The target of the drug rapamycin is TOR, an enzyme. An enzyme is a protein that serves as a biological catalyst in living systems. TOR has been shown to play a key role in cell growth and the metabolic pathways that maintain homeostasis on both the cellular and organismal levels. Insulin and insulin-like growth factors are activators of TOR. Additionally, caloric restriction (CR) triggers a biochemical signal that inhibits TOR activation acting as negative feedback.
Persistent activation of TOR has been clearly shown to be involved in various diseases including cancer, cardiac performance and obesity-related ailments. Conversely, the inhibition of TOR has been shown to prolong life span. The positive effect of CR on longevity has been demonstrated in many animal species. CR may exert its effect through the inhibition of TOR.
Sestrins (Sesns) are proteins that are highly conserved in nature – found in many mammalian species across the evolutionary spectrum. They increase within cells that are exposed to stress such as CR. There is evidence that they also may function as antioxidants. Sesns are, in fact, feedback inhibitors of TOR.
There is mounting evidence that Sesns are involved in preventing age-related disease and, therefore, prolonging life. This kind of understanding of the aging process may find some future application.