The Multitalented Marvels: Exploring the Versatile Potential of Natural Products in Osteosarcoma Treatment

Abstract

Osteosarcoma (OS) is a malignant neoplasm arising from bone tissue. The OS exhibited a significant degree of heterogeneity, with a high incidence of local invasion and a high rate of metastasis. Approximately 25% of those diagnosed with OS present with metastases, with the lungs being the most prevalent site, followed by the bones or lymph nodes. The 5-year survival rate for patients with OS with lung metastasis is only 10% to 30%. Adjuvant chemotherapy regimens significantly enhanced the 5-year survival rate in patients diagnosed with non-metastatic OS. However, the same regimens did not provide a substantial improvement in survival for patients with OS who had acquired lung metastasis or had recurrence. Moreover, the extensive use of chemotherapy medications often results in the development of resistance to chemotherapy in patients with OS, which frequently culminates in treatment ineffectiveness. Natural products (NPs) are significant reservoirs of anti-cancer medications. Preclinical investigations have shown that certain NPs had substantial promise for treating OS. However, there is currently a lack of a comprehensive overview of the use of NPs in OS treatment. In this review, we provide a comprehensive overview of the NPs, which include polyphenols, alkaloids, and terpenoids, that have the potential to be effective in the treatment of OS.

1. Introduction

Osteosarcoma (OS) is a prevalent primary malignant bone tumor, typically arising in the epiphyses of the long bones in the lower extremities. ¹ It is the second most frequent bone tumor in children and adolescents after myeloma. ² The mortality rate of OS is substantial, significantly compromising the well-being and quality of life of patients. Current primary treatment strategies include radiotherapy, chemotherapy, and surgical resection.^3,4 Despite the widespread adoption of diverse surgical approaches and combination regimens incorporating high-dose methotrexate, doxorubicin (Dox), and cisplatin, the overall prognosis of patients with OS has not shown considerable improvement. ⁵ This limited progress may be partly attributable to the high incidence of metastasis (over 80 %) and frequent therapeutic resistance. ⁶ The lungs are the primary location of metastasis for OS. The reported 5-year survival rates for patients without pulmonary metastasis range from 70 % to 80 %, whereas those with lung metastasis fall to only 10 %-30 %. ² Dox and cisplatin are the primary medications used for chemotherapy in the treatment of OS. Chemotherapy medications are crucial in enhancing the survival rate of patients with OS and decreasing lung metastasis. ⁷ Nevertheless, the inherent resistance of OS to chemotherapy often fails treatment. ²

Natural products (NPs) refer to the constituents or byproducts derived from animals, plant extracts, insects, marine species, or microbes. ⁸ NPs constitute a significant reservoir of anti-tumor medications, with around two-thirds of anti-tumor treatments originating from NPs. ⁹ Paclitaxel and vinblastine, well-recognized as primary chemotherapeutic agents, are derived from botanical sources. In a recent study, Kan et al. ¹⁰ provided a comprehensive overview of the use of NPs in combination treatment and immunomodulation for breast cancer. Guo et al. ¹¹ examined the mechanisms by which NPs regulate miRNA expression to cure colorectal cancer. Han et al. ¹² examined the capacity of NPs to alleviate cancer-related cachexia. Several preclinical studies have indicated that various NPs, such as bisdemethoxycurcumin, ¹³ emetine, ¹⁴ phillygenin, ¹⁵ 6-Hydroxythiobinupharidine, ¹⁶ dryofragin, ¹⁷ selaginella tamariscina (Beauv.), ¹⁸ curcumin, ¹⁹ ganoderma lucidum, ²⁰ chlorogenic acid, ²¹ and green tea polyphenols, ²² exhibit significant potential in treating OS. However, there is currently a lack of a comprehensive overview of the use of NPs in OS treatment.

This paper summarizes the various pathways by which NPs, such as polyphenols, alkaloids, and terpenoids, might inhibit metastasis and resistance of OS. The focus is on the regulatory effects of NPs on tumor-related signaling networks, components of the tumor microenvironment (TME), and programmed cell death during OS development.

2. Methods

Our literature sources comprised the Web of Science and PubMed databases. The search term included “osteosarcoma,” “metastasis,” “resistance”, “terpenoid”, “polyphenol”, “alkaloid”, “flavonoid”, “chalcone”, “saponin,” and “natural product” combined with Boolean operators as appropriate. Eligible publications were restricted to those written in English and published between 2015 and 2025. Furthermore, we only prioritize original research. The inclusion criteria were: 1) original research articles with clearly described experimental designs; 2) studies evaluating the effects of natural products on OS metastasis or chemoresistance; 3) for metastasis-related studies, in vivo experiments in OS mouse models with assessment of lung metastasis were mandatory; 4) for resistance-related studies, either in vivo or in vitro studies assessing the sensitizing effect of natural products on chemotherapeutic agents were acceptable. The exclusion criteria were: 1) reviews, meta-analyses, case reports, editorials, or conference abstracts; 2) studies without original experimental data; 3) studies not specifically focused on OS. The screening process was conducted as follows: two independent researchers screened all retrieved records by title and abstract against the eligibility criteria. Full texts of potentially relevant articles were then retrieved and assessed for final inclusion. Any disagreements between the two researchers were resolved through discussion or, if necessary, consultation with a third researcher. Refer to Figure 1 for details of the search strategy.

Figure 1.

