PERK, a type I ER-resident transmembrane protein, has dual enzymatic activity of serine/threonine protein kinase and endonuclease. When the unfolded/misfolded protein exceeds a certain amount, GRP78 detaches and binds to them, causing PERK to undergo autophosphorylation and then be activated to become p-PERK (Wang P et al., 2018). p-PERK specifically induces translation eukaryotic translation initiation factor 2α (eIF2α) phosphorylation of serine at position 51, which deprives eIF2α of its ability to initiate protein translation and reliefs ER burden (Oyadomari S et al., 2008; Rozpedek W et al., 2016). Meanwhile, p-eIF2α selectively activates the translation of ATF4 mRNA and upregulates ATF4 expression, which in turn promotes expression of CCAAT/enhancer binding protein homologous protein (CHOP) and growth arrest and DNA damage-inducible protein (GADD34), inhibiting B-cell lymphoma-2 (Bcl-2) transcription and ultimately inducing apoptosis (Hu H et al., 2019).

In the UPR signaling system, the PERK-eIF2α-ATF4 signaling pathway is the main pathway to induce CHOP expression (Liu Z et al., 2016).

Including IRE1α (expressed widely) and IRE1β (expressed mainly in gastrointestinal tract and lung), IRE1 is a conserved ER type I transmembrane protein with dual activity of protein kinase and ribonucleic acid endonuclease (Karagöz GE et al., 2017). When ERS occurs, IRE1 dissociates from GRP78 and undergoes autophosphorylation, and its ribonucleic acid endonuclease activity is activated to specifically convert X-box binding protein-1 (XBP1) mRNA into active XBP1 splicing (XBP1s). The latter one is translated by ribosomes to form the transcription factor XBP1-s with strong transcriptional activity, which is able to regulate the expression of a variety of protein folding-related genes such as foldase, oxidoreductase, and glycosylase at the level of protein transcription, and promotes endoplasmic reticulum-associated degradation kinase (ERAD) to mitigate ERS (Bartoszewska S et al., 2019). If ERS is not alleviated, IRE1 can activate c-Jun N-terminal (JNK) via tumor necrosis factor receptor associated factors 2 (TRAF2), in the presence of apoptotic signaling kinase (ASK1) signaling pathway to induce cellular autophagy (Li Y et al., 2019). In addition, XBP1, as a target of other proteins during ERS, can alleviate ERS by regulated IRE1α-dependent decay (RIDD) which causes selective degradation of ERS-related proteins (Adams CJ et al., 2019).

ATF6, consisting of the two isoforms ATF6α and ATF6β and other membrane proteins related to ATF6, is an ERS-regulated transmembrane transcription factor whose N-terminal structural domain is in the cytoplasm while the C-terminal is in the ER lumen, and acts to activate the transcription of ER molecular chaperones in order to detect the ERS. Upon ERS onset, GRP78 is dissociated from the N-terminal end of ATF6, allowing ATF6 to be packaged into COPII pericycle vesicles and transported from the ER lumen to the Golgi complex via its Golgi localization sequence. It is subsequently spliced and proteolytically hydrolyzed by Golgi site 1 protease (S1P) and site 2 protease (S2P), converted to the active form p50 ATF6 and translocated to the nucleus where it binds to the ERS response element (ERSE), inducing transcriptional regulation and activating downstream target genes such as GRP78, GRP94 and CHOP (Walter F et al., 2018). In addition, ATF6α and IRE1α can regulate the quantity and quality of XBP1 to fully activate the UPR, relieve ERS and restore ER homeostasis, respectively (Lee K et al., 2002).

When ERS is so severe that the UPR cannot compensate for its damage, cells will initiate cellular autophagy and/or initiate apoptosis mediated by 3 pathways: (1) the CHOP pathway mediated by PREK, IRE1 and ATF6, (2) the IRE1-TRAF2-JNK pathway, and (3) the caspase-12 pathway, thereby removing the abnormal cells. This lethal ERS has been shown to be one of the viable anti-tumor targets (Wu H et al., 2020; Song SE et al., 2023) (Figure 1).

Many studies have shown that ERS exerts a predominantly anticancer effect by inhibiting the growth and drug-resistant behavior of tumors from the oral cavity. For example, when human tongue squamous cell carcinoma Tca8113 and CAL-27 cells were in ERS state, expression of tribbles related protein 3 (TRB 3) mRNA and its protein, an important signaling molecule in ERS signaling pathway, was significantly elevated, which could possibly induce apoptosis by inhibiting AKT phosphorylation (Zhang J et al., 2012). Wang J et al. (2019) confirmed that phosphorylation of nuclear factor kappa-B (NF-κB), a crucial transcription factor, mediated by PERK-eIF2α was able to inhibit ERS and thus proliferation and radio resistance of oropharyngeal cancer Fadu and Detroit cells. Lyu X et al. (2019) also reported that IRE1 regulates radio resistance in HPV-negative oropharyngeal carcinoma through activation of IL-6, and enhances X-ray-induced DNA double-strand breaks and apoptosis. Upregulation of GRP78 expression and activation of the PERK-eIF2α-ATF4 pathway via ERS is one of the mechanisms by which an antitumor drug oxaliplatin is able to induce apoptosis of oral squamous carcinoma HSC-3 cells to occur in vitro (Li HR et al., 2023).

