Copper nanoparticles and their future in drug delivery and anticancer therapy

1 Introduction

1.1 Inorganic nanoparticles in nanomedicine

Inorganic nanoparticles (NPs) have been used as powerful therapeutics in drug delivery and anticancer therapy mainly due to their specific physicochemical properties, such as large surface area, adjustable morphology, optical activity, magnetic properties, and excellent stability (Shirazi et al., 2025). Inorganic NPs, on the other hand, with superior structural robustness, are promising for the fabrication of multifunctional biomedical materials, for drug delivery, diagnostic imaging, biosensing, photothermal therapy, and tissue engineering. The most ubiquitous inorganic nanomaterials in medicine are gold, gadolinium, iron, zinc oxide, copper, and titanium dioxide nanoparticles (Shirazi et al., 2025; Zhang et al., 2016; Parang et al., 2026; Shirazi et al., 2026; Shirazi et al., 2025; Lee et al., 2025; Yu et al., 2025; Vikal et al., 2025; Sidhic et al., 2025). Their nanoscale form enables strong interactions with biological systems, facilitating effective cellular uptake, targeted delivery, and controlled release of therapeutic agents. Recent years have witnessed an increase in the use of inorganic NPs to enhance the bioavailability and therapeutic efficacy of drug candidates while reducing systemic toxicity (Mohapatra et al., 2024; Woźniak-Budych et al., 2023).

Among the many inorganic nanomaterials, copper nanoparticles (CuNPs) are of interest due to their favorable biological and therapeutic activities combined with a low production cost. CuNPs exhibit remarkable electrical, optical, catalytic, and antimicrobial properties that can be harnessed for different kinds of biomedical applications (Woźniak-Budych et al., 2023; Vodyashkin et al., 2024). Their high surface-to-volume ratio allows efficient drug loading and surface functionalization with polymers, peptides, antibodies, and targeting ligands (Pedroso-Santana and Fleitas- Salazar, 2023). Furthermore, CuNPs exhibit intrinsic anticancer, antimicrobial, anti-inflammatory, and antioxidant activities, which can synergistically enhance therapeutic outcomes (Abdolmaleki et al., 2024; Devaraji et al., 2024; Surya et al., 2024). Owing to these properties, CuNPs are being extensively investigated as nanocarriers for targeted drug delivery, photothermal therapy, gene delivery, wound healing, and theranostic applications (Aishajiang et al., 2023; Zhuo et al., 2023; Tao et al., 2019).

The biomedical performance of CuNPs is strongly influenced by their size, shape, surface chemistry, and synthesis method. Various fabrication approaches, including chemical reduction, physical synthesis, and green synthesis using plant extracts or biological agents, have been developed to improve nanoparticle stability, biocompatibility, and therapeutic efficiency (Pourmadadi et al., 2024; Vodyashkin et al., 2024).

Although these candidates have great potential for treatment, copper-induced oxidative stress, cytotoxicity (Karlsson et al., 2008), long-term accumulation (Bondarenko et al., 2013), and potential environmental effects pose significant challenges for clinical application. Consequently, current work has centered on the formation of surface-modified, biocompatible CuNP formulations that maximize therapeutic benefits while minimizing adverse effects (Woźniak-Budych et al., 2023). Overall, CuNPs represent an emerging and versatile class of inorganic nanomaterials with significant potential for advancing next-generation nanomedicine and targeted therapeutic systems (Vodyashkin et al., 2024).

Although several reviews have addressed copper-based nanomaterials, most have concentrated on a single facet, such as synthesis and catalysis, antimicrobial activity, or copper-based anticancer compounds considered broadly (Woźniak-Budych et al., 2023; Vodyashkin et al., 2024; Gawande et al., 2016; Pourmadadi et al., 2024; Chakraborty et al., 2022; Crisan et al., 2022; Abdolmaleki et al., 2024; Devaraji et al., 2024; Surya et al., 2024). The present review is distinguished by its integrative scope: it connects the fundamental redox chemistry and physicochemical behavior of CuNPs to their biological fate, that is, their absorption, distribution, metabolism, elimination, and toxicity, and then to the full spectrum of therapeutic applications spanning direct anticancer cytotoxicity, cuproptosis, photothermal and photodynamic therapy, controlled and targeted drug delivery, and gene delivery. By explicitly linking the recently elucidated mechanism of cuproptosis to the rational design of multifunctional CuNP platforms, and by treating safety and clinical-translation challenges alongside therapeutic opportunity, this review offers a unifying framework that is not provided by earlier, more narrowly focused surveys. Accordingly, this review is deliberately organized to follow the biological journey of a copper nanoparticle, from the redox and physicochemical chemistry that governs its behavior, through the absorption, distribution, metabolism, elimination, and toxicity (ADMET) profile that determines its biological fate, to the full range of therapeutic applications, and finally to the safety and translational barriers that separate current preclinical advances from clinical use. This organization was chosen to make explicit the mechanistic thread linking copper chemistry to therapeutic outcome, a connection that topic-segregated reviews do not surface.

Distinct from all prior surveys, this review explicitly treats the ADME profile of CuNPs as a mechanistic foundation for understanding both their therapeutic potential and their toxicological limitations and directly connects the newly elucidated cuproptosis pathway to the rational engineering of next-generation copper-based drug and gene delivery platforms. Because copper is a constituent of CuNPs, we first consider its biological role in the body. This is relevant because CuNPs may release copper ions upon metabolism, and the biological fate of the metal can lead to different outcomes.

1.2 Copper

1.2.1 Energy production

Copper is an essential cofactor for oxidase enzymes that catalyze oxidation-reduction reactions in various metabolic pathways. These copper-dependent enzymes, or cuproenzymes, participate in energy (ATP) production, iron metabolism, connective tissue formation, and neurotransmission (Higdon et al., 2014). More specifically, cytochrome c oxidase requires copper for ATP production in mitochondria. Without adequate copper, the electron transport chain cannot function efficiently, impairing cellular energy generation across virtually every tissue in the body (Leary et al., 2009).

1.2.2 Copper metabolism

Copper is an essential trace element that plays a central role in human redox biology and systemic iron homeostasis. Disruption of copper metabolism leads to secondary iron deficiency due to impaired iron mobilization and utilization (Arredondo and Núñez, 2005). Clinically, copper deficiency is associated with reduced physical performance, impaired cognitive development, altered skeletal mineralization, and weakened immune function (Arredondo and Núñez, 2005).

A key mechanism underlying these effects involves the copper-dependent enzyme ceruloplasmin, a multicopper ferroxidase that catalyzes the oxidation of ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). This oxidation step is essential for iron loading onto transferrin, the plasma transport protein that delivers iron to tissues such as bone marrow for erythropoiesis. In the absence of adequate copper, ceruloplasmin activity is reduced, leading to impaired iron export from cells and a functional iron deficiency despite normal or increased iron stores (Osaki et al., 1966).

1.2.3 Connective tissue formation

Copper is critical for human health because it is involved in the synthesis of collagen and elastin, which are two key proteins indispensable for the strength and elasticity of connective tissues. Copper also acts as a cofactor for the enzyme lysyl oxidase, which cross-links these proteins to increase tissue strength (Rucker et al., 1998). Copper deficiency has been associated with increased risk of osteoporosis, joint pain, and connective tissue diseases. Without sufficient copper, bones become brittle, cartilage can wear down, and joints can be more prone to inflammation and degeneration (Rucker et al., 1998; Qu et al., 2018).

1.2.4 Nervous system health

Copper is a critical trace element in biological systems because many essential enzymes require it as a cofactor, including cytochrome c oxidase, superoxide dismutase, and dopamine-β-hydroxylase (Gale and Aizenman, 2024). Because copper is known for its roles in oxidative metabolism, antioxidant defense, and neurotransmitter synthesis, it plays a particularly critical role in neuronal development and neuronal function (Gale and Aizenman, 2024). Copper-dependent enzymes synthesize phospholipids and cholesterol, which are essential components of myelin; therefore, copper is fundamental to keeping nerve cells structurally sound and functioning properly. It is also a cofactor of enzymes (e.g., dopamine beta-hydroxylase) that convert dopamine into norepinephrine, an important neurotransmitter involved in mood, attention, and stress response (Gale and Aizenman, 2024; Gonzalez-Lopez and Vrana, 2020).

