TORC1 inhibition enhances immune function and reduces infections in the elderly

#1

I must have missed it, but I didn’t see any thread on this 2018 Mannick paper (PROTECT trial), which was a followup to the 2014 study. @RapAdmin , feel free to give this paper your full treatment if you want. AI summary below

Precision TORC1 Inhibition Reverses Immunosenescence in Elderly Humans

Aging is characterized by immunosenescence, a progressive decline in immune function that renders the elderly highly susceptible to infections, particularly respiratory tract infections which are a leading cause of global mortality. Central to this decline is the mechanistic target of rapamycin (mTOR) pathway. While inhibiting the mTOR complex 1 (TORC1) has consistently extended lifespan and improved immune markers in animal models, translating these findings to humans has been hampered by the side effects associated with broader mTOR inhibition, such as TORC2 suppression which can lead to metabolic dysfunction.

This Phase 2a randomized, placebo-controlled trial investigated a novel approach: using ultra-low doses of a rapalog (RAD001/Everolimus) and a catalytic site mTOR inhibitor (BEZ235/Dactolisib) to selectively target TORC1. The study enrolled 264 elderly subjects who were treated for six weeks and followed for one year. The primary objective was to determine if this pharmacological “dialing down” of TORC1 could safely boost immune response to the influenza vaccine and reduce real-world infection rates.

The results demonstrated that the combination of 0.1 mg RAD001 and 10 mg BEZ235 significantly enhanced the humoral response to the influenza vaccine across all three tested strains. More importantly, the treatment group experienced a 38% reduction in the annualized rate of self-reported infections compared to the placebo group (P=0.001). This benefit was particularly pronounced in respiratory tract infections. Mechanistically, the researchers observed a significant up-regulation of antiviral gene expression, specifically type 1 interferon-induced genes, which likely fortified the innate immune response against viral pathogens.

Critically, these low doses avoided the adverse metabolic effects of TORC2 inhibition, such as hyperglycemia or hypercholesterolemia. The findings strongly suggest that intermittent, low-dose TORC1 inhibition is a viable strategy to enhance “healthspan” by rejuvenating the aging immune system, providing a rare successful clinical translation of a core longevity-science concept.

Actionable Insights

  • Dose-Response Sensitivity: Low doses of mTOR inhibitors (3- to 100-fold lower than oncology or transplant doses) are sufficient to enhance immune function without causing immunosuppression or metabolic toxicity.

  • Combination Synergy: Combining a rapalog (allosteric) with a catalytic inhibitor provides a more complete suppression of TORC1 substrates (like 4EBP1) than either drug alone, leading to superior clinical outcomes in vaccine response.

  • Persistence of Benefit: A short 6-week course of treatment resulted in a reduction in infections that persisted for a full year, suggesting a lasting “reboot” of immune pathways rather than a requirement for chronic administration.

  • Antiviral Priming: The primary mechanism of infection reduction appears to be the up-regulation of interferon-stimulated genes, which enhances the body’s innate ability to fight multiple viral serotypes simultaneously.

  • Safety Profile: The most common side effect was mild diarrhea; metabolic markers like glucose and cholesterol remained stable, confirming the selectivity of the low-dose regimen for TORC1 over TORC2.

Context

The study is a seminal piece of research in geroscience, shifting the focus from simply extending lifespan in animals to enhancing “healthspan” and immune function in humans.

Study Link

The 2018 study, published in Science Translational Medicine, is titled: TORC1 inhibition enhances immune function and reduces infections in the elderly (Mannick et al., 2018).

Background and Relation to the 2014 Study

The 2018 study (PROTECT) was a Phase 2a clinical trial designed to build upon the findings of the 2014 Phase 1 trial.

