Shark tissues show the promise of preventing tumours from regenerating
FOR the first time sharks may have to
play the role of lifeguards for humans.
An extract from shark tissues will be
tested on cancer patients later this year.
The extract, called squalamine, could
help in cutting the blood supply of the
tumours. The extract was discovered in
the stomach of Squalus acanthias (dog
fish) by researchers working for
Magainin Pharmaceuticals, a biotechnology company based in Plymouth
Meeting, Pennsylvania (New Scientist, Vol 154, No 2079).
Trials of the drug are expected to
begin in autumn, in patients with brain
or breast cancer. The idea is to use the
drug to mop up stragglers after treatment and prevent a relapse, rather than
as a primary anti-cancer drug.
In tests on animals with human tumours, company researchers
found that squalamine
starved the cancer of
blood by preventing them from developing
their own blood supply.
This process of developing a blood supply,
called angiogenesis, is
essential for the growth
and spread of invasive
cancer from small tumours, and also
enables fragments of a
cancer left over after
treatment to grow
again. The company
hopes that squalamine
will prevent the fragments from rebuilding
blood vessels and thus
stop the cancer from returning.
Tumours generate their own blood supplies by secreting chemical signals that order healthy blood vessels nearby to
build new channels that connect to
them. The signals from the original
tumour tell endothelial cells, which line
the neighbouring blood vessels, to
divide and from the new vessels.
Squalamine appears to stop this
happening by making endothelial cells
too acidic to divide. It does this by
blocking a docking point, or receptor
on the cell surface. This, in turn:
disrupts a pumping system which gets
rid of excess acid in the cell. "When
squalamine hits the receptor, it shuts
down the ability of this pump to excrete
acid from the endothelial cell," says Jay
Moorin, the chairperson of Magainin.
This prevents the cell from obeying
orders from the cancer to divide.
Moorin thinks that humans may
have cell receptors for squalamine,
because we make similar substances in
our bodies. He says that in sharks,
squalamine might be important for preventing damaged cartilage, which forms the shark's skeleton, from calcifying.
He doubts whether cancers will
develop resistance to squalamine,
which often happens with conventional
anti-cancer drugs because the substance
acts on the cells of existing blood
vessels, not on cancers themselves.
And virtually no toxic effects have
been seen in the animals that have
received the drug.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.