Cuproptosis, How much do you know?
01 Copper: An essential nutrient
Copper is an indispensable transition metal that has redox properties. It serves as a cofactor for many enzymes involved in mitochondrial respiration, antioxidant defense, and the synthesis of biomolecules by providing or accepting electrons[1].
Copper is also an essential micronutrient, and people mainly obtain it from food to maintain whole-body copper homeostasis (organ meats and shellfish are often the richest food sources, with adults typically consuming 0.8-2.4 mg of copper per day). The human body primarily absorbs copper through the small intestine, then transports it via the bloodstream to the liver, where excess copper is excreted into bile and eliminated from the body[2][3][4].
Figure 1. Schematic of systemic and cellular copper metabolism[4].
The uptake of copper is mainly through the small intestine, where the epithelial cells of the small intestine take up copper ions via CTR1/SLC31A1, which are transported to the other side of the epithelium via ATOX1 (copper chaperone antioxidant 1) and exported to the blood via ATP7A (ATPase Copper transporter α). Copper ions are transported in the blood by binding to proteins. Eventually the copper ions are transported to the liver and the excess copper is excreted into the bile and leaves the body.
However, once copper concentrations exceed the threshold for maintaining homeostasis, it can lead to a series of disruptions in cellular metabolic functions, ultimately resulting in cell death, a process known as "cuproptosis"[5].
02 Cuproptosis: Different from other known cell death pathways
Copper-induced cell death has been known since the 1980s, but the exact mechanism of how copper ions cause cell death has been controversial[6]. It wasn't until March 2022 that Tsvetkov et al. elucidated the mechanism of copper-induced cell death, naming it "cuproptosis". This involves the excessive accumulation of copper ions leading to abnormal aggregation of thiol-containing proteins, which disrupts iron-sulfur cluster proteins related to mitochondrial respiration, triggering a proteotoxic stress response and ultimately causing cell death[7].
Furthermore, inhibitors of apoptosis, necroptosis, ROS-induced cell death, and ferroptosis cannot rescue copper-induced cell death. Therefore, cell death induced by copper-carrier compounds is a distinct form of cell death driven by excessive copper accumulation, unrelated to other known cell death modalities (ferroptosis, pyroptosis, etc.) (Figure 2).
Figure 2. Comparison of multiple cell death modes[3][8][9][10][11].
03 Copper Death and Cancer
Copper (Cu) is a key signaling factor in cells and is closely related to cancer. Compared to normal patients, tumor tissues and/or serum from patients with various types of cancers such as breast, lung, gastrointestinal, oral, gallbladder, and pancreatic cancers show elevated copper concentrations. Copper accumulation can promote cancer cell migration, proliferation, and tumor growth[3].
Figure 3. Copper and cancer singnaling pathways[4].
Copper directly binds or activates EGFR, PDK1 or PI3K to promotes tumorigenesis. Copper also influences MAPK and autophagic pathways or indirectly changes c-Myc stability to influence tumor growth. Copper ions indirectly promotes HIFα or indirectly inhibits the Notch pathway ligand Jagged1 thus promoting vascular neoplastic migration. In addition, copper can also regulate PDE3B or S6K1 and thus modulates tumor metabolism.
Copper is also involved in multiple signaling pathways in tumor cells, influencing cancer development by binding and activating key molecules in these pathways (Figure 3). This has accelerated the development of Cu-coordinating compounds for anti-cancer therapy.
Two main strategies have been proposed: 1) Using Cu chelators to reduce the bioavailability of Cu, and 2) Using Cu ionophores to deliver Cu into cells and increase intracellular Cu levels.
Cu ionophores
Cu ionophores can induce copper-dependent cell death, or "cuproptosis". Examples include Elesclomol , Cu(II) bis(thiosemicarbazone) complexes [CuII(atsm) and CuII(gtsm) ], and Disulfiram (DSF). These have shown anti-cancer activities and have been evaluated in clinical trials (Table 1).
Table 1. Clinical trials for copper ionophores[4].
Elesclomol can transport Cu to the mitochondria, where excess Cu promotes the aggregation of lipoylated proteins and the destabilization of Fe-S cluster proteins, leading to proteotoxic stress and cell death[7]. Elesclomol has been shown to enhance the efficacy of paclitaxel in patients with refractory solid tumors and stage IV metastatic melanoma.
In a phase III clinical trial with late-stage melanoma patients, Elesclomol showed stronger anti-tumor activity in patients with lower lactate dehydrogenase (LDH) levels compared to those with high LDH levels. Lower LDH levels indicate a higher mitochondrial metabolic state. This further validates that Elesclomol is more sensitive to cells with high levels of lipidated TCA enzymes and hyperactive mitochondrial respiration[3].
Figure 4. Two potential therapeutic strategies to target cuproptosis in cancer[3].
a. The Cu ionophore elesclomol is believed to induce cuproptosis in cancer cells that either express high levels of lipoylated mitochondrial enzymes or are in a hyperactive respiratory state. b. Disulfiram combined with Cu selectively targets cancer cells with high ALDH expression. Created with BioRender.