EC is divided into two subtypes as esophageal squamous cell carcinoma (ESSC) and esophageal adenocarcinoma (EAC), with the former occupying more than 90% of clinical cases. The important and dual regulatory role played by ERS on early adaption, proliferation and drug resistant survival of EC has been demonstrated.

It’s GC that threats human health with low survival and high recurrence rates along with the high incidence, in which ERS affects tumor progression and regression through multiple pathways (YANG and LU, 2021).

CRC is the digestive tumor with the highest morbidity (10.0%) and mortality (9.4%) nowadays, accounting for about one-tenth of tumor deaths and for which there is no effective clinical therapies worldwide (Cao W et al., 2021). However, there are still relatively few studies of CRC from the ERS pathway.

Study have demonstrated that glucose deprivation upregulates GRP78 expression in pancreatic cancer (PDA) cells, implying activated ERS in PDA (Zhao T et al., 2023). Another study reported that squalene epoxidase mitigates ERS by downregulating GRP78 expression and ultimately promotes the proliferation of PDA cells AsPC-1 and BxPC-3 in vitro and in vivo. Squalene epoxidase inhibitors terbinafine and NB-598 were able to reverse the above effects and to perform anti-tumor effects (Xu R et al., 2023).

Above all, ERS in digestive system tumors can either enhance their migration and drug resistance contributing to the tumor progression or exert antitumor effects by inducing tumor cell death, and the effect varies significantly in different types and stages of tumors. Since ERS hardly occurs in normal cells, selecting appropriate targets to adjust ERS and its downstream pathways according to tumor progression can specifically block or even reverse the development of digestive system tumors compared with contemporary treatment, which may lead to the new breakthrough clinically.

Icariin, a flavonoid glycoside from botanical drugs such as Epimedium brevicornu Maxim, has been used in the treatment of a variety of tumors such as prostate cancer (Chen C et al., 2023). Fan C et al. (2016) reported that icariin (20, 40, 80 μM for 12, 24, 36 h) dose-dependently upregulated the expression of p-PERK, GRP78, ATF4, p-eIF2α, CHOP and pro-apoptotic protein PUMA and downregulated the expression of anti-apoptotic protein Bcl2 in human EC cells EC109 and TE1 ESCC, ultimately interfering tumor cell adhesion and migration, which were attenuated after inhibition of ERS by eIF2α siRNA.

Corilagin is a quinone extracted from many botanical drug such as Punica granatum L. with effects such as anticoagulant and antitumor (Wang X et al., 2023). Wu C et al. (2021) found that corilagin (10, 20, 40 μM for 24 h) was able to time- and dose-dependently upregulate cleaved Caspase-7 and cleaved Caspase-12 expression, to downregulate GRP78 expression, to inhibit ESC cell ECA-109, KYSE150 and HEEPIC migration, blocking the cell cycle at G0/G1 phase and promoting apoptosis in vitro and ex vivo.

Tanshinone IIA is a quinone metabolite extracted from the botanical drug Salvia miltiorrhiza Bge, which has anti-inflammatory and cardioprotective effects (Xu Q et al., 2023). Zhu YQ et al. (2016) reported that tanshinone IIA (2, 4, 8 μg/mL for 12, 24, 36 h) was able to induce apoptosis by upregulating Caspase-4 and CHOP levels in human EC cells ECA109 in a time- and dose-dependent manner. Further study confirmed that tanshinone IIA (25, 40, 60 μg/mL for 24h, 48h, 72 h) induced death of EC109 by dose-dependent upregulation of Caspase-9, downregulation of BIP and then activation of CHOP (Zhang Y et al., 2017).

Acetylshikonin is a quinone with strong anticancer effect isolated from the botanical drug Lithospermum erythrorhizon Sieb. et Zucc. (Cha HS et al., 2023). Yuan YJ et al. (2023) reported that acetylshikonin (10 mM for 24 h) inhibited the proliferation of ESCC cells in vitro at KYSE450, TE10, KYSE180, KYSE510, EC109, EC9706 and blocked cell cycle in G1/S phase. Additional experiments in vitro and in vivo revealed that increased apoptosis in KYSE180 and KYSE450 cells was accompanied with upregulation of BIP, ATF3, ATF4, p-eIF2α, and XBP-1 and was attenuated by CHOP knockdown and the PERK inhibitor GSK2606414, which demonstrated that acetylshikonin inhibits ESCC through activation of the PERK/eIF2α/CHOP axis.