1.2.5 Antioxidant defense

Superoxide dismutase (SOD) functions as an antioxidant by catalyzing the conversion of reactive oxygen species (ROS), such as the superoxide anion (O₂ ⁻) and the hydroxyl radical (•OH), into less harmful molecules, thereby shielding cells from oxidative damage. (Uriu-Adams and Keen, 2005).

Copper plays a vital role in SOD, an enzyme that mitigates the harmful free radicals, thereby protecting neural tissues from oxidative damage, which is implicated in neurodegenerative diseases. This antioxidant function makes copper especially vital for long-lived cells, such as neurons and cardiomyocytes (Uriu-Adams and Keen, 2005).

1.2.6 Immune function

Copper is required for the function of over 30 proteins, including SOD, ceruloplasmin, lysyl oxidase, cytochrome c oxidase, tyrosinase, and dopamine-β-hydroxylase, many of which directly support immune cell activity (Gale and Aizenman, 2024; Arredondo and Núñez, 2005).

Copper deficiency impairs the development and function of neutrophils and macrophages, the body’s frontline defenders against pathogens. Systemic copper deficiency results in diminished immune response, underscoring the central role of copper in overall immune competence (Arredondo and Núñez, 2005).

1.2.7 Melanin production

The cuproenzyme tyrosinase (TYR) is necessary for the synthesis of melanin by melanocytes, which is essential for normal pigmentation of hair, skin, and eyes (Higdon et al., 2014). A lack of TYR activity may cause achromotrichia, a type of hair pigmentation loss seen in copper-deficient laboratory and agricultural animals, and depigmentation in severely copper-depleted patients with Menkes disease (Higdon et al., 2014). Besides photoprotective effects on appearance, melanin absorbs ultraviolet light and reduces DNA damage to skin cells (Tadokoro et al., 2003).

1.2.8 Bone health

Based on in vitro and in vivo research, small amounts of copper ions promote osteoblast proliferation and help mesenchymal stem cells differentiate into the osteogenic lineage (Li et al., 2025; Qu et al., 2018). In humans and animals, copper deficiency is known to cause abnormal bone formation and fractures in newborn babies, infants, and adults. Copper plays a critical role in bone remodeling and the maintenance of sound bones. It underlies osteoblast activity (bone formation) and regulates osteoclasts (bone resorption). Increased fracture and osteoporosis risk is due to lower bone mineral density resulting from low copper levels (Li et al., 2025).

2 Chemistry of CuNPs

2.1 Oxidation state, chemical forms, and redox chemistry

The chemistry of CuNPs is fundamentally governed by copper’s exceptional versatility as a transition metal, capable of existing in multiple oxidation states - Cu⁰ (metallic copper), Cu⁺ (cuprous), and Cu²⁺ (cupric), each giving rise to chemically and physically distinct nanoparticle forms.

In practice, the three dominant nanoparticle phases are metallic Cu⁰, cuprous oxide (Cu₂O), and cupric oxide (CuO), and their chemical identities profoundly affect their reactivity, optical behavior, and biological interactions (Gawande et al., 2016). It is crucial to acknowledge that the electrical conductivity of copper in a zero-oxidation state (Cu⁰) is considerably high; nevertheless, this conductivity diminishes when CuO nanoparticles are formed through oxidation (Liu et al., 2011).

Copper oxide, with a band gap of 1.7 electron volts, is an extremely significant metal oxide and quasi-metal, with CuO nanoparticles retaining distinctive characteristics such as p-type semiconductor behavior, a narrow band gap, a high surface-area-to-volume ratio, and Cu⁺/Cu²⁺ redox activity, that render them advantageous for particular biomedical and catalytic applications despite this reduction in conductivity (Abdelkareem et al., 2025; Ghareib et al., 2019; Yasin et al., 2022; Iqbal et al., 2022).

The redox interconversion between these oxidation states is chemically accessible and is, in fact, the mechanistic basis for CuNPs’ biological activity: through Fenton-like reactions, Cu⁺ and Cu²⁺ cycle between oxidation states, catalyzing the conversion of hydrogen peroxide into highly reactive hydroxyl radicals (•OH), enabling CuNPs to function simultaneously as antimicrobial agents and pro-oxidant cancer therapeutics (Lyu et al., 2020; Gawande et al., 2016).

Notably, due to its greater reactivity, Cu(II) is considered more biologically hazardous than Cu(I) and Cu(0), with the main harmful impact of CuNPs arising from the release of free copper ions, which are further influenced by biological fluid breakdown (Lyu et al., 2020; Wang et al., 2013).

2.2 Synthetic chemistry

The chemical routes used to produce CuNPs directly determine their size, shape, phase composition, surface chemistry, and ultimately their functional properties, making synthesis chemistry central to their applications (Pourmadadi et al., 2024; Gawande et al., 2016).

The most widely used approach is wet-chemical reduction, in which a copper salt precursor such as copper sulfate (CuSO₄) or copper chloride (CuCl₂) is reduced by a reducing agent, commonly ascorbic acid, sodium borohydride, or hydrazine, to yield zero-valent Cu⁰ nanoparticles. Due to copper’s reactivity, capping agents are necessary to prevent particle aggregation and/or oxidation; in some cases, the reducing molecule can act as a capping and stabilizing agent as well, as in many biogenic-mediated syntheses where reducing molecules of natural provenance stabilize the produced nanostructures (Pourmadadi et al., 2024; Crisan et al., 2022).

Green synthesis has proven to be a critical alternative, with plant extracts superseding synthetic alternatives. CuNP green synthesis utilizes biological resources, specifically plant extracts, microorganisms, and biopolymers, to reduce copper ions and stabilize these nanoparticles; phytochemicals like polyphenols, flavonoids, and alkaloids, acting as reducing and capping agents jointly, offer an eco-friendly alternative to conventional chemical routes (Chakraborty et al., 2022; Sportelli et al., 2023). The synthesis technique reported for CuO, Cu₂O, and Cu₄O₃ is fundamentally the same in principle across chemical, physical, and green synthesis routes; however, variables such as precursor concentration, pH, and temperature have the greatest impact on the type of Cu particles generated (Crisan et al., 2022; Pourmadadi et al., 2024).

During green synthesis, for example, biomolecules present in plant extracts reduce Cu²⁺ ions to Cu⁰ while simultaneously facilitating oxidation to form CuO nanoparticles, with certain biomolecules also serving as capping agents that stabilize the produced nanoparticles (Chakraborty et al., 2022).

Regulating pH, temperature, extract concentration, and reaction time allows optimization of particle size, shape, and surface characteristics, yielding spherical, rod-like, or flower-shaped nanoparticles that typically range from 5 to 50 nm. Surface engineering through polymer functionalization (e.g., polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP), silica shells, or organic ligands is critical chemical strategy to stabilize CuNPs in physiological environments and for biomedical deployment (Sportelli et al., 2023, Pedroso-Santana and Fleitas-Salazar, 2023).

2.3 Surface plasmon resonance of CuNPs and oxidation susceptibility

CuNPs composed of metallic copper exhibit localized surface plasmon resonances (LSPR), which arise from the collective oscillations of conduction-band electrons when stimulated by electromagnetic waves at specific wavelengths (Chan et al., 2007). For spherical Cu⁰ nanoparticles, the LSPR band is typically centered around 580 nm, with a molar extinction coefficient (ε) of approximately 7.7 × 10⁷ M^-1 cm^-1 at that wavelength values comparable to those reported for gold and silver nanoparticles of similar dimensions (Wei et al., 2010; Tyagi et al., 2024).

The resonance position is size- and shape-dependent: 20 nm CuNPs exhibit a plasmon excitation onset near 530 nm, with all sizes showing a strong transmission minimum around 590 nm in the visible spectrum, and anisotropic morphologies such as nanorods can shift the resonance further into the near-infrared. These resonances produce strong extinction coefficients across the visible and near-infrared spectrum (Huang et al., 2020; Liu et al., 2015), comparable to those observed in gold and silver nanoparticles (Tyagi et al., 2024).

