Cholangiocarcinoma refers to an epithelial cell malignancy with poor prognosis. Existing therapeutic strategies for patients with cholangiocarcinoma consist of surgery, liver transplantation and chemotherapy. Surgery is a prioritized treatment for all subtypes of cholangiocarcinoma, while lymph nodes and vascular structures should be considered. It was elucidated that for perihilar cholangiocarcinoma patients who have undergone either surgical treatment or liver transplantation, their 5-year survival rates were relatively low [1]. Besides, chemotherapy might cause adverse effects and lower patients’ quality of life [9, 18].
Accordingly, traditional Chinese medicine, an effective and safe complementary and alternative therapy, is considered to be able to treat cholangiocarcinoma. YCHD is a notable traditional Chinese medicine prescription, which consisting of three Chinese herbs, namely, Artemisiae Scopariae Herba, Gardeniae Fructus and Radix Rhei et Rhizoma; it has been adopted to clear heat, eliminate dampness and remove jaundice [19]. As demonstrated by pharmacological researches, YCHD can modulate inflammatory as well as immune response, ameliorate liver function, and regulate multiple pathways in cancer [11, 20]. YCHD exerts therapeutic effects on liver disorders and metabolic diseases, whereas its mechanisms on cholangiocarcinoma remain unclear. In the present study, network pharmacology approach was adopted to describe the relationship among active compounds, compound targets and signaling pathways, thereby revealing the potential mechanisms of YCHD.
According to the results achieved here, 32 active compounds in YCHD with 209 compound targets were identified, suggesting that YCHD exerted its pharmacological effects on treating cholangiocarcinoma via multiple targets. Quercetin, kaempferol, beta-sitosterol, isorhamnetin, and stigmasterol were identified as the vital active compounds with top five degrees. As for quercetin, existing studies have indicated that quercetin is capable of inhibiting cell proliferation of cancer cell lines and regulating cancer metabolisms by modulating the PI3K-Akt-mTOR signaling and MAPK/ERK1/2 pathways [21, 22]. A previous experimental research has proved that quercetin could inhibit inflammatory and tumorigenesis processes and suppress growth and migration of cholangiocarcinoma cell lines [23]. Kaempferol is reported to inhibit the growth and metastasis of cholangiocarcinoma through suppressing the PI3K-AKT pathway and their downstream proteins [24]. As to beta-Sitosterol, it has anticancer properties associated with cell cycle, proliferation, apoptosis, etc [25]. Isorhamnetin, a flavonoid metabolite, has been demonstrated to be able to produce anti-tumor effects by inhibiting the expression of NF-κB [26]. With regard to stigmasterol, it’s a major phytosterol in herbal plants, which can downregulate levels of inflammatory cytokines involving TNF-α, repress VEGF signaling, produce anti-angiogenic effects, thus inhibit cholangiocarcinoma growth in mice [27]. On the whole, it was speculated that YCHD is a multicomponent formula with multitarget therapeutic effects. Associations between these active compounds and cholangiocarcinoma are supposed to be deeply investigated.
In this study, AKT1, IL6, MAPK1, TP53, and VEGFA were identified as the 5 hub protein targets related to cholangiocarcinoma. Quercetin and kaempferol were proved to decrease the protein expression of AKT, VEGFA and IL-6, and increase P53 and MAPK levels. Previous study has reported that combined mTOR and AKT inhibition may significantly inhibit the tumor growth and proliferation of cholangiocarcinoma cell lines [28]. Similarly, the levels of AKT and IL6 can be decreased by genistein, which is associated with inhibitory effects on growth of cholangiocarcinoma cells [29]. Regarding MAPK1, it can be activated by osteopontin, a phosphorylated glycoprotein involved in various human cancers, and implicated in activating the MEK/MAPK pathway, therefore promote the growth and metastasis of intrahepatic cholangiocarcinoma [30]. TP53 loss may drive the reprogramming of hepatocytes to biliary cells, which may be related to the formation of intrahepatic cholangiocarcinoma [31]. VEGFA plays an important part in tumor angiogenesis. An experimental research has verified that interactions of LOXL2 with GATA6 can induce the expression of VEGFA, which may promote angiogenesis in cholangiocarcinoma subcutaneous tumors and tumor growth [32].
