Association of the EPHA5 mutation status with clinical characteristics of patients with LUAD
To identify the mutated genes that might be related to the response to ICIs in advanced LUAD patients, we first investigated genes with different mutation frequencies between patients who achieved a DCB and those who achieved NDB among all patients who received ICIs in the ICI-treated LUAD cohort. The gene mutation pattern showed that EPHA5 was one of the top 20 frequently mutated genes in patients who achieved DCB compared to patients who achieved NDB. Since EPHA5 encodes an RTK involved in cancer development, and EPHA5 was found to be mutated in multiple cancers. We thus speculated that EPHA5 may be related to the response to ICIs. To verify our hypothesis, we initially analyzed the mutation characteristics of EPHA5 based on both the ICI-treated LUAD and TCGA-LUAD datasets. The results revealed that the mutation sites of EPHA5 spanned the entire gene, including the ligand binding site and receptor activity sites, which might affect the protein structure and function of EPHA5 (Fig. 1a). We then divided the two cohorts into the EPHA5-WT and EPHA5-MT subgroups and analyzed the correlation between the EPHA5 mutation status and clinical characteristics of patients. As shown in Fig. 1b, c, analysis of the two datasets showed that a history of tobacco exposure exhibited the strongest association with the EPHA5 mutation status among all clinical variables considered. Interestingly, EPHA5 mutation was also associated with TMB and neoantigen load. EPHA5 mutation also showed a positive correlation with the mutation frequency of several common mutations found in LUAD, such as missense mutations in TP53, KEAP1 and LRP1B, which affect the efficacy of immunotherapies, suggesting that EPHA5 mutations may be related to the response to ICIs in patients with LUAD.
EPHA5 mutation is associated with the clinical benefit of ICIs in LUAD patients
Since TMB and neoantigen load serve as predictive markers of the response to ICIs, we first aimed to determine whether EPHA5 mutation in LUAD patients affects the whole TMB and alters tumor antigenicity. By analyzing the ICI-treated LUAD and non-ICI-treated TCGA-LUAD datasets, we determined that the EPHA5-MT subgroups had a higher TMB and neoantigen load (Fig. 2a), suggesting a potential relationship between mutated EPHA5 and the response to ICIs in LUAD patients. We then assessed the association of EPHA5 mutation with the prognosis of LUAD patients. The results showed that patients in the EPHA5-MT subgroup experienced longer PFS than those in the EPHA5-WT subgroup when analyzing the ICI-treated LUAD cohorts (p = 0.039) (Fig. 2b); however, there was no significant difference in either DFS or OS between the EPHA5-WT subgroup and the EPHA5-MT subgroup in the non-ICl-treated TCGA-LUAD cohort (p>0.05) (Fig. 2c). This finding suggests that LUAD patients with EPHA5 mutations benefit from ICI treatment but not non-ICI treatment.
EPHA5 Mutation Is Associated With High CNV Counts
The acquisition of tumor aneuploidy correlates with markers of immune evasion and is associated with reduced immune-mediated cytotoxic function, and high CNV counts have been confirmed to be associated with poor clinical outcomes regarding NSCLC immunotherapy. Therefore, we explored the associations of the EPHA5 mutation status with CNVs at the chromosome arm level in the TCGA-LUAD cohorts. As shown in Fig. 3, we found that CNV counts were relatively lower in the EPHA5-MT subgroup than in the EPHA5-WT subgroup at 1q21.2, 1q22, 8q24.21, 9p21.3, and 14q13.3. However, CNV counts could not be validated in the ICI-treated LUAD dataset due to limited genomic coverage of the targeted panel.
EPHA5 Mutation Is Associated With Activated Antitumor Immunity
TILs are important markers for predicting the response to ICI treatment. We thus continued to survey the relationships between EPHA5 mutation and common immune infiltrates in the LUAD-TCGA cohort. Our results showed that tumor-infiltrating T lymphocytes, including CD8 + T cells, CD4 + resting memory T cells and macrophage M1 cells, were generally more abundant in the EPHA5-MT tumors than in the EPHA5-WT tumors, as evaluated by the expression levels of immune cell marker genes and CIBERSORT analysis (Fig. 4a, b). The immune signature analysis also revealed significantly increased expression levels of chemokines and cytolytic activity-associated gene signatures (CCL5, CXCL9, CD8A, CD8B, and GZMB) in EPHA5 mutant tumors compared to wild-type EPHA5 tumors. We also found that the levels of LAG3, an immune checkpoint marker, were higher in the EPHA5 mutation subgroups (Fig. 4c).
These results indicate that EPHA5 mutation is strongly associated with a relatively hot immune microenvironment, which firmly supports its ability to predict the response to ICIs in LUAD patients.
EPHA5 mutation is associated with high mutation frequencies of DDR pathway genes
Considering that DDR gene alterations are associated with the response to ICIs in tumors, we further examined the association of the EPHA5 mutation status and DDR gene mutations in both the ICI-treated LUAD cohort and the non-ICI-treated TCGA-LUAD cohort. We observed a trend towards an enrichment of DDR gene alterations in the EPHA5 mutation subgroups. Although this trend was not observed in the base excision repair (BER) pathway in the ICI-treated LUAD cohort, eight other pathways (i.e., homologous recombination (HR), mismatch repair (MMR), Fanconi anemia (FA), nucleotide excision repair (NER), nonhomologous end joining (NHEJ), DDR, DNA double-strand breaks (DSBs) and single-strand breaks (SSBs)) demonstrated enrichment for mutations in the EPHA5-MT subgroups versus the EPHA5-WT subgroups (Fig. 5).
EPHA5 Mutation And Drug Selection Of LUAD Cells
In addition to examining the role of EPHA5 mutation in disease progression, we also investigated the role of EPHA5 mutation in chemotherapy and molecular-targeted drug therapy in LUAD patients. By analyzing the GDSC database, we found that the mutation status of EPHA5 had no effect on cell sensitivity to common chemotherapy drugs, such as cisplatin and irinotecan (Fig. 6a). Interestingly, the EPHA5-WT subgroup and the EPHA5-MT subgroup had different sensitivities to 37 molecular-targeted drugs, of which serdemetan, lox2 and PF1-1 were relatively sensitive in the EPHA5-MT subgroup, while the other 34 drugs were more resistant in the EPHA5-MT subgroup (Fig. 6b and Fig. S1). This result may provide a reference for the treatment choice in LUAD patients with EPHA5 mutations.
Pathway Enrichment Analysis Of EPHA5 Mutation
Finally, we investigated whether EPHA5 mutation is involved in immune-related pathways using the LUAD-TCGA cohorts. GSEA showed that the insulin receptor, negative regulation of Notch signaling, MHC II antigen presentation, regulation of p53, and NK cell-mediated cytotoxicity pathways, which enhance antitumor immune activity in cancers, were significantly enriched in with the EPHA5-MT subgroup, while the positive regulation of the ERK1 and ERK2 cascade, PI3K cascade, FGFR2 function, and NF-kappaB signaling pathways were significantly enriched in the EPHA5-WT subgroup. In addition, consistent with previous studies showing that microRNAs (miRNAs) may play a role in regulating tumor immunity through the direct regulation of genes involved in immune activation [38], our results revealed a significant enrichment of gene silencing by miRNAs in the EPHA5-MT subgroup (Fig. 7). These results suggest that EPHA5 mutation might affect tumor immunity in LUAD patients by influencing multiple pathways.