Although osteosarcoma is the most common primary bone cancer in children and young adults, it is still rare. Metastasis, especially in the lung, is the main cause of death due to osteosarcoma. The current standard of osteosarcoma treatment was established in the 1980s and included surgery and chemotherapy. Standard therapy can achieve more than 60% longer-term survival in patients with localized osteosarcoma. Unfortunately, there has been little progress in treating osteosarcoma since these standard treatments were established [45]. Some osteosarcoma patients have shown tolerance to traditional chemotherapy drugs, presenting clinical challenges to their treatment. Currently, there is still a lack of accurate and effective therapeutic targets for the treatment of osteosarcoma. Thus, it is necessary to explore novel biomarkers of OS.
Necroptosis is mediated by the RIPK1-RIPK3-MLKL signaling cascade downstream of TNFα [11, 46, 47] and MLKL is a key molecule [48]. Necroptosis is closely related to infectious diseases, nervous system diseases, inflammation, and cancer [49, 50]. Apoptosis and necroptosis antagonize each other; loss of enzymatic Caspase8 activity, which plays an essential role in the regulation of apoptosis, leads to the activation of necroptosis [51]. Caspase8 cleaves RIPK prompting TNF-induced apoptosis [52]. Most traditional chemotherapy drugs kill tumor cells by inducing apoptosis. However, chemotherapy failure is mainly due to resistance to apoptosis. Programmed tumor death and exploration of tumor microenvironment have attracted increasing attention, and evidence has indicated that targeting necroptosis is a new stage in tumor therapy [20, 53, 54].
In this study, through an extensive analysis of OS data, five NRGs closely related to the prognosis of patients with OS were selected, and a prognostic model of OS was successfully constructed. Toll-like receptors (TLRs) are classical pattern recognition receptors regulating initiate immune responses [55, 56]. TLR4 activation triggers necroptosis and mediates inflammation caused by necroptosis [17, 57]. STAT5A is a member of the JAK-STAT signaling pathway, involved in the cell's response to various cytokines and growth factors [58]. It’s role in tumors has been widely reported in colorectal cancer [59], breast cancer [60], Prostate Cancer [61], and even osteosarcoma.[62] IFNGR1 is the receptor of IFNγ that inhibits tumor proliferation and induces apoptosis. Mutations in the IFNGR1 gene indicate that tumors are insensitive to immunotherapy [63–65]. PYGM, glycogen phosphorylase, is involved in glycogen metabolism, and its low and high expression level shows a significant difference in the survival rate of patients with head and neck squamous cell carcinoma [66]. Charged multivesicular body protein 4C (CHMP4C), the tumor suppressor gene, is the target gene of TP53[67]. Therefore, dysregulation of CHMP4C may promote genomic instability and tumorigenesis [68].
Tumor immunotherapy has received extensive attention, therefore, deep insight into the tumor microenvironment is crucial. This study calculated 47 types of immune cells in the TARGET cohort. As mentioned above, many immunotherapies-related immune cells, including CD4 + T cells, type 1 T helper cells, memory T cells, and gamma delta T cells, were positively associated with risk scores generated by the model, demonstrating increased immune cells associated with the osteosarcoma prognosis. However, the potential mechanism was still unclear. With DEGs between the two risk groups, enrichment analysis was performed in GO, GSVA, and GSEA in KEGG. Many BPs associated with tumor progression, including blood vessel development associated with tumor metastasis [69], cytokine signing in the immune system [70], and adaptive immune system [71], were successfully enriched at the top of the GO enrichment analysis. Similarly, BPs associated with tumor development and immunity were successfully enriched in GSVA. In the KEGG enrichment analysis, the RIBOSOME pathway, considered a new therapeutic avenue [72], was enriched in the high-risk phenotype, indicating that the high-risk group had a higher protein anabolism. Furthermore, the APOPTOSIS pathway was enriched in the low-risk phenotype, consistent with better results in the low-risk group. This study found that necroptosis was associated with tumor development and immunity. Although the molecular mechanisms behind necroptosis need to be further identified, our study provides new insight into the molecular mechanisms behind osteosarcoma. It also provides some new ideas for identifying potential therapeutic targets in the future, which is vital for patients resistant to conventional chemotherapy.