Literature search strategy

3. Overview of OS

Epigenetic modification contributes significantly to OS initiation, dissemination, and treatment resistance. ²³ A prevalent RNA modification form, N6-methyladenine (m6A) methylation, is composed of reader protein, methyltransferase, and demethylase, which are accountable for the addition, elimination, and recognition of m6A. ²⁴ m6A methylation is involved in the control of RNA expression, splicing, translation, stability, and degradation. There is strong evidence from two prior reviews^25,26 showing that m6A-related regulatory factors are considerably aberrant in OS tissues and are linked to tumor metastasis and patient prognosis. Mechanistically, Li et al. ²⁷ revealed that methyltransferase-like 14 (METTL14) is an OS-related methyltransferase that controls the stability and translation of meningioma 1, hence promoting carcinogenesis and development and all-trans retinoic acid resistance. Tumor size, clinical stage, and distant metastasis were shown to be linked with METTL3 expression in OS tissues, which was reported to be considerably elevated. ²⁸ Up-regulation of histone deacetylase 5 expression may be connected to the fact that METTL3 deletion reduces OS cell proliferation, migration, and invasion. Wang et al. ²⁹ documented the function of METTL3 in maintaining tumor necrosis factor receptor-associated factor 6 expression throughout the onset and progression of OS. Previous research has shown that METTL3 impacts the stability of differentiation antagonizing non-protein coding RNA and tripartite motif-containing protein 7 mRNA in the progression of OS.^30,31 The fat mass and obesity-associated (FTO) protein is a significant demethylase that has been shown to be connected with the onset and progression of OS. FTO enhances the Wnt signaling pathway by destabilizing Dapper1/Dpr1 mRNA, facilitating OS progression and treatment resistance. ³² Furthermore, Shan et al. ³³ discovered that FTO suppressed the expression of Krüppel-like factor 3 in a YthDF2-dependent manner, subsequently stimulating the proliferation, migration, and invasion of OS cells. Wilms’ tumor 1-associating protein, functioning as a methyltransferase, has been shown to impact the progression of OS significantly. This effect is likely due to its ability to suppress the expression of homeobox-containing 1 and modulate the PI3K/AKT signaling pathway. ³⁴ Non-coding RNAs (ncRNAs) are a group of functional transcripts that cannot encode proteins. NcRNAs are categorized into many types based on length, form, and location. ³⁵ These types include microRNAs (miRNAs), long ncRNAs (lncRNAs), circular RNAs (circRNAs), small interfering RNAs, and Piwi-interacting RNAs. Mounting evidence substantiates that ncRNAs govern the onset, metastasis, and resistance to the treatment of OS by modulating the expression of target genes. ³⁶ CircRNAs possess a high abundance of miRNA binding sites and function as a “sponge” to alleviate the suppressive effect of miRNA on target genes. ³⁷ Feng et al. ³⁸ discovered that Circ-CTNNB1 is significantly upregulated in OS tissues and boosts aerobic glycolysis in OS cells by facilitating RBM15-mediated m6A methylation modification. LncRNAs are a subclass of ncRNAs with a length exceeding 200 nucleotides. DIO3OS has been identified as a promising biomarker for OS that may be used for diagnosis and prognosis. ³⁹ It is believed that DIO3OS may inhibit tumor progression by blocking the TGF-β signaling pathway. Wang et al. ⁴⁰ suggest EBLN3P was discovered to increase the stability of Annexin A3 mRNA by recruiting human antigen R. As a result, this promoted the proliferation, migration, and invasion of OS cells. Furthermore, it has been shown that NUCKS1 ⁴¹ and Circ_0000073 ⁴² are also associated with metastasis and resistance to drugs in OS.

Exosomes are a class of extracellular vesicles that contain a high concentration of proteins, lipids, and nucleic acids. They are secreted by virtually all cell types. ⁴³ Exosomes are ubiquitously present in many physiological fluids and tissues and have a significant function in facilitating intercellular communication. ⁴⁴ Through the transport of proteins and nucleic acids, exosomes contribute to therapy resistance, as well as tumor cell proliferation, angiogenesis, and metastasis during OS progression. NcRNAs comprise a substantial portion of the cargo generated by exosomes. ⁴⁵ Macrophage-derived exosome-specific LIFR-AS1, as previously described by Zhang et al., ⁴⁶ may contribute to the onset and progression of OS via controlling miR-29a/NFIA signaling. According to research by Liu et al., ⁴⁷ OS cells strongly polarized tumor-associated macrophages (TAMs) toward the M2-type. In addition, M2-type TAMs may secrete exosome-specific miR-221-3p. MiR-221-3p enhances the development and metastasis of OS cells by blocking the transcription factor suppressor of cytokine signaling 3 and subsequently activating the JAK2/STAT3 signaling pathway. By releasing exosome-specific let-7a, TAMs may also hasten the development of OS. ⁴⁸ Mesenchymal stem cells (MSCs) interact with other cells in the TME to promote tumor development and metastasis. Following recruitment into OS tissues, bone marrow-derived MSCs have been shown to secrete exosome-specific XIST, a long non-coding RNA. ⁴⁹ By modulating miR-655/ACLY signaling, XIST greatly aided OS cell proliferation and invasion.

4. Application of NPs Against OS

Amputation was the traditional treatment for OS; however, the 5-year survival rate of patients with this singular treatment is less than 20%. ⁵⁰ The 5-year survival rate of patients with OS has increased to 60 % to 80 % in recent years as a result of the development of surgical techniques, radiation therapy, chemotherapy, targeted therapy, and multidisciplinary integrated therapy. ⁵¹ Nevertheless, OS still ranks first in mortality among malignant bone tumors. ⁵² This situation indicates that it is imperative to investigate more effective treatments for OS in order to enhance the prognosis of patients. This paper opportunities using OS and NPs as search terms, summarizes NP related to OS treatment and evaluates its potential challenges.

A valuable resource for the discovery of novel pharmaceuticals is plant-derived NPs. NPs, including polyphenols, terpenes, alkaloids, and saponins, hold potential for combating OS. Soybean isoflavone (SI) is a secondary metabolite that occurs during the growth process of soybeans. ⁵³ This compound possesses a structure closely resembling that of estrogen. Research has indicated that SI can regulate the immune system, combat tumors, and prevent cardiovascular diseases and osteoporosis. They are considered to have significant potential for further development. The study conducted by Zheng et al suggests that SI has the potential to address OS through its impact on mitochondrial autophagy effectively. ⁵⁴ Mitochondria, being energy factories, have a crucial role in numerous biological processes within cells. Indeed, mitochondrial autophagy can have both promoting and suppressing effects on cancer, making it a complex factor in tumor development. Furthermore, its role varies across different types and stages of cancer. According to Zheng and colleagues, the study revealed that SI has a dose-dependent effect on autophagy, proliferation, migration, and invasion of OS cells. Inhibition of mitochondrial autophagy reversed the anti-tumor effects of SI. In addition, Akt agonists were found to counteract the promoting effect of SI on mitochondrial autophagy. This indicates that SI may exert a regulatory role in the process of OS by influencing Akt/mTOR-mitochondrial autophagy axis. Genipin (Gen) is a compound derived from gardenia. It is produced through the hydrolysis of geniposide by β-glucosidase, an enzyme produced by intestinal flora, resulting in deglycosylation. Gen possesses various pharmacological properties, including anti-inflammatory, hepatoprotective, hypoglycemic, hypolipidemic, anti-depressant, and anti-tumor activities.^55,56 Huang et al have reported that Gen can inhibit OS by regulating the PI3K/Akt signaling pathway. ⁵⁷ Gen has been shown to effectively induce apoptosis in OS cells in vitro. Gen also reduced the size of tumors in vivo. Asiaticoside (ATS) is a pentacyclic triterpene saponin known for its various pharmacological effects, including anti-inflammatory, anti-oxidant, neuroprotective, and wound-healing properties. ⁵⁸ The study conducted by Li et al found that ATS has the potential to hinder the proliferation, migration, and invasion of OS cells by influencing the polarization of macrophages towards the M2 type. ⁵⁹ Mechanistically, ATS may inhibit macrophage polarization toward the M2 type via suppression of the TRAF6/NF-κB signaling pathway. Furthermore, the potential value of quercetin,^60,61 vitexicarpin, ⁶² asiatic acid, ⁶³ oridonin, ⁶⁴ urolithin B, ⁶⁵ betanin, ⁶⁶ stylopine, ⁶⁷ protodioscin, ⁶⁸ astaxanthin, ⁶⁹ dioscin, ⁷⁰ asiaticoside, ⁵⁹ hydroxygenkwanin, ⁷¹ andrographolide, ⁷² nerolidol, ⁷³ resveratrol, ⁷⁴ butein, ⁷⁵ peiminine, ⁷⁶ hederoside C, ⁷⁷ panax notoginseng saponins, ⁷⁸ tanshinone I, ⁷⁹ tanshinone IIA, ⁸⁰ scutellarin, ⁸¹ emetine, ¹⁴ timosaponin AIII, ⁸² and arthpyrone L ⁸³ against OS was also demonstrated.

