Ligand-Directed Photocatalysts and Far-Red Light Enable Catalytic Bioorthogonal Uncaging inside Live Cells

Abstract

Described are ligand-directed catalysts for live-cell, photocatalytic activation of bioorthogonal chemistry. Catalytic groups are localized via a tethered ligand either to DNA or to tubulin, and red light (660 nm) photocatalysis is used to initiate a cascade of DHTz oxidation, intramolecular Diels−Alder reaction, and elimination to release phenolic compounds. Silarhodamine (SiR) dyes, more conventionally used as biological fluorophores, serve as photocatalysts that have high cytocompatibility and produce minimal singlet oxygen. Commercially available conjugates of Hoechst dye (SiR-H) and docetaxel (SiR-T) are used to localize SiR to the nucleus and microtubules, respectively. Computation was used to assist the design of a new class of redox-activated photocage to release either phenol or n-CA4, a microtubule-destabilizing agent. In model studies, uncaging is complete within 5 min using only 2 μM SiR and 40 μM photocage. In situ spectroscopic studies support a mechanism involving rapid intramolecular Diels−Alder reaction and a rate-determining elimination step. In cellular studies, this uncaging process is successful at low concentrations of both the photocage (25 nM) and the SiR-H dye (500 nM). Uncaging n-CA4 causes microtubule depolymerization and an accompanying reduction in cell area. Control studies demonstrate that SiR-H catalyzes uncaging inside the cell, and not in the extracellular environment. With SiR-T, the same dye serves as a photocatalyst and the fluorescent reporter for microtubule depolymerization, and with confocal microscopy, it was possible to visualize microtubule depolymerization in real time as the result of photocatalytic uncaging in live cells.

Bioorthogonal Bond Cleavage Chemistry for On-demand Prodrug Activation: Opportunities and Challenges

“…It was confirmed that the oxidation did not involve the generation of cytotoxic singlet oxygen or superoxide . Recently, this system was adapted to develop a photoinitiated intramolecular click-and-release system for organelle-targeted drug activation . Specifically, a dihydrotetrazine molecule 144 was designed, which by itself cannot be oxidized to the tetrazine in the biological system.…”

“…132 Recently, this system was adapted to develop a photoinitiated intramolecular click-and-release system for organelle-targeted drug activation. 133 Specifically, a dihydrotetrazine molecule 144 was designed, which by itself cannot be oxidized to the tetrazine in the biological system. In the presence of a SiR-based photocatalyst, 144 can be efficiently oxidized into tetrazine by using 660 nm light.…”

Bioorthogonal chemistry for prodrug activation in vivo

“…Notably, in addition to drug release, light-induced functional molecule synthesis ( e.g. , tetrazines 92,93 ) and light-induced photocatalytic reactions for proximity labeling 94,95 are also important applications of photochemistry. However, providing exhaustive coverage of this subject matter exceeds the scope of this review.…”

“…Additionally, a class of upconversion nanoparticles (UCNPs), designed to be excited by NIR light and emit visible or UV light, has been employed for controlled drug molecule release or single oxygen production as well. 90,91 Notably, in addition to drug release, light-induced functional molecule synthesis (e.g., tetrazines 92,93 ) and lightinduced photocatalytic reactions for proximity labeling 94,95 are also important applications of photochemistry. However, providing exhaustive coverage of this subject matter exceeds the scope of this review.…”

Recent advances in porous molecular cages for photocatalytic organic conversions

“…The unique nature of this natural enzyme has inspired numerous researchers to develop highly efficient and specific artificial catalysts through synthetic chemistry. 14–19…”