Linkers Having a Crucial Role in Antibody–Drug Conjugates

Abstract

Antibody–drug conjugates (ADCs) comprised of a desirable monoclonal antibody, an active cytotoxic drug and an appropriate linker are considered to be an innovative therapeutic approach for targeted treatment of various types of tumors and cancers, enhancing the therapeutic parameter of the cytotoxic drug and reducing the possibility of systemic cytotoxicity. An appropriate linker between the antibody and the cytotoxic drug provides a specific bridge, and thus helps the antibody to selectively deliver the cytotoxic drug to tumor cells and accurately releases the cytotoxic drug at tumor sites. In addition to conjugation, the linkers maintain ADCs’ stability during the preparation and storage stages of the ADCs and during the systemic circulation period. The design of linkers for ADCs is a challenge in terms of extracellular stability and intracellular release, and intracellular circumstances, such as the acid environment, the reducing environment and cathepsin, are considered as the catalysts to activate the triggers for initiating the cleavage of ADCs. This review discusses the linkers used in the clinical and marketing stages for ADCs and details the fracture modes of the linkers for the further development of ADCs.

Qualitative analysis of antibody–drug conjugates (ADCs): an experimental comparison of analytical techniques of cysteine-linked ADCs

“…Hence, there is a dire need for reliable analytical techniques to meet those requirements. Whilst much work has been done to control the regioselectivity of the covalent attachment of drug molecules onto the antibodies and new modes of drugrelease, [12][13][14][15] little attention has been paid to ADC-analyses until recently. Recent publications described both novel techniques for the assessment of the drug-to-antibody ratio (DAR), [16][17][18][19][20][21] ADC stability, [22][23][24][25] aggregation degree assessment, [26][27][28] bioanalysis, 29 the quantification of unconjugated drug molecules 22 and PTMs.…”

Systematic identification of regulators of antibody-drug conjugate toxicity using CRISPR-Cas9 screens

“…Here, we used CRISPR-knockout screens to evaluate the mechanism of toxicity for antibodydrug conjugates (ADCs) bearing non-cleavable and cleavable valine-citrulline (VC) linkers, which are known to have critically different efficacies toward different tumors 4,12,15,16,45 . We identified many known and novel genetic modifiers of ADC toxicity, and uncovered critical roles for a number of endolysosomal regulators in mediating the toxicity of ADCs.…”

“…Although ADCs with noncleavable linkers are more stable and thus elicit less off-target toxicity when used in vivo 2,45 , they are not effective against all ADC targets, and some tumors show marked resistance to these agents 4,16,45 . Our work shows that noncleavable-linker ADCs show greater reliance on late endosomal trafficking regulators (RAB7, RMC1, WDR81, and WDR91) and lysosomal cathepsins (Cathepsins A, C, and S) for toxicity, whereas surprisingly ADCs with VC-cleavable linkers (designed to be cleaved by cathepsin B), do not.…”

Human Antibody Fusion Proteins/Antibody Drug Conjugates in Breast and Ovarian Cancer

“…In ADCs, non-cleavable linkers or chemically labile linkers, including acid-cleavable linkers and reducible linkers, help conjugate antibody to drug [29,30,31]. Due to the chemical method of conjugation, most of these ADCs exist as heterogeneous mixtures, which can result in a narrow therapeutic window and have major pharmacokinetic implications [32].…”

“…The expressed fusion protein is highly selective, site-specific, and versatile due to its high affinity for an array of BG substrates, e.g. toxins, fluorophores or photosensitizers [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66]. The conjugation of photosensitizers to SNAP-tag has made it an indispensable tool in photoimmunotherapy.…”