Fig. 3: Screening IL8 as the therapeutic target after chemotherapy resistance.

A The volcano plot of RNA transcription sequencing of the first-line chemotherapy group and the sequential chemotherapy group. A total of 256 differentially expressed genes (DEGs) with fold-change greater than 2. B KEGG pathways enriched by DEGs in the transcriptome affected by sequential chemotherapy compared with first-line chemotherapy. C qRT-PCR assays were performed to detect the changes of the DEGs in the three enriched signaling pathways most associated with cancer in tumor tissues treated with sequential and first-line chemotherapy. D, E IL8 expression at different periods of chemotherapy was detected by qRT-PCR assays and western blot analysis. Data are mean ± standard deviation. *P < 0.05, **P < 0.01. F Upregulation of IL8 in GC samples was obtained in the GEPIA database. G Kaplan–Meier OS curves in GC patients according to the expression of IL8. H Kaplan–Meier OS curves in GC patients after 5-Fu therapy according to the expression of IL8. I Western blot analysis of IL8 expression in BGC823 cells transfected with siRNAs against IL8. J CCK8 assays was carried out to detect the viability of BGC823 cells transfected with si-IL8#2 and si-IL8#3. **P < 0.01, ***P < 0.001. K, L Representative images (K) and quantification (L) of BGC823 cells transfected with si-IL8#2 and si-IL8#3 by EdU staining assays. Data are mean ± standard deviation. **P < 0.01. M–O Representative images (M) and quantification (N, O) of BGC823 cells transfected with si-IL8#2 and si-IL8#3 by colony-forming experiments and transwell assays. Data are mean ± standard deviation. **P < 0.01, ***P < 0.001.