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Published online : 28 March 2007; | doi:10.1038/446474a / http://www.nature.com/news/2007/070326/full/446474a.html
Cancer patients opt for unapproved drug
Internet trade pre-empts clinical trial.An experimental cancer drug shrinks tumours in rats with no apparent side effects. The scientists behind the study plan to do a clinical trial in humans, but it could take years to complete. Meanwhile, dying patients begin taking the unapproved drug and collect their results on the web. Both groups desperately want to save lives: but which is the right route to follow?
This scenario has been playing out in recent weeks for a compound called dichloroacetate (DCA). It taps into long-running issues about whether terminally ill patients should be able to get access to drugs that have not yet had formal approval. Researchers fear that those taking the drug could suffer unanticipated side effects; patients argue they don't have the luxury of waiting for clinical trials to find out.
In January this year, Evangelos Michelakis at the University of Alberta in Edmonton, Canada, and his colleagues reported that DCA has seemingly remarkable anticancer properties (S. Bonnet et al. Cancer Cell 11, 37-51; 2007). DCA is a small molecule that blocks an enzyme in mitochondria - the energy-production centres in cells - causing more glucose to be metabolized in the mitochondria rather than by a different pathway in the cytoplasm. The compound has been in clinical trials for years as a treatment for certain mitochondrial diseases, but it has not yet been approved.
Mitochondria also control cell suicide, and Michelakis wondered whether cancer cells were suppressing these cellular structures to prevent the cells from dying - and so thought DCA might reactivate them. When his team gave DCA to rats that were growing human lung tumours, the tumours stopped growing within a week, and three months later were half the size of those in untreated animals. Other experimental drugs have had similar effects. But DCA stands out because it seems to leave healthy cells untouched, has been relatively safe in human trials, can be taken by mouth and easily penetrates tissues. "If there were a magic bullet," wrote Newsweek about the discovery, "it might be something like dichloroacetate."
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http://www.nature.com/news/2007/070326/full/070326-13.html
Published online: 29 March 2007; | doi:10.1038/news070326-13
Corals can survive acidic waters
Mediterranean corals could strip, but not die, in response to climate change.Daemon Fairless
Reef-building corals may be more resilient against climate change than scientists had previously thought. Researchers have discovered that some species are able to survive an increase in seawater acidity, even though it strips the individual coral polyps of their protective calcium carbonate skeletons. This may be good news for individual polyps, but it doesn't change the gloomy outlook for reef ecosystems.
All dressed up: the hard skeleton of a coral is essential for reefs, but maybe not for the coral itself.
Punchstock
As atmospheric carbon dioxide levels continue to rise, so do the levels of dissolved carbon dioxide in sea water. This leads to an increase in ocean-borne carbonic acid, which is capable of dissolving calcium carbonate. "This is a major problem for corals," says Maoz Fine, a marine zoologist at Bar-Ilan University in Israel. "Essentially, acidification leads to naked coral."
Researchers estimates that ocean surface pH could decrease from 8.2 to 7.8 by the end of this century - more acidic than it has been for the past 20 million years.
Fine set out to study the effects of this ocean acidification on two species of Mediterranean coral, Oculina patagonica and Madracis pharencis.
He subjected specimens in the lab to increasingly acidic conditions. It didn't take long for the colonies in the most acidic environments - those with pH levels as low as 7.3 - to show remarkable changes; within a few weeks, their calcium carbonate skeletons had started to dissolve and the polyps became entirely exposed, he and a colleague report in Science.
Surprisingly, the polyps seemed to fare well under these conditions, growing up to three times their original size and reproducing unhindered. "No one expected that corals could survive such low pH," says Fine.
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Au niveau des dorsales océaniques, l'activité magmatique crée des sources hydrothermales,
telles ce "fumeur noir", qui abritent des écosystèmes primitifs
http://www.techno-science.net/?onglet=news&news=3877
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Des chercheurs du CNRS et du Laboratoire européen de biologie moléculaire à Grenoble ont déterminé la structure d'une enzyme permettant la synthèse d'un ARN à partir de l'ADN. Cette structure apporte des informations nouvelles concernant le déroulement de cette transcription.
La structure tridimensionnelle de l'ARN polymérase III permet de mieux comprendre comment cette enzyme contrôle la transcription de l'ADN en ARN
Les cellules eucaryotes (dotées d'un noyau) possèdent trois types d'ARN principaux : les ARN messagers, qui sont traduits en protéines au niveau des ribosomes (1), les ARN de transfert, qui se lient aux ARN messager lors de la traduction et les ARN ribosomiques (associés à des protéines, ils constituent les ribosomes). A chacun de ces ARN correspond une enzyme, l'ARN polymérase, qui se fixe sur l'ADN et à partir duquel elle synthétise l'ARN.L'ARN polymérase de type II (associée aux ARN messagers) est bien connue : elle a valu le prix Nobel 2006 au chercheur américain qui l'a étudiée, mais ce n'était pas jusqu'à présent le cas de l'ARN polymérase de type III (associée aux ARN de transfert) que les chercheurs ont étudié chez la levure. Ils ont déterminé sa structure tridimensionnelle par cryo-microscopie électronique: l'échantillon et l'intérieur du microscope sont refroidis à -180 °C afin d'éviter l'évaporation de l'eau contenue dans la structure de l'enzyme et donc de la figer dans son état natif.
Leurs résultats, publiés dans Molecular Cell du 23 mars 2007, montrent l'organisation supra moléculaire de l'ARN polymérase de type III et en particulier la localisation de cinq sous unités supplémentaires impliquées dans les phases initiale et finale de la transcription: elles permettent non seulement de reconnaître l'ADN, mais constituent également une plate-forme de fixation de différents facteurs contrôlant la transcription.
http://www.techno-science.net/?onglet=news&news=3885
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