Research progress on the signaling pathway mechanism of terpenoids against breast cancer

Abstract

Breast cancer is the most common malignant tumor in women worldwide. Current treatments include chemotherapy, hormone therapy, radiotherapy and surgery. Terpenoids have great anti-cancer potential due to their anti-inflammatory, antioxidant, anti-tumor, antiviral and other biological activities. They have become the central drug for the prevention and treatment of breast cancer. However, their low bioavailability and stability are urgent issues that need to be addressed. This article aims to sort out the mechanism of action of terpenoids in the treatment of breast cancer. By reviewing different signal transduction pathways, it is hoped that new ideas for the joint action of multiple pathways and multiple targets will be provided, and a theoretical basis will be provided for improving basic research and clinical treatment of breast cancer.

Breast cancer is the fifth leading cause of cancer deaths worldwide. In the global cancer data analysis in 2020, female breast cancer has become the main cause of morbidity, with an estimated 2.3 million new cases, accounting for 11.7% of all cancer cases [1]. According to the expression of tumor molecular markers, breast cancer can be classified into three subtypes: estrogen receptor/progesterone receptor positive breast cancer, human epidermal growth factor receptor 2 positive breast cancer, and triple-negative breast cancer [2]. Breast cancer is highly heterogeneous, with high incidences of drug resistance, recurrence, and metastasis. Surgery, radiotherapy, chemotherapy, immunotherapy, and endocrine therapy are the main treatment methods for breast cancer at present. However, these treatment methods have certain side effects and limitations [2, 3]. Therefore, it is very necessary to find safe and effective drugs, and the research on terpenoid-derived anticancer agents is an important focus in improving cancer treatment.

Terpenoids are an important group of secondary metabolites in plants and have various structures. They are usually classified into subclasses based on their structures, including monoterpenoids, sesquiterpenoids, diterpenoids, triterpenoids, tetraterpenoids, and polyterpenoids. Terpenoids have antitumor, anti-inflammatory, antibacterial, antioxidant, antiviral, and immunomodulatory effects, etc. [4, 5]. Some studies have demonstrated that terpenoids have great potential in the prevention and treatment of breast cancer. Bishayee et al. [6] studied the potential role of plant-derived triterpenoids and their derivatives in the chemoprevention and treatment of breast tumors and introduced the related molecular mechanisms. Yang et al. [7] emphasized that natural terpenoids can inhibit a variety of cancer-specific targets and induce tumor cell apoptosis. Chen et al. [8] found that the sesquiterpenoid obtained from Aquilaria sinensis has obvious anticancer effects on human breast cancer cells, and it can exert anticancer activity by regulating ROS-induced apoptosis. Therefore, this article elaborates on the mechanism of action and related signal transduction pathways of natural terpenoids against breast cancer. Through the study of pathways and targets, it is expected to discover new drug action methods, optimize delivery systems and develop new derivatives, providing a theoretical basis and new direction for the research, development, treatment and clinical application of breast cancer in the clinic.

Structure and classification of terpenoids

Terpenoids are composed of isoprene units (C5H8)n and are usually classified based on the number of carbons in the skeleton structure, which can be divided into types such as monoterpenes, sesquiterpenes, diterpenes, triterpenes, and tetraterpenes. Common terpenoids include curcumol, artemisinin, oridonin, maslinic acid, triptolide, lycopene, betulinic acid, ursolic acid, forskolin, etc. [4].

Research on the mechanism of action of terpenoids against breast cancer

In recent years, studies have found that terpenoids exert inhibitory effects on breast cancer through multiple signal transduction pathways.This article summarizes the various signaling pathways by which terpenoids inhibit the occurrence and development of breast cancer (Fig. 1), providing an important theoretical basis for further developing specific drugs for breast cancer treatment and researching new treatment methods.We first introduce representative terpenoid compounds and the mechanisms of action of terpenoids in different signal transduction pathways, as shown in Tables 1 and 2.

Fig. 1.

Terpenoid-related signal transduction pathways

Table 1.

Sources and chemical structures of 34 representative terpenoids with anticancer activity

Category	Compound	Source	Structure
Monoterpene	Paeoniflorin	Peony
	Limonene	Lemon
	Cantharidin	Southern cantharides 、 yellow and black cantharides
	Carvacrol	Thyme oil, oregano oil and other essential oils
	Thymol	Thyme
Sesquiterpene	Artemisinin	Sweet wormwood
	Curcumol	Zedoary turmeric
	Elemene	Zedoary turmeric
	Helenalin	Not herbivorous
	Alismoxide	Rhizoma alismatidis
	Costunolide	costus
	Germacrone	Zedoary turmeric
Diterpene	Oridonin	Rabdosia rubescens
	Glaucocalyxin A	Caryophyllum
	Triptolide	Thunder God vine
	Andrographolide	Andrographis andrographis
	Eriocalyxin B	Trichocalyx fragrant tea
	Forskolin	Monkey scabbard flower
	Carnosol	Rosemary
	Tanshinones	Salvia miltiorrhiza
	Betulinic acid	Astragalus, Paeony, Birch bark
Triterpene	Hederagenin	Clematis, intermittent
	Saikosaponin	Bupleurum
	Ginsenoside	Ginseng
	Ursolic acid	Fructus ligustris, summer withered grass
	Lupeol	Lupine, geese are not herbivorous
	Celastrol	Thunder God vine
	Alisol	Rhizoma alismatidis
	Maslinic acid	Hawthorn
	Ganoderic acid	Reishi
	Pachymic acid	Tuckahoe
	Asiatic acid	Centella
	Corosolic acid	Loquat, crape Myrtle
Tetriterpene	Lycopene	Tomato, carrot

Table 2.

