#118 - Lloyd Klickstein, M.D., Ph.D.: Rapamycin, mTOR inhibition, and the biology of aging
Lloyd Klickstein, Chief Science Officer at resTORbio, discusses the clinical application of rapamycin and its derivatives, focusing on mTOR inhibition's dose-dependent impact on immune function in the elderly. He shares insights from his pivotal 2014 and 2018 papers, comparing rapalogs to fasting and caloric restriction for longevity.
Deep Dive Analysis
17 Topic Outline
Lloyd Klickstein's Background and Career Transition
Defining Translational Medicine and its Importance
Introduction to mTOR and its Role in Cellular Processes
Evolutionary Context of mTOR and Lysosomal Association
Understanding mTOR Complexes: TORC1 and TORC2
Rapamycin's Mechanism of Action and FKBP Binding
Dose-Dependent Effects of Rapamycin on TORC1 and TORC2
Comparing Rapamycin and Rapalogs: Everolimus (RAD001)
The 2014 Manick-Klickstein Study Design and Rationale
Key Findings of the 2014 Study: Immune Function and Side Effects
Novartis's Response and the Development of RTB101
Formation of resTORbio and Licensing of RTB101
RTB101's Mechanism and Phase 2B Study Results
Comparing Rapamycin, Fasting, and Caloric Restriction
Selective mTORC1 Inhibitors and Immunophyllins
mTOR Activation and Depression Treatment with Ketamine
Epigenetic Clocks and Anti-Aging Interventions
8 Key Concepts
Translational Medicine
Translational medicine bridges the gap between basic scientific observations and practical applications for human health. It involves taking basic science insights and developing them into useful treatments, while also providing clinical input early in the drug development process to focus on patient needs.
mTOR
mTOR (mechanistic Target of Rapamycin) is a master integrator of nutrient availability and growth factors within cells. It regulates cellular decisions on whether to grow (synthesize proteins, lipids, nucleic acids) or conserve resources and recycle during times of scarcity.
TORC1
TORC1 (Target of Rapamycin Complex 1) is one of two main mTOR complexes. It primarily regulates protein synthesis, lipid biosynthesis, and protein translation, driving cell growth. Rapamycin and rapalogs inhibit TORC1 activity.
TORC2
TORC2 (Target of Rapamycin Complex 2) is the second main mTOR complex. It regulates cytoskeletal organization and growth decisions. Unlike TORC1, TORC2 is not directly inhibited by rapamycin in the short term, but can be down-regulated by sustained rapamycin exposure through indirect feedback mechanisms.
Rapamycin Mechanism of Action
Rapamycin does not directly bind to mTOR. Instead, it binds tightly to an immunophyllin called FKBP (specifically FKBP12). This rapamycin-FKBP complex then binds to the TORC1 complex, inhibiting its activity, particularly the phosphorylation of S6 kinase, which is crucial for protein translation.
Allosteric Inhibition
Allosteric inhibition occurs when an inhibitor binds to a site on an enzyme or protein that is not the active (catalytic) site, but still causes a conformational change that reduces the enzyme's activity. In the context of mTOR, the rapamycin-FKBP complex acts as an allosteric inhibitor of TORC1.
Catalytic Inhibition
Catalytic inhibition refers to an inhibitor that binds directly to the active site of an enzyme, blocking its catalytic function. In the context of mTOR, a catalytic inhibitor would bind directly to the TOR protein and prevent its phosphorylation of downstream targets.
Epigenetic Clocks
Epigenetic clocks, such as the Horvath clock, measure biological age by analyzing methylation patterns on DNA, particularly in peripheral blood leukocytes. These patterns change predictably with chronological age, and can indicate how old a person is within a relatively narrow margin.
11 Questions Answered
resTORbio aims to develop medications that target the biology of aging to address serious aging-associated diseases, with the ultimate side effect being increased longevity.
Rapamycin directly inhibits TORC1 activity in the short term. However, with sustained, continuous administration, it can also indirectly down-regulate TORC2 activity through feedback signaling pathways.
Inhibition of TORC2 can lead to undesirable metabolic phenotypes such as hyperglycemia and hypertriglyceridemia, and mouse genetic experiments suggest it can accelerate death.
The two-week washout period was implemented to ensure the drug was completely cleared from the body at the time of vaccination, allowing researchers to assess a residual, indirect effect of the drug on the immune system rather than a direct effect.
The study's primary endpoint was the response to seasonal flu vaccination, specifically looking for a 1.2-fold or greater improvement in antibody titers for at least two out of three flu strains in the drug-treated groups compared to placebo.
The study observed a decrease in overall infections, particularly respiratory tract infections and UTIs, in the drug-treated groups compared to placebo, which was an unanticipated finding from reviewing adverse event listings.
No, when patients were revaccinated a year later, the improvement in immunologic function observed after the initial treatment did not persist.
RTB101 (formerly BEZ235) is a catalytic inhibitor that binds directly to mTOR, showing some preference for TORC1. It is distinct from rapamycin or Everolimus, which are allosteric inhibitors that bind to FKBP before inhibiting TORC1.
