Recent Advances in Herbal Medicines for Digestive System Malignancies

Herbal medicines, as an important part of traditional Chinese medicine (TCM), have been used to treat digestive system malignancies (DSM) for many years, and have gradually gained recognition worldwide. The role of herbal medicines in the comprehensive treatment of DSM is being improved from adjuvant treatment of the autologous immune function in cancer patients, to the treatment of both the symptoms and disease, direct inhibition of tumor cell growth and proliferation, and induction of tumor cell autophagy and apoptosis. Their specific mechanisms in these treatments are also being explored. The paper reviews the current anti-tumor mechanisms of TCM, including single herbal medicines, Chinese herbal formulations, Chinese medicine preparations and TCM extract, and their application in the comprehensive treatment of digestive system tumors, providing a reference for clinical application of TCM.


INTRODUCTION
Digestive system malignancies (DSM) are a common cancer worldwide. They include esophageal, liver, pancreatic, gallbladder, gastric, and colorectal cancers. Due to their high incidence, rapid disease progression, and poor prognosis, they are a leading cause of death, and a public health burden around the world (Siegel et al., 2018). Of the available treatments for DSM, including surgery, radiotherapy, chemotherapy, targeted therapy, and immunotherapy, no current treatment can completely prevent tumor recurrence and metabolism (Tomasello et al., 2017;Finn et al., 2018;Iñarrairaegui et al., 2018;Toesca et al., 2018). Therefore, the development of new methods and drugs is particularly urgent for patients with DSM. Herbal medicine, as represented by traditional Chinese medicine (TCM), is an important component of complementary and alternative medicine, and has been developed in Asian countries, especially China.
Because of its potential for preventing and treating cancer, TCM has received wide attention from around the world, including Western countries. Many studies found that TCM combined with radiotherapy or chemotherapy for malignant tumors could significantly reduce the incidence of adverse reactions to radiotherapy or chemotherapy and improve cellular immunity and quality of life for patients (Qi et al., 2010;Ge et al., 2016;Liu et al., 2016a,b). Even some TCM preparations have a synergistic effect on chemotherapy, which can both prolong patient survival and reduce tumor recurrence and metastasis (Tian et al., 2012a;Pandey et al., 2015). Many studies have also shown that TCM could directly inhibit tumor cell growth and proliferation and directly or indirectly mediate their autophagy and apoptosis (Tang et al., 2009;Deng et al., 2013). Therefore, TCM, as an anti-tumor therapy, could play an important role in the treatment of DSM. In this paper, we mainly review the clinical application and possible mechanisms of herbal medicine in treating DSM, and consider their possible applications, to provide a reference for treatment of DSM.

