{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,23]],"date-time":"2026-08-23T16:07:08Z","timestamp":1787501228425,"version":"build-2736575974"},"reference-count":49,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,6,8]],"date-time":"2021-06-08T00:00:00Z","timestamp":1623110400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Wetenschappelijk Onderzoek Vlaanderen (FWO)","award":["1S64220N"],"award-info":[{"award-number":["1S64220N"]}]},{"name":"Agentschap Innoveren en Ondernemen","award":["VLAIO HCB 2019. 2446"],"award-info":[{"award-number":["VLAIO HCB 2019. 2446"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Recently, the first squaramide-(SA) containing FAP inhibitor-derived radiotracers were introduced. DATA5m.SA.FAPi and DOTA.SA.FAPi with their non-radioactive complexes showed high affinity and selectivity for FAP. After a successful preclinical study with [68Ga]Ga-DOTA.SA.FAPi, the first patient studies were realized for both compounds. Here, we present a new squaramide-containing compound targeting FAP, based on the AAZTA5 chelator 1,4-bis-(carboxylmethyl)-6-[bis-(carboxymethyl)-amino-6-pentanoic-acid]-perhydro-1,4-diazepine. For this molecule (AAZTA5.SA.FAPi), complexation with radionuclides such as gallium-68, scandium-44, and lutetium-177 was investigated, and the in vitro properties of the complexes were characterized and compared with those of DOTA.SA.FAPi. AAZTA5.SA.FAPi and its derivatives labelled with non-radioactive isotopes demonstrated similar excellent inhibitory potencies compared to the previously published SA.FAPi ligands, i.e., sub-nanomolar IC50 values for FAP and high selectivity indices over the serine proteases PREP and DPPs. Labeling with all three radiometals was easier and faster with AAZTA5.SA.FAPi compared to the corresponding DOTA analogue at ambient temperature. Especially, scandium-44 labeling with the AAZTA derivative resulted in higher specific activities. Both DOTA.SA.FAPi and AAZTA5.SA.FAPi showed sufficiently high stability in different media. Therefore, these FAP inhibitor agents could be promising for theranostic approaches targeting FAP.<\/jats:p>","DOI":"10.3390\/molecules26123482","type":"journal-article","created":{"date-parts":[[2021,6,8]],"date-time":"2021-06-08T12:08:55Z","timestamp":1623154135000},"page":"3482","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":25,"title":["In Vitro Evaluation of the Squaramide-Conjugated Fibroblast Activation Protein Inhibitor-Based Agents AAZTA5.SA.FAPi and DOTA.SA.FAPi"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0447-1355","authenticated-orcid":false,"given":"Euy Sung","family":"Moon","sequence":"first","affiliation":[{"name":"Department of Chemistry\u2013TRIGA, Johannes Gutenberg University Mainz, 55128 Mainz, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2443-5864","authenticated-orcid":false,"given":"Yentl","family":"Van Rymenant","sequence":"additional","affiliation":[{"name":"Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, 2610 Wilrijk, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sandeep","family":"Battan","sequence":"additional","affiliation":[{"name":"Department of Chemistry\u2013TRIGA, Johannes Gutenberg University Mainz, 55128 Mainz, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joni","family":"De Loose","sequence":"additional","affiliation":[{"name":"Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, 2610 Wilrijk, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"An","family":"Bracke","sequence":"additional","affiliation":[{"name":"Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, 2610 Wilrijk, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pieter","family":"Van der Veken","sequence":"additional","affiliation":[{"name":"Laboratory of Medicinal Chemistry, Department of Pharmaceutical Sciences, University of Antwerp, 2610 Wilrijk, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3421-0124","authenticated-orcid":false,"given":"Ingrid","family":"De Meester","sequence":"additional","affiliation":[{"name":"Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, 2610 Wilrijk, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Frank","family":"R\u00f6sch","sequence":"additional","affiliation":[{"name":"Department of Chemistry\u2013TRIGA, Johannes Gutenberg University Mainz, 55128 Mainz, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,6,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"D624","DOI":"10.1093\/nar\/gkx1134","article-title":"The MEROPS database of proteolytic enzymes, their substrates and inhibitors in 2017 and a comparison with peptidases in the PANTHER database","volume":"46","author":"Rawlings","year":"2018","journal-title":"Nucleic Acids Res."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"567","DOI":"10.1007\/s10585-011-9392-x","article-title":"Fibroblast activation protein-\u03b1 promotes tumor growth and invasion of breast cancer cells through non-enzymatic functions","volume":"28","author":"Huang","year":"2011","journal-title":"Clin. 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Imaging"}],"container-title":["Molecules"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1420-3049\/26\/12\/3482\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:12:00Z","timestamp":1760163120000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1420-3049\/26\/12\/3482"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,6,8]]},"references-count":49,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2021,6]]}},"alternative-id":["molecules26123482"],"URL":"https:\/\/doi.org\/10.3390\/molecules26123482","relation":{},"ISSN":["1420-3049"],"issn-type":[{"value":"1420-3049","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,6,8]]}}}