They suggest that Sirtris' earlier findings to the contrary might be due to an experimental artifact.
Sirtris' raison d'etre was to create more potent versions that could combat myriad diseases of aging.
However, it is hard to believe that GSK bought Sirtris for the promise of anti-aging compounds.
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It is "almost certainly the case" that there are problems with the Sirtris compounds, he argues.
Sirtris had a technology platform involving resveratrol, believed to be the biologically active component of red wine.
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Since then rival researchers at Pfizer have questioned whether Sirtris' drugs work by the mechanism Glaxo claims.
Journal of Biological Chemistry that neither resveratrol nor several other Sirtris drugs hit the SIRT1 enzyme at all.
Tests of one Sirtris drug had to be halted after it was linked to kidney damage in cancer patients.
Not everyone is convinced, but Dr Sinclair has done experiments on mice that look promising, and has started a company called Sirtris Pharmaceuticals to follow it up.
Sirtris Pharmaceuticals, a firm based in Cambridge, Massachusetts, of which Dr Sinclair is a co-founder, has identified a number of synthetic molecules whose effect on yeast is many times more potent than resveratrol's.
The Pfizer scientists "have thrown down the gauntlet: They claim that the reported Sirtris compounds do not do what they are claimed to do, " pharmaceutical chemist Derek Lowe, wrote recently on his popular In The Pipeline blog.
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