Astragalus membranaceus
Astragalus membranaceus is a kind of tonifying TCM. It is often used in various advanced cancers to strengthen and consolidate body resistance Qi et al., 2017). Traditional Chinese medicine indications for A. membranaceus focus on "qi deficiency, " and patients often feel anorexia, a lack of strength, spontaneous sweating. Chemical extraction analysis shows that A. membranaceus contain many active components, such as astragalosides I-VIII, flavonoids, polysaccharides, amino acids and trace elements Lu et al., 2016). Several clinical studies and animal experiments have confirmed that the effective components of A. membranaceus can enhance immune function and have anti-tumor effect (Cho and Leung, 2007;Huang et al., 2013;He et al., 2016;. Astragalus polysaccharides are among the main active components of A. membranaceus, which are extracted with water from Astragalus roots (Xu et al., 2008). They have many biological functions such as immunomodulation, antiinflammatory, antioxidants, anti-HBV, etc. (Dang et al., 2009;Huang et al., 2013;Yang et al., 2013;. Some studies have found that Astragalus polysaccharides can inhibit or kill tumor cells of digestive system (Tian et al., 2012b;Huang et al., 2016). Lai X et al. found that astragalus polysaccharides (100 mg·kg −1 ) could inhibit hepatoma tumor growth in H22 cell tumor-bearing mice. They also increase serum interleukin (IL) 2, IL-6, and tumor necrosis factor (TNF)-α concentrations (Lai et al., 2017), which suggests that astragalus polysaccharides play an anti-tumor role by regulating the immune system. The study also found that Astragalus polysaccharides could affect tumors by regulating the expression of Bcl-2 family proteins (up-regulated Bax, down-regulated Bcl-2; Lai et al., 2017). Notch receptors (Notch 1-4) are a kind of transmembrane protein receptor composed of extracellular domain, transmembrane domain and intracellular region. The main function of the extracellular domain is to bind specific ligands, and the intracellular region is mainly used for transcriptional regulation (Yoshida et al., 2013). Huang WH et al. found that, compared with normal tissues, mRNA expression and protein expression of Notch1 in HCC tissues increased significantly, and knockout of Notch1 significantly inhibited the expression of apoptosis suppressor gene Bcl-2, and enhanced the expression of pro-apoptotic gene Bax, which indicates that astragalus polysaccharides may mediate apoptosis of human HCC cells through regulating Bcl-2 family proteins by inhibiting Notch1 . Some studies have found that astragalus polysaccharides can reduce adverse effects of chemotherapeutics while enhancing tumor cell sensitivity to them, thus functioning as an adjuvant therapy and improving therapeutic effects in DSM .
Multidrug resistance (MDR) is a difficult problem in treating cancer; one cause of multidrug resistance is overexpression of Pglycoprotein (P-GP) in cells, which is encoded by the Multidrug Resistance 1 (MDR1) gene and acts as an efflux pump for various chemotherapeutics (Syed and Coumar, 2016). Tian et al. found that astragalus polysaccharides increased sensitivity of H22 HCC cell lines resistant to Adriamycin (H22/ADM cell lines) to chemotherapeutic agents, which may be related to downregulation of P-glycoprotein and MDR1 mRNA expression (Tian et al., 2012a).
Astragalus saponins are active ingredients extracted from Astragalus roots, and mainly include astragalosides (I-VIII) and isomer iso-astragalosides (I, II) (Auyeung et al., 2010;Liu et al., 2010). Many recent studies suggest their potential value in the treatment of DSM Qi et al., 2017;. In a study of patients with advanced gastric cancer, Auyeung et al. found that astragalus saponins may mediate apoptosis in gastric cancer cells by activating caspase 3 and subsequently degradation of poly (ADP-ribose) polymerase. In addition, Astragalus saponins reportedly can induce stagnation of cell cycle of G 2 /M phase in gastric cancer cells and promote the down-regulation of the angiogenic protein vascular endothelial growth factor (VEGF) and metastatic proteins metalloproteinase (MMP), thus inhibiting tumor cell growth (Auyeung et al., 2012). This suggests that astragalus saponins may inhibit angiogenesis and metastasis of digestive system tumor cells. Wang et al. have found that astragalosides can combine with calpain inhibitor to induce endoplasmic reticulum stress-mediated apoptosis in colon cancer cells . Wang T et al. found that astragalus saponins can inhibit the growth of human gastric cancer cell line BGC-823 cells in vitro and vivo, decrease its invasive ability . In addition, some studies have found that astragalosides can enhance the sensitivity of tumor cells to chemotherapeutic drugs Xie et al., 2016;Ye et al., 2017). Wang et al. found Astragalus Saponin II could enhance the sensitivity of human HCC cells to 5-fluorouracil by suppressing autophagy via MAPK-mTOR pathway, thus improving the antitumor effects of chemotherapeutic drugs . These findings suggest that Astragalus saponins could be developed into an effective chemotherapeutic agent or adjuvant drug for the comprehensive treatment of DSM.

