[¹⁸F]FPyZIDE: A versatile prosthetic reagent for the fluorine‐18 radiolabeling of biologics via copper‐catalyzed or strain‐promoted alkyne‐azide cycloadditions

Abstract

Methods for the radiolabeling of biologics with fluorine-18 have been of interest for several decades. A common approach consists in the preparation of a prosthetic reagent, a small molecule bearing a fluorine-18 that is conjugated with the macromolecule to an appropriate function. Click chemistry, and more particularly cycloadditions, is an interesting approach to radiolabel molecules thanks to mild reaction conditions, high yields, low by-products formation, and strong orthogonality. Moreover, the chemical functions involved in the cycloaddition reaction are stable in the drastic radiofluorination conditions, thus allowing a simple radiosynthetic route to prepare the prosthetic reagent.We report herein the radiosynthesis of 18 F-FPyZIDE, a pyridine-based azidebearing prosthetic reagent. We exemplified its conjugation via coppercatalyzed cycloaddition (CuAAC) and strain-promoted cycloaddition (SPAAC) with several terminal alkyne or strained alkyne model compounds.

Recent Advances in Bioorthogonal Click Chemistry for Efficient Synthesis of Radiotracers and Radiopharmaceuticals

“…To improve the efficiency of 18 F radiolabeling, Roche et al explored a new 18 F-labeled azide prosthetic group, 18 F-FPyZIDE (Table 1, entry 6). In their study, the radiolabeled tracers were evaluated in both CuAAC- and SPAAC-based ligations and the labeling results showed that both radiolabeling methods provided high RCYs under mild reaction conditions (room temperature or 40 °C) [60]. Evans et al investigated the radiosynthesis of 68 Ga-labeled peptide using azide group-bearing 1,4,7,10-tetraazacyclododecane-tetraacetic acid (DOTA) chelator and DBCO group conjugated cRGD peptide (Table 1, entry 7) [61].…”

Recent Advances in Bioorthogonal Click Chemistry for Enhanced PET and SPECT Radiochemistry

“…103 This work suggested that this tracer could be potentially employed to noninvasively quantify PD-1/PD-L1 expression in clinical studies. Zeng et al described the production and evaluation of 64 Cu-labeled ubiquitin protein ([ 64 Cu]CB-1K1P-UbCG4), synthesized using the TCO-Tz ligation of IEDDA, for a chemokine receptor (CXCR4) imaging (Figure 4C). 104 In this study, the results demonstrated that 64 Cu-labeled ubiquitin displayed selective and specific binding affinities with CXCR4 receptors, and PET imaging results in mice bearing 4T1-xenograft tumors revealed clear visualization of the xenografted tumor at 1 and 2 h as well as comparable tumor uptake values between [ 64 Cu]CB-1K1P-UbCG4 and [ 64 Cu]AMD3465.…”

“…The 64 Cu-labeled cetuximab radiotracers conjugated with two cross-bridged macrocyclic chelators (CBTE1A1P and CBTE1K1P) were constructed based on SPAAC reaction. 105 Compared with other 64 Cu-labeled cetuximab radio-conjugates, the results of these two radiotracers in PET imaging experiment showed a more rapid renal elimination and a more remarkable tumor-tobackground ratio. Using the same radiometal, Lee et al reported the radiolabeling of trastuzumab using a CuAAC reaction, in which the propylene cross-bridged chelator (PCB-TE2A-alkyne) reacted with a Tz-containing azide.…”

“…In 2010, Rossin et al developed the TCO/Tz SPECT pretargeting by the injection of an [ 111 In]In-DOTA-Tz radioligand 24 h post-CC49 mAb-TCO administration and displayed specific tumor targeting and a rapid clearance of Tzbased radioligands via kidneys. 133 The pretargeting research based on the same click chemistry was also performed to construct radioimmunoconjugate in mice bearing colorectal cancers with the injection of huA33 mAb modified by PEGylated TCO moieties followed 24 h later by the injection of a 64 Cu-labeled tetrazine radioligand. 134 Altai et al reported bioorthogonal chemistry-mediated pretargeting in which a TCO module was first conjugated to anti-HER2 affibody Z2395 and then a radiometal-labeled Z2395 molecule was created by the IEDDA reaction.…”

Modular PET Agent Construction Strategy through Strain-Promoted Double-Click Reagent with Efficient Photoclick Step

“…The azide–alkyne Huisgen reaction has become a widely used cross-coupling strategy in various fields including radiolabeling. − While typical click reactions require transition metal catalysts, SPAAC is catalyst free and biorthogonal and has no residual metal toxicity concerns. , 18 F PET agent constructions utilizing SPAAC alkynes have been reported by various groups (Figure b). − Even though the reported examples are successful, the implications of these methods in new PET agent development remain limited. This could be caused by the lack of modular design and incompatibility between substrate stability and reaction rate.…”