Biodegradable pyroptosis inducer with multienzyme-mimic activity kicks up reactive oxygen species storm for sensitizing immunotherapy.

Triggering pyroptosis is a major new weathervane for activating tumor immune response. However, biodegradable pyroptosis inducers for the safe and efficient treatment of tumors are still scarce. Herein, a novel tumor microenvironment (TME)-responsive activation nanoneedle for pyroptosis induction, copper-tannic acid (CuTA), was synthesized and combined with the sonosensitizer Chlorin e6 (Ce6) to form a pyroptosis amplifier (CuTA-Ce6) for dual activation and amplification of pyroptosis by exogenous ultrasound (US) and TME. It was demonstrated that Ce6-triggered sonodynamic therapy (SDT) further enhanced the cellular pyroptosis caused by CuTA, activating the body to develop a powerful anti-tumor immune response. Concretely, CuTA nanoneedles with quadruple mimetic enzyme activity could be activated to an "active" state in the TME, destroying the antioxidant defense system of the tumor cells through self-destructive degradation, breaking the "immunosilent" TME, and thus realizing the pyroptosis-mediated immunotherapy with fewer systemic side effects. Considering the outstanding oxygen-producing capacity of CuTA and the distinctive advantages of US, the sonosensitizer Ce6 was attached to CuTA via an amide reaction, which further amplified the pyroptosis and sensitized pyroptosis-induced immunotherapy with the two-pronged strategy of CuTA enzyme-catalyzed cascade and US-driven SDT pathway to generate a "reactive oxygen species (ROS) storm". Conclusively, this work provided a representative paradigm for achieving safe, reliable and efficient pyroptosis, which was further enhanced by SDT for more robust immunotherapy.