Programming Injectable DNA Hydrogels Yields Tumor Microenvironment-Activatable Chemo-Immunotherapy

Injectable hydrogels have been investigated extensively to incorporate with drugs for tumor treatment because those materials can simultaneously deliver multiple drugs to the target sites with rational ratios and minimal invasion, and elevate their tumor accumulation, blood stability, and half-lives. Importantly, the local treatment of hydrogel-encapsulated drugs showed superior tumor growth inhibition compared to the local or systemic delivery of non-encapsulated chemotherapeutics and immunomodulators. However, since current studies regarding injectable chemo-immunotherapeutic hydrogels are mainly based on the intratumoral gelation of soluble precursors, sol-gel transformation may be impeded by the complex physiological environment, resulting in the reduced cross-linking degree, abrupt drug leakage, and unpredictable pharmacokinetics. Besides, conventional polymers lack molecular, structural, and functional programmability, which results in significant challenges in tailoring the biofunctionalities of hydrogel scaffolds for intimately interacting with tumor tissue.<br/>Here, we describe an unprecedented injectable DNA hydrogel in which the repeats of cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN) and adenosine triphosphate (ATP) aptamer are encoded on the ultralong DNA building blocks by RCA-mediated DNA polymerization. By sequentially incorporating DNA hydrogel with immune checkpoint inhibitor anti-programmed cell death protein ligand 1 (aPDL1) and chemotherapeutic agent doxorubicin (DOX), a chemo-immunotherapeutic DNA hydrogel adjuvant (aPDL1/DOX@DNA Gel) is formed. Due to its super-soft property, this DNA hydrogel encoded with ATP aptamers can be readily injected into tumor tissues in which the overexpressed ATP binds to the corresponding aptamer. This results in the conformational change of aptamer and volume expansion of the gelmatrix to stimulate the distinct release kinetics of co-encapsulated therapeutics. DOX is first released to induce immunogenic cell death that intimately works together with the polymerized CpG ODN in gel scaffold for effectively recruiting and activating dendritic cells. While, the polymerized CpG ODN displayed very high tumor retention with a significant reduction of the systemic circulation, which is attributed to the restricted in vivo motility and metabolism of the polymerized CpG ODN, thereby reducing the adverse effects of CpG ODN while enhancing its tumor immunomodulatory efficacy. Furthermore, aPDL1 antibody was subsequently released from DNA hydrogel to block the immune inhibitory checkpoint molecules PD-L1 on the tumor cell surface, thus reversing the tumor microenvironment immunosuppression through potentiating T-cell mediated immune responses. The programmed aPDL1/DOX@DNA Gel demonstrated potent suppression of tumor growth and lung metastasis via the induced strong systemic immune response and immune memory effect. This work thus contributes to the first proof-of-concept demonstration of a programmable super-soft DNA hydrogel system that perfectly matching the sequence programmability to the synergistic therapeutic modalities based on chemotherapeutic toxicity, in situ vaccination, and immune checkpoint blockade. With the high programmability of design principle, we believe that our approach can be combined with DNA-protein conjugation chemistry, DNA nanotechnology, and microfluidic technique to develop a library of biomaterial systems in new biomedical applications beyond chemo-immunotherapy of tumors.