Despite its optical similarity to noble metals, copper is highly prone to oxidation, forming copper oxide, which lacks plasmonic properties. Oxidation in air proceeds rapidly: an oxide shell comprising roughly 1 nm of Cu₂O and ∼1.1 nm of CuO can form within 16 h of air exposure, and small CuNPs below 25 nm oxidize under air to stable Cu₂O rather than to the thermodynamically preferred bulk phase CuO. This oxidation tendency, along with the relatively weaker and broader plasmonic bands of CuNPs (Liu et al., 2015; Dabera et al., 2017), has constrained their utility as optical agents in biosensing applications.

The high sensitivity of the LSPR peak wavelength to the local dielectric environment spanning 575–635 nm, depending on capping ligand, makes LSPR shift measurements a particularly sensitive probe of oxide shell growth, further illustrating how rapidly even a thin oxide layer disrupts plasmonic fidelity (Dabera et al., 2017).

One of the most chemically significant characteristics of CuNPs and a major challenge for their application is their high susceptibility to surface oxidation, which occurs spontaneously upon exposure to air or aqueous environments and transforms the metallic Cu⁰ core into a layered Cu₂O/CuO shell (Ghodselahi et al., 2008; Gonzalez-Posada et al., 2014).

This core-shell oxidation chemistry profoundly alters both optical and biological properties. CuNPs are an attractive alternative to gold and silver, offering comparable electrical and thermal conductivity and a narrow LSPR absorption at a wavelength between those of Ag and Au; however, both Cu₂O and CuO are semiconductors, and so the formation of a thin oxide layer at the nanoparticle surface does not necessarily impede charge transfer, although it does degrade the optical properties by damping the LSPR response (Dabera et al., 2017).

The LSPR itself, a quantum optical phenomenon in which conduction electrons oscillate collectively in resonance with incident light, is highly sensitive to nanoparticle geometry: the thickness of the oxide layer significantly affects the LSPR peak position, with a blue shift observed upon removal of the oxide layer, and the inter-nanoparticle spacing of dimers shifts the LSPR peak to longer wavelength and enhances intensity as spacing decreases (Liu et al., 2023).

These structure property relationships are not merely academic; they are the chemical basis for engineering CuNPs with specific absorption wavelengths for photothermal therapy, photoacoustic imaging, and biosensing (Wang et al., 2023). The size-dependent quantum confinement of electrons, shape-dependent surface area exposure, and phase composition together constitute a rich, tunable chemical parameter space that distinguishes CuNPs from any other form of copper and underlies their unique multifunctional potential (Liu et al., 2023).

3 Absorption, distribution, metabolism, elimination, and toxicity of CuNPs

The ADME and toxicity profile of CuNPs is summarized in Figure 1. Following administration via inhalation, oral, dermal, or parenteral routes, CuNPs enter systemic circulation, undergo protein corona formation, and preferentially accumulate in the liver and spleen. At the cellular level, lysosomal dissolution releases Cu²⁺ ions that integrate into endogenous copper homeostasis pathways, while toxicity is mediated through oxidative stress, mitochondrial dysfunction, membrane damage, inflammation, and genotoxicity. Elimination occurs predominantly via hepatobiliary excretion, with a secondary renal route, raising concerns about potential tissue accumulation following prolonged exposure.

3.1 Absorption

Absorption of CuNPs into biological systems occurs via multiple routes, depending on the route of exposure. Inhalation is considered one of the most significant routes, as inhaled nanoparticles are rapidly deposited on the alveolar surface with high efficiency and can harm the respiratory system by injuring epithelial cells (Lai et al., 2018). The small size of nanoparticles allows them to reach the periphery of the lung (Vyas et al., 2026), where gas exchange occurs, to transmigrate across the alveolar epithelium and enter systemic circulation, as well as connective and lymphatic tissue of the lung (Fröhlich and Salar-Behzadi, 2014).

Gastrointestinal absorption can occur after ingestion, with efficiency affected by particle size, surface coating, pH, and the presence of food or mucus, which can agglomerate particles and decrease their bioavailability. Numerous physicochemical characteristics and experimental parameters, comprising, for example, the type, size, surface charge, zeta potential, surface coating, and protein binding, are capable of influencing the nanoparticle pharmacokinetics and absorption efficacy at various exposure routes (Owens and Peppas, 2006; Moghimi et al., 2001; Gong et al., 2026). Dermal absorption is generally considered minimal in intact skin but may be enhanced when skin barriers are compromised. Regardless of route, smaller nanoparticles tend to exhibit greater absorption efficiency due to their increased surface-area-to-volume ratio and their ability to exploit endocytic and transcytotic pathways at the cellular level (Crisan et al., 2022; Vyas et al., 2026).

3.2 Distribution

Distribution of CuNPs following systemic uptake is largely governed by particle size, surface chemistry, and protein corona formation. It is well established that nanoparticles gather molecules on their surfaces upon contact with biological fluids, forming a “protein corona” that can significantly affect their fate and therapeutic or diagnostic performance (Cox et al., 2018).

In the blood circulation, the mononuclear phagocyte system (MPS), made up of dendritic cells, blood monocytes, and macrophages in the liver, spleen, and lymph nodes, clears, processes, and degrades foreign substances present in the body; thus, nearly all nanoparticles injected without a surface modification strategy are cleared by this system within a few hours of entering the systemic circulation (Moghimi et al., 2001). Nanoparticles accumulate preferentially in the liver and spleen, distribute to other tissues such as the heart, lungs, and kidneys, and are then primarily eliminated via hepatobiliary and renal elimination pathways (Lee et al., 2025). CuNPs have also demonstrated the ability to cross the blood-brain barrier, raising particular toxicological concerns for neurological effects (Cox et al., 2018). Within tissues, particles may dissolve, releasing Cu²⁺ ions, and the in vitro and in vivo toxicity of CuNPs is attributed to both the particulate form and the dissolved copper ion species, with the relative contributions of each shifting over time as the particle dissolves (Boyadzhiev et al., 2021).

In addition, Tang et al. investigated the acute toxicity and biodistribution of differently sized CuNPs in rats following oral administration, revealing a clear and inverse size-dependent toxicity profile. The oral LD₅₀ values were determined as 359.6 mg/kg for Cu ions, 1,022 mg/kg for 30 nm CuNPs, 1,750 mg/kg for 50 nm CuNPs, 2,075 mg/kg for 80 nm CuNPs, and greater than 5,000 mg/kg for 1 μm copper microparticles, classifying the nanoparticulate forms as slightly hazardous and the ionic form as moderately hazardous according to Organisation for Economic Co-operation and Development (OECD) criteria.

Despite having the highest LD₅₀, 80 nm CuNPs produced the most severe physiological and biochemical toxic effects in a 7-day repeated-dose study at 400 mg/kg, inducing the greatest elevations in white blood cell count, AST, ALT, urea, and creatinine, alongside the most pronounced histopathological damage to the liver, spleen, and kidneys.

Biodistribution analysis following a single oral dose of 200 mg/kg showed that the liver and kidneys were the primary organs of Cu accumulation, with tissue Cu content peaking at 24–48 h post-administration and reaching levels 5- to 6-fold above baseline; notably, CuNPs were cleared significantly more slowly than Cu ions or microparticles, with 30 nm particles showing persistent elevated accumulation in the brain and kidneys at 1 week post-dosing.

The investigators concluded that the toxic effects of CuNPs likely result from a dual mechanism involving both the nanoparticles themselves and the Cu²⁺ ions released upon dissolution, with particle size governing not only the magnitude of toxicity but also the specific organ targeting profile (Tang et al., 2018).

3.3 Metabolism

The metabolism of CuNPs is intricately linked to the broader homeostatic determinants of copper in the body. Upon internalization, the toxicity of CuNPs has previously been linked to the so-called “Trojan horse” mechanism, in which excessive intracellular copper ions are released upon particle internalization, driven by the acidic pH of lysosomes (Strauch et al., 2020). The released free copper ions pass into the usual copper metabolic sequence, in which Atox1 is a copper carrier that facilitates the movement of copper in the secretory pathway, where copper-dependent enzymes that participate in neurotransmitter biosynthesis, iron efflux, neovascularization, wound healing, and blood pressure regulation are activated (Hatori and Lutsenko, 2016). Copper is also sequestered by metallothioneins and incorporated into ceruloplasmin, key proteins involved in copper storage and systemic transport (Patil et al., 2013). Copper overload shifts the balance between the reduced and oxidized forms of glutathione (GSH and GSSG), making the cellular environment more oxidizing and negatively impacting many cellular processes that rely on a precise glutathione balance (Moschini et al., 2023).

