Renal cell carcinoma accounts for 3% of adult malignancies and is the deadliest of all urinary cancers. The most common type is ccRCC[24]. It has shown strong resistance to conventional therapies such as chemotherapy and radiotherapy, and 2-year survival rate in metastatic patients < 20%[25]. Due to the important role of the immune system in cancer, the immune microenvironment has attracted people's attention. The prognosis of ccRCC is mostly related to immunity. Studies have shown that CD8+ T cells in ccRCC are significantly correlated with the prognosis of patients[26]. Therefore, in order to improve the prognosis of ccRCC and provide reliable information for guiding correct individualized treatment strategies, it is urgent to screen out reliable immune predictors and prognostic indicators.
LncRNA is closely related to the occurrence, development and prognosis of cancer. It does not encode proteins, but in the form of RNA regulates gene expression at various levels, including epigenetic, transcriptional, or post-transcriptional regulation. The abnormal expression of some lncrnas may be related to the invasion, metastasis and poor prognosis of renal clear cell carcinoma[27]. LncRNA regulation of the immune microenvironment of ccRCC has become a research hotspot. Some studies have shown that a large number of different types of immune cells infiltrate around and in the stroma of ccRCC. However, current studies mainly focus on finding single genes as prognostic markers for patients with malignant tumors. These markers are based on quantitative expression levels of transcripts and may be subject to occasional errors. Therefore, in this study, two lncRNAs were used to form lncRNA pairs to construct a reasonable model to evaluate the prognosis and immune cell infiltration of patients with ccRCC.
First, we retrieved the original lncRNA data from TCGA, conducted differential co-expression analysis to classify DEirlncRNA, and verified the lncRNA pairs using the improved 0 or 1 matrix cyclic single pairing method. Second, we performed a univariate analysis in combination with an improved Lasso penalty regression that included cross-validation, multiple repetitions, and random stimulus procedures to identify pairs of DEirlncRNAs. Then, AUC values under each ROC were calculated to obtain the optimal model, and AIC values of each point on AUC were also calculated to distinguish the optimal cut-off points for HCC patients in the high and low risk groups. Finally, we evaluated the new model in a variety of clinical Settings including survival, clinicopathological features, tumor-infiltrating immune cells, chemotherapy, and checkpoint-related biomarkers.
In general, high abundance lncRNAs have important biological functions. GAS5 is a well-known lncRNA, as a tumor suppressor, its expression is down-regulated in bladder cancer, kidney cancer and other cancers, which is negatively correlated with tumor size, grade and prognosis[28]. Dasgupta et al. [29]investigated the role of the interaction between lncRNA CDKN2B-AS1 and miR-141-3p in the progression and metastasis of renal cancer. CDKN2B-AS1 overexpression was positively correlated with poor overall survival in RCC patients, and miR-141 expression could also effectively distinguish malignant tissues from non-malignant tissues. Zhu et al. [30]found that lncRNA HIF1A-AS2 was highly expressed in renal carcinoma tissues and renal clear cell carcinoma cells. In vivo, HIF1A-AS2 interferes with cell proliferation, invasion and migration, and accelerates cell apoptosis. However, current studies mainly focus on the evaluation of cancer prognosis by single lncRNA, which is contingent to a certain extent, while two or more biomarkers have higher sensitivity and specificity in cancer diagnosis and prognosis prediction. Deng et al. [31]extracted 9 kinds of hepatocellular carcinoma related lncRNAs from TCGA database and established a model to analyze the prognosis and clinical characteristics of hepatocellular carcinoma, which is conducive to individualized treatment of cancer patients. Sun et al. [32]developed a new immune-related lncRNA marker and constructed 5 lncRNA prognostic models, which have important clinical significance for the prognostic prediction of renal cancer.
