Tunable and self-reporting esterase-activated cyanide prodrugs exert cytoprotective effects

Hydrogen cyanide (HCN) is increasingly recognized as a mammalian gasotransmitter with biphasic biological effects, but its study is limited by the lack of controllable delivery tools. Here we report esterase-activated, self-reporting cyanide donors with tunable release kinetics and fluorogenic readout. Upon esterase activation, the donors synchronously release cyanide and regenerate an ICT-based fluorophore. Steric modulation at the cyanohydrin α-carbon controls the release rate over one order of magnitude (k_obs = 0.04-0.83 min^-1). In cell-based assays, biological outcomes correlate with cyanide generation rate rather than nominal donor concentration, producing proliferation at low rates and toxicity at higher rates. Cytoprotection occurs within an experimentally observed range of 0.3-0.7 nmol mg^-1 protein h^-1 under these conditions. In the MCAO model, the lead donor Et-1 administered at 1 μmol kg^-1 (0.3 mg kg^-1) reduces infarct volume and attenuates lipid peroxidation and inflammation.