This integration into endogenous copper metabolism means that CuNP toxicity is partly a function of the body’s capacity to buffer copper ion release, a capacity that can be overwhelmed at high nanoparticle doses, leading to oxidative stress and cellular damage (Boyadzhiev et al., 2021).

3.4 Elimination

Elimination of CuNPs and their ionic byproducts occurs through several pathways, with biliary excretion via the liver into feces representing the dominant route for copper clearance in mammals.

Since the primary route of copper elimination is biliary excretion, the liver plays a critical role in copper homeostasis by tightly regulating hepatic copper output (Schilsky, 2017). The transporter ATP7B, located in the trans-Golgi network of hepatocytes, accepts copper from Atox1 and, when cellular copper is elevated, traffics it to vesicles near the apical membrane where it facilitates the release of copper into the bile, the principal excretory mechanism maintaining whole-body copper balance (Huffman and O’Halloran, 2001).

Renal excretion plays a secondary but meaningful role, particularly for smaller dissolved copper species that pass through the glomerular filtration barrier. Notably, the threshold for renal clearance of intact metal-based nanoparticles is approximately 6 nm, and ultrasmall nanoparticles undergo rapid renal clearance faster than larger particles, reducing the duration of organ exposure to dissociated copper ions (Gitlin, 2003).

Chronic or high-level exposure can overwhelm excretory capacity, leading to bioaccumulation, particularly in the liver; loss of ATP7B function leads to reduced biliary excretion and reduced copper incorporation into ceruloplasmin, resulting in accumulation and toxicity in the liver, brain, and other tissues, a condition that closely resembles Wilson’s disease in severe cases (Schilsky, 2009; Bull et al., 1993).

Most studies suggest that the toxicity of CuNPs is primarily associated with their accumulation near cells, dissolution, and subsequent attachment to the cell membrane through electrostatic interactions. The binding of these nanoparticles to the membrane, along with the release of copper ions, disrupts membrane integrity and promotes the penetration of CuNPs and ions into the cell. Once inside, the released copper ions can elevate ROS production, induce protein oxidation, decrease ATP synthesis, and cause DNA damage (Naz et al., 2020).

3.5 Toxicity

The cytotoxicity of CuNPs is strongly governed by both the administered dose and the duration of biological exposure. Acutely elevated local concentrations have been shown to trigger harmful intracellular cascades, including excessive ROS generation, progressive membrane destabilization, and dose-dependent cytotoxicity (Lan et al., 2013; Naz et al., 2020).

By contrast, prolonged exposure to low subtherapeutic doses has been linked to gradual tissue accumulation, predominantly within highly vascularized organs possessing fenestrated endothelial linings, particularly the liver and spleen, ultimately leading to persistent disruption of intracellular redox balance (Moghimi et al., 2001).

The resulting toxic outcomes are further substantially shaped by the route of administration through which the nanoparticles are delivered. Topically applied formulations typically produce localized exposures with inherently limited percutaneous absorption and correspondingly reduced systemic bioavailability (Hadiwinata et al., 2026).

In contrast, intravenously administered colloidal CuNP preparations are rapidly recognized and phagocytically cleared by mononuclear phagocytes of the reticuloendothelial system, leading to pronounced accumulation in hepatic and splenic tissues and necessitating rigorous long-term evaluation of the associated chronic systemic toxicological consequences.

For instance, He et al. investigated the molecular mechanisms underlying copper oxide nanoparticle (CuONP) cytotoxicity in human umbilical vein endothelial cells (HUVECs), demonstrating that CuONP-induced oxidative DNA damage and cell death are mediated by a copper-ion-driven p38 mitogen-activated protein kinase (MAPK) signaling cascade. CuONPs, characterized as subglobose particles with an average size of less than 50 nm, were endocytosed by HUVECs and predominantly deposited within lysosomes, as confirmed by transmission electron microscopy and FACS analysis, with treated cells exhibiting a statistically significant increase in scatter intensity relative to untreated controls.

Exposure to 20 μg/mL CuONPs for 24 h reduced HUVEC viability in a dose-dependent manner, with concentrations of 10, 20, and 40 μg/mL inducing progressively greater cytotoxicity, while Calcein AM assay confirmed that CuONP exposure caused more than 50% cell death. CuONP-induced DNA damage was evidenced by γH2AX foci formation and markedly elevated phosphorylation levels of ATR, ATM, p53, and H2AX via an ATM/ATR-p53-dependent pathway.

Oxidative stress was confirmed by significantly elevated intracellular superoxide anion levels, dose-dependent upregulation of the antioxidant enzymes HO-1 and GCLM, increased malondialdehyde (MDA) accumulation, and a reduced GSH/GSSG ratio, all of which were ameliorated by pretreatment with the antioxidant N-acetyl-L-cysteine (NAC).

Critically, CuONPs robustly activated the p38 MAPK signaling pathway with consequent phosphorylation of downstream effectors HSP27 and ATF-2, while siRNA-mediated knockdown of p38α significantly rescued HUVECs from CuONP-induced DNA damage and cell death in a dose-dependent manner. Furthermore, the divalent copper ion chelator tetrathiomolybdate (TTM) at concentrations of 0.03 and 0.1 mM substantially attenuated CuONP-induced superoxide anion accumulation, lipid peroxidation, p38 MAPK pathway activation, and γH2AX foci formation, collectively identifying the copper ion–superoxide anion–p38 MAPK–DNA damage axis as the principal mechanistic pathway governing CuONP-induced vascular endothelial cytotoxicity (He et al., 2020).

4 CuNPs in anticancer therapy

The anticancer mechanisms of CuNPs are illustrated in Figure 2. Following tumor targeting and cellular uptake, intracellular release of Cu²⁺ ions drives the generation of reactive oxygen species (ROS), culminating in oxidative DNA damage, activation of apoptotic pathways, and induction of cuproptosis, a copper-dependent cell death mechanism distinct from classical apoptosis. The convergence of these cytotoxic processes ultimately results in inhibition of tumor growth and enhanced overall therapeutic efficacy.

4.1 Anticancer therapy

Direct cytotoxicity against cancer cells via oxidative stress is one of the most well-characterized anticancer mechanisms of CuNPs, driven by their capacity to generate intracellular reactive oxygen species (ROS) that overwhelm tumor cell defenses. Upon internalization, CuNPs release Cu²⁺ ions that trigger oxidative stress and induce programmed cell death in cancer cells through pathways including apoptosis, ferroptosis, and pyroptosis (Aishajiang et al., 2023).

Cancer cells are particularly susceptible to copper-mediated oxidative damage because of their already elevated basal ROS levels and reduced antioxidant capacity compared to normal cells, a vulnerability that CuNPs selectively exploit. Notably, copper ions released by nanoparticles can selectively attack cancer cells while sparing healthy cells, a selectivity attributed in part to the enhanced permeability and retention (EPR) effect, which enables nanoparticles to preferentially accumulate in tumor tissue by exploiting the leaky, poorly organized vasculature characteristic of solid tumors (Wu, 2021).

Copper-mediated oxidative damage also causes DNA strand breaks, cell cycle arrest, and caspase activation, collectively amplifying cancer cell death across a broad range of tumor types, including colon, breast, liver, and lung cancer (He et al., 2020). This intrinsic cytotoxic selectivity makes CuNPs a compelling platform for anticancer therapy with fewer off-target effects than conventional chemotherapeutic agents.

Cuproptosis, Copper-Induced Cancer Cell Death, represents a newly defined and mechanistically distinct form of regulated cell death that has profoundly shifted understanding of how copper overload kills cancer cells. In a study, Tsvetkov et al. (Tsvetkov et al., 2022) demonstrated that excess copper directly binds to lipoylated proteins of the tricarboxylic acid (TCA) cycle, causing their aberrant aggregation and the loss of iron-sulfur (Fe-S) cluster proteins, ultimately inducing proteotoxic stress and cell death, a process that is distinct from apoptosis, ferroptosis, and necroptosis. The enzyme ferredoxin-1 (FDX1) was identified as a central upstream regulator: it reduces Cu²⁺ to the more toxic Cu⁺ form, which then drives lipoylation of dihydrolipoamide S-acetyltransferase (DLAT), and deletion of FDX1 or lipoyl synthase (LIAS) conferred significant resistance to copper-induced cell death, confirming the specificity of the pathway (Tsvetkov et al., 2022).

