Angiogenesis is a critical process in the progression of malignant tumors and one of the hallmarks of cancer development[27]. Under normal physiological conditions, when the organism is mature, the vascular system will remain in a stationary phase for
a long time. As tumors continue to grow, the demand for oxygen and nutrients gradua -lly increases, and angiogenesis satisfies the metabolic demand of tumor cells.
Studying the relationship between tumor growth and angiogenesis, Folkman[28] found that cutting off the blood supply of the tumor would lead to tumor shrinkage or regression due to hypoxia. Several independent research groups have found that angiogenesis levels are significantly upregulated in most cancers[29–34].Dhar et al[35] found that angiogenesis was significantly increased in differentiated thyroid carcino ma and that DFS was significantly (P < 0.05) shorter in patients with hypervascular tumors. The study of Mohammed et al.[36] indicated that a high level of angiogenesis was closely related to metastasis and recurrence of colorectal cancer as well as a high mortality. Angiogenesis promoted the proliferation ability of breast cancer cells and shortened the metastasis time. With the increase in the microvascular density grade, the time to metastasis was shorter[37]. This evidence has demonstrated that angioge -nesis has a certain correlation with tumor growth and progression.
As a solid tumor, high vascularization is one of the most marked characteristics of KIRC, and with the development of KIRC, the expression of VEGF and PDGF increases[38]. Therefore, inhibition of angiogenesis has proven to be an effective and promising treatment option for advanced KIRC.This evidence has demonstrated that angiogenesis is correlated with tumor development and therapy. At present, the study of AAGs has become a research hotspot because of its important significance in the treatment and prognosis of many tumors, which has attracted the attention of many researchers. However, these studies were limited to single AAGs, and the holistic impact of AAGs on KIRC is unknown. Therefore, it is necessary to explore the integral controlled action of AAGs in KIRC.
In our research, we studied the transcriptional expression, mutation and CNV alterations of AAGs. We obtained 15 differentially expressed AAGs, and most DEGs were upregulated in KIRC. Evident CNV alterations and the highest mutation incidence of AAGs imply that as oncogenes, these genes drive the evolution of tumorigenesis.The TCGA_KIRC dataset was divided into AAG Cluster 1 and AAG Cluster 2. Comparing the OS between the two subgroups, Kaplan‒Meier analysis results showed that the OS of patients with low AAGs_scores was better than that of patients with high AAGs_scores, and a high AAG_score was associated with poor prognosis, indicating that AAG_scores had a superior predictive performance. GSEA findings demonstrated the close relationship between AAGs and metabolism-associated pathways. As a metabolic disease, mutations in key genes involved in the development of KIRC, such as VHL and MET, are closely related to metabolic pathways and reprogramming of metabolic networks. These results confirmed that AAGs could regulate metabolism-related activities of RCC through different pathways.
Recent studies have confirmed the promising efficacy of ICIs in the treatment of KIRC, but only some patients benefit from ICIs. One of the reasons may be the existence of an immunosuppressive tumor microenvironment (TME) in RCC. Studies have shown that the TME in KIRC is widespread compared to that in other solid tumors. Such abnormal pathologic vessel formation in the tumor with flexion, disorder and high leakage can create an immunosuppressive state of hypoxia, acidosis and elevated interstitial pressure in the tumor TME[39]. The evidence indicates that proangiogenic factors are involved in immunosuppressive activity[40], and inhibition of abnormal blood vessel formation can reverse this immunosuppressive state and enhance the efficacy of immunotherapy. The immunoinvasiveness and highly vascularized characteristics, which are the basis for immunotherapy in RCC, also have a substantial impact on the treatment response of patients through complex effects. Therefore, our study further explored the relationship between AAGs and the TME and aimed to provide a theoretical basis for the combination of immunotherapy and targeted therapy. CTLA4, PD-1 and its death-ligand 1 (PD-L1), as targets of immune checkpoint inhibitors, have made breakthrough progress in the treatment of a variety of advanced tumors, bringing survival benefits to patients, but the clinical treatment response of different patients is variable. This study showed that the AAG score was not related to PD-1 expression in KIRC but was related to PD-L1 and CTLA4. The results indicated that the TME is involved in many important biological processes and that the AAG_score can accurately predict the immunotherapeutic effect of KIRC. The ImmuneScore and StromalScore assessed by the ESTIMATE method can be used to predict tumor purity and