The new data builds on earlier work by Dr. Shindler in the same preclinical model showing that activation of the SIRT1 enzyme with SRT501 is neuroprotective for optic neuritis (inflammation of the optic nerve that can cause a complete or partial loss of vision) by reducing the loss of retinal ganglion cells. Optic neuritis is common in patients with multiple sclerosis and can be an early warning sign for the disease. Sirtris Pharmaceuticals Senior Vice Present for Development, Peter Elliott, PhD, was a co-author of this work published in the August 2007 issue of Investigative Opthalmology & Visual Science.

In the new work, Dr. Shindler’s team used mice with experimental autoimmune encephalomyelitis (EAE), which causes the autoimmune system to attack the eye and central nervous system. These effects on the central nervous system mirror symptoms observed in patients with multiple sclerosis.

The mice were observed for clinical signs of EAE, measured by the strength and duration of tail and limb paralysis. Mice were given daily oral doses of SRT501 at 1000 mg/kg beginning at day 10 through day 14, the peak day of the autoimmune system attack. The paralysis scores of the treated mice improved more completely than the untreated mice following the first clinical episode of EAE.

“We have previously established that we can reduce the loss of retinal ganglion cells during acute optic neuritis in EAE mice with SRT501 when injected into the vitreous layer of the eye,” said Dr. Shindler. “This work shows oral SRT501 exerts similar effects in optic neuritis and leads to suppression of observed dysfunction in the first clinical episode of EAE, suggesting added neuroprotective benefits of SIRT1 activation.”

About Sirtris Pharmaceuticals

Sirtris Pharmaceuticals is a biopharmaceutical company focused on discovering and developing proprietary, orally available, small molecule drugs with the potential to treat diseases associated with aging, including metabolic diseases such as Type 2 Diabetes. Our drug candidates are designed to mimic certain beneficial health effects of calorie restriction, without requiring a change in eating habits, by activation of sirtuins, a recently discovered class of enzymes that the Company believes control the aging process. The company's headquarters are in Cambridge, Massachusetts.

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, the potential therapeutic effects of SIRT1 activators for diseases of aging, such as Type 2 Diabetes, neurodegenerative disorders and cancer; the progress and results of pre-clinical studies of SIRT1 activators; and the potential of sirtuin modulators to receive regulatory approval. These forward-looking statements about future expectations, plans and prospects of Sirtris Pharmaceuticals involve significant risks, uncertainties and assumptions, including risks related to the lack of results that would provide a basis for predicting whether any of the Company's product candidates will be safe or effective, or receive regulatory approval, the possibility that results of pre-clinical studies are not necessarily predictive of clinical trial results, the Company's potential inability to initiate and complete pre-clinical studies and clinical trials for its product candidates, the fact that none of the Company's product candidates has received regulatory approvals, the potential inability of the Company to gain market acceptance of the Company's product candidates, and those other risks factors that can be found in the Company's filings with the Securities and Exchange Commission. Actual results may differ materially from those Sirtris Pharmaceuticals contemplated by these forward-looking statements. Sirtris Pharmaceuticals does not undertake to update any of these forward-looking statements to reflect a change in its views or events or circumstances that occur after the date of this release.

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