Reversible Spatiotemporal Control of Induced Protein Degradation by Bistable PhotoPROTACs

Abstract

Off-tissue effects are persistent issues of modern inhibition-based therapies. By merging the strategies of photopharmacology and small-molecule degraders, we introduce a novel concept for persistent spatiotemporal control of induced protein degradation that potentially prevents off-tissue toxicity. Building on the successful principle of bifunctional all-small-molecule Proteolysis Targeting Chimeras (PROTACs), we designed photoswitchable PROTACs (photoPROTACs) by including ortho-F4-azobenzene linkers between both warhead ligands. This highly bistable yet photoswitchable structural component leads to reversible control over the topological distance between both ligands. The azo-cis-isomer is observed to be inactive because the distance defined by the linker is prohibitively short to permit complex formation between the protein binding partners. By contrast, the azo-trans-isomer is active since it can engage both protein partners to form the necessary and productive ternary complex. Importantly, due to the bistable nature of the ortho-F4-azobenzene moiety employed, the photostationary state of the photoPROTAC is persistent, with no need for continuous irradiation. This technique offers reversible on/off switching of protein degradation that is compatible with an intracellular environment and, therefore, could be useful in experimental exploration of biological signaling pathways—such as those crucial for oncogenic signal transduction. Additionally, this strategy may be suitable for therapeutic intervention to address a variety of diseases. By enabling reversible activation and deactivation of protein degradation, photoPROTACs offer advantages over conventional photocaging strategies that irreversibly release active agents.

Prey for the Proteasome: Targeted Protein Degradation—A Medicinal Chemist's Perspective

“…The design of photo‐switchable PROTACs allows for temporal control of TPD (Figure a) . These PHOTACs or PhotoPROTACs can be switched between a biologically active and inactive state using different wavelength of visible light. In an additional approach to gain temporal control of protein degradation, photocaged PROTACs have been described (Figure b) .…”

The Potential of Proteolytic Chimeras as Pharmacological Tools and Therapeutic Agents

“…Interestingly, by irradiation at 340 nm (by π→π* excitation), a substantial amount of the cis isomer is produced, whereas the trans isomer can be regenerated again in the dark or by irradiation at 450 nm (n→π* excitation). Despite the fact that the change in the distance between the carbon atoms at the para position is around 3.5 Å, the molecular shape is dramatically altered upon irradiation, which justifies its use as a photoswitch for the spatio-temporal modification of protacs and other biomolecules [ 93 ].…”

Beute für das Proteasom: Gezielter Proteinabbau aus medizinalchemischer Perspektive

“…Die Entwicklung von photoschaltbaren PROTACs ermöglicht eine zeitliche Kontrolle des TPD (Abbildung a) . Solche PHOTACs oder PhotoPROTACs werden durch Einstrahlung von Licht unterschiedlicher Wellenlängen von einem biologisch aktiven in ein inaktives Stadium überführt. Photocaged PROTACs wurden als weiterer Ansatz beschrieben und ermöglichen eine zeitliche Steuerung des Proteinabbaus (Abbildung b) .…”