Research progress of nano drug delivery systems in the anti-tumor treatment of traditional Chinese medicine monomers

Nanotechnology improves the bioavailability of TCM monomers (Fu et al., 2021)

The active ingredients of TCM need to reach a certain blood concentration in the body to play a role, but the absorption and utilization of most poorly soluble ingredients in the preparation of dosage forms after oral administration cannot achieve the expected effect, so the solubility and stability of the drug should be increased as much as possible. Most TCM monomers have low bioavailability and efficacy due to their poor solubility and inability to pass through the cell lipid membrane (Tian et al., 2021). The particle size of nano TCM carriers has a great influence on the efficacy of drugs. When the particle size of nanoparticles is smaller, its specific surface area will increase and it will be more soluble in the medium, thereby increasing the dissolution and utilization of drugs in the body (Alharbi et al., 2021). In recent years, more and more studies have shown that nanotechnology can effectively improve the bioavailability of TCM monomers. In order to improve the bioavailability of resveratrol, Wang et al. (2019) prepared resveratrol PEG-PLGA nanoparticles, and then evaluated their anti-colitis effect in vitro. The results showed that nanoparticles enhanced the inhibitory effect of resveratrol on the proliferation of colon cancer cells and improved the bioavailability of resveratrol. He et al. (2005) conducted a comparative study on the oral absorption of silymarin solid lipid nanoparticles of different particle sizes in rats and found that the bioavailability of 150 nm solid lipid nanoparticles was significantly higher than that of two preparations with particle sizes of 500 and 1,000 nm. The particle size has a significant effect on the oral absorption of silymarin. The use of nanotechnology to process TCM can break the cell wall of plants and facilitate the exudation of effective ingredients. Yuan et al. (2013) prepared cell-penetrating peptide-coated celastrol (CT)-loaded nanostructured lipid carriers-nanostructured lipid carriers (CT-NLCs). Compared with celastrol free drugs, CT-NLCs can significantly enhance the anti-prostate cancer activity in vitro and significantly improve the bioavailability of drugs.

Nanotechnology improves the targeting of TCM monomers

Targeting refers to the ability of drugs to selectively and purposefully reach specific parts, which can enhance the efficacy of drugs and avoid the side effects caused by systemic diffusion of drugs (Hristova-Panusheva et al., 2024). In the early 20th century, Paul Ehrlich proposed the concept of targeted drugs, which consists of three parts: drugs, targeting parts and drug carriers. In the clinical treatment of tumors, targeted drug delivery methods are selected to deliver drugs to specific tumor tissues, cells or organelles to overcome the bottlenecks of aimless distribution of drugs after entering the body, toxic side effects on normal tissues and high-dose administration (Li et al., 2023). It can be seen that the drug delivery system loaded with TCM monomers for the treatment of tumors by nanomaterials shows great potential. The targeting of nanomedicines enables the effective ingredients to specifically bind to the lesion site, thereby significantly improving the therapeutic effect of TCM. On the one hand, nano TCM monomers can be designed as a targeted drug delivery system, and on the other hand, the introduction of messenger drugs is conducive to synergistically enhancing targeting.

Targeted drug delivery system

The drug delivery system must meet two conditions: minimal loss in the blood to achieve characteristic site targeting and killing tumor cells without side effects on the body. Once the nanoparticles enter the body, they will be quickly wrapped by the regulatory proteins in the blood to form large aggregates. The regulated nanoparticles can be recognized by the reticuloendothelial system (RES) or the mononuclear phagocyte system (MPS), which is composed of macrophages associated with the spleen and liver (Dutta, Barick & Hassan, 2021). The above physicochemical properties of nanocarriers usually determine their fate in biological systems, such as whether they are cleared by the body’s clearance system or internalized by tumor cells to trigger biological responses (Liu et al., 2020). Internalization includes two methods: passive targeting and active targeting. (1) Passive targeting: Due to the high permeability and poor lymphatic flow of tumor blood vessels, they have an enhanced permeability and retention effect (EPR), which is the main driving force of passive targeting (Wu, 2021). This phenomenon is conducive to the targeted entry of nanocarriers into tumor vascularized areas through leaky vascular systems such as tumors, infections, and inflammations via oral or intravenous injection. Vascular leakage can increase the concentration of nanocarriers in target tissues, and damaged lymphatic systems can increase the aggregation of nanocarriers in tumor vascularized areas (process as shown in Fig. 1), allowing the nano-drug delivery system to exist in tissues for a long time (He et al., 2022; Wang et al., 2023b). However, some tumors do not have the EPR effect, and passive targeting still has some limitations. (2) Active targeting: Through the binding of specific ligands to receptors (such as ligand-receptor interaction, antibody-antigen interaction), drugs are selectively delivered to specific target areas (Yang et al., 2021). This method can directly target the corresponding site while avoiding related systemic adverse reactions. It is initiated by the specific interaction between ligands and extracellular receptors. For example, antibodies, nucleic acid chains, peptides and other ligands on the surface of nanomaterials are bound to receptors on the surface of tumor cells, which greatly improves the specificity of recognizing tumor cells. Hu, Zhou & Zhang (2010) prepared a novel lactosylnorcantharidin nanoparticle (Lac-NCTD-NPs) encapsulating a new compound, lactosylnorcantharidin (Lac-NCTD). The galactose residues on lactosylnorcantharidin (Lac-NCTD) can be specifically recognized by the asialoglycoprotein receptor (ASGPR) on the surface of hepatocytes in vivo, achieving active liver targeting.