Terpenoids in different signal transduction pathways and their mechanisms of action

Signaling pathways	Terpenoids	Cell lines	Mechanisms	Refs
PI3K/Akt/mTOR signaling pathway	Paeoniflorin	MDA-MB-231	Modulating the PI3K/Akt signaling pathway inhibits HIF-1α expression and prevents hypoxia-induced EMT in breast cancer cells	[9]
	Cantharidin	MDA-MB-231 MDA-MB-468	Downregulate PI3K subunits, inhibit the phosphorylation of AKT and mTOR, and enhance the inhibitory effect of AG1478 on AKT and mTOR phosphorylation	[10]
	Tanshinone IIA	MCF-7	Reduces levels of activated PI3K (p-PI3K), Akt (p-Akt), and mTOR (pmTOR), inducing cell cycle arrest and autophagy	[11]
	Oridonin	4T1	Reduces levels of activated PI3K (p-PI3K), Akt (p-Akt), and mTOR (pmTOR), inducing cell cycle arrest and autophagy	[12]
	Andrographolide	MCF-7 MDA-MB-231	Down-regulates the expression of ERα, PI3K and mTOR, and inhibits the proliferation of MCF-7 cells	[13]
	Pristimerin	SK-BR-3	Decreases fatty acid synthase and modulates Akt、MAPKs and mTOR signaling pathways, affecting metastasis and apoptosis	[14]
	Ginsenoside Rg5	MCF-7	Significantly reduced phosphorylation of PI3K, Akt and mTOR, inhibiting PI3K/Akt/mTOR pathway	[15]
	Celastrol	MDA-MB-231	Effectively reduces PI3 K110α/85α enzyme activity, Akt phosphorylation	[16]
MAPK/ERK signaling pathway	Paeoniflorin	MCF-7	The expression of Ki67, PCNA and MMP-9 was decreased, and the expression of p-p38 and HSP27 was increased, which may inhibit the proliferation, metastasis and invasion of breast cancer cells by inhibiting p38MAPK signal pathway	[17]
	Cantharidin	MDA-MB-231 MDA-MB-468	Significantly down-regulated phosphorylation of MEK and ERK, key proteins of MAPK signaling pathway, and inhibited nuclear accumulation of p-ERK in MDA-MB-231 and MDA-MB-468 cells	[10]
	Germacrone	MDA-MB-231	Inhibition of NF-κB and MAPK signaling pathways by direct inhibition of IκBα, P38 and ERK phosphorylation during osteoclast formation	[18]
	Tanshinone IIA	MCF-7	Decreased phosphorylated cRaf, MEK and Erk1/2 levels in a concentration-dependent manner, significantly reduced the amount of active gtp bound Ras, without affecting total Ras protein levels	[11]
	20(S)-Protopanaxadiol	MDA-MB-231SUM-159	Inhibits metastasis of triple-negative breast cancer by inhibiting EGFR-mediated activation of MAPK signaling pathway, thereby modulating MMPs/TIMPs balance and reversing EMT	[19]
	Pristimerin	SK-BR-3	Induced changes in HER2 and FASN expression alter Akt and mitogen-activated protein kinase (MAPK) phosphorylation levels (Erk1/2, p38 and c-Jun N-terminal kinase (JNK)	[14]
	Ganoderma lucidum	MCF-7	Down-regulation of MAPK signaling inhibits oxidative stress-induced MCF-7 cell migration, inhibits oxidative stress-stimulated extracellular signal-regulated protein kinase (Erk1/2) phosphorylation, and inhibits transcription factors AP-1 and NF-kappaB	[20]
Bax/Bcl-2/Caspase-3 signaling pathway	Thymol	MCF-7	The increased expression of BAX and CASP8 gene inhibited cell proliferation by activating apoptosis pathway	[21]
	Germacrone	MCF-7 MDA-MB-231	Inhibition of proliferation of breast cancer cell lines by induction of cell cycle arrest and apoptosis via mitochondrial mediated caspase pathway	[22]
	Artemisinin	T-47D	Significantly increases caspase-8 protein expression, cleaves caspase-9, activates Bid and induces cytochrome c release from mitochondria into the cytosol; inhibits MCF-7 breast cancer cell growth by inducing apoptosis through intrinsic and extrinsic caspase dependent pathways	[23, 24]
	Andrographolide	MCF-7 MDA-MB-231	Apoptosis is induced by inhibiting Bcl-2 and enhancing Bax expression at mRNA and protein levels	[13]
	Eriocalyxin B	MDA-MB-231	Apoptosis of cancer cells induced by inhibition of NF-κ Bp65 and STAT3 phosphorylation, increase of Bax/Bcl-2 ratio and activation of caspase-3	[25]
	Celastrol	MDA-MB-231	It caused the decrease of mitochondrial membrane potential, down-regulation of Bcl-2 expression, up-regulation of Bax expression, and enhanced activation of caspase-3 and PARP cleavage	[16]
	Hederagenin	MCF-7	Bax increased, Bcl-2 decreased, Caspase-9 and Caspase-3 were activated and cytochrome C was released in breast cancer cells	[26]
	Pachymic acid	MDA-MB-231	down-regulation of Bcl-2, up-regulation of Bax expression, and promotion of cytochrome C release and activation of lytic Caspase-3, 9 and Caspase-8 via mitochondrial and death receptor-mediated signaling pathways	[27]
	Lycopene	MDA-MB-231	Inhibition of Bcl-2, Ki-67, VEGF, IL-1β and TNF-α protein levels enhances apoptosis and reduces inflammation	[28]
NF-κB/EMT signaling pathway	Paeoniflorin	MDA-MB-231	Prevention of Hypoxia-Induced EMT in Breast Cancer Cells by Modulation of the PI 3 K/Akt/HIF-1α Axis	[9]
	Germacrone	MDA-MB-231	Inhibition of NF-κB and MAPK signaling pathways by direct inhibition of IκBα, P38 and ERK phosphorylation during osteoclast formation	[18]
	Lycopene	MDA-MB-231	Recombinant IκB kinase beta (IKKβ) kinase activity is inhibited, NF-κB response gene regulation is reduced	[29]
Autophagy pathway	Artemisinin	MCF-7 4T1 MDA-MB-231	Regulation of PHB2 and PINK1 expression, inhibition of tumor cell proliferation through mitochondrial autophagy, increase of tumor growth inhibition rate	[30]
	β-elemene	Bcap37 MBA-MD-231	Transforming LC3-I into LC3-II and inducing autophagy lysosome formation, activating autophagy	[31]
	Oridonin	+ SA CL-S1	Significantly enhanced the expression of autophagic cell markers, including the conversion of LC3B-I to LC3B-II, beclin-1, Atg3, Atg7, Atg5-Atg12, LAMP-1, and cathepsin-D	[32]
	Carnosol	MDA-MB-231	ROS-dependent induced endoplasmic reticulum stress contributes to ROS-induced apoptosis and autophagy in breast cancer cells	[33]
	Saikosaponin D	MDA-MB-231	Inhibits the formation of autophagosomes by inhibiting the fusion of autophagosomes with lysosomes, inducing cell apoptosis and blocking autophagic degradation	[34]
