Zinc Peroxide-Coated Gold Nanorods Turn Tumors From Cold to Hot by Fusing Photothermal Heat, Chemodynamic Radical Attack, and Metal Ion Immune Signaling

A single nanoparticle that heats tumors, manufactures its own chemical weapon, and then hands the immune system the keys to finish the job has been unveiled by researchers writing in the Journal of Advanced Research. The team, led by Dong-Yang Zhang and Yue Zheng, constructed what they call AZP: a gold nanorod core wrapped in a shell of zinc peroxide and coated with polyethylene glycol. In mouse models of breast cancer, the platform eliminated primary tumors outright when activated by near-infrared light, and when paired with an anti-PD-1 checkpoint antibody it nearly abolished lung metastases. The design is notable less for any single component than for the way it choreographs three therapeutic modes—photothermal therapy, chemodynamic therapy, and zinc-mediated immunostimulation—within one acid-responsive particle.

The architecture begins with gold nanorods synthesized by a seed-mediated growth process, measuring roughly 7.5 by 48 nanometers. A hydrothermal step coats each rod with zinc oxide, and a subsequent anion exchange in hydrogen peroxide converts that shell to zinc peroxide, a compound far richer in peroxide ions. Transmission electron microscopy confirmed the core-shell geometry, with a zinc-and-oxygen shell about 32 nanometers thick around the gold core. X-ray photoelectron spectroscopy pinned the oxidation states, showing the oxygen 1s binding energy shift from 530.9 electron volts in zinc oxide to 531.9 electron volts in the peroxide shell, a fingerprint of the added peroxide chemistry. Inductively coupled plasma mass spectrometry measured a zinc-to-gold mass ratio of 25 to 13 in the final construct. A DSPE-PEG coating then rendered the particles water-dispersible and biocompatible, yielding hydrodynamic diameters near 209 nanometers and a mildly negative surface charge.

The shell’s most consequential property is its acidity sensitivity. At physiological pH 7.4 the particles remained stable, but at pH 6.5 they partially degraded and at pH 5.0 they nearly completely dissolved. Because solid tumors run more acidic than healthy tissue, this pH gradient acts as a trigger: after six hours in acidic buffer, roughly 80 percent of the zinc was released at pH 6.5 and essentially all of it at pH 5.0, while less than 5 percent escaped at neutral pH. The degradation also liberates hydrogen peroxide, the fuel that conventional chemodynamic therapy agents chronically lack. Quantification with a cerium sulfate assay showed about 0.56 to 0.62 millimolar hydrogen peroxide released within half an hour under acidic conditions, roughly five to six times the amount released at pH 7.4. This self-supply mechanism directly addresses the insufficient endogenous hydrogen peroxide that has long hampered Fenton-based radical therapies in tumors.

The gold core supplies the second act. Under an 808-nanometer near-infrared laser at 1 watt per square centimeter, AZP solutions at 100 micrograms per milliliter heated by 36 degrees Celsius in five minutes, against a mere 1.7-degree rise in pure water. The photothermal conversion efficiency came out at approximately 38 percent, competitive with or better than previously reported nanoplatforms, and the particles withstood four repeated heating-cooling cycles without loss of performance. Crucially, the heat does more than cook tumor cells. The gold nanorods possess intrinsic peroxidase-like activity, and that catalytic activity is temperature-dependent. When the researchers tested hydroxyl radical generation using the colorimetric indicator TMB, radical production rose sharply under acidic conditions and climbed further with elevated temperature or laser irradiation. Electron spin resonance spectroscopy with a DMPO spin trap confirmed the characteristic quartet signal of hydroxyl radicals, strongest in the irradiated group. In effect, the photothermal effect amplifies the chemodynamic effect, converting light into both heat and a surge of membrane-shredding radicals.

Inside 4T1 breast cancer cells, the consequences were severe and selective. Bio-TEM imaging showed the particles internalized within 12 hours, their peroxide shells visibly degrading in the cellular environment. Intracellular zinc concentrations climbed from a baseline of 66.8 to 204 nanograms per million cells at 50 micrograms per milliliter of AZP. Cell viability dropped in a concentration-dependent manner, and light pushed mortality dramatically higher: AZP alone killed about 40 percent of cells at 50 micrograms per milliliter, while the combined treatment killed 80 percent, with flow cytometry recording apoptosis and necrosis in 97.8 percent of irradiated cells. Strikingly, the same concentration killed only 3 percent of non-tumorigenic MCF-10A breast cells, a selectivity the authors attribute to the acidic, endocytosis-rich physiology of cancer cells. Fluorescent probes documented a cascade of intracellular damage: surging reactive oxygen species, collapse of mitochondrial membrane potential measured by JC-1 staining, and reduced basal respiration, maximal respiration, and ATP production on a Seahorse metabolic analyzer.

