Ferroptosis-related lncRNAs guiding osteosarcoma prognosis and immune microenvironment

Osteosarcoma (OS) stands as the prevailing malignant neoplasm affecting bone tissue, with a predilection for the adolescent demographic [1]. This condition is typified by frequent vascular infiltration, adjacent soft tissue infiltration, a notable proclivity for local recurrence and premature distant metastasis [2]. Approximately one-fifth of OS patients experience the emergence of metastatic lesions, while the remainder often develop subclinical micrometastases. Standard therapeutic modalities encompass the deployment of chemotherapy and surgical resection [3]. Notwithstanding the comprehensive implementation of a multidisciplinary regimen, which encompasses chemotherapeutic intervention and extensive surgical excision, discernible enhancements in clinical outcomes have been documented in patients with OS. However, in instances of advanced disease with remote metastasis and local recurrence, even with the rigorous administration of chemotherapy, clinical outcomes and 5-year overall survival rates remain suboptimal [4]. A burgeoning corpus of scientific inquiry posits that a multifaceted interplay of cellular and molecular events may underlie the pathogenesis of OS [1]. Long non-coding RNA (lncRNA) constitutes a pivotal regulator in a myriad of biological processes, including cell proliferation, apoptosis, invasion and migration. Anomalous expression of lncRNA assumes a pivotal role in the orchestration of tumoral metastasis [5, 6]. The nexus between lncRNA and OS is undeniably close, as investigations have unearthed compelling evidence. For instance, lncRNA LOC100129620 has been implicated in the promotion of OS progression through the modulation of cyclin dependent kinase 6 (CDK6) expression, tumor angiogenesis and macrophage polarization [5]. Conversely, LncRNA FTX exerts an inhibitory effect on OS proliferation and migration via its regulatory influence on the miR-320a/TXNRD1 axis [6]. The exploration of the interrelationship between lncRNA and OS bears paramount significance in the context of disease prognosis and therapeutic intervention. Consequently, the quest for novel prognostic markers in the realm of OS and the pursuit of strategies to enhance clinical efficacy remain imperatives in the management of this disease.

Ferroptosis constitutes a tightly regulated mode of cellular demise, triggered by perturbations in the intracellular milieu, primarily governed by the activity of glutathione peroxidase 4 (GPX4) [7]. The pivotal drivers of ferroptosis initiation encompass the accrual of ferrous iron (Fe²⁺) and the subsequent peroxidation of lipids [7]. Notably, ferroptosis is amenable to inhibition via iron-chelating agents and lipophilic antioxidants [7]. This multifaceted cellular event intricately interweaves processes inclusive of iron homeostasis, lipid metabolism, oxidative stress, as well as the synthesis of essential molecules such as nicotinamide adenine dinucleotide phosphate (NADPH), glutathione (GSH) and coenzyme Q10 (CoQ10) [8]. Accumulating investigations have underscored the pivotal role of ferroptosis in various malignancies. In the context of breast cancer cells, both a lysosome-disrupting agent, silamesine and a tyrosine kinase inhibitor, lapatinib, have been demonstrated to induce ferroptosis [9]. Furthermore, in the realm of pancreatic ductal adenocarcinoma (PDAC), the agent artesunate (ART) exerts its ferroptosis effects through the generation of reactive oxygen species (ROS) in an iron-dependent manner [10]. These findings collectively emphasize the burgeoning potential of ferroptosis as a therapeutic modality in the domain of oncology, consequently intensifying research efforts toward the design and development of anticancer agents capable of inducing ferroptosis [11]. Moreover, an emerging intersection has been observed between ferroptosis and OS. For instance, tirapazamine has been shown to exert partial inhibition of OS cells through the mediation of solute carrier family 7 member 11 (SLC7A11)-associated ferroptosis [12]. Similarly, EF24 has been identified as an inducer of ferroptosis in OS cells, operating via heme oxygenase 1 (HMOX1)-dependent mechanisms [13]. Furthermore, the identification and characterization of ferroptosis-related genes (FRGs) capable of prognosticating outcomes in OS patients have constituted pivotal advancements in this realm of study [14].

