Cuproptosismechanisms and links with cancers

Copper is one of those elemental paradoxes in biology. You need it to live, but too much of it causes cells to fall apart. For a long time, people observed copper ionophores — drugs that smuggle copper into cells — killing tumor cells and debated what type of death was occurring. Apoptosis? Autophagy? Ferroptosis? In two thousand twenty-two, the field finally assigned this phenomenon its own name and mechanism: cuproptosis. And as Xie, Yang, Gao, and He explain in their two thousand twenty-three review, this isn’t just "death by rust." It’s a very specific, mitochondrial, lipoylation-dependent collapse. Here’s the core idea; then we’ll fill in the proof. Inside mitochondria, there’s a small but significant modification called lipoylation, which involves attaching a lipoic acid-based handle to certain enzymes. One of those enzymes is DLAT, the E2 subunit of the pyruvate dehydrogenase complex. When DLAT is properly lipoylated, it does its job funneling carbon into the tricarboxylic acid cycle. When copper enters and binds that lipoyl moiety in its monovalent state, known as Cu(I), DLAT molecules begin to stick to one another. They oligomerize. That clumping creates proteotoxic stress, which results in misfolded, jammed-up protein machinery right at the heart of mitochondrial metabolism, leading to cell death. The lipoylation machinery operates through a neat assembly line. Lipoic acid synthase, referred to as LIAS, builds the lipoyl group; LIPT1, a lipoyltransferase, transfers it onto target proteins like DLAT. Upstream of both is FDX1, ferredoxin 1. You can think of FDX1 as the switchboard operator of this circuit. It controls the lipoylation pathway, and it can also reduce copper from Cu(II) to Cu(I), the more reactive form that binds to the lipoyl handle. Genome-wide knockout screens make the point clear: if any of seven genes are deleted — FDX1, the lipoylation pair LIAS and LIPT1, or the pyruvate dehydrogenase players DLAT, DLD, PDHA1, and PDHB — cells suddenly become resistant to copper ionophore-induced death. This genetic map is hard to ignore. It highlights lipoylated DLAT as the target, and FDX1, LIAS, and LIPT1 as the enablers. If you’re wondering whether this could just be reactive oxygen species in disguise, the answer appears to be no. Copper ionophores can increase reactive oxygen species, but antioxidants only partially mitigate the cell death. In experiments, even strong scavengers like N-acetylcysteine do not fully rescue cells, indicating that the lethal factor is the lipoylation-linked proteotoxicity, not a generic oxidative burn. How does copper arrive at that mitochondrial stage in the first place? The body absorbs copper in the small intestine and transports it bound to proteins in the blood. Roughly three-quarters rides on ceruloplasmin, about a quarter on albumin, and a small amount — around two-tenths of a percent — binds to histidine. Excess copper returns to the liver and is expelled into bile by ATP7B, with ATP7A assisting in other tissues. At the cell surface, a transporter called CTR1, also known as SLC31A1, imports copper primarily as Cu(I), often after enzymes called STEAPs reduce it from Cu(II). Inside, glutathione and metallothioneins buffer the free metal, while chaperones like ATOX1 and CCS deliver it to where it’s needed, such as ATP7A and ATP7B for export or superoxide dismutase in the cytosol. The mitochondrion has its own pathway: SLC25A3 moves copper into the matrix, and in the intermembrane space, COX17 transfers it to SCO1 and SCO2, with COA6 assisting in forming the necessary disulfide bonds to build cytochrome c oxidase. It’s a well-organized logistics network, until copper levels are elevated or the process is disrupted. That’s where ionophores come into play. Elesclomol and disulfiram are two of the most studied. Elesclomol transports copper into mitochondria; the elesclomol-copper complex, in an FDX1-dependent manner, also destabilizes iron-sulfur clusters, adding metabolic strain to the DLAT issue. Disulfiram binds with copper and interacts with Npl4, a cofactor for the p97 segregase in the ubiquitin-proteasome system. Disrupting the Npl4-p97 axis increases proteotoxic stress from a different angle. Different entry points lead to the same outcome: more mitochondrial copper, more DLAT oligomerization, and more stress. You can also tip the balance in simpler ways. Overexpressing CTR1, the copper importer, causes cells to absorb more copper. Blocking glutathione synthesis with buthionine sulfoximine weakens buffering. Reducing ATP7B, the copper exporter, leads to copper accumulation. Each of these changes makes cells more