Rapamycin is a natural macrolide immunosuppressant that activates mTORC1. Seco Rapamycin (sodium salt) is a nonenzyme-dependent degradation product of rapamycin resulting from ester hydration followed by dehydration. It has less than 4% of the potency of rapamycin in a thymocyte proliferation assay. Rapamycin quickly degrades to two ring-opened products, including seco rapamycin, in the cytoplasm or in homogenates of Caco-2 cells. Like rapamycin, seco rapamycin is secreted from cells by P-glycoprotein and metabolized to a common dihydro species. While seco rapamycin poorly activates mTOR, it mimics rapamycin in its ability to inhibit the proteasome.
