SRT-501, the company’s special formulation of resveratrol, is being tested against two cancers, multiple myeloma and colon cancer that has spread to the liver. A chemical mimic of resveratrol, known as SRT-2104, is in a Phase 2 trial for Type 2 diabetes, and in a Phase 1 trial in elderly patients. (Phase 1 trials test for safety, Phase 2 for efficacy.)

Image AGE WELL David Sinclair, left, and Christoph Westphal, co-founders of Sitris Pharmaceuticals, in Dr. Sinclairs laboratory in Cambrdge, Mass. The company develops drugs that mimic resveratrol, a chemical found in some red wines. Credit... Robert Spencer for The New York Times

Dr. Gallagher said that unpublished tests in mice showed that another chemical mimic, SRT-1720, increased both health and lifespan; after two years, twice as many mice taking the drug were alive compared with the undosed animals. Resveratrol itself has not been shown to increase lifespan in normal mice, although it does so in obese mice, laboratory roundworms and flies.

Sirtris has so far been doubly fortunate. No severe side effects have yet emerged from the clinical trials. The company has also been lucky in having apparently picked the right horse, or at least a good one, in a fast-developing field.

Besides the sirtuins, several other proteins are now known to influence longevity, energy use and the response to caloric restriction. These include the receptors for insulin and for another hormone called IGF-1, and a protein of increasing interest called TOR (“target of rapamycin”). Rapamycin is an antimicrobial that was recently found to extend lifespan significantly, even when given to mice at an advanced age. Since TOR is involved in the response to caloric restriction, rapamycin may extend life through this pathway.

Sirtuins may not be the most important genes for longevity, Dr. Sinclair conceded at the conference, because the pathways controlled by the sirtuins, TOR and the others “all talk to each other, often by feedback loops.”

Many theories of aging attribute senescence to the inexorable buildup of mutations in a person’s DNA. Dr. Sinclair said that in his view “aging can be reversed” because the DNA mutations did not directly cause aging. Rather, they induce the sirtuin molecules that help control the genome to divert to the site of damage. With the sirtuins absent from their usual post, genes are not regulated efficiently, and the cells’ performance degrades. Diversion of the sirtuins should be a reversible process, in Dr. Sinclair’s view, unlike DNA damage, which is not.

“In five or six or seven years,” said Christoph Westphal, Sirtris’s other co-founder, “there will be drugs that prolong longevity.”