	Ginsenoside Rg3	MCF-7 MDA-MB-231	Inhibits CoCl2-induced spheroid formation and cell viability of breast cancer cells and promotes apoptosis by inhibiting lysosomal degradation of autophagosomal contents in CoCl2-induced autophagy	[35]
Wnt/β-catenin signaling pathway	Triptolide	BT-474 MCF-7 MDA-MB-231	The expression of β-catenin is significantly reduced, inducing breast cancer cell apoptosis through a mechanism related to the Wnt/β-catenin signaling pathway	[36]
	Andrographolide	4 T-1 HCC1806 MDA-MB-231	Inhibitory effect on triple-negative breast cancer by regulating macrophage polarization and function through Wnt5a signaling pathway	[37]
	Saikosaponin D	HCC1937	Inhibits Wnt/β-catenin signaling and inhibits β-catenin and its downstream target genes, leading to apoptosis of triple-negative breast cancer cells	[38]
	Ursolic acid	T-47D MCF-7 MDA-MB-231	Significantly reduced expression of oncogenic miR-499a-5p targets breast cancer stem cells via Wnt	[39]
Notchsignaling pathway	Paeoniflorin	MCF-7	The expression levels of Notch-1 and HES-1 mRNA and protein were reduced, inhibiting the proliferation and invasion of breast cancer cells	[40]
	Artemisinin	MDA-MB-231	Down-regulate the expression of Notch signaling pathway-related factors Notch1, Dll4 and Jagged1, and reduce the levels of VEGF and HIF-1α	[41]
	Oridonin	4T1	Significantly reduces the expression of Notch1-4 protein	[42]
	Celastrol	BT20 MDA-MB-231	Reduced Notch-1 activation and expression of its downstream target proteins HES-1 and HEY-1	[43]
	Triptolide	BT20 MDA-MB-231	Reduced Notch-1 activation and expression of its downstream target proteins HES-1 and HEY-1	[43]
	Ginsenoside Rg3	FM3A	Inhibits STAT3 and NOTCH signaling pathways to inhibit myeloid suppressor cells (MDSC) and exert anti-cancer effects	[44]
JAK/STAT signaling pathway	Ginsenoside Rh4	EMT-6	Induces apoptosis of breast cancer cells through the histone deacetylase 2 (HDAC2)-mediated Caspase pathway and inhibits the HDAC2-mediated JAK/STAT pathway to regulate the immune microenvironment	[45]
	Ganoderic acid A	MDA-MB-231	Directly inhibits JAK2 phosphorylation and downstream activation of STAT3, suppresses STAT3 target gene expression, and leads to increased levels of proteins associated with mitochondrial apoptosis	[46]
	Corosolic acid	MCF-7 MDA-MB-231	Inhibits the JAK/STAT signaling pathway by reducing the expression of phosphorylated forms of JAK2 and STAT3 proteins	[47]
Other mechanisms	Cantharidin	MCF-7 MDA-MB-231	Decreased extracellular acidification rate (ECAR) of highly metastatic cells, increased oxygen consumption rate (OCR), inhibited aerobic glycolysis; inhibited PKM2 nuclear translocation and disrupted GLUT1/PKM2 glycolytic loop, converted aerobic glycolysis to oxidation, reversed breast cancer metastasis	[48]
	Carvacro	MDA-MB-231	Destroy the stability of MDA-MB-231 cells in acidic tumor microenvironment and regulate apoptosis	[49]
	Artemisinin	MCF-7	Drug delivery systems can reach deep into solid tumors, producing large amounts of ROS and inducing DNA damage	[50]
	Elemene	4T1	It can effectively scavenge reactive oxygen species (ROS) in vivo and in vitro, reduce the stability of hypoxia-inducible factor-1 α(HIF-1α), reduce angiogenesis in tumor microenvironment, reduce the level of NLRP3 inflammatory bodies and IL-1β production	[51]
	Oridonin	MCF-7 MDA-MB-231	Augmentation of RSL3-induced iron death in breast cancer cells by activation of JNK/Nrf2/HO-1 axis; enhancement of antitumor effects and reduction of adverse cardiotoxic effects of doxorubicin by activation of apoptosis and inhibition of angiogenesis at tumor sites	[52, 53]
	Triptolide	MCF-7 MDA-MB-231	Targeting CD44 molecule, inhibiting cell proliferation, blocking cell cycle, inhibiting cell migration and invasion, and showing higher efficacy in reducing tumor size and blocking lung metastasis in mouse models	[54]
	Andrographolide	4T1 MCF-7 MDA-MB-231	Elimination of tumor stem cells in triple negative breast cancer by down-regulating NF-κB-thoc1 axis; inhibition of angiogenesis via VEGF pathway by inhibiting cox-2 expression	[55, 56]
	Eriocalyxin B	4T1 MDA-MB-231	Inhibits breast cancer cell migration, inhibits adhesion to extracellular matrix proteins, and reduces ALDH1A1 expression and colony formation in cancer stem cell-enriched MDA-MB-231 cells	[57]
	Forskolin	MCF-7 MDA-MB-231	Efficient reprogramming/differentiation of cancer stem cells	[58]
	桦木酸	MDA-MB-231	Inhibit tumor cell activity and migration ability, inhibit osteoclast differentiation induced by tumor cells, inhibit breast cancer bone metastasis	[59]
	Ginsenoside Rg3	MCF-7 MDA-MB-231	Reduces the expression of stem cell-associated transcription factors, including c-Myc, Oct4, Sox2, and Lin28, inhibiting breast cancer stem cell-like properties	[60]
	Ursolic acid	MCF-7 MDA-MB-231	Induce a decrease in the expression of stem cell biomarkers, including Nanog and Oct4 genes, reducing the level of epithelial-to-mesenchymal transition (EMT)	[61]
	Celastrol	MDA-MB-231	Down-regulation of DEGS1, CD146, S1PR1 -3 expression and S1P production inhibits angiogenesis and biological processes of breast cancer cells through DEGS1/S1P signaling pathway	[62]
	Ganoderic acid DM	MCF-7 MDA-MB-231	Significantly decreased CDK2, CDK6, p-Rb and c-Myc protein levels, induced DNA fragmentation and PARP cleavage, decreased mitochondrial membrane potential in MCF-7 cells	[63]
	Asiatic acid	4T1	Significantly inhibit HUVEC proliferation, migration and duct formation in vitro, significantly reduce tumor microvessel density and vascular permeability in vivo, inhibit breast cancer through VEGF/VEGFR2 signaling axis	[64]
	Lycopene	MCF-7	Significantly induces apoptotic processes and cell cycle arrest in MCF-7 tumor cell line; provides antioxidant defense and has potent chemopreventive effects against breast cancer	[65, 66]