Synergistic enhancement of targeting

In brain targeting, the blood-brain barrier (BBB) makes drug treatment of brain diseases complicated. The blood-brain barrier refers to the barrier between plasma and brain cells formed by the capillary wall and glial cells, and the barrier between the choroid plexus and cerebrospinal fluid, which can help the brain resist foreign substances in the blood (Boyé et al., 2022). The blood-brain barrier strictly limits the types of molecules that pass through, but it also prevents drugs and macromolecules from entering the brain. While the BBB absorbs the nutrients needed by brain cells to ensure nutritional balance in the brain, it also excretes metabolites. This material exchange under physiological conditions enables drug design to have a special transport mechanism, including mainly transcellular membrane channel transport and cell paracellular channel transport (the process is shown in Fig. 2). Borneol and musk belong to aromatic TCMs in natural medicines, and their effects are equivalent to targeted preparations. Qi et al. (2022) prepared a liposome (Lf-LP-Mu-DTX) loaded with docetaxel (DTX) modified with musk ketone (Mu) that can cross the blood-brain barrier and target the brain. Compared with unmodified liposomes, Lf-LP-Mu-DTX is concentrated in the brain glioma area, and with its own lipid solubility advantage, it enhances the penetration of BBB into the brain and enhances the brain protection effect of the drug.

Nanotechnology controls the release of TCM monomers

Nanoformulations control the release of TCM monomers mainly in the form of sustained release and responsive triggered release under specific conditions (Sun & Jiang, 2023). Sustained release means that the nanosystem loaded with TCM monomers enters the human body and releases the drug evenly, slowly and continuously at a specific targeted site, avoiding premature or sudden release of the drug in large quantities, reducing blood drug concentration fluctuations, and achieving the purpose of sustained release and long-term effect (Dong et al., 2021). Based on this principle, a responsive TCM nano-drug delivery system is designed by researchers, which triggers the disintegration, instability, isomerization, polymerization or aggregation of nanocarriers under internal or external stimulation from various physical, chemical or biochemical sources, and releases drug molecules at appropriate concentrations at the target site, thereby leading to controlled release of the drug, avoiding being attacked by the human immune system, and making them more intelligent.

Nanotechnology inhibits multidrug resistance of tumor

Tumor multidrug resistance (MDR) refers to the phenomenon that tumor cells develop tolerance to one or more chemotherapy drugs, leading to drug treatment failure. The mechanisms of MDR include the heterogeneity of tumor cells, changes in the tumor microenvironment, and overexpression of cell membrane transport proteins. The heterogeneity of tumor cells is the basis for tumor resistance to drugs (Goyette, Lipsyc-Sharf & Polyak, 2023). Different subpopulations of tumor cells have different sensitivities to drugs. Some cells can survive under the action of drugs and gradually develop into drug-resistant populations. Changes in the TME also play a key role. For example, hypoxia, acidic environment and changes in extracellular matrix components can affect the response of tumor cells to drugs and promote the formation of drug resistance. Guo et al. (2024) prepared a natural polysaccharide-based nanoplatform (TDTD@UA/HA micelles) with dual targeting capabilities for both cells and mitochondria, which was used to co-deliver ursolic acid (UA) and doxorubicin (DOX) for combined treatment of multidrug resistance (MDR). P-glycoprotein (P-gp) is the most typical cell membrane transporter. Drug-resistant tumor cells will produce a large number of membrane transporters such as P-gp on the membrane surface that can expel drugs from the cell, while preventing drug intake, resulting in a significant reduction in the total amount of drugs in the cell. Zhang et al. (2023) prepared pH-sensitive liposomes (LPs) encapsulating dihydroartemisinin (DHA) and tetrandrine (TET). Under acidic conditions, the drug release rate significantly increased. By enhancing the cellular uptake capacity, the cytotoxic effect on tumor cells was strengthened. DHA and TET were encapsulated within the nanoparticles. By inhibiting the p53 (R248Q)-ERK1/2-NF-κB signaling pathway, the expression of the CIZ1 gene associated with TGF-β1/Smad signal transduction was down-regulated. Subsequently, the expression of P-gp was inhibited, reducing drug efflux and decreasing the drug resistance of tumor cells.

Nano drugs have shown great potential in overcoming the MDR problem, especially after loading TCM monomers. Enhanced permeability and retention (EPR) and targeting ligands can be used to increase the accumulation of drugs in tumor sites and reduce the toxic side effects of normal tissues. The shielding effect of nanocarriers can also be used to avoid being recognized and excreted by transporters and increase the concentration of drugs in cells. Nanocarriers have endocytosis, which can promote the entry of drugs into cells and release them through endosomal escape or dissolution to avoid lysosomal degradation. The combination of nanotechnology and TCM monomers has opened up a new way to improve the efficacy and safety of TCM monomers in anti-tumor treatment.

Inhibition of tumor cell proliferation and metastasis

Tumor cells have the characteristics of unlimited proliferation. TCM monomers can inhibit tumor cell proliferation by promoting tumor cell apoptosis, inducing cell autophagy, enhancing oxidative stress, promoting sensitization and blocking cell cycle, thereby achieving the effect of treating tumors (Srimanta et al., 2021).

Tumor cell metastasis is the main feature of malignant tumors and the primary factor causing death in cancer patients. Tumor cells release various proteolytic enzymes to destroy the tissues at their adhesion sites, that is, to destroy the basement membrane of the extracellular matrix and the vascular wall, to achieve infiltration metastasis and the formation of new blood vessels (Zhao et al., 2023b; Ma et al., 2021).

