Salidroside Combats Aging and Cancers through Oxidative Stress Mitigation

Rhodiola genus (e.g., Rhodiola crenulata and Rhodiola rosea) is a class of relatively rare and valuable plants native to high-altitude regions of Asia, Europe, and North America. Rhodiola grows under the forest or on grassy slopes in cold areas at an altitude of 1800-2700 m, mostly distributed in the Northern Hemisphere¹. In China, the production areas of Rhodiola are concentrated in the Qinghai-Tibet Plateau and the high mountains in the southwest and northwest, including Tibet, Yunnan, Sichuan, Qinghai, Xinjiang, and Gansu². Traditionally, the root or extracts of the Rhodiola genus have been employed to treat altitude sickness, fatigue, headaches, hysteria, hernias, discharges, and blood stasis, etc.³.

Due to the health benefits of Rhodiola, these plants, in particular their roots, are usually dried and processed into precious medicinal herbs. In addition to decoction according to traditional Chinese medicine formulas, this herb can also be consumed in daily life. The daily consumption methods include brewing tea or wine, stewing soup, cooking porridge, and mixing powder in boiled water^1,4.

In the 1960s and 1970s, with the development of phytochemistry, Soviet and Chinese scientists began to systematically study the chemical composition of Rhodiola rosea. Researchers isolated a component with significant physiological activity from the roots of this plant. This chemical is named salidroside (Sal), and is also known as rhodioloside or rhodosin, belonging to the phenyl-ethanolic glycoside class of compounds. Further studies demonstrated that in most cases, Sal, but not other compounds from R. rosea, can reproduce the therapeutic effects of this plant, suggesting that it is the major active constituent^3,5. Afterwards, Sal has also been found in other species, including R. crenulate, R. semenovii, R. quadrifida, Artemisia capillaris Thunb., Leonurus japonicus Houtt. and Rehmannia glutinosa Libosch, as well as traditional Chinese medicine prescriptions such as Yinchenhao Tang, Shuanghong Huoxue Capsule, and Nuodikang Capsule³. It can be directly extracted from these plants using physical methods such as ultrasonic-assisted extraction and supercritical carbon dioxide (SC-CO₂) extraction⁶. Sal can also be synthesized through biological, chemical, and biocatalytic routes⁷.

In recent years, Sal has garnered significant attention due to its potential in regulating diverse biological processes, with demonstrated effects of resisting stresses, modulating the immune system, relieving fatigue, inhibiting malignancies, etc.⁸. These pharmacological properties position Sal as a critical focus in modern medical research, particularly in aging-related diseases and malignancies. This review comprehensively summarizes the mechanisms of Sal's anti-aging and anti-cancer effects, involving its antioxidant activity, cellular targets, and downstream pathways. This article has potential significance for understanding the biological activity of Sal and promoting its applications in human wellness.

Chemical properties and organismal targets of Sal related to human wellness
The chemical formula of Sal is C₁₄H₂₀O₇, with the chemical name 2-[4-hydroxyphenyl] ethyl β-D-glucopyranoside. It is highly soluble (≥ 100 mg/mL) in water or methanol but poorly soluble (≤ 0.1 mg/mL) in diethyl ether, and appears as a white to pale yellow crystalline powder possessing excellent thermal stability (with a melting point of about 160 °C)⁶.

Sal contains multiple hydroxyl groups (as shown in Figure 1), which enable this phenylpropanoid to interact with and scavenge free radicals. Additionally, Sal exerts its free radical-scavenging effects by modulating signaling pathways associated with the generation or elimination of reactive oxygen species (ROS)⁹.

Moreover, the molecular structure of Sal facilitates interactions with various cellular proteins, inducing a wide range of pharmacological activities. Specifically, Sal contains multiple active sites, such as hydroxyl groups, glycosidic bonds, etc. These groups can form hydrogen bonds, hydrophobic interactions, or electrostatic interactions with specific structural domains of different proteins (such as enzyme active centers, receptor binding sites). For example, its glycoside portion may bind to the protein surface through hydrogen bonding, while the benzene ring structure may be embedded in hydrophobic pockets. Using real-time surface plasmon resonance (SPR) technology, Yao et al. demonstrated that Sal directly binds to Nrf2, stabilizing this transcription factor¹⁰. A study by Hong et al. revealed that Sal augments the ATPase activity of HSC70¹¹. Recently, it was reported that Sal activates PI3K and AKT, likely through physical interaction with both kinases¹². This is consistent with molecular docking results from Zhang et al., which identified additional potential Sal-associated proteins such as albumin, IL6, MMP9, and caspase-3, although these interactions require experimental validation¹³. In addition to these proteins, other reported direct targets of Sal include hypoxia-inducible factor-1α (HIF-1α), aryl hydrocarbon receptor (AhR), and epidermal growth factor receptor (EGFR), as listed in Table 1. Through these chemical characteristics and cellular targets, Sal modulates a wide array of signaling pathways. These pathways are listed in Table 2 and described in the following sections.

