It is well known that the tumor immune microenvironment plays a crucial role in tumor development [77, 78]. Furthermore, copper is involved in various biological processes in the body and maintains homeostasis. Disruption of copper homeostasis causes a novel form of cell death known as cuproptosis, characterized by an excess of copper ions and lipid-acylated proteins. Here, we constructed an independent novel model using cuproptosis and TIP-related characteristics based on multiple statistical methods—CTIPRGs. Using the training database (TCGA-BRCA) and validation databases (GSE20685, GSE42568, GSE88770), we classified BRCA patients into high- and low-CTIPRGs groups. As expected, the high-CTIPRGs group had a worse prognosis and response to immunotherapy. By building a nomogram, we could quantitatively assess and precisely stratify risk in BRCA patients, providing new ideas for future immunotherapy. In conclusion, our study showed that CTIPRGs could assess the prognostic characteristics of BRCA patients and evaluate their response to chemotherapy and immunotherapy, thereby helping to provide a more accurate clinical diagnosis and treatment for BRCA patients.
Nowadays, more and more gene signatures have surfaced to elucidate the prognostic stratification of BRCA. For example, Yang et al. [79] identified a fifteen-gene prognostic model based on immune infiltration of breast cancer and obtained favorable results, Sha et al. [80] constructed two gene signatures predicting BRCA OS based on cuproptosis. However, tumors are complex masses comprising multiple cellular components and confounding factors; most research has, however, focused on the role of a single factor in BRCA, which is limiting. Moreover, both cuproptosis and the tumor microenvironment (TME) play crucial roles in the development of BRCA.[17, 81, 82]. Therefore, a comprehensive understanding of the interrelationship between cuproptosis and immune-related features, as well as their role in BRCA, will enhance our understanding of immune regulation in the TME and aid in the development of corresponding therapeutic strategies. Here, we identified, for the first time, a green module containing 178 genes based on the expression patterns of cuproptosis and TIP-related genes using WGCNA, and constructed 14 gene signatures, termed "CTIPRGs," for predicting the prognosis of BRCA patients. This represents a novel genetic model that integrates various characteristics. In contrast to previous studies, we conducted a comprehensive analysis, elucidating differences in immune infiltration among subgroups and predicting potential sensitive drugs and treatment efficacy based on the model.
Additionally, further exploration of the differences in biological behavior between high- and low-CTIPRGs groups provided deeper insights into the regulatory mechanisms of CTIPRGs. We found that low-CTIPRGs groups were more active in well-established immune-related signaling pathways, including the NOD-like receptor signaling pathway and the T cell receptor signaling pathway. [83, 84]. In contrast, high-CTIPRGs groups were more closely associated with metabolic activities. Tumor initiation and progression require the metabolic reprogramming of cancer cells. Cancer cells autonomously alter their fluxes through various metabolic pathways to meet increased bioenergetic and biosynthetic demands and to mitigate oxidative stress necessary for their proliferation and survival.[85]. And both glycolysis and TCA cycle supports tumor growth and produces the War-burg effect through metabolite biosynthesis [86, 87]. Reactive oxygen species (ROS) generated by oxidative metabolism at levels that don’t cause cell death can further support tumorigenesis [88, 89]. The metabolic pathways enriched in the high-CTIPRGs group are likely major contributors to tumor development and poor prognosis. Furthermore, cuproptosis predominantly occurs in cells with high mitochondrial respiration, and this novel mode of cell death likely plays a critical role in metabolically active high-CTIPRGs groups, offering new directions and ideas for BRCA treatment. In contrast, patients in the low-CTIPRGs group had significantly longer overall survival (OS), higher levels of infiltration by adaptive and innate immune cell types, and were also enriched in pathways related to apoptosis, mismatch repair, and various immune responses. Apoptosis and mismatch repair can inhibit tumor cell proliferation, metastasis, and tumorigenesis through APA sites in genes. [90, 91]. The innate immune system, comprising Toll-like receptors (TLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs), plays a pivotal role in immune response and immunosurveillance. Natural and synthetic agonists of these receptors can induce cell death in malignant cells and recruit immune cells, such as dendritic cells (DCs), CD8 + T cells, and NK cells, into the tumor microenvironment (TME), thereby exerting anti-tumor efficacy. [92]. The concentration of these characteristics in low-CTIPRGs groups were likely to be the main reason for their better prognosis.
In this study, we explored the correlation between CTIPRGs and T cell infiltration as well as anti-tumor immune responses. As expected, the validity of CTIPRGs in characterizing the immune landscape was further confirmed by significant negative correlations with immunization-related items. Mutation profiles and differential oncogenes revealed oncogenic pathways associated with CTIPRGs, suggesting a potential link between specific immune traits and oncogenes. Based on these analyses, we determined that CTIPRGs are potent biological indicators capable of classifying BRCA patients into distinct subgroups.