Therapeutic strategies of nano TCM monomers in the tumor microenvironment

TME refers to the microenvironment surrounding tumor cells, which is composed of surrounding blood vessels, immune cells, fibroblasts, myeloid inflammatory cells, various signaling molecules and extracellular matrix. The structure is shown in Fig. 3. Its unique physiological and pathological characteristics have a profound impact on the occurrence, development, metastasis and treatment response of tumors (de Visser & Joyce, 2023; Zhao et al., 2023a). In recent years, drug delivery systems loaded with traditional TCM monomers have played a significant role in interacting and regulating with TME. Therefore, in-depth exploration of the mechanism of their interaction is of great significance for tumor treatment. The size, shape and surface charge of nanomaterials determine the action pathway in TME. Nanoparticles are more likely to pass through abnormal blood vessel walls in tumor tissues due to their smaller particle size, thereby achieving passive targeted enrichment (Manikkath et al., 2023). At the same time, surface modification of nanomaterials can regulate their interaction with various components in TME. For example, by modifying hydrophilic polymers such as polyethylene glycol (PEG), the nonspecific adsorption of nanoparticles in the blood circulation can be reduced, their circulation time in the body can be prolonged, and the chance of reaching the tumor site can be increased (Naito et al., 2022). The TME has the characteristics of low pH, high reactive oxygen species (ROS) levels, and abnormal angiogenesis. Therefore, these characteristics can be used to achieve intelligent responsive release using nanomaterial-loaded TCM monomer delivery systems (Zhu et al., 2023). In the TME with low pH and high ROS levels, nano-TCM can trigger the responsive nanomaterials to release drugs, allowing the drugs to act more precisely on the tumor site.

From a cellular level, immune cells in the TME play a key role in tumor immune surveillance and escape. Nanomaterial-loaded TCM monomer delivery systems can regulate the functions of immune cells. On the one hand, some TCM monomers can activate immune cells, such as macrophages and T cells. The delivery of nanomaterials can increase the uptake of TCM monomers in immune cells and enhance their immunoregulatory effects (Park et al., 2023). On the other hand, there are immunosuppressive cells in the TME, such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). Nanomaterials inhibit the activity of these immunosuppressive cells by delivering TCM monomers with immunomodulatory functions, thereby reversing the immunosuppressive microenvironment and restoring the body’s anti-tumor immune response (Mao et al., 2021). Tumor-associated fibroblasts (CAFs) are an important component of the TME. They secrete a large amount of extracellular matrix components that affect the migration and invasion of tumor cells. These extracellular matrices provide physical support for tumor cells and interact with cell surface receptors to affect cell signaling (Siska et al., 2020). The nanomaterial-loaded TCM monomer delivery system may inhibit the metastasis of tumor cells by regulating the function of CAFs and changing the composition and structure of the extracellular matrix. Nanomaterials protect TCM monomers from passing through the ECM to reach the TME, thereby regulating ECM metabolism and reducing the migration of tumor cells.

Tumor angiogenesis also has an impact on tumor growth and metastasis. The vascular structure and function in the TME are abnormal. The nanomaterial-loaded TCM monomer delivery system can affect the formation of tumor blood vessels by regulating angiogenesis-related signaling pathways. On the one hand, TCM monomers may inhibit the expression or activity of angiogenic factors such as vascular endothelial growth factor (VEGF) and reduce the formation of new blood vessels (Zou et al., 2020); on the other hand, nanomaterials can improve the permeability of tumor blood vessels and enhance the delivery efficiency of drugs, so that more TCM monomers can reach tumor cells (Zeng et al., 2023).

Lipid nanomaterials

Amphiphilic phospholipids form a bilayer structure, and cholesterol supports and maintains the bilayer structure. According to the pharmacokinetic properties, this structure can contain both hydrophilic and hydrophobic drugs (Amiri et al., 2023). Therefore, the TCM monomers wrapped inside the liposomes can increase their solubility and avoid being degraded by the environment during the blood circulation of the human body.

Liposomes improve the stability and biocompatibility of TCM monomers with poor water solubility by loading them. Curcumin is a poorly soluble TCM monomer with a diketone structure in its structure, which can be complexed with metal ions to form a stable poorly soluble complex. Liu et al. (2021) invented a method of using metal ions as the inner water phase to prepare liposomes with a transmembrane metal ion gradient to actively load curcumin, thereby achieving effective drug delivery. Quercetin is a TCM monomer which has a significant effect of inhibiting EMT, thereby inhibiting tumor growth. Quercetin can induce apoptosis of Y79 cells through the JNK and P38MAPK pathways, and inhibit the multidrug resistance of tumor cells by downregulating p-gp expression. However, the poor solubility of quercetin limits its use. Lin et al. (2024) loaded the poorly soluble quercetin and the hydrophilic doxorubicin into the lipid shell and the aqueous core of the liposome to form QD Lipo. The extremely high compatibility of the liposome improved the internalization of quercetin into Y79 cells. When mitochondria are overproduced, EMT is activated. QD Lipo reduces the expression level of ROS and significantly downregulates Vimentin and α-SMA proteins, indicating that the prepared AD Lipo can enhance the tumor-killing effect of quercetin. Liposomes can also improve the pharmacokinetics and tissue distribution of TCM monomers, reduce the toxicity of TCM monomers, and improve the therapeutic index. Xia et al. (2022) prepared Rg3-Lp/DTX by thin film hydration method, which inhibited the NF-κB signaling pathway, reduced the expression of anti-apoptotic protein Bcl2, increased the expression of pro-apoptotic protein Bax, and enhanced the toxicity and apoptotic effect of DTX on tumor cells. At the same time, Rg3 inhibited STAT3 activation, reduced tumor cell secretion of CCL2, reduced the recruitment of MDSCs and TAMs in the lungs, destroyed the metastatic microenvironment, inhibited tumor cell growth and metastasis, increased tumor cell apoptosis, and reduced tumor size.

