AAZTA5/AAZTA5-TOC: synthesis and radiochemical evaluation with 68Ga, 44Sc and 177Lu

Abstract

Purpose AAZTA (1,4-bis (carboxymethyl)-6-[bis (carboxymethyl)]amino-6-methylperhydro-1,4-diazepine) based chelators were initially developed in the context of magnetic resonance imaging. First radiochemical studies showed the capability of AAZTA to form stable complexes with radiolanthanides and moderately stable complexes with 68 Ga. For a systematic comparison of the labelling capabilities with current diagnostic and therapeutic trivalent radiometals, AAZTA 5 (1,4-bis (carboxymethyl)-6-[bis (carboxymethyl)]amino-6-[pentanoic-acid]perhydro-1,4-diazepine) was synthesized representing a bifunctional version with a pentanoic acid at the carbon-6 atom. To evaluate the effect of adding a targeting vector (TV) to the bifunctional chelator on the complex formation, AAZTA 5 -TOC was synthesized, radiolabeled and tested in comparison to the uncoupled AAZTA 5 . Methods AAZTA 5 was synthesized in a 5-step synthesis. It was coupled to the cyclic peptide TOC (Phe 1 -Tyr 3 octreotide) via amide bound formation. AAZTA and AAZTA 5 -TOC complex formations with 68 Ga, 44 Sc and 177 Lu were investigated at different pH, temperature and precursor amounts. Stability studies against human serum, PBS buffer, EDTA and DTPA were performed. Results AAZTA 5 and AAZTA 5 -TOC achieved quantitative labelling (> 95%) at room temperature in less than 5 min with all three nuclides at pH ranges from 4 to 5.5 with low precursor amounts of 1 to 10 nmol. [ 44 Sc]Sc-AAZTA 5 complexes as well as [ 44 Sc]Sc-AAZTA 5 -TOC were completely stable. The 177 Lu complexes of AAZTA 5 and AAZTA 5 -TOC showed high stability comparable to the 44 Sc complexes. In contrast, the [ 68 Ga]Ga-AAZTA 5 complex stability was rather low, but interestingly, [ 68 Ga]Ga-AAZTA 5 -TOC was completely stable. Conclusion AAZTA 5 appears to be a promising bifunctional chelator for 68 Ga, 44 Sc and 177 Lu with outstanding labelling capabilities at room temperature. Complex stabilities are high in the case of 44 Sc and 177 Lu. While [ 68 Ga]Ga-AAZTA complexes alone lacking stability, [ 68 Ga]Ga-AAZTA ...

Chelation with a twist: a bifunctional chelator to enable room temperature radiolabeling and targeted PET imaging with scandium-44

“…1), which forms kinetically inert and thermodynamically stable Sc(III)-complexes at room temperature and provides a viable alternative to DOTA. 24,25 However, the hydrophilicity of the corresponding complexes can result in accelerated excretion and diminished accumulation in the site of interest. We sought to develop alternative, more lipophilic chelator structures that would enable robust room temperature radiolabeling with Sc(III) isotopes and form kinetically inert complexes, especially in their bifunctional form.…”

Radiolabelled Peptides for Positron Emission Tomography and Endoradiotherapy in Oncology

“…Attempts have been made to develop chelator systems allowing labelling under so-called "kit conditions" (room temperature, pH 5-6). Recently, 6-Amino-6-(5-methoxy-5-oxopentyl)-1,4-diacepine-tetraacetate (AAZTA-5) was introduced and demonstrated that by conjugation to TOC labelling with lutetium-177 in high yield was possible with low tracer amounts in less than 10 min at room temperature at a pH between 4.5 and 5.5 [104].…”

AAZTA5-squaramide ester: promising tool for 177Lu-labeling of monoclonal antibodies under mild conditions

“…Radiolabeling of DOTA-SA with 177 Lu Radiolabeling of AAZTA 5 -SA-bevacizumab and DOTA-SAbevacizumab with 177 Lu and puri cation of [ 177 (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55) MBq in 14-50 µL 0.04 M HCl) was diluted with 0.5 M HEPES-buffer (pH 7) to a total volume of 550 µL. Afterwards a solution of either AAZTA 5 -SA-bevacizumab (125-900 µg, 0.8-6.0 nmol) or DOTA-SA-bevacizumab (272-900 µg, 1.8-6.0 nmol) in PBS (450 µL) was added and the mixture (1 mL) was shaken for 60-90 min at 550 rpm and either at room temperature or 37 °C via thermomixer.…”

“…The tert-butyl-protected derivative of AAZTA 5 (4, Fig. class="InternalRef">2) could be successfully synthesized with an overall yield of 32% within four steps according to the work recently published by our group (Sinnes et al 2019). The initial step rst includes an in situ ring-opening reaction of 2nitrocyclohexane followed by formation of the diazepane scaffold via double Nitro-Mannich reaction of the resulting nucleophilic compound with N,N'-dibenzylethylenediamine and paraformaldehyde.…”

“…Though there are a few studies featuring DOTA-functionalized proteins (Fortin et al 2007 In this study we wanted to evaluate the applicability of AAZTA 5 for radiolabeling of antibodies with 177 Lu regarding radioimmunotherapy compared to DOTA as the gold standard for complexation of this radiometal. For this purpose, we rst synthesized AAZTA 5 as recently reported by our group and extended the basic scaffold with an ethylenediamine unit (Sinnes et al 2019). In the next step, we introduced a squaric acid diethyl ester (SA(OEt) 2 ) as linker entity via selective formation of a vinylogous monoamide (Fig.…”