In summary, the use of dozens of NPs offers advantages for OS treatment by virtue of their multi-target and multi-pathway characteristics. However, several obstacles have hindered their clinical application. Mechanistic studies frequently focus on isolated signaling cascades within single cell lines, which may not adequately reflect the interconnected nature of OS pathogenesis or the multi-target pharmacology inherent to NPs. The molecular and phenotypic heterogeneity of OS further complicates the translational outlook, as most experimental systems do not account for patient variability. Moreover, the predominant use of in vitro systems and immunodeficient murine models limits the generalizability of findings, given that the tumor microenvironment and host immunity are known to modulate therapeutic responses substantially. Issues related to low purity and structural complexity also remain, necessitating further optimization and characterization. These considerations suggest that the current literature, while informative for compound screening, remains largely preclinical in scope and lacks clinical data to support the therapeutic efficacy of NPs against OS.

A recent meta-analysis of clinical studies evaluating traditional Chinese medicine combined with chemotherapy in OS patients demonstrated that the combination approach significantly improved treatment efficiency compared with chemotherapy alone (OR = 2.56, 95 % CI 1.36–4.79) while alleviating chemotherapy-induced adverse effects such as nausea, hepatotoxicity, and myelosuppression. However, this analysis was limited by the small number of available trials and heterogeneity among study designs, underscoring the need for larger, well-controlled prospective studies. To our knowledge, only one registered clinical trial is currently underway-a Phase II study investigating Ganoderma lucidum spore powder in combination with doxorubicin and cisplatin for postoperative OS patients (NCT04319874). The scarcity of clinical investigations highlights a critical gap between preclinical promise and clinical application, reinforcing the urgent need for translational efforts to bridge this divide.

5. Application of NPs Against OS Metastasis

Diverse tumor cells exhibit distinct patterns of organotropism. Furthermore, the metastasis potential varies across different tumor cells. OS is very susceptible to developing malignant tumors that metastasis to the lungs. ⁸⁴ This has a substantial impact on the prognosis of patients. ⁸⁵ The intricate TME, consisting of blood vessels, immune cells, tumor cells, and extracellular matrix, creates a conducive setting for the development and metastasis of OS. In addition, tumor cells can evade immune surveillance through remodeling the TME to facilitate metastasis.^6,86 For OS patients with lung metastasis, the long-term survival rate remains less than 30 %. Unfortunately, there is presently no viable therapy available. ⁸⁷ Several comprehensive reviews have examined the potential of polyphenols and flavonoids in targeting tumor metastasis specifically. We provide a concise overview of the molecular mechanism behind the effects of terpenoid, sesquiterpene lactone, polyphenol, naphthoquinone, flavonoid, and chalcone on the metastasis of OS (Table 1).

Table 1.

Application of Natural Products Against Lung Metastasis of Osteosarcoma

Ingredient	Classification	Dose and drug administration time	References
Corosolic acid	Terpenoid	30 μM for Saos2, HSOS-1, and 40 μM for LM8 cells, 17.5 mg/kg for mice.	Horlad et al.
Tanshinone I	​	IC50: 1.048 μM for U-2OS and 1.321 μM for MOS-J cells, 20 mg/kg/day for mice.	Wang et al.
Toosendanin	​	25, 50, 100, 200 μM for 143B, HOS and MG63 cells, 1, 2 mg/kg/2 days for mice.	Zhang et al.
Oridonin	​	0.5, 1, 2 μM for MG-63, U-2OS and 143B cells, 5, 10, 15 mg/kg/day for mice.	Sun et al.
Glaucocalyxin A	​	0.25 0.5, 1 μM for MG-63, U-2OS and 143B cells, 10, 20, 40 mg/kg/day for mice.	Jianng et al.
Costunolide	Sesquiterpene lactone	10 μM for 143B, HOS and MG63 cells, 10, 20 mg/kg/day for mice.	Jin et al.
Epigallocatechin gallate	Polyphenol	10, 20, 30 40, 50 μM for 143B, MG63, and SaOS-2 cells, 10, 20, 40 mg/kg/2 days for mice.	Dong et al.
Shikonin	Naphthoquinone	1, 3, 5, 7.5, 10 μM for K7, K12, K7M3, U2OS, and 143B cells, 2 mg/kg for mice.	Fu et al.
Ononin	Flavonoid	0.1, 0.3, and 1 μM for U-2OS and MG-63 cells, 1, 3, and 10 mg/kg/intraperitoneal injection	Gong et al.
Flavokawain A	Chalcone	12.5 μg/ml for 143B and SaOS-2 cells, 200 mg/kg/day for mice.	Zhang et al.
Rhizoma Paridis saponins	——	1 μg/mL for 143B and MG63 cells, 25, 100 mg/kg/day for mice.	Yao et al.

Furthermore, to systematically understand the structural basis underlying the anti-lung-metastasis effects of the aforementioned natural products against osteosarcoma from a chemical standpoint, we compiled the physicochemical properties and structural attributes of each compound (Supplementary Table S1). Based on their core skeletons, these compounds fall into six major groups: triterpenoids, diterpenoids, sesquiterpene lactones, polyphenols, naphthoquinones, isoflavones, and chalcones. Of note, despite considerable variations in their structural frameworks and physicochemical profiles, all of these compounds exhibit favorable blood–brain barrier permeability (BBB > 0.94) and high plasma protein binding rates (PPB ranging from 80% to 99%). From a structure–activity relationship perspective, compounds bearing α,β-unsaturated carbonyl moieties-such as costunolide, oridonin, and glaucocalyxin A-are prone to forming covalent adducts with nucleophilic residues of target proteins via Michael addition, thereby giving rise to irreversible inhibitory effects. In contrast, polyhydroxylated compounds, including epigallocatechin gallate and corosolic acid, tend to engage in non-covalent interactions with their targets through hydrogen bonding and π–π stacking.