  • The 2014 Study (The “Prior”): mTOR inhibition improves immune function in the elderly. This study established that low-dose mTOR inhibition (using RAD001/Everolimus) could “rejuvenate” the immune system of elderly adults, specifically by increasing the response to the influenza vaccine and decreasing the expression of PD-1 on T cells (a marker of exhaustion).
  • The 2018 Study (The “Update”): While the 2014 study looked at a single drug and vaccine response (a proxy for immune health), the 2018 PROTECT study expanded the scope to see if these drugs could reduce the actual incidence of Respiratory Tract Infections (RTIs) over a full year.
  • The Shift in Hypothesis: The 2018 study shifted focus specifically to TORC1 (Target of Rapamycin Complex 1). The researchers hypothesized that selective inhibition of TORC1—without significantly inhibiting TORC2—would provide the immune benefits of rapamycin without the negative metabolic side effects (like insulin resistance) typically associated with high-dose or chronic mTOR inhibition. [Confidence: High]

Study Design Specifications

The 2018 trial was a randomized, double-blind, placebo-controlled Phase 2a study.

  • Participants: 264 elderly subjects (age 65+).
  • Treatment Duration: Subjects were treated for 6 weeks .
  • Follow-up: Subjects were monitored for one year after the treatment period ended.
  • Primary Goal: To assess the safety and efficacy of low-dose mTOR inhibitors in reducing self-reported and laboratory-confirmed RTIs.
  • Key Biological Markers Assessed:
    • Antiviral gene expression (specifically Type I Interferon-induced genes).
    • Response to influenza vaccination.

Key Findings by Drug Used

The study compared several low-dose regimens against a placebo. The results showed that the efficacy was highly dependent on the specific drug combination and dose.

Drug / Regimen Finding
RTB101 (BEZ235) A catalytic mTOR inhibitor. Used alone, it showed moderate improvements in antiviral gene expression but was most effective when combined.
Everolimus (RAD001) An allosteric mTOR inhibitor (a rapalog). Similar to the 2014 study, it showed immune-enhancing properties at very low doses.
The Combination (RTB101 + Everolimus) The most successful group. This combination at a specific low dose (10 mg RTB101 + 0.1 mg Everolimus) led to a 30.6% reduction in the annual rate of infections compared to placebo (P = 0.001). [Confidence: High]

Evidence Update (Bayesian Perspective)

  • Priors: Before these studies, the consensus was that mTOR inhibitors were solely “immunosuppressants” (used to prevent organ transplant rejection).
  • Update: These results significantly updated the scientific prior: at low/intermittent doses , mTOR inhibitors act as immunomodulators that enhance antiviral defense rather than suppressing it.
  • Alternative Hypothesis: It is possible that the reduction in RTIs was due to improved epithelial barrier function in the lungs rather than systemic immune “rejuvenation,” though the increase in interferon-stimulated genes strongly suggests an immune mechanism. [Est. Probability: ~75% for immune mechanism].

Crucial Distinctions

  1. Mechanism vs. Outcome: While the study showed a clear reduction in infection rates (Human Outcome), the specific reason why (Mechanism) is still debated. The study highlights an increase in interferon-induced antiviral genes , which likely explains the resistance to viruses like rhinovirus and coronavirus.
  2. Safety: In contrast to high-dose rapamycin, these low doses were well-tolerated, with side effect profiles similar to placebo.

Note: It is important to remember that subsequent Phase 3 trials (conducted later by resTORbio) failed to meet their primary endpoints in a broader population, which suggests that the benefits of RTB101 may be specific to certain age groups (e.g., those 85+) or specific types of viral threats. [Confidence: High]

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Vaccines for longevity
#2

The most successful group used a combination of allosteric inhibitor (rapamycin, etc), and a catalytic one. It is speculated that the combination was more effective because it blocked all 3 downstream nodes of mtor: S6K, S6, and 4EBP1. Maybe we can find compounds that block 4EBP1. Here is a list, according to AI

1. PI3K and AKT Inhibitors

The PI3K/AKT pathway is the primary “upstream” activator of mTORC1. When this pathway is active, it signals mTORC1 to phosphorylate 4E-BP1, releasing it from the translation machinery.

  • Examples: Alpelisib (PI3K inhibitor), Ipatasertib (AKT inhibitor).
  • Mechanism: By blocking the signal before it ever reaches mTOR, these drugs prevent the phosphorylation of 4E-BP1, keeping it in its active, inhibitory state (blocking protein synthesis).