Disulfiram (DSF) can also deliver Cu into cells and induce cuproptosis. DSF can cross the blood-brain barrier and has shown anti-cancer and/or chemosensitizing effects in clinical trials for glioblastoma patients. DSF and Cu can also downregulate the tumor suppressor gene PTEN and activate the AKT signaling pathway in human breast cancer.
Furthermore, DSF can inhibit aldehyde dehydrogenase (ALDH) and selectively target and kill ALDH+ cancer stem cells, reducing the risk of tumor recurrence. Cu ionophores can be combined with targeted therapies like TKIs and PI3K inhibitors, and are particularly effective against tumors with high mitochondrial metabolic states[3].
For the bis(thiosemicarbazone) class of compounds, Cu II (atsm) has shown anti-cancer activity in hamsters bearing colon cancer tumors. Cu II (gtsm) exhibited tumor-killing effects on prostate cancer cells in vitro and significantly reduced the prostate cancer burden in an in situ mouse model[3].
Cu chelators
In addition to copper ionophores, using chelating agents to deplete copper has also been shown to delay cancer metastasis by inhibiting pathological angiogenesis in various animal models.
Research has shown that many copper chelators such as Tetrathiomolybdate (TTM), Trientine, and D-penicillamine have demonstrated good anti-tumor activity in animal models and clinical trials (Table 2).
Table 2. Overview of the clinical development of Cu-modulating agents[3].
Among them, TTM has been the most extensively studied. Lowering copper levels using TTM affects the activity of MEK1/2 kinase and BRAF-driven tumorigenesis, thereby reducing the growth of BRAFV600E tumor xenografts. TTM can also inhibit copper chaperone proteins, blocking the delivery of copper to enzymes like LOX. Furthermore, in a phase II trial for malignant mesothelioma, TTM exhibited anti-angiogenic effects, delaying disease progression in stage I or II mesothelioma patients[3].
For Trientine, it can inhibit the expression of IL-8 and exhibit anti-tumor effects in hepatocellular carcinoma. Trientine can also reduce CD31 expression and inhibit endothelial cell proliferation. D-penicillamine, on the other hand, can suppress the activity of LOX, leading to impaired collagen crosslinking, reduced VEGF expression, and delayed progression of intracranial glioblastoma[3].
Furthermore, genes related to copper-induced cell death have been found to be associated with the tumor microenvironment, and copper can also regulate the expression of PD-L1, providing new insights into the connection between copper-induced cell death and cancer immunotherapy.
| Related products |
| Elesclomol Elesclomol (STA-4783) is a potent copper ionophore and promotes copper-dependent cell death (cuproptosis). Elesclomol specifically binds ferredoxin 1 (FDX1) α2/α3 helices and β5 strand. Elesclomol inhibits FDX1-mediated Fe-S cluster biosynthesis. Elesclomol is an oxidative stress inducer that induces cancer cell apoptosis. Elesclomol is a reactive oxygen species (ROS) inducer. Elesclomol can be used for Menkes and associated disorders of hereditary copper deficiency research. |
| Disulfiram Disulfiram (Tetraethylthiuram disulfide) is a specific inhibitor of aldehyde-dehydrogenase (ALDH1), used for the treatment of chronic alcoholism by producing an acute sensitivity to alcohol. Disulfiram inhibits gasdermin D (GSDMD) pore formation in liposomes and inflammasome-mediated pyroptosis and IL-1β secretion in human and mouse cells. Disulfiram, a copper ion carrier, with Cu2+ increases intracellular ROS levels and induces cuproptosis. |
| Cu(II)GTSM Cu(II)GTSM, a cell-permeable Cu-complex, significantly inhibits GSK3β. Cu(II)GTSM inhibits Amyloid-β oligomers (AβOs) and decreases tau phosphorylation. Cu(II)GTSM also decreases the abundance of Amyloid-β trimers. Cu(II)GTSM is a potential anticancer and antimicrobial agent. |
| Tetrathiomolybdate Tetrathiomolybdate, an orally active anti-copper agent, reduces copper levels in the body. Tetrathiomolybdate has a protective effect on collagen-induced arthritis in mice. Tetrathiomolybdate also reduces blood sugar, but has no effect on mice with hereditary diabetes (db/db). Tetrathiomolybdate inhibit angiogenesis, also shows antiangiogenic effects in malignant pleural mesothelioma. |
References
[1] Festa RA, et al. Curr Biol. 2011;21(21):R877-R883.[2] Ge EJ, et al. Nat Rev Cancer. 2022;22(2):102-113.[3] Chen L, et al. Signal Transduct Target Ther. 2022;7(1):378.[4] Xie J, et al. Mol Cancer. 2023;22(1):46. Published 2023 Mar 7.[5] Cobine PA, et al. Biochim Biophys Acta Mol Cell Res. 2021;1868(1):118867. [6] Halliwell B, et al. Biochem J. 1984;219(1):1-14. [7] Tsvetkov P, et al. Science. 2022;375(6586):1254-1261.[8] Wang Y, Zhang L, Zhou F. Cell Mol Immunol. 2022;19(8):867-868. [9] Jiang X, et al. Nat Rev Mol Cell Biol. 2021;22(4):266-282.[10] Wei X, et al. Cell Mol Immunol. 2022;19(9):971-992. [11] Bertheloot D, et al. Cell Mol Immunol. 2021;18(5):1106-1121. 
