Background: Cetuximab has been regularly added to the treatments for metastatic colorectal cancer worldwide. However, due to its therapeutic insensitivity and underlying mechanisms being largely unknown, the clinical implementation of cetuximab in colorectal cancer remains limited.
Methods: The gene expression profile GSE56386 was retrieved from the Gene Expression Omnibus database. Differentially expressed genes were identified between cetuximab-responsive patients and nonresponders, annotated by gene ontology, Kyoto Encyclopedia of Genes and Genomes pathway analysis, and further analyzed by protein-protein interaction networks. The integrative prognostic analysis was based on The Cancer Genome Atlas and PrognoScan.
Results: 1350 differentially expressed genes were identified with 298 upregulated and 1052 downregulated. Epidermis development, the cornified envelope, calcium ion binding, and amoebiasis were enriched in upregulated genes while digestion, the apical part of the cell, the 3',5'-cyclic-adenosine monophosphate phosphodiesterase activity and pancreatic secretion were found enriched in downregulated genes. The top 10 hub genes were identified, including epithermal growth factor, G-protein subunit β 5, G-protein subunit γ 4, fibroblast growth factor 2, B-cell lymphoma protein 2, acetyl-coenzyme A carboxylase β, KIT proto-oncogene receptor tyrosine kinase, adenylate cyclase 4, neuropeptide Y, and neurotensin. The hub genes exhibited distinct correlations in cetuximab-treated and untreated genomic profiles (GSE56386, GSE5851 and GSE82236). The highest correlation was found between B-cell lymphoma protein 2 and acetyl-coenzyme A carboxylase β in GSE56386. The mRNA expression of hub genes was further validated in the genomic profile GSE65021. Furthermore, B-cell lymphoma protein 2 and acetyl-coenzyme A carboxylase β also exhibited highest degrees among the hub genes correlation networks based on The Cancer Genome Atlas. Both B-cell lymphoma and acetyl-coenzyme A carboxylase β were not independent prognostic factors for colorectal cancer in univariate and multivariate Cox analysis. However, integrative survival analysis indicated that B-cell lymphoma protein 2 was associated with favorable prognosis (hazard ratio = 0.62, 95% confidence interval, 0.30-0.95, P = .024).
Discussion: This in silico analysis provided a feasible and reliable strategy for systematic exploration of insightful target genes, pathways and mechanisms underlying the cetuximab insensitivity in colorectal cancer. B-cell lymphoma protein 2 was associated with favorable prognosis.
Keywords: KEGG pathway; cetuximab; colorectal cancer; differentially expressed genes; gene ontology; protein–protein interaction.