanks to genetic features called LINEs. These small DNA segments are a kind of transposon, meaning they can move around on their own. And the proportion of LINEs in the white shark genome is among the highest found in vertebrates so far.

That’s of note because LINEs can cause genomes to become unstable, resulting in cancer. You see, a cell only becomes cancerous after enough errors have accumulated in its DNA—errors that make it grow and divide when it shouldn’t, for example. So with all those jumping genes, you’d think white sharks were super prone to developing cancer.

But they’re probably not, and that’s likely thanks to remarkable DNA repair. The researchers working on the white shark genome discovered the animals also have a lot of tweaks to genes that help fix DNA damage. That suggests the sharks have evolved a very effective genome clean-up crew— though functional studies would have to be done to confirm that’s true.

Their repair mechanisms might even be good enough to make their risk of getting cancer lower than other animals’. But... that doesn’t mean they can’t get cancer. Scientists don’t actually have any evidence that sharks develop tumors less often than other vertebrates.

And they have caught wild great whites with cancerous tumors. But let’s say for a moment these DNA repair mechanisms are so amazing that the animals get cancer less often than, say, humans. That still doesn’t really help us treat humans with cancer.

DNA repair mechanisms aren’t things we can inject or swallow to improve our cells’ ability to fix genetic mistakes. If we wanted to take advantage of them, we’d have to do something drastic like add them to our DNA. And I think we’ve all learned from King Shark’s supervillainous ways that engineering human-shark hybrids is bad idea.

Also, that would only maybe prevent cancer. Great DNA repair can help keep a cell from developing cancer-causing mutations. But once a cell is past that tipping point, it’s not able to undo them.

In fact, making DNA repair better once you have a tumor actually makes matters worse. That’s because health professionals often use treatments like radiation therapy to damage the genetic material of cancerous cells, effectively killing them, and stopping their growth. But if repair mechanisms in those cancerous cells work too well, they might fix the damage, allowing the tumor to bounce back.

So oncologists are actively looking for ways to block DNA repair. There are molecules, called DNA repair inhibitors, that gum up these processes. And in theory, if you treat a patient with one of those, then traditional measures like chemotherapy or radiation therapy will inflict enough damage to kill the cancerous cells.

The hard part is finding something that can slow or stop DNA repair in tumor cells without causing too much harm to healthy cells, because, you know, you don’t want to make more cancers while you’re treating one. Still, there are some potential candidates already being tested. For example, a compound called mibefradil dihydrochloride can hamper DNA repair in brain tumor cells, and clinical trials of the stuff to date have been promising.

So in short: sharks are awe-inspiring creatures. They’re amazing and we should learn as much as we can about them. But the cure to cancer is not locked away in their cartilage or their DNA, since their effective repair mechanisms can’t reverse cancerous mutations.

We maybe, maybe could learn a bit more about DNA repair by studying their unique mechanisms for it, and that, in a very tangential way, could eventually lead to new drugs that help shut it down when we need to. But that even is kind of a stretch. And all this focus on how they’re going to cure cancer distracts from the important stuff we can learn by studying them.

Digging deeper into those novel infection-fighting mutations could lead to new kinds of antibiotics that help us stay one step ahead of resistant microbes, for example. Or, understanding how sharks repair their flesh so quickly could lead to topical treatments that help seal up surgical wounds faster or reduce scarring. And ultimately, most of what we learn from sequencing shark genomes isn’t directly related to human health.

Comparing their genes to ours and other animals can provide new insights into how these animals evolved and how evolution works in general. So sharks can help us answer bigger questions about life on this planet and how we all got here. And that makes them worth studying, even though they probably aren’t going to cure cancer.

There’s just so much we that other living things on this planet can teach us. And if you like learning about those things, you might like the videos you can watch through Curiosity Stream. CuriosityStream is a subscription streaming service that offers over 2,000 documentaries and nonfiction titles from some of the world's best filmmakers, including exclusive originals.

They have videos on history, technology, society and lifestyle—and of course, nature. You can watch the entire first season of Catalyst, for example— an Australian series of short videos that cover all kinds of science from the world around us. And the second episode is all about shark social behavior!

For as little as $2.99 a month, you could watch it and thousands of other videos. And as a SciShow viewer, your first 30-days could be completely free if you sign up at curiositystream.com/SciShow and use the promo code ‘scishow’ during the sign-up process. { ♪OUTRO }.