α-asarone is a phenylpropanoid extracted from the botanical drug Acorus tatarinowii Schott and serves effectively in several systems’ diseases with antilipidemic, antioxidant and anti-inflammatory effects (Shi et al., 2021; Fan et al., 2022). Early study has found that α-asarone (25, 50, 100 μg/mL for 12h, 24h, 36h, 48 h) exerts an inhibitory effect on the proliferation of human EC cells ECA-109 by decreasing the expression of Caspase-4 mRNA and protein, and increasing the expression of GRP78 mRNA and protein (Shi JJ et al., 2017). A recent study revealed that α-asarone (25, 50, 100 mg/L for 48 h) was sufficient to dose-dependently upregulate the expression of GRP78 and CHOP proteins, downregulate the expression of BIP, significantly promoted apoptosis and inhibited proliferation of Eca-109 cells (Li H et al., 2022).

Wogonoside, a major metabolite of the botanical drug Scutellaria baicalensis Georgi, is a flavonoid with antitumor and other effects (Luo M et al., 2018). Gu Q et al. (2021) found that wogonoside (10, 25, 50, 75 μM for 0, 6, 12, 24, 48, 72, 96 h) significantly upregulated expression of CHOP, GRP78, GRP94, IRE1α, TRAF1, p-ASK and p-JNK in AGS and MKN-45 cells, reduced cell viability and induced apoptosis in GC cells, and its biological effects could be blocked by IRE1α knockdown.

Kaempferol is a flavonoid widely distributed in botanical drug Kaempferia galanga Lt and various types of fruits and vegetables, having a strong anticancer ability (Guo HQ et al., 2021). It has been reported that kaempferol (50 μM for 8, 16, 24 h) was able to inhibit AGS, SNU-216, NCI-N87, SNU-638, NUGC-3 and MKN-74 cells’ viability. Further study revealed that kaempferol promoted apoptosis in GC cells via the IRE1-JNK-CHOP signal pathway by upregulating the expression of IRE1, p-IRE1, p-JNK, CHOP and cleaved Caspase-12 in AGS and SUN-638. This effect was blocked upon inhibition of autophagy or IRE1 (Kim TW et al., 2018).

Baicalein, a flavonoid extracted from the root of the botanical drug Scutellaria baicalensis Georgi or Oroxylum indicum (L.) Vent., protects cells and fights against a variety of tumors (Gan YC et al., 2023). Shen J et al. (2023) found that baicalein (30, 60, 120 μM for 48 h) dose-dependently upregulated the expression of GRP78 and CHOP and blocked the PI3K/AKT pathway to trigger the ERS, blocking the cell cycle at G0/G1 phase and inhibited the proliferation of GC HGC-27 and AGS cells. The above effects were reversed with the addition of ERS inhibitor 4-PBA. In vivo experiments also confirmed that GC progression was significantly prevented in AGS subcutaneous xenograft mice treated with baicalein (15, 50 mg/kg/d for 4 weeks).

Isoquercitrin is a flavonoid widely found in many botanical drugs such as Follum Mori, which has pro-healing and anti-tumor effects (Wang YB et al., 2023). Liu J et al. (2023) reported that isoquercitrin showed to be effective in the treatment of GC cell lines such as HGC-27, AGS, MKN-45 and SNU-1 by upregulating BAX, cleaved Caspase-3 and Caspase-12, and downregulating BCL-2.

Nobiletin, a flavonoid from the botanical drug Pericarpium Citri Reticulatae and its variants, has a variety of biological effects such as antithrombotic, anti-inflammatory and antioxidant (Geng YZ et al., 2023; Huang L et al., 2023). Chen M et al. (2023) found that nobiletin inhibited the proliferation of GC cells HGC-27 and MKN-28, which may be mediated through the activation of IRE-1α/GRP78/CHOP axis.

Salidroside is a glucoside extracted from the botanical drug Rhodiola crenulata (Hook. f. and Thomson) H. Ohba with proved anticancer effects (Zhang QL et al., 2023). Yan W et al. (2019) reported that salidroside (1,2.5,5,10,25,50,100,250 μM for 48 h) was able to dose-dependently upregulate CHOP and cleaved Caspase-12 levels and significantly downregulate GADD34 and BiP levels in SGC-7901 cells, inhibiting GC cell growth and migration and PI3K/Akt/mTOR thereby promoting cancer cell apoptosis, which can be blocked by autophagy inhibitors. Animal experiments also confirmed that salidroside (50 mg/kg/2d for 1 week) inhibited GC growth in tumor-bearing mice.

