1. Identification of DEGs
To screen for meaningful biomarkers between the EGFR-TKI-sensitive and -resistant groups, using the R limma package and the p < 0.05 and [logFC] > 2 cutoff criteria, we detected a total of 1302 DEGs when comparing the EGFR-TKI-resistant and -sensitive groups based on the GSE64472 and GSE130160 datasets.773 DEGs were obtained in the resistant group of GSE64472, including 339 upregulated and 436 downregulated DEGs. A total of 529 DEGs were obtained, including 479 upregulated and 52 downregulated DEGs in the resistant group of GSE130160. The volcano plot of DEGs is presented in Fig. 1a, 1b, and the expression heatmap of the top 50 DEGs is presented in Fig. 1c, 1d (ranked by padj. value).
2. GO and KEGG enrichment analyses of DEGs
To clarify the role of these DEGs in the progression of EGFR-TKI resistance in NCLC, we immediately predicted the functional role of these genes. GO analysis, including cellular components (CC), molecular function (MF), biological process (BF), and KEGG analysis, was performed using the DAVID database to understand the functions of DEGs. With an FDR-corrected p value < 0.05 and enrichment score > 1.5 as the cutoff value, GO functional enrichment analysis resulted in a total of 1302 DEGs mapped to 48 significantly enriched functional clusters. In total, 11 GO terms were significantly enriched in cellular components, including 'plasma membrane', 'extracellular region', 'extracellular space', 'extracellular exosome' and 'proteinaceous extracellular matrix' (Fig. 2a). Enrichment of 8 GO terms, such as 'integrin binding', 'cytokine activity', 'growth factor activity', 'protein homodimerization activity', 'platelet-derived growth factor binding', 'calcium ion binding', 'extracellular matrix structural constituent' and 'transmembrane signaling receptor activity', belonged to molecular functions (Fig. 2b). A total of 29 biological processes were enriched, mainly involving 'immune response', 'cell adhesion', 'extracellular matrix organization', 'positive regulation of bone mineralization' and 'positive regulation of T-cell proliferation' (Fig. 2c). A total of 1303 DEGs were mapped into the KEGG database using DAVID, and enrichment score > 1.5 and p value < 0.05 were used as enrichment screening standards. In total, 16 enriched functional clusters of the DEGs were obtained (Fig. 2b), such as ‘cytokine–cytokine receptor interaction’ (34 genes), ‘melanogenesis’ (18 genes), ‘circadian entrainment’ (17 genes), ‘basal cell carcinoma’ (12 genes), and ‘dopaminergic synapse’ (20 genes).
3. Integration of the protein–protein interaction network and module analysis
The PPI network of 1302 DEGs was constructed and visualized using the STRING database. The isolated nodes and partially loosely connected gene nodes were removed, and the remaining DEGs together constituted a complex multicenter interaction network map, which contained 1402 nodes and 4761 edges (Fig. 3a). The average node degree was 7.92, and the average local clustering coefficient was 0.286. Among the 1402 nodes, the top 20 and top 10 DEGs with the highest degree of nodes were screened based on the Cytoscape software analysis results (Fig. 3b, 3c). The expression of the top 20 genes in GSE64472 and GSE130160 samples is shown in Fig. 3d and 3e. The results of the top 10 DEGs were as follows: IL6, IL10, CXCL9, ITGAM, CCL5, CD4, IDO1, HAVCR2, TLR9, and CCR7. The full name and function of these hub genes are listed in Table 1.
Table 1
Functional roles of 10 hub genes
No.
|
Gene symbol
|
Full name
|
Function
|
1
|
IL6
|
interleukin 6
|
a cytokine that functions in inflammation and the maturation of B cells.
|
2
|
IL10
|
Interleukin 10
|
a cytokine produced primarily by monocytes and to a lesser extent by lymphocytes. This cytokine has pleiotropic effects in immunoregulation and inflammation.
|
3
|
CXCL9
|
C-X-C Motif Chemokine Ligand 9
|
The protein encoded is thought to be involved in T-cell trafficking. The encoded protein binds to C-X-C motif chemokine 3 and is a chemoattractant for lymphocytes but not for neutrophils.
