3.1 Network pharmacology analysis
3.1.1 Prediction and acquisition of Saikosaponin-d monomeric targets and gastric cancer targets
The Canonical SMILES of Saikosaponin-d were obtained from the Pubchem website. A total of 107 targets were identified by removing null values and weighting the predicted targets in the Swiss Target Prediction database. To predict gastric cancer target genes, the GSE49051 GeneChip dataset from the GEO database will be used. The predicted gastric cancer target genes in the Gene Cards database will be intersected with the selected dataset to obtain 3535 differentially expressed genes. Among these, 3292 genes were up-regulated and 243 genes were down-regulated, as shown in Figure 2A.
3.1.2 Acquisition of Saikosaponin-d and gastric cancer intersection target genes
The 54 intersecting target genes were obtained by comparing the differential genes of gastric cancer with the target genes of Saikosaponin-d monomer. Fig.2B, 2C, and 2D show the Venn diagram, heat map, and volcano diagram, respectively. Among the intersecting target genes, 49 were up-regulated and 5 were down-regulated. Bar graphs were drawn using the first 10 and first 5 target genes, as shown in fig.2E and 2F, respectively.
3.1.3 Construction of interaction networks between target proteins and screening of core targets
The 54 intersecting target genes were analyzed in the STRING database, resulting in 54 nodes and 203 edges. Fig.3A illustrates this, including 4 free target genes. After removing the free target genes, Cytoscape software was used to obtain 50 associated target genes. By setting the filtering condition to a degree value > 8, 17 core target genes were identified, as shown in Fig.3B. These 17 core target genes were then visualized in a bar chart, considering degree information, similar to the example in Fig.3C.
3.1.4 GO biofunctional enrichment analysis
The 54 intersecting target genes were enriched with GO function using the DAVID database. A total of 205 BP items, 43 CC items, and 53 MF items were obtained. The top 5 entries with the lowest P-values were selected and plotted in bubble diagrams, as illustrated in Fig.4A. These entries were primarily related to cell migration, apoptosis, and protein hydrolysis.
3.1.5 KEGG pathway enrichment analysis and construction of pathway-target network interactions
The 54 intersecting target genes were analyzed for KEGG pathway enrichment using the DAVID database. A total of 101 relevant pathways were identified, and the top 15 pathways with the highest P-value values were selected to create a bubble map (Fig.4B). The KEGG pathway bubble diagram revealed that the pathway with the highest number of enriched cells was 'Pathways in Cancer.' This pathway was primarily associated with apoptosis, inhibition of tumor angiogenesis, and inhibition of cell migration and invasion. To further explore the interactions between the top 15 pathways and their enriched target genes, the data was imported into Cytoscape software, and a pathway-target network was constructed (Fig.4C).
3.1.6 Genome enrichment analysis (GSEA)
The genes in the GSE49051 dataset file underwent GSEA enrichment analysis, revealing that the target genes were primarily associated with gastric cancer through complement and coagulation as well as cytokine receptor interactions, as depicted in Fig.4D.
3.1.7 Clinical relevance analysis
The 17 core target genes were analyzed for clinical relevance using the GEPIA database. From this analysis, six genes were identified as having clinical relevance in the therapy of stomach carcinoma: VEGFA, IL2, CASP3, BCL2L1, MMP2, and MMP1. Among these genes, MMP2 showed high expression in stomach carcinoma progression. The overall survival curves of individuals with stomach carcinoma who had higher expression of VEGFA and MMP2 were found to be lower than those with lower expression, as depicted in Fig.5A-D.
3.1.8 Molecular docking
The molecular docking of Saikosaponin-d with six core target proteins (VEGFA, IL2, CASP3, BCL2L1, MMP2, and MMP1) was verified using Auto Duck Tools software. The docking findings were visualized using Pymol, as shown in Fig.5E-J. The corresponding binding energy values were represented using trilinear tables and heat maps, with low energies indicated by the blue region and high energies indicated by the red region, as depicted in Fig.5K and 5L.
