| 1. |
- Mitran, Bogdan, et al.
(författare)
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Selection of optimal chelator improves the contrast of GRPR imaging using bombesin analogue RM26.
- 2016
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Ingår i: International journal of oncology. - : Spandidos Publications. - 1791-2423 .- 1019-6439. ; 48:5, s. 2124-2134
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Tidskriftsartikel (refereegranskat)abstract
- Bombesin (BN) analogs bind with high affinity to gastrin-releasing peptide receptors (GRPRs) that are up-regulated in prostate cancer and can be used for the visualization of prostate cancer. The aim of this study was to investigate the influence of radionuclide-chelator complexes on the biodistribution pattern of the 111In-labeled bombesin antagonist PEG2-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (PEG2-RM26) and to identify an optimal construct for SPECT imaging. A series of RM26 analogs N-terminally conjugated with NOTA, NODAGA, DOTA and DOTAGA via a PEG2 spacer were radiolabeled with 111In and evaluated both in vitro and in vivo. The conjugates were successfully labeled with 111In with 100% purity and retained binding specificity to GRPR and high stability. The cellular processing of all compounds was characterized by slow internalization. The IC50 values were in the low nanomolar range, with lower IC50 values for positively charged natIn-NOTA-PEG2-RM26 (2.6±0.1 nM) and higher values for negatively charged natIn-DOTAGA-PEG2-RM26 (4.8±0.5 nM). The kinetic binding studies showed KD values in the picomolar range that followed the same pattern as the IC50 data. The biodistribution of all compounds was studied in BALB/c nu/nu mice bearing PC-3 prostate cancer xenografts. Tumor targeting and biodistribution studies displayed rapid clearance of radioactivity from the blood and normal organs via kidney excretion. All conjugates showed similar uptake in tumors at 4 h p.i. The radioactivity accumulation in GRPR-expressing organs was significantly lower for DOTA- and DOTAGA-containing constructs compared to those containing NOTA and NODAGA. 111In-NOTA-PEG2-RM26 with a positively charged complex showed the highest initial uptake and the slowest clearance of radioactivity from the liver. At 4 h p.i., DOTA- and DOTAGA-coupled analogs showed significantly higher tumor-to-organ ratios compared to NOTA- and NODAGA-containing variants. The NODAGA conjugate demonstrated the best retention of radioactivity in tumors, and, at 24 h p.i., had the highest contrast to blood, muscle and bones.
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| 2. |
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| 3. |
- Varasteh, Zohreh, et al.
(författare)
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In Vitro and In Vivo Evaluation of a F-18-Labeled High Affinity NOTA Conjugated Bombesin Antagonist as a PET Ligand for GRPR-Targeted Tumor Imaging
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:12, s. e81932-
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Tidskriftsartikel (refereegranskat)abstract
- Expression of the gastrin-releasing peptide receptor (GRPR) in prostate cancer suggests that this receptor can be used as a potential molecular target to visualize and treat these tumors. We have previously investigated an antagonist analog of bombesin (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, RM26) conjugated to 1,4,7-triazacyclononane-N,N',N ''-triacetic acid (NOTA) via a diethylene glycol (PEG(2)) spacer (NOTA-P2-RM26) labeled with Ga-68 and In-111. We found that this conjugate has favorable properties for in vivo imaging of GRPR-expression. The focus of this study was to develop a F-18-labelled PET agent to visualize GRPR. NOTA-P2-RM26 was labeled with F-18 using aluminum-fluoride chelation. Stability, in vitro binding specificity and cellular processing tests were performed. The inhibition efficiency (IC50) of the [F-nat]AlF-NOTA-P2-RM26 was compared to that of the Ga-nat-loaded peptide using I-125-Tyr(4)-BBN as the displacement radioligand. The pharmacokinetics and in vivo binding specificity of the compound were studied. NOTA-P2-RM26 was labeled with F-18 within 1 h (60-65% decay corrected radiochemical yield, 55 GBq/mu mol). The radiopeptide was stable in murine serum and showed high specific binding to PC-3 cells. [F-nat]AlF-NOTA-P2-RM26 showed a low nanomolar inhibition efficiency (IC50=4.4 +/- 0.8 nM). The internalization rate of the tracer was low. Less than 14% of the cell-bound radioactivity was internalized after 4 h. The biodistribution of [F-18]AlF-NOTA-P2-RM26 demonstrated rapid blood clearance, low liver uptake and low kidney retention. The tumor uptake at 3 h p. i. was 5.5 +/- 0.7 % ID/g, and the tumor-to-blood, -muscle and -bone ratios were 87 +/- 42, 159 +/- 47, 38 +/- 16, respectively. The uptake in tumors, pancreas and other GRPR-expressing organs was significantly reduced when excess amount of non-labeled peptide was co-injected. The low uptake in bone suggests a high in vivo stability of the Al-F bond. High contrast PET image was obtained 3 h p. i. The initial biological results suggest that [F-18]AlF-NOTA-P2-RM26 is a promising candidate for PET imaging of GRPR in vivo.
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| 4. |
- Varasteh, Zohreh, et al.
