3.1 Identification and Validation of Metabolism-Associated Subtypes in NBL
In the TARGET-NBL cohort,56 metabolic genesets associated with prognosis were obtained by univariate Cox analysis. The "ConsensusClusterPlus" package in R was used to classify metabolic subtypes of NBL. The cluster effect was best when 150 samples were divided into two subtypes(Figure 1A). The t-SNE showed that most Cluster A and Cluster B samples could be well distinguished, indicating that this subgroup clustering was a reasonable choice (Figure 1B). Kaplan-Meier survival curves were performed to analyze the prognostic characteristics of metabolic subtypes. As shown in (Figure 1C-D), Cluster A presented a more favorable OS and EFS than Cluster B. The same metabolic genesets and cluster methods were employed for molecular subtyping of GSE62564, and similar conclusions were obtained (Figure 1E-H). The heatmap revealed the expression of prognosis-related metabolic genesets in different clusters and the correlation between molecular subtypes and clinical features, such as Age, INSS, and MYCN. As shown in (Figure 1I-J), patients with MYCN amplification, age >1.5 years, and stage IV are primarily concentrated in Cluster B. Meanwhile, metabolic profiles in the different subtypes were consistent between TARGET and GSE62564.
3.2 Hallmark pathway and immune-related characteristics of subtypes
In TARGET-NBL, we performed GSVA to identify Hallmark pathways' differences between two metabolic-related subtypes. As shown in (Figure 2A), the higher correlations of Mitotic Spindle, DNA Repair, G2M Checkpoint, E2F Targets, MYC Targets-V1, MYC Targets-V2, and Spermatogenesis were found in ClusterB compared to ClusterA. On the other hand, other pathways were upregulated in Cluster A. Tumor microenvironment (TME) in NBL samples was estimated via the ESTIMATE algorithm. Our results showed that the immune score, stromal score, and ESTIMATE score displayed higher in Cluster A, and in contrast, tumor purity was higher in Cluster B (Figure 2B). Subsequently, we analyzed the immune features of two subgroups. According to (Figure 2C), most of the immune cells had higher scores in Cluster A, and no significant difference in Activated CD4 T cell and Type 2 T helper cell were detected between the two clusters. Similarly, various immune processes of Cluster A are more vigorous than Cluster B (Figure 2D). Furthermore, it was also shown that most immune checkpoints and HLAs were highly expressed in Cluster A compared to Cluster B (Figure 2E-F). To verify the above conclusions, we got similar results from GSE62564 through the same methods(S1A-F).
3.3 Construction of Networks Among Metabolic processes, Hallmark Pathways, and Immune Signatures
To explore the connection among metabolic processes, Hallmark pathways, and immune signatures, we performed WGCNA on TARGET to construct the co-expression networks. After setting soft-threshold power(β) = 7 (Figure 3A), a scale-free network was constructed based on the scale-free topology R2 = 0.92 (Figure S2). Then seven co-expression modules were eventually identified by cutting MEs' clustering height = 0.35 (Figure 3B-C). According to the heatmap of module-trait relationships, the yellow and black module demonstrates the highest correlations with metabolic clusters and MYCN status (Figure 3D). Correlation analysis was performed between gene significance (GS) for cluster and module membership (MM) for genes in each module to test the relationships between the module and metabolic cluster. The results showed that the yellow module (correlation coefficient = 0.63, P value = 1e-48) and the black module(correlation coefficient = 0.68, P value = 2e-172) exhibited the most significant positive correlation with the metabolic cluster (Figure S3-4). Finally, we applied Cytoscape to visualize the networks in the yellow and black modules. It was shown that the genes in the yellow module are mainly involved in the MYCN signaling pathway and the metabolic processes of RNA, pyrimidine, and folic acid (Figure 3E). On the other hand, the genes in the black module are linked to various immune-mediated signaling pathways and metabolic processes (Figure 3F).
