Assessing Photostability of mAb Formulations In Situ Using Light-Coupled NMR Spectroscopy

Biopharmaceuticals, such as monoclonal antibodies (mAbs), need to maintain their chemical and physical stability in formulations throughout their lifecycle. It is known that exposure of mAbs to light, particularly UV, triggers chemical and physical degradation, which can be exacerbated by trace amounts of photosensitizers in the formulation. Although routine assessments of degradation following defined UV dosages are performed, there is a fundamental lack of understanding regarding the intermediates, transient reactive species, and radicals formed during illumination, as well as their lifetimes and immediate impact post-illumination. In this study, we used light-coupled NMR spectroscopy to monitor in situ live spectral changes in sealed samples during and after UV-A illumination of different formulations of four mAbs without added photosensitizers. We observed a complex evolution of spectra, reflecting the appearance within minutes of transient radicals during illumination and persisting for minutes to tens of minutes after the light was switched off. Both mAb and excipient signals were strongly affected by illumination, with some exhibiting fast irreversible photodegradation and others exhibiting partial recovery in the dark. These effects varied depending on the mAb and the presence of excipients, such as polysorbate 80 (PS80) and methionine. Complementary ex situ high-performance size-exclusion chromatography analysis of the same formulations post-UV exposure in the chamber revealed significant loss of purity, confirming formulation-dependent degradation. Both approaches suggested the presence of degradation processes initiated by light but continuing in the dark. Further studies on photoreaction intermediates and transient reactive species may help mitigate the impact of light on biopharmaceutical degradation.

Site-Selective Tyrosine Reaction for Antibody-Cell Conjugation and Targeted Immunotherapy

Targeted immunotherapies capitalize on the exceptional binding capabilities of antibodies to stimulate a host response that effectuates long-lived tumor destruction. One example is the conjugation of immunoglobulins (IgGs) to immune effector cells, which equips the cells with the ability to recognize and accurately kill malignant cells through a process called antibody-dependent cellular cytotoxicity (ADCC). In this study, a chemoenzymatic reaction is developed that specifically functionalizes a single tyrosine (Tyr, Y) residue, Y296, in the Fc domain of therapeutic IgGs. A one-pot reaction that combines the tyrosinase-catalyzed oxidation of tyrosine to o-quinone with a subsequent [3+2] photoaddition with vinyl ether is employed. This reaction installs fluorescent molecules or bioorthogonal groups at Y296 of IgGs or the C-terminal Y-tag of an engineered nanobody. The Tyr-specific reaction is utilized in constructing monofunctionalized antibody-drug conjugates (ADCs) and antibody/nanobody-conjugated effector cells, such as natural killer cells or macrophages. These results demonstrate the potential of site-selective antibody reactions for enhancing targeted cancer immunotherapy.

Endogenous Photosensitizers in Human Skin

Endogenous photosensitizers play a critical role in both beneficial and harmful light-induced transformations in biological systems. Understanding their mode of action is essential for advancing fields such as photomedicine, photoredox catalysis, environmental science, and the development of sun care products. This review offers a comprehensive analysis of endogenous photosensitizers in human skin, investigating the connections between their electronic excitation and the subsequent activation or damage of organic biomolecules. We gather the physicochemical and photochemical properties of key endogenous photosensitizers and examine the relationships between their chemical reactivity, location within the skin, and the primary biochemical events following solar radiation exposure, along with their influence on skin physiology and pathology. An important take-home message of this review is that photosensitization allows visible light and UV-A radiation to have large effects on skin. The analysis presented here unveils potential causes for the continuous increase in global skin cancer cases and emphasizes the limitations of current sun protection approaches.