Sophora flavescens
The dried root of Sophora flavescens Ait is used in TCM. Its active constituents include matrine, oxymatrine, sophocarpine, and oxysophocarpine Ni et al., 2017). Basic studies found that alkaloids like matrine and oxymatrine could exert anti-tumor effects on various DSM, which has also been verified by many clinical studies and animal experiments Yong et al., 2015;Zhang and Yu, 2016;Wang X. et al., 2017).
Receptor-interacting protein-3(RIP3) is a serine-threonine kinase in the RIP kinase family, which can mediate the celldeath switch from apoptosis to necrosis in TNFα-induced necroptosis (Koo et al., 2015). Xu et al. found that matrine might promote expression of RIP3, thus promoting an antitumor effect in cholangiocarcinoma cells (Xu B. et al., 2017). The WNT signaling pathway is crucial for the generation and progression of both normal tissues and tumors (Pećina-Slaus, 2010). Ma Y et al. found that matrine (50 µg/ml) could inhibit migration and invasiveness of HPAC cells in pancreatic cancer. Moreover, expression of MT1-MMP, was reduced in matrinetreated HPAC cells, suggesting that matrine could be a pancreatic cancer treatment, through WNT-mediated down-regulation of MT1-MMP . Caspase-dependent apoptosis is a kind of programmed cell death. Wu et al. found that oxymatrine could mediate apoptosis in gallbladder cancer cells by activating caspase-3 and Bax and inhibiting Bcl-2 and NF-κB . Liang et al. found that oxymatrine regulated expression of epithelial-mesenchymal transition (EMT) markers such as E-cadherin, Snail and N-cadherin in colon cancer; expression of p65, a key protein in the NF-κB pathway was lowered at the same time (Liang and Huang, 2016). The results suggested that oxymatrine exerts an anti-tumor effect by down-regulating NF-κB, thus preventing EMT in colon cancer cells.
Moreover, studies found that matrine and oxymatrine could alleviate the toxicity of chemotherapeutic drugs, providing an adjuvant therapeutic approach for comprehensive treatment of digestive system malignancies (Liu et al., 2016b). The antitumor effect of gemcitabine on gallbladder carcinomas can be enhanced by suppressing the NF-κB pathway , which suggests that oxymatrine may increase efficacy of chemotherapeutic drugs by down-regulating the NF-κB pathway. Duan et al. found that the percentage of colon cancer cells suppressed with a combination of matrine and irinotecan (CPT-11), a first-line drug for colon cancer, was higher than that with either matrine or irinotecan alone, which might be associated with up-regulation of Topoisomerase (TOPO) I, Bax and Caspase-3 . The results suggested that matrine has a synergistic effect with irinotecan in the treatment of colon cancer. An experiment by Li et al. tested combined treatment with oxymatrine and 5-FU on human HCC both in vitro and in vivo, and found that tumor mass and volume in rats were more suppressed in the combined treatment group than in the single-drug groups (Liu et al., 2016a).

Huangqin Tang/PHY906
Huangqin Tang, whose main components are Scutellaria baicalensis, Paeonia lactiflora Pall, Glycyrrhiza uralensis Fisch, and Ziziphus jujuba Mill, is a classical TCM preparation, first recorded in the book "Shang Han Lun" by Zhongjing Zhang during the Han Dynasty about 1800 years ago. It has been widely used to treating digestive system diseases that are accompanied with symptoms such as diarrhea, nausea, emesis and abdominal colic . PHY906, which is the improved version of Huangqin Tang, contains the same four herbs as Huangqin Tang but with a different weight ratio of 3:2:2:2 . The application of PHY906 as an adjuvant for radiotherapy, chemotherapy, and targeted therapy in cancer has been explored by dozens of studies (Kummar et al., 2011;Liu and Cheng, 2012;Rockwell et al., 2013). Some studies confirmed the adjuvant role of PHY906 in treating DSMs, such as colon and pancreatic carcinoma (Farrell and Kummar, 2003;Yen et al., 2009;Kummar et al., 2011;Liu and Cheng, 2012;Saif et al., 2014). Lam et al. investigated PHY906 combined with irinotecan in a mouse colon cancer model . Overall survival in the PHY906 group was significantly better than in the control group; and intestinal mucosa in the control group was more severely damaged than in the PHY906 group, indicating that PHY906 decreases gastrointestinal damage caused by irinotecan. Yen Y et al. evaluated combined PHY906 and capecitabine for 42 patients with late-stage HCC who had lost the opportunity for resection (Yen et al., 2009). After two courses of treatment, 60% of patients showed stable or improved conditions; their median overall survival was 9.2 months with no significant quality of life reduction, implying that PHY906 could be used with capecitabine in treating HCC and providing support for a larger-cohort study. Saif et al. found that PHY906 significantly reduced nausea and emesis caused by capecitabine in 25 patients including 15 men and 10 women with pancreatic cancer in a Phase I clinical trial (Saif et al., 2014), which suggests that PHY906 combined with capecitabine is a safe substitute for gemcitabine for treating advanced pancreatic cancer.
Meanwhile, some studies investigated the mechanism of PHY906 in increasing the anti-tumor effect (Lam et al., 2015;Su et al., 2017). Sorafenib is the only drug approved by FDA for treating HCC, which inhibits the RAF/MEK/ERK pathways and tyrosine kinase receptors such as PDGF, VEGF and Kit (Wilhelm et al., 2004). Lam et al. discovered Huangqin and Shaoyao, which are the two main components of PHY906, might change the inflammatory state of tumor microenvironment and enhance the anti-tumor effect of sorefenib by inhibiting ERK1/2 phosphatase and thus increasing ERK1/2-P in HepG2 cells (Lam et al., 2015). Another study found that PHY906 could mediate apoptosis of colon cancer cells by regulating IFN-γ and activating responses toward steroid hormones, thus exerting an anti-tumor effect by protecting the epithelial barrier from being invaded by tumor cells . The role of PHY906 in the comprehensive treatment of DSM warrants further research.