Sal-mediated regulation of signaling pathways related to human health
Sal has exhibited therapeutic effects for diverse disorders, including malignancies, especially pancreatic ductal adenocarcinoma, which is known as the king of cancers, as well as neurodegenerative diseases such as Alzheimer's syndrome. In the development and progression of these diseases, numerous cellular signaling pathways are involved. Therapies of Sal are attributed to their regulation on these pathways, either through direct interaction with proteins or by scavenging free radicals. Notably, these pathways are intertwined and form a complicated network. The signaling pathways regulated by Sal are summarized below and illustrated in Figure 1.

Sal directly reduces ROS to regulate its downstream pathways
As shown in Figure 1, several hydroxyl groups are contained in Sal. These reducing groups can directly react with ROS, effectively neutralizing their activity and blocking oxidative chain reactions¹⁴. At low levels, ROS function as redox signaling molecules, playing crucial roles in maintaining cell proliferation, differentiation, and migration. However, excessive ROS production leads to oxidative modifications and damage of DNA, proteins, lipids, and polysaccharides, impairing their functions and promoting the onset and progression of diseases¹⁵. ROS are primarily generated in mitochondria due to electron leakage and their interaction with oxygen during ATP synthesis. In cancer cells, ROS levels are markedly elevated due to incomplete consumption of oxygen and glucose, as well as accelerated glycolysis¹⁶.

Several proteins, particularly kinases, are activated by ROS. By decreasing ROS levels, Sal induces the inactivation of these signaling molecules, such as hypoxia-inducible factor-1α (HIF-1α)^17,18,19, AMP-activated protein kinase (AMPK)²⁰, phosphatase and tensin homolog (PTEN)²¹, Src kinase²², Phosphoinositide 3-kinase (PI3K)^23,24, and heat shock protein 70 (HSP70)²². These inactivated signaling molecules subsequently regulate downstream effectors, including VEGF, AKT, and NOX2.

In addition to its direct ROS-reducing effects, Sal also indirectly reduces ROS by modulating axes involved in ROS production or clearance. For example, it regulates the SIRT1/PGC-1α, Nrf2/SIRT3, AhR/CYP1A1, and HSP90/SMYD3 pathways^25,26,27, which are discussed in greater detail below.

Sal regulates Nrf2 and its downstream genes
Nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical transcription factor that plays a pivotal role in cellular responses to oxidative stress and antioxidant defense²⁸. It helps cells counteract oxidative damage caused by both internal and external stressors by regulating the expression of a series of antioxidant and detoxifying enzymes²⁹.

A molecular docking study indicates that Sal exhibits a high binding affinity for Nrf2³⁰. The physical association interaction between Sal and Nrf2 has been confirmed by means of surface plasmon resonance and cellular thermal shift assays¹⁰. This interaction likely stabilizes Nrf2 by reducing its ubiquitination and degradation mediated by Keap1, thereby increasing Nrf2 protein levels and promoting its translocation to the nucleus³¹. Once in the nucleus, Nrf2 binds to proteins such as Maf and Jun to form heterodimers, which interact with the antioxidant response element²⁸. This interaction enhances the expression of downstream target genes, including glutathione peroxidase 4 (GPX4), system X− transporter (SLC7A11)³⁰, heme oxygenase 1 (HO1), NAD(P)H: quinone reductase 1 (NQO1)²⁸, and sirtuin 3 (SIRT3)¹⁰. These genes collectively protect cells from oxidative stress, ferroptosis, apoptosis, and cellular senescence^30,32.

Sal activates SIRT1/3 and regulates their downstream pathways
Sirtuins (SIRTs) are a family of NAD⁺-dependent histone deacetylases (SIRT1-7) that play significant roles in metabolism, inflammation, aging, and antioxidant responses³³.

Several studies demonstrate that Sal can directly bind to and activate SIRT1⁸ , or upregulate its expression by inhibiting miR-22³⁴. This leads to the deacetylation of key transcription factors such as peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), p53, and nuclear factor-κB (NF-κB), thereby regulating the expression of genes involved in mitochondrial function and homeostasis (e.g., Nrf1/2, TFAM, Drp1)⁸. Additionally, Sal reduces the levels of inflammatory cytokines like TNF-α, IL-1β, and IL-6 through the SIRT1/NF-κB axis³⁵. A recent work found that Sal downregulates NF-κB and its target gene NOD-like receptor family pyrin domain containing 3 (NLRP3), inducing the formation of the NLRP3 inflammasome, caspase-1 activation, and the subsequent maturation and secretion of pro-inflammatory cytokines IL-1β and IL-18^36,37.