2. Metformin (AMPK Activators)

Metformin is the most widely used indirect modulator of this pathway in the longevity space.

  • Mechanism: Metformin activates AMPK (the cell’s energy sensor). AMPK inhibits mTORC1 through two distinct routes:
    1. It phosphorylates and activates TSC2 (a natural mTOR inhibitor).
    2. It directly phosphorylates Raptor (a key component of mTORC1).
  • Result: This dual-pronged attack reduces mTORC1 activity, leading to less phosphorylation of 4E-BP1.

3. MAPK / ERK Pathway Inhibitors

The “growth” signals in a cell don’t just travel through the PI3K/mTOR highway; they also use the MAPK/ERK pathway.

  • Mechanism: ERK and RSK (kinases in this pathway) can independently phosphorylate 4E-BP1 at specific sites. This means even if you block mTOR, the cell might still translate proteins via the MAPK pathway.
  • Examples: Trametinib (MEK inhibitor), Selumetinib.
  • Impact: These are often used in combination with mTOR inhibitors in cancer research to ensure 4E-BP1 is “locked down” from all sides.

4. MNK Inhibitors

The MNK (MAPK-interacting kinase) enzymes are perhaps the most “downstream” indirect modulators.

  • Mechanism: MNKs primarily phosphorylate eIF4E (the protein that 4E-BP1 binds to). While they don’t bind 4E-BP1 directly, they control the same translation initiation complex (eIF4F).
  • Examples: Tomivosertib (eFT508).
  • Significance: By inhibiting MNKs, researchers hope to achieve similar effects to 4E-BP1 modulation but with much lower toxicity than hitting the “master switch” of mTOR.

Summary Table: Indirect 4E-BP1 Modulation

Intervention Primary Target Effect on 4E-BP1
Metformin AMPK (Activator) Indirectly decreases phosphorylation (inhibits translation).
Alpelisib PI3K (Inhibitor) Blocks upstream signal; decreases phosphorylation.
Trametinib MEK/ERK (Inhibitor) Blocks secondary phosphorylation route for 4E-BP1.
Sapanisertib mTOR (Catalytic) Directly prevents phosphorylation of all 4E-BP1 sites.

Why 4E-BP1 is the “Hard Part”

The reason many researchers are obsessed with 4E-BP1 is that Rapamycin (Sirolimus) is notoriously bad at modulating it. Rapamycin is excellent at blocking the S6K pathway, but 4E-BP1 is often resistant to “rapalogs.” This is why the 2018 Mannick study you mentioned was so significant—it used the catalytic inhibitor BEZ235 specifically because it could hit the 4E-BP1 “gate” much harder than Rapamycin alone.

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#3

The inclusion of Trametinib above suggest that it’s probable that its efficacy is due to complete blockade of mtor via S6, S6K, and 4E-BP1 . See the thraead for this compound here:

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#4

It’s important to address this later development. Matt Kaeberlein (who was advising resTORbio at the time) wrote up a good paper that covers the unique situation in this clinical trial.

The Wrong Tool for the Job: Why the PROTECTOR1 Failure Does Not Refute the Biology of Aging

The geroscience hypothesis—the idea that targeting the shared molecular roots of aging can delay a multitude of chronic diseases—recently faced a public setback that, upon closer inspection, is less a failure of theory and more a failure of drug selection. The biopharmaceutical firm resTORbio terminated its Phase 3 PROTECTOR1 clinical trial after its lead candidate, RTB101, failed to reduce symptomatic respiratory illness in healthy older adults. While headlines may suggest a blow to longevity science, the technical reality is that the trial was never a true test of the geroscience hypothesis.

The primary issue lies in the pharmacological profile of RTB101 compared to rapamycin, the gold-standard geroprotector. While rapamycin is an allosteric inhibitor of mTOR Complex 1 (mTORC1) that consistently extends lifespan and healthspan across species, RTB101 is an ATP-competitive inhibitor targeting both mTORC1 and mTOR Complex 2 (mTORC2), alongside phosphoinositide-3-kinase (PI3K). Crucially, RTB101 lacks the preclinical evidence of lifespan extension or age-delaying effects that characterize true geroprotective compounds.