Bu-Zhong-Yi-Qi-Tang
Bu-zhong-yi-qi-tang (also known as TJ-41) is a traditional medicine widely used in China, Japan and Korea. It contains 7 herbs, including Scutellaria baicalensis, Pinellia tuber, Zizyphi fructus, Zingiberis rhizoma, Glycyrrhiza radix, Coptidis rhizoma, and Panax ginseng (Qi et al., 2010). Reportedly, TJ-41 can decrease side effects and increase curative effects of radiotherapy and chemotherapy in treating DSM (Qi et al., 2010). Jeong et al. randomly divided 40 patients with liver-cancer into an experimental group who received two weeks' treatment with TJ-41, and a control group. They found that the experimental group had significantly less fatigue than did the control group (Jeong et al., 2010). Interleukin-6 (IL6) affects development of cachexia, which is a major cause of cancer-related death. Yae et al. found that macrophages and serum IL-6 expression were reduced, and cachexia alleviated, in mice with colon cancer treated by TJ-41 (Yae et al., 2012). Kuo et al. found that TJ-41 enhanced toxicity of mitomycin C for human gastric adenocarcinoma MKN-74 cells, probably through a non-apoptotic mechanism (Kuo et al., 2014). Kao et al. found that TJ-41 mediated apoptosis by inducing stagnation of G 0 /G 1 cell-cycle phases and inhibiting DNA synthesis, thus preventing proliferation of human Hep3B and HepG2 liver cancer cell (Kao et al., 2001).

