Synthesis and single-molecule imaging reveal stereospecific enhancement of binding kinetics by the antitumour eEF1A antagonist SR-A3

Ternatin-family cyclic peptides inhibit protein synthesis by targeting the eukaryotic elongation factor-1 alpha. A potentially related cytotoxic natural product ('A3') was isolated from Aspergillus, but only 4 of its 11 stereocentres could be assigned. Here, we synthesized SR-A3 and SS-A3-two out of 128 possible A3 epimers-and discovered that synthetic SR-A3 is indistinguishable from naturally derived A3. Relative to SS-A3, SR-A3 exhibits an enhanced residence time and rebinding kinetics, as revealed by single-molecule fluorescence imaging of elongation reactions catalysed by eukaryotic elongation factor-1 alpha in vitro. An increased residence time-stereospecifically conferred by the unique beta-hydroxyl in SR-A3-was also observed in cells. Consistent with its prolonged duration of action, thrice-weekly dosing with SR-A3 led to a reduced tumour burden and increased survival in an aggressive Myc-driven mouse lymphoma model. Our results demonstrate the potential of SR-A3 as a cancer therapeutic and exemplify an evolutionary mechanism for enhancing cyclic peptide binding kinetics via stereospecific side-chain hydroxylation.

Automated summary

Ternatin-family cyclic peptides inhibit protein synthesis by targeting eukaryotic elongation factor-1 alpha. The synthetic SR-A3 showed enhanced residence time and rebinding kinetics compared to SS-A3, both in vitro and in cells. Thrice-weekly dosing with SR-A3 reduced tumor burden and increased survival in a mouse lymphoma model. These findings demonstrate the potential of SR-A3 as a cancer therapeutic and suggest an evolutionary mechanism for enhancing cyclic peptide binding kinetics via stereospecific side-chain hydroxylation.