The lysosomes fared no better, and that proved pivotal for the immune story. Acridine orange staining, which glows red in intact lysosomes, faded markedly after AZP treatment, and a cathepsin B probe that normally appears as punctate lysosomal signal diffused throughout the cytoplasm, both hallmarks of lysosomal membrane permeabilization. Western blots showed accumulation of p62 and an elevated LC3-II to LC3-I ratio, the same signature produced by chloroquine, indicating that AZP blocks the fusion of autophagosomes with lysosomes. When cells were pre-treated with the autophagy inducer rapamycin, AZP’s cytotoxicity dropped significantly, demonstrating that autophagy blockade is a necessary condition for the cell death the platform induces. This matters because impaired autophagic flux is known to potentiate antitumor immunity, stacking another immunological card on top of the direct killing.

That immunological payoff arrived through the cGAS-STING pathway, the signaling cascade that links innate immune detection of stray DNA to adaptive antitumor responses. Cell death from photothermal and chemodynamic stress releases cytoplasmic double-stranded DNA, and zinc ions are known to enhance cGAS activity by increasing its affinity for DNA and stabilizing the enzyme-DNA complex. AZP delivered both inputs at once. Western blotting revealed a 6.6-fold increase in phosphorylated STING at 50 micrograms per milliliter, rising to 7.9-fold with irradiation, and chelation of zinc with TPEN downregulated the pathway, confirming its zinc dependence. Interferon-beta secretion climbed 3-fold with AZP and 5.1-fold with added light. The treated tumor cells also displayed the classic badges of immunogenic cell death: calreticulin translocated to the cell surface, HMGB1 drained from nuclei, and extracellular ATP rose from 9.4 to 18.2 micromolar. Dendritic cells co-cultured with the treated tumor cells phagocytosed more antigen and matured, upregulating CD86.

Macrophage reprogramming completed the microenvironmental overhaul. When immunosuppressive M2-polarized macrophages were exposed to AZP, the proportion of CD206-positive cells fell from about 49 percent to 22.5 percent, and to just 13 percent with irradiation, while CD86-positive M1 macrophages rose from roughly 13 to 26 percent, and to 34 percent with light. The anti-inflammatory cytokine IL-10 fell to 0.24-fold of control levels under combined treatment, while pro-inflammatory IL-12 rose. RNA sequencing of treated tumor cells corroborated the mechanism at the transcriptome level: 301 genes were upregulated and 146 downregulated, with enrichment in lysosome, apoptosis, p53 signaling, immune response, and mTORC1-related autophagy-inhibition pathways.

In mice bearing bilateral 4T1 breast tumors, intratumoral AZP injection followed by laser irradiation raised tumor temperature by 19 degrees Celsius versus 5.9 degrees in controls. By day 14, AZP alone had inhibited primary tumor volume by 44.4 percent, but the irradiated group achieved complete elimination of all primary tumors, with a 100 percent inhibition rate by tumor weight. Distant, untreated tumors shrank by 20 percent with AZP and 48.4 percent with added light, evidence of a systemic abscopal immune effect, though the authors note it remained moderate and that checkpoint blockade was needed for full metastatic control. Flow cytometry of spleens showed mature dendritic cells rising from 6 to 12.8 percent, M1 macrophages increasing 1.9-fold, M2 macrophages declining, and CD8-positive and CD4-positive T cells expanding 2.5-fold and 3.3-fold respectively under the combined treatment. Biosafety profiling showed stable body weights, clean organ histology, and normal liver and kidney markers.

The decisive test came in a rechallenge model simulating metastasis and recurrence. When mice received intravenous 4T1-luciferase cells after primary tumor treatment, the combination of AZP, laser irradiation, and anti-PD-1 antibody produced almost no lung metastases, far outperforming any single or double combination, and splenic CD8-positive T cell frequencies climbed to 11.2 percent. The authors are candid about limitations: the individual components are not new, the novelty lies in their spatiotemporal integration; intravenous administration, long-term biodistribution, and the quantitative disentangling of zinc, reactive oxygen, and autophagy contributions remain open questions, as do the clinical power densities and scalable manufacturing. Yet as a proof of principle, AZP demonstrates that a rationally layered nanoparticle can convert an immunologically cold tumor into a hot one without exogenous immune agonists, using nothing more exotic than gold, zinc, peroxide, light, and an existing checkpoint antibody.

Subject of Research: A pH-responsive zinc peroxide-coated gold nanorod nanoplatform integrating photothermal therapy, chemodynamic therapy, and zinc-mediated cGAS-STING immunostimulation for cancer treatment

Article Title: Zinc peroxide-coated gold nanorods as the therapeutic adjuvants for photothermal enhanced chemodynamic therapy and metalloimmunotherapy against tumor

Article References: Yi, H., Jiang, C., Pan, Z.-Y., Fu, N., Guo, L., Zhan, Z., Li, J., Zhao, X., Zhang, L., Zheng, Y., & Zhang, D.-Y. (2026). Zinc peroxide-coated gold nanorods as the therapeutic adjuvants for photothermal enhanced chemodynamic therapy and metalloimmunotherapy against tumor. Journal of Advanced Research. https://doi.org/10.1016/j.jare.2026.10.011

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.10.011

Keywords: gold nanorods, zinc peroxide, photothermal therapy, chemodynamic therapy, cGAS-STING pathway, immunogenic cell death, tumor microenvironment, autophagy blockade, metalloimmunotherapy, anti-PD-1, breast cancer, nanomedicine