However, liposomes have the disadvantages of being easily degraded and easily cleared by macrophages in the body, resulting in a short maintenance time in the body. The drugs encapsulated by biomodified liposomes have longer circulation time, stronger targeting and less toxicity. Its mechanism of action is mainly to avoid rapid phagocytosis of the reticuloendothelial system (Almeida et al., 2020). Erythrocytes are highly biocompatible, rich in content, and have long circulation. Since they come from the body, they can avoid being cleared by macrophages and increase the uptake of their modified nanomaterials by tumor cells. Zhong et al. (2021) prepared a triptolide-erythrin co-loaded liposome, and then wrapped the erythrocyte membrane outside to make this biomembrane biomimetic drug delivery system to promote the delivery of triptolide in tumors. Liposomes accumulate in tumor sites through the EPR effect with the help of nano-scale particle size; their unique “core-shell” structure has sustained-release properties and can maintain drug efficacy for a long time; compared with free triptolide, liposomes are more easily taken up by tumor cells, and the inhibitory effect of C+TRB CMlip on tumor cells is stronger than the combination of C+T/Lip and free drugs, and can more effectively inhibit the growth and proliferation of tumor cells.

Exosomes

Extracellular vesicles (EVs) in bilayer phospholipids are nanoscale membrane vesicles secreted by cells, and their size is generally between 50–1,000 nm. EVs are recognized as a natural drug delivery system with low immunogenicity, strong homologous targeting ability, and high biocompatibility. They can be used as a good drug delivery carrier in tumor treatment. According to their origin, EVs can be divided into three categories: exosomes, microvesicles and apoptotic bodies (Wang et al., 2024b). Exosomes are nanoparticles of 40–200 nm, and their functions depend on the cells of origin (Fig. 4). Since exosomes contain lipids and molecules similar to those of their origin cells, exosome nanoparticles can escape immune surveillance and be smoothly internalized with target cells. Exosomes contain a variety of bioactive substances such as proteins, DNA, microRNA, long non-coding RNA, messenger RNA, tumor genes and transcription factors (Negri et al., 2020). The levels of these bioactive substances are related to tumor invasion and TME.

As endogenous substances, exosomes not only have cancer-promoting properties, but also can be used to make them an effective way of anti-tumor treatment by using their immunomodulatory and tumor microcirculation remodeling properties.

TCM can inhibit the development of tumor cells by affecting the intercellular communication of exosomes and the immunomodulatory effect of the tumor microenvironment. Tumors can use the spatiotemporal characteristics of tumor-associated macrophages (TAMs) migration and differentiation in tumor tissues to dynamically educate them, polarizing them into a series of TAMs with different degrees of activation (Liu et al., 2021). Tumor-derived exosomes can regulate the tumor microenvironment by transferring miRNA to immune cells. Epigallocatechin gallate (EGCG) has a strong anti-tumor effect both in vitro and in vivo. Nie et al. (2019) studied the anti-tumor mechanism of resveratrol against glioblastoma multiforme (GBM) using two GBM cell lines. The anti-tumor mechanism of resveratrol on GBM was studied, and it was found that exosomes secreted by U251 cells (U251/N/Exo) were rich in the pro-apoptotic protein H2AX, which could significantly enhance the sensitivity of LN428 cells to resveratrol. However, the level of H2AX in U251 exosomes (U251/Res/Exo) treated with resveratrol decreased, while the levels of anti-apoptotic proteins Rap1 and F-actin increased, resulting in the loss of its ability to reverse LN428 resistance. This suggests that the protein composition in exosomes can affect the sensitivity of GBM cells to resveratrol by regulating cell apoptosis-related signaling pathways. Zhang et al. (2022) found that curcumin can be delivered to recipient liver cancer cells through exosomes in tumor treatment. Experiments have shown that curcumin exosomes can enter HepG2 cells through endocytosis and inhibit their vitality. They regulate the HepG2 cell cycle, significantly increase the proportion of cells in the S phase and G2/M phase, significantly decrease the proportion of cells in the G0/G1 phase, block the cell cycle in the G2/M and S phases, and inhibit cell proliferation. At the same time, curcumin exosomes induce apoptosis of HepG2 cells. It can upregulate the expression of the pro-apoptotic protein BAX and downregulate the expression of the anti-apoptotic protein Bcl-2. Through the mitochondrial apoptosis pathway, it breaks the mitochondrial membrane homeostasis, promotes the release of cytochrome C, activates the caspase cascade reaction, and finally exerts an anti-tumor effect. In addition, cell cycle arrest may increase the sensitivity of cells to apoptotic signals. The two synergistically inhibit tumor cell growth.

TCM can also inhibit tumor formation and metastasis by inhibiting the secretion of tumor-derived exosomes (TDEs). Wang et al. (2020a) used RT-qPCR to detect that exosome delivery promoted verbbascoside to deliver miR-7-5p to recipient glioblastoma (GBM) cells in subcutaneous tumors and metastatic tumors in mice.The results showed that verbascoside can promote the expression of miR-7-5p in glioblastoma (GBM) and promote its delivery to recipient GBM cells. MiR-7-5p inhibits GBM cell proliferation, migration, invasion and microtubule formation by inhibiting the epidermal growth factor receptor (EGFR)/phosphatidylinositol 3-kinase (PI3K) protein kinase B (PKB/Akt) signaling pathway, and can inhibit GBM tumorigenesis and metastasis in vivo, thereby inhibiting the occurrence of GBM (Fig. 5). Tong et al. (2024) explored the effect of resveratrol on exosome secretion and the role of resveratrol-induced exosomes in the progression of hepatocellular carcinoma. It was found that resveratrol inhibited exosome secretion by downregulating the expression of Rab27a, thereby inhibiting the proliferation, migration and epithelial-mesenchymal transition of Huh7 cells. In addition, resveratrol-induced exosomes can also inhibit the malignant phenotype of Huh7 cells by inhibiting the nuclear translocation of β-catenin and the activation of autophagy mediated by lncRNA SNHG29. Du et al. (2020) found that the total steroidal alkaloid glycosides in Solanum lyratum Thunb. The experimental results show that exosomes secreted by A549 cells can promote the transformation of HUVECs into tumor-associated endothelial cells (Td-ECs), while steroidal glycoalkaloids (such as TSGS and SA1) can significantly inhibit this transformation. This indicates that Steroidal glycoalkaloids from Solanum lyratum can directly affect the formation of tumor exosomes by agglutinating tumor cell membrane lipid cholesterol, leading to changes in their function, thereby inhibiting tumor angiogenesis and inhibiting the development of lung cancer A549 cells.