vulnerable to the lipoylation-linked death. Cuproptosis occupies a significant role in cancer biology. Copper isn’t merely a poison; it’s also a cofactor in signaling. By increasing copper levels, receptor tyrosine kinase pathways become more active. Copper can bind to PDK1 at two histidines, specifically histidine 117 and histidine 203, which primes AKT. AKT then phosphorylates transcription factors like FoxO1a and FoxO4, driving proliferation. In the mitogen-activated protein kinase pathway, copper directly binds to MEK1, boosting the phosphorylation of ERK1 and ERK2, the extracellular signal-regulated kinases, and even influences c-Jun N-terminal kinase, or JNK, which supports growth. Autophagy joins in as well: copper binds to the ULK kinases — the UNC-51-like kinases, ULK1 and ULK2 — promotes phosphorylation of ATG13, and aids in assembling the autophagy initiation complex. In BRAF-driven lung adenocarcinoma models, if you remove CTR1, the copper-dependent activities, including MEK1, MEK2, ULK1, and ULK2, decrease, emphasizing that even oncogenic circuits have copper dependencies. There’s more. Copper modulates Notch signaling through the copper-dependent shedding of Jagged1, which enhances migration. Angiogenesis increases because copper stabilizes HIF-1 alpha and upregulates vascular endothelial growth factor, even when oxygen is plentiful. In inflammatory environments, copper can activate the X-linked inhibitor of apoptosis protein, or XIAP, and promote NF-kappa B–dependent tumorigenesis. Metabolically, copper influences lipid and sugar regulation, binding phosphodiesterase 3B, or PDE3B, to adjust cyclic AMP levels and reduce S6K1 alongside glycolysis regulators like GLUT1, PKM2, and LDHA. The Wnt and c-Myc dynamics are context-sensitive: in certain scenarios, copper decreases beta-catenin and c-Myc, while in others it appears to stabilize c-Myc by phosphorylating it at two sites — threonine 58 and serine 62. This intricate network of influence sets the stage for cuproptosis to be significant in tumors. Many cancers demonstrate elevated serum copper levels, including lung, prostate, breast, gallbladder, stomach, and thyroid cancers, with some studies linking copper levels to cancer stage. The review suggests that since the lipoylation machinery and the pyruvate dehydrogenase complex are distinctly mitochondrial, tumors that rely heavily on oxidative metabolism may be predisposed to copper-dependent collapse. Conditions like melanoma, certain breast cancers, leukemias, and even drug-resistant states that revert to mitochondria for energy are potential candidates. Looking more broadly, bioinformatics has attempted to transform this mechanistic understanding into prognostic tools. Across The Cancer Genome Atlas and various other datasets, researchers have constructed cuproptosis-related gene signatures. Some of these are strictly associated with the pathway, while others combine genes linked to necroptosis or ferroptosis to stratify patients. The usual analytical toolbox is employed, including Cox regression and occasionally least absolute shrinkage and selection operator, known as LASSO, to refine features, along with pathway enrichment analyses to draw conclusions. The same seven mitochondrial genes are frequently identified: FDX1, LIAS, LIPT1, DLAT, DLD, PDHA1, and PDHB. However, their associations can vary depending on tissue context. DLAT may act as a risk factor in pancreatic adenocarcinoma while providing protection in glioma. High LIAS expression may indicate poor prognosis in lung adenocarcinoma but better outcomes in clear cell renal cell carcinoma and ovarian cancer. DLD seems to be a risk gene in uveal melanoma, glioma, and lung adenocarcinoma. FDX1 displays variability; it predicts worse survival in head and neck squamous cancers and low-grade glioma, but better outcomes in cervical cancer and clear cell renal. PDHA1 also shows variability; in some lung adenocarcinoma cohorts, higher PDHA1 levels correlate with better survival. Additionally, the copper transport dynamics matter: high levels of SLC31A1, the CTR1 importer, have been linked to worse outcomes in breast cancer, and microsatellite variants in SLC31A1 and ATP7B have been associated with lung cancer risk. These signatures not only differentiate patient survival but also reveal insights into the tumor microenvironment. High-risk groups typically exhibit more advanced T and N stages and poorer overall, disease-free, or progression-free survival. Their tumor microenvironments often appear colder, with lower immune activation, fewer infiltrating immune cells, and worse composite scores. However, there are exceptions; gliomas often defy this