The GO analysis has demonstrated that YCHD is associated with the major biological process (e.g., positive regulation of transcription from RNA polymerase II promoter, negative regulation of apoptosis process, and positive regulation of transcription, DNA-templated). Regarding the RNA polymerase II promoter, a transcriptional regulatory element, was served as a sequence initiating transcription and regulating epigenetics [33, 34]. The RNA polymerase II binding to the tumor suppressor CDC73 contributed to transcriptional repression of oncogenes, conversely, oncogene overexpression could down-regulate CDC73 in tumors and lead to cell proliferation [35]. As for apoptosis, a physiological cell death, can regulate development of organisms, remove cells no longer available or differentiated ones incompatible with the body and maintain organizational homeostasis [36]. Tumor will be induced once cell apoptosis is out of control. Caused by many risk factors, chronic inflammation and cholestasis are driving forces in cholangiocarcinoma development [37]. The accumulation of bile acids from cholestasis lead to pH reduction, increase in apoptosis and activation of ERK1/2, Akt and NF-κB pathways [38]. A previous research [39] has confirmed that cholangiocarcinoma cell apoptosis was induced by THZ1 inhibiting the synthesis of antiapoptotic protein, and THZ1 could down-regulate the transcriprion of RNA polymerase II promoter in cancer cells and produce anti-tumour effects. In addition, the transcription of DNA-templated possibly related to the anti-tumor property of THZ1 [39]. The existing studies haven’t reported the relationship between DNA-templated transcription and cholangiocarcinoma, and this may become the further research direction. Therefore, we could speculate that the effects of YCHD on cholangiocarcinoma may relate to the above-mentioned biological processes.
As revealed from the KEGG pathway analysis, YCHD produced therapeutic effects on cholangiocarcinoma by regulating pathways (e.g., hepatitis B, the MAPK signaling pathway, the PI3K-Akt signaling pathway, and MicroRNAs in cancer). Recent epidemiological studies reported hepatitis B virus infection as a risk factor of intrahepatic cholangiocarcinoma [40, 41]. Intrahepatic cholangiocarcinoma patients with current and past hepatitis B virus infection were reported to display a better prognosis as compared with those without a history of hepatitis B virus infection [42]. Experimental results in this study confirmed that the active compounds of YCHD inhibited cell proliferation, induced apoptosis of cholangiocarcinoma cells, thus delayed the progression of cholangiocarcinoma. The MAPK signaling pathway participated in a variety of biological processes such as inflammatory response, cell differentiation, cell apoptosis and tumor invasiveness and so on [43]. A previous study confirmed that the MAPK signaling pathway was activated in intrahepatic cholangiocarcinoma cells by TRIM44, a protein involved in several kinds of cancers, to inhibit cell apoptosis and promote tumour invasion and metastasis [44]. For PI3K-Akt signaling pathway, it has been proved to regulate cell growth and proliferation and be critical to cancers [45, 46]. As one of the most intensively explored signaling pathways in tumorigenesis, PI3K-Akt signaling pathway may participate in the initiation, maintenance and metastasis of cholangiocarcinoma [47]. Existing research has elucidated that the inhibitory of transcription factor 21 mediated by PI3K-Akt signaling pathway could inhibit the progression of cholangiocarcinoma[48]. With respect to microRNAs, a group of small RNAs regulating genes expression, are modulators to suppress or progress tumor [49]. According to one previous research, microRNA-329 had an inhibitory effect on the expression of PTTG1 and inactivated the MAPK signaling pathway to inhibit the cholangiocarcinoma cell proliferation, induce cell cycle arrest as well as promote cell apoptosis, thus prevented the progression of cholangiocarcinoma [50]. Accordingly, it could be assumed that YCHD regulated hepatitis B, the MAPK signaling pathway, the PI3K-Akt signaling pathway, as well as MicroRNAs in cancer, so it could treat cholangiocarcinoma.
The molecular docking validated that vital active compounds and major targets showed good binding interactions. Except for regulation of quercetin on the PI3K-AKT and MAPK pathways described above, quercetin has the ability of inhibiting cell migration and angiogenesis mediated by downregulating VEGFA levels in glioblastoma cells [51],whereas no study has focused on the relationship of quercetin and VEGFA in treating cholangiocarcinoma. Kaempferol can treat cholangiocarcinoma through the PI3K-AKT pathway [24]. Moreover, kaempferol lowers the levels of TP53, which is involved in attenuating apoptosis mediated by Cisplatin [52]. In terms of beta-sitosterol, it is reported to induce MAPK phosphorylation, downregulate the PI3K/Akt, thus promote cell apoptosis and cell death [53]. Results from KEGG pathway analysis indicated that the action mechanisms of YCHD for cholangiocarcinoma were implicated in hub targets of AKT1 and MAPK1. We could speculate that YCHD exerts therapeutic effects on cholangiocarcinoma through these active compounds, target genes and signaling pathways.
There are some limitations in this study. First, some critical targets and active compounds may be ignored due to the incomplete information of databases. Second, multiple signaling pathways of YCHD acting on cholangiocarcinoma were predicted using the network pharmacology strategy, but the contribution of each pathway hasn’t been detected. Third, our current experiment and network pharmacology results provide directions for subsequent researches, whereas mechanisms still need fully investigated in future researches.