|
4
|
ITGAM
|
Integrin Subunit Alpha M
|
This gene encodes the integrin alpha M chain. This I-domain containing alpha integrin combines with the beta 2 chain (ITGB2) to form a leukocyte-specific integrin. The alpha M beta 2 integrin is important in the adherence of neutrophils and monocytes to stimulated endothelium, and in the phagocytosis of complement coated particles.
|
5
|
CCL5
|
C-C Motif Chemokine Ligand 5
|
This gene is one of several chemokine genes clustered on the q-arm of chromosome 17. This chemokine, a member of the CC subfamily, functions as a chemoattractant for blood monocytes, memory T helper cells and eosinophils.
|
6
|
CD4
|
CD4 molecule
|
the CD4 membrane glycoprotein acts as a coreceptor with the T-cell receptor on the T lymphocyte to recognize antigens displayed by an antigen presenting cell in the context of class II MHC molecules.
|
7
|
IDO1
|
Indoleamine 2,3-Dioxygenase 1
|
a heme enzyme that acts on multiple tryptophan substrates. This enzyme is thought to play a role in a variety of pathophysiological processes such as antimicrobial and antitumor defense, neuropathology, immunoregulation, and antioxidant activity.
|
8
|
HAVCR2
|
Hepatitis A Virus Cellular Receptor 2
|
The protein belongs to the immunoglobulin superfamily, and TIM family of proteins. CD4-positive T helper lymphocytes can be divided into types 1 (Th1) and 2 (Th2) on the basis of their cytokine secretion patterns.
|
9
|
TLR9
|
Toll Like Receptor 9
|
The protein encoded by this gene is a member of the Toll-like receptor (TLR) family, which plays a fundamental role in pathogen recognition and activation of innate immunity.
|
10
|
CCR7
|
C-C Motif Chemokine Receptor 7
|
The protein encoded by this gene is a member of the G protein-coupled receptor family. This receptor is expressed in various lymphoid tissues and activates B and T lymphocytes.
|
4. Disease-free surviva (DFS) analyses of hub genes in NSCLC
Based on the practicality of clinical guidance, we needed to find genes in these hub genes that could promote EGFR-TKI resistance and could be used for cancer progression prediction. We used the Kaplan–Meier Plotter database to explore how these hub genes were related to NSCLC patient DFS. Of these genes, we found that only elevated ITGAM expression was linked to better NSCLC patient DFS (HR = 0.73, 95% CI: 1.26–1.81, P = 0.045) (Fig. 4). Taken together, the results show that ITGAM functions as a core gene that has a close relationship with EGFR-TKI resistance.
5. Drug Interaction Prediction for EGFR-TKI resistance
The relationship between the EGFR-TKI resistance-specific gene ITGAM and the corresponding potential therapeutic candidates was retrieved from DGIdb. A total of 207 drugs were predicted to interact with ITGAM. Among them, the drugs with the highest number of target genes were liarozole, rovelizumab, dimethyl, sulfoxide, clarithromycin, fentanyl, phenylephrine, theophylline, morphine, hydrocortisone, and atorvastatin (Table 2).
Table 2
Top 10 drug predictions for the EGFR-TKI resistance-specific key gene TIMP1
Drug
|
Interaction Type & Directionality
|
Sources
|
Query Score
|
Interaction Score
|
Liarozole
|
n/a
|
NCI
|
2.92
|
4.25
|
Rovelizumab
|
antagonist (inhibitory)
|
ChemblInteractions
|
1.46
|
2.13
|
Dimethyl Sulfoxide
|
n/a
|
NCI
|
1.46
|
2.13
|
Clarithromycin
|
n/a
|
NCI
|
1.35
|
0.98
|
Fentanyl
|
n/a
|
NCI
|
0.67
|
0.49
|
Phenylephrine
|
n/a
|
NCI
|
0.63
|
0.91
|
Theophylline
|
n/a
|
NCI
|
0.37
|
0.53
|
Morphine
|
n/a
|
NCI
|
0.28
|
0.41
|
Hydrocortisone
|
n/a
|
NCI
|
0.23
|
0.34
|
Atorvastatin
|
n/a
|
NCI
|
0.15
|
0.21
|