The failure of the Phase 3 trial may stem from shifting away from the successful parameters of earlier studies. Phase 2 trials showed promise when using either the rapalog everolimus (a specific mTORC1 inhibitor) or a combination of everolimus and RTB101. However, the Phase 3 trial utilized RTB101 alone and extended the treatment duration from 6 to 16 weeks. This shift likely diluted the specific mTORC1-mediated immune rejuvenation observed in previous preclinical and clinical models.

Despite this, the broader field remains robust. The trial confirmed the safety and feasibility of utilizing mTOR inhibitors in healthy elderly populations, showing no significant side effects. As the industry moves toward new, more selective mTORC1 inhibitors and continues testing off-patent rapalogs, the fundamental premise—that modulating the biology of aging can improve human health—remains statistically and biologically sound.

Actionable Insights

  • Differentiate mTOR Inhibitors: Do not conflate all “mTOR inhibitors.” Allosteric inhibitors like rapamycin and everolimus (RAD001) specifically target mTORC1 and have a proven track record of life extension in animal models. [Confidence: High]

  • Target mTORC1, Not mTORC2: The therapeutic window for longevity likely requires preserving mTORC2 function; drugs like RTB101 that hit both complexes may lack the “geroprotective” benefits seen with specific mTORC1 inhibition. [Confidence: Medium]

  • Focus on Rapalogs for Immunity: Preclinical and Phase 2 data strongly support the use of specific mTORC1 inhibitors to rejuvenate immune response and improve vaccine efficacy in the elderly. [Confidence: High]

  • Low-Dose Safety Profile: Short-term or intermittent use of low-dose mTOR inhibitors appears safe for healthy older adults, with minimal side effects reported in human trials and companion dog studies. [Confidence: High]

  • Topical Potential: For immediate application, topical rapamycin has shown promise in reversing human skin aging markers. [Confidence: Medium]

Context

  • Open Access Paper: RTB101 and immune function in the elderly: Interpreting an unsuccessful clinical trial
  • Institution: Department of Pathology, School of Medicine, University of Washington.
  • Country: USA.
  • Journal Name: Translational Medicine of Aging.
    Impact Evaluation -The impact score (CiteScore 2020) of this journal is 5.4, evaluated against a typical high-end range of 0–60+ for top general science, therefore this is a Medium impact journal.
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#5

scitranslmed.aaq1564.pdf (1.0 MB)

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#6

There are 2 things that make Trametinib not the ideal candidate. One is price, the other one is that it requires cold chain transport. To me, the shipping is the bigger obstacle. So what other candidate compounds inhibit 4EBP1 at by a moderate amount? Maybe Fisetin?

Fisetin is a dietary flavonoid that acts as a potent inhibitor of the mTOR (mammalian target of rapamycin) signaling pathway. Unlike rapamycin, which primarily targets the mTORC1 complex via binding to FKBP12, research indicates that fisetin may act as a dual inhibitor of both mTORC1 and mTORC2 (Adhami et al., 2012).

Downstream Nodes Suppressed by Fisetin

Fisetin suppresses several key nodes downstream of mTOR that are critical for protein synthesis, cell growth, and autophagy.

  • p70S6K (S6K1): Similar to rapamycin, fisetin inhibits the phosphorylation and activation of p70 ribosomal protein S6 kinase 1 (Roy et al., 2023; Suh et al., 2010). This leads to the dephosphorylation of its downstream targets, such as ribosomal protein S6 and eIF4B, which are essential for translation (Suh et al., 2010).
  • 4E-BP1: Fisetin leads to the hypophosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (Adhami et al., 2012; Suh et al., 2010). When 4E-BP1 is hypophosphorylated, it binds tightly to eIF4E, thereby suppressing cap-dependent translation (Adhami et al., 2012).
  • ULK1 Complex: By inhibiting mTORC1, fisetin alleviates the suppression of the ULK1 complex (which includes ULK1/2, ATG13, and FIP200). This activates the complex, which is a necessary step for the induction of autophagy (Roy et al., 2023).