Terpenoids are a significant component of NPs, with over 50,000 terpenoids documented. ⁸⁸ Corosolic acid, a pentacyclic triterpenoid derived from Lagerstroemia speciosa, gained considerable recognition for its notable hypoglycemic properties and came to be referred to as “phyto-insulin”. ⁸⁹ Subsequently, scientists identified the anti-tumor properties of corosolic acid. Corosolic acid has been discovered to cause an excessive buildup of reactive oxygen species (ROS) and stimulate apoptosis by disrupting the intracellular redox system in non-small cell lung cancer. ⁹⁰ In a previous study, Cai et al. ⁹¹ found that corosolic acid-induced apoptosis in OS cells was both time- and dose-dependent. Horlad et al. ⁹² validated that corosolic acid has a notable capacity to hinder OS-induced lung metastasis. This effect appears to result from its ability to block the immunosuppressive activity of myeloid-derived suppressor cells (MDSCs). MDSCs are a diverse population of immature immunosuppressive cells, hinder T cell activation by the secretion of immunosuppressive chemicals, hence impairing the body’s immunological response. ⁹³ Horlad and colleagues discovered that corosolic acid had no impact on the quantity of MDSCs in OS mice. However, it did effectively counteract their immunosuppressive action. ⁹² Corosolic acid also overcomes the resistance of OS cells to adriamycin and cisplatin. This finding is supported by in vitro research.

Salvia miltiorrhiza, a traditional Chinese medicine, is extensively used in Chinese medical facilities to treat cardiovascular ailments. ⁹⁴ To date, over 50 bioactive compounds have been isolated and identified from Salvia miltiorrhiza. ⁹⁵ These compounds mainly consist of water-soluble polyphenols, such as salvianolic acid and tanshosu, and lipophilic terpenoids, such as tanshinone and cryptotanshinone. Tanshinone (Tan) is the primary bioactive compound found in Salvia miltiorrhiza. Its therapeutic significance in treating tumors, reducing chemotherapy resistance, and ameliorating adverse effects has been extensively validated.^95,96 In a previous study, Huang et al. ⁹⁷ provided a comprehensive description of the pharmacological action, synthesis, and structural alteration of Tan I. We further elaborate on the potential of Tan I in OS treatment, with particular emphasis on its effects on metastasis and therapy resistance. CircRNAs are a class of ncRNAs with a closed loop structure, which renders them resistant to exonuclease degradation and allows for stable expression levels. CircRNAs exhibit many intricate biological roles, such as their ability to interact with RNA-binding proteins, undergo translation into peptides, and exert specialized “sponge” effects. ⁹⁸ CircRNAs have shown a strong association with several disorders, particularly the proliferation of tumors. ⁹⁹ The oncogenic nature of Circ_0000376 has been verified, with its aberrant expression being strongly associated with the expansion, migration, and invasion of tumor cells. ¹⁰⁰ Circ_0000376 exhibits significant overexpression in OS tissues and cells and functions as an oncogenic factor by sponging miR-432-5p and promoting the upregulation of B-cell lymphoma-2 (BCL2) expression. In their study, Ye et al. ⁷⁹ discovered that treatment with Tan I had a strong inhibitory effect on OS cells’ proliferation, migration, invasion, and glycolysis. Circ_0000376 overexpression markedly diminished the anti-cancer efficacy of Tan I via its mechanism. Furthermore, the pharmacological effectiveness of Tan I in suppressing OS metastasis was also validated. Wang et al. ¹⁰¹ demonstrated that administering Tan I at a dosage of 20 mg/kg effectively suppressed the lung metastasis of OS.

Toosendanin is a tetracyclic triterpenoid chemical extracted from Melia toosendan Sieb.et Zucc. Toosendanin, known for its effective insect-repellent properties, was used as China’s primary ingredient in roundworm repellents. ¹⁰² Toosendanin has shown potential efficacy in analgesia, anti-inflammatory, anti-tumor, and improving chemotherapy sensitivity.^103,104 Zhang et al. ¹⁰⁵ discovered that Toosendanin can inhibit STAT3, a transcription factor that controls the production of specific genes such as BCL2, myeloid cell leukemia-1, survivin, vascular endothelial growth factor, and matrix metalloproteinases (MMPs). This inhibition occurs by preventing the phosphorylation of STAT3, ultimately suppressing OS cell proliferation, migration, and invasion. In vivo, investigations further showed that Toosendanin effectively suppressed the metastasis of OS to the lungs and increased the lifespan of mice.

A research team in Nanjing has independently shown the therapeutic properties of two terpenoids, namely oridonin and glaucocalyxin A, in treating OS-related lung metastasis. Oridonin, a diterpenoid molecule derived from Rabdosia rubescens, has notable therapeutic efficacy against several human malignancies, such as lung, breast, ovarian, and liver.^106,107 It has earned the “second paclitaxel” moniker due to its anti-tumor effectiveness. ¹⁰⁷ TGF-β, a polypeptide cytokine, is primarily localized in the extracellular matrix and exhibits differential functions across different tumor stages. ¹⁰⁸ TGF-β can suppress the growth of cancer cells during the first phase of tumor development. Conversely, once a tumor has formed, excessive activation of TGF-β encourages epithelial-mesenchymal transformation, angiogenesis, and tumor cell metastasis. ¹⁰⁹ According to reports, oridonin can hinder the phosphorylation of suppressor of mother against decapentaplegic (Smad) 2/3 by triggering TGF-β. Glaucocalyxin A, another kind of terpenoid, can also potentially inhibit the lung metastasis of OS by targeting the TGF-β/Smad 2/3 signaling pathway. ¹¹⁰

Aside from terpenoids, many additional kinds of NPs have shown promise in combating pulmonary metastasis of OS. Costunolide (COS) is a sesquiterpenoid compound with diverse pharmacological properties, such as anti-inflammatory, antioxidant, and anti-tumor. ¹¹¹ Recently, the anti-cancer properties of COS, such as its ability to hinder the growth of tumor cells, trigger tumor cell apoptosis, and reverse resistance to chemotherapy, have garnered significant interest from several research teams. ¹¹² Jin et al. ¹¹³ discovered that COS has the ability to inhibit STAT3. COS suppresses STAT3 phosphorylation, leading to downregulation of anti-apoptotic and cell cycle-regulating genes. As a result, COS hinders OS cells’ proliferation, migration, and invasion. It is noteworthy that COS may also effectively inhibit the lung metastasis of OS.

Extensive research has shown the significant potential of green tea in managing cancer, diabetes, cardiovascular disease, and neurological disorders. Tea polyphenols contain over 30 chemicals, including catechins, flavonoids, anthocyanins, phenolic acids, and polyphenolic acids.^114,115 These compounds are the primary active constituents found in green tea. Epigallocatechin gallate (EGCG) is a catechin compound with a high concentration in green tea. ¹¹⁶ It has been scientifically shown to possess pharmacological actions that include anti-inflammatory, antioxidant, control of glucolipid metabolism, and anti-tumor effects. Jiang et al. ¹¹⁷ previously demonstrated that EGCG effectively hinders the growth of OS cells in a way that depends on both the dosage and duration of treatment. Overexpression of miR-126 dramatically increases the sensitivity of OS cells to EGCG. Furthermore, EGCG can potentially impede the metastasis of OS cells by suppressing mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling. ¹¹⁸ EGCG can effectively suppress the proliferation, migration, and invasion of OS cell lines including 143B, MG63, and SaOS2, while inducing tumor cell apoptosis. ¹¹⁹ Upregulation of β-catenin attenuated the antitumor efficacy of EGCG. On the other hand, reducing the expression of β-catenin increased the effectiveness of EGCG in inducing the death of OS cells. EGCG has been validated via in vivo trials to effectively mitigate bone tissue damage, suppress lung metastasis, and impede tumor proliferation.