Inhibition of the PI3K/Akt/mTOR signaling pathway

The PI3K/Akt/mTOR signaling pathway is an important intracellular signal transduction pathway. Natural products and bioactive components are becoming new inhibitors of the PI3K signal, and have become emerging anticancer drugs by interfering with the development and progression of breast cancer at various stages [67, 68].

Paeoniflorin, a monoterpene glycoside extracted from the roots of Paeonia lactiflora, has been shown to prevent the expression of phosphorylated PI3K and Akt in hypoxic-induced triple-negative breast cancer cells [9]. The monoterpene compound cantharidin can also inhibit the proliferation of triple-negative breast cancer cells by targeting EGFR. The mechanism study shows that cantharidin can exert its effect by blocking the downstream PI3K/AKT/mTOR signaling pathway. In addition, sodium cantharidate, a derivative of cantharidin obtained by the reaction of cantharidin with alkali, can promote apoptosis of breast cancer cells by inhibiting the PI3K-Akt-mTOR pathway and inducing autophagy [10, 69].

The diterpenoid compound tanshinone IIA can inhibit the activation of the PI3K/Akt/mTOR pathway and induce cell cycle arrest and autophagy in breast cancer cells [11]. Oridonin can also affect the PI3K/Akt/mTOR signaling pathway by inhibiting the biosynthesis of valine, leucine, etc. Oridonin has strong antitumor activity both in vitro and in vivo, and is likely to be an adjuvant drug in breast cancer treatment regimens [12]. Andrographolide inhibits the proliferation of breast cancer cells by down-regulating the expression levels of ERα, PI3K and mTOR, and inhibits the proliferation of MDA-MB-231 breast cancer cells by inducing apoptosis [13].

Methyl pristimerin, a natural triterpene compound, has multiple pharmacological activities such as immunosuppression, anti-inflammation and pro-apoptosis. Studies have shown that it can affect the apoptosis of HER2-positive breast cancer cells by regulating the Akt, MAPK and mTOR signaling pathways [14].

Ginsenoside Rg5, as a potential breast cancer treatment drug, can also reduce the phosphorylation levels of PI3K, Akt, mTOR and Bad in breast cancer, and inhibit the PI3K/Akt signaling pathway [15]. Celastrol also regulates signal transduction through the PI3K/Akt/mTOR axis to exert anti-breast cancer effects. Experiments have shown that the PI3K/Akt/mTOR inhibitor PF-04691502 and the mTOR inhibitor rapamycin can enhance the effect of celastrol-induced apoptosis of triple-negative breast cancer cells [16].

Inhibition of the MAPK/ERK signaling pathway

The MAPK signaling pathway is involved in various tumor biological pathways, such as metabolic reprogramming, cell proliferation, metastasis and invasion. The MAPK signaling pathway mainly includes multiple pathways such as ERK1/2, JNK, P38 and ERK5, among which the ERK-related pathway is the classic MAPK signaling pathway [70]. Mutations in key molecules involved in MAPK/ERK signal transduction and dysregulation of this pathway are very common events in various human malignancies [71].

