Caloric restriction mimetics (CRMs)
Examples of the most studied CRM and their anti-cancer effects include metformin, rapamycin, aspirin, and resveratrol and its by-products.
Calorie Restriction Mimetics — Calorie restriction mimetics (CRMs) are a mechanistic class of compounds intended to reproduce selected biochemical effects of caloric restriction without requiring sustained energy restriction. They are best viewed as a research/therapeutic concept rather than a single drug entity or a formally approved regulatory class. Standard abbreviation: CRM or CRMs. In the oncology literature, the most commonly cited CRMs are metformin, rapamycin or rapalogs, aspirin or salicylate, resveratrol, spermidine, and hydroxycitrate; broader candidate lists often also include EP300-inhibitory or sirtuin-linked dietary compounds such as curcumin, garcinol, anacardic acid, EGCG, and some synthetic sirtuin activators. Their shared functional identity is partial imitation of nutrient-deprivation signaling, especially autophagy induction, lowered protein acetylation, AMPK-SIRT engagement, and relative suppression of anabolic growth signaling. In practice, however, CRM biology is highly heterogeneous, agent-specific, and often limited by pharmacokinetics, dose ceilings, or context-dependent tumor effects.
Primary mechanisms (ranked):
- Autophagy induction and proteostasis remodeling, often via reduced cytosolic acetyl-CoA signaling and lower global protein acetylation
- AMPK activation with downstream suppression of PI3K-AKT-mTOR growth signaling and reduced anabolic drive
- EP300 acetyltransferase inhibition or functional opposition, promoting deacetylation-linked fasting-like signaling
- Sirtuin-linked stress adaptation and mitochondrial remodeling, especially with resveratrol-like or NAD-related CRM candidates
- Systemic insulin-glucose-IGF axis attenuation, reducing nutrient availability and mitogenic support for susceptible tumors
- Immune-context effects, including improved chemotherapy responsiveness and, in some models, enhanced anticancer immunosurveillance
- Secondary anti-inflammatory and HIF-1α-glycolysis dampening effects in subsets of CRMs
Bioavailability / PK relevance: PK is not class-uniform. Metformin is orally available but hydrophilic and tissue-distribution dependent; rapamycin is orally active but shows variable exposure and clinically important immunosuppressive toxicity; aspirin is systemically available but dose-limited by bleeding risk; resveratrol has poor oral bioavailability and rapid metabolism; spermidine supplementation can show only modest increases in circulating polyamines because of strong homeostatic control. Many “dietary CRM” candidates therefore have more convincing mechanistic than translational PK support.
In-vitro vs systemic exposure relevance: This is a major translation issue for the class. Many in-vitro CRM studies use concentrations that are not cleanly achievable in human plasma or tumors, especially for metformin and several polyphenols such as resveratrol. Accordingly, class-level conclusions should prioritize pathway directionality and combination/adjunct effects over direct cytotoxicity observed at high in-vitro doses.
Clinical evidence status: Mixed and agent-dependent. For cancer, CRM evidence is strongest at the preclinical and adjunct-mechanistic level. Human data exist mainly for individual agents such as metformin, aspirin, and rapalogs rather than for “CRMs” as a validated class, and results remain heterogeneous across tumor types and trial designs. At present, CRMs are better regarded as a translational framework and combination strategy than as an established standalone oncology therapy category.
CRM Product/Priority Table
| Tier |
Priority |
Agent |
CRM Strength |
Main Rationale |
Comments |
| 1 |
1 |
Spermidine |
Very strong |
Among the cleanest strict CRMs; promotes autophagy and opposes protein acetylation through EP300-related mechanisms |
Best fit for a mechanistically strict CRM |
| 1 |
2 |
Hydroxycitrate |
Very strong |
Strong strict CRM; reduces acetyl-CoA availability, lowers protein acetylation, and induces autophagy |
Also has notable anticancer adjunct evidence |
| 1 |
3 |
Aspirin/ salicylate |
Strong |
Can inhibit EP300 and induce fasting-like autophagy signaling |
Good translational relevance compared with many dietary CRMs |
| 2 |
4 |
Metformin |
Strong but indirect |
Major CRM-associated drug due to AMPK activation, reduced anabolic signaling, and host metabolic effects |
Important in oncology, though less strict mechanistically than tier 1 |
| 2 |
5 |
Rapamycin / rapalogs |
Strong but indirect |
Suppresses mTOR and reproduces part of the nutrient-deprivation program |
Highly important, but more targeted than classic acetylation-centered CRMs |
| 2 |
6 |
Resveratrol |
Moderate to strong |
Historically prominent due to SIRT1-linked and autophagy-related fasting-like signaling |
Limited by weak pharmacokinetics and broader mechanistic ambiguity |
| 3 |
7 |
EGCG |
Moderate |
Often included as a putative CRM because it can affect acetyltransferase activity and autophagy-related signaling |
Less central than higher-tier agents |
| 3 |
8 |
Curcumin |
Moderate |
Frequently listed as a CRM-like dietary compound through acetylation and autophagy-related effects |