Building on this (Springer et al., 2024; Tang et al., 2024), noted that copper ionophores such as elesclomol and disulfiram, capable of dramatically elevating intracellular copper levels, trigger oxidative stress, disrupt mitochondrial respiration, and impair protein lipoylation, collectively offering potent implications for targeted cancer therapy. The unique dependence of cuproptosis on mitochondrial metabolism means that cancer cells relying heavily on oxidative phosphorylation are especially vulnerable, opening a selective therapeutic window that copper-based nanomaterials are well positioned to exploit (Springer et al., 2024; Tang et al., 2024; Tarin et al., 2023).

4.2 Dual anticancer therapy and drug delivery

CuNPs have remarkable physicochemical properties, especially a large surface area, which can be conjugated with different biomolecules, making them attractive candidates for anticancer therapy and drug delivery. Kang et al. illustrated this potential by developing copper diethyldithiocarbamate nanoparticles (Cu(DDC)₂ NPs) to circumvent therapeutic resistance in prostate cancer. Tumor xenograft models in male athymic nude mice exhibited dual capabilities of these nanoparticles in preclinical studies, inhibiting cancer metastasis and overcoming drug resistance. The mechanism proposed to achieve this was a selective evasion of P-glycoprotein (P-gp)-mediated drug efflux, a membrane transport system that usually results in the expulsion of chemotherapeutic agents from tumors and renders them ineffective. Importantly, this selective action did not affect the physiological function of P-gp transporters in healthy tissues, where they are indispensable in eliminating harmful toxins, demonstrating the favorable safety profile of this nanoparticle-based therapeutic approach (Kang et al., 2023). Chen et al. reported that disulfiram copper nanoparticles (Cu(DDC)₂ NPs) prepared using the novel Stabilized Metal Ion Ligand Complex (SMILE) method demonstrated remarkable anticancer activity against drug-resistant prostate cancer and other cancer cell lines. The SMILE method achieved near 100% drug-loading efficiency with a drug concentration of 2 mg/mL, representing a greater than 200-fold increase compared to traditional micelle formulations, which yielded concentrations below 10 μg/mL with loading efficiencies under 2%.

The optimized PEG-PLA-stabilized NPs had a particle size in the sub-100 nm range (40–80 nm) and exhibited outstanding serum stability for at least 72 h and room-temperature storage stability for over 30 days. In cytotoxicity assays against paclitaxel-resistant DU145-TXR prostate cancer cells (IC₅₀ of paclitaxel: 2,575 nM), Cu(DDC)₂ NPs formulated with PEG-PLA, TPGS, and DSPE-PEG demonstrated potent anticancer activity with IC₅₀ values of 85, 172, and 193 nM at 48 h, respectively. Similarly, against MDA-MB-231 triple-negative breast cancer cells, IC₅₀ values of 104 and 123 nM were recorded for PEG-PLA and TPGS formulations, respectively. Colony formation in DU145-TXR cells was nearly completely inhibited at a Cu(DDC)₂ NP concentration of 0.2 μM. Mechanistically, the authors demonstrated that cell death occurred primarily through paraptosis rather than apoptosis, evidenced by extensive cytoplasmic vacuolation originating from the endoplasmic reticulum, lack of significant caspase 3/7 activation, and inhibition of vacuolation by the paraptosis inhibitor cycloheximide but not by the autophagy inhibitor chloroquine.

Akash et al. reported the hydrothermal synthesis of β-cyclodextrin citrate-coated copper nanoparticles (Cu@β-CD-citrate NPs) as a nanocarrier for 5-fluorouracil (5-FU), and evaluated against triple-negative breast cancer (MDA-MB-231) cells. The near-spherical nanoparticles (10 ± 3 nm by TEM, 18 nm by DLS) exhibited soft ferromagnetic behavior and broad NIR absorption. 5-FU encapsulation efficiency reached 94.28%, with sustained, pH-responsive release (∼50% at 221 h, pH 7.4). In vitro cytotoxicity gave IC50 values of 200.0 and 55.3 μg mL-1 for empty and drug-loaded nanocarriers, respectively, with the drug-loaded system inducing early apoptosis in 68.35% of MDA-MB-231 cells and non-specific cell cycle arrest across multiple phases (Akash et al., 2024).

Ahmed et al. reported the development of soy lecithin liposome-encapsulated copper nanoparticles (Cu/SLP) as a nanocarrier for breast cancer treatment, and evaluated their effects on MCF-7 cells. Encapsulation increased particle size from 34.88 nm (free CuNPs) to 81.59 nm and improved colloidal stability (zeta potential: −50.7 mV), with a drug-loading efficiency of 78.9% and near-complete sustained copper release predicted at 21 h. The liposomal formulation showed enhanced cytotoxicity against MCF-7 cells (IC₅₀: 0.91 μg/mL) compared to free CuNPs (IC₅₀: 2.05 μg/mL), while remaining less toxic to normal Vero cells, highlighting Cu/SLP as a promising nanotherapeutic platform for breast cancer (Ahmed et al., 2023).

4.3 Combinatorial cancer therapy

Integrating chemotherapy with photothermal, photodynamic, or cuproptosis-inducing modalities represents the most advanced frontier of CuNP-based cancer treatment, offering synergistic efficacy that far exceeds any single modality alone. Ling et al. (2024) reported that polydopamine-modified copper-coordinated mesoporous silica nanoparticles loaded with the anticancer drug disulfiram (DSF) achieved pH-responsive release of the cytotoxic CuET [bis(diethyldithiocarbamate)-copper(II), the active cytotoxic complex formed when disulfiram chelates copper] complex (in the tumor microenvironment, and when combined with 808 nm NIR laser irradiation, effectively inhibited tumor growth in HCT116 colorectal cancer cells, demonstrating that combined chemo-photothermal therapy achieves synergistic anticancer effects superior to either approach alone.

Sharda et al. (2025) reported the synthesis of lactoferrin-coated copper nanoparticles (Cu-LFNPs) as a novel therapeutic strategy against malignant melanoma. The nanoparticles were spherical, with an average TEM size of 8 ± 2 nm and a hydrodynamic diameter of 85 nm, and elemental analysis confirmed a copper content of 38.2%. The Cu-LFNPs demonstrated excellent drug-loading capability with an encapsulation efficiency of 86.14% ± 3.45% and a sustained release profile, achieving 86.99% ± 1.77% drug release over 36 h. In vitro cytotoxicity studies against A375 melanoma cells revealed a dose-dependent reduction in cell viability, with Cu-LFNPs decreasing viability to 78.92% ± 2.43%, 76.43% ± 0.98%, 51.99% ± 1.03%, 47.37% ± 0.42%, and 23.24% ± 1.84% at concentrations of 1, 5, 10, 20, and 40 μg/mL, respectively, demonstrating substantially greater anticancer activity than free copper sulfate, lactoferrin alone, or their physical mixture.

Scratch migration assays also confirmed the pronounced blocking of melanoma cell migration for Cu-LFNPs after 48 h, with 64.78% ± 8.01% of scratch width remaining (vs. 44.98% ± 0.70% for copper sulfate-treated cells and 33.41% ± 4.45% for untreated controls). The CI values from combination index analysis ranged from 0.000526 to 0.006884, indicating a strong synergistic interaction between copper and lactoferrin. The authors concluded that Cu-LFNPs exhibit enhanced stability, controlled drug release, potent anti-melanoma activity, and antibacterial effects, making them a promising multifunctional nanoplatform for future cancer therapy (Sharda et al., 2025).

