Synthesis and Characterization of a High-Affinity NOTA-Conjugated Bombesin Antagonist for GRPR-Targeted Tumor Imaging
2013 (English)In: Bioconjugate chemistry, ISSN 1043-1802, E-ISSN 1520-4812, Vol. 24, no 7, 1144-1153 p.Article in journal (Refereed) Published
The gastrin-releasing peptide receptor (GRPR/BB2) is a molecular target for the visualization of prostate cancer. This work focused on the development of high-affinity, hydrophilic, antagonistic, bombesin-based imaging agents for PET and SPECT. The bombesin antagonist analog D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 ([D-Phe(6),Sta(13),Leu(14)]-bombesin[6-14]) was synthesized and conjugated to 1,4,7-triazacyclononane-N,N',N ''-triacetic acid (NOTA) via a diethylene glycol (PEG(2)) linker. The resulting conjugate, NOTA-PEG(2)-[D-Phe(6),Sta(13),Leu(14)]bombesin[6-14] (NOTA-P2-RM26), was labeled with Ga-68 (T-1/2 = 68 min, positron emitter) and In-111 (T-1/2 = 2.8 days, gamma emitter). The labeling stability, specificity, inhibition efficiency (IC50), and dissociation constant (K-D) of both labeled compounds as well as their cellular retention and internalization were investigated. The pharmacokinetics of the dual isotope) (In-111/Ga-68)-labeled peptide in both normal NMRI mice and PC-3 tumor-bearing Balb/c nu/nu mice was also studied. NOTA-P2-RM26 was labeled with In-111 and Ga-68 at a radiochemical yield of >98%. Both conjugates were shown to have high specificity and binding affinity for GRPR. The K-D value was determined to be 23 +/- 13 pM for the In-111-labeled compound in a saturation binding experiment. In addition, In-nat- and Ga-nat-NOTA-P2-RM26 showed low nanomolar binding inhibition concentrations (IC50 = 1.24 +/- 0.29 nM and 0.91 +/- 0.19 nM, respectively) in a competitive binding assay. The internalization rate of the radiolabeled conjugates was slow. The radiometal-labeled tracers demonstrated rapid blood clearance via the kidney and GRPR-specific uptake in the pancreas in normal mice. Tumor targeting and biodistribution studies in mice bearing PC-3 xenografts displayed high and specific uptake in tumors (8.1 +/- 0.4%ID/g for Ga-68 and 5.7 +/- 0.3%ID/g for In-111) and high tumor-to-background ratios (tumor/blood: 12 +/- 1 for Ga-68 and 10 +/- 1 for In-111) after only 1 h pi of 45 pmol of peptide. The xenografts were visualized by gamma and microPET cameras shortly after injection. In conclusion, the antagonistic bombesin analog NOTA-PEG(2)-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (NOTA-P2-RM26) is a promisindg candidate for prostate cancer imaging using PET and SPECT/CT.
Place, publisher, year, edition, pages
2013. Vol. 24, no 7, 1144-1153 p.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:uu:diva-207041DOI: 10.1021/bc300659kISI: 000322103200003OAI: oai:DiVA.org:uu-207041DiVA: diva2:646634
FunderSwedish Cancer SocietySwedish Research Council