Expansion of the Structure-Activity Relationship Profile of Triaminopyrimidines as Inhibitors of Caspase-1

Caspase-1 is a sought-after therapeutic target for inflammatory conditions due to its role in activation and release of pro-inflammatory cytokines, but there has been little success getting drugs into the clinic. We have previously shown triaminopyrimidines such as CK-1-41 are potent, reversible small molecule inhibitors of caspase-1, likely binding in an allosteric site within the enzyme. A series of analogs of CK-1-41 were synthesized and tested against caspase-1 to develop a more robust structure-activity relationship profile. In general, alkyl and aryl groups were well tolerated via an ethylene or methylene linkage to the piperazine nitrogen, with IC50 values ranging from 13 to 200 nM. The most potent compounds were methylene linked o-tolyl (AE-2-21) and ethylene linked 4-trifluoromethylphenyl (AE-2-48) with IC50 values of 18 and 13 nM, respectively. Derivatives with electrophilic covalent warheads linked via an amide bond to the piperazine nitrogen were synthesized and characterized. CA-1-11 and EM-1-10 were semi-reversible, non-competitive inhibitors of caspase-1 with slightly reduced potencies of 134 and 144 nM, respectively. All derivatives docked well into the allosteric site, supporting our hypothesis that this family of caspase-1 inhibitors function via an allosteric non-competitive mechanism of inhibition.