Shikonin (SK) is a naphthoquinone isolated from Lithospermum erythrorhizon Sieb.et Zucc. Zhang et al. ¹²⁰ first demonstrated that SK suppressed the growth of OS cells in a way dependent on both the dosage and duration of treatment. Treatment with N-acetylcysteine, an antioxidant, effectively negates the anti-tumor action of SK. This suggests that the effectiveness of SK against OS relies on forming ROS. With regard to drug resistance, SK can enhance the sensitivity of OS cells to Dox by upregulating the expression of caspase-3 and caspase-8. ¹²¹ The most captivating aspect is examining SK’s potential in addressing OS-associated pulmonary metastases. A research team based in Shanghai, China ¹²² created an in situ OS mouse model by injecting K7 cells. The researchers showed that SK effectively suppressed lung metastasis generated by OS, as seen by decreased lung weight and less necrotic tissue. The mechanism could be associated with the facilitation of RIP1/3-mediated necroptosis. Necroptosis is a distinct form of programmed cell death that differs from classical apoptosis. The impact of necroptosis on the development and advancement of tumors varies depending on the specific characteristics of the cancer, including its kind, stage, and grade. ¹²³ The team in Shanghai successfully developed a nano gel filled with SK that specifically targets OS. ¹²⁴ It was confirmed that the nanogel was superior to free SK in both OS treatment and reduction of lung metastases.

Ononin is an isoflavone glycoside with anti-inflammatory, antioxidant, and hypoglycemic properties. Previous investigations have revealed Ononin’s in vitro anti-cancer activity.^125,126 Gong et al. ¹²⁷ reported that ononin inhibited the proliferation, migration, and invasion of OS cells and induced their apoptosis in a dose-dependent manner. Furthermore, they showcased that ononin effectively suppressed the lung metastasis of OS, as shown using bioluminescence imaging assays. The inhibitory effect of ononin on lung metastasis was found to be dependent on the dosage administered.

S-phase associated kinase protein 2 (Skp2), a protein involved in the S-phase of the cell cycle, plays a crucial role in the development, therapy, and prognosis of many types of malignancies. ¹²⁸ Skp2 exhibits little expression during the G0-G1 phase, initiates expression during the G1-S phase, steadily intensifies during the S-G2 phase, and quickly diminishes during the M phase. Cyclin-dependent kinases (CDK) complexes serve as positive cell cycle regulators, while CDK inhibitors (CKI) function as negative cell cycle regulators. ¹²⁹ Skp2 can break down CKI and enhance the progression of the cell cycle. ¹³⁰ The expression of Skp2 was increased in OS tissues and showed a negative correlation with both metastasis-free survival and overall survival. Suppression of Skp2 may impede the infiltration of OS and lung metastasis. ¹³¹ Zhang et al. ¹³¹ discovered that flavokawain A functions as a Skp2 inhibitor and effectively suppresses the lung metastasis of OS. This effect is mediated by inducing G2/M cell cycle arrest.

Rhizoma Paridis is a valuable botanical species originating from China and serves as a primary constituent in several Traditional Chinese Medicine formulations. ¹³² The principal active elements of Rhizoma Paridis include steroid saponins, flavonoids, triterpenes, and other chemical ingredients. ¹³³ Among these, saponins are the predominant compounds. Recent pharmacological research has shown that Rhizoma Paridis saponins (RPS) can stimulate programmed cell death, hinder angiogenesis, and counteract the resistance to chemotherapy. ¹³³ Vasculogenic mimicry (VM) is a process whereby tumor cells mimic blood vessel formation. This involves adhesion, remodeling of the extracellular matrix, and actin rearrangement. VM is critical for tumor progression and metastasis and is also an indicator of poor prognosis in OS. ¹³⁴ In their study, Yao et al. ¹³⁵ discovered 34 chemicals derived from RPS and verified their impact on the proliferation, migration, and invasion of OS cells. Functionally, RPS hinders the metastasis of OS cells by suppressing the activation of migration-inducing gene 7 and PI3K/MMPs/Ln-5γ2 signaling pathways via the up-regulation of miR-520d-3p expression, ultimately leading to a decrease in VM. Furthermore, RPS has the potential to diminish significantly the pulmonary metastasis of OS while causing little harm to other organs.

Despite belonging to disparate chemical classes, these natural products converge on several common signaling axes in countering osteosarcoma lung metastasis. Their mechanisms can be broadly categorized into four interconnected modes: (1) suppression of the STAT3 signaling cascade; (2) modulation of the TGF-β/Smad pathway; (3) remodeling of the immunosuppressive tumor microenvironment; and (4) induction of diverse cell death modalities. Thus, although the initial molecular targets of individual compounds may differ, their actions ultimately coalesce around a limited set of core signaling networks, collectively enabling multi-level and multi-stage blockade of pulmonary metastasis. This “multi-target, multi-pathway, multi-mechanism” profile represents a distinctive advantage of natural products over single-target synthetic drugs. Building on this integrative framework, we assembled the molecular events elicited by each natural product into a multi-step signaling network (Figure 2). At the extracellular and membrane-proximal levels, corosolic acid acts on myeloid-derived suppressor cells to alleviate immunosuppression, whereas Rhizoma Paridis saponins modulate miR-520d-3p expression, thereby influencing extracellular matrix remodeling and vasculogenic mimicry. Within the cytoplasmic compartment, multiple signaling pathways engage in extensive crosstalk: upon TGF-β binding to its receptor, oridonin and glaucocalyxin A interfere with Smad2/3 phosphorylation, curbing epithelial–mesenchymal transition; simultaneously, toosendanin and costunolide directly target the JAK/STAT3 axis to prevent STAT3 nuclear translocation; and shikonin triggers ROS accumulation, which in turn activates the RIP1/RIP3/MLKL necroptotic cascade. At the nuclear level, tanshinone I modulates BCL2 transcription via a circRNA sponging mechanism, flavokawain A suppresses Skp2 activity to alleviate CDK inhibitor degradation and thereby impose G2/M cell cycle arrest, and epigallocatechin gallate attenuates β-catenin signaling and ERK phosphorylation, leading to reduced transcription of pro-metastatic genes. Given the extensive cross-talk among these pathways, the network architecture suggests that these natural products may exert synergistic effects in restraining lung metastasis in vivo, while also facing the potential challenge of compensatory pathway activation.

Figure 2.