There are many studies on the role and related mechanisms of tumor-derived exosomes in the occurrence, development, invasion and metastasis of lung cancer, but There are still many problems to be solved by researchers in the study of exosomes, such as the purification and labeling methods of exosomes, how to find the target genes of exosomes, the mechanism of action and signal pathways of exosomes, etc. In short, the study of exosomes has broad prospects.

Polymer micelles

The particle size of polymer micelles is in the range of 10–100 nanometers. They are not easily recognized and captured by the endothelial reticular system res in the blood circulation. The nano drug delivery system can exist stably and for a long time in the blood, and at the same time achieve passive targeting to the tumor site through the EPR effect (Zheng et al., 2020). The solubility of conventional polymers will decrease after loading hydrophobic drugs, while polymer micelles still have good water solubility after loading a large amount of hydrophobic drugs. This is because the distribution coefficient of hydrophobic drugs in the hydrophobic core of polymer micelles is high, which can achieve a higher drug loading and encapsulation rate, while hydrophilic drugs are encapsulated. The shell-core interface can load amphiphilic drugs and widely deliver anti-cancer drugs (Thotakura, Parashar & Raza, 2021).

Polymer micelles can promote intracellular drug accumulation and anti-tumor effects. SMVT, the main transporter of biotin, is overexpressed in many cancer cells (such as lung cancer cells) and mediates the internalization of biotin-modified micelles. Wang et al. (2020c) prepared a poly(HPMAm)-based biotin-modified micelle loaded with paclitaxel for anti-tumor nano-drug delivery system. Biotin-modified micelles bind to biotin receptors (SMVT) on the surface of tumor cells, enter cells through receptor-mediated endocytosis, release paclitaxel (PTX) to exert cytotoxicity, and non-cancerous cells (HEK293 cells, biotin receptor negative) have low uptake of micelles. Li et al. (2021) prepared polymer micelles (SK/ siIDO1-HMS) loaded with shikonin (SK) and IDO-1 knockout siRNA (siIDO1). The results showed that SK/Siido1-HMS could trigger immunogenic cell death (ICD), promote CRT exposure, increase the DC maturation rate in the draining lymph nodes to 46.9 ± 7.3%, increase the infiltration of CD8⁺ T cells in the tumor, increase the concentration of γ-interferon (Interferon-γ, IFN-γ) and tumor necrosis factor-α (Tumor Necrosis Factor-α, TNF-α) in the tumor, reduce the expression level of IDO-1 and the ratio of kynurenine to tryptophan, reduce the frequency of infiltrating regulatory T cells (Treg) in the tumor, and increase the anti-tumor effect compared with free monomers.

Since the optimal drug concentration is required at the tumor site and in the cell to effectively kill the cell, and the hydrophilic shell of the micelle can be modified, it is necessary to effectively release the drug to the tumor site by introducing a stimulus-responsive prodrug. At present, the most widely studied is pH-responsive micelles. Liang et al. (2023) designed an amphiphilic polymer micelle (p(mPEG-co-HPBE-co-EMD)CLB) with dual reactive oxygen species (ROS)/pH responsiveness to enhance the anti-tumor effect. In the polymer experiment, the proliferation of 4T1 breast cancer cells was significantly inhibited, and the tumor volume was significantly reduced in the in vivo experiment. By consuming intracellular glutathione (GSH) and increasing the level of ROS, the antioxidant system of tumor cells is destroyed, the oxidative stress response in the cells is activated, and then apoptosis is induced. In addition, the structure of the polymer is destroyed in the tumor microenvironment, releasing the drug and enhancing the cellular uptake and accumulation of the drug, further improving the anti-tumor effect. Sun et al. (2020) designed an enzyme-sensitive core-targeted bifunctional polymer micelle (9-NC/HATPC) to enhance the anti-tumor effect of 9-nitrocamptothecin (9-NC). The micelle achieves enzyme responsiveness through the cathepsin B-sensitive ALAL peptide segment, and forms a positively charged secondary micelle (9-NC/TPC) after cleavage, which promotes lysosomal escape and enters the cell nucleus with the help of TAT peptide, inhibits topoisomerase I, and induces tumor cell apoptosis. The micelle increases the drug loading capacity through π-π stacking to ensure stable drug delivery, while using the acidic environment and enzyme activity in tumor cells to achieve targeted release, enhancing the cellular uptake and nuclear accumulation of drugs. In recent years, although many polymer micelle drug-loaded samples have entered the clinical trial stage, the toxicological and pharmacological properties of the anti-tumor active ingredients of traditional Chinese traditional medicine are not yet fully understood, and the delivery of anticancer drugs by polymer micelles still faces many challenges, such as its potential toxicity, the potential mechanism between the stability of micelles and drug delivery is not yet fully understood, and how micelles interact with drugs.