Another member of the sirtuin family, SIRT3, is positively regulated by the Nrf2 transcription factor, which is directly targeted and stabilized by Sal as mentioned above¹⁰. On the other hand, NF-κB can be suppressed by SIRT3³⁸. These findings imply that Sal may dictate diverse downstream players of Nrf2, SIRT3, and NF-κB through the crosstalk between these axes^10,39.

Sal suppresses NF-κB not only through SIRT1/3 but also through other pathways. By binding to the AhR, Sal inhibits its nuclear translocation and downregulates AhR-dependent transcription of CYP1A1/1B1. These downstream genes have been reported to mediate ROS generation^32,40,41. Furthermore, Sal blocks the interaction between AhR and NF-κB, reducing NF-κB activation and subsequent expression of inflammatory factors such as CD68 and ICAM1³².

Sal inhibits or activates PI3K/AKT and downstream pathways
The PI3K/AKT pathway is a crucial signaling cascade that regulates cell growth, proliferation, survival, metabolism, and migration⁴². Sal appears to either inhibit or activate the PI3K/AKT pathway, depending on the cellular context.

Studies suggest that Sal can inhibit the PI3K/AKT pathway in cancer cells through various mechanisms. On one hand, Sal suppresses ROS-mediated activation of Src and HSP70; subsequently, PI3K and AKT are inactivated^22,43. Additionally, through an unknown mechanism, Sal activates PTEN, which inhibits the phosphorylation and activation of AKT²¹. On the other hand, Sal inhibits AKT by upregulating the expression of miR-195, although the exact mechanism remains unclear⁴⁴. Downstream effectors of AKT, such as the mammalian target of rapamycin (mTOR), extracellular signal-regulated kinases (ERK1/2), and FOXO1, are regulated by Sal, affecting the activation or expression of proteins related to autophagy and ferroptosis, such as LC3, p62, GPX4, SREBP1, and SCD1^21,44,45. Sal also directly binds to mTOR to stabilize it; however, the phosphorylation/activation of mTOR is downregulated by Sal²¹.

Conversely, some evidence suggests that Sal activates the PI3K/AKT pathway in non-cancerous cells. By directly binding to key amino acid residues of PI3K and AKT, Sal enhances the phosphorylation of both kinases, promoting cellular survival and enhancing antioxidant capacity¹². Moreover, Sal activates AMPK, which directly phosphorylates AKT^46,47. This results in the translocation of FOXO1 from the nucleus to the cytoplasm⁴⁸, relieving its inhibition of PDX1 and restoring PDX1 nuclear localization to enhance β-cell function²⁰. Reverse virtual docking predicts that Sal binds to the nucleotide-binding domain of HSC70, activating it to upregulate brain-derived neurotrophic factor (BDNF) expression. The upregulation of BDNF further enhances AKT phosphorylation and promotes genes related to cell survival, while reducing pro-apoptotic gene expression^11,49,50.

The discrepancy in the effects of Sal on PI3K/AKT signaling between cancerous and non-cancerous cells could be attributed to the differential ROS levels as well as mTOR status in these cell types. Cancer cells typically have elevated ROS levels, which can activate the PI3K/AKT pathway by stimulating multiple players, including PI3K, Src, and HSP70; the potent antioxidant activities of Sal are likely to result in downregulation of this axis^22,43. The abnormally activated mTOR, which is a direct target of Sal, may also contribute to the inhibitory effect of this small molecule on the PI3K/AKT/mTOR pathway in cancer cells²¹. With normal levels of ROS and mTOR protein, Sal can activate this pathway through PI3K, AMPK, and HSC70 in non-cancerous cells^12,46,47.

Sal inhibits JAK2/STAT3 pathway
The JAK/STAT pathway, particularly the JAK2/STAT3 axis, plays a crucial role in immunity, hematopoiesis, cell survival, and cancer progression⁵¹.

Experimental evidence shows that Sal reduces the phosphorylation of JAK2 and STAT3⁵¹. Phosphorylated STAT3 forms dimers and translocates to the nucleus, where it binds to the promoter regions of MMP-2 and MMP-9, thus promoting their transcription⁵². Therefore, inhibition of STAT3 by Sal decreases the expression of these matrix metalloproteinases (MMPs). The downregulation of these MMPs leads to suppression of invasion and metastasis in colon cancer cells. Additionally, Sal inhibits the JAK2/STAT3 pathway in osteosarcoma cells, miraculously downregulating the anti-apoptotic protein Bcl-2 while upregulating pro-apoptotic proteins such as Bax, cleaved caspase-3/7/9⁵³.

