Antibody Conjugates: From Heterogeneous Populations to Defined Reagents

Abstract

Monoclonal antibodies (mAbs) and their derivatives are currently the fastest growing class of therapeutics. Even if naked antibodies have proven their value as successful biopharmaceuticals, they suffer from some limitations. To overcome suboptimal therapeutic efficacy, immunoglobulins are conjugated with toxic payloads to form antibody drug conjugates (ADCs) and with chelating systems bearing therapeutic radioisotopes to form radioimmunoconjugates (RICs). Besides their therapeutic applications, antibody conjugates are also extensively used for many in vitro assays. A broad variety of methods to functionalize antibodies with various payloads are currently available. The decision as to which conjugation method to use strongly depends on the final purpose of the antibody conjugate. Classical conjugation via amino acid residues is still the most common method to produce antibody conjugates and is suitable for most in vitro applications. In recent years, however, it has become evident that antibody conjugates, which are generated via site-specific conjugation techniques, possess distinct advantages with regard to in vivo properties. Here, we give a comprehensive overview on existing and emerging strategies for the production of covalent and non-covalent antibody conjugates.

Photochemical Reactions in the Synthesis of Protein–Drug Conjugates

“…Our laboratory recently reported the synthesis, radiolabelling, and bimolecular coupling of photoactivatable chelates bearing the photoactive aryl azide (ArN 3 ) group to antibodies for use in immuno‐PET and RIT (Figure ) . Remarkably, switching the conjugation chemistry from traditional, thermally mediated reactions to a photo‐initiated reaction allowed us to produce radiolabelled mAbs in a simultaneous (one‐pot) process directly from fully formulated antibodies (including trastuzumab which targets the human epidermal growth‐factor receptor 2 [HER2/ neu ], and onartuzumab which binds to the human hepatocyte growth‐factor receptor [c‐MET]). Radiochemical yields (RCYs) of the isolated radiotracers varied substantially depending on the nature of the chelate and the radionuclide using narrow‐band light sources with peak emissions at 365 or 395 nm.…”

“…[61] Our laboratory recently reported the synthesis, radiolabelling, and bimolecular couplingo fp hotoactivatable chelates bearingt he photoactive aryl azide (ArN 3 )g roup to antibodies for use in immuno-PET and RIT ( Figure 2). [41][42][43][44][45] Remarkably, switching the conjugation chemistry from traditional, thermally mediated reactions [10][11][12][13] to ap hoto-initiated reaction allowed us to produce radiolabelled mAbs in as imultaneous( one-pot) process directly from fully formulated antibodies (including Figure 1. Timelines howing the evolution of different photoactive groups used in PAL.…”

Alteration of Physicochemical Properties for Antibody-Drug Conjugates and Their Impact on Stability

“…A wide range of excellent reviews cover the different linker chemistries, 3 the toxins used for ADCs, 14,15 the variety of conjugation strategies and techniques, [16][17][18] analytical techniques, 8,9,19 and ADC PKs. 20,21 This review pursues the path of Ross and Wolfe 4 with a focus on physical and chemical stabilities of ADCs but sets the mAb component and its structure and biophysical properties in the primary focus, supported by currently available literature.…”

Chemical aspects of metal ion chelation in the synthesis and application antibody‐based radiotracers

“…Functionalization usually involves posttranslational modification of amino-acid side chains (particularly peptide bond formation by using the primary amine group of lysine residues), derivatization of cysteine sulfhydryl groups, or site-specific labeling of glycans by using chemical and/or enzymatic methods. 7,8 More recent protein engineering routes have also exploited site-specific enzymatic ligation with prominent methods including transglutaminase derivatization, sortase coupling, and formylglycine reactions to produce a range of ADCs. 7,9 While the chemical nature of the linker group plays an important role in determining the metabolic stability and pharmacokinetics of a radiolabeled mAb, an equally important decision revolves around the choice of the radiometal ion and the chelation chemistry used to produce thermodynamically and kinetically stable radiometal ion complexes.…”

“…7,8 More recent protein engineering routes have also exploited site-specific enzymatic ligation with prominent methods including transglutaminase derivatization, sortase coupling, and formylglycine reactions to produce a range of ADCs. 7,9 While the chemical nature of the linker group plays an important role in determining the metabolic stability and pharmacokinetics of a radiolabeled mAb, an equally important decision revolves around the choice of the radiometal ion and the chelation chemistry used to produce thermodynamically and kinetically stable radiometal ion complexes. 10 In this review, we discuss the chemical requirements for chelation of various radiometal ions and highlight selected applications of radiometal chemistry in the development of radiotracers for immuno-PET, immune-SPECT, and RIT.…”