We developed a risk prognostic model for assessing the OS-related FRLncs based on a comprehensive analysis of data from both TCGA and GEO databases. This model incorporates information from seven FRLncs classified into two categories: three high-risk FRLnc and four low-risk FRLncs. The risk prognosis model constructed in this study can well predict the survival of patients with OS, and has a certain impact on the immune microenvironment of patients with OS. Compared with the low-risk group, the immune cells and immune function of patients with OS in the high-risk group showed a downward trend. Immune checkpoint-related genes also differed between the two group.

Previous study has shown that LncRNA APTR participates in the progression of OS by repression of miR-132-3p and upregulation of Yes-associated protein 1 (YAP1) [23]. The expression of APTR in OS tumor tissues and four OS cell lines (MG63, 143B, Saos-2 and HOS) was significantly up-regulated compared with that of in neighboring tissues and human osteoblast cell lines hFOB1.19, respectively. MiR-132-3p is the target of APTR, and its expression is inhibited by APTR. Both knockdown of APTR and overexpression of miR-132-3p can significantly inhibit the proliferation, invasion and migration of human OS cells, and induce cell apoptosis. In addition, YAP1 was identified as a target for the inhibition of miR-132-3p [23]. LncRNA DSCR8 promotes the proliferation of liver cancer cells and inhibits apoptosis via the miR-22-3p/ARPC5 axis [24]. LncRNA DSCR8 mediates miR-137/Cdc42 to regulate gastric cancer cell proliferation, invasion and cell cycle as a competitive endogenous RNA [25]. The study found that smoking promoted the development of lung adenocarcinoma and lung squamous cell carcinoma by affecting gender-specific lncRNA changes. In women with lung squamous cell carcinoma, changes in LOH12CR2 were positively associated with smoking index [26]. AC027307.2↗ can not only be used as an enhancer-associated lncRNA to become a specific prognostic marker for breast cancer, but also as an immune-associated lncRNA to predict the survival rate of patients with colorectal adenocarcinoma [27, 28]. Notably, of the seven FRLncs that can guide OS prognosis and immunity, APTR, DSCR8, LOH12CR2 and AC027307.2↗ were all associated with tumor progression and prognosis. Among them, APTR has been found to be involved in the development of OS in previous studies. These findings underscore the robustness of our results. In the existing literature, AC105914.2↗, AL139246.5↗ and AC025048.2↗ remain to be elucidated and documented.

The immune system was one of the major components in the tumor microenvironment and was often suppressed in hypoxia [29]. The study found that the pre-treatment neutrophil-to-lymphocyte ratio was of diagnostic and prognostic value for OS [30]. Clinical data suggest that NK cells may play an important role in the prevention and therapeutic response of OS. In patients with OS, the number of circulating NK cells in peripheral blood was lower than in normal controls, suggesting that NK cells play a preventive role in the development of OS tumors [31]. pDCs exhibit remarkable proficiency in the rapid and robust production of type I interferon (IFN-I/α) [32]. Nevertheless, in the context of cancer, pDCs demonstrate a diminished responsiveness to Toll-like receptor 7 and 9 (TLR7/9) activation, resulting in a marked reduction or outright loss of IFN-α production. This diminished IFN-α contributes to the establishment of an immunosuppressive tumor microenvironment [33]. Notably, pDCs play a pivotal role in the regulation of both innate and adaptive immune systems, rendering them essential actors in the realm of cancer immunity [33]. Investigations focusing on the interplay between immune cell populations and the OS microenvironment have elucidated that cancer progression is most expedited when anti-tumor immune cells, including DCs, helper T cells, cytotoxic cells and IFN-γ, exhibit a decline in abundance, while regulatory T cells (Treg) undergo an increase [34]. Several studies have posited that the secretion of cytokines and the proliferative capacity of T follicular helper (Tfh) cells are markedly impaired in OS patients. This diminishment in functionality may underlie the body's compromised ability to resist OS development [35]. Importantly, miR-138 serves as an inhibitor of the PI3K/Akt/mTOR pathway by specifically targeting and negatively regulating pyruvate dehydrogenase kinase 1 (PDK1), thereby mitigating Tfh dysfunction in OS [36]. The TIL tasked with combating tumor cells within the OS microenvironment experience depletion, thus hastening tumor recurrence [37]. Notably, the incorporation of adjuvant chemotherapy in conjunction with TIL therapy has demonstrated the capacity to extend survival in OS patients with a suboptimal response to neoadjuvant chemotherapy [37]. Within the cancer microenvironment, innate immunity is systematically suppressed in the context of immune tolerance. A pivotal mechanism underlying immune tolerance is the immune checkpoint mechanism, which operates to restrain T cell activity in order to prevent undue immune responses [38].