Further study has shown that the Sal-mediated inhibition of the JAK2/STAT3 pathway occurs through inactivation of EGFR. EGFR is a transmembrane receptor protein that, upon phosphorylation, activates the downstream kinase JAK2⁵⁴. In triple-negative breast cancer (TNBC) cells, Sal binds to the ATP-binding site of EGFR, reducing its phosphorylation and inactivating it. This leads to a decrease in JAK2 phosphorylation, STAT3 nuclear translocation, and DNA-binding activity, ultimately downregulating the expression of MMPs and other pro-invasive and pro-angiogenic factors⁵⁵.

Other axes
Besides the abovementioned axes, other cellular molecules have also been reported to be subject to Sal. For instance, NADPH oxidase 2 (NOX2) and its downstream kinase JNK are inactivated as a result of Sal-induced AMPK stimulation²⁰; in addition to heat shock proteins HSP70 and HSC70, HSP90 is reported to be directly bound to Sal, inducing a prominent inhibition of its ATPase activity and a blockage of its interaction with SMYD3, which is a histone methylase and a client protein of HSP90⁵⁶. By directly binding to HIF-1α, Sal dampens the degradation of this transcription factor and upregulates its downstream genes, such as Vascular endothelial growth factor (VEGF)^57,58. Recently, Sal was found to activate the Notch pathway and upregulate the expression of Notch1, Hes1/5, and ITGB1 with an unknown mechanism⁵⁹.

By affecting these signaling pathways, Sal exhibits multiple biological activities, including anti-inflammatory, anti-tumor, and anti-fatigue effects, endowing it with broad potential medical applications, particularly in anti-aging and anti-cancer therapeutics.

Anti-aging effects of Sal and related mechanisms
In many ancient Chinese medical texts, including Shen Nong's Herbal Classic and Compendium of Materia Medica, the plant Rhodiola has been documented for its ability to resist fatigue and slow the aging process. Recent research indicates that the major active constituent of this herb, Sal, prolongs lifespan and ameliorates aging-related diseases through multiple mechanisms.

Relieving oxidative stress
Oxidative stress (OS) occurs when there is an imbalance between the excessive accumulation of ROS produced by various cellular organelles and the levels of antioxidants⁶, leading to oxidative damage of cellular macromolecules. This damage contributes to a decline in cellular function and the progression of aging⁶⁰.

As mentioned above, the hydroxyl groups in Sal directly interact with and neutralize free radicals to remove ROS^9,28. Simultaneously, Sal's regulation of downstream pathways may also contribute to its ROS scavenging effects. Specifically, Sal activates the SIRT1/PGC-1α, AMPK/NOX2, and Nrf2/SIRT3 axes, and helps to decrease ROS generation by modulating mitochondrial biogenesis/homeostasis or enhancing intracellular antioxidant enzyme levels^61,62. These effects protect various cells (e.g., neurons, cardiomyocytes, and β-cells) from ROS-induced damage^10,13,20.

On the other hand, Sal reduces OS-induced inflammatory responses. OS can elevate the secretion of pro-inflammatory factors, leading to inflammatory responses that further exacerbate OS. This positive feedback regulation plays a key role in cell senescence and aging-related diseases⁶³. Sal has been shown to modulate multiple signaling cascades, particularly the SIRT1/NF-κB pathway, to downregulate inflammatory cytokines such as IL-1β/6/18, TNF-α, and others^35,36,37. This may explain Sal's efficacy in ameliorating myocardial fibrosis (MF), as well as its ability to attenuate brain injury and endothelial cellular senescence^13,35,36,37. Other signaling pathways, including KLF4/eNOS⁶⁴ and NF-κB/NLRP3³⁶, are also involved. Furthermore, it mitigates OS-induced cellular damage, enhances antioxidant capacity, and improves repair mechanisms by stabilizing homeostasis of intracellular calcium⁶⁵.

Oxidative stress and neuroinflammation exacerbate neuropathology, especially in the context of Alzheimer's disease (AD)^66,67. Numerous studies have shown that Sal reduces OS and neuroinflammation in AD models. Abnormal proteolytic processing of amyloid precursor protein (APP) into amyloid β (Aβ) induced by neuroinflammation is considered a major culprit in AD^67,68. In vitro study with SH-SY5Y human neuroblastoma cells indicates that Sal attenuates abnormal APP processing, mitigating the progression of AD⁶⁹. It not only reduces the solubility and insoluble deposition of Aβ but also increases the expression of synapse-associated proteins, activates the PI3K/AKT/mTOR signaling pathway in hippocampal neurons, and promotes neuronal survival and repair⁷⁰. On the other hand, Sal alleviates mitochondrial fragmentation through the Nrf2/SIRT3 pathway: it alleviates Aβ-induced neurite shortening and mitochondrial fragmentation, enhances mitochondrial autophagy, and activates SIRT3 expression through Nrf2 transcriptional activation to exert neuroprotective effects on either cultured SH-SY5Y cells or hippocampal neurons in vivo¹⁰. In an AD mouse model treated with Sal, results showed reduced levels of nitrate, malondialdehyde, IL-6, and TNF-α, as well as decreased apoptosis in the CA1 region, along with increased levels of GSH and SOD in hippocampal tissues. These changes induced by Sal may account for its neuroprotective effects on hippocampal neurons⁷¹. Furthermore, Sal inhibits the NF-κB/NLRP3 pathway to reduce neuroinflammation: it reduces NLRP3 inflammasome-mediated pyroptosis and ameliorates AD by inhibiting the NF-κB/NLRP3/Caspase-1 signaling pathway in hippocampal neurons⁷². In D-galactose-induced rat models of AD, it has also been shown to mitigate neuroinflammation through the inhibition of the NF-κB pathway³⁵. Additionally, it is reported that the inactivation of HSP90 ATPase and its client protein SMYD3⁵⁶, as well as the induction of antioxidant enzymes (e.g., TRX, HO-1, and PRX1)⁷³, leading to a decrease in ROS production, ultimately delaying the aging process.

