rats do not get cancer, and last week,
scientists announced that they have
finally discovered why. They hope the
"gloop" that they have identified in the
animal could, in due time, form the
basis of a host of new medicines to
treat not only cancer but diseases
ranging from atherosclerosis to
arthritis.
It seems odd that the naked mole rat
could spark any kind of medical
revolution. In terms of its ecology and
physiology, these animals are outliers.
Naked mole rats are small, almost
hairless rodents, about four inches long,
that live in eastern and southern Africa.
They are the only known "eusocial"
mammal; the structure of a mole rat
colony is identical to that of hive insects
such as bees, and other arthropods
such as termites. There is one female, a
queen, who mates with a handful of
fertile males; the rest of the colony,
which may number 80 or so, consists of
sterile "workers".
That is only the start of the weirdness.
They are, as their name suggests,
naked (or nearly so – the odd whisker
sprouts from their faces). They can run
backwards as fast as forwards, and can
manipulate their goofy incisor teeth
individually, like chopsticks. Unlike all
other mammals, naked mole rats are
not truly warm-blooded: they regulate
their temperature in a crude fashion,
more like a lizard than, say, a mouse.
The oddities continue. Mole rats, which
live off underground roots and tubers,
appear not be able to feel pain, at least
on their skin. The pain receptors found
in all mammals – called nociceptors –
are there, but they appear to be turned
off, as German scientists found when
they studied the way the receptors
reacted to being immersed in corrosive
chemicals. Douse a naked mole rat in
acid, and it will not flinch. (It is finding
out how these nociceptors operate that
could be the key to new treatments for
arthritis.) Mole rats can also survive
extraordinarily high degrees of carbon
dioxide, which builds up in their tunnels
to levels that would kill a human in
minutes. In terms of cancer, numerous
studies have failed to find a single
tumour in the thousands of individuals
sampled.
Finally, there is the curious fact that
these little rodents live for around 30
years – 10 to 20 times the lifespan of
relatives such as rats and mice. For
most species, there is a rough
correlation between size and longevity.
Big animals, the theory goes, tend to
live longer because they are less likely
to die quickly of cold or starvation or be
eaten. Thus genes that confer health
into old age can be passed on. That is
why whales and giant tortoises live
longer than shrews and mice. Mole rats
should live a few years at most, but
instead they can outlast chimpanzees.
It is, however, that resistance to cancer
– which is probably related to their
longevity – that has proved the most
intriguing puzzle. Now, Vera Gorbunova
and colleagues at the University of
Rochester in New York have identified a
polysaccharide – a gloopy, sugar-based
natural polymer – found in naked mole
rat cells that stops tumours growing.
The scientists, whose study was
published in the current edition of
Nature, suggest that the finding "opens
new avenues for cancer prevention and
life-extension".
The chemical, called high-molecular-
mass hyaluronan (HMM-HA), acts as a
kind of lubricant, allowing mole rats to
squeeze their Plasticine-like bodies
through the smallest and most
convoluted tunnels: "They can virtually
turn somersaults in their skin," Chris
Faulks, a scientist at Queen Mary,
University of London said this week.
It seems, therefore, that the ability of
HMM-HA to confer cancer resistance
was a happy evolutionary accident. And
one day, it may be possible to engineer
the ability to produce HMM-MA in
human tissues – hopefully without the
side effect, as Dr Faulks says, of making
us all end up looking like naked mole
rats.
Of course, this isn't the first time that
an extraordinary feature in an animal
has been seized on as a possible cure
for human ailments. While the thesis of
Dr I. William Lane's Sharks Don't Get
Cancer, published in 1992, is now
widely held to be incorrect, crocodiles
have an extraordinary ability to fight off
bacterial infections: injured crocs have
been in bacterially infested swamps,
blood pouring out of open wounds, yet
remained infection-free.
Then there is one of the most intriguing
findings of recent decades – that
chimpanzees do not get Aids, despite
being susceptible to the same group of
retroviruses as humans. In fact, it is
now believed that the Aids epidemic
started when the virus jumped species
from ape to human, probably in the
forests of west Africa around 100 years
ago, as a result of a hunting accident or
by consumption of ape meat. While
chimps can get infected by the virus,
they do not go on to suffer the disease:
the reason why may lurk in the one per
cent of the chimp genome that differs
from ours.
That we can solve medical mysteries by
looking at our close cousins is not
surprising; yet finding that an animal so
weird, and so ugly, as the naked mole
rat could one day lead to a cure for
cancer seems utterly bizarre. However,
this creature has gained the respect of
an increasing number of scientists:
robust to the point of near-
indestructibility, living in perfect
conflict-free communes, immune to
pain and capable of spending years
underground at a time, this meekest of
animals could, should the apocalypse
strike, be in pole position to inherit the
Earth.
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