5 CuNPs in controlled and targeted drug and gene delivery systems

The versatility of CuNPs as a drug delivery platform is summarized in Figure 3. Core physicochemical properties and surface functionalization strategies enable their integration into a broad range of nanocarrier architectures, including liposomes, polymeric nanoparticles, micelles, and metal-organic frameworks (MOFs). Tumor-selective delivery is achieved through passive accumulation via the EPR effect and active targeting ligands, while stimuli-responsive release mechanisms, triggered by the acidic or redox microenvironment of tumor tissue, afford precise spatiotemporal control over drug release. Nanocarriers for controlled and targeted drug release represent one of the most therapeutically promising roles of CuNPs, owing to their versatile physicochemical properties, high surface-area-to-volume ratio, and intrinsic biological activity (Abdelkareem et al., 2025). CuNPs and copper-based nanomaterials serve as multifunctional vehicles capable of encapsulating or surface-loading chemotherapeutic agents and delivering them with spatial and temporal precision to tumor sites.

Among the nanomaterial platforms employed in copper-based nanomedicines, polymer nanoparticles (PNPs), liposomes, polymer micelles, and metal-organic frameworks (MOFs) are widely preferred for their versatility, biocompatibility, controlled release profiles, biodegradability, and adjustable size, shape, and surface charge (Beach et al., 2024). The enhanced permeability and retention (EPR) effect plays a key role in passive tumor accumulation, with nanoparticles exploiting the leaky vasculature and impaired lymphatic drainage of solid tumors to concentrate at the tumor site, reducing systemic toxicity while improving local drug concentration (Wu, 2021). Table 1 summarizes representative CuNPs for anticancer therapy and drug or gene delivery.

TABLE 1. Representative CuNP-based systems for anticancer therapy and drug or gene delivery.

Passeri et al. (2023) demonstrated that encapsulation of a cytotoxic copper(II) complex within PEG-PLGA polymeric nanoparticles yielded controlled payload release and potent anticancer stem cell activity, highlighting the capacity of copper-loaded polymeric nanocarriers to simultaneously deliver therapeutic copper species and conventional chemotherapeutic agents in a stable, biocompatible format.

Maor et al. (2021) further demonstrated that PLGA nanospheres encapsulating CuO nanoparticles exhibit dual antitumor activity and laser-responsive controlled drug release, with polydopamine coating enabling simultaneous photothermal functionality, illustrating the evolving sophistication of CuNP-based nanocarrier design.

pH-Responsive and Stimulus-Triggered Release Platforms are among the most actively developed CuNP delivery architectures, designed to exploit the distinctive biochemical characteristics of the tumor microenvironment (TME) to achieve precise, on-demand therapeutic release. The TME is characterized by several unique properties, including acidity, elevated glutathione (GSH) levels, hypoxia, overexpressed enzymes, and excessive ROS, which can be harnessed by smart drug delivery systems to release drugs specifically within tumor tissue while remaining inert in healthy tissue (Zhou et al., 2022).

Copper-based nanoplatforms are particularly well suited to pH-responsive delivery because CuNPs and their oxides readily undergo accelerated dissolution under the mildly acidic conditions (pH 5.0–6.5) typical of endosomes, lysosomes, and the extracellular tumor environment, triggering controlled Cu²⁺ ion and drug release precisely where needed (Ling et al., 2024). As Thomas et al. (2020) summarized, stimuli-responsive nanoparticles can maintain stability under normal physiological conditions (pH 7.4) while responding rapidly to internal tumor stimuli, including pH, GSH, ROS, enzyme activity, and hypoxia to prolong blood circulation and enhance cancer cellular uptake, achieving superior therapeutic performance with improved biosafety compared to conventional drug formulations.

Multistimuli-responsive platforms incorporating dual pH/redox triggers have demonstrated especially high drug release fidelity; for example, Badparvar et al. (2023) showed that dual pH/redox-responsive size-switchable nanovehicles loaded with doxorubicin achieved nearly 100% cellular internalization within 30 min in tumor cells and induced significantly higher rates of apoptosis compared to free drug, a framework equally applicable to copper-based delivery systems operating through the same TME-responsive principles.

Surface functionalization for cell-specific targeting and co-delivery of multiple therapeutic agents represents the most advanced dimension of CuNP-based delivery systems, enabling them to discriminate between cancerous and healthy cells and deliver complex combinatorial payloads within a single nanoplatform.

Surface modification of CuNPs with targeting ligands, such as folic acid, antibodies, aptamers, and peptides, enables receptor-mediated endocytosis in cancer cells that overexpress the cognate receptor, thereby significantly enhancing tumor accumulation, drug utilization, and therapeutic efficacy while reducing off-target toxicity (Yan et al., 2024).

Moreover, Laha et al. (2015) confirmed that folate-conjugated CuONPs enhanced selective uptake in folate receptor-overexpressing cervical cancer cells, while also improving nanoparticle stability, biocompatibility, and loading capacity, illustrating how surface functionalization simultaneously addresses targeting, stability, and safety in a single engineered construct. CuNPs are also well suited to co-delivery of multiple therapeutic agents within a unified nanoplatform (Mariadoss et al., 2020).

Ling et al. (2024) demonstrated that copper-coordinated mesoporous silica nanoparticles co-loaded with disulfiram achieved synergistic chemo-photothermal tumor killing through pH-responsive CuET formation and NIR-triggered heat generation, outperforming either modality alone.

At the systems level, Gao et al. (2024) described that co-delivering drugs, siRNA, and copper ions from a single nanocarrier enables simultaneous targeting of multiple tumor survival pathways, including GSH depletion, ROS amplification, ferroptosis, and apoptosis, yielding synergistic anticancer effects that are deeply resistant to compensatory resistance mechanisms. This capacity to serve as a multimodal therapeutic platform that simultaneously delivers chemotherapeutics, nucleic acids, photosensitizers, and copper ions, while bearing cell-specific targeting ligands, positions CuNPs as one of the most versatile and compelling architectures in contemporary nanomedicine.

Nanomedicine research by Kang et al. (2023) demonstrated that diethyldithiocarbamate copper nanoparticles [Cu(DDC)₂ NPs] effectively overcame paclitaxel resistance in prostate and non-small-cell lung cancer models by bypassing P-glycoprotein (P-gp)-mediated drug efflux. The nanoparticles were prepared using the stabilized metal-ion ligand complex (SMILE) method and exhibited a spherical morphology, with an average particle size of approximately 46.6 nm and a production yield exceeding 90%.

In vitro studies showed that Cu(DDC)₂ NPs maintained potent anticancer activity in both drug-sensitive and drug-resistant cell lines, including DU145-TXR, PC3-TXR, and A549-TXR cells, whereas paclitaxel displayed markedly higher resistance indices of 222, 80, and 118, respectively. The nanoparticles significantly reduced colony formation, disrupted tumor spheroids, and induced predominantly non-apoptotic cell death through paraptosis-like mechanisms rather than caspase-dependent apoptosis (Kang et al., 2023).

In vivo xenograft studies further confirmed their therapeutic efficacy, with intravenous administration of Cu(DDC)₂ NPs (3 mg/kg) significantly reducing tumor volume and weight in DU145-TXR-bearing mice without causing notable body weight loss or systemic toxicity. Mechanistic investigations revealed that Cu(DDC)₂ NPs neither inhibited P-gp activity nor altered P-gp expression, but instead escaped transporter-mediated efflux because Cu(DDC)₂ itself was not a P-gp substrate. Additionally, treatment with Cu(DDC)₂ NPs reversed epithelial–mesenchymal transition (EMT) biomarkers by increasing E-cadherin expression while decreasing Vimentin and N-cadherin levels, suggesting further potential to suppress metastasis and multidrug resistance in cancer therapy (Kang et al., 2023).

Moreover, Gene Delivery and Silencing via CuNP-based platforms represents a rapidly growing application in which the physicochemical properties of CuNPs, particularly their positive surface charge, nucleic acid-binding capacity, and ability to facilitate endosomal escape are harnessed to deliver therapeutic genetic cargo, including small interfering RNA (siRNA) and plasmid DNA (pDNA) into target cells (Zhou et al., 2022).

Jagaran and Singh (2023) demonstrated that CuO nanoparticles biologically synthesized using plant extract, functionalized with chitosan and polyethylene glycol (PEG), and conjugated to folate as a targeting ligand successfully bound and protected a reporter plasmid (pCMV-Luc-DNA), enabling efficient and targeted gene delivery to folate receptor-overexpressing cervical cancer cells, representing a landmark demonstration of CuNPs as viable inorganic non-viral gene delivery vectors. The cationic surface charge of chitosan-functionalized CuNPs facilitates electrostatic complexation with negatively charged nucleic acids, forming compact nanoparticle-nucleic acid complexes (nanoplexes) that protect genetic cargo from enzymatic degradation during systemic transit (Jagaran and Singh, 2023).