In summary, Sal reduces ROS or suppresses the oxidative stress responses to protect cells and organs from damage and aging.

Preventing cellular senescence
Cellular senescence is a hallmark of aging, characterized by a stable exit from the cell cycle⁷⁴. It is also a key pathological mechanism underlying aging-related diseases such as cardiovascular diseases, diabetes, and neurodegenerative disorders⁷⁵.

A study with various cell types has shown that Sal can prevent cellular senescence, largely due to its antioxidant and anti-inflammatory activities. In a human fibroblast model treated with H₂O₂, Sal was found to improve cell morphology and reduce SA-β-gal staining, which is a hallmark of cellular senescence²³. In another human fibroblast model, Sal was shown to modulate the miR-22/SIRT1/PGC-1α axis, resulting in enhanced expression of key mitochondrial biogenesis regulators such as Nrf1 and TFAM. This promotes mitochondrial generation, which likely accounts for the delay in cellular senescence induced by Sal³⁴. Using human umbilical vein endothelial cells as an experimental model, it was found that Sal dramatically reduces cellular lipid deposition and the proportion of senescent cells, while decreasing the expression of senescence-associated molecules (e.g., p63, p53, p21)^75,76,77. This suggests that Sal inhibits cellular senescence through the Rb phosphorylation pathway⁷⁸. Additionally, Sal can upregulate the expression of SIRT3 and suppress inflammatory responses during endothelial cell senescence³⁹.

By counteracting the senescence of these cells, Sal helps to improve the progressive dysfunction of corresponding organs and slows down the aging of the body.

Improving cardiovascular function
Sal has been widely studied for its therapeutic potential in treating coronary heart disease, angina pectoris, and improving cardiac function⁷⁹, as well as in treating cerebral ischemia⁸⁰. It can also protect blood vessels and reduce the degree of arteriosclerosis⁷⁸. On the other hand, Rhodiola rosea has shown potential therapeutic effects in alleviating altitude-related diseases such as acute mountain sickness and high-altitude pulmonary edema in high-altitude environments^57,81. To some extent, these applications are attributed to the role of Sal in improving cardiovascular function, which contributes to its anti-aging effects.

Research has shown that Sal facilitates vascular remodeling in ischemic conditions, which is common in stroke and myocardial infarction. In a cerebral small vessel disease model, Sal can repair the blood-brain barrier (BBB) through the Notch/ITGB1 signaling pathway, alleviating BBB disruption caused by cerebral ischemia. By activating the Notch signaling pathway, Sal upregulates the expression of ITGB1, thereby promoting angiogenesis⁵⁹. In a study of peripheral artery disease, Sal was also found to upregulate the secretion of angiogenic factors in skeletal muscle by inhibiting PHD3, enhancing the formation of new blood vessels⁸². Another study has shown that Sal exerts protective effects in myocardial ischemia/reperfusion injury through various mechanisms, including regulating O-GlcNAc modification, promoting glucose uptake, and reducing cytosolic calcium concentrations⁸³. Furthermore, Sal has been shown to improve angiogenesis and remodeling by regulating the HIF-1α/VEGF signaling pathway⁵⁸. These findings provide strong evidence for the potential of Sal in the treatment of cardiovascular and cerebrovascular diseases.