Studies have shown that the monoterpene paeoniflorin reduces the expression levels of Ki67, proliferating cell nuclear antigen (PCNA), matrix metalloproteinase 9 (MMP-9), etc. in breast cancer cells, and increases p-p38 and heat shock protein 27 (HSP27), suggesting that paeoniflorin may inhibit the proliferation, metastasis and invasion of breast cancer cells by inhibiting the MAPK signaling pathway and regulating related proteins [17]. In addition, cantharidin may also become a potential candidate drug for the treatment of triple-negative breast cancer by blocking the downstream PI3K/AKT/mTOR and ERK/MAPK signaling pathways through miR-607-mediated EGFR downregulation [10].

Bone is one of the most common metastatic sites for breast cancer patients. The sesquiterpene compound germacrone can inhibit osteoclastogenesis by inhibiting the MAPK/NF-κB signaling pathway. Germacrone can also inhibit the proliferation, migration and invasion of triple-negative breast cancer MDA-MB-231 cells, inhibit osteoclastogenesis induced by breast cancer cells in vitro, and alleviate breast cancer-related osteolysis in a mouse model of breast cancer bone metastasis [18]. The diterpenoid tanshinone IIA can inhibit total protein kinase C (PKC) activity and selectively inhibit the expression of cytoplasmic and plasma membrane PKC subtypes. Tanshinone IIA exerts antitumor efficacy by inhibiting the Ras/MAPK pathway closely regulated by the PKC signal and synergistically enhancing the effect of Hsp90 inhibitors in human breast cancer cells [11].

20(S)-Protopanaxadiol (PPD), a triterpene, is one of the main active metabolites of ginseng and has pleiotropic anticancer effects in various cancers. In TNBC xenograft and syngeneic models, PPD treatment significantly reduces tumor growth and lung metastasis, reverses epithelial-mesenchymal transition (EMT), and reduces the expression and activity of matrix metalloproteinases (MMPs). PPD has the potential to treat breast cancer metastasis by targeting the EGFR-mediated MAPK pathway [19]. Methyl pristimerin, a triterpene compound, can also change the phosphorylation levels of Akt and MAPK and serve as a chemotherapy drug for HER2-positive breast cancer [14]. Ganoderma lucidum extract inhibits the migration of MCF-7 cells induced by oxidative stress by down-regulating the MAPK signal. It not only inhibits the invasive behavior of oxidative stress-induced breast cancer cells by regulating the Erk1/2 signal, but also can play a role as an antioxidant in adjuvant cancer treatment [20].

Regulation of the Bax/Bcl-2/Caspase-3 signaling pathway

Apoptosis is a process strictly controlled by multiple genes and is closely related to the Bcl family, Caspase family, etc. Among them, Bax, Bcl-2 and Caspase-3 are key regulators of apoptosis in breast cancer cells [72, 73]. Terpenoids can regulate the expression of these factors and promote the apoptosis of breast cancer cells [21].

The toxicity of monoterpene compound thymol-modified iron oxide nanoparticles to breast cancer cells is greater than that to normal human cells. After treatment, the expression of BAX and CASP8 genes in the cells increased significantly [21]. The sesquiterpene compound germacrone was found to induce the cleavage of Caspase-3, 7, 9 and PARP when treating breast cancer cells. The conclusion drawn from the experiment is that germacrone induces cell cycle arrest and apoptosis through the mitochondrial-mediated Caspase pathway, thereby inhibiting the proliferation of breast cancer cell lines [22]. The combination treatment of metformin and artemisinin-loaded PLGA-PEG NPs can lead to a significant down-regulation of Bcl-2 and cyclin D1 in cells, while up-regulation of caspase-3, caspase-7 and Bax. It indicates that the combination of metformin and artemisinin-loaded PLGA-PEG NPs in the treatment of breast cancer can significantly improve the therapeutic effect [74].

The diterpenoid andrographolide induces apoptosis in both MCF-7 and MDA-MB-231 cells by inhibiting Bcl-2 and enhancing Bax expression at the mRNA and protein levels [13]. Eriocalyxin B, a diterpenoid compound extracted from Rabdosia eriocalyx, induces apoptosis of triple-negative breast cancer cells by inhibiting STAT3 phosphorylation, increasing the Bax/Bcl-2 ratio and activating Caspase-3 [25].

The triterpene celastrol can cause a decrease in mitochondrial membrane potential, down-regulation of Bcl-2 expression, up-regulation of Bax expression, and generation of reactive oxygen species [16]. Studies have shown that platelet membrane vesicles as shells encapsulating multiple highly efficient drug-loaded nanonuclei can target tumor sites and significantly improve antitumor activity. Using a platelet membrane camouflaged nanoplatform carrying hederagenin, it was found that the pro-apoptotic factor Bax in breast cancer cells increased, the anti-apoptotic molecule Bcl-2 decreased, and Caspase-9 and Caspase-3 were also activated, and cytochrome C was released [26]. In addition, pachymic acid can down-regulate the apoptotic regulator Bcl-2 of triple-negative breast cancer cells, increase the expression of the pro-apoptotic protein Bax, and promote the release of cytochrome C and the activation of cleaved Caspase-3, 9 and Caspase -8 through mitochondrial-mediated and death receptor-mediated signaling pathways [27].

The tetraterpene lycopene is the strongest antioxidant among carotenoids. In a rat model of breast cancer, lycopene inhibits tumor growth by increasing the levels of apoptotic proteins Bax and Caspase-3 and Caspase-9, while reducing the level of Bcl-2 [75]. The combination of sorafenib and lycopene also shows inhibition of Bcl-2, Ki-67, VEGF, IL-1βand TNF-αprotein levels. In addition, the number of Bax, P53 and Caspase 3 proteins increases. The combined treatment of sorafenib and lycopene enhances apoptosis and reduces tumor weight and volume [28].