RTB101 is believed to decrease respiratory tract infections by upregulating an interferon-stimulated antiviral gene response in peripheral blood leukocytes, enhancing innate immunity rather than acquired immunity.
Experiments in old rats showed that even with fasting, their mTOR remained active in the liver, unlike young rats where it was suppressed, suggesting an age-related impairment in responding to nutrient reduction.
Ketamine, a drug showing rapid and significant efficacy for recalcitrant depression, is believed by some to exert its effects by activating mTOR, although the specific cellular mechanism is not fully understood.
9 Actionable Insights
1. Optimize Rapamycin Dosing Strategy
To maximize benefits and minimize side effects of rapamycin or its analogs, consider intermittent dosing rather than continuous administration. This approach helps avoid undesirable mTORC2 inhibition and allows cellular organelles to recover from trough-driven toxicities.
2. Rapamycin Boosts Elderly Immunity
For individuals aged 65 and older, low-dose, intermittent rapamycin (Everolimus 0.5mg daily or 5mg weekly) can significantly improve the immune response to flu vaccination and reduce the incidence of respiratory tract infections. This effect is observed after a washout period, suggesting an indirect, lasting benefit on immune function.
3. Rapamycin Effects Are Temporary
The immune-enhancing benefits of intermittent rapamycin dosing in the elderly do not persist for an entire year. Therefore, periodic re-dosing may be necessary to maintain improved immune function.
4. Metformin for Healthy Individuals
For perfectly healthy individuals without diabetes or pre-diabetes, there is currently no clear evidence of a longevity benefit from taking metformin. It may also pose risks as a weak mitochondrial toxin, potentially dwarfing any perceived benefit.
5. DHEA Supplementation Lacks Benefit
Despite DHEA levels decreasing substantially with age, multiple studies on DHEA replacement have shown no clinical benefit for longevity or overall health.
6. Older Adults Impaired Fasting Response
In older individuals, the body’s ability to suppress mTOR activity in response to fasting appears to be impaired compared to younger individuals. This suggests older adults may not experience the same metabolic benefits from fasting alone.
7. RTB101 Reduces Elderly Infections
For individuals aged 65 and older, especially those with asthma or diabetes, 10 milligrams of RTB101 taken once daily for 16 weeks during cold and flu season can decrease the incidence of respiratory tract infections. This is believed to occur by upregulating antiviral gene expression, but it did not show benefit for smokers or those with COPD.
8. Ketamine for Severe Depression
Intravenous ketamine can act as a rapid and highly effective treatment for patients suffering from severe, recalcitrant major depression. Its effects can be observed within minutes to hours, offering a significant and swift impact.
9. Rapamycin Common Side Effect
Mouth ulcerations are a common and fairly specific side effect of rapamycin and its analogs. The incidence of these ulcers varies based on the specific dose and frequency of the drug.
6 Key Quotes
Our approach is not necessarily what you might read in the popular press about making medicines for aging. Our approach is to address serious aging-associated diseases. And if we're successful, the side effect will be longevity.
Lloyd Klickstein
In a nutshell, mTOR is the master integrator of external availability of nutrients and growth factors, and then is the master regulator of the outputs of that integration, deciding whether cells are going to make proteins, make lipids, make nucleic acids grow, or are we going to circle the wagons, conserve resources, recycle, and wait during times of little for hopefully future times of plenty?
Lloyd Klickstein
The simplest argument is that things that have been conserved from single cell organisms to us are probably important.
Lloyd Klickstein
It's all about the dose.
Lloyd Klickstein
If the drug works, this is what we should have seen.
Lloyd Klickstein
Great scientists say, I don't know, probably more than they know the answer.
Peter Attia
3 Protocols
2014 Manick-Klickstein Study Dosing Regimens (RAD001)
Lloyd Klickstein- Group 1: 0.5 milligrams of RAD001 (Everolimus) taken daily for 6 weeks.
- Group 2: 5 milligrams of RAD001 (Everolimus) taken once a week for 6 weeks.
- Group 3: 20 milligrams of RAD001 (Everolimus) taken once a week for 6 weeks.
- All groups underwent a 2-week washout period after treatment.
- Flu vaccination was administered after the 2-week washout period.
RTB101 Phase 2B Study Dosing Regimens
Lloyd Klickstein- Patients received 5 milligrams of RTB101 (formerly BEZ235) daily for 16 weeks.
- Patients received 10 milligrams of RTB101 daily for 16 weeks.
- Patients received 10 milligrams of RTB101 twice daily for 16 weeks.
- Some arms included a combination of RTB101 with RAD001 (Everolimus).
- The study covered a winter cold and flu season, with patients followed for respiratory tract infections.
RTB101 Phase 3 'Protector' Program Dosing Regimen
Lloyd Klickstein- Patients receive 16 weeks of RTB101 drug treatment.
- Patients are followed for respiratory tract infections using electronic records.
- Treatment is administered during the winter cold and flu season.