Photochemical Reactions in the Synthesis of Protein–Drug Conjugates

Abstract

The ability to modify biologically active molecules such as antibodies with drug molecules, fluorophores or radionuclides is crucial in drug discovery and target identification. Classic chemistry used for protein functionalisation relies almost exclusively on thermochemically mediated reactions. Our recent experiments have begun to explore the use of photochemistry to effect rapid and efficient protein functionalisation. This article introduces some of the principles and objectives of using photochemically activated reagents for protein ligation. The concept of simultaneous photoradiosynthesis of radiolabelled antibodies for use in molecular imaging is introduced as a working example. Notably, the goal of producing functionalised proteins in the absence of pre‐association (non‐covalent ligand‐protein binding) introduces requirements that are distinct from the more regular use of photoactive groups in photoaffinity labelling. With this in mind, the chemistry of thirteen different classes of photoactivatable reagents that react through the formation of intermediate carbenes, electrophiles, dienes, or radicals, is assessed.

Light‐Activated Protein Conjugation and 89Zr‐Radiolabelling with Water‐Soluble Desferrioxamine Derivatives

“…Reagents that undergo photochemical activation are striking alternatives to the well‐established thermochemically activated routes toward protein functionalisation . The absorption of light by compounds containing benzophenone, diazirine or ArN 3 groups generates highly reactive diradical, carbene or nitrene intermediates, which under optimised conditions can form covalent bonds to protein.…”

Design of a Multiuse Photoreactor To Enable Visible‐Light Photocatalytic Chemical Transformations and Labeling in Live Cells

“…Azido phenol probes have recently been used for protein proximity labeling through a technique called enzyme-mediated activation of radical sources (EMARs) where a peroxidase is used to generate a radical labeling species. [39] As phenyl azides are known to undergo UV-activated protein labeling, [5,7] we wondered whether the presence of a hydroxy group on the ring system would make the probe sensitive to visible-light activation for protein labeling as the hydroxy group has been shown to induce a bathochromic shift in absorption spectra when present on a benzene ring (Figure 5a, protein labeling B). [40] CA protein was mixed with the azido phenol biotin probe and irradiated with visible light to yield time-dependent protein labeling (Figure 5b).…”

Design of a Multi-Use Photoreactor to Enable Visible Light Photocatalytic Chemical Transformations and Labeling in Live Cells

“…called enzyme mediated activation of radical sources (EMARs) where a peroxidase is used to generate a radical labeling species. [34] Since phenyl azides are known to undergo UV activated protein labeling, [5,7] we wondered whether the presence of a hydroxy group on the ring system would make the probe sensitive to visible light activation for protein labeling as the hydroxy group has been shown to induce a bathochromic shift in absorption spectra when present on a benzene ring (Figure 5a, Protein labeling B). [35] CA protein was mixed with the azido phenol biotin probe and irradiated with visible light to yield time dependent protein labeling (Figure 5b).…”

“…For these applications, substrates including aryl azides, diazirines and benzophenones are activated by UV light (~300 nm) for covalent cross linking to biomolecules. [5,6] Probes based on these substrates have found applications in radiolabeling, [5] drug-antibody conjugation, [7] chemoproteomics, [8] target ID [9] and protein cross linking. [10] In some cases, the reactive intermediate used for these applications forms from the T 1 excited state.…”