Several studies have revealed the multi-targeted mechanisms of Sal in alleviating altitude-related diseases to improve the body's adaptability to hypoxic conditions at high altitudes, primarily by regulating oxidative stress, inflammation, metabolic reprogramming, and other pathways. As mentioned above, Sal mediates the regulation of the HIF-1α/VEGF axis, as well as the subsequent improvement of microcirculation. This alleviates hemodynamic changes and pulmonary hypertension induced by hypoxia, thereby reducing the occurrence and development of altitude sickness⁵⁷. Additionally, by enhancing the release of nitric oxide (NO) and inhibiting the secretion of endothelin-1 (ET-1), Sal immensely improves pulmonary arterial hypertension induced by hypoxia at high altitudes, reducing pulmonary vascular contraction and remodeling⁸⁴. Recently, the Pin-Fang Kang group used a rat model of hypoxic pulmonary hypertension (HPH) and found that Sal mitigates HPH by restoring the function of the TWIK-related acid-sensitive potassium channel 1⁸⁵. On the other hand, oxidative stress and inflammatory responses are important mechanisms underlying high-altitude reactions. Sal, through its powerful antioxidant properties, can prodigiously reduce the levels of oxidative stress markers while increasing the levels of GSH and SOD to scavenge ROS. Concomitantly, it can alleviate fatigue-related inflammation induced by high-altitude hypoxia by inhibiting the NF-κB via SIRT1 and reducing the release of pro-inflammatory factors such as TNF-α and IL-1β^32,36.

Anti-cancer effects of Sal and related mechanisms
Malignant tumors, commonly referred to as cancer, represent a group of over 100 related diseases caused by genetic or environmental factors. These diseases are characterized by the uncontrolled proliferation of abnormal cells that eventually form tumors. Malignant tumor cells can invade and destroy adjacent tissues and organs⁸⁶. Moreover, cancer cells can detach from the primary tumor, enter the bloodstream or lymphatic system, and spread to other organs, forming new tumors. This process is known as cancer metastasis⁸⁷. In these cancer types, pancreatic cancer, 90% of which belongs to pancreatic ductal adenocarcinoma (PDAC), is often referred to as the king of cancers because of its highly aggressive metastatic potential and extremely poor prognosis⁸⁸. Recent studies reveal that small-molecule compounds can efficiently intervene in tumorigenesis and the progression of malignancies^{89,90,91,92,93}. The anti-tumor effects of Sal have been validated across multiple cancer types⁹⁴. Recently, the Jibin Song and Yu Cai groups have independently coupled Sal with specialized materials for delivery, demonstrating potent therapeutic efficacy in malignancies in animal models^19,95. The mechanisms of Sal's anti-cancer activity are complex and involve the inhibition of tumor cell proliferation, survival, and metastasis, as well as modulation of immune responses⁹⁴.

Suppressing cell proliferation
Sal has been reported to suppress the proliferation of various tumor cells through multiple mechanisms.

Sal induces cell cycle arrest to inhibit the proliferation of cancer cells. This effect is associated with the regulation of several pathways. It was reported that Sal induces cell cycle arrest in breast cancer (BRC) cells^96,97. This occurs due to the inhibition of intracellular ROS formation and the MAPK pathway (e.g., ERK1/2, JNK, and p38), which may contribute to the inhibition of tumor growth⁷⁰. In lung cancer (LUC), Sal impedes cancer cell proliferation by protecting cells from LPS-induced AMPK inhibition, ROS production, and NLRP3 inflammasome activation⁹⁸. In the study by Sun et al., it was found that Sal immensely reduces the phosphorylation levels of JAK2 and STAT3, and suppresses VEGF to regulate the proliferation of colorectal cancer (CRC) cells⁵¹. Sal also inhibits the proto-oncogene Src-associated signaling pathways and the accumulation of the tumor-associated factor HSP70, thereby suppressing cell proliferation and tumor growth in gastric cancer (GC)²². Furthermore, Wang et al. discovered that Sal signally upregulates the expression of the tumor suppressor gene miR-1343-3p and downregulates signaling molecules such as MAP3K6, STAT3, and MMP24, thereby inhibiting the proliferation and metastasis of GC cells⁹⁹. Other studies have revealed that Sal inhibits the proliferation of pancreatic ductal adenocarcinoma (PDAC)^88,100, nasopharyngeal carcinoma (NPC)¹⁰¹, non-small cell lung cancer (NSCLC)¹⁰², and chronic myeloid leukemia (CML) cells¹⁰³.

Promoting programmed cell death
Sal promotes tumor cell death through multiple mechanisms, including apoptosis, autophagy, and ferroptosis.

Apoptosis is a mechanism by which cells eliminate abnormal or damaged cells through programmed death, and it serves as one of the critical pathways to inhibit tumor growth. Cancer cells often evade apoptosis to sustain uncontrolled proliferation¹⁰⁴. As mentioned above, Sal induces cell cycle arrest, which not only inhibits cell proliferation but also promotes apoptosis in various cancer cells^{53,96,97,100,103,105,106}. Through the Sal-mediated suppression of pathways (e.g., PI3K, ERK, JNK, and STAT3), the downstream intrinsic apoptotic pathways are activated. One such mechanism involves inducing an imbalance in the Bax/Bcl-2 ratio⁹⁵, enhancing mitochondrial membrane permeability, and promoting the activation of apoptosis-related enzymes such as Caspase-3 and Caspase-9, which initiate the apoptotic process⁵³. Additionally, Sal plays a key role in cancer cell apoptosis by upregulating the expression of p53, p21^Cip1/Waf1, and p16^INK4a proteins, while downregulating X-linked inhibitor of apoptosis protein (XIAP)¹⁰⁶.

