Near-infrared light-induced photothermal and immunotherapy system for lung cancer bone metastasis treatment with simultaneous bone repair

Approximately half of lung cancer patients experience bone metastasis, leading to bone loss, fracture, and other skeletal-related events. Although immunotherapies have significantly advanced the therapeutic landscape for lung cancer, bone metastases have an immunologically "cold" microenvironment, representing a challenging obstacle when treating lung cancer. The combination of immunotherapy and photothermal therapy (PTT) for treating tumor-induced bone defects holds promise for enhancing the efficacy of local tumor ablation and inhibiting tumor recurrence and metastasis through activating systemic immune responses. Herein, we developed an injectable hydrogel-based photothermal immunotherapy system (BP@Gel-CD[SA] hydrogel) incorporating STING agonists (SA) and black phosphorus nanosheets (BPNSs) for high-efficiency tumor elimination, immune activation, and bone regeneration. The photothermal and photodynamic activities of BPNSs induce hyperthermia and ROS-mediated apoptosis of tumor cells. Meanwhile, SA loaded into the nano-boxes in BP@Gel-CD[SA] hydrogel by host-guest interaction significantly activates the cGas-STING pathway. It stimulates immunogenic cell death (ICD), synergistically promoting immune cell infiltration. Single-cell RNA sequence analysis confirms the modulation of the tumor microenvironment (TME) through the PTT-mediated ICD effect and the transactivation of the cGAS-STING pathway in immune cells of the TME. More importantly, the system can significantly inhibit the growth of distant tumors via systemic immune activation and elicit long-term immune memory in addition to tumor eradication. In the long term, this hydrogel system can promote the formation of new bone at sites of tumor-induced bone destruction, improving bone strength in the affected area. Collectively, this strategy provides an effective and safe option for treating lung cancer bone metastases.