Rapamycin — mTOR (mechanistic target of rapamycin) inhibitor — macrolide antibiotic / FDA-approved immunosuppressant with longevity off-label use

Rapamycin (sirolimus) is a macrolide produced by Streptomyces hygroscopicus that binds FKBP12 to form a complex that allosterically inhibits mTORC1 (mechanistic Target Of Rapamycin Complex 1). mTORC1 is a master regulator of anabolic metabolism: it promotes protein synthesis, inhibits autophagy, and drives cellular growth. Chronic mTORC1 overactivation contributes to aging-associated pathologies (senescence, metabolic syndrome, cancer). Longevity rationale: (1) The NIA Interventions Testing Program showed 9–14% lifespan extension in mice even when started late in life (600 days); (2) Mannick et al. (2014, 2018 PLOS Biology/Science Translational Medicine) demonstrated that a 6-week course of everolimus (rapalog) improved vaccine response by 20% and reduced infections in elderly humans — direct anti-aging immune benefit; (3) mTORC1 inhibition activates autophagy (cellular self-cleaning), reduces senescent cell accumulation, and restores immune function. CRITICAL: Rapamycin also partially inhibits mTORC2 with chronic/continuous dosing — this is responsible for insulin resistance and metabolic side effects. Intermittent dosing (once weekly) spares mTORC2 and retains mTORC1 inhibition benefits.