It refers to the balance and regulation of copper levels in the body. Copper is an essential mineral that plays a critical role in various cellular functions, including enzyme regulation, mitochondrial respiration, and antioxidant defense (Burkhead et al., 2009). Copper misbalance affects central nervous system, liver function, lipid metabolism and resistance to chemotherapy (Gaetke et al., 2014). Copper in the diet is mainly stored in the muscular and bone tissues, with 20% stored in the liver and 10% in the blood (Miranda et al., 2010). Copper is absorbed in the form of Cu2+ and then reduced to Cu + by reductases on the surface of epithelial cells in the digestive tract. Cu+ is then transported into cells via copper transporter 1 (CTR1) and combined with copper chaperone protein antioxidant-1 (Atox1) to enter hepatocytes through copper transporting ATPase β (ATP7B) Golgi complex pathway to form ceruloplasmin (Kamiya et al., 2018). The distribution of ATR1 in cells is dynamic, elevation of extracellular copper induces endocytosis of CTR1 to vesicles, whereas a decrease in extracellular cooper restores CTR1 (Lutsenko, 2010). Excessive copper is excreted into bile in the form of vesicles by ATP7B, while ATP7A can mobilize copper from liver storage to maintain effective copper concentration (Polishchuk Elena et al., 2014). Copper deficiency can lead to oxidative stress and cytotoxicity, while copper excess can also be toxic. Menkes disease is a rare genetic disorder that results in copper deficiency due to mutations in the ATP7A gene (Kaler, 2011).

It is a term used to describe the role of copper in promoting cell growth and proliferation. This process is regulated by signaling pathways and can involve both enzymatic and non-enzymatic activities of copper (Ge et al., 2022). Cuproplasia can lead to the development of neoplasia or hyperplasia, and can be targeted using copper-selective chelators or metal ionophores. Additionally, proteins involved in copper homeostasis can be genetically or pharmacologically manipulated to modulate cuproplasia. It refers to a condition in which there is an abnormal accumulation of copper in tissues or organs due to a genetic or metabolic disorder. It is a pathological condition that results from an imbalance in copper homeostasis. Cuproplasia is linked to several cellular processes, such as mitochondrial respiration, redox signaling, autophagy, antioxidant defence and kinase signaling (Ge et al., 2022).

In 2022, Todd’s et al. found copper directly binds to thioctylated components of the TCA cycle and leads to the downregulation of Fe-S cluster proteins and abnormal aggregation of thiotylated proteins, resulting in a distinct form of cell death named “cuprotosis” which is a significant contribution to our understanding of cell death mechanisms (Tsvetkov et al., 2022). This process involves increased mitochondrial energy metabolism and the accumulation of reactive oxygen species, ultimately leading to cell death. The fact that knocking down Bax BAK1 did not obstruct copper-induced cell death suggests that cuprotosis is distinct from apoptosis, which involves the activation of Bax BAK1.

Further studies on the mechanism of cuprotosis, exploring the relationship between ferroptosis and cuprotosis. In colon cancer cells treated with a combination of elesclomol (an anticancer drug that targets mitochondrial metabolism) and copper, it was found that copper accumulation in the mitochondria led to an increase in reactive oxygen species and the solute carrier family 7 member 11 (SLC7A11) protein, which is involved in the regulation of cellular antioxidant response (Gao et al., 2021). However, subsequent studies found that mitochondrial antioxidants and inhibitors of mitochondrial function were more effective at inhibiting cell death induced by elesclomol than ferroptosis inhibitors (Tsvetkov et al., 2022). Moreover, studies have shown that prolonged use of elesclomol can lead to an increase in the TCA cycle metabolites produced by non-small cell lung cancer cells, suggesting that the target of copper-induced cell death may be the TCA cycle process itself (Zheng P. et al., 2022). Based on these latest researches, cuprotosis does not seem to be a copper-dependent form of ferroptosis. Instead, it appears to target the TCA cycle process rather than the electron transport chain process. This suggests that targeting mitochondrial metabolism, rather than the regulation of cellular antioxidant response, may be a more effective strategy for preventing cuprotosis in cancer cells.

Furthermore, Multiple CRISPR knockout screens were performed to identify cuprotisis-relating gens. The result showed FDX1, LIAS, LIPT1, DLD, DLAT, PDHA1, and PDHB are positively regulated genes. On the other hand, MTF1, GLS, and CDKN2A were confirmed as negatively genes (Tsvetkov et al., 2022). Of these genes, FDX1 and protein lipoylation were identified as key factors of cuprotosis genes led to enhanced resistance to cuprotosis, indicating a strong connection between FDX1, protein lipoylation, and cuprotosis (Wang et al., 2022; Schulz et al., 2023; Shen et al., 2023).

Copper plays a crucial role in promoting tumor growth by promoting angiogenesis. It is involved in the activity of several angiogenic factors, including vascular endothelial growth factor (VEGF) and angiogenin. Copper ions can bind to VEGF and promote its dimerization, which is required for VEGF to bind to its receptor and initiate signaling pathways that promote angiogenesis. Therefore, blocking copper-dependent angiogenesis is a potential strategy for inhibiting tumor growth. The copper participates in angiogenesis in two aspects: 1) it interacts with cellular matrix with an increased redox potential to product oxidative products, then revealing DNA mutations in the nucleus and mitochondria or alternations to membrane phospholipids; 2) it regulates angiogenesis even in the absence of angiogenic molecules (Antoniades et al., 2013). Study found that the copper chelator inhibited the growth of pancreatic cancer cells in vitro and in vivo by inducing apoptosis and reducing the levels of copper-dependent angiogenic factors such as VEGF (Zhao et al., 2020).