Daikenchuto
Daikenchuto (TJ-100) is a traditional herbal medicine, also called Kampo, composed of Capsicum Annuum, dried ginger, ginseng and cerealose (Endo et al., 2017) and can be used for gastrointestinal diseases including intestinal obstruction and Crohn's disease (Kominato et al., 2016;Okada et al., 2016). Some studies found that TJ-100 can suppress tumor development and alleviate side effects of surgery (Yoshikawa et al., 2015;Nagata et al., 2016;Hasebe and Matsukawa, 2017 (Yoshikawa et al., 2015). The result showed theTJ-100 group had a shorter median time to first bowel movement than the placebo group (94.7 vs. 113.9 h), and a lower incidence of gastrointestinal dysfunction at 12 days after surgery than did the placebo group. Mylabris has been used in cancer treatment for more than 2000 years (Lao et al., 2013;Zeng et al., 2016). Cantharidin (CTD) (Supplementary Figure 1), a terpenoid, is the main active ingredient of Mylabris, and it has a significantly cytotoxic effect on tumor cells (Kadioglu et al., 2014;Hsia et al., 2016). However, its clinical application is limited by strong irritation of the urinary system and digestive system when taken orally or intravenously (Wang G. et al., 2018). Norcantharidin (NTCD), a demethylated derivative of CTD, has relatively low toxicity and similarly antitumor activity to cantharidin (Puerto Galvis et al., 2013). Studies have shown that CTD and NCTD might mediate apoptosis to inhibit tumor development and have a metabolic impact on tumor cells (Rauh et al., 2007). CTD and NCTD were also shown to inhibit serine/threonine protein phosphatase 1 and serine/threonine protein phosphatase 2A (Bian et al., 2014). These terpenoids affect intracellular signal transduction and cellcycle progression (Yeh et al., 2010).
Reportedly, CTD and NCTD inhibit DSM proliferation and metabolism, including liver cancer Su et al., 2015). Le et al. found that CTD (5 µM) had an antitumor effect on HCC stem cells in a dose-and time-dependent manner, which may be associated with down-regulation of β-catenin and cyclin D1, and inhibition of cell self-renewal ability (Le et al., 2016). Shen et al. found that CTD inhibited invasiveness of pancreatic cancer cells by downregulating matrix metalloproteinase 2, which has a major role in remodeling extracellular matrix . Another study suggested that CTD might induce apoptosis of SGC-7901 and BGC-823 cells and G 2 /M phase arrest by activating Bcl-2 proteins in gastric cancer . Overexpression of family-with-sequence-similarity-46C (FAM46C) reportedly inhibits invasiveness of liver cancer cells by suppressing transforming growth factor-β-Smad signaling and EMT; FAM46C-knockout can change the anti-metastatic effect of NCTD on tumor cells, suggesting the anti-hepatoma impact of NCTD is affected by up-regulating FAM46C . MiR-214 is significantly down-regulated in HCC tissues, which is associated with low clinical progression and poor prognosis in HCC (Shih et al., 2012). Overexpression of miR-214 could inhibit growth and invasiveness in HCC . Lu S et al. found that NCTD could significantly inhibit tumor growth in liver cancer-bearing mice, and the inhibitory effect may be associated with enhanced anti-tumor activity of tumor-associated macrophages (Lu et al., 2014). In addition, NCTD significantly inhibited β-catenin expression, which could be reversed by miR-214 inhibitor (Lu et al., 2014).
Moreover, some studies have also found that combining radiotherapy or chemotherapy with CTD and NCTD could reduce the side effects of radiotherapy and chemoradiotherapy, and increase sensitivity of tumor cells to chemotherapeutic drugs, thus enhancing their efficacy . Wang et al. have found that CTD and NCTD might enhance the toxicity of gemcitabine and erlotinib for human pancreatic cancer cells by inhibiting the beta-catenin pathway, thus augmenting treatment of pancreatic cancer .

Berberine(C 20 H 18 ClNO 4 )
Berberine (Supplementary Figure 2) is an isoquinoline alkaloid, extracted as a quaternary ammonium compound from Coptis Frontiers in Pharmacology | www.frontiersin.org chinensis (Huanglian in Chinese), Hydrastis canadensis, Berberis aristata, Berberis vulgaris, and Berberis aquifolium (Tang et al., 2009). Berberine is used for bringing down fevers and fighting intestinal bacterial infections due to its antibiotic effect. Berberine usually utilized in TCM to treat infectious diseases, including bacterial diarrhea, intestinal parasitic infection and ocular Chlamydia trachomatis infection, based on its robust resistance to bacteria, viruses, fungi, protozoa, worms and chlamydia (Tang et al., 2009). In the recent years, several studies have found that berberine might suppress tumor invasiveness and metastasis through multiple mechanisms (Wang et al., 2010;Liu et al., 2015). Yu et al. found that berberine could mediate apoptosis and autophagic death in HepG-2 cells through activation of AMPK, which is a kind of metabolic-sensing protein kinase . Wang et al. found that berberine (>100 µM) may inhibit HCC cell invasiveness and metastasis through up-regulation of plasminogen activator inhibitor-1 and down-regulation of urokinase-type plasminogen activator . Yi et al. found that berberine can significantly inhibit activation of the Akt pathway and inhibit the growth of tumors (Yi et al., 2015).
Other studies found that berberine could be combined with chemotherapeutics to neutralize their toxicity, thereby enhancing their anti-tumor effects (Pandey et al., 2015;You et al., 2016;Gong et al., 2017). Epidermal growth factor receptor (EGFR), a receptor for the ErbB family, is usually overexpressed in gastric cancer cells, which is associated with poor prognosis (Kim et al., 2008). Wang J et al. found that berberine can mediate apoptosis by inhibiting the EGFR pathway and enhance the efficacy of cetuximab or erlotinib in gastric cancer cell lines, which provide strong support for the potential of berberine in the treatment of DSM .