Carbon nanotubes

Carbon nanotubes have extremely high tensile strength and elastic modulus. Their structure is a sp hybridized hexagonal arrangement. They are one of the hardest materials in the world and can conduct heat and electricity. Carbon nanotubes are generally divided into single carbon nanotubes (SWCNTs) and multi-carbon nanotubes (MWCNTs). Single carbon nanotubes consist of a single cylindrical graphene, covered with two segments in a hemispherical arrangement of a carbon grid (Qian et al., 2021). Multi-carbon nanotubes consist of several to dozens of concentric cylindrical graphene shells with higher lumen filling (Mohd Nurazzi et al., 2021). Due to its hollow physical structure and chemical properties that are easy to modify on the surface, carbon nanotubes can be developed based on these excellent characteristics for the delivery of therapeutic drug carriers to enhance the pharmacological activity of TCM monomers, while reducing the side effects of drugs on the body, and increasing the accumulation of drugs at the tumor site.

The inherent stability and structural flexibility of single carbon nanotubes (SWNTs) can prolong the blood circulation time of drugs and improve the bioavailability of drugs. Mohammadi et al. (2024) studied the application of platinum-modified carbon nanotube (CNT-Pt-CUR) nanosystem loaded with curcumin (CUR) in tumor treatment. CUR has antioxidant and anti-inflammatory properties, but its poor water solubility limits its application. By loading CUR onto CNT-Pt, efficient drug delivery and tumor microenvironment-responsive release were achieved. Experiments showed that the drug release rate of CNT-Pt-CUR in an acidic environment (pH 4.7) was significantly higher than that in a physiological environment (pH 7.4), showing good pH sensitivity. In addition, combined with X-ray radiation, CNT-Pt-CUR significantly enhanced the killing effect on tumor cells. In PC-3 cells, SWCNT-Cur showed a higher inhibitory effect compared with natural curcumin. In view of the shortcomings of plumbagin in anti-tumor applications, Zhong (2011) covalently coupled water-soluble SWNTs modified with PEG to plumbagin to prepare a stable complex (PLB-PEG-SWENTs). The experimental results showed that after PLB-PEG-SWENTs were internalized into cells, the amide bonds and ester bonds connecting the drug molecules and SWNTs were hydrolyzed and broken, directly releasing the drug molecules to act directly on the G2/M phase control point of tumor cells to initiate the cell apoptosis pathway, thereby affecting cell division and proliferation. Ginsenoside Rg3 is a component of puffed ginseng with anticancer activity. Luo, Wang & Ji (2021) prepared multi-walled carbon nanotubes (Rg3-MWCNT) loaded with ginsenoside Rg3. The study found that Rg3 promoted apoptosis of triple-negative breast cancer (TNBC) cells. Rg3-CNT treatment enhanced the phenotype within T cells, reduced interferon γ-induced PD-L1 upregulation in breast cancer cells (IFN-γ), and reduced PD-1 expression in activated T cells. This indicates that Rg3-CNT enhances the anticancer effect of Rg3 on TNBC by inhibiting the PD-1/PD-L1 axis.

Dendritic macromolecules

Dendritic macromolecules form highly bifurcated, monodisperse macromolecules similar to dendritic structures through continuous repetition, growth, and polarization. With the increase of polymerization generations, the degree of polarization continues to expand, and finally a three-dimensional spherical structure consisting of a central core connected to branches, branching units, and external capping groups is formed (Singh & Kesharwani, 2021). These special highly branched structures provide functional advantages for the application of dendritic macromolecules. Dendritic macromolecules can prevent drugs from being rapidly enzymatically hydrolyzed, hydrolyzed, or cleared by the immune system, thereby reducing the frequency of administration. Its structural characteristics limit the circulation of drugs in the body and reduce the adverse reactions of drugs, so the dosage can be increased. Its surface is densely covered with various functional groups, and specific functional groups can recognize target cells to achieve targeted drug delivery (Sharma et al., 2017). Connecting poorly soluble drugs to the branched structure can greatly improve the solubility of the drug and increase its bioavailability. In short, dendritic macromolecules have the advantages of being well absorbed by cells, clear molecular weight, adjustable branches, multifunctionality, and cavity encapsulation of drugs to improve solubility, making them ideal candidates for delivering anti-tumor drugs.

Different dendrimers have been used in the development of nano-drug delivery systems, such as polyamide, polyamide silicone, polypropylene imine and sugar dendrimers. Dendrimers load drugs through simple encapsulation, electrostatic interaction and covalent coupling. However, so far, only a few active ingredients of traditional TCM, such as puerarin, curcumin, resveratrol, genistein and podophyllotoxin, have been encapsulated in dendrimers. Khalil et al. (2021) designed and synthesized a third-generation triazine-based dendrimer and combined it with magnolol and targeting ligands lactobionic acid and folic acid to inhibit matrix metalloproteinases (MMP-2/9) to inhibit the progression of hepatocellular carcinoma (HCC). The results showed that dendrimers and their derivatives inhibited tumor growth by inhibiting MMP-2/9 activity, reducing tumor cell proliferation, invasion and migration. However, the article did not discuss specific signaling pathway proteins in detail. Gallien et al. (2021) verified the antitumor effect of G4 90/10-Cys dendrimers on multiple glioblastoma cell lines. Experiments have shown that G4 90/10-Cys dendrimers can effectively encapsulate curcumin and significantly reduce the activity of human (U87), mouse (GL261) and rat (F98) glioblastoma cells, while having little effect on normal cells such as HEK 293, mouse and rat bone marrow mesenchymal stem cells. Encapsulated curcumin significantly improves the anti-tumor effect by increasing its bioavailability.