Saikosaponin A is a triterpenoid derived from botanical drug Bupleurum scorzonerifolium Willd. or Bupleurum chinense DC. and has inhibitory effects on HCC, nasopharyngeal carcinoma and lung cancer (Gao W and Wang JY, 2023). Kim et al. (2018) reported that saikosaponin A (1, 2.5, 5, 10, 20 μM for 24 h; 0, 8, 16, 24 h, 10 μM) inhibited the viability of GC cell lines AGS, SNU-638, SNU-216, MKN-74, MKN-7 and NCI-N87. Additional study revealed that saikosaponin A induced apoptosis by upregulating the levels of GRP78, p-PERK, p-eIF2α, ATF4, and CHOP in AGS and MKN-74, and overcome radio resistance in GC cells thus, a process that could be blocked by GRP78 or PERK knockdown.

Cinnamaldehyde is an aldehyde metabolite from botanical drug Cinnamomum cassia Presl, which has good antibacterial and anticancer effects (Wu, J.D. et al., 2023; Tang, T, et al., 2023). Kim et al. (2018) revealed that cinnamaldehyde(10, 25, 50, 100 μg/mL for 0, 8, 16, 24 h) inhibited the cellular growth of human GC cells SNU-638, SNU-216, AGS, NCI-N87 MKN-45 and MKN-74. What’s more, study also showed that cinnamaldehyde induced autophagic GC cell death by increasing the expression of GRP78, p-PERK, p-eIF2α and CHOP in GC cells NCI-N78 and MKN-74, a result that could be blocked by PERK or CHOP knockdown.

Chicoric acid, a phenolic compound, is the main active metabolite of botanical drug Echinacea purpurea (L.) Moench and has antioxidant and antitumor effects (Gao HY et al., 2022). Sun X et al. (2019) found that chicoric acid dose-dependently and significantly increased the expression of CHOP, BIP, Parkin, p-PERK, PERK, p-IREα, IREα, p-eIF2α, ATF4, and ATF6 in human GC cells SGC-7901 and MGC-803 (5, 10, 20, 40, 80, 100 μM for 24, 48 h) and SGC-7901 constructed xenograft mice (12.5, 25, 50 mg/kg/2d for 27d), induced apoptosis by upregulating level of p70s6k signal thereby activating the AMPK signaling pathway, and had anticancer effects both in vivo and ex vivo, an effect that was blocked by the ERS blocker 4-PBA.

Oxymatrine from the root of the botanical drug Sophora flavescens Aiton has anti-inflammatory and antioxidant effects and is an alkaloid able to ameliorate a variety of diseases of the cardiovascular system and digestive system (Huang X et al., 2023; Xu DR et al., 2023). Fang W et al. (2019) observed that oxymatrine (30, 60, 90 μmol/L for 24, 48, 72 h) upregulated intracellular GRP78/Bip and Caspase-12 gene and protein expression levels, inhibited cancer cell growth, and induced Caspase-12-dependent ERS apoptosis and G2/M phase cell block in GC cells BGC-823 in a time- and concentration-dependent manner. The application of the ERS inhibitor salubrinal was able to inhibit the above effects, proving that oxymatrine functions through the ERS apoptosis.

Berbamine is a flavonoid widely distributed in Phellodendron chinense C.K.Schneid. , Phellodendron amurense Rupr. and other botanical drugs with anti-inflammatory and anti-tumor effects (Chen Y et al., 2022; Tao L and Yan JD, 2023). Xu H et al. (2022) reported that berbamine(10, 20, 40, 80, 120, 160 μg/mL for 48 h) induced apoptosis in GC cells AGS via ERS pathway by dose-dependently upregulating the expression of Bax, CHOP, GRP78 and cleaved Caspase-12 and downregulating the expression level of Bcl-2.

Allicin is a propyl ether from botanical drug Allium sativum L. with good antibacterial, anti-inflammatory, and anticancer effects (Cai YY et al., 2023; Wu JL et al., 2023). Wu SF and Li ZJ (2019) reported that allicin (12, 24, 48 μg/mL for 24, 48, 72 h) inhibited the proliferation of GC cells SGC-7901and promoted their apoptosis by dose-dependently increasing the expression of GRP78, PERK, p-PERK, eIF2a, ATF-4 and CHOP.

Myristicin is an extract from the botanical drug Myristica fragrans Houtt, which has anti-inflammatory, antioxidant and other effects (Ismail Abo El-Fadl and Mohamed, 2022). Song J et al. (2023) found that myristicin (7.8125, 15.625, 31.25 μM for 48 h) inhibited the growth of AGS and MKN-45 cells by increasing the expression of GRP78 and ATF6 and suppressing the EGFR/ERK signaling pathway.

