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An improved synthesis of NHS-MAG3 for conjugation and radiolabeling of biomolecules with 99mTc at room temperature


The mercaptoacetyltriglycine (MAG3) chelator has been shown to stably complex technetium-99m (99mTc) for nuclear imaging and radiorhenium (186/188Re) for tumor radiation therapy studies. The bifunctional N-hydroxysuccinimidyl ester of MAG3 with S-acetyl protection (N-hydroxysuccinimidyl S-acetylmercaptoacetyltriglycinate (NHS-MAG3)) has been successfully used to covalently conjugate a MAG3 chelator to primary amine functionalized biomolecules. We describe herein a simplified synthesis of NHS-MAG3 that begins with the preparation of the N-hydroxysuccinimidyl ester of S-acetylmercaptoacetic acid (N-succinimidyl S-acetylmercaptoacetate (SATA)) from mercaptoacetic acid and is followed by the synthesis of S-acetylmercaptoacetyltriglycine from SATA, together requiring about 14 days. Finally, the synthesis of NHS-MAG3 from S-acetylmercaptoacetyltriglycine requires a further 5 days. We had earlier described a method for the preparation of MAG3-conjugated and 99mTc-radiolabeled biomolecules that required elevated temperatures during postconjugation purification. We now report a modified method for the preparation that is accomplished at room temperature and therefore applicable to temperature-sensitive biomolecules. The conjugation and radiolabeling of bovine serum albumin is used as an example. The conjugation and purification requires about 2–3 h and the radiolabeling and postlabeling purification requires about an additional 2 h.

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Figure 1
Figure 2: A mass spectrum of NHS-MAG3 synthesized by the method described in text.
Figure 3: Size-exclusion HPLC analyses of 99mTc-labeled MAG3-BSA before (trace A) and after (trace B) postlabeling purification on a P4 column.


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Correspondence to Yi Wang or Donald J Hnatowich.

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Wang, Y., Liu, X. & Hnatowich, D. An improved synthesis of NHS-MAG3 for conjugation and radiolabeling of biomolecules with 99mTc at room temperature. Nat Protoc 2, 972–978 (2007).

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