Application of NPs against OS metastasis

6. Application of NPs Against Therapeutic Resistance in OS

Chemotherapy and molecular targeted therapy are preferred treatment modalities for OS in clinical practice. The intended goal of these medications is evident, and their effectiveness is commendable. ¹³⁶ However, the occurrence of significant adverse effects and the frequent development of drug resistance in OS cells often limit the full therapeutic potential of these drugs. ¹³⁷ Elucidating the mechanism of drug resistance, overcoming drug resistance, and mitigating the toxicity of chemotherapeutic medications are three crucial clinical challenges that need resolution in the laboratory. ¹³⁸ According to reports, using NPs in conjunction with chemotherapy treatments may effectively counteract the drug resistance shown by OS cells, enhance the effectiveness of chemotherapy drugs, and mitigate the adverse effects on organs induced by chemotherapy drugs.^139,140 We provide a concise overview of the molecular mechanism behind the effects of terpenoids, saponin, polyphenols, flavonoids, and alkaloids on the resistance of OS (Table 2).

Table 2.

Application of Natural Products Against Therapeutic Resistance in Osteosarcoma

Ingredient	Classification	Dose and drug administration time	Main effects	References
Chrysanthemulide A	Terpenoid	10, 15, 20 μM, (IC50: 13.523 μM for U-2OS and 8.3 μM for HOS cells).	Facilitates TRAIL-induced apoptosis	Horlad et al.
Curcumol	​	IC50: 37.67 μM for U-2OS, 41.61 μM for MG-63, and 28.3 μM for KHOS cells.	Facilitates cisplatin sensitivity	Wang et al.
Notoginsenoside R1	Saponin	100, 200 μM for U-2OS cells.	Offsets doxorubicin resistance	Zhang et al.
Astragaloside IV	​	40 μM for 143B and MG63 cells, 20 mg/kg/day for mice.	Facilitates cisplatin sensitivity	Sun et al.
Chlorogenic Acid	Polyphenol	100, 200, 400 μM for U-2OS and MG-63 cells.	Facilitates doxorubicin sensitivity	Jianng et al.
Polydatin	​	200 μM for U-2OS and MG-63 cells.	Facilitates paclitaxel sensitivity	Jin et al.
Polydatin	​	200 μM for U-2OS and MG-63 cells,150 mg/kg/day for mice.	Facilitates doxorubicin sensitivity	Dong et al.
Echinatin	Flavonoid	30, 40, 50 μM, (IC50: 36.42 μM for 143B and 37.07 μM for MG63 cells), 20, 40, 60 mg/kg/2 days for mice.	Facilitates cisplatin sensitivity	Fu et al.
Chrysin	​	IC50: 45.1 μM for Saos-2 and 38.5 μM for MG-63 cells.	Facilitates TRAIL-induced apoptosis	Gong et al.
Tetrandrine	Alkaloid	1 μM for U-2OS cells.	Prevents paclitaxel-induced multidrug resistance	Zhang et al.

Similarly, we compiled the physicochemical properties and structural attributes of each compound (Supplementary Table S2). Based on their core skeletons, these compounds fall into several major categories, including sesquiterpenoids, triterpenoid saponins, phenolic acids, stilbenoids, flavonoids, and bisbenzylisoquinoline alkaloids. In terms of molecular weight, notoginsenoside R1 and astragaloside IV possess relatively high molecular masses and are classified as high-molecular-weight saponins, whereas chrysin, echinatin, and curcumol have lower molecular weights, which may facilitate their transmembrane diffusion. With regard to lipophilicity, chrysin and tetrandrine exhibit greater lipid solubility, favoring their passage across biological membranes, whereas notoginsenoside R1 and chlorogenic acid are comparatively more hydrophilic. All tested compounds demonstrate favorable blood–brain barrier permeability, suggesting potentially adequate distribution within the central nervous system. Regarding plasma protein binding rates, chrysin, echinatin, and curcumol display relatively high values, while notoginsenoside R1 and astragaloside IV show lower binding affinities. From a structure-activity relationship standpoint, compounds bearing multiple hydroxyl substituents-such as chlorogenic acid and polydatin-tend to establish strong non-covalent interactions with target proteins through hydrogen bonding. For saponins, including notoginsenoside R1 and astragaloside IV, the glycan moieties may contribute to target affinity by participating in hydrogen-bonding networks.

Terpenoids exhibit a distinct ability to overcome treatment resistance in OS, similar to their effectiveness against OS lung metastasis. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), belonging to the TNF cytokine superfamily, selectively binds to the death receptor (DR) found on tumor cells. TRAIL exhibits no toxicity towards healthy cells and selectively triggers programmed cell death (such as apoptosis) in tumor cells.^141,142 TRAIL is regarded as a potent anti-cancer medication with encouraging progress in clinical trials. ¹⁴³ Nevertheless, several tumor cells exhibited substantial resistance to TRAIL, limiting its potential for future use. Zhuo et al. ¹⁴⁴ discovered that chrysanthemulide A (CA) can activate DR5. CA may increase the expression of DR5 by causing autophagosome accumulation via c-Jun N-terminal kinase signaling. This, in turn, enhances the ability of TRAIL to induce programmed cell death in OS cells. Chrysin has shown synergistic effects with TRAIL in the management of OS. Chrysin, a flavonoid obtained from plants, has been extensively verified for its significant role in inhibiting tumor growth. ¹⁴⁵ Chrysin has been shown to significantly enhance the cytotoxicity of cisplatin against human liver cancer cells. ¹⁴⁶ Chrysin has been shown in both cell and animal studies to sensitize pancreatic cancer cells to gemcitabine by inducing ferroptosis. ¹⁴⁷ A recent research discovered that chrysin enhanced the cytotoxic effects of TRAIL on OS cells. Chrysin depends explicitly on the caspase 8 pathway to increase the pro-apoptotic impact of TRAIL in OS cells. ¹⁴⁸

Curcumol is a sesquiterpenoid compound that has been extracted from ginger. Multiple preclinical studies have shown the efficacy of curcumol in treating many types of human malignancies. ¹⁴⁹ Curcumol has also demonstrated significant efficacy in overcoming chemotherapy resistance. Huang et al. ¹⁵⁰ found that curcumol may increase the responsiveness of gastric cancer cells to cisplatin by blocking the PI3K/AKT pathway. In their study, Gan et al. ¹⁵¹ discovered that curcumol can potentially increase the responsiveness of colorectal cancer cells to 5-fluorouracil via modulating the glycolysis process in tumor cells. The alteration of the TME is intricately linked to developing resistance to chemotherapy. The TME is composed of diverse components, including cancer-associated fibroblasts, adipocytes, and immune cells. TAMs are the predominant immune cells in the TME. TAMs may be categorized into two distinct phenotypes: M1 and M2. ¹⁵² The M1 phenotype exhibits pro-inflammatory properties and anti-tumor actions, whereas the M2 phenotype is capable of suppressing the host’s immune and inflammatory responses. ¹⁵³ Additionally, M2-type TAMs facilitate tumor mesenchymal remodeling, tumor growth, and invasion. ¹⁵⁴ M2-type TAMs may also contribute to the establishment of a hypoxic microenvironment through secretion of cytokines, thereby promoting tumor cell resistance to chemotherapeutic agents. Curcumol has been shown to increase the sensitivity of OS cells to cisplatin by decreasing the M2-type polarization of TAMs. ¹⁵⁵