Not a class-defining CRM |
| 3 |
9 |
Garcinol |
Moderate |
Mechanistically interesting EP300-related candidate |
Mostly preclinical and less developed clinically |
| 3 |
10 |
Anacardic acid |
Moderate |
Acetyltransferase-inhibitory CRM candidate |
Mainly mechanistic and preclinical |
| 4 |
11 |
Acarbose |
Plausible but broad |
Blunts postprandial glucose and nutrient signaling |
More of a systemic metabolic mimic than a strict autophagy-centered CRM |
| 4 |
12 |
Glucosamine |
Plausible but weak |
Sometimes classified as a CRM-like metabolic agent |
Cancer-specific relevance is much weaker |
| 4 |
13 |
Nicotinamide / nicotinamide riboside / other NAD-linked agents |
Debatable |
Occasionally placed in broad CRM lists |
Less standardized as oncology CRMs |
Mechanistic Pathway Table
| Rank |
Pathway / Axis |
Cancer Cells |
Normal Cells |
Primary Effect |
Notes / Interpretation |
| 1 |
Autophagy induction |
↑ autophagic flux; may reduce growth fitness, stress tolerance mismatch, or therapy resistance |
↑ stress adaptation, proteostasis, organelle quality control |
Core fasting-like reprogramming |
This is the most coherent class-defining mechanism across stricter CRMs. In cancer, benefit is context-dependent because autophagy can also support survival in some settings. |
| 2 |
AMPK activation |
↑ energy stress signaling; proliferation programs ↓ |
↑ metabolic efficiency and adaptive stress signaling |
Nutrient-sensing reset |
Especially relevant for metformin-like CRMs; often linked secondarily to mTOR suppression and lower biosynthetic drive. |
| 3 |
mTORC1 anabolic signaling |
↓ protein synthesis, cell growth, and proliferation |
↓ excessive anabolism; may support maintenance programs |
Antiproliferative restraint |
Rapamycin and rapalogs act most directly here. This axis has strong industry relevance because it is already druggable and clinically validated in oncology for specific agents. |
| 4 |
EP300 acetyltransferase and protein acetylation |
↓ protein acetylation; fasting-like deacetylation programs ↑ |
↓ acetylation tone; autophagy competence ↑ |
Autophagy-permissive deacetylation |
Hydroxycitrate acts upstream through acetyl-CoA depletion; spermidine and salicylate can oppose EP300 activity more directly. This is a key stricter CRM-defining axis. |
| 5 |
Acetyl-CoA supply and citrate-ACLY axis |
↓ lipogenic and acetylation-supportive substrate availability |
↓ anabolic surplus signaling |
Metabolic substrate restriction |
Most class-relevant for hydroxycitrate-like CRMs. Mechanistically central in strict CRM literature, but less clinically deployed than AMPK-mTOR agents. |
| 6 |
Sirtuin signaling and NAD-linked stress adaptation |
↑ stress-response remodeling; growth signaling ↓ (context-dependent) |
↑ mitochondrial maintenance and stress resilience |
CR-like adaptive signaling |
Most associated with resveratrol and synthetic sirtuin activators. Mechanistically plausible, but human translational strength is weaker than for metformin or rapamycin. |
| 7 |
Insulin glucose IGF signaling |
↓ nutrient-driven mitogenic support |
Improved insulin sensitivity and metabolic control |
Systemic host-level antitumor pressure |
Important because some CRM benefits may be host-mediated rather than directly tumoricidal. Likely most relevant in hyperinsulinemic or metabolically dysregulated settings. |
| 8 |
Mitochondrial energetics and OXPHOS stress |
↓ mitochondrial energy throughput or biosynthetic support (agent-dependent) |
Adaptive remodeling more likely than outright injury at therapeutic exposure |
Bioenergetic constraint |
Metformin-like CRMs can stress complex I-linked metabolism, but many direct mitochondrial effects reported in vitro occur at supra-clinical concentrations. |
| 9 |
HIF-1α glycolysis axis |
↓ hypoxia-adaptive and glycolytic signaling (secondary, context-dependent) |
Usually limited or indirect effect |
Secondary metabolic suppression |
This is not universal across CRMs, but often appears downstream of AMPK-mTOR and lower anabolic signaling. |
| 10 |
Inflammation COX prostaglandin signaling |
Inflammatory support programs ↓ |
Inflammation tone ↓ |
Microenvironmental restraint |
Most relevant to aspirin or salicylate-containing CRM interpretations. Important clinically, but not a universal class-defining axis. |
| 11 |
Chemosensitization and anticancer immunity |
Therapy responsiveness ↑ in selected models |
Normal-tissue stress tolerance may improve (context-dependent) |
Adjunct therapeutic leverage |
Preclinical work with hydroxycitrate and spermidine suggests improved chemotherapy efficacy and altered tumor immune contexture, but this remains incompletely validated in human oncology. |
| 12 |
Clinical Translation Constraint |
Heterogeneous exposure-response; tumor context strongly modifies benefit |
Host toxicity and metabolic background shape tolerability |
Limits class-wide deployment |
The CRM concept is stronger than the class-level clinical evidence. Main constraints are nonuniform PK, supra-physiologic in-vitro dosing, immunosuppression for rapamycin-class agents, bleeding for aspirin, renal/lactic-acidosis concerns for metformin, and weak systemic exposure for several dietary polyphenols. |
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