This study is the first to provide the comprehensive analysis of 12 different mtPCD modes, constructed a cell death signature in TCGA NSCLC cohort, and further validated its performance in three other external cohorts (GSE29013, GSE31210, and GSE37745). A nomogram, combining the clinical characteristics of NSCLC patients and mtPCD-related gene expression pattern, was constructed and shown to perform well in predicting prognosis. Similarly, we determined that mtPCD genes were strongly associated with immune cell infiltration and the response to immunotherapy.
mtPCD is a cell death process mediated by molecular programs with the regulated of specific genes, and plays a key role in the normal development and maintenance of homeostasis in organism (37, 38). A signature with 18 mtPCD-related genes (AP3S1, CCK, EIF2AK3, ERO1A, KRT8, PEBP1, PIK3CD, PPIA, PPP3CC, RAB39B, RIPK2, RUBCNL, SELENOK, SQLE, STK3, TRIM6, VDAC1, and VPS13D) was identified and confirmed to predict the OS of NSCLC patients with extremely high accuracy. Notably, AP3S1 is overexpressed in most tumors and has a significant inverse correlation with survival (39), and we found that AP3S1 was a risk factor for NSCLC survival. CCK is a neuropeptide that regulates digestion, neurotransmitters, and memory (40). We found an inverse correlation between CCK expression and NSCLC survival. ERO1A can promote breast cancer metastasis (41), targeting ERO1A can activate anti-tumor immunity (42), and our study found that high ERO1A was associated with poor prognosis of NSCLCs. KRT8 is abnormally expressed in LUAD and is inversely associated with patient prognosis (43); this was confirmed by our study. VPS13D deletion leads to impaired mitophagy, while VPS13D mutation leads to VPS13D-related dyskinesia (44); VPS13D was a prognostic factor for NSCLC OS in our study. As a key regulator of the cell death pathway, RIPK2 has become a target for cancer therapy (45); the present study also identified RIPK2 as a risk factor for NSCLC. SQLE attenuates ER stress and promotes pancreatic cancer growth (46), which is consistent with our study showing that high SQLE expression level was associated with poor prognosis in NSCLC. STK3 promotes pancreatic cancer cell proliferation through the P13K/AKT pathway (47), and our results indicated that STK3 was negatively correlated with NSCLC OS. Notably, PPP3CC was proved to promote the apoptosis of epithelial cells and inhibit tumor proliferation in ovarian cancer (48); however, our results show that it was a risk factor for NSCLC OS through the prognostic model. VDAC1 is located on the outer mitochondrial membrane and regulates energy production. Studies have shown that VDAC1 is overexpressed in breast cancer and is associated with the suppression of tumor immunity (49); our data show that VDAC1 was a prognostic factor in NSCLC.
Immunotherapy has substantially improved overall survival of patients with unresectable tumors (50). In general, decreased infiltration of antitumor immune cells and increased infiltration of pro-tumor immune cells indicate that the tumor immune microenvironment is compromised (51–53). Tregs have immunosuppressive effects and inhibit immune responses of other immune cells (54). Our results showed that Treg cell infiltration was significantly higher in the high-risk group than in the low-risk group. The high-risk group patients may exhibit immune escape, resulting in poor patient prognosis. In addition, we found a significant difference in the TME scores between the high- and low-risk groups, and the high TME score corresponded to the positive response to immune checkpoint inhibitor treatment (55). Therefore, based on these results, we speculated that the high-risk patients in this study might be more suitable for immunotherapy. At the same time, we found a significant difference in the TMB scores between the high- and low-risk groups, in which higher TMB scores corresponded to a more active response to immune checkpoint inhibitors (56), suggesting that high-risk patients might benefit from immunotherapy.
Although mtPCD may be used as an independent prognostic factor for NSCLC, and our model showed good performance in both training and validation datasets, our study still has some limitations. First, the patients included in the study were recruited retrospectively, which may have inevitably led to bias. Second, the clinical information of our patients was obtained from public databases and lacked validation using our own independent external cohort. Therefore, more in-depth studies, such as prospective clinical studies with high quality, large sample sizes, and sufficient follow-up data for additional validation, are needed to investigate the feasibility of using this model to predict prognosis and guide NSCLC treatment.
A variety of agents targeting PCD are being developed for potential clinical applications. For example, a small compound resibufogenin inhibits colorectal cancer development and metastasis by inducing receptor-interacting protein kinase 3 (RIPK3) -mediated necrosis (57). Simvastatin induces pyroptosis and inhibits NSCLC cell migration by activation of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome and caspase-1 (58). Artesunate, a derivative of artemisinin, inhibits ovarian cancer cell proliferation by increasing reactive oxygen species production and triggering ferroptosis (59). The administration of nanoparticles can reverse cisplatin resistance in cancer cells by inducing cuproptosis (60). Additionally, the induction of ferroptosis can improve the therapeutic efficacy of immune checkpoint inhibitors (61). More studies should be carried out to determine the therapeutic potentials of PCD-targeting agents in NSCLC.