Exploration | Radiolabeled Coordination Polymer Microneedles Synergistically Enhance Melanoma Immunotherapy through STING Pathway Activation and GSDME-Mediated Pyroptosis

This study presents an innovative strategy combining transdermal local radiotherapy with immunomodulation, offering a novel approach to overcome the immunosuppressive tumor microenvironment in melanoma and the low response rates of current immune checkpoint inhibitors. It provides significant insights, particularly in enhancing anti-tumor immune responses and abscopal effects.

 

Literature Overview

The article titled 'Radiolabeled Coordination Polymer-Loaded Microneedles for Synergistic Melanoma Brachytherapy–Immunotherapy via STING Activation and Pyroptosis,' published in the journal Exploration, systematically investigates the synergistic effects of local brachytherapy and immunotherapy achieved by constructing radiolabeled coordination polymer microneedles (¹⁷⁷Lu-GAMP@MN). The authors utilized ¹⁷⁷Lu³⁺ to self-assemble with adenosine monophosphate (AMP) and guanosine monophosphate (GMP), forming a nanoscale coordination polymer with a structure similar to cGAMP. This polymer acts not only as a STING pathway agonist but also induces DNA damage and pyroptosis via β-radiation from ¹⁷⁷Lu, thereby reshaping the tumor immune microenvironment. The microneedle delivery system enables transdermal, minimally invasive, and targeted drug release, significantly improving treatment safety and patient compliance. When combined with anti–PD-L1 antibodies, the system demonstrates potent local and distant anti-tumor immune memory, offering a new paradigm for comprehensive melanoma therapy.

Background Knowledge

Melanoma is a highly aggressive skin malignancy with early metastasis and high recurrence rates, resulting in poor prognosis. The five-year survival rate for advanced patients is less than 30%. Although immune checkpoint inhibitors (e.g., anti–PD-1/PD-L1) have significantly improved outcomes for some patients, the overall response rate remains below 40%, primarily limited by the immunosuppressive tumor microenvironment (TME), characterized by insufficient T-cell infiltration, impaired dendritic cell (DC) maturation, enrichment of immunosuppressive cells such as Tregs and MDSCs, and low tumor immunogenicity. Current strategies to activate the STING pathway are hindered by poor in vivo stability, low bioavailability, and inefficient cellular uptake. Free cGAMP is easily degraded by phosphodiesterases and struggles to penetrate cell membranes. Additionally, while conventional radiotherapy can induce immunogenic cell death (ICD), its application is limited by systemic toxicity. Therefore, achieving sustained, efficient, and safe immune activation within the TME remains a major research challenge. This study ingeniously leverages the self-assembly of ¹⁷⁷Lu³⁺ with nucleotide ligands to form coordination polymers with both radioactivity and STING agonist activity, while utilizing microneedles for localized delivery to precisely target melanoma lesions in the epidermis, effectively avoiding systemic exposure and off-target toxicity—offering an innovative solution to overcome the aforementioned challenges.

 

 

Research Methods and Experiments

The authors used the B16-F10 mouse melanoma model for in vivo validation, a model with strong immunogenicity widely used in immunotherapy research. First, ¹⁷⁷Lu-GAMP was synthesized via a self-assembly method, and its nanostructure and elemental homogeneity were confirmed using transmission electron microscopy (TEM), dynamic light scattering (DLS), and energy-dispersive X-ray spectroscopy (EDX). Subsequently, ¹⁷⁷Lu-GAMP was loaded into a hyaluronic acid (HA) matrix and fabricated into soluble microneedle patches (¹⁷⁷Lu-GAMP@MN) using micromolding techniques, with structural integrity and skin penetration ability verified by SEM and mechanical testing. At the cellular level, Nile Red-labeled Lu-GAMP was used to track cellular uptake and lysosomal escape, combined with qPCR and Western blot to detect STING pathway activation (p-STING, p-TBK1, IFN-β) and pyroptosis-related proteins (GSDME-N, cleaved Caspase-3). In animal models, primary and distant dual-tumor models were established by subcutaneously inoculating B16-F10 cells to evaluate the anti-tumor efficacy of monotherapy and combination therapy, including tumor volume, survival rate, immune cell infiltration (flow cytometry), and immune memory formation.

Key Conclusions and Perspectives

• ¹⁷⁷Lu-GAMP effectively activates the STING pathway in B16-F10 cells, significantly upregulating Ifnb1 expression and promoting DC maturation, indicating its potential as a potent STING agonist and providing a structural template for designing future STING-targeted nanomedicines
• ¹⁷⁷Lu induces GSDME-mediated pyroptosis, evidenced by increased GSDME-N fragments, LDH release, and plasma membrane rupture, revealing an immune-activating mechanism of radionuclides beyond direct tumor killing and suggesting pyroptosis as a key effector pathway for radiotherapy combined with immunotherapy
• ¹⁷⁷Lu-GAMP@MN significantly suppresses tumor growth and prolongs survival in mouse models, with synergistic effects observed when combined with anti–PD-L1 antibodies, markedly enhancing T-cell infiltration and function. This indicates that localized immune activation can effectively overcome TME suppression, providing preliminary evidence for clinical combination strategies
• Combination therapy induces a significant abscopal effect and immune memory, manifested by regression of distant tumors and expansion of memory T cells (TEM, TCM), suggesting the strategy has the potential to elicit systemic anti-tumor immunity, offering important guidance for treating metastatic melanoma

Research Significance and Prospects

This study provides a novel platform for drug development: integrating radiotherapy and immune stimulation into a single nanosystem, with precise delivery via microneedles greatly enhancing the therapeutic index. Its dual mechanism (STING activation + pyroptosis) effectively enhances tumor immunogenicity and overcomes the 'cold' tumor microenvironment, offering a replicable molecular design framework for next-generation melanoma immunotherapies.

In terms of clinical monitoring, the localized application of this strategy reduces systemic toxicity risks, while the γ-rays from ¹⁷⁷Lu enable SPECT imaging, facilitating theranostics—allowing real-time monitoring of drug distribution and treatment response and providing imaging evidence for personalized therapy.

In disease modeling, this system can be used to construct more clinically relevant 'immunotherapy-resistant' melanoma models. By evaluating the combined effects of different immune checkpoint blockades and localized immune activation, it enables systematic dissection of resistance mechanisms and screening of effective intervention targets, thereby advancing the development of precision immunotherapy.

 

 

Conclusion

The ¹⁷⁷Lu-GAMP@MN microneedle system developed in this study represents an innovative transdermal, localized immuno-radiotherapeutic strategy that effectively remodels the melanoma immune microenvironment by integrating STING pathway activation with GSDME-mediated pyroptosis. This platform not only achieves high drug accumulation and sustained release at tumor sites, reducing systemic toxicity, but also significantly enhances dendritic cell maturation, T-cell infiltration, and immune memory formation. When combined with anti–PD-L1 antibodies, it demonstrates robust local control and abscopal effects, offering new therapeutic hope for patients with advanced or metastatic melanoma. From bench to bedside, this strategy features favorable manufacturability and safety profiles, with microneedle patches easy to store and use—making it suitable for outpatient settings and potentially a key component in future comprehensive melanoma management, especially for local control and immune priming of superficial skin lesions. Moreover, its modular design provides a referenceable paradigm for localized immunotherapy of other solid tumors.

 

Pian Yu, Shijun Xiang, Lu Hao, Peng Liu, and Shuo Hu. Radiolabeled Coordination Polymer‐Loaded Microneedles for Synergistic Melanoma Brachytherapy–Immunotherapy via STING Activation and Pyroptosis. Exploration.