Inhibition of the NF-κB/EMT signaling pathway

The activation of the NF-κB signaling pathway is closely related to the invasion and metastasis of breast cancer, and epithelial-mesenchymal transition (EMT) is an important process of breast cancer cell metastasis. The initiation of EMT endows cancer cells with the ability to migrate and invade [76].

Research shows that under hypoxic conditions, the expression levels of EMT markers E-cadherin, N-cadherin, and vimentin in breast cancer cells significantly decrease, while the application of paeoniflorin can partially restore the levels of these proteins. The monoterpenoid compound paeoniflorin can prevent hypoxia-induced EMT in breast cancer cells by regulating the PI3K/Akt/HIF-1αaxis [9]. The sesquiterpenoid germacron inhibits the NF-κB signaling pathway by directly inhibiting the phosphorylation of IκBα, P38, and ERK during osteoclastogenesis [18]. The anticancer properties of lycopene may also be achieved by inhibiting the NF-κB signaling pathway. Lycopene can inhibit NF-κB in triple-negative breast cancer cells and reduce cell viability [29].

Inhibition of cell autophagy pathways

Autophagy, a catabolic process, is upregulated in many cancers. Both cell-autonomous autophagy (also known as tumor autophagy) and non-cell-autonomous autophagy (also known as host autophagy) support tumorigenesis through different mechanisms, and targeting autophagy may be a new strategy for cancer treatment [77].

Mitochondrial autophagy is one of the important anti-tumor mechanisms of the sesquiterpene compound artemisinin (Artemisinin). However, the lack of specific tumor-targeting ability limits its anti-tumor activity. Studies have synthesized GSH-sensitive artesunate intelligent conjugates (TPP-SS-ATS) and further prepared liposomes targeting tumor cells and mitochondria (TPP-SS-ATS-LS). It can inhibit tumor cell proliferation and increase the tumor growth inhibition rate by regulating the expression of PHB2 and PINK1 through mitochondrial autophagy [30]. In addition, β-elemene can convert LC3-I into LC3-II and induce the formation of autophagic lysosomes to activate autophagy. In human breast cancer cells, β-elemene induces not only apoptosis but also cell-protective autophagy. Inhibition of autophagy significantly enhances the cytotoxicity of β-elemene to human breast cancer cells [31].

γ-Tocotrienol and the diterpene oridonin are natural plant compounds with anticancer activity. Studies have shown that combined treatment with low-dose γ-tocotrienol and oridonin can synergistically inhibit breast cancer cells. This combination significantly enhances the expression of autophagy cell markers, including the conversion of LC3B-I to LC3B-II, beclin-1, Atg 3, Atg 7, Atg 5-Atg 12, LAMP-1, and cathepsin-D. Pretreatment with the autophagy inhibitor 3-methyladenine (3-MA) or Baf 1 can block these effects [32]. Breast cancer cells treated with the diterpene salvianol show an enlarged endoplasmic reticulum and characteristics of ER stress. The research results indicate that ROS-dependent induction of endoplasmic reticulum stress contributes to salvianol-induced apoptosis and autophagic cell death in breast cancer cells [33].

Studies have shown that the triterpenoid saikosaponin D inhibits the formation of autophagosomes by inhibiting the fusion of autophagosomes with lysosomes rather than by disrupting lysosomal function. In addition, blocking autophagic degradation is not related to its mediated apoptosis of breast cancer cells. Gene knockdown of autophagy-related protein 5 significantly reduces LC3B-II accumulation mediated by saikosaponin D but does not affect p38 phosphorylation, PARP cleavage, or apoptosis mediated by saikosaponin D. In conclusion, saikosaponin D may induce apoptosis and block autophagic degradation [34]. Ginsenoside Rg 3, the main active component of red ginseng, has anti-tumor effects. Studies have also shown that ginsenoside Rg 3 can inhibit CoCl2-induced breast cancer cell spheroid formation and cell viability, promote apoptosis by inhibiting the lysosomal degradation of autophagosome contents in CoCl 2-induced autophagy, and induce apoptosis and inhibit cell proliferation and autophagy in in vivo xenograft models [35].

Inhibition of the Wnt/β-catenin signaling pathway

The Wnt/β-catenin pathway regulates cell proliferation, migration, apoptosis, differentiation, and stem cell self-renewal [78, 79].

After treatment with the diterpene triptolide on breast cancer MDA-MB-231, BT-474, and MCF7 cells, the expression of β-catenin significantly decreased, indicating that triptolide induces apoptosis in breast cancer cells through a mechanism related to the Wnt/β-catenin signaling pathway [36]. In addition, the regulation of the diterpene andrographolide on M2-type macrophages is particularly related to the Wnt5a/β-catenin pathway. Andrographolide can regulate the polarization and function of macrophages through the Wnt5a signaling pathway and exert an inhibitory effect on triple-negative breast cancer [37]. The triterpene saikosaponin D can significantly inhibit Wnt/β-catenin signal transduction and β-catenin and its downstream target genes, leading to apoptosis of triple-negative breast cancer cells [38].

Ursolic acid is a pentacyclic triterpene compound that can inhibit EMT through the Wnt/β-catenin signaling transduction and is highly effective against breast cancer stem cells. Ursolic acid can also initiate the extracellular Wnt antagonist sFRP4, inhibit Wnt activity, and disrupt target genes related to drug resistance and self-renewal [39].

