Marine medicine
a chance discovery that a stingy little invertebrate is not always what is seems will soon help in the development of a promising new anticancer drug. Researchers in California have discovered why some populations of Bugula neritina ( B neritina ), a marine fouling organism, produce the drug but others do not. The reason, say marine biologists, is because the organism comes in two genetically-distinct types ( New Scientist , Vol 157, No 2119).
One form of B neritina makes a chemical called bryostatin-1. This is one of the few drugs e x tracted from marine animals that shows real promise as an anticancer drug, and could eventually form the basis of a market worth over a whooping us $1 billion every year. Now, in advanced trials as a possible treatment for leukaemia, and at an earlier stage of testing against melanoma (skin cancer), it also shows potential for stimulating the immune systems of breast-cancer patients.
"Bryostatin-1 has a unique mode of action against cancer cells, so it would be a useful addition to the anticancer armoury,' says Margo Heywood of the Scripps Institution of Oceanography in La Jolla, California, usa . The compound has been licensed to the pharmaceuticals company Bristol-Myers Squibb. CalBioMarine, a small company in California, usa , is currently perfecting methods of culturing B neritina on coastal "ranches'.
If ranchers are to produce a steady supply of bryostatin, they need to breed their stock from animals which, they know make the drug. "For production purposes it is important to know that not all B neritina is the same,' says Haygood. And their discovery should help to identify populations of B neritina suitable for agriculture.
By chance, Haygood and Davidson discovered that there are two "chemotypes' of B neritina . They were more interested in a bacterium called Endobugula sertula ( E sertula ) that lives inside the bryozoan, and which they suspect plays a key role in the production of bryostatin-1.
It was only when they sequenced a ribosomal gene from bacteria taken from 10 populations of B neritina , from different parts of the us , that they found that there are two distinct types of E sertula . "The two groups differ by four nucleotides, but the difference is very striking indeed,' says Haygood. One type occurred in bryozoans that produce bryostatin-1; the other was found only in nonproducers.
Interestingly, when the two researchers checked where each population of B neritina had been collected, they found that all those that produced bryostatin-1 came from water deeper than 10 metres. None of those from shallower water made the drug.
With such a clear ecological difference, Haygood and Davidson wondered if their hosts were genetically different too. Davidson sequenced a stretch of dna from B neritina and again found two types. "The difference is not trivial,' says Haygood. "They may be two different subspecies or even two different species entirely.'
This does not solve the issue whether the bacterium makes the chemical, but it gives drug prospectors a better idea where to get the right sort of B neritina .
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