Saponins may be classified into terpenoid saponins and steroid saponins based on their chemical structure. Saponins have several pharmacological properties, including antioxidant, anti-aging, anti-inflammatory, and anti-tumor actions. Notoginsenoside R1 (NGR1) is an exclusive bioactive compound found in Panax notoginseng (PN) and is a reliable indicator for assessing the quality of PN. ¹⁵⁶ The pharmacological properties of NGR1, a well-researched triterpenoidal saponin, have been verified to include anti-inflammatory, antioxidant, vascular protecting, and anti-tumor effects. ¹⁵⁷ MSCs are multipotent stem cells with the capacity for self-renewal and multilineage differentiation. They have a dual impact on the initiation and progression of different types of malignant tumors. ¹⁵⁸ MSCs support tumor development by releasing cytokines and exosomes that enhance treatment resistance. According to reports, MSCs can inhibit tumor cells’ growth and metastasis by affecting immune cells’ properties in the TME. ¹⁵⁹ The impact of MSCs on malignancies is contingent upon the origin of MSCs and the type of the tumor. Many sources of MSCs within the OS perform distinct functions. In their study, Qi et al. ¹⁶⁰ found that exosomes obtained from bone marrow MSCs enhance the growth and metastasis of OS by transferring microRNAs. Lu et al. ¹⁶¹ discovered that the conditioned media derived from bone marrow MSCs enhanced the resistance of OS cells to adriamycin. NGR1 treatment effectively mitigates the drug resistance caused by MSCs in the bone marrow. This effect is likely due to its ability to regulate the interleukin 6/JAK2/STAT3 signaling pathway.

Astragaloside IV (AS-IV) is a naturally saponin extracted from Astragalus membranaceus. It has pharmacological qualities such as anti-inflammatory, anti-fibrotic, and antioxidant effects.^162,163 Prior research has shown the potential of AS-IV when used in conjunction with chemotherapeutic drugs. ¹⁶⁴ Zheng et al. ¹⁶⁵ found that AS-IV increased the responsiveness of breast cancer to paclitaxel by causing an abnormal buildup of ROS via the suppression of caveolin-1 expression. Subsequent research has consistently verified the ability of AS-IV to enhance the sensitivity of platinum medicines.^166,167 AS-IV can improve the specific therapeutic impact of bevacizumab by suppressing the protective autophagy. ¹⁶⁸ Fas is a transmembrane protein whose interaction with its ligand FasL initiates the apoptotic cascade. Tumor cells have high levels of intelligence. ¹⁶⁹ On the one hand, they can live by resisting programmed cell death triggered by the Fas protein; on the other hand, tumor-specific antigens may cause a significant increase in the production of Fas in immune cells that have infiltrated the tumor, leading to the death of T cells and allowing tumor cells to escape detection by the immune system. ¹⁷⁰ Hu et al. ¹⁷¹ discovered that AS-IV can increase the responsiveness of OS cells to cisplatin by controlling the caspase-dependent Fas/FasL pathway.

Polyphenols are abundant in several plant tissues and organs, including roots, skins, and leaves. Their content is second only to that of cellulose, hemicellulose, and lignin. Polyphenol molecules have few adverse responses and are regarded as the “seventh essential nutrient” for humans. ¹⁷² Currently, over 8,000 polyphenols and their derivatives have been discovered and characterized. The present pharmacological study primarily focuses on flavonoids and phenolic acids. Chlorogenic acid (CGA) is a polyphenolic compound formed from caffeic acid and quinic acid. ¹⁷³ It is often present in food, as well as in fruits and plants. CGA, often used as a food additive, promotes the storage and transportation of food. ¹⁷⁴ In a previous study, Zhang et al. ¹⁷⁵ discovered that CGA suppressed the growth of OS cells in a manner that depended on the dosage. CGA may have an anti-cancer effect by blocking the STAT3/Snail pathway. ERK is a ubiquitous serine and threonine kinase found in mammalian cells. ERK1/2 is a crucial molecule in the cellular signaling cascade that plays a significant role in cancer cells’ growth, metastasis, and programmed cell death. According to reports, CGA can potentially induce programmed cell death in OS cells by stimulating the ERK1/2 signaling pathway. ²¹ Dox, a frontline chemotherapeutic agent, is a potent and often used antineoplastic medication for OS. ¹⁷⁶ Nevertheless, the high occurrence of Dox resistance and its cardiotoxicity significantly restricts the therapeutic efficacy. Salzillo et al. ¹⁷⁷ discovered that CGA may greatly amplify the harmful impact of Dox on OS cells. This enhancement is likely due to the activation of caspase-3 and Poly (ADP-ribose) polymerase and the suppression of p44/42 MAPK. CGA can also mitigate the harmful impact of Dox on cardiomyocytes. The research above indicates that CGA has the potential to act as a synergistic and attenuated adjuvant for Dox.

Polydatin (PD) is a stilbenoid derived from cuspidatum Sieb and serves as the natural precursor of resveratrol. Recently, several studies have shown the pharmacological effects of PD, such as its ability to prevent fibrosis, reduce inflammation, regulate metabolism, and preserve the liver and kidneys. ¹⁷⁸ In a previous study, Shah et al. ¹⁷⁹ provided detailed information on the intricate mechanism by which PD inhibits tumor cells’ growth, metastasis, and infiltration. We particularly focus on the potential of PD in overcoming treatment resistance in OS. Zhao et al. ¹⁸⁰ verified that PD substantially impacts the expression of proteins associated with cell growth, metastasis, programmed cell death, and resistance to drugs via the regulation of Akt activation. Similarly, Hu et al. ¹⁸¹ discovered that administering the same amount of PD may hinder OS resistance to Dox via regulating TUG1/Akt signaling. The lncRNA TUG1 shows a considerable increase in expression in OS tissues and is positively associated with an adverse prognosis for patients. ¹⁸² Experimental investigations have shown that TUG1 plays a pivotal role in the invasion and migration of OS.^183,184

Echinatin (Ecn), a flavonoid derived from Glycyrrhiza inflata, has notable anti-inflammatory, antioxidant, and anti-cancer properties. ¹⁸⁵ Ecn is widely used as a food additive owing to its abundant supply, low cost, and minimal toxicity to human health. ¹⁸⁶ Multiple preclinical investigations have shown the therapeutic efficacy of Ecn in malignant tumors, namely its identification as a possible sensitizer for chemotherapeutic drugs.^187,188 Oh et al. ¹⁸⁷ discovered that Ecn may trigger apoptosis in lung cancer cells resistant to gefitinib by suppressing the expression of epidermal growth factor receptor and MET. Wang et al. ¹⁸⁸ provided more evidence that Ecn may augment the therapeutic efficacy of cisplatin or gemcitabine in bladder cancer cells. In a recent study, Lu et al. ¹⁸⁹ discovered that Ecn had a notable inhibitory effect on the proliferation, migration, and invasion of OS cells. Network pharmacology-based mechanism studies validate that Ecn may partially exert its anti-cancer effects by blocking the Wnt/β-catenin signaling pathway. Significantly, data confirms that combining Ecn and cisplatin is more successful than using either treatment alone.