Avoidance of the use of tryptophan in buried chromosomal proteins as a mechanism for reducing photo/oxidative damage to genomes

In cells that are exposed to terrestrial sunlight, the indole moiety in the side chain of tryptophan (Trp) can suffer photo/oxidative damage (POD) by reactive oxygen species (ROS) and/or ultraviolet light (UV-B). Trp is oxidized to produce N-formylkynurenine (NFK), a UV-A-responsive photosensitizer that further degenerates into photosensitizers capable of generating ROS through exposure to visible light. Thus, Trp-containing proteins function as both victims, and perpetrators, of POD if they are not rapidly replaced through protein turnover. The literature indicates that protein turnover and DNA repair occur poorly in chromosomal interiors. We contend, therefore, that basic chromosomal proteins (BCPs) that are enveloped by DNA should have evolved to lack Trp residues in their amino acid sequences, since these could otherwise function as 'Trojan horse-type' DNA-damaging agents. Our global analyses of protein sequences demonstrates that BCPs consistently lack Trp residues, although DNA-binding proteins in general do not display such a lack. We employ HU-B (a wild-type, Trp-lacking bacterial BCP) and HU-B F47W (a mutant, Trp-containing form of the same bacterial BCP) to demonstrate that the possession of Trp is deleterious to BCPs and associated chromosomal DNA. Basically, we show that UV-B and UV-A (a) cause no POD in HU-B, but cause extensive POD in HU-B F47W (in vitro), as well as (b) only nominal DNA damage in bacteria expressing HU-B, but extensive DNA damage in bacteria expressing F47W HU-B (in vivo). Our results suggest that Trp-lacking BCPs could have evolved to reduce scope for protein-facilitated, sunlight-mediated damage of DNA by UV-A and visible light, within chromosomal interiors that are poorly serviced by protein turnover and DNA repair machinery.

Primary Processes of Free Radical Formation in Pharmaceutical Formulations of Therapeutic Proteins

Oxidation represents a major pathway for the chemical degradation of pharmaceutical formulations. Few specific details are available on the mechanisms that trigger oxidation reactions in these formulations, specifically with respect to the formation of free radicals. Hence, these mechanisms must be formulated based on information on impurities and stress factors resulting from manufacturing, transportation and storage. In more detail, this article focusses on autoxidation, metal-catalyzed oxidation, photo-degradation and radicals generated from cavitation as a result of mechanical stress. Emphasis is placed on probable rather than theoretically possible pathways.

Advanced Oxidation Processes in Pharmaceutical Formulations: Photo-Fenton Degradation of Peptides and Proteins

Formulations of therapeutic proteins are sensitive to photo-degradation by near UV and visible light. Mechanistically, especially the processes leading to protein modification under visible light exposure are not understood. Potentially, these processes may be triggered by a ligand to metal charge transfer in excipient-metal complexes. This article summarizes recent analytical and mechanistic work on such reactions under experimental conditions relevant to pharmaceutical formulations.

Spontaneous and Ionizing Radiation-Induced Aggregation of Human Serum Albumin: Dityrosine as a Fluorescent Probe

The use of spectroscopic techniques has shown that human serum albumin (HSA) undergoes reversible self-aggregation through protein−protein interactions. It ensures the subsequent overlapping of electron clouds along with the stiffening of the conformation of the interpenetrating network of amino acids of adjacent HSA molecules. The HSA oxidation process related to the transfer of one electron was investigated by pulse radiolysis and photochemical methods. It has been shown that the irradiation of HSA solutions under oxidative stress conditions results in the formation of stable protein aggregates. The HSA aggregates induced by ionizing radiation are characterized by specific fluorescence compared to the emission of non-irradiated solutions. We assume that HSA dimers are mainly responsible for the new emission. Dityrosine produced by the intermolecular recombination of protein tyrosine radicals as a result of radiolysis of an aqueous solution of the protein is the main cause of HSA aggregation by cross-linking. Analysis of the oxidation process of HSA confirmed that the reaction of mild oxidants (Br2•−, N3•, SO4•−) with albumin leads to the formation of covalent bonds between tyrosine residues. In the case of •OH radicals and partly, Cl2•−, species other than DT are formed. The light emission of this species is similar to the emission of self-associated HSA.

