Bioinspired enzyme-catalytic nanoreactor enhances immunotherapy for spinal metastases by activating pyroptosis and the cGAS-STING pathway.

Bone is one of the most common sites for tumor metastasis. The "seed-and-soil" relationship renders bone tissue a favorable microenvironment for the growth of circulating tumor cells. While immunotherapies, particularly immune checkpoint blockade (ICB), have achieved breakthroughs in primary solid tumors, bone metastases often respond poorly to ICB treatment. Herein, we developed an enzyme-loaded, self-cascading nanoreactor (mCL) that integrates a CaO core and l-Arginine (L-Arg) with iNOS-rich macrophage membranes. This design ensures efficient tumor targeting and, upon acid-triggered decomposition, initiates a self-reinforcing cycle of Ca overload and nitric oxide (NO), reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation. Upon targeted accumulation and penetration in tumors, CaO undergoes reactive decomposition in the acidic tumor microenvironment (TME), releasing Ca, HO, and L-Arg. Subsequently, membrane derived iNOS cooperates with HO to catalyze the conversion of L-Arg into NO, successfully overcoming the limitation of insufficient NO production within tumor cells. NO further enhances intracellular Ca accumulation and reacts with ROS to generate highly cytotoxic RNS. These self-amplifying cascading reactions activate caspase-3/gasdermin E (GSDME)-dependent pyroptosis and the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, promoting dendritic cell maturation and T cell activation, thereby remodeling the immunosuppressive TME. When used in combination with ICB, mCL significantly inhibits the growth and recurrence of hepatocellular carcinoma spinal metastasis (HCC-SM) while establishing long-lasting immune memory, providing a promising new strategy for the immunotherapy of HCC-SM.