Esculetin, a type of coumarin, is the main active metabolite of botanical drug Fraxinus rhynchophylla Hance with anti-cellular-damage effect (Cheng T et al., 2021). Yan TH (2020) found that esculetin (0.28, 0.56,1.12 mmol/L for 48 h) dose-dependently upregulated GRP78, p-PERK, p-eIF2α, ATF-4, and CHOP expression in human GC cells SGC-7901, and this effect would be reduced by the ERS inhibitor Tauro ursodeoxycholic acid (TUDCA), implying that esculetin promotes apoptosis of tumor cells through oxidative stress with ERS.

Schizandrin A and schizandrin B are both active lignan metabolites extracted from the botanical drug Schisandra chinensis (Turcz.) Baill with antioxidant and antitumor effects (Xiang LB et al., 2023; Zeng J et al., 2023). Pu H et al. (2021) found that schizandrin A (10, 20, 30, 40, 50 μg/mL for 24, 48, 72 h) was able to upregulate the expression of p-PERK, p-eIF2α, and CHOP in GES-1 and AGS cells, inhibiting GC cells’ viability and inducing apoptosis, which could be reversed by the ERS inhibitor 4-PBA. Another study demonstrated that schizandrin B (12.5, 25, 50, 100, 150, 200 μmol/L for 24 h) inhibited tumor cell viability and induced apoptosis through the upregulation of Bax, Caspase-3, CHOP, p-PERK, p-eIF2α, and ATF4 expression, and downregulation of p-PI3K and p-Akt expression to regulate ERS and promote apoptosis in GC cells BGC-823 (Ge YN et al., 2022).

Resveratrol is a polyphenolic metabolite distributed in a variety of botanical drugs such as Reynoutria japonica Houtt. with antioxidant, anti-inflammatory and other effects (Liu LJ and Zheng HJ, 2023). Ren M et al. (2020) found that resveratrol (10, 20, 30, 40, 50, 60, 70, 80 μM for 24, 48, 72 h) could synergize with chemotherapeutic drug cisplatin to significantly increase the expression of GRP78, PERK, p-eIF2α, CHOP and cleaved Caspase-12 in GC cells AGS, blocking the cell cycle at G2/M phase and inducing apoptosis.

RTR-1, an active metabolite from the root of Rhodomyrtus tomentosa (Aiton) Hassk., is a potent antioxidant (Saising J and Voravuthikunchai SP, 2012). Zhang X et al. (2020) reported that RTR-1 (3.12, 6.25, 12.5, 25, 50, 100 μmol/L for 48 h) was able to increase the expression of IRE1α, CHOP, PERK, and BiP proteins in GC cells BGC-823 and SGC-7901, to block the cell cycle, to inhibit cancer cell growth and to induce apoptosis.

Ethanolic extract of Cordyceps cicadae comes from the complex formed by the zygote and its larvae parasitized by the fungus Cordyceps sinensis (BerK.) Sacc on the larvae of Bat Moths, a widely used botanical drug, and its extracts have immune-enhancing, anti-inflammatory, and antioxidant effects (Xing SL et al., 2023). Study showed that its ethanol extract was able to dose-dependently increase Bax, AIF, caspase-8, caspase-6 and caspase-3 activities and decrease Bcl-2 activity in human GC cells SGC-7901. It also upregulated the expression of calpain-1, caspase-12 and caspase-9, blocking the cells at S phase and exerting anti-tumor effects (Xie H et al., 2019).

Youchasaponin is a triterpenoid saponin extracted from Camellia oleifera Abel, which has the efficacy of lowering blood lipids, relieving cough and calming asthma (Zhou GH et al., 2021). Ma LY et al. (2011) found that youchasaponin (10, 20, 30 μg/mL for 24 h) induced apoptosis in human HCC cells HepG2 by upregulating the expression of IRE1, PERK, eIF2α and eEF2 proteins.

Ginsenoside CK is a triterpenoid derivative extracted from the botanical drugs Panax ginseng C. A. Mey and Panax notoginseng (Burkill) F. H. Chen ex C. H. Chow, which has anti-inflammatory, antioxidant, and other effects (Yang et al., 2022; Liu J et al., 2023). Lv (2019) found that ginsenoside CK (5, 10, 20 mg/kg/d for 15 d) was able to dose-dependently induce apoptosis and inhibit tumor growth in SMMC-7721 cells and xenograft mice by up-regulating the expression of GRP78, p-IF2α, p-JNK, Caspase4 and CHOP. Chen JX et al. (2020) further revealed that ginsenosides CK(20, 40, 60 μg/mL for 24, 48, 72 h) induced apoptosis in HCC cells HepG2 by upregulating the expression of cleaved Caspase3, cleaved PARP, GRP78, CHOP, cleaved Caspase 4, p-PERK, p-IRE1, p-JNK and p-eIF2α, and downregulating the expression of p-STAT3.