Based on Lasso Penalized Modeling proposed by Sveen et al. [33], we constructed a risk assessment model for renal clear cell carcinoma and improved the model to improve the prognostic accuracy. After differentiating the high and low risk groups with this new escalation, we reassessed survival outcomes, performed univariate and multifactorial clinicopathological analyses, and analyzed the efficacy of chemotherapy agents for ccRCC treatment, tumor immune invasion, and biomarkers associated with checkpoint inhibitors. This model only needs to detect pairs of high or low expression, rather than the specific expression value of each lncRNA, which has strong clinical practicability and can be used to distinguish high and low risk clinical cases.
Stephane Chevrier et al. identified 17 tumor-associated macrophage phenotypes, 22 T-cell phenotypes, and a unique immune component associated with progression-free survival by in-depth immunoassay of 73 patients with ccRCC and 5 healthy controls.[34] We used 7 commonly used immune infiltrating cell assessment methods, including TIMER, CIBERSORT, XCELL, QUANTISEQ, MCPcounter, EPIC and CIBERSORT-ABS, to explore the relationship between risk model and tumor infiltrating immune cells. Our results showed that natural killer cells, macrophages, T cell regulatory (Tregs), CD4+ Th1 and B cells which are tumor-infiltrating immune cells were positively correlated with DEirlncRNAs. Tumor infiltrating immune cells can regulate cancer progression, showing potential prognostic value. CD4+ helper T cells can target antigenic tumors and inhibit tumor growth[35]. CD4+ T cell infiltration regulates the proliferation of renal cell carcinoma cells by regulating TGFβ1/YBX1/HIF2α signaling[36]. Macrophages are a very important immune group in tumor immunity, which can promote or prevent tumor development and metastasis[37], high expression of M2 macrophages in KIRP is often associated with poor clinical prognosis[38].
For renal cell carcinoma, based on Hsieh et al. [39]the US Food and Drug Administration approved immune checkpoint inhibitors as second-line treatment for advanced renal cancer in 2015, bringing the treatment of advanced renal cancer into the era of immunotherapy. Immune checkpoint mainly refers to the negative regulatory molecules in the body's immune system that maintain tolerance and regulate immune response[40], mainly include cytotoxic T cell associated protein-4 (CTLA-4), programmed death molecule-1 (PD-1), lymphocyte activation gene-3 (LAG-3), IDO, etc[41, 42]. Immune checkpoint inhibitors can inhibit tumor growth by specifically blocking immune examination sites and eliminating their immunosuppressive function. Therefore, it is very important to determine the expression level of immune checkpoint related genes in patients for the accurate selection of immune checkpoint inhibitors[43]. In the high-risk group of our risk assessment model, the expression of PDCD1, CTLA4, LAG3 and TIGIT immune checkpoint genes was high, while the expression of HAVCR2 decreased, suggesting that PDCD1, CTLA4, LAG3 and TIGIT immune checkpoint inhibitors may have better efficacy for patients in the high-risk group.
Advanced metastatic ccRCC is preferred for targeted therapy, with different targeted drug pathways. VEGFR1-3 and c-KIT inhibitors include Asitinib, Prazopanib, Sorafenib, Sunitinib and Capotinib; VEGFR2 antibodies include Bevacizumab and EGFR inhibitors include Erlotinib. Among them, Sorafenib could inhibit Raf nodes in RAS-ERK pathway, while Temsirolimus, Everolimus and Captinib could inhibit mTOR nodes downstream of PI3K pathway[44, 45]. Therefore, determining whether patients are resistant to chemotherapy drugs is the premise of individualized treatment. In our risk assessment model, the sensitivity of commonly used targeted chemotherapy drugs Vinblastine, Sunitinib, Rapamycin, Mitomycin.C, Cisplatin and Temsirolimus is different between high and low risk groups. And their 50% inhibitory concentration (IC50) in the high-risk group was lower than in the low-risk group, suggesting that patients in the high-risk group were more sensitive to these drugs. They can as a potential predictor of chemotherapy sensitivity.