Thanks for CuriosityStream for supporting this episode! 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
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around us. And the second episode is all about shark
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the sign-up process. { ♪OUTRO }