In anticancer therapies, chemotherapy remains a primary strategy for treating breast cancer patients. Chemotherapy can activate the immune system by promoting the release of danger signals from dying tumor cells and/or eliminating immunosuppressive cells, thereby enhancing the immune response and increasing the likelihood of tumor elimination following anticancer therapy. In BRCA, the crucial role of anti-tumor immunity in enhancing the effectiveness of anticancer therapies has been clearly established [93, 94]. Here, we evaluated the sensitivity of high- and low-CTIPRGs groups to commonly used chemotherapeutic agents for BRCA, including lapatinib, methotrexate, cyclopamine, paclitaxel, gemcitabine, and doxorubicin. We found that the low-CTIPRGs groups were more sensitive to most of the commonly used chemotherapeutic agents. This increased sensitivity may be related to the enrichment of various immune cell infiltrates in the low-CTIPRGs groups. Additionally, the immunogenic cancer cell death induced by chemotherapy can enhance the phagocytosis of dying tumor cells by abundant dendritic cells (DCs), leading to T-cell activation for anti-tumor effects [95]. And chemotherapy can also further induce genotoxic cellular stress triggering the expression of ligands that activate the NK cell receptor NKG2D, which leads to NK cell activation [96]. Given that CTIPRGs was constructed based on CRGs, we further explored the sensitivity of different subgroups to elesclomol. Consistent with the results of previous studies [75], we found that high-CTIPRGs groups were more susceptible than low-CTIPRGs groups. Consistent with the previous observation[97], elesclomol induces cell death by accumulating excess ROS. This finding indicates that cuproptosis plays a crucial role in the development of BRCA, and we believe that elesclomol holds promise as a therapeutic agent for BRCA.
Tumor tolerance is maintained through various mechanisms, including regulatory immune cells, immunosuppressive cytokines and chemokines, and immune checkpoint pathways that downregulate immune function. The PD-1 (also known as PDCD1)–PD-L1 receptor-ligand pair is a predominant immune checkpoint pathway in the tumor microenvironment (TME), capable of enabling cancer cells to evade immune attack [98, 99]. Unlike PD1-PDL1, CTLA acts mainly during T cell triggering and activation, and it can enhance the immunosuppressive activity of Treg cells and have a broad impact on the immune system [100]. Currently, anti-cancer immunotherapies targeting PD-1, PD-L1, and CTLA-4 have shown positive results in BRCA patients; however, only a small proportion of patients have responded to these treatments [101], the main reason for this might be the limitation of the immune status [102]. To assess the ability of CTIPRGs to predict the response rate of BRCA patients to anti-cancer immunotherapies, we examined the expression levels of 49 commonly tested immune checkpoints in high- and low-CTIPRGs groups. As expected, given the immune-inflamed phenotype characteristics of the low-CTIPRGs groups, more than half of the immune checkpoints were highly expressed in these groups, indicating that patients in the low-CTIPRGs groups were more likely to benefit from immunotherapy. Considering the critical role of CD8 + T cells in anti-tumor immunity, we evaluated key molecules in CD8 + T cell-related pathways in the high- and low-CTIPRGs groups, revealing significant differences between the groups. Additionally, we found that the low-CTIPRGs groups had a lower TIDE score. These results suggest that CTIPRGs could serve as a significant predictive marker for immunotherapy response in BRCA.
In this study, we screened and analyzed two CTIPRGs signatures, CCL8 and GZMB. Verified the high expression of CCL8 in BRCA tumor samples and GZMB in normal breast samples using IHC. Additionally, high CCL8 expression and low GZMB expression were associated with worse survival in breast cancer patients. GZMB is a serine protease with a perforin-dependent pro-apoptotic function, relying on cytotoxic immune cells like cytotoxic T-lymphocytes (CTLs) and natural killer (NK) cells to kill tumor and virally infected cells[103]. Recent studies have demonstrated GZMB expression in tumor cells, including those in breast and prostate cancer[104]. CCL8 is a member of the conserved chemokine cluster (CC cluster), located in the MCP region of mouse chromosome 11C and human chromosome 17q12[105]. It participates in the immune response by attracting T lymphocytes, monocytes, eosinophils, and natural killer (NK) cells[106]. Human studies have demonstrated that CCL8 is highly expressed during mammary gland degeneration, promoting breast carcinogenesis by enhancing the infiltration of M2 subtype macrophages[107]. CCL8 and IL-8 can also work together to mediate crosstalk between endothelial colony-forming cells (ECFCs) and triple-negative breast cancer (TNBC), leading to increased tumorigenicity[108].