The term “herb pair” refers to the combined use of two single herbs that are used to treat a specific disease in order to enhance clinical efficacy or minimize adverse effects [42]. SB belongs to the labiaceae, and it is sour in taste and cold in nature [43]. HD belongs to the genus Hedyotis of Rubiaceae, and it is bitter, light, and cold in nature [44]. As a common herb pair, SBHD have the functions, such as clearing away heat and toxins, removing blood stasis, promoting blood circulation, diuresis, and detumescence, which can be used as clinical adjuvant therapy for a variety of cancers [16, 45]. However, the therapeutic effects and specific mechanisms of SBHD on ESCC remain unclear.
In this study, network pharmacological was used to systematically study the active ingredients of SBHD in treatment of ESCC. The results indicate that quercetin, baicalein, luteolin, stigmasterol, and wogonin have more targets than other active compounds, which may be the core active components of SBHD treating of ESCC. Quercetin and stigmasterol are both the main active components shared by SB and OD, and the other three are the main active components of SB. It has been reported that a dietary pattern rich in quercetin may play a protective role in the development of ESCC [46]. Zheng et al. [47] found that quercetin could increase apoptotic effects for ESCC. Zhao et al. [48] found that quercetin inhibited the formation of esophageal precancerous lesions, and the inhibition was associated with decreased inflammation and esophageal cancer cell proliferation. Baicalein, a natural flavonoid, not only could directly induce apoptosis, but also inhibits the progression and promotes radiosensitivity for ESCC [49, 50]. Luteolin is also plant flavonoid which can inhibits cell proliferation and induces cell apoptosis for human ESCC [51, 52]. Stigmasterol is a natural phytosterols, and it could increase dietary intake of stigmasterol were associated with a decreased risk of ESCC [53]. Wogonin is a plant flavonoid extracted from roots, which has various anti-cancer effects [54].
PPI core network analysis found that the 6 hub genes, such as IL6, CASP3, MYC, AR, CAV1, and RUNX2, which may be the key targets for SBHD treating ESCC. IL6, one of the major cytokines in the tumor microenvironment, and its over-expression has been reported in almost all types of tumors [55]. IL6’s over-expression is also a key event for ESCC carcinogenesis [56]. Tong et al. [57] found that IL-6 was closely related to the pathological development of ESCC, and mainly involved in tumor tissue angiogenesis and endothelial cell formation. CASP3 is the main effector of apoptosis and involved in tumor development [58]. Zhang et al. [59] found that the decrease of CASP3 transcriptional activity and gene expression might inhibit apoptosis, and thus be associated with an increased risk of ESCC. Luo et al. [60] found that the decrease of CASP3 transcriptional activity could promote cell proliferation and inhibit apoptosis, thereby exhibited its oncogenic role in ESCC. MYC encodes a transcription factor involved in the regulation of cellular proliferation, differentiation and apoptosis [61]. Lian et al. [62] found that MYC expression in tumor tissues was obviously higher than the adjacent normal tissues, and might be a new diagnostic indicator of ESCC. Wang et al. [63] reported that MYC amplification induced cell cycle dysregulation is a common cause for ESCC, while targeting MYC could cause significant tumor suppression both in vitro and in vivo. AR was widely expressed in human several tissues, and plays an important role in many kinds of cancers [64]. Zhang et al.[65] found that the protein expression of AR is up-regulated in the ESCC tissue samples, and AR over expression induced increases in ESCC cell invasion and proliferation in vitro. CAV1 is one of the major structural proteins of caveolae, and its overexpression correlates with a poor prognosis and tumor progression in ESCC [66]. Several studies have also confirmed that CAV1 expression is closely related to ESCC, and it could be a powerful prognostic marker for patients with ESCC [67–69]. RUNX2 is related to a variety of tumors, particularly tumor invasion and metastasis [70]. It has been reported that RUNX2 was highly expressed in esophageal carcinoma tissues and cells, while knockdown of RUNX2 markedly suppressed tumor formation in vivo [71].
GO enrichment analysis showed that the biological processes related to SBHD in treatment of ESCC were mainly containing response to oxygen-containing compound, response to chemical, response to nitrogen compound, cellular response to nitrogen compound, response to organonitrogen compound, response to endogenous stimulus, response to ketone, response to hormone, response to organic substance, regulation of cell proliferation, cellular response to organonitrogen compound, response to organic cyclic compound, cellular response to chemical stimulus, intracellular signal transduction, and cellular response to endogenous stimulus. The KEGG pathways were mainly involved chemical carcinogenesis-receptor activation, cellular senescence, hepatitis B, MAPK signaling pathway, colorectal cancer, transcriptional misregulation in cancer, kaposi sarcoma-associated herpesvirus infection, IL-17 signaling pathway, proteoglycans in cancer, AGE-RAGE signaling pathway in diabetic complications, amoebiasis, human T-cell leukemia virus 1 infection, TNF signaling pathway, salmonella infection, and apoptosis. The studies have shown that these signaling pathways play an important role in the occurrence and development of ESCC, such as cellular senescence [72], hepatitis B [73], MAPK signaling pathway [74], proteoglycans in cancer [75], and apoptosis [76]. The study results suggest that SBHD may play a therapeutic role in ESCC through the above pathways.
Molecular docking reveals the interaction between the components of the network, thus improving the accuracy of the network[77]. In this study, the key target protein of SBHD on ESCC was docked with core compounds. The results showed that the 5 core active components (quercetin, baicalein, luteolin, stigmasterol, and wogonin) had good binding properties with the 6 key therapeutic targets (IL6, CASP3, MYC, AR, CAV1, and RUNX2) related to ESCC, which further verified the accuracy of target prediction by network pharmacology. These datas may be of great significance for further experimental study to determine the molecular mechanisms of SBHD on ESCC and the development of anti-tumor natural herbal medicines.