Site-Specific 89Zr- and 111In-Radiolabeling
and In Vivo Evaluation of Glycan-free Antibodies by Azide–Alkyne
Cycloaddition with a Non-natural Amino Acid
posted on 2020-03-16, 17:37authored byShin Hye Ahn, Brett A. Vaughn, Willy A. Solis, Mark L. Lupher, Trevor J. Hallam, Eszter Boros
Antibody–drug
conjugates (ADCs) are a class of targeted
therapeutics consisting of a monoclonal antibody coupled to a cytotoxic
payload. Various bioconjugation methods for producing site-specific
ADCs have been reported recently, in efforts to improve immunoreactivity
and pharmacokinetics and minimize batch variancepotential
issues associated with first-generation ADCs prepared via stochastic
peptide coupling of lysines or reduced cysteines. Recently, cell-free
protein synthesis of antibodies incorporating para-azidomethyl phenylalanine (pAMF) at specific locations within the
protein sequence has emerged as a means to generate antibody–drug
conjugates with strictly defined drug–antibody-ratio, leading
to ADCs with markedly improved stability, activity, and specificity.
The incorporation of pAMF enables the conjugation of payloads functionalized
for strain-promoted azide–alkyne cycloaddition. Here, we introduce
two dibenzylcyclooctyne-functionalized bifunctional chelators that
enable the incorporation of radioisotopes for positron emission tomography
with 89Zr (t1/2 = 78.4 h, β+ = 395 keV (22%), γ = 897 keV) or single
photon emission computed tomography with 111In (t1/2 = 67.3 h, γ = 171 keV (91%), 245 keV
(94%)) under physiologically compatible conditions. We show that the
corresponding radiolabeled conjugates with site-specifically functionalized
antibodies targeting HER2 are amenable to targeted molecular imaging
of HER2+ expressing tumor xenografts in mice and exhibit a favorable
biodistribution profile in comparison with conventional, glycosylated
antibody conjugates generated by stochastic bioconjugation.