Glycyrrhetinic acid is a triterpenoid derived from the root of the botanical drug Glycyrrhiza uralensis Fisch. ex DC., Glycyrrhiza inflata Batalin or Glycyrrhiza glabra L., which has anti-inflammatory and antitussive effects (Li Y et al., 2023). Chen J (2019) found that 18β-glycyrrhetinic acid was able to promote the expression of ATF4, CHOP, IRE1, XBP1s and LC3BII in vivo (25, 50 mg/kg/d for 1 month) and in vitro (100,150,200 μM for 24 h), to block the cell cycle at G0/G1 through ERS, and to induce apoptosis and autophagy in HCC cells SMMC-7721 and HepG2. The siRNA knockdown experiment on ATF4, CHOP, and IRE1 demonstrated that the above effects were realized by the ATF4/CHOP pathway.

Celastrol is a triterpenoid extracted from the root of the botanical drug Tripterygium wilf. i Hook F and is able to fight against a variety of tumors (Xu and Li, 2017; Yu B et al., 2022). Ren B (2018) found that celastrol upregulated the expression levels of p-elF2α and p-IRE1, Bip, ATF4, CHOP, and XBP1s in HCC cells HepG2 and Bel7402, to undergo G2/M-phase cell cycle block, decreased viability, and then induced apoptosis.

Cryptotanshinone is a diterpene derived from the root of the botanical drug Salvia miltiorrhiza Bge, which has a variety of biological effects such as anti-inflammatory and anti-tumor (Liu JL et al., 2021; Niu and Zhang, 2023). Wang ZL et al. (2022) reported that cryptotanshinone (10, 15, 30 μmol/L for 48 h) significantly upregulated cleaved caspase-3 expression, decreased BIP and p-PERK expression, inhibit ERS, and promoted apoptosis in HepG2 cells.

Quercetin is a flavonoid from botanical drugs such as Styphnolobium japonicum (L.) Schott with anti-inflammatory, antioxidant, and estrogen-like effects (Wang YT et al., 2023). Quercetin (12.5, 25, 50, 100, 200, 400 μmol/L for 48 h) was found to cause a decrease in GRP78, Snail, and Vimentin mRNA and protein expression levels in HCC cells HepG2, inhibiting ERS and its epithelial mesenchymal transition to suppress the proliferation and metastasis of tumor cells (Li SS et al., 2017).

Arctigenin is a lignan-like metabolite distributed in botanical drugs such as Arctium lappa L. with antioxidant and antitumor effects (Zhao J et al., 2023). Study have shown that arctigenin (10, 50, 100 μmol/L for 48 h) dose-dependently upregulate the expression of GRP78, CHOP, and caspase-12, and induce apoptosis of HCC cells SMMC-7721 in vitro (Chang L et al., 2020).

Tannic acid is a polyphenolic metabolite distributed in a variety of food crops such as Rhus potaninii Maxim., with antibacterial, antitumor, and other bioactivities (Xie Y et al., 2023). Geng NN et al. (2018) reported that tannic acid (90, 180, 270, 360, 450, 540 μmol/L for 24 h) synergized with cisplatin to increase the expression of GRP78, GRP94 in HCC cells HepG2, inhibited cancer cell proliferation and induced apoptosis.

Furanocoumarin is one of the main coumarin components of the botanical drug Hansenia weberbaueriana (Fedde ex H. Wolff) Pimenov and Kljuykov, which has antiviral effect among others (Zhao J, 2015). Cell experiments (12.5, 25, 50, 100 μmol/L for 24, 48, 72 h) and animal experiments (30 Μm/d for 4 weeks) in mice showed that furanocoumarins inhibit HepJ5 and Mahlavu cell viability and induce apoptosis in HCC cells in vitro and in vivo by upregulating PERK and CHOP (Huang TY et al., 2023).

Licochalcone B is a chalcone metabolite present in botanical drug Glycyrrhiza inflata Batalin, which has antioxidant and various anticancer effects (Chen J et al., 2023). Zhang YY et al. (2022) demonstrated that licoricechalcone B significantly inhibited the viability of HCC cells HepG2 and Huh7 through the Akt/mTOR pathway. This could be attenuated by the PERK inhibitor PD9805 or the JNK inhibitor SP600125.

Saponin fraction from Gleditsia sinensis is a saponin analog present in botanical drug Gleditsia sinensis Lam with antioxidant and HCC cell inhibitory effects (Dong et al., 2022). It was found that saponin fraction from Gleditsia sinensis (5, 10, 20 μg/mL for 24 h) dose-dependently upregulated GRP78 and CHOP protein expression in murine HCC cells H22, enhanced the anti-hepatocellular carcinoma effects of the chemotherapeutic drug sorafenib, inhibited HCC cell proliferation and induced apoptosis in HCC cells, which could be attenuated by ERS inhibitor TUDCA (Yin C et al., 2019).