Beyond plasmid delivery, copper-based bimetallic drug-gene co-delivery systems such as Cu/ZIF-8@U-104@siNFS1-HA nanoplatforms have been shown to utilize Cu²⁺/Cu⁺ redox cycling to inhibit the GSH/GPX4 axis while simultaneously delivering siRNA targeting resistance pathways, activating immunogenic ferroptosis, and amplifying antitumor immunity (Wei et al., 2026). This convergence of gene silencing with copper-mediated oxidative cell death mechanisms underscores the distinctive therapeutic potential of CuNPs as dual-function gene and cytotoxic delivery vehicles. Table 1 depicts CuNP-based systems for anticancer therapy and drug or gene delivery.

Photothermal Therapy (PTT) and Photodynamic Therapy (PDT). The notable photothermal responses of CuNPs have been investigated for both preclinical and clinical photothermal applications (Wang et al., 2023; Tao et al., 2019). PTT and PDT represent two rapidly advancing light-activated modalities in which CuNPs play a central enabling role. Due to the localized surface plasmon resonance (LSPR) feature of copper, CuNPs exhibit strong near-infrared (NIR) absorption and excellent photothermal conversion properties, enabling them to transform light energy into heat that induces apoptosis or necrosis of tumor cells at elevated temperatures (Zhuo et al., 2023).

In PTT, CuS nanoparticles in particular have emerged as highly efficient photothermal agents, with studies confirming that their penetrating NIR-mediated heat generation can precisely target tumor sites while minimizing damage to surrounding healthy tissue (Gao et al., 2024). In PDT, Cu-based nanomaterials generate cytotoxic ROS particularly singlet oxygen (¹O₂) and superoxide radicals under light irradiation, inducing oxidative damage that destroys tumor cells. As Zhuo et al. (2023) further described, in the tumor microenvironment, Cu²⁺ combines with H₂O₂ to generate oxygen, which is subsequently reduced to Cu⁺ by glutathione via a Fenton-like reaction, simultaneously reducing tumor hypoxia and amplifying ROS production a self-reinforcing mechanism that enhances the efficacy of both PTT and PDT. This capacity to exploit the biochemical characteristics of the tumor microenvironment makes CuNPs particularly powerful as light-responsive anticancer agents (Goel et al., 2014; Wang et al., 2015; Laxmanan et al., 2025).

6 Critical analysis

CuNPs are a scientifically compelling and mechanistically rich class of nanomaterials with genuine therapeutic potential, particularly in oncology, where the convergence of ROS-mediated cytotoxicity, cuproptosis, photothermal activity, and targeted drug delivery offers a multi-pathway approach that is fundamentally resistant to single-mechanism drug resistance. Despite this promise, a rigorous appraisal of the current literature reveals several substantive and interrelated limitations that collectively constrain clinical translation.

The field is at an early preclinical stage, and the gap between published in vitro data and clinical readiness is substantial. The same redox activity that underlies the anticancer potency of CuNPs is also responsible for their principal safety liability. Uncontrolled Cu²⁺ release in non-target tissues generates oxidative stress, membrane damage, mitochondrial dysfunction, and genotoxicity in healthy cells by the same mechanisms operative in tumor cells.

The overwhelming majority of studies cited in this review are in vitro, with a much smaller subset reporting in vivo xenograft data, and essentially no clinical trial data for CuNP-based therapeutics as injectable medicines. The most urgent needs are rigorous in vivo pharmacokinetic and toxicology studies, standardized characterization protocols, well-powered animal efficacy studies in immunocompetent models, and the development of biomarkers to identify patient populations most likely to respond to cuproptosis-based therapies. Investment in these foundational studies, rather than further expansion of in vitro screening, will determine whether CuNPs fulfill their considerable promise as next-generation cancer nanomedicines. It is instructive to benchmark CuNPs against clinically approved or more advanced nanomedicine platforms. Liposomal formulations such as Doxil and AmBisome have achieved clinical approval because they address a clear pharmacokinetic problem without introducing new toxicological unknowns.

Another major obstacle to synthesizing the CuNP literature is the profound heterogeneity of experimental systems. Studies differ in CuNP composition (Cu⁰, CuO, Cu₂O, CuS, copper complexes), size, shape, surface coating, synthesis method, cell line, animal model, dose metric, and endpoint measured. This makes quantitative cross-study comparison almost impossible and hinders the identification of generalizable structure-activity relationships.

For CuNPs specifically, several regulatory challenges deserve acknowledgment. The absence of harmonized guidelines for characterizing copper-based nanomedicines means that different regulatory agencies may apply different standards, complicating multinational development. Batch-to-batch reproducibility of CuNP synthesis is difficult to control and validate at scale, and physicochemical properties such as size distribution, surface chemistry, and phase composition can shift significantly between batches, potentially altering pharmacokinetics and safety profiles.

Direct comparison of the potency data reported across these studies underscores how strongly formulation strategy, rather than the copper core alone, determines therapeutic outcome. Kang et al.’s SMILE-formulated Cu(DDC)₂ nanoparticles (Kang et al., 2023) achieved sub-200 nM IC₅₀ values (85–193 nM across PEG-PLA, TPGS, and DSPE-PEG variants) against paclitaxel-resistant DU145-TXR cells, a potency roughly three to four orders of magnitude below the micromolar-range activity typical of first-generation copper nanoformulations such as Akash et al.’s Cu@β-CD-citrate/5-FU carrier (Akash et al., 2024) (IC₅₀ 55.3 μg/mL, equivalent to a much higher molar concentration) tested against MDA-MB-231 cells. Even accounting for differences in cell line and copper species, this gap is too large to attribute to assay variability alone and instead reflects the fact that Cu(DDC)₂ delivers a highly potent preformed cytotoxic copper complex directly, whereas 5-FU-loaded and liposomal systems rely on slower, diffusion- or pH-limited release of a comparatively less potent payload. Ahmed et al.’s Cu/SLP liposomal system (Ahmed et al., 2023) illustrates this release-dependent effect within a single study: encapsulation alone improved potency roughly two-fold over free CuNPs in MCF-7 cells (IC₅₀ 0.91 versus 2.05 μg/mL), a modest gain compared with the orders-of-magnitude improvement Kang et al. achieved through drug-loading engineering rather than encapsulation per se, indicating that the choice of carrier chemistry, and not merely the act of nanoformulation, is the dominant variable governing potency.

These potency differences map onto genuinely distinct cell-death mechanisms rather than a single shared copper-toxicity pathway, a mechanistic heterogeneity that is easily obscured when studies are summarized only by IC₅₀ values. Kang et al. (Kang et al., 2023) showed that Cu(DDC)₂ nanoparticles kill resistant prostate cancer cells predominantly through paraptosis, characterized by endoplasmic reticulum-derived cytoplasmic vacuolation and an absence of caspase 3/7 activation, and act by evading P-glycoprotein-mediated efflux rather than inhibiting it outright. This is mechanistically distinct from the canonical ROS-driven apoptotic route described for CuO nanoparticles by He et al. (2020), in which copper-ion-triggered p38 MAPK signaling drives DNA damage and caspase-dependent death, and is distinct again from cuproptosis as defined by Tsvetkov et al. (2022), in which excess Cu⁺ drives aggregation of lipoylated TCA-cycle proteins independent of caspase activation or classical oxidative DNA damage. Akash et al.’s 5-FU-loaded system (Akash et al., 2024), by contrast, induced early apoptosis in 68.35% of MDA-MB-231 cells alongside non-specific cell-cycle arrest, a more conventional apoptotic signature. The practical implication is that reported potency cannot be extrapolated across platforms: a Cu(DDC)₂ formulation optimized for paraptosis induction in efflux-competent resistant tumors would not be expected to reproduce equivalent efficacy against a tumor type whose resistance operates through anti-apoptotic rather than efflux-based mechanisms, and vice versa for cuproptosis-dependent designs targeting oxidative-phosphorylation-reliant cancers. Structure-activity comparisons across the CuNP literature therefore need to specify not just potency but which death pathway is engaged, since two formulations with similar IC₅₀ values may be therapeutically interchangeable in one tumor context and clinically inert in another.