In addition, tetrandrine (TET) is one of the most potent bisbenzylisoquinoline alkaloids isolated from Stephania tetrandra S. Moore. Tao et al. ¹⁹⁰ discovered that treatment with TET effectively increased programmed cell death in OS cells. Tian et al. ¹⁹¹ investigated the impact of TET on the formation of OS. They focused on phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor gene that is crucial in regulating tumor cell proliferation via its dual protein and lipid phosphatase activities. ¹⁹² TET has been identified as a promising stimulator of PTEN, and its anti-cancer properties rely to some extent on PTEN. Wang et al. ¹⁹³ conducted further research to investigate the probable mechanism of TET in the therapy of OS. TET effectively inhibits OS by selectively targeting many signaling pathways, including MAPK, PTEN, and Wnt signals. Lu et al. ¹⁹⁴ have shown that TET may suppress the production of P-glycoprotein by blocking the NF-κB signaling pathway. This mechanism helps to counteract the development of multidrug resistance caused by paclitaxel. Fortunately, researchers are actively working to enhance the bioavailability of TET. Tian et al. ¹⁹⁵ produced nanoparticles that included TET and showed a significantly improved anti-tumor effectiveness compared to TET used alone. Zhang et al. ¹⁹⁶ created liposomes containing dihydroartemisinin and TET, resulting in a roughly 50-fold increase in the effectiveness of reversing Dox resistance. To summarize, enhancing the bioavailability of TET and creating nanomedicine based on TET are potentially significant approaches to address chemotherapy resistance in OS.

Despite their structural diversity, the aforementioned compounds converge on several common regulatory axes in reversing chemotherapy resistance in osteosarcoma. These mechanisms can be broadly grouped into four interconnected categories: 1) reprogramming of the immune microenvironment; 2) counteracting tumor microenvironment-driven resistance; 3) sensitization of death receptor-mediated pathways; and 4) cross-regulation of multiple intracellular signaling cascades. Building on this framework, we assembled the molecular events associated with the reversal of chemoresistance by these natural products into a multi-node signaling network (Figure 3). At the tumor microenvironment level, curcumol suppresses M2-type polarization of tumor-associated macrophages, thereby reducing the release of immunosuppressive cytokines and alleviating the microenvironment-mediated negative impact on chemotherapeutic efficacy. Meanwhile, notoginsenoside R1 targets bone marrow-derived mesenchymal stem cells and blocks their resistance-inducing effects on osteosarcoma cells through the IL-6/JAK2/STAT3 axis. At the cell membrane receptor level, chrysanthemulide A upregulates death receptor DR5 expression, while chrysin potentiates caspase-8-dependent apoptotic signaling, and both compounds jointly sensitize the TRAIL-mediated apoptotic pathway. Astragaloside IV initiates the extrinsic apoptotic cascade through modulation of the Fas/FasL pathway. In the cytoplasmic signaling compartment, chlorogenic acid activates ERK1/2 signaling while concurrently suppressing p44/42 MAPK, thereby exerting a counter-regulatory effect on chemoresistance. Polydatin functions through the TUG1/Akt axis, whereas tetrandrine simultaneously engages MAPK, PTEN, and Wnt signaling cascades. At the nuclear effector level, echinatin blocks Wnt/β-catenin signaling, leading to downregulation of genes involved in proliferation and survival. At the drug efflux level, tetrandrine reduces P-glycoprotein expression via inhibition of the NF-κB pathway, thereby diminishing the extrusion of chemotherapeutic agents from tumor cells-a direct and pivotal mechanism for reversing multidrug resistance. Given the extensive interconnections among these pathways-for instance, the IL-6/JAK2/STAT3 axis can upregulate P-glycoprotein, and Akt signaling exhibits cross-talk with the Wnt/β-catenin cascade-the multi-tiered architecture of this network implies that these natural products restore chemosensitivity in osteosarcoma through concurrent modulation of multiple resistance-related nodes, yielding integrated effects that surpass those achievable by single-target agents.

Figure 3.

Application of NPs against therapeutic resistance in OS

7. Conclusion and Prospect

To summarize, NPs can effectively counteract the lung metastasis of OS cells and overcome drug resistance. More specifically, NPs, such as polyphenols, alkaloids, and terpenoids, can modulate intercellular interactions within the TME, regulate the OS cell cycle, and induce apoptosis through modulation of various signaling pathways, including JAK/STAT, TGF-β, PI3K/AKT, and Wnt/β-catenin.

While NPs have significant promise, it is essential to acknowledge their inherent limits. The inclusion of some NPs may lead to organ toxicity. For example, toosendanin exhibits specific toxicity against liver cells. Furthermore, unaltered NPs often show the drawbacks of limited water solubility and reduced bioavailability. To enhance the accessibility of NPs, it is essential to conduct drug design techniques such as delivery systems and skeleton modification in the future.

Appendix.

Abbreviations

OS

Osteosarcoma

NPs

Natural products

TME

Tumor microenvironment

JAK

Janus-associated kinase

STAT

Signal transducer and activator of transcription

TGF-β

Transforming growth factor-beta

PI3K

Phosphatidylinositol-3-kinase

AKT

Protein kinase B

m6A

N6-methyladenine

METTL14

Methyltransferase-like 14

FTO

Fat mass and obesity-associated

ncRNAs

Non-coding RNAs

MiRNAs

MicroRNAs

LncRNAs

Long ncRNAs

CircRNAs

Circular RNAs

TAMs

Tumor-associated macrophages

MSCs

Mesenchymal stem cells

MDSCs

Myeloid-derived suppressor cells

Tan

Tanshinone

COS

Costunolide

EGCG

Epigallocatechin gallate

ERK

Extracellular signal-regulated kinase

SK

Shikonin

ROS

Reactive oxygen species

Dox

Doxorubicin

Skp2

S-phase associated kinase protein 2

CDK

Cyclin-dependent kinases

CKI

CDK inhibitors

RPS

Paridis saponins

VM

Vasculogenic mimicry

MMPs

Matrix metalloproteinases

Smad

Suppressor of mother against decapentaplegic

TRAIL

Tumor necrosis factor-related apoptosis-inducing ligand

CA

Chrysanthemulide A

DR

Death receptor

NGR1

Notoginsenoside R1

PN

Panax notoginseng

AS

Astragaloside

CGA

Chlorogenic acid

MAPK

Mitogen-activated protein kinase

PD

Polydatin

Ecn

Echinatin

TET

Tetrandrine

PTEN

Phosphatase and tensin homolog deleted on chromosome 10.

ORCID iDs

Chenxu Jia https://orcid.org/0009-0002-0219-9319

Qingtao Meng https://orcid.org/0000-0002-7440-1283