Gallium‐68‐labelled NOTA‐oligonucleotides: an optimized method for their preparation

Abstract

One of the most essential aspects to the success of radiopharmaceuticals is an easy and reliable radiolabelling protocol to obtain pure and stable products. In this study, we optimized the bioconjugation and gallium-68 ((68) Ga) radiolabelling conditions for a single-stranded 40-mer DNA oligonucleotide, in order to obtain highly pure and stable radiolabelled oligonucleotides. Quantitative bioconjugation was obtained for a disulfide-functionalized oligonucleotide conjugated to the macrocylic bifunctional chelator MMA-NOTA (maleimido-mono-amide (1,4,7-triazanonane-1,4,7-triyl)triacetic acid). Next, this NOTA-oligonucleotide bioconjugate was radiolabelled at room temperature with purified and pre-concentrated (68) Ga with quantitative levels of radioactive incorporation and high radiochemical and chemical purity. In addition, high chelate stability was observed in physiological-like conditions (37 °C, PBS and serum), in the presence of a transchelator (EDTA) and transferrin. A specific activity of 51.1 MBq/nmol was reached using a 1470-fold molar excess bioconjugate over (68) Ga. This study presents a fast, straightforward and reliable protocol for the preparation of (68) Ga-radiolabelled DNA oligonucleotides under mild reaction conditions and without the use of organic solvents. The methodology herein developed will be applied to the preparation of oligonucleotidic sequences (aptamers) targeting the human epidermal growth factor receptor 2 (HER2) for cancer imaging.

Bifunctional Gallium-68 Chelators: Past, Present, and Future

“…127,133,134 Besides those methods, there are less used ones such as clickable compounds, 99 coupling with thiols, 135 or the use of maleimidoethylmonoamide NOTA. 136 The disadvantage of this conjugation is the loss of one carboxylic acid arm, which becomes a less coordinating amide bond. 126 NODAGA is one of the most important bifunctional chelators (besides p-SCN-Bn-NOTA) for gallium and it has been synthesized in 2002 for the first time by Eisenwiener et al 125 Using glutaric acid as conjugation arm instead of acetic acid has the following two advantages: on the one hand the hexadentate N 3 O 3 structure does not get destroyed as in direct conjugated NOTA.…”

“…There are many publications with several target vectors. 113,118,127,136,143,[149][150][151][152][153][154][155][156][157] A really new and promising TACN derivate is TRAP (3,3 0 ,3″- (((1,4,7-triazonane-1,4,7-triyl)tris(methylene))tris(hydroxyphosphoryl))tripropanoic acid). It has been mentioned 2010 by Notni et al 120 and many articles have been published about this topic during the past 5 years.…”

Development and characterization of aptamer-conjugated imaging tools for diagnostic applications

“…Scheme S3.1: Reaction scheme outlining the cleavage of the thiol-modifier C6 S-S and subsequent conjugation to maleimido-monoamide-NOTA to produce FA-NOTA conjugate. 109 xviii xxi The introduction chapter was written by A Koudrina and is in part based on a review, which was written and edited by A Koudrina and MC DeRosa; it contains literature up to June 2020.…”

“…108 A similar approach was explored by Gijs et al in the production of 1,4,7-triazanonane-1,4,7-triyl)triacetic acid (NOTA)-conjugated oligonucleotides, which were subsequently radiolabelled with gallium-68 for molecular imaging of epidermal growth factor receptor 2 (HER2). 109 The aptamer was initially functionalized at the 5'-end with a hexyldisulfide group, which generated a singular binding site for the incorporation of the chelator. This controls for the position and the precision of subsequent complexation, avoiding undesirable sideproducts.…”

“…This controls for the position and the precision of subsequent complexation, avoiding undesirable sideproducts. 109 Noteworthy, while other single-step bioconjugation strategies exist, such as hexylamine-modified aptamer with isothiocyanatobenzyl chelator, it is unclear whether amino groups within the aptamer bases may become involved. 14,110 Both 1,4,7,10tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and NOTA-apt bioconjugates were produced in a two-step synthesis.…”