In addition to their anti-angiogenic effects, copper chelators can also induce cancer cell death by disrupting the balance of copper ions in cells (Lowndes and Harris, 2005). Copper is required for the activity of several enzymes that regulate cellular processes, and an excess of copper can lead to oxidative stress and damage to cellular components (Antoniades et al., 2013). Furthermore, it can reduce the levels of copper ions in cells, leading to the activation of apoptotic pathways and ultimately inducing cancer cell death (Finney et al., 2009).

Cancer cells have been shown to have higher copper levels compared to normal cells. Thus, by reducing the amount of copper available to cancer cells, it is possible to sensitize them to chemotherapy and radiotherapy. A study reported that copper depletion sensitized ovarian cancer cells to radiation therapy by increasing the production of reactive oxygen species and inducing DNA damage (Kim et al., 2012). Similarly, another study found that copper chelation enhanced the effectiveness of the chemotherapy drug cisplatin in lung cancer cells by inducing oxidative stress and inhibiting DNA repair mechanisms (Nechushtan et al., 2015). Combination of anti-copper drugs and chemotherapy or radiotherapy are now becoming a new strategy and there are several preclinical studies showed promising results in melanoma, colorectal cancer and (Gartner et al., 2009; Ikeda et al., 2011; Grimaldi et al., 2017).

Some studies have suggested that copper may play a role in enhancing the efficacy of immunotherapy. One potential mechanism by which copper may enhance immunotherapy is through the release of damage-associated molecular patterns (DAMPs) from dying cancer cells. DAMPs are molecules that are released by dying cells and can stimulate the immune system to mount an anti-tumor response. In addition, copper treatment may also enhance the activity of immune cells, such as T cells and natural killer cells, which can recognize and eliminate cancer cells (Hu et al., 2020). Study showed that a copper complex (Cu-Cy NPs) could enhance checkpoint blockade melanoma immunotherapy (Zhang et al., 2020).

There are limited studies on cuprotosis and immunotherapy. Integrative analysis showed cuprotosis reshaped tumor microenvironment and response to immunotherapy of colorectal cancer by collecting 1,226 samples for genomic testing (Xu et al., 2023). In another study, Cuprotosis-related LncRNA models was constructed in liver cancer samples. The results showed six differentially expressed immune functions were found it high and low-risk groups. And the survival rate is significantly worse in high mutation groups compared with low risk groups (Chen et al., 2023). With the same technology in pancreatic ductal adenocarcinoma patients, Some LncRNA s are thought to have strong correlations with ductal adenocarcinoma outcomes, including AC005332.6, LINC02041, LINC00857, and AL117382 (Chi et al., 2022). The same results in lung adenocarcinoma were seen (Zheng M. et al., 2022). Cuprotosis can affect the polarization and function of tumor-associated macrophages (TAMs), which are immune cells that play a crucial role in the tumor microenvironment. TAMs can exhibit either pro-tumor (M2-like) or anti-tumor (M1-like) phenotypes. Cuprotosis has been shown to promote the polarization of TAMs toward the M1-like phenotype, which is associated with anti-tumor activity. This shift in TAM polarization can lead to a more favorable tumor microenvironment for immune responses. All these results suggested that cuprotosis may have a role in reshaoing tumor microenvironment and regulate efficacy of immunotherapy.

Copper compounds have been studied for their potential use in cancer treatment, as cancer cells are known to have a higher copper uptake and retention compared to normal cells. The idea behind using copper compounds in cancer treatment is to selectively target cancer cells by inducing excessive copper accumulation in them, leading to cuprotosis. Several copper compounds have been studied for their ability to induce cell death in cancer cells.

It refers to the use of copper-chelating agents such as clioquinol and tetrathiomolybdate to disrupt the function of proteasomes in cancer cells (Zhang et al., 2017). Proteasomes are large protein complexes that play a critical role in the degradation and recycling of intracellular proteins, including those involved in cell cycle regulation, DNA repair, and apoptosis. Cancer cells are known to have high levels of proteasome activity, which helps them to survive and proliferate. By chelating copper ions, clioquinol and tetrathiomolybdate can inhibit proteasome activity in cancer cells, leading to the accumulation of toxic protein aggregates and ultimately causing cell death (Wehbe et al., 2017). Additionally, the accumulation of toxic protein aggregates can also enhance the sensitivity of cancer cells to chemotherapy and radiation therapy. There are several clinical trials involving copper-chelating agents in cancer patients such as NCT01837329, NCT00150995, NCT00176800, NCT00352742 and NCT00383851. These trials are investigating the safety and efficacy of copper-chelating agents in combination with chemotherapy, immunotherapy, or other agents for the treatment of various types of solid tumors. The results of these trials will help to determine the potential of copper-chelating agents targeting cooper-dependent enzymes as a novel approach to cancer therapy.