The translational significance of these cross-study contrasts is that potency alone is a poor predictor of clinical viability; manufacturability and mechanistic specificity matter at least as much. The SMILE method’s near-100% drug-loading efficiency at 2 mg/mL, a greater than 200-fold improvement over the sub-2% loading and sub-10 μg/mL concentrations achievable with conventional micelle formulations, addresses a scale-up bottleneck that has historically stalled nanomedicine translation independent of any gain in cytotoxic potency, and is arguably the more clinically consequential result of that study. Kang et al.’s confirmation (Kang et al., 2023) that Cu(DDC)₂ nanoparticles reduced tumor volume in DU145-TXR xenografts at 3 mg/kg without measurable body-weight loss or systemic toxicity represents a genuine, if still early, step from in vitro potency toward an in vivo safety signal, in contrast to the Akash, Ahmed, and Sharda systems discussed above, which remain characterized only at the cytotoxicity-assay stage. Sharda et al.’s lactoferrin-coated formulation (Sharda et al., 2025), despite its strong synergy data (combination-index values as low as 0.000526), likewise has no reported in vivo pharmacokinetic or toxicology data, illustrating the broader pattern noted earlier in this section: encouraging in vitro comparisons do not by themselves establish a path to the clinic, and the field’s near-total reliance on cytotoxicity assays and single-xenograft studies, rather than the standardized pharmacokinetic, immunocompetent-model, and biomarker-driven designs typical of approved nanomedicines, remains the central obstacle to converting these mechanistically diverse and often highly potent in vitro results into clinically actionable therapeutics.

7 Future perspectives

The future of CuNPs in drug delivery is exceptionally promising, yet the path to clinical reality demands that the field confront several persistent and interrelated challenges before the remarkable preclinical achievements of CuNP-based platforms can be translated into tangible patient benefit.

On the scientific frontier, the integration of CuNPs with emerging therapeutic paradigms, most notably cuproptosis-based immunotherapy, represents a transformative opportunity, with recent preclinical work demonstrating that copper-mediated cell death synergizes powerfully with immune checkpoint blockade by inducing immunogenic cell death, and remodeling immunosuppressive tumor microenvironments (Noh et al., 2024).

Equally compelling is the convergence of CuNP platforms with combination modalities: co-delivering copper ions alongside chemotherapeutics, photosensitizers, and nucleic acids within a single intelligently engineered nanocarrier simultaneously engages GSH depletion, ROS amplification, ferroptosis, cuproptosis, and apoptosis, a multipronged attack on tumor survival pathways that is fundamentally resistant to the compensatory mechanisms underpinning conventional drug resistance.

The development of stimuli-responsive, size-switchable, and actively targeted CuNP architectures continues to refine the spatial and temporal precision of drug release, and future designs are expected to increasingly incorporate biomimetic coatings, cell membrane camouflage, and artificial intelligence-assisted nanoparticle optimization to further sharpen tumor specificity and reduce systemic exposure.

Nevertheless, the critical bottlenecks constraining clinical translation remain formidable. As Woźniak-Budych et al. (2023) comprehensively document, biocompatibility and controlled copper ion release remain among the most pressing unsolved challenges. Excess free Cu²⁺ induces oxidative stress in healthy tissues, and achieving selective, tumor-confined copper liberation without off-target toxicity requires far more sophisticated engineering than most current platforms provide.

Beyond toxicology, concerns around manufacturing scalability, batch-to-batch reproducibility, long-term physicochemical stability, and the absence of harmonized regulatory frameworks for copper-based nanomedicines collectively represent significant translational barriers that will require sustained interdisciplinary collaboration between chemists, clinicians, engineers, and regulatory scientists.

Comprehensive in vivo pharmacokinetic profiling, rigorous genotoxicity studies, and well-powered clinical trials remain largely absent from the CuNP literature, and the field must invest heavily in this infrastructure if copper nanomedicine is to follow the clinical precedent set by liposomal and polymeric platforms. Here, the future of CuNPs in drug delivery is one of extraordinary potential constrained by equally extraordinary complexity, and it is precisely this tension that defines the most important research agenda for the decade ahead.

8 Conclusion

This review has integrated the chemistry, biological fate, and therapeutic applications of CuNPs within a single framework, and several principal findings emerge. The evidence reviewed here demonstrates that CuNPs can exploit the distinctive biochemistry of the tumor microenvironment, its acidity, elevated GSH, ROS, and enzymatic activity to achieve spatially and temporally precise therapeutic release, while their capacity for surface functionalization with targeting ligands such as folic acid, aptamers, antibodies, and peptides enables receptor-mediated, cancer cell-selective delivery that substantially reduces off-target toxicity.

The discovery of cuproptosis as a mechanistically distinct, mitochondria-dependent form of copper-induced cell death has fundamentally expanded the therapeutic logic of CuNP-based platforms, revealing a selective vulnerability in cancer cells that is orthogonal to the pathways targeted by conventional chemotherapy and therefore deeply resistant to established resistance mechanisms.

When combined with photothermal therapy, photodynamic therapy, ferroptosis induction, or immune checkpoint blockade and further empowered by co-delivery of siRNA, chemotherapeutics, and photosensitizers from a single nanocarrier, CuNPs achieve synergistic, multi-pathway tumor suppression whose therapeutic ceiling has not yet been defined.

Nevertheless, the field remains at a critical inflection point: the same redox reactivity that underpins the biological potency of CuNPs also generates the principal safety concern, as uncontrolled Cu²⁺ release induces oxidative stress and organ toxicity in non-target tissues, and rigorous, systematic solutions to this challenge through advanced surface engineering, biocompatible coatings, and tumor-selective stimuli-responsive architectures remain incompletely realized.

Challenges of manufacturing scalability, physicochemical stability, regulatory harmonization, and the near-complete absence of clinical trial data further constrain the translation of CuNP-based nanomedicines from bench to bedside. Moving forward, the most productive trajectory for the field will require converging materials science innovation with rigorous in vivo pharmacology, toxicology, and translational medicine, integrating biomimetic design, artificial intelligence-assisted nanoparticle optimization, and interdisciplinary collaboration to responsibly advance copper nanomedicine toward the clinical impact its compelling preclinical promise suggests.

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Glossary

ADMET Absorption, Distribution, Metabolism, Elimination, and Toxicity ATP Adenosine Triphosphate ATP7B Copper-Transporting P-Type ATPase (Wilson Disease Protein) CuNP Copper Nanoparticle CuO Copper(II) Oxide Cu _**2** O Copper(I) Oxide Cu ^**0** Metallic Copper Cu ^**+** Cuprous Ion Cu ^**2+** Cupric Ion DLAT Dihydrolipoamide S-Acetyltransferase DSF Disulfiram EGFR Epidermal Growth Factor Receptor EMT Epithelial-Mesenchymal Transition EPR Enhanced Permeability and Retention FDX1 Ferredoxin-1 Fe-S Iron-Sulfur Cluster GSH Glutathione GSSG Oxidized Glutathione HUVEC Human Umbilical Vein Endothelial Cell LD _**50** Lethal Dose 50% LSPR Localized Surface Plasmon Resonance MOF Metal-Organic Framework MPS Mononuclear Phagocyte System NAC N-Acetyl-L-Cysteine NIR Near-Infrared NP Nanoparticle PDT Photodynamic Therapy PEG Polyethylene Glycol P-gp P-Glycoprotein PLGA Poly(Lactic-co-Glycolic Acid) PTT Photothermal Therapy PVP Polyvinylpyrrolidone ROS Reactive Oxygen Species siRNA Small Interfering RNA pDNA Plasmid DNA SOD Superoxide Dismutase TCA Tricarboxylic Acid Cycle TME Tumor Microenvironment TNBC Triple-Negative Breast Cancer TYR Tyrosinase

Footnotes

Edited by: Kamil Reza Khondakar, The University of Queensland, Australia

Reviewed by: Behrooz Maleki, University of Mazandaran, Iran

Ali Hheidari, Islamic Azad University System, Iran