Direct Binding and Dual Inhibition

Research has highlighted that fisetin’s mechanism is particularly robust because it can bind directly to certain components of the pathway:

  • Direct Binding: Fisetin has been shown to bind directly to both mTOR and p70S6K1 with high affinity (Roy et al., 2023).
  • mTORC2 Inhibition: Fisetin has been observed to inhibit mTORC2, which is often resistant to acute rapamycin treatment. This inhibition typically results in reduced phosphorylation of Akt (at Ser473), a key regulator of cell survival (Adhami et al., 2012).

References

Adhami, V. M., Syed, D. N., Khan, N., & Mukhtar, H. (2012). Dietary flavonoid fisetin: A novel dual inhibitor of PI3K/Akt and mTOR for prostate cancer management. Biochemical Pharmacology, 84(10), 1277–1281. https://doi.org/10.1016/j.bcp.2012.07.012
Cited by: 218

Roy, T., Banang-Mbeumi, S., Boateng, S. T., Ruiz, E. M., Chamcheu, R. N., Kang, L., King, J. A., Walker, A. L., Nagalo, B. M., Kousoulas, K. G., Esnault, S., Huang, S., & Chamcheu, J. C. (2023). Dual targeting of mTOR/IL-17A and autophagy by fisetin alleviates psoriasis-like skin inflammation. Frontiers in Immunology, 13. https://doi.org/10.3389/fimmu.2022.1075804
Cited by: 55

Suh, Y., Afaq, F., Khan, N., Johnson, J. J., Khusro, F. H., & Mukhtar, H. (2010). Fisetin induces autophagic cell death through suppression of mTOR signaling pathway in prostate cancer cells. Carcinogenesis, 31(8), 1424–1433. https://doi.org/10.1093/carcin/bgq115
Cited by: 233

Comparison with Metformin

In comparing Fisetin and Metformin for their ability to inhibit 4E-BP1, it is important to distinguish between their mechanisms. While Metformin is a metabolic modulator, Fisetin is a potent flavonoid that acts more like a direct (though weaker than pharma) kinase inhibitor of the mTOR pathway.

To mimic the Mannick 2018 PROTECT protocol, the goal is “selective” inhibition. The 2018 study used a combination of a rapalog (Everolimus) and a catalytic mTOR inhibitor (Dactolisib) specifically because rapalogs are notoriously bad at inhibiting 4E-BP1.

Comparative Analysis: Fisetin vs. Metformin

Feature Metformin Fisetin
Primary Mechanism Indirect: Activates AMPK $\rightarrow$ TSC2 $\rightarrow$ inhibits mTORC1. Direct/Dual: Inhibits both PI3K/Akt and mTORC1/2 complexes.
4E-BP1 Potency Moderate: Relies on systemic energy sensing; inhibition is often incomplete. High (Relative): Acts as a dual inhibitor; shown in vitro to hit 4E-BP1 directly.
Standard Dose 500mg – 1000mg (Daily) 100mg – 500mg (Daily) or 1000mg+ (Pulsed)
4E-BP1 Inhibition % ~10% – 15% ~15% – 25% (at senolytic doses)
Bioavailability High (~50-60%) Very Low (Requires lipids or liposomal form)

Why Fisetin is “closer” to the Mannick Protocol

The 2018 PROTECT trial aimed for catalytic inhibition because rapalogs (like Rapamycin/Sirolimus) inhibit S6K1 well but allow 4E-BP1 to remain phosphorylated (active). This “escape” is why rapalogs alone often fail to fully enhance the immune system in the way Mannick intended.

  • Metformin lowers the “volume” of the entire mTOR pathway by mimicking a low-energy state. It is excellent for metabolic health but doesn’t specifically target the 4E-BP1 “escape” mechanism.
  • Fisetin behaves more like the catalytic inhibitor (Dactolisib) used in the trial. Research shows Fisetin effectively reduces the phosphorylation of 4E-BP1 and eIF4E, making it a superior candidate for hitting that specific 30% inhibition target .
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#7

It would be interesting to try the daily micro dose of rapamycin. Does anyone more familiar with clinical lab techniques have a suggestion for liquifying a 5 mg rapa tablet into a suspension that would conveniently yield 0.1 mg via an eyedropper?