PAMAM polyaminoamine dendrimer is one of the most widely studied dendrimers because it is water-soluble and can promote metastasis through the paracellular pathway through epithelial tissue. Sharma et al. (2019) prepared a PAMAM-encapsulated antitumor drug podophyllotoxin nano-drug delivery system to evaluate the therapeutic effect of the polymer on hepatocellular carcinoma HCC. In cell experiments, different doses of Opodo significantly reduced the levels of inflammatory factors IL-6 (interleukin-6) and NF-κB (nuclear factor κB). After induction by Dena, liver fibroblast markers TGF-β (transforming growth factor β) and α-SMA (α-smooth muscle actin) were expressed in hepatocellular carcinoma. These proteins play a key role in the progression of HCC, indicating that the development of HCC is through regulating the inflammatory and fibrotic factors DPODO by inhibiting the expression of these proteins. The results showed that the Dpodo group was significantly inhibited after treatment, reducing inflammatory response and liver fibrosis, thereby inhibiting tumor development.

Other nanoparticles

The delivery system for the encapsulation of anti-tumor active components of traditional TCM also includes nanocages, metal-organic frameworks(MOF), nanohydrogels, and carrier-free nanoformulations. So far, there has been little research on these nanodelivery systems, but their application potential is worthy of attention. Wu et al. (2022) studied the therapeutic mechanism of a new type of nanogel (Rhein-DOX nanogel) for liver cancer. The experiment used HepG2 liver cancer cell line and nude mouse subcutaneous transplant tumor model. The results showed that Rhein-DOX nanogel significantly increased the level of intracellular ROS by targeting mitochondria, reduced mitochondrial membrane potential (ΔΨm), and induced cell apoptosis. The experimental results show that the nanogel exerts its anti-tumor effect by enhancing ROS-mediated mitochondrial damage and inducing cell apoptosis. Among them, iron-based MOF combines the advantages of MOF and the role of iron in tumor treatment, and has good application prospects in the development of iron-involved multimodal tumor treatment strategies. In particular, it is used to develop iron-involved multimodal cancer treatment strategies. Wang et al. (2023a) constructed a BSA-FA functionalized iron-containing metal organic framework (TPL@TFBF). The experimental results showed that TPL inhibited Nrf2 expression and interfered with the de novo synthesis of glutathione (GSH), increasing the sensitivity of cells to ferroptosis. At the same time, Fe³⁺ increased the intracellular ROS level through the Fenton reaction after entering the cells. The two synergistically amplified ROS generation and induced ferroptosis, which was manifested as downregulation of Nrf2 and GPX4 expression and decreased GSH levels. On the other hand, TPL can induce GSDME-dependent cell pyroptosis. Fe³⁺ enhances this process by activating caspase-3, causing it to cut GSDME to produce N fragments, forming pores in the cell membrane, causing cell swelling, membrane rupture, and release of IL-1β and LDH, etc., triggering cell pyroptosis. Chen et al. (2025) prepared anisamide-modified ursolic acid nanoparticles, and the experimental results showed that it could significantly downregulate the expression of NRG1 in CAF cells, thereby reducing the phosphorylation levels of HER3 and AKT in LNCaP cells, thereby alleviating enzalutamide resistance. This mechanism suggests that the nanoparticles enhance the sensitivity of prostate cancer cells to enzalutamide by targeting CAF cells and regulating signaling pathways in the tumor microenvironment.

Table 2 summarizes and lists the types of nanomaterials loaded with TCM monomers, and compares the efficacy of different nanomaterials when loaded with TCM monomers and their anti-tumor mechanisms. In terms of detection, dynamic light scattering (DLS) is often used to detect the particle size of nanomaterials, electrophoretic light scattering is used to detect Zeta potential, high performance liquid chromatography (HPLC) or ultraviolet-visible spectrophotometry (UV-Vis) is used to detect drug loading, and dialysis or ultracentrifugation is used to detect encapsulation efficiency. In addition, the characterization of nanoparticles after drug loading is also listed, so as to comprehensively study and analyze the relevant characteristics of nanomaterials loaded with TCM monomers.

Clinical trial of nano TCM monomer delivery system

In the field of research on nano TCM monomers for anti-tumor effects, only the nano drug delivery system loaded with paclitaxel has been clinically studied. Genexol^® PM is the first polymer micelle approved for the treatment of human diseases. It was developed by Samyang Biopharm, a Korean biopharmaceutical company, and is a polymer micelle that encapsulates paclitaxel without polyoxyethylene castor oil (Gupta et al., 2021). The polymer material used in this product is methoxypolyethylene glycol-b-poly D, L-lactide (mPEG-b-PDLLA), with a particle size of 20~50 nm and a drug loading of 16.7%. It was first launched in South Korea for the treatment of metastatic breast cancer (MBC), non-small cell lung cancer (NSCLC) and ovarian cancer. In Phase II clinical studies, this product was used alone to treat metastatic breast cancer, or in combination with cisplatin to treat non-small cell lung cancer. Compared with paclitaxel injection and paclitaxel albumin nanoparticles, the efficacy was significantly improved. As a result, Genexol PM was approved in South Korea in 2007 for the treatment of non-small cell lung cancer, metastatic breast cancer and ovarian cancer, and was subsequently launched in India, Serbia, the Philippines and Vietnam. Lipusol (liposomal paclitaxel for injection) was granted by the China National Drug Administration for the treatment of ovarian cancer and breast cancer receiving chemotherapy containing doxorubicin (Wang et al., 2022). Lipusol combined with cisplatin can be used to serve patients with non-small cell lung cancer who cannot undergo surgical resection or radiotherapy. Compared with free treatment, lipusol can alleviate the side effects involving blood pressure, peripheral blood, medulla and liver after injection, thereby improving the efficacy of the drug. Albumin-bound paclitaxel (hereinafter referred to as albumin paclitaxel) prepared using albumin nanotechnology can solve the patient’s allergy problem and improve the anti-tumor effect. The reason why the efficacy of albumin paclitaxel can be improved is that the nanocarrier can quickly deliver the drug to the cancer tissue and retain it for a longer time. In the treatment of breast cancer, conventional paclitaxel treatment can only achieve a remission rate of 19%, while albumin paclitaxel can increase it to 33% (Gupta & Gupta, 2022). In a clinical trial (CA201) for the first-line treatment of advanced breast cancer conducted in China, the objective response rate after albumin-paclitaxel treatment reached 56%, while the control group using conventional chemotherapy drugs could only reach 27% (Guo et al., 2019). In addition, albumin-paclitaxel also greatly reduced its toxicity to neutrophils, and the incidence of severe neutropenia after treatment was only half that of paclitaxel. It also greatly shortened the time required for injection, and the injection can be completed in half an hour. These clinical experiments have strongly confirmed the effectiveness and potential of nanomaterial-loaded TCM monomers in anti-tumor treatment, providing a solid foundation for its further clinical application.