Ferroptosis is a form of programmed cell death driven by iron-dependent oxidative stress, primarily mediated through lipid peroxidation and redox imbalance¹⁰⁷. According to data from the Tianhua Yan group, Sal promotes ferroptosis by inhibiting stearoyl-CoA desaturase 1 (SCD1)-mediated monounsaturated fatty acid synthesis, thereby enhancing lipid peroxidation. It also upregulates NCOA4, facilitating ferritin degradation and increasing intracellular ferrous iron levels²¹. Through synergistic inhibition of signaling pathways, Sal amplifies the effects of SCD1 and NCOA4, exacerbating ferroptosis in TNBC cells²¹.

Autophagy refers to the process by which damaged, degenerated, or aged proteins or organelles in cells are transported to lysosomes for digestion and degradation. It plays a vital role in cellular stress responses, energy metabolism, and growth¹⁰⁸. As a negative regulator of autophagy, mTOR is targeted by Sal, which primarily promotes autophagy through the PI3K/Akt/mTOR pathway¹⁰⁹. LC3 and p62 are autophagy-specific diagnostic markers, and are negatively regulated by mTOR, a serine/threonine protein kinase¹¹⁰. Studies across multiple cancer types reveal that Sal directly targets and stimulates mTOR or activates its upstream PI3K/AKT pathway. The activation of the PI3K/Akt/mTOR axis subsequently leads to the downregulation of LC3 and p62, thus slowing tumor progression^{24,109,111,112}.

Inhibiting cell migration and metastasis
Tumor cell metastasis is a crucial step that leads to cancer treatment failure and patient mortality, and it is a major cause of tumor recurrence and poor prognosis⁸⁷. During metastasis, primary tumor cells with epithelial properties typically undergo epithelial-mesenchymal transition (EMT), which allows them to lose their epithelial adhesion abilities and acquire mesenchymal migratory properties. This enables them to infiltrate surrounding tissues, penetrate blood and lymphatic vessels, and invade distant organs, ultimately colonizing these tissues and organs¹¹³.

It has been documented that Sal inhibits the migration and metastasis of diverse malignant cells by affecting various axes. For example, in human fibrosarcoma (FS) cells, Sal reduces the phosphorylation/activation of ERK1/2, resulting in inhibition of EMT-related matrix metalloproteinases (MMPs), including MMP2 and MMP9¹¹⁴; in breast cancer cell lines, Sal suppresses migration, invasion, and angiogenesis by inhibiting the EGFP/JAK2/STAT3 pathway⁵⁵. In GC cells, Sal markedly reduces the activation of the Src signaling pathway, thereby suppressing the migration and invasion of GC cells²². There are also reports on Sal-mediated inhibition of the migration/metastasis of other cancer cells, including PDAC¹⁰⁰, LUC^44,98, CRC⁵¹, etc.

Modulating tumor microenvironment and immunity
The tumor microenvironment (TME) refers to the complex three-dimensional environment in which tumor cells grow, develop, and metastasize. Various immune cells are key components of the TME, influencing the initiation and progression of tumors ⁸⁷.

Sal has been shown to inhibit cancer progression by improving the TME through addressing hypoxia and reducing oxidative stress. Although several studies indicate that HIF-1α is activated by Sal in normal cells^115,116,117, other groups have reported that Sal inhibits hypoxia-induced EMT and chemoresistance in hepatocellular carcinoma (HCC), as well as in GC and TNBC, by suppressing the HIF-1α pathway^17,18,19. This may be attributed to Sal's reduction of ROS in the TME, which induces stabilization and activation of HIF-1α^118,119. Cancer cells generally contain elevated levels of ROS, which impact the interaction between cancer cells and immune cells in the TME, leading to inflammation and cachexia¹⁶. It is plausible that the excessive ROS makes the difference in Sal's effects on HIF-1α between normal cells and cancer cells. In glioma, Sal inhibits the formation and growth of glioma both in vivo and in vitro, improving the TME by inhibiting oxidative stress and astrocytes¹²⁰. Notably, based on cancer type-specific mechanisms, Sal improves the hypoxic microenvironment and enhances the efficacy of chemotherapeutic or targeted drugs. For example, Sal significantly increased sensitivity to platinum drugs and inhibited hypoxia-induced EMT in HCC by inactivating the HIF-1α signaling pathway17; when co-loaded with apatinib using nanoparticles, Sal improved the chemosensitivity of GC cells by reprogramming the tumor hypoxia microenvironment and inducing cell apoptosis¹⁸.