CHINESE MEDICINE PREPARATIONS FOR DSM Huaier Granules
Huaier granules are a new anti-tumor drug extracted from Trametes robiniophila Murr (Huaier) . Its main active ingredient is a proteoglycan composed of 41.53% polyose, 12.93% amino acid, and 8.72% H 2 O . The drug has been approved by (CFDA) the Chinese Food and Drug Administration for patients with malignancies, especially those with primary liver cancer who have lost the opportunity for surgery and chemotherapy (CFDA approval number, Z20000109; Bao et al., 2016). Various studies confirm that Huaier granules can inhibit tumor growth, promote tumor cell apoptosis, induce secretion of various cytokines, and increase immunity, while enhancing sensitivity to chemotherapeutics and reversing drug resistance. Because of the wide potential applications of Huaier granules, many studies have focused on its use and mechanisms for the treatment of DSM Song et al., 2015).
Pathways for hypoxia-inducible factor (HIF)-1α, VEGF, RNAbinding factor 1(AUF-1), and astrocyte elevated gene-1 (AEG-1) play roles in the progression of liver cancer Liu et al., 2017). Cong et al. did a series of invivo and in-vitro experiments with human HCC SMMC-7721 cells . The results suggested that Huaier polysaccharide (TP-1) inhibits the above pathways by partially down-regulating HIF-1α, VEGF, AUF-1, and AEG-1 proteins, thereby suppressing revascularization, growth and metabolism of liver cancer cells. Mitogen-activated protein kinase (MAPK), which mediates cell proliferation, differentiation, stress reaction and apoptosis, mainly via p38 MAPK pathway, can induce apoptosis by adjusting the expression of several relevant proteins including p53 and Bcl-2 (Chang and Karin, 2001;Taylor et al., 2013;Hui et al., 2014;. Activity of the p38-MAPK pathway is significantly reduced in liver cancer cells and activation of p38 may induce apoptosis (Lamy et al., 2013). Bao HD et al. tested the anti-tumor effect of TP-1 in HepG2 and Huh7 HCC cells. Expression of Bax, Bcl-2 and survivin in the cells treated with TP-1 was obviously enhanced, leading to apoptosis of liver cancer cells due to activation of p38-MAPK pathway (Bao et al., 2016). A study by Xie et al. found that Huaier could mediate apoptosis of gastric cancer cells through the PI3K-AKT signaling pathway and prevent their proliferation by suppressing cyclin B1 expression and promoting G 2 /M-phase arrest (Xie H. X. et al., 2015).
Huaier granules can also increase the sensitivity of human hepatoma cell lines SKHEP-1 and HepG2 to rapamycin and cisplatin and thus enhance the anti-tumor effect of chemotherapeutics, probably by activating thr mTOR pathway (Hu et al., 2016). Huaier granules combined with DC-CIK showed increased efficacy in treating mice with HT-29 colon carcinoma cell line than either single method . Even so, the mechanisms of Huaier granules require further study.

