Tumor Sensitization via the Extended Intratumoral Release of a STING Agonist and Camptothecin from a Self-Assembled Hydrogel

Introduction: Cancer immunotherapy has shown great promise in treating patients with advanced or metastatic tumors. However, effective clinical responses are typically limited to patients with immune-stimulating tumors, which are characterized by favorable tumor-infiltrating lymphocytes (TILs). The tumor microenvironment (TME) is the primary location where tumor cells and TILs interact, influencing the responsiveness of tumors to immunotherapy. The activation of the STING signaling pathway has been proposed as a method for enhancing tumor immunogenicity, stimulating both innate and adaptive immune responses in the TME. This study aims to explore a novel approach to sensitizing tumors to cyclic dinucleotides (CDNs) while minimizing immune-related adverse events, through the development of a drug-bearing supramolecular hydrogel system for intratumoral delivery of CDNs, achieving cancer chemoimmunotherapy.

Materials and

Methods: The study developed a drug-bearing supramolecular hydrogel system by chemically conjugating hydrophilic peptide moiety iRGD to the hydrophobic anticancer drug camptothecin (CPT). The resulting peptide-drug conjugate self-assembled into nanotubes, which complexed with the STING agonist cyclic di-AMP (CDA). The mixture was injected intratumorally into mouse models of murine tumors. The system was characterized using transmission electron microscopy, zeta potential analysis, and confocal imaging. The release behavior of the drug and the agonist was evaluated in PBS and fetal bovine serum. The efficacy of the treatment was assessed using multiple mouse models, including GL-261 brain cancer, CT26 colon cancer, and 4T1 breast cancer, with bioluminescence imaging, flow cytometry, and survival analysis performed to evaluate tumor regression, immune activation, and long-term immunity.

Results, Conclusions, and Discussions: In this study, the extended intratumoral release of the STING agonist cyclic di-AMP (CDA) transformed the tumor microenvironment from immunosuppressive to immunostimulatory, enhancing antitumor therapies. The CDA was complexed with nanotubes comprising a peptide-drug conjugate that self-assembled into a supramolecular hydrogel. The system exhibited localized drug release, promoting tumor elimination. The treatment led to tumor regression, increased animal survival, and long-term immunological memory in multiple mouse models. The hydrogel system enabled the local retention and extended release of CDA, enhancing immune activation and tumor regression through the STING-dependent immune stimulation. The hydrogel also promoted durable immune responses, protecting against tumor recurrence and metastasis. The study demonstrates that the developed drug-based supramolecular hydrogel can locally deliver the STING agonist and chemotherapeutic agents to promote an immune-stimulating tumor microenvironment, inducing tumor regression and preventing tumor recurrence and metastasis. The hydrogel facilitated localized delivery, enhancing the efficacy of immunotherapy and minimizing systemic toxicity. The findings suggest that this localized chemoimmunotherapy hydrogel offers a potential strategy to sensitize tumors to immunotherapies in a safe and effective manner. The results highlight the importance of the STING pathway in stimulating both innate and adaptive immune responses, contributing to robust antitumor immune responses and long-term immunity against tumor recurrence.

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