Cucurbitacin, triterpenoid including cucurbitacin B and cucurbitacin E, are triterpenoids from the cucurbitaceae family Cucumis melo L., which have therapeutic effects on a wide range of tumors (Hong T et al., 2023; Hsu HL et al., 2023; Yang Y et al., 2023). Huang JL et al. (2023) found that cucurbitacin B (0.005, 0.01, 0.05, 1, 5, 10, 20, 40, 100 μM for 48 h) inhibited the proliferation and induced apoptosis of CRC cells HT-29 and SW620 by concentration-dependently increasing the protein expression of p-PERK, p-eIF2α, ATF4, IRE1α and XBP1. After CHOP knockdown, the apoptosis rate was significantly decreased. Sui HH et al. (2020) reported that cucurbitacin E (0.001, 0.01, 0.1, 1, 10 μmol/L for 24, 48, 72 h) upregulated the expression of CHOP and GRP78 in HT-29 cells and induced apoptosis of CRC cells.

Emodin is an anthraquinone metabolite extracted from a botanical drug Rheum officinale Baill with anti-inflammatory and anticancer effects (Lan WB et al., 2023). Liu BR et al. (2016) observed that emodin (30, 60, 90 μmol/L for 48 h) inhibited the proliferation and promoted the apoptosis of CRC cells SW620 through concentration-dependent upregulation of GRP78, CHOP and cleaved Caspase-12 expression. The above effects were attenuated by the addition of the ERS inhibitor 4-PBA, indicating that emodin inhibits CRC via ERS.

Konjac glucomannan, a polysaccharide from botanical drug Amorphophallus konjac K. Koch or Amorphophallus variabilis Blume sinensis Belval is able to fight against a variety of tumors (Tao QQ et al., 2020). Lu MJ and Chu WJ (2021) observed that the konjac glucomannan (50 μmol/L for 5 d) dose-dependently upregulated the protein levels of cleaved caspase-3, cleaved caspase-9, Bax, PERK, p-eIF2α, ATF4, and CHOP, and downregulated the protein level of Bcl-2, induced apoptosis, and reversed the resistance to 5-Fluorouracil (5-FU) in CRC cells HCT-28.

Bufalin is a steroid presented in the secretion of the botanical drug Bufo gargarizans Cantor or Bufo melanostictus Schneider, which has good anticancer effects (Zheng YD et al., 2023). Shang J et al. (2023) reported that bufalin (2.5, 5, 10 nmol/L for 48 h) leaded to concentration-dependent upregulation of Bax, GRP78, p-PERK, p-eIF2α, and CHOP proteins expression, downregulation of Bcl-2 and eIF2α, inhibition of CRC cell proliferation, and induction of cancer cell apoptosis in HCT116 cells. The above effects were attenuated by the addition of the ERS inhibitor 4-PBA.

Dehydrodiisoeugenol is a lignan-like metabolite from botanical drug Myristica fragrans Houtt with antibacterial, antioxidant and other effects (Xu J et al., 2022). Li C et al. (2023) observed that dehydrodiisoeugenol (10, 20, 30, 40, 50, 60, 70, 80 μM for 24,48,72 h) dose-dependently upregulated BiP, Ero2-Lα, PERK, eIF2α, p-eIF1α, IRE1α, XBP-48s and CHOP expression in HCT116 and SW620 cells, blocking the CRC cell cycle at G1/S, inducing cell autophagy, and inhibiting cell proliferation and tumor growth. The above effects were attenuated after knockdown of PERK or IRE1α, indicating the anti-tumor effects mentioned above are achieved by ERS. Animal study (40 mg/kg/2d for 14 d) also confirmed its specific inhibitory effect on CRC growth in mice.

Usnic acid, a furan metabolite derived from the botanical drug Usnea diffracta Vain, has anti-inflammatory and anti-tumor effects (Xie LS et al., 2023). Gimła M et al. (2023) demonstrated that usnic acid upregulated the expression of BIP, IRE1α and GADD153 in human PDA cells MIA PaCa-2 and PANC-1, blocking the cell cycle at G0/G1, inhibiting tumor growth and inducing apoptosis.

Some extracts, as the studies proved, have treatment effect on more than one digestive system tumor.

Gambogenic acid is a flavonoid isolated from the botanical drug Garcinia hanburyi Hook. f and has a good multi-pathway anti-tumor effect but low toxicity (Zhan et al., 2020). Xu T and Li QL (2017) reported that compared with blank control group, gambogenic acid (1, 2, 4 μmol/L for 24 h) affected human nasopharyngeal carcinoma CNE-2Z cells growth and proliferation and induced apoptosis in a concentration-dependent manner by downregulating GRP78 and upregulating CHOP and ATF4 protein expression. Moreover, TT Dai et al. (2014) found that gambogenic acid (2.5, 5, 7.5 μmol/L for 24 h) concentration-dependently inhibited the proliferation and induced apoptosis of CRC cells HCT116, which could be inhibited by the ERS inhibitor 4-PBA and inversely proved to be realized by the ERS pathway.