Inhibition of the notch signaling pathway

The action of the monoterpene paeoniflorin on MCF-7 cells showed decreased expression levels of NOTCH-1 and HES-1 mRNA. Moreover, the protein levels of NOTCH-1 and HES-1 presented a similar trend to the mRNA levels. The results indicate that paeoniflorin may inhibit the proliferation and invasion of breast cancer cells by inhibiting the NOTCH-1 signaling pathway [40]. The action of the sesquiterpene artemisinin on nude mouse models can downregulate the expression of Notch signaling pathway-related factors Notch1, Dll4, and Jagged1 and reduce the contents of angiogenesis-related factors VEGF and hypoxia-inducible factor HIF-1α in the serum, thereby inhibiting tumor development [41].

The treatment with the diterpene oridonin not only inhibits the migration and invasion of breast cancer cells but also significantly reduces the expression of Notch1-4 proteins. This indicates that it is likely to increase the apoptosis of breast cancer cells by inhibiting the Notch signaling pathway [42]. Both the terpenoid compound celastrol and triptolide reduce the activation of Notch -1 and the expression of its downstream target proteins HES-1 and HEY-1 in triple-negative breast cancer cells [43]. The triterpenoid ginsenoside Rg3 can effectively inhibit breast cancer progression. Mechanistic studies have shown that the inhibitory effect of ginsenoside Rg3 on myeloid-derived suppressor cells (MDSC) and the corresponding cancer progression in breast cancer cells depends on the inhibition of the STAT3-dependent pathway, tumor-derived cytokines, and the NOTCH signaling pathway [44].

Inhibition of the JAK/STAT signaling pathway

The triterpenoid compound ginsenoside Rh4 can significantly inhibit the proliferation of breast cancer cells, induce apoptosis of breast cancer cells through the Caspase pathway mediated by histone deacetylase 2 (HDAC2), and inhibit the JAK/STAT pathway mediated by HDAC2 to regulate the immune microenvironment, thereby inhibiting the growth of breast cancer [45]. The triterpenoid ganoderic acid A can directly inhibit JAK2 phosphorylation and downstream activation of STAT3, inhibit the expression of STAT3 target genes, and lead to an increase in the protein levels related to mitochondrial apoptosis [46]. In addition, the combined use of ganoderic acid A and JAK2/STAT3 inhibitors further reduces the viability of breast cancer cells [46]. In addition, corosolic acid can induce apoptosis of triple-negative breast cancer cells by reducing the expression of phosphorylated forms of JAK2 and STAT3 proteins and inhibiting JAK/STAT signal transduction [47].

Other mechanisms

In addition to the above-mentioned signaling pathways, terpenoid compounds may exert anti-breast cancer effects through other mechanisms such as inhibiting glycolysis, regulating the tumor microenvironment, controlling tumor angiogenesis, reducing toxic side effects, enhancing the immune system, and optimizing the delivery system [48, 50, 53, 59, 64].

The monoterpene cantharidin has significant anti-metastasis activity against breast cancer, which depends on the inhibition of aerobic glycolysis and subsequently reverses the metastasis of breast cancer [48]. The pH of most solid tumors is low, and pH-responsive drug delivery systems may provide extensive methods for tumor-targeted therapy. Carvacrol-zinc oxide quantum dots (CVC-ZnO QDs) disrupt the stability of breast cancer cells in the acidic tumor microenvironment and regulate apoptosis [49].

The sesquiterpene artemisinin can be loaded into Mn2O3 to construct the drug delivery system TKD@RBCm-Mn2O3-ART. After entering breast cancer cells, it synchronously releases Mn2 + and artemisinin, generating a large amount of ROS and inducing DNA damage. In vivo experimental results prove that TKD@RBCm-Mn2O3/ART can reach the deep part of solid tumors and achieve precise diagnosis and treatment of breast cancer [50]. Elemene injection can significantly reduce the drug resistance of paclitaxel in breast cancer. It can target and inhibit the AR/RUNX1 axis, effectively inhibit the protein expression levels of AR and RUNX1 in paclitaxel-resistant and sensitive breast cancer cell lines, and downregulate the mRNA expression levels of stem cell-like characteristic markers KLF4 and OCT4 in these cell lines [51].

Diterpenoid oridonin can enhance the inhibitory effect of RSL3 on the viability of breast cancer cells by inducing ferroptosis. Mechanistically, oridonin enhances RSL3-induced ferroptosis in breast cancer cells by activating the JNK/Nrf2/HO-1 axis [52]. In addition, oridonin can enhance the anticancer effect of doxorubicin and reduce its adverse cardiotoxic effects. It enhances the antitumor effect of doxorubicin by activating apoptosis and inhibiting angiogenesis at the tumor site and reverses doxorubicin-induced cardiotoxicity in mouse models [53]. By constructing triptolide nanoparticles (TPL/NPs), it was found that compared with free triptolide, TPL/NPs can target CD44 molecules and more effectively inhibit cell proliferation, block the cell cycle, inhibit cell migration and invasion in breast cancer cells. Moreover, in the mouse model of breast cancer, it also shows higher efficacy in shrinking tumor size and blocking lung metastasis and reducing systemic toxicity [54]. THOC1 promotes the cancer stem cell characteristics of triple-negative breast cancer, and andrographolide eliminates the tumor stem cells of triple-negative breast cancer by down-regulating the NF-κB-thoc1 axis [55]. Andrographolide has the effect of inhibiting the growth and angiogenesis of breast cancer, and its mechanism of action may be to inhibit the expression of cox-2 and angiogenesis through the VEGF pathway to inhibit breast cancer [56]. Maoeryuic acid is a diterpenoid compound that can inhibit the migration of breast cancer cells, inhibit adhesion to extracellular matrix proteins, and reduce the expression of ALDH1A1 and colony formation in cancer stem cell-enriched MDA-MB-231 cells [57]. In a single nanoformulation, co-delivery of forskolin and paclitaxel was found that forskolin can effectively reprogram/differentiate cancer stem cells, and paclitaxel can simultaneously induce cytotoxicity in differentiated cancer stem cells and bulk tumor cells [58]. The derivative of betulinic acid, SH-479, can inhibit bone metastasis of triple-negative breast cancer and the proliferation of triple-negative breast cancer cells. In addition, SH-479 can also inhibit the migration of breast cancer cells, inhibit the differentiation of osteoclasts induced by breast cancer cells, and affect the bone marrow immune microenvironment [59].