(författare)
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Synthesis and Characterization of a High-Affinity NOTA-Conjugated Bombesin Antagonist for GRPR-Targeted Tumor Imaging
- 2013
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Ingår i: Bioconjugate chemistry. - : American Chemical Society (ACS). - 1043-1802 .- 1520-4812. ; 24:7, s. 1144-1153
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Varasteh, Zohreh, et al.
(författare)
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The effect of macrocyclic chelators on the targeting properties of the 68Ga-labeled gastrin releasing peptide receptor antagonist PEG2-RM26
- 2015
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Ingår i: Nuclear Medicine and Biology. - : Elsevier BV. - 0969-8051 .- 1872-9614. ; 42:5, s. 446-454
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionOverexpression of gastrin-releasing peptide receptors (GRPR) has been reported in several cancers. Bombesin (BN) analogs are short peptides with a high affinity for GRPR. Different BN analogs were evaluated for radionuclide imaging and therapy of GRPR-expressing tumors. We have previously investigated an antagonistic analog of BN (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, RM26) conjugated to NOTA via a PEG2 spacer (NOTA-PEG2-RM26) labeled with 68Ga, 111In and Al18F. 68Ga-labeled NOTA-PEG2-RM26 showed high tumor-to-organ ratios.MethodsThe influence of different macrocyclic chelators (NOTA, NODAGA, DOTA and DOTAGA) on the targeting properties of 68Ga-labeled PEG2-RM26 was studied in vitro and in vivo.ResultsAll conjugates were labeled with generator-produced 68Ga with high yields and demonstrated high stability and specific binding to GRPR. The IC50 values of natGa-X-PEG2-RM26 (X = NOTA, DOTA, NODAGA, DOTAGA) were 2.3 ± 0.2, 3.0 ± 0.3, 2.9 ± 0.3 and 10.0 ± 0.6 nM, respectively. The internalization of the conjugates by PC-3 cells was low. However, the DOTA-conjugated analog demonstrated a higher internalization rate compared to other analogs. GRPR-specific uptake was found in receptor-positive normal tissues and PC-3 xenografts for all conjugates. The biodistribution of the conjugates was influenced by the choice of the chelator moiety. Although all radiotracers cleared rapidly from the blood, [68Ga]Ga-NOTA-PEG2-RM26 showed significantly lower uptake in lung, muscle and bone compared to the other analogs. The uptake in tumors (5.40 ± 1.04 %ID/g at 2 h p.i.) and the tumor-to-organ ratios (25 ± 3, 157 ± 23 and 39 ± 4 for blood, muscle and bone, respectively) were significantly higher for the NOTA-conjugate than the other analogs.ConclusionsChelators had a clear influence on the biodistribution and targeting properties of 68Ga-labeled antagonistic BN analogs. Positively charged [68Ga]Ga-NOTA-PEG2-RM26 provided a low kidney radioactivity uptake, high affinity, high tumor uptake and high image contrast.
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| 7. |
- Varasteh, Zohreh, et al.
(författare)
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The Effect of Mini-PEG-Based Spacer Length on Binding and Pharmacokinetic Properties of a Ga-68-Labeled NOTA-Conjugated Antagonistic Analog of Bombesin
- 2014
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Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 19:7, s. 10455-10472
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Tidskriftsartikel (refereegranskat)abstract
- The overexpression of gastrin-releasing peptide receptor (GRPR) in cancer can be used for peptide-receptor mediated radionuclide imaging and therapy. We have previously shown that an antagonist analog of bombesin RM26 conjugated to 1,4,7-triazacyclononane-N, N', N ''-triacetic acid (NOTA) via a diethyleneglycol (PEG(2)) spacer (NOTA-PEG(2)-RM26) and labeled with Ga-68 can be used for imaging of GRPR-expressing tumors. In this study, we evaluated if a variation of mini-PEG spacer length can be used for optimization of targeting properties of the NOTA-conjugated RM26. A series of analogs with different PEG-length (n = 2, 3, 4, 6) was synthesized, radiolabeled and evaluated in vitro and in vivo. The IC50 values of Ga-nat-NOTA-PEG(n)-RM26 (n = 2, 3, 4, 6) were 3.1 +/- 0.2, 3.9 +/- 0.3, 5.4 +/- 0.4 and 5.8 +/- 0.3 nM, respectively. In normal mice all conjugates demonstrated similar biodistribution pattern, however Ga-68-NOTA-PEG(3)-RM26 showed lower liver uptake. Biodistribution of Ga-68-NOTA-PEG(3)-RM26 was evaluated in nude mice bearing PC-3 (prostate cancer) and BT-474 (breast cancer) xenografts. High uptake in tumors (4.6 +/- 0.6% ID/g and 2.8 +/- 0.4% ID/g for PC-3 and BT-474 xenografts, respectively) and high tumor-to-background ratios (tumor/ blood of 44 +/- 12 and 42 +/- 5 for PC-3 and BT-474 xenografts, respectively) were found already at 2 h p.i. of Ga-68-NOTA-PEG(3)-RM26. Results of this study suggest that variation in the length of the PEG spacer can be used for optimization of targeting properties of peptide-chelator conjugates. However, the influence of the mini-PEG length on biodistribution is minor when di-, tri-, tetra- and hexaethylene glycol are compared.
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