Potential of nano-TCM monomers in combination with radiotherapy

The unique size and structure of nanomaterials enable them to more effectively deliver TCM monomers to tumor sites (Zhang et al., 2024). Radiotherapy is one of the important means of tumor treatment, but the radiotherapy resistance of tumor cells and the damage of radiotherapy to normal tissues limit its efficacy. The combination of nanomaterial-loaded TCM monomer delivery system and radiotherapy shows great potential to overcome these problems. Nanomaterials have unique size, shape and surface properties, which can change the interaction between radiotherapy rays and tumor tissues. Nanomaterials can be used as radiotherapy sensitizers to enhance the absorption and scattering of rays, increase local energy deposition, and thus increase radiation damage to tumor cells. At the same time, its size advantage enables it to passively or actively target tumor tissues, increase the enrichment of drugs in tumor sites, and achieve synergistic enhancement of radiotherapy and drug therapy (Qian et al., 2022). In terms of tumor microenvironment regulation, nanomaterial-loaded TCM monomer delivery system can effectively improve the adverse microenvironment faced by radiotherapy. The hypoxic state of the tumor microenvironment is an important factor leading to radiotherapy resistance. Some TCM monomers can promote the normalization of tumor blood vessels and increase oxygen supply. Nanomaterials can accurately deliver these TCM monomers to the tumor area, improve the hypoxic microenvironment, and increase radiotherapy sensitivity. In addition, there are immunosuppressive cells and factors in the tumor microenvironment. The TCM monomers delivered by nanomaterials can regulate the immune microenvironment, activate immune cells, inhibit the function of immunosuppressive cells, and enhance the body’s immune clearance ability of tumor cells after radiotherapy, forming a combined effect of radiotherapy and immunotherapy. For tumor cells, the combination of nanomaterial-loaded TCM monomer delivery system and radiotherapy has a multi-faceted effect on their biological behavior. Radiotherapy induces DNA damage in tumor cells, and TCM monomers can affect the DNA damage repair mechanism of tumor cells through various pathways (Deng et al., 2023b). At the same time, nanomaterials can accurately deliver TCM monomers into tumor cells, enhance their regulatory effect on the cell cycle, and make tumor cells more stagnant in the cell cycle phase sensitive to radiotherapy, thereby improving the efficacy of radiotherapy.

Potential of combining nano-TCM monomers with immunotherapy

Immunotherapy has become an important breakthrough in the field of tumor treatment, but it still faces many challenges, such as immune escape and insufficient immune activation. The combination of nano TCM monomer delivery system and immunotherapy shows great potential to overcome these problems. Nanomaterials can effectively improve the pharmacokinetic properties of TCM monomers with their unique size, shape and surface properties, and achieve precise targeted delivery to the tumor microenvironment and immune cells. From the perspective of antigen presentation, nanomaterials can encapsulate or adsorb TCM monomers and deliver them to antigen-presenting cells. TCM monomers may promote the maturation of dendritic cells and enhance their ability to take up, process and present tumor antigens, thereby activating naive T cells and initiating anti-tumor immune responses (Shen et al., 2024). There are immunosuppressive cells and factors in the tumor microenvironment, such as regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs) and immune checkpoint molecules, which hinder the effectiveness of immunotherapy. Nano TCM monomer delivery system can regulate this unfavorable environment. TCM monomers may enhance the activity, proliferation and cytotoxicity of immune effector cells by regulating intracellular signaling pathways, thereby significantly improving their ability to kill tumor cells (Miao et al., 2023). Wang et al. (2020b) constructed an enzyme-sensitive AP (Angelica Polysaccharide)-PP-DOX (doxorubicin) tumor-targeted nanodrug delivery system (PP MMP2-cleavable peptide). MMP2 can cleave AP-PP-DOX (Angelica 1 doxorubicin) to release the AP part (AP-GPLG). AP-GPLG does not affect the immunomodulatory activity of AP. It increases the proliferation of mouse spleen cells and regulates Th1/Th2 cytokines (upregulating IL-2 and downregulating IL-10), which is expected to restore the immune balance of the tumor microenvironment and fight tumors. The combination of TCM-loaded monomer delivery system and immunotherapy has opened up a new path to overcome the difficulties of immunotherapy and improve the effect of tumor treatment through the synergistic effects of multiple mechanisms such as optimizing antigen presentation, reshaping the tumor immune microenvironment, and activating immune effector cells. It is expected to bring better treatment options for cancer patients.