On the other hand, Sal can modulate immune responses by targeting immune cells in the TME. In a murine non-small cell lung cancer (NSCLC) model, Sal was shown to modulate the tumor immune microenvironment by stimulating the expression of HSP70 and Stub1 in regulatory T cells (Tregs), thereby promoting FOXP3 degradation; Tregs are consequently suppressed, and CD8⁺ T cells, as well as effector CD4⁺ T cells, are ultimately activated¹²¹. Tyagi et al. reported that Sal selectively suppresses nicotine-induced N2-neutrophil polarization and lung metastasis in BRC by inhibiting STAT3-activated release of lipocalin 2 (LCN2). This secretory glycoprotein from N2-neutrophils induces EMT of tumor cells, facilitating colonization and metastatic outgrowth¹²². Sal elevates the immune activity of CD8+ T cells by repressing circ_0009624-mediated expression of PD-L1 in LUC cells, resulting in the suppression of immune escape¹²³. Additionally, Sal can suppress inflammation by inhibiting the production or activation of pro-inflammatory cytokines and macrophages^{124,125,126,127}. These anti-inflammatory roles of Sal, to some extent, contribute to its anti-cancer activities.

Sal, the principal bioactive compound derived from the Rhodiola genus, has demonstrated promising therapeutic potential across a broad range of biomedical areas, including anti-aging, antioxidant, anti-tumor, and immunomodulatory applications. Its unique molecular structure, characterized by glycosidic bonds and hydroxyl groups, underpins its exceptional water solubility, antioxidant capacity, and multi-target pharmacological activities. Preclinical studies have elucidated its ability to mitigate oxidative stress and delay cellular senescence by activating key pathways such as SIRT1 and NRF2, thus improving aging-related pathologies like cardiovascular diseases, neurodegenerative disorders, and metabolic dysregulation61,62.

In oncology, Sal exerts potent anti-cancer effects by modulating critical signaling cascades (e.g., PI3K/Akt/mTOR, JAK2/STAT3) to suppress tumor proliferation, induce apoptosis and ferroptosis, and inhibit metastasis. Furthermore, its immunomodulatory properties, including regulation of Tregs and cytokine production, highlight its role in reshaping tumor microenvironments and combating inflammatory diseases. Given the cancer type-specific mechanisms and microenvironments, Sal shows promising potential as a combination therapy with chemotherapeutic or targeted drugs for distinct cancers.

Despite these promising findings, challenges remain in translating Sal's preclinical efficacy into clinical practice. Key limitations include optimizing its pharmacokinetic profiles, enhancing target specificity, and addressing potential off-target effects. Future research should focus on integrating multi-omics technologies (e.g., genomics, proteomics) to systematically unravel its pleiotropic mechanisms. Directed modification of this moleculecould offer a solution to prevent activation of unwanted targets. For example, specifically designed derivatives can be employed to circumvent Sal's biphasic effects on PI3K/AKT signaling under particular conditions. By addressing these gaps, Sal could become a cornerstone in the development of next-generation therapeutics for aging-related conditions, including Alzheimer's disease and Parkinson's disease, as well as diverse malignancies, especially pancreatic cancer. Ultimately, Sal may fulfill its promise as a natural, multifunctional agent in precision medicine.

Figure 1: Signaling pathways regulated by Sal. Sal contains multiple hydroxyl groups, enabling it to reduce reactive oxygen species (ROS) or directly bind to and modulate proteins, including SIRT1, Nrf2, HIF-1α, AhR, EGFR, AKT, PI3K, HSC70, and HSP90. Sal also regulates the expression of Notch1 and microRNAs (e.g., miR-22, miR-195) with unknown mechanisms. Pathways downstream of these molecules are resultantly affected. Notably, ROS can affect diverse pathways and be downregulated by several Salicylate-Dictated axes. Please click here to view a larger version of this figure.

Table 1: Major proteins directly targeted by Sal. Names, natures, and identification status of Sal-targeted proteins, as well as the effects of Sal on them and the references, are listed. - means that the Sal-protein association is only supported by molecular docking or single experiments, with unclear validation status, while + represents the identified physical interaction confirmed by experimental data.

Table 2: Mechanisms of Sal-mediated anti-aging and anti-cancer effects. Therapeutic effects, related diseases, pathways, and mechanisms involved, as well as the references, are listed. Abbreviations: BRC = breast cancer; CML = chronic myeloid leukemia; CRC = colorectal cancer; FS = fibrosarcoma; GC = gastric cancer; HCC = hepatocellular carcinoma; LUC = lung cancer; NPC = nasopharyngeal carcinoma; OSC = osteosarcoma; OVC = ovarian cancer; PDAC = pancreatic ductal adenocarcinoma; ROS = reactive oxygen species.