Osthole, extracted from the fruit of the botanical drug Cnidium monnieri (L.) Cuss, is a coumarin analog possessing anti-inflammatory, antioxidant, antifibrotic, and antitumor effects (Wang, XW et al., 2023; Zhao, LN et al., 2023). Pan et al. (2019) found that osthole (20, 40, 60, 80, 100 μM for 24, 48, 72 h) concentration-dependently promoted GRP78, CHOP, ATF-4, GADD34, and XBP-1s expression, downregulated Bax expression, blocked cancer cells at G1 phase, inhibited the proliferation of HCC cells SMMC7721 and induced the apoptosis. In addition, Zhou XH et al. (2021) demonstrated that osthole (25, 50, 100 μM for 24 h) could upregulate GRP78, p-PERK/PERK, p-elF2α/elF2α and CHOP expression, to effectively inhibit the proliferation of HCT-29 and to induce apoptosis in CRC cells, which could be blocked by the autophagy inhibitor 3 MA and ERS inhibitor 4-PBA.

Curcumin is a diketone from the root of botanical drug Curcuma longa L with good antibacterial, antioxidant, and antitumor effects (Lei H et al., 2023; Zhang X et al., 2023). Earlier study observed that curcumin (2.5, 5, 10, 20, 50 μM for 12, 24, 48 h) could time- and concentration-dependently promote the expression of GRP78, Caspase-12, and CHOP, inhibit the proliferation of HCC cells SMMC-7721 and induce apoptosis (Xu XM et al., 2018). Li YY and Lu MJ (2020) demonstrated that curcumin (25,50 μmol/L for 1d) could reduce the activity of HCC cells SMMC-7721 and induce apoptosis through ERS signaling pathway. Another study also showed that curcumin (20, 40, 60 μmol/L for 24, 48, 72 h) dose-dependently upregulated the expression of GRP78, p-elF2α, p-JNK, CHOP, and Caspase-4 in BEL-7404 cells, inhibited HCC cell proliferation, and induced apoptosis (Zhang et al., 2021). Huang et al. (2017) reported that curcumin (0.001, 0.01, 0.1, 1, 10 μmol/L for 24,48,72 h) was able to individually or synergized with irinotecan to increase the expression of BIP, PDI, and CHOP in LoVo and HCT-29 cells, blocking the CRC cells at S phase and inducing apoptosis. Apoptosis was alleviated after interfering with the CHOP gene. Zhu C et al. (2022) separately demonstrated a similar effect of curcumin on CRC cells CT-26.

Oridonin, a diterpenoid isolated from Rabdosia rubescens (Hemsl.) Hara, is able to fight against a variety of tumors such as leukemia and ovarian (He J et al., 2023; Li M and Wang XX, 2023). Zhou F et al. (2023) demonstrated that oridonin (5, 10, 15, 20, 25, 30 μM for 24, 48, 72 h) increased ATF4 and CHOP concentrations of CRC cells NCM460, HCT116, LoVo, SW480, RKO, HeLa, PC-3 and A594, inhibited TCF4 activation and induced ERS dysregulation and death of tumor cells. Animal study demonstrated the inhibitory effect of oridonin (160 mg/kg/d for 14 d) on the proliferation of TCF4 and Mock cells as well. What’s more, Liu DL et al. (2022) observed that compared to the control, oridonin (5, 10, 20, 40, 80 μmol/L for 24, 48, 72 h) inhibited the proliferation and induced apoptosis of PDA SW1990 and Panc-1 cells as well in a time- and dose-dependent manner by upregulating the protein expression levels of GRP78, CHOP, and cleaved Caspase-12, which could be blocked by the ERS blocker 4-PBA.

Piperlongumine is an alkaloid from botanical drug Piper nigrum L. with anti-inflammatory and anti-tumor effects (Li YD et al., 2022). Zou P et al. (2016) found that piperlongumine (0.625, 1.25, 2.5, 5, 10, 20 μmol/L for 24, 48 h) upregulated the expression of p-eIF2α, ATF4, and CHOP in SGC-7901 and BGC-823 cells, activating the lethal ERS to promote GC cell apoptosis. Upon inhibition of CHOP, apoptosis was attenuated. Animal experiment also confirmed the inhibitory effect of piperlongumine (4.12 mg/kg/2d for 15d) on GC proliferation in mice. A recent study observed that piperlongumine also synergized with a chemotherapeutic agent bortezomib to inhibit cholangiocarcinoma (Naradun N et al., 2023).