Injectable hydrogel-assisted local lipopolysaccharide delivery improves immune checkpoint blockade therapy

Tumor-associated macrophages (TAMs) significantly influence the clinical outcomes of immune checkpoint blockade (ICB) therapy. Strategies aimed at reprogramming TAMs from the immunosuppressive M2 phenotype to the pro-inflammatory M1 phenotype hold promise for enhancing ICB efficacy. Lipopolysaccharide (LPS), a potent Toll-like receptor 4 (TLR4) ligand, can reprogram TAMs toward an M1 phenotype. However, the systemic application of LPS is restricted due to its pronounced pro-inflammatory properties, which limit safe dosing in cancer treatment. To address this, thermosensitive hydrogels offer a viable solution by optimizing drug bioavailability and reducing systemic dissemination. In our study, carboxymethyl chitosan (CS) was incorporated into Pluronic F127 to extend the hydrogel's degradation period, facilitating the localized delivery and accumulation of LPS within tumor sites. Peritumoral injection of this hydrogel enhanced the tumor-inhibitory effects of anti-PD-1 antibodies, significantly improving the survival of 4T1 tumor-bearing mice. The GelF127CS-LPS hydrogel also increased the expression of the activation marker on tumor-infiltrating dendritic cells, promoted a higher M1/M2 TAM ratio, and enhanced CD8⁺ T cell infiltration into tumors—key indicators of T-cell-mediated anti-tumor immunity. Notably, no significant liver or hematological toxicity was observed with GelF127CS-LPS treatment, underscoring its favorable safety profile. These findings demonstrate the potential of GelF127CS-LPS as a TAMs-modulating agent and a promising combinatorial strategy to boost ICB therapy effectiveness.

Statement of significance

LPS, a potent TLR4 ligand, can reprogram tumor-associated macrophages (TAMs) toward an M1 phenotype, thereby contributing to tumor inhibition. However, its anti-tumor application is constrained by the contradiction between high-dose toxicity and insufficient efficacy at low doses. To address this issue, we developed a thermosensitive hydrogel encapsulating LPS, GelF127CS-LPS, which allows localized LPS release within the tumor area. This hydrogel reprograms TAMs at a picogram level of LPS to achieve a favorable M1/M2 ratio and promotes the activation of T cell-mediated antitumor immunity without observable toxicity. Consequently, when combined with immune checkpoint blockade (ICB), the hydrogel can inhibit tumor growth and improve overall survival. This study provides an effective method for tumor-targeted therapeutic LPS delivery to enhance the efficacy of ICB.