Oxidative Crosslinking of Peptides and Proteins: Mechanisms of Formation, Detection, Characterization and Quantification

Covalent crosslinks within or between proteins play a key role in determining the structure and function of proteins. Some of these are formed intentionally by either enzymatic or molecular reactions and are critical to normal physiological function. Others are generated as a consequence of exposure to oxidants (radicals, excited states or two-electron species) and other endogenous or external stimuli, or as a result of the actions of a number of enzymes (e.g., oxidases and peroxidases). Increasing evidence indicates that the accumulation of unwanted crosslinks, as is seen in ageing and multiple pathologies, has adverse effects on biological function. In this article, we review the spectrum of crosslinks, both reducible and non-reducible, currently known to be formed on proteins; the mechanisms of their formation; and experimental approaches to the detection, identification and characterization of these species.

Photosensitized Dimerization of Tyrosine: The Oxygen Paradox†

In electron-transfer initiated photosensitization processes, molecular oxygen (O₂ ) is not involved in the first bimolecular event, but almost always participates in subsequent steps giving rise to oxygenated products. An exception to this general behavior is the photosensitized dimerization of tyrosine (Tyr), where O₂ does not participate as a reactant in any step of the pathway yielding Tyr dimers (Tyr₂ ). In the pterin (Ptr) photosensitized oxidation of Tyr, O₂ does not directly participate in the formation of Tyr₂ and quenches the triplet excited state of Ptr, the reactive species that initiates the process. However, O₂ is necessary for the dimerization, phenomenon that we have named as the oxygen paradox. Here, we review the literature on the photosensitized formation of Tyr₂ and present results of steady-state and time resolved experiments, in search of a mechanistic model to explain the contradictory role of O₂ in this photochemical reaction system.

Photosensitized Oxidative Dimerization at Tyrosine by a Water-Soluble 4-Amino-1,8-naphthalimide

The oxidation of proteins generates reactive amino acid (AA) residue intermediates, leading to protein modification and cross-linking. Aerobic studies with peptides and photosensitizers allow for the controlled generation of reactive oxygen species (ROS) and reactive AA residue intermediates, providing mechanistic insights as to how natural protein modifications form. Such studies have inspired the development of abiotic methods for protein modification and crosslinking, including applications of biomedical importance. Dityrosine linkages derived from oxidation at tyrosine (Tyr) residues represent one of the more well-understood oxidation-induced modifications. Here we demonstrate an aerobic, visible light-dependent oxidation reaction of Tyr-containing substrates promoted by a water-soluble 4-amino-1,8-naphthalimide-based photosensitizer. The developed procedure converts Tyr-containing substrates into o,o'-Tyr-Tyr linked dimers. The regioselectively formed o,o'-Tyr-Tyr linkage is consistent with dimeric standards prepared using a known enzymatic method. A crossover study with two peptides provides a statistical mixture of three distinct o,o'-Tyr-Tyr linked dimers, supporting a mechanism that involves Tyr residue oxidation followed by intermolecular combination.

Oxidative radicals (HO• or N3•) induce several di-tyrosine bridge isomers at the protein scale

Among protein oxidative damages, di-tyrosine bridges formation has been evidenced in many neuropathological diseases. Combining oxidative radical production by gamma radiolysis with very performant chromatographic separation coupled to mass spectrometry detection, we brought into light new insights of tyrosine dimerization. Hydroxyl and azide radical tyrosine oxidation leading to di-tyrosine bridges formation was studied for different biological compounds: a full-length protein (Δ25-centrin 2), a five amino acid peptide (KTSLY) and free tyrosine. We highlighted that both radicals generate high proportion of dimers even for low doses. Surprisingly, no less than five different di-tyrosine isomers were evidenced for the protein and the peptide. For tyrosine alone, at least four distinct dimers were evidenced. These results raise some questions about their respective role in vivo and hence their relative toxicity. Also, as di-tyrosine is often used as a biomarker, a better knowledge of the type of dimer detected in vivo is now required.