IC50: 0.9 μM ( trans -translation tagging reaction)

KKL-35 exhibits broad-spectrum antibiotic activity. KKL-35 prevents growth of B. anthracis and M. smegmatis with minimum inhibitory concentration (MIC) values of less than 6 μM. KKL-35 inhibit trans-translation at some step before proteolysis of tagged proteins. KKL-35 inhibits tagging of DHFR-ns. A large amount of untagged DHFR is produced in reactions with the highest concentrations of KKL-35, indicating that KKL-35 does not inhibit translation. KKL-35 prevents growth of WT S. flexneri with a MIC of 6 μM, and addition of KKL-35 to a growing culture of S. flexneri stops growth. In an S. flexneri strain expressing ArfA and deleted for ssrA, addition of KKL-35 has little effect on viability or growth rate. KKL-35 inhibits the growth of E. coli ?tolC, which is deficient in small molecule efflux, with an MIC of 0.3 μM.

Evidence suggest that the in vivo effects of KKL-35 are caused by inhibition of the release of nonstop translation complexes by trans-translation. KKL-35 inhibits trans-translation and prevents growth of S. flexneri strains that require trans-translation. The correlation between inhibition of trans-translation and growth is supported by genetic and pharmacological experiments showing that alternative mechanisms to release nonstop translation complexes relieve the growth suppression of KKL-35.