By preparing triterpenoid ginsenoside Rg3 liposomes and loading paclitaxel to establish Rg3-PTX-LPs, it was found that it can be used for drug-resistant cancer treatment by dual-targeting the tumor microenvironment and cancer cells to improve the tumor inhibition rate [80]. In addition, ginsenoside Rg3 can also reduce the expression of stem cell-related transcription factors (including c-Myc, Oct4, Sox2, and Lin28) and inhibit the stem cell-like properties of breast cancer [60]. The triterpenoid ursolic acid can induce a decrease in the expression of stem cell biomarkers, including Nanog and Oct4 genes. And it changes the invasion and migration ability by reducing the level of epithelial-mesenchymal transition (EMT) [61]. Celastrol can down-regulate the expression of DEGS1, CD146, S1PR1-3 and the production of S1P, and inhibit angiogenesis and biological processes of breast cancer MDA-MB-231 cells through the DEGS1/S1P signaling pathway [62]. Ganoderic acid DM is a triterpenoid compound isolated from Ganoderma lucidum, which can significantly reduce the protein levels of CDK2, CDK6, p-Rb and c-Myc in breast cancer MCF-7 cells, induce DNA fragmentation and PARP cleavage, and reduce the mitochondrial membrane potential in cells [63]. The triterpenoid asiatic acid can significantly inhibit angiogenesis and vascular permeability through the VEGF/VEGFR2 signaling axis, reduce the microvessel density of breast cancer tumors, thereby inhibiting the growth and metastasis of breast cancer [64].

The tetraterpenoid lycopene is a potent antioxidant and anticancer herbal bioactive substance that can improve the therapeutic effect of exemestane through synergy. This nano-enhanced oral combination therapy may pave the way for the safe and effective treatment of breast cancer [81]. Adding lycopene and melatonin to the diet can provide antioxidant defense and have a strong chemopreventive effect on breast cancer [66].

Summary and outlook

In conclusion, as natural products, terpenoids have a wide range of biological activities, low toxic side effects and strong antioxidant and anti-inflammatory effects, can slow down cancer-related malignant reactions, have good patient tolerance, and are potential drugs for the treatment of breast cancer [4, 5]. Terpenoids and their derivatives can inhibit the growth, migration and invasion of breast cancer tumor cells at multiple signaling pathways and multiple targets [9, 44, 45, 82]. Terpenoids and their derivatives can also be combined with chemotherapy and radiotherapy to enhance the effect of traditional treatment methods and reduce side effects [28].

In recent years, new treatment methods have emerged in an endless stream, but challenges still exist. The development of new terpenoid derivatives and the construction of nano-drug delivery systems have achieved initial research results and shown great potential in inhibiting breast cancer and enhancing drug efficacy. Loading terpenoids into nanoparticles and preparing targeted tumor cell liposomes can improve their bioavailability and targeting [26, 30, 74, 81, 83]. Triterpenoid derivatives with stronger antitumor activity can also be synthesized through chemical modification and structural modification [21, 84]. In addition, combining terpenoids with other natural products or drugs to form new therapeutic combinations can synergistically improve the therapeutic effect [11, 32, 81]. However, the limitations of treatment cannot be ignored. The absorption and utilization rate of many terpenoids in the body is low, limiting their clinical effect. Secondly, terpenoids have multi-target effects, but lack high targeting to specific cancer cells, which may affect normal cells. At present, most of the studies on natural plant extracts in the treatment of breast cancer are small-scale clinical trials or in vitro experiments, lacking large-scale and long-term clinical research data support. In addition, the interaction of terpenoids with other drugs may also lead to reduced drug efficacy or increased side effects.

In the future, through further research, the delivery system can be optimized, new nano-carriers, liposomes and polymer microparticles can be developed to improve the stability and bioavailability of terpenoids. The anticancer activity and selectivity of terpenoids can be enhanced by changing the structure through chemical modification. In addition, exploring the combined use of terpenoids with other anticancer drugs, immunotherapy or radiotherapy, or through different sequential administration methods, can also enhance the therapeutic effect. With the development of the study of different signal transduction pathways of terpenoids in the treatment of breast cancer and network pharmacology, the study of multi-target and multi-pathway also has theoretical and technical support.

In summary, this article systematically expounds the mechanism of action of terpenoids in inhibiting breast cancer and summarizes different signal transduction pathways, providing a theoretical basis for the multi-pathway and multi-target research of terpenoids in inhibiting breast cancer. With the progress of science and technology, it is expected to overcome the existing shortcomings and challenges and develop terpenoids and their derivatives suitable for clinical treatment, making terpenoids more effective and safe anti-breast cancer drugs.

Author contributions

Shengnan Tu wrote the manuscript, Fen Hu and Juan Zhang made the forms and pictures, Haifeng Cai and Junquan Yang proofread and reviewed the manuscript.

Funding

Wu Jieping Medical Foundation Clinical Research Special Fund (320.6750.17209).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Competing interests

The authors declare no competing interests