Single Mutation on Trastuzumab Modulates the Stability of Antibody-Drug Conjugates Built Using Acetal-Based Linkers and Thiol-Maleimide Chemistry

Advances in acid-degradable and enzyme-cleavable linkers for drug delivery

Drug delivery vectors have the potential to improve the efficacy of therapeutics, including small molecules and nucleic acid-based drugs. However, challenges remain in developing linkages that enable the precise and efficient release of therapeutic cargo in response to mildly acidic environments or lysosomal enzymes. This review highlights recent advances in acid-degradable acetal/ketal and enzyme-cleavable linkages for endolysosomal release. These innovations include the developments of azido-acetal linkers with improved stability and hydrolysis kinetics, organocatalytic trans-isopropenylation for synthesizing asymmetric ketals and their applications in drug delivery, and enzyme-cleavable linkers activated by cathepsin B or β-galactosidase.

Light-Activated Reactivity of Nitrones with Amino Acids and Proteins

Controlled modifications of amino acids are an indispensable tool for advancing fundamental and translational research based on peptides and proteins. Yet, we still lack methods to chemically modify each naturally occurring amino acid sidechain. To help address this gap, we show that N,α-diaryl oxaziridines expand the scope of bioconjugation methods to chemically modify cysteine, methionine, and tryptophan residues with evidence for additional tyrosine labelling in a proteomic context. Conjugation primarily at tryptophan sites can be accessed by selective cleavage of modifications at other sidechains. The N,α-diaryl oxaziridine reagents are accessed through photoisomerization of nitrones, which serve as photocaged reagents, thus providing an additional level of control over reactivity. Initial guiding principles for the design of nitrone reagents are developed by exploring the impact of structure on UV/Vis absorption, photoisomerization, and reactivity. We identify a nitrone structure that maximizes photoisomerization efficiency, the aqueous stability of the oxaziridine, the extent of amino acid modification, and the stability of the resulting amino acid conjugates. We then translate nitrone reagents to modify proteins in aqueous conditions. Finally, we use nitrones to profile reactive residues across the proteome of a mammalian cell line and find that they expand the proteome coverage.

Reference-free thio-succinimide isomerization characterization by electron-activated dissociation

RATIONALE

Isomerism can be an important aspect in pharmaceutical drug development. Identification of isomers can provide insights into drug pharmacology and contribute to better design of drug molecules. The general approaches to differentiate isomers include Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and circular dichroism. Additionally, a commonly used method to differentiate isomers is liquid chromatography coupled with mass spectrometry (LC-MS). Notably, LC-MS is routinely applied to leucine and isoleucine differentiation to facilitate protein sequencing. This work focuses on isomer differentiation of widely employed thio-succinimide structure bridging the antibody backbone and linker-payload of antibody-drug conjugates (ADCs). Thio-succinimide hydrolysis stabilizes the payload-protein structure while generating a pair of constitutional isomers: thio-aspartyl and thio-isoaspartyl.

METHODS

This paper introduces a hybrid method using ligand binding assay (LBA) and liquid chromatography coupled with tandem MS (LC-MS/MS) to reveal isomerization details of thio-succinimide hydrolysis over time in plasma samples incubated with ADC. Application of two orthogonal dissociation methods, collision-induced dissociation (CID) and electron-activated dissociation (EAD) revealed different MS/MS spectra for this pair of isomers. This observation enables a unique approach in distinguishing thio-succinimide hydrolysis isomers.

RESULTS

We observed signature [R1 + Thio + 57 + H]+, [R2 + Succ + H2O - 57 + H]+, and [R2 + Succ + H2O - 44 + 2H]2+ product ions (Succ = succinimide) that differentiated thio-aspartyl and thio-isoaspartyl isomers using EAD. A newly discovered [R2 + ThioSucc + H2O - 44 + 2H]2+ ion also served as additional evidence that further supported our findings.

CONCLUSIONS

This study is a first-to-date identification of thio-succinimide hydrolysis isomers without using synthesized reference materials. This approach should be applicable to all thio-succinimide-linked molecules. Correct identification of thio-succinimide hydrolysis isomers may eventually benefit the development of ADCs in the future.

