mTORC1-selective (mTORC2-sparing) dosing captures longevity without insulin resistance
Studies point in different directions · confidence 85% · Atlas ID H2
The gap
The lifespan benefit of blocking mTOR seems to come specifically through mTORC1, while the main side effect (insulin resistance) comes from also disrupting mTORC2. In mice, giving rapamycin less often (weekly instead of daily) avoided the glucose problems while still only hitting mTORC1. Newer, more selective drugs aimed only at mTORC1 have shown a low rate of blood-sugar side effects in an early human cancer trial — encouraging, but that trial wasn't designed to test ageing and had no comparison group.
Technical framing: Longevity comes from mTORC1 but chronic rapamycin's harm (insulin resistance) comes from mTORC2 disruption (LAM2012). QUANTIFIED (full text): ARR2015 - daily 2 mg/kg rapamycin impaired glucose tolerance (+71% AUC) and inhibited BOTH mTORC1 and mTORC2 (AKT-S473), while weekly / every-5-days caused NO glucose impairment and inhibited mTORC1 only -> intermittent dosing decouples benefit from harm in vivo. Dose-response MIL2014 (4.7/14/42 ppm; top dose +23% M / +26% F). PEARL tested 5 vs 10 mg/week but its primary endpoint was visceral fat (missed) - no mTORC1-selective human aging readout exists. UPDATE (2026-07-09, revised 2026-07-29): early clinical evidence now exists outside the rapamycin/rapalog class. Bi-steric mTORC1-selective inhibitors (>25-fold selectivity over mTORC2) were validated preclinically (MEN2023: RMC-6272 overcomes drug resistance via complete mTORC1 suppression, sparing mTORC2) and clinically (SCH2025: RMC-5552 Phase 1, n=57 solid tumors) -- treatment-related hyperglycemia was only 4%, which is consistent with the hypothesis that sparing mTORC2 reduces the glucose-intolerance signature seen with chronic rapamycin/rapalogs. Because SCH2025 was open-label, single-arm and had no rapamycin or ATP-site comparator, the low hyperglycaemia rate is a supportive signal, not a causal attribution: it is compared against historical rapalog experience, not against a randomised control. This is the strongest human evidence yet for the mechanistic premise of H2, but it is preliminary, and it comes from an oncology trial, not an aging/longevity endpoint -- the missing link is still a healthspan/lifespan readout for a selective inhibitor.
The hypothesis
Educated guess: a drug (or dosing schedule) that blocks mTORC1 while leaving mTORC2 alone should give the longevity benefit of rapamycin without the blood-sugar downside.
Technical framing: An intervention that suppresses the mTORC1/4E-BP1 arm while sparing mTORC2 -- now achievable with bi-steric mTORC1-selective inhibitors (RMC-6272/RMC-5552) in addition to intermittent/low-dose rapamycin -- yields the lifespan benefit without glucose intolerance.
How it could be tested
Mouse lifespan under continuous vs intermittent vs low-dose rapamycin; endpoints lifespan + insulin sensitivity + mTORC2 activity (Akt-Ser473). Mirrors the human EVERLAST daily-vs-weekly design. NEW (sharper test enabled by 2023-2025 tools): repeat using a bi-steric mTORC1-selective inhibitor (RMC-6272 class) instead of rapamycin -- this removes the mTORC2-sparing question as a confound, so if lifespan extension still occurs without glucose intolerance, that is a cleaner causal test than intermittent-dosing rapamycin.