3.4 Development of Metabolic Risk Score for NBL
We applied univariate-cox regression analysis to assess the prognostic implications of the key module genes (KMGs). As a result, 18 prognostic-related genes were found in the TARGET dataset (Figure S5). Subsequently, LASSO-Cox regression analysis was utilized to screen the candidate prognostic KMGs (Figure 4A). As a result, four candidate metabolic-related genes were identified for model construction. The risk score formula was as follows: Risk score = 0.0537897200512298 mRNA expression of POLR3D + 0.173843171484948 mRNA expression of PAM16 + 0.138278386088605 mRNA expression of RPL18A + (-0.636625110125905) mRNA expression of ITPRID2. All patients were stratified into high-risk and low-risk subgroups according to median risk scores. Both overall survival (OS) and Event Free survival (EFS) analyses showed that the low-risk group displayed a better prognosis than the high-risk group (Figure 4B). Then, ROC curves were conducted to evaluate the metabolic risk score accuracy and sensitivity. Risk score showed a better predictive performance than Age, INSS, and MYCN. Meanwhile, the AUC values of 1, 3, and 5-year OS were 0.772, 0.780, and 0.713, respectively (Figure 4C). The distribution of survival status and the expression of candidate genes in the groups were visualized in (Figure 4D). It was found that the high-risk group had a significantly increased number of dead status than the low-risk group. In addition, POLR3D, PAM16, and RPL18A were significantly upregulated in high-risk samples, and ITPRID2 was higher expressed in low-risk samples. Finally, the same results were found in GSE62564 (Figure 4E-G).
3.5 Correlation of Risk Model with Clinical and Immune Features
We analyzed the clinical characteristics of different risk groups. The alluvial diagram clearly showed the relationships among the risk groups, metabolic clusters, and patients' overall survival status. Most of the patients in the low-risk group belong to Cluster A, and they were primarily associated with a better prognosis (Figure 5A). Most patients under 1.5 years, III or IVS stage, were enriched in the low-risk group. In contrast, MYCN-amplified patients were more likely to be in the high-risk group(Figure 5B). As shown in (Figure 5C), our model had a good prediction performance in both patients with normal or amplified MYCN. Through GSEA, we found that the high-risk group was associated with cell cycle pathways such as base excision repair, DNA replication, pyrimidine metabolism, ribosome, and RNA polymerase. While neural function pathways(axon guidance, dorsal-ventral axis formation, and long-term potentiation) and immune pathways(FcγR mediated phagocytosis, natural killer cell-mediated cytotoxicity) in the low-risk group were more potent than high-risk group (Figure 5D). Subsequently, We analyzed the immune features of different risk groups. It was confirmed that more immune cell infiltration appeared in the low-risk group of patients using different calculation methods (Figure 5E). Furthermore, Risk scores were inversely proportional to the degree of infiltration of various immune cells (Figure 5F).
3.6 Prediction of Immunotherapeutic and Chemotherapy Sensitivity
In TARGET-NBL, we evaluated the expression of immune checkpoints between the two prognostic risk subgroups. As shown in (Figure 6A), most of the checkpoints had higher expression in the low-risk group. According to the TIDE algorithm, almost all patients in both high-risk and low-risk groups exhibited a positive response to ICIs. Moreover, the TIDE score was lower in the high-risk group (Figure 6B). Overall, ICIs are effective in most NBL patients, and the high-risk group is more sensitive to immunotherapy. Based on the connectivity map (CMap), mechanism of action (MoA) analysis was employed to identify potential compounds capable of targeting high-risk groups. The mechanisms of action, which contained >3 compounds, were screened, and we found 12 targets shared by 55 compounds.14 compounds shared the MoA of HDAC inhibitor. Aurora kinase, Topoisomerase, CDK, FLT3, MEK, and VEGFR contained 6 compounds as the target (Figure 6C). Subsequently, we analyzed the CMap score of drugs commonly used in NBL and pediatric malignant tumors (Figure S6-7). Furthermore, we investigated drugs used in clinical therapy and intersected drugs with a score of <-95 in UGS and drugs of >95 in the favorable gene signature (FGS) (Figure 6D) and finally, employed the R package "pRRophetic" to verify the sensitivity of candidate drugs. The results demonstrated the clinical implications of these drugs and were consistent with the conclusions of CMap (Figure 6E).