Shenqi Fuzheng Injection
Shenqi fuzheng injection (SFI) was approved by Chinese Food and Drug Administration in 1999 for clinical application (CFDA approval number, Z19990065). It mainly includes Codonopsis pilosula and A. membranaceus (ratio of 1:1) . Studies showed that SFI significantly suppressed tumor growth, neutralized toxicity of chemotherapeutics and increased   immunity (Qi et al., 2015). Yang et al. conducted an animal experiment to treat nude mice induced by cyclophosphamide with SFI of low, medial and high doses . The results showed that SFI could dose-dependently increase the spleen index of mice, promote recovery of peripheral white blood cells and marrow cells, stimulate the proliferation of T cells and B cells, increase activity of splenic natural killer cells and peritoneal macrophages, and renew the level of serous IL-2. Many studies have indicated that SFI combined with systemic chemotherapeutics can generate a synergetic antitumor effect that improves the objective response rate (ORR), increases Karnofsky performance score (KPS) and immunity, and decreases the adverse event rate . In a meta-analysis of 15 random clinical trials (RCTs) among patients with late-stage gastric cancer, Yao et al. showed the ORR for patients treated with SFI and chemotherapy was significantly higher than for patients treated with chemotherapy alone (OR = 1.66, 95% confidence interval [CI]: 1.20-2.29, P < 0.05; Yao et al., 2014). Furthermore, KPS was significantly increased by the combinatorial treatment (OR = 3.74, 95% CI: 2.66-5.27, P < 0.05). Another meta-analysis that included a combined cohort of 722 patients with colon cancer found that the group treated with SFI combined with chemotherapeutics had a higher ORR and lower gastrointestinal toxicity than did the group treated with chemotherapy only. This result suggests that SFI can enhance the efficacy of chemotherapeutics while decreasing their side effects .

Aidi Injection
Aidi injection (CFDA approval number, Z52020236) is an anti-tumor Chinese medicine from the spotted jellyfish, A. membranaceus, Acanthopanax, and ginseng (Xiao et al., 2017). Aidi injections can reportedly alleviate side effects of chemotherapeutics and exert an adjuvant effect on the comprehensive treatment of DSM (Wang T. et al., 2014;Ge et al., 2016). In a meta-analysis of 32 RCTs by Wang et al., Aidi injections combined with chemotherapeutics improved the effective rate of chemotherapeutics for gastric cancer and the patient's quality of life, and decreased incidences of side effects such as nausea and vomiting, diarrhea, leukopenia III-IV, and thrombocytopenia III-IV (Jiancheng et al., 2015). Wang et al. treated patients with advanced colon cancer using Aidi injections combined with FOLFOX4 and found that the experimental group (n = 63) had a much lower rate of grade-II nausea, vomiting, and diarrhea than did the control group (n = 58) for 7 days .

Kanglaite Injection
Kanglaite injection is an anti-tumor medication mainly extracted from Chinese herb-coix seed (Semen coicis yokuinin), and has been approved by CFDA to treat gastric cancer, liver cancer, etc. (Qi et al., 2015). Kanglaite injection can reduce side effects of chemotherapy and radiotherapy, improve patients' quality of life, and reverse drug resistance to some extent. In a meta-analysis of Kanglaite injection combined with hepatic arterial intervention for the treatment of non-resectable HCC, the ORR and KPS of patients who received the combined treatments were both higher than for patients treated with a single method (Fu et al., 2014).

CONCLUSIONS
In summary, we have reviewed the current anti-tumor mechanisms of TCM, including single herbal medicines (Table 1), Chinese herbal formulations, Chinese medicine preparations ( Table 2), and TCM extract (Table 3), and their application in the comprehensive treatment of digestive system tumors ( Table 4). TCM has a long history, and its application in many diseases, especially malignant tumors, has been widely reported (Wong et al., 2015;Xu et al., 2015;. However, due to the variety of medicinal plants (estimated over 12,000 species) and their complex components, TCM has not been widely recognized in Western countries . In recent years, with more extensive TCM investigations, continuous progress has been made in extraction technology, and standardization of TCM. The value of TCM in modern medical and health services is becoming more widely recognized. However, there are still some difficulties in the study of TCM for DSM, such as the determination of active substances and the accuracy of chemical composition determination (Zhang et al., 2018). Unlike Western medicine, the anti-metastatic effects of TCM reflect comprehensive treatment of multiple targets and components, which can inhibit the various links of metastasis from many aspects, with less toxicity. Although some progress has been made in basic research and clinical application of TCM in the treatment of DSM, many components and mechanisms still need to be clarified. Modern scientific and technological means are being used to study anti-tumor mechanisms of TCM at the cellular, molecular and genome levels, to make full use of TCM in the management of digestive system malignancies.

AUTHOR CONTRIBUTIONS
JS, ZC, XZ and YX wrote the manuscript. JS, WY ,YL and RC provided the critical revisions. All authors approved the final version of the manuscript for submission.