Exploring Photoswitchable Binding Interactions with Small‐Molecule‐ and Peptide‐Based Inhibitors of Trypsin

Abstract

The ability to photochemically activate a drug, both when and where needed, requires optimisation of the difference in biological activity between each isomeric state. As a step to this goal, we report small molecule and peptide‐based inhibitors of the same protease – trypsin – to better understand how photoswitchable drugs interact with their biological target. The best peptidic inhibitor displayed a >5‐fold difference in inhibitory activity between isomeric states, whereas the best small molecule inhibitor only showed a 3.4‐fold difference. Docking and molecular modelling suggests this result is due to a large change in 3D structure in the key binding residues of the peptidic inhibitor upon isomerisation, which is not observed for the small molecule inhibitor. Hence, we demonstrate that significant structural changes in critical binding motifs upon irradiation are essential for maximising the difference in biological activity between isomeric states. This is an important consideration in the design of future photoswitchable drugs for clinical applications.

Photopharmacology of Protease Inhibitors: Current Status and Perspectives

“…The fold difference in activity was modest with values up to 2.2. [77] Another photo-induced ring opening reaction that influences the activity against chymotrypsin was reported by Pal and colleagues. They reported that the dihydroindolizine scaffold 14, and the UV-induced ring-opened compound 15 (Figure 9A) both inhibit chymotrypsin, but to a different extent.…”

“…Note that these do not contain an electrophile that binds the active site serine of the targeted trypsin. The fold difference in activity was modest with values up to 2.2 [77] …”

“…Specifically, they based their design on a modified STFI‐1, which has its structural loop replaced by a di‐proline beta‐turn analog [81] . An azobenzene photoswitch served as replacement of this motif (Figure 9D) or of another dipeptidyl element within the structure [77] . The authors found that compound 18 , which lost substantial activity compared with the parent compound containing the diproline motif, displayed a 2.3 fold increase in potency when irradiated, as judged from the K i .…”

“…[81] An azobenzene photoswitch served as replacement of this motif (Figure 9D) or of another dipeptidyl element within the structure. [77] The authors found that compound 18, which lost substantial activity compared with the parent compound containing the diproline motif, displayed a 2.3 fold increase in potency when irradiated, as judged from the K i . Compound 19, which differs only in the substitution pattern of the azobenzene, displayed a slightly higher fold difference in activity upon irradiation (2.9 fold) and also had a tenfold higher overall potency than 18, but still a 25 fold lower activity than the parent compound.…”