Understanding the Effects of Site-Specific Light Chain Conjugation on Antibody Structure Using Hydrogen Exchange-Mass Spectrometry (HX-MS)

Antibody drug conjugates (ADCs) represent one of the fastest growing classes of cancer therapeutics. Drug incorporation through site-specific conjugation in ADCs leads to uniform drug load and distribution. These site-specific modifications may have an impact on ADC quality attributes including protein higher order structure (HOS), which might impact safety and efficacy. In this study, we conducted a side-by-side comparison between the conjugated and unconjugated mAb. In the ADC, the linker-pyrrolobenzodiazepine was site specifically conjugated to an engineered unpaired C215 residue within the Fab domain of the light chain. Differential scanning calorimetry (DSC) and differential scanning fluorimetry (DSF) indicated a decrease in thermal stability for the CH2 transition of the ADC. Size exclusion chromatography (SEC) analysis showed that conjugation of the mAb resulted in earlier aggregation onset and increased aggregation propensity after 4 weeks at 40 °C. Differential hydrogen-exchange mass spectrometry (HX-MS) indicated that upon conjugation, light chain residues 150-155 and 197-204, close to the conjugation site, showed significantly faster HX kinetics, suggesting an increase in backbone flexibility within this region, while heavy chain residues 32-44 exhibited significantly slower kinetics, suggesting distal stabilization of the mAb backbone.

Water-Degradable Oxygen-Rich Polymers with AB/ABB Units from Fast and Selective Copolymerization

Researchers have been chasing plastics that can automatically and fully degrade into valuable products under natural conditions. Here, we develop a series of water-degradable polymers from the first reported fast and selective cationic copolymerization of formaldehyde (B) with cyclic anhydrides (A). In addition to readily accessible monomers, the method is performed at industrially relevant temperatures (~100 °C), takes tens or even minutes, and uses common acid as the catalyst. Interestingly, such polymers possess tunable AB/ABB-type repeating units, which are considered to be thermodynamic and kinetic products, respectively, resulting in low carbon content ([O] : [C] up to 1 : 1). Notably, the polymers can completely degrade to valuable diacids within 150 days in water at ambient temperature owing to the incorporation of carboxyl terminals and acid-responsive acetal units. By washing with aqueous sodium carbonate, the polymers are relatively stable over several months.

Selenium chemistry for spatio-selective peptide and protein functionalization

The ability to construct a peptide or protein in a spatio-specific manner is of great interest for therapeutic and biochemical research. However, the various functional groups present in peptide sequences and the need to perform chemistry under mild and aqueous conditions make selective protein functionalization one of the greatest synthetic challenges. The fascinating paradox of selenium (Se) - being found in both toxic compounds and also harnessed by nature for essential biochemical processes - has inspired the recent exploration of selenium chemistry for site-selective functionalization of peptides and proteins. In this Review, we discuss such approaches, including metal-free and metal-catalysed transformations, as well as traceless chemical modifications. We report their advantages, limitations and applications, as well as future research avenues.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

Microcrystals of Ketal-Linked Paliperidone Prodrugs for Long-Acting Antipsychotics

Intramuscularly injectable long-acting prodrug-based microcrystals (MCs) are of particular interest for chronic disease management. Nevertheless, current prevalently used linkers degraded by enzymes have the potential drawback of substantial differences in enzyme levels between individuals. Here, we reported the synthesis of a stearyl-modified paliperidone prodrug (SKP) with an acid-sensitive ketal linker for developing long-acting MC antipsychotics. SKP-MCs of three different sizes were prepared and systematically examined. We found that paliperidone exposure in SKP-MC-treated rats was prolonged compared with that in rats treated with the commercial antipsychotic Invega Sustenna and that the drug release rate decreased with increasing MC size. In inflammation-inhibition-model rats, paliperidone release from the SKP-MCs was considerably decreased, indicating that the immune-mediated foreign-body response after intramuscular administration boosted paliperidone release. Our findings will provide valuable insights into in vivo drug release from prodrug-based MC formulations. The ketal-linked prodrug strategy might be a new solution for developing long-acting prodrug formulations of hydroxyl-group-bearing drugs.

Advanced Pyrrolidine-Carbamate Self-Immolative Spacer with Tertiary Amine Handle Induces Superfast Cyclative Drug Release

Amine-carbamate self-immolative (SI) spacers represent practical and versatile tools in targeted prodrugs, but their slow degradation mechanism limits drug activation at the site of disease. We engineered a pyrrolidine-carbamate SI spacer with a tertiary amine handle which strongly accelerates the spacer cyclization to give a bicyclic urea and the free hydroxy groups of either cytotoxic (Camptothecin) or immunostimulatory (Resiquimod) drugs. In silico conformational analysis and pKa calculations suggest a plausible mechanism for the superior efficacy of the advanced SI spacer compared to state-of-art analogues.