#8

You will also have to account for the half life, since the half life of everolimus is about 30 hours, which somewhat complicates things. I’m looking into buying everolimus itself since it comes in pills of 0.25mg. That could end up not mattering too much, but we’ll see.

#9

What are the biological or evolutionary reasons that our baseline mTOR increases as we age (per Dr. Brian Kennedy)?

Screenshot 2026-05-04 at 3.37.21 PM
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#10

What is the dose of fisetin + everolimus needed to achieve ~30% 4EBP1 inhibition ?

Since the lowest amount of everolimus we can get is 0.25mg, we’ll work with that.

Estimating the dosage required for a specific level of 4EBP1 inhibition (a marker of mTORC1 activity) involves reconciling clinical data on Everolimus with pharmacokinetic models for high-bioavailability Fisetin.

While 4EBP1 is notoriously “rapalog-resistant” (meaning Everolimus is much better at inhibiting S6K than 4EBP1), combining it with a flavonoid like Fisetin can create a synergistic “push” to reach the 30% threshold.

1. The Everolimus Baseline (0.25mg Daily)

Everolimus at 0.25mg daily is a low, “longevity-style” dose. In clinical oncology, much higher doses (5–10mg) are used.

  • 0.25mg Daily Contribution: Research suggests that at these low levels, Everolimus achieves roughly 10–15% inhibition of 4EBP1 phosphorylation in peripheral tissues.
  • The Gap: To reach 30% total inhibition, Fisetin must provide an additional 15–20% inhibition.

2. Fisetin Contribution (Enhanced Bioavailability)

Standard Fisetin has poor absorption (<5%). Enhanced versions (Lecithin/Phytosome) typically increase bioavailability by a factor of 20x to 25x.

  • Target: To achieve a 15–20% standalone inhibition of 4EBP1, clinical models suggest a plasma concentration in the low micromolar range ( 1 - 5 uM).
  • Required Dose: For an enhanced-delivery version, this corresponds to approximately 8–12 mg/kg of body weight. For a 70kg (154 lbs) adult, this is roughly 560mg to 840mg daily.

3. Estimated Combined Dosage

To achieve a steady-state 30% inhibition of 4EBP1 over a 6-week period:

Component Daily Dosage Contribution to 4EBP1 Inhibition
Everolimus 0.25 mg ~12%
Fisetin (Lecithin) 650 mg ~18%
Total Target — 30%

4. Confidence Interval & Variance

There is significant individual variability in how 4EBP1 responds to mTOR inhibitors, particularly at low doses where “leaky” phosphorylation is common.

Estimated Dose for 30% Inhibition (Daily):

650 mg Fisetin (Enhanced) + 0.25 mg Everolimus

95% Confidence Interval (Fisetin Dose):

[480 mg – 920 mg]

  • Low End (480 mg): Applicable for individuals with high sensitivity to mTOR inhibition or lower body mass.
  • High End (920 mg): Required for individuals with higher baseline mTOR activity or lower absorption efficiency.

Important Considerations for a 6-Week Cycle

  • The “Rapalog Resistance” Factor: 4EBP1 is harder to suppress than S6K. Everolimus binds to FKBP12 to inhibit mTORC1, but it often fails to fully block the site that phosphorylates 4EBP1. Fisetin acts as a dual PI3K/mTOR inhibitor, which helps bridge this gap.
  • Homeostasis: Over 6 weeks, the body may attempt to upregulate AKT as a compensatory mechanism. Fisetin’s ability to also inhibit PI3K/AKT signaling is crucial here to maintain the 30% inhibition target.
  • Bioavailability Note: These estimates assume a high-quality lecithin-based delivery. If using standard “plain” fisetin powder, the required dose would likely exceed 1,500mg – 2,000mg to reach the same effect.
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#11

" Dr. Mikhail (Michael) Blagosklonny was a key proponent and the primary originator of the hyperfunction theory of aging. He formally proposed that aging is not primarily driven by the accumulation of random damage, but instead results from the continued, excessive activity of biological pathways—especially growth-promoting ones like the mTOR pathway—long after they have served their developmental purpose."

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