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Bioorthogonal chemistry capable of operating in live animals is needed to investigate biological processes such as cell death and immunity. Recent studies have identified a gasdermin family of pore-forming proteins that executes inflammasome-dependent and -independent pyroptosis1-5. Pyroptosis is proinflammatory, but its effect on antitumour immunity is unknown. Here we establish a bioorthogonal chemical system, in which a cancer-imaging probe phenylalanine trifluoroborate (Phe-BF3) that can enter cells desilylates and 'cleaves' a designed linker that contains a silyl ether. This system enabled the controlled release of a drug from an antibody-drug conjugate in mice. When combined with nanoparticle-mediated delivery, desilylation catalysed by Phe-BF3 could release a client protein-including an active gasderminfrom a nanoparticle conjugate, selectively into tumour cells in mice. We applied this bioorthogonal system to gasdermin, which revealed that pyroptosis of less than 15% of tumour cells was sufficient to clear the entire 4T1 mammary tumour graft. The tumour regression was absent in immune-deficient mice or upon T cell depletion, and was correlated with augmented antitumour immune responses. The injection of a reduced, ineffective dose of nanoparticle-conjugated gasdermin along with Phe-BF3 sensitized 4T1 tumours to anti-PDl therapy. Our bioorthogonal system based on Phe-BF3 desilylation is therefore a powerful tool for chemical biology; our application of this system suggests that pyroptosis-induced inflammation triggers robust antitumour immunity and can synergize with checkpoint blockade.
As a positron emission tomography (PET) imaging probe for cancers, [18F]Phe-BF3 has a comparable sensitivity to-but a higher specificity than-[18F]fluorodeoxyglucose6-8. Free fluoride, which is a deprotection agent in organic synthesis9, catalyses efficient desilylation. We wondered whether Phe-BF3 could also induce desilylation, and whether it could be developed into a bioorthogonal system for tumour-selective manipulation. To this end, we designed an ortho-carbamoylmethylene silyl-phenolic ether system attached to a client molecule, coumarin (Fig. 1a, Extended Data Fig. 1a). Desilylation of this system will cause the release of free coumarin, which becomes fluorescent (Extended Data Fig. 1b). We began with the tert-butyldimethyl silyl (TBS) group, and synthesized TBSO-coumarin with incorporation of a para-N,Ndimethylaminoacetamide for conjugation to a potential carrier (Fig. 1a, Extended Data Fig. 1a-c). Upon incubation with Phe-BF3, TBSOcoumarin released fluorescent coumarin and the reaction-rate constant was comparable to that of sodium fluoride (Fig. 1b, Extended Data Fig. 2a-c). TBSO-coumarin did not react with hydrogen peroxide,...