The high-risk group exhibited significant down-regulation of immune functions, including APC-co-stimulation, immune checkpoint regulation, cytolytic activity and T cell co-inhibition. Study revealed that the administration of the anti-epidermal growth factor receptor (EGFR) antibody, cetuximab, resulted in an augmentation of the cytolytic activity exhibited by NK cells in the context of OS [39]. Immune checkpoint inhibitors (ICIs) have been recognized for their capacity to reshape the course of various malignancies by eliciting a disruption in immune homeostasis, thereby empowering the host's immune system to combat the tumor [40]. In a comprehensive analysis focusing on hypoxic prognostic indicators associated with OS metastasis and immune cell infiltration, a pronounced down-regulation of immune checkpoint mechanisms was identified among high-risk populations [29]. Regrettably, the precise correlation between APC-co-stimulation and T cell co-inhibition with respect to OS remains an area of investigation that warrants further elucidation in the scientific literature.

CD200R1 is not only differentially expressed in non-small cell lung cancer and has a prognostic effect, but also predicts survival in patients with head and neck squamous cell carcinoma [41, 42]. Previous study has found that HAVCR2 can be used as immune signature to accurately predict the prognosis of patients with OS, high expression of HAVCR2 is associated with improved prognosis [43, 44]. A comprehensive investigation has revealed significant alterations in Galectin-9, encoded by the LGALS9, across various cancer types [45]. Remarkably, LGALS9 not only exhibits associations with mRNA expression levels in cervical cancer cells but also emerges as a potential prognostic biomarker in pancreatic cancer [46]. The CD70-CD27 interaction is important for the regulation of adaptive immunity. Phospholipase C epsilon 1(PLCE1) is a marker of poor prognosis and may promote immune escape of OS through the CD70-CD27 signaling pathway [47]. LAIR1 overexpression inhibits the epithelial–mesenchymal transformation of OS through glucose transporter (Glut) 1-related energy metabolism [48]. The construction and validation of an oxidative stress-related prognostic risk model for OS suggests that LAG3 is a potential immunotherapeutic target for patients with OS [49]. In all melanoma patients and in the stage III and IIIc-IV patient cohorts, low expression of TNFSF4 was associated with a poorer prognosis. In the subgroup of patients with low lymphocytic infiltration, low expression of TNFSF4 was also associated with a poorer prognosis [50]. It is suggested that TNFSF4 is associated with tumor prognosis.

Nevertheless, it is imperative to acknowledge the presence of several limitations within the scope of this investigation. Firstly, the study's sample size remained relatively small, and the sampling methodology employed did not successfully mitigate the potential confounding influence of gender and underlying medical conditions. Secondly, the FRLncs identified in this study, which bear the potential to prognostic outcomes in the context of OS and contribute insights into the immune microenvironment, have not yet undergone experimentally validation. However, it is noteworthy that this validation process constitutes a focal point for our forthcoming research endeavors.

In this study, a prognostic risk model for OS was formulated by integrating data from the TCGA and GEO databases. Concurrently, immune analysis was conducted, yielding seven FRLncs identified as potential prognostic markers for OS and influencers of the immune microenvironment. Differential profiles of immune cells and functional characteristics were delineated within the context of the risk prognostic model. Furthermore, we identified seven immune checkpoint-associated genes with notable implications for OS prognosis. The discovery of these FRLncs, their pivotal roles in OS prognosis, the modulation of the immune microenvironment, as well as the identification of immune checkpoint-related genes, collectively furnish a solid theoretical foundation for advancing research in OS survival and facilitating informed clinical decision making.