{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,27]],"date-time":"2026-09-27T04:56:18Z","timestamp":1790484978474,"version":"4.1.0"},"reference-count":43,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2020,7,28]],"date-time":"2020-07-28T00:00:00Z","timestamp":1595894400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Background: The frequent overexpression of gastrin-releasing peptide receptors (GRPRs) in human cancers provides the rationale for delivering clinically useful radionuclides to tumor sites using peptide carriers. Radiolabeled GRPR antagonists, besides being safer for human use, have often shown higher tumor uptake and faster background clearance than agonists. We herein compared the biological profiles of the GRPR-antagonist-based radiotracers [99mTc]Tc-[N4-PEGx-DPhe6,Leu-NHEt13]BBN(6-13) (N4: 6-(carboxy)-1,4,8,11-tetraazaundecane; PEG: polyethyleneglycol): (i) [99mTc]Tc-DB7 (x = 2), (ii) [99mTc]Tc-DB13 (x = 3), and (iii) [99mTc]Tc-DB14 (x = 4), in GRPR-positive cells and animal models. The impact of in situ neprilysin (NEP)-inhibition on in vivo stability and tumor uptake was also assessed by treatment of mice with phosphoramidon (PA). Methods: The GRPR affinity of DB7\/DB13\/DB14 was determined in PC-3 cell membranes, and cell binding of the respective [99mTc]Tc-radioligands was assessed in PC-3 cells. Each of [99mTc]Tc-DB7, [99mTc]Tc-DB13, and [99mTc]Tc-DB14 was injected into mice without or with PA coinjection and 5 min blood samples were analyzed by HPLC. Biodistribution was conducted at 4 h postinjection (pi) in severe combined immunodeficiency disease (SCID) mice bearing PC-3 xenografts without or with PA coinjection. Results: DB7, -13, and -14 displayed single-digit nanomolar affinities for GRPR. The uptake rates of [99mTc]Tc-DB7, [99mTc]Tc-DB13, and [99mTc]Tc-DB14 in PC-3 cells was comparable and consistent with a radioantagonist profile. The radiotracers were found to be \u224870% intact in mouse blood and &gt;94% intact after coinjection of PA. Treatment of mice with PA enhanced tumor uptake. Conclusions: The present study showed that increase of PEG-spacer length in the [99mTc]Tc-DB7\u2013[99mTc]Tc-DB13\u2013[99mTc]Tc-DB14 series had little effect on GRPR affinity, specific uptake in PC-3 cells, in vivo stability, or tumor uptake. A significant change in in vivo stability and tumor uptake was observed only after treatment of mice with PA, without compromising the favorably low background radioactivity levels.<\/jats:p>","DOI":"10.3390\/molecules25153418","type":"journal-article","created":{"date-parts":[[2020,7,30]],"date-time":"2020-07-30T12:15:38Z","timestamp":1596111338000},"page":"3418","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":13,"title":["[99mTc]Tc-DB1 Mimics with Different-Length PEG Spacers: Preclinical Comparison in GRPR-Positive Models"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0617-3936","authenticated-orcid":false,"given":"Panagiotis","family":"Kanellopoulos","sequence":"first","affiliation":[{"name":"Molecular Radiopharmacy, INRASTES, NCSR \u201cDemokritos\u201d, 15341 Athens, Greece"},{"name":"Molecular Pharmacology, School of Medicine, University of Crete, Heraklion, 70013 Crete, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Emmanouil","family":"Lymperis","sequence":"additional","affiliation":[{"name":"Molecular Radiopharmacy, INRASTES, NCSR \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aikaterini","family":"Kaloudi","sequence":"additional","affiliation":[{"name":"Molecular Radiopharmacy, INRASTES, NCSR \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marion","family":"de Jong","sequence":"additional","affiliation":[{"name":"Department of Radiology &amp; Nuclear Medicine Erasmus MC, 3015 CN Rotterdam, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eric P.","family":"Krenning","sequence":"additional","affiliation":[{"name":"Cyclotron Rotterdam BV, Erasmus MC, 3015 CE Rotterdam, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6028-9112","authenticated-orcid":false,"given":"Berthold A.","family":"Nock","sequence":"additional","affiliation":[{"name":"Molecular Radiopharmacy, INRASTES, NCSR \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1123-2486","authenticated-orcid":false,"given":"Theodosia","family":"Maina","sequence":"additional","affiliation":[{"name":"Molecular Radiopharmacy, INRASTES, NCSR \u201cDemokritos\u201d, 15341 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,7,28]]},"reference":[{"key":"ref_1","first-page":"1152","article-title":"Gastrin-releasing peptide receptors in the human prostate: Relation to neoplastic transformation","volume":"59","author":"Markwalder","year":"1999","journal-title":"Cancer Res."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1002\/pros.22743","article-title":"Early over-expression of GRP receptors in prostatic carcinogenesis","volume":"74","author":"Waser","year":"2014","journal-title":"Prostate"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"318","DOI":"10.1002\/pros.21434","article-title":"Profiling gastrin-releasing peptide receptor in prostate tissues: Clinical implications and molecular correlates","volume":"72","author":"Beer","year":"2012","journal-title":"Prostate"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2067","DOI":"10.1016\/S0002-9440(10)65525-3","article-title":"Gastrin-releasing peptide receptors in non-neoplastic and neoplastic human breast","volume":"155","author":"Gugger","year":"1999","journal-title":"Am. 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