MTOR and diabetes mellitus: Sirolimus, a macrocyclic lactone, inhibits mammalian target of rapamycin (mTOR) thereby blocking cell division by interfering at the transition from G1 to S phase.28 People with diabetes show a breakdown in the phosphatidylinositol 3 kinase insulin signal transduction pathway, where mTOR has an important role,29 and this has been thought to limit the effectiveness of sirolimus in people with diabetes mellitus.