trend. Immune checkpoint gene expression tends to be higher in high-risk groups, yet in certain cancers, including cervical, breast, and skin melanoma, some high-risk cohorts display the opposite trend. When examining immunotherapy datasets, lower-risk groups often outperform higher-risk ones, although glioma and uveal melanoma complicate the findings. Copper's role in biology also ties into immune regulation, including the expression of programmed death-ligand 1, or PD-L1, but clear causal relationships in patients are still limited. Emerging drug response clues are beginning to surface. Some reports indicate that proteasome inhibitors like bortezomib show improved efficacy in specific cuproptosis-risk groups. This is intriguing, considering the link between disulfiram, copper, Npl4, and proteostasis. However, these findings stem from retrospective analyses, and broad preclinical validation remains insufficient. What about translating cuproptosis into clinical practice? Disulfiram and elesclomol have both been extensively studied. Disulfiram, well known as an alcohol aversion medication, has been tested in oncology at daily doses between one hundred twenty-five and five hundred milligrams and is generally well tolerated. Elesclomol has a solid safety profile, but in phase three trials, the overall efficacy did not outperform the control group in unselected patients. There was a notable detail: people with low serum lactate dehydrogenase, a rough marker for more oxidative tumors, seemed to respond differently in the elesclomol arm. This raises the possibility that lactate dehydrogenase could serve as a predictor. In combination treatments, there are promising signs. Disulfiram in conjunction with temozolomide demonstrated acceptable safety and a potential increase in progression-free survival. Elesclomol paired with paclitaxel doubled median progression-free survival in one context with manageable toxicity. Disulfiram combined with cisplatin and vincristine was well tolerated and may extend survival. Moreover, researchers are exploring ways to encapsulate copper and ionophores in nanomedicines to target tumors more precisely while sparing normal tissues. Despite these advancements, two significant mechanistic gaps remain. First, the pathway from DLAT oligomers to cell death is still not completely understood. We can see the clumps forming, observe the rise in proteotoxic stress, and measure the decline in cell viability. However, the execution step — the sequence of events leading from those observations — needs further exploration. Second, the stress cross-talk is complex. The collapse of iron-sulfur clusters, the Npl4-p97 bottleneck, and copper's well-documented tendency to displace iron in enzymes such as aconitase may add to the complexity, or they may represent parallel pathways modulating sensitivity to cuproptosis itself. The field also hasn’t reached a consensus on a distinct cellular "face" of cuproptosis; there is no clear morphology akin to the membrane blebbing and nuclear condensation seen in apoptosis. While this ambiguity is acceptable at this stage, it has implications for diagnostics. If you’re considering, "Okay, how do we apply this?," Xie and colleagues emphasize the importance of biomarkers. Low lactate dehydrogenase provides a starting point, but we will probably need composite markers, such as the expression of FDX1, LIAS, and LIPT1, perhaps a cuproptosis risk score correlated with mitochondrial dependency, and maybe even functional measurements of lipoylation. We should also prepare for resistance; cancer cells can adjust copper import and export levels, increase metallothioneins, or reroute their metabolism away from the pyruvate dehydrogenase complex. Additionally, there’s the challenge of off-target stress: if you push copper levels too high, you risk affecting noncancerous tissues that rely on mitochondrial respiration. The synthesis here is both straightforward and stimulating. Copper can act as a toxin, but only when it encounters the appropriate molecular handle. In mitochondria, that handle is the lipoyl group on enzymes like DLAT. The upstream components — FDX1, LIAS, and LIPT1 — set the stage for what follows. The downstream turmoil, characterized by proteotoxic stress, iron-sulfur instability, and proteasome traffic jams, pushes cells past their limits. In tumors that depend heavily on mitochondrial function, directing copper efficiently towards that handle could be a viable strategy for inducing cell death. The next step is to definitively identify which patients will benefit from this approach, doing so with the same level of precision that elucidated the mechanism in the first place.