describe the proportion of immune cells and stromal cells. Our study demonstrated that the high AAG_score group had higher ImmuneScores and StromalScores, suggesting that angiogenesis could be associated with immune cell infiltration and that the stromal cell content affected KIRC invasion and migration to a certain extent. The TME includes a large number of immune cells and can be further divided into killer cells related to tumor killing and immunosuppressive cells related to tumor evasion from immune surveillance. Immunosuppressive cells mainly include tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). Tregs also play an important role in tumor evasion by suppressing the activity of immune killer cells by secreting TGF-β and IL-10 and reducing the activation of effector T cells by downregulating the expression of dendritic cell costimulatory molecules. Tregs are associated with poor survival[41]. The study demonstrated that patients with high AAG scores had abundant Tregs. In addition, the previous results showed that high AAGs were associated with poor survival, which is concordant with our findings. Therefore, the combination of antiangiogenesis and immunotherapy should theoretically have a synergistic antitumor effect. This study further investigated the relationship between the AAG score and the response to immunotherapy and targeted therapy. An increased mutation rate is a distinctive feature of cancer. The accumulation of gene mutations leads to carcinogenesis. As TMB has gradually developed as a biomarker for predicting ICI efficacy, numerous studies have described changes in TMB levels in different tumor types and histologies. In a study by Chalmers et al.[42], TMB levels varied widely among tumors, with melanoma having the highest TMB levels, while leukemia and childhood tumors had the lowest TMB levels, and cancers such as breast and ovarian cancer showed moderate TMB levels. In previous studies, higher TMB levels have been associated with poor outcomes in patients, and low levels of TMB may be better for the prognosis of patients[43–49]. It is generally believed that immune infiltration caused by tumor antigens generated by tumor-specific mutations is a prerequisite for ICI function. The TMB of RCC is moderate to low. Many studies have indicated that the TMB in RCC alone cannot be used as a predictor of ICI drug response[50–51]. Carcinogenesis caused by gene mutation is associated with neoangiogenesis. Therefore, exploring the correlation between the AAG score and gene mutations in RCC is helpful to reveal the mechanism of ICI therapy and evaluate its important efficacy value. Our results proved that patients with lower TMB have favorable outcomes. Although there was no significant difference, there was a positive association trend between the AAG score and TMB. We performed survival analysis of KIRC with the combined TMB and AAG score and found that the low AAG score + low TMB group had a better OS than the high AAG score + high TMB group, suggesting that the AAG score combined with TMB effectively predicts the responsiveness to immunotherapy.
The extensive immune infiltration, abnormal vascularization and highly fibrotic TME in RCC provide the material basis for tumor cell proliferation and metastasis and limit the immune surveillance of tumor killer cells, finally leading to immunotherapy drug resistance. By reducing the permeability of tumor blood vessels to reduce vascular pressure, improve tissue hypoxia, induce vascular normalization and inhibit the formation of abnormal blood vessels, the state of immune suppression can be reversed[52] and the efficacy of immunotherapy enhanced. On the other hand, ICIs can activate CD4 + T lymphocytes, CD8 + T lymphocytes, and Th1 cells, which secrete antitumor cytokines, such as interferon γ (INF-γ) and tumor necrosis factor (TNF), to regulate the immune microenvironment and play a role in anti-abnormal angiogenesis and the promotion of vascular normalization[53–54].At present, there is still a lack of effective predictors of ICI efficacy in KIRC.Most of the KIRC patients either had no initial response to antiangiogenic therapy and ICIs (primary resistance) or were in relapse after a period of treatment (acquired resistance). Investigating the sensitivity of different AAG_score groups to chemotherapy and target drugs helps to find biomarkers that could predict the response so that it could be used only in patients who would benefit from it. The TIDE score showed that low-AAG score patients had low dysfunction and ESTIMATE scores and high IPSs, suggesting that low-AAG score patients could present better efficacy after ICI treatment, thus obtaining greater survival benefit.
This study also has some limitations: (1)This study is a single-center retrospective study, and there is a certain selection bias in the study subjects, which may mean that the results are not universally applicable.(2)The sample size included in this study was not large enough. (3) This study lacks external verification and needs to be continuously improved upon in future clinical work.