3.2 Experimental results
3.2.1 Saikosaponin-d inhibits cell viability
AGS, HGC-27, and GES-1 cells were treated with different concentrations of Saikosaponin-d (6 μM, 8 μM, 10 μM, 12 μM, 14 μM, 16 μM, 18 μM, 20 μM, 22 μM) for 12 h, 24 h, and 48 hours. CCK8 datas revealed that Saikosaponin-d significantly reduced the cell viability of stomach carcinoma cells. The inhibitory effect of the drug increased gradually with higher concentrations and longer treatment times. GES-1 cells showed the highest cell viability, but their proliferation was significantly inhibited after 24 h of drug intervention in AGS and HGC-27 cells. Therefore, a 24 h time period was chosen for drug intervention, and the low, medium, and high concentrations of the drug for stomach carcinoma cells were defined as follows: AGS (11 μM, 13 μM, 15 μM) and HGC-27 (14 μM, 16 μM, 18 μM). (Fig.6-A, B and C)
3.2.2 Saikosaponin-d promotes cell apoptosis
The outcomes of apoptosis study displayed that Saikosaponin-d significantly increased the rate of apoptosis. After 24 hours of Saikosaponin-d intervention at low, medium, and high concentrations, the apoptosis rates of AGS cells were (3.98±2.42)%, (10.5±1.98)%, and (17.7±2.81)% (Fig.6-D, E), respectively. These rates were higher compared to the control group (1.63±1.10%) (P<0.01). Similarly, the apoptosis rates of HGC-27 cells after 24 hours at low, medium, and high concentrations were (1.21±6.18)%, (1.43±8.98)%, and (3.53±43.2)%, respectively, which were also more than those of the control (1.21±4.96)% (P<0.05) (Fig.6-G, F).
3.2.3 Saikosaponin-d inhibits cellular wound healing
The impact of Saikosaponin-d on the horizontal migratory capacity of cells was assessed utilising the wound scratch test. The findings revealed that the number of cells entering the 'wound zone' increased over time after 24 hours of culture, compared to the initial measurement at 0 hours. Saikosaponin-d intervention at low, medium, and high concentrations in stomach carcinoma cells prominently hindered the wound healing ability of the cells, as compared to the control (P<0.001) (Fig.7-A, B, C, and D).
3.2.4 Saikosaponin-d inhibits cell migration and invasion
The influence of Saikosaponin-d on gastric cancer cell migration and invasion were assessed by observing changes in cell number using Transwell chambers. The outcomes indicated that Saikosaponin-d markedly decreased the number of AGS and HGC-27 cells (P<0.001), indicating its interference with cell migration (Fig.8-A, B, C, and D). Furthermore, Saikosaponin-d was found to reduce the invasive ability of AGS and HGC-27 cells as its concentration increased (P<0.001) (Fig.8-E, F, G, and H). These findings suggest that Saikosaponin-d exhibits strong cytotoxic effects and potential anti-tumor properties on gastric cancer cells, effectively inhibiting tumor metastasis even at low concentrations.
3.2.5 qRT-PCR
The outcomes manifested that the mRNA levels of BCL2L1, VEGFA, MMP1, and MMP2 were prominently reduced (P<0.001) in Saikosaponin-d intervened AGS cells compared to the control. Additionally, the mRNA levels of CASP3 and IL-2 were noticeably increased (P<0.05) (Fig.9-A).
3.2.6 Western Blot
To define the influence of Saikosaponin-d on apoptosis and cell migration and invasion, a Western Blot assay was conducted. The outcomes indicated that Saikosaponin-d significantly decreased the protein expression of apoptosis pathway-related proteins Caspase 3, Cleaved-Caspase 3, and BAX (P<0.05), while increasing the protein expression of BCL-2 (P<0.05) in AGS cells after 24 hours of intervention. Moreover, Saikosaponin-d also significantly reduced the protein expression of migration- and invasion-related proteins MMP1 and MMP2 (P<0.01). Additionally, the network pharmacologically enriched core protein IL-2 expression increased, and VEGFA expression decreased (P<0.05) in response to Saikosaponin-d (Fig.9-B, C, D, and E).