Page last updated at 17:25 GMT, Thursday, 29 January 2009

Tadpoles may hold cancer clue

Xenopus Laevis frog whose pigments can be manipulated by the new compound

Tadpoles could hold the key to developing effective skin cancer drugs according to researchers at the University of East Anglia.

The scientists have identified a compound which blocks the movement of the pigment cells that give the tadpoles their distinctive markings.

It is the uncontrolled movement of pigment cells that causes skin cancer in both humans and frogs.

The next step, the researchers say, is to test the compound in other animals.

The man-made compound, NSC 84093, was chosen out of a list of 3,000 which were screened to see if they affected the pigment cells.

It produced a distinct change in the colour markings on the tadpoles at very low concentrations.

The continuous stripe along the back of a wild tadpole was replaced by a pattern of individual blocks of colour.

The study is published in the journal, Chemistry & Biology.

Top tadpole has normal markings. The one underneath has broken markings along back

Grant Wheeler, a developmental biologist and lead researcher at the University of East Anglia, said:

"Forty of the compounds gave us an interesting difference which we wanted to follow up."

"The reason we were able to look at so many compounds was because it's very easy to look at the embryos and see the colour change."

"The pigment cells are interesting for a number of reasons.

"The first is that the place where they develop is not where they end up - they move through the embryo in a process called cell migration."

Invasive melanomas

It is when melanoma cells migrate through the body to the organs and cause secondary tumours that the disease becomes deadly.

Melanomas are one of the most dangerous forms of skin cancer because they are highly invasive and resistant to treatment.

Scientists hope that if they can block this process they can halt the cancer.

The compound in this study works by inhibiting matrix metaloproteinases (MMP) which are expressed by melanoma tumours in both humans and frogs.

Also known as South African Clawed Frog
Has same organs, molecules and physiology as man
Can produce eggs all year round
From 1930s to 1960s was used for human pregnancy testing by injecting woman's urine sample into them and seeing if the frog laid eggs within 24 hours indicating that the woman was pregnant
Mr Wheeler said a chemist at the university recognised the structure of their compound and realised that part of it had known properties that meant it should bind to a zinc molecule.

MMPs are zinc-dependant enzymes and the researchers observed varying changes to the patterning on the tadpoles according to the strength of dose they were receiving.

Mr Wheeler added: "It's a long shot. We are quite far away from a cure for melanoma."

Ed Yong, health information manager at Cancer Research UK, said:

"There is still a lot of work to do before these interesting but preliminary results can be used to benefit people affected by cancer.

"But it just goes to show that studying animals like tadpoles, which may seem unusual, could lead to potential cancer drugs in the future."

Bevis Man from the British Skin Foundation said: "This is certainly an interesting discovery and is worth keeping an eye on, but is unlikely to get a breakthrough in terms of treatment within the next ten years."

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