Comparative Studies of Three⁶⁸Ga-Labeled [Des-Arg¹⁰]Kallidin Derivatives for Imaging Bradykinin B1 Receptor Expression with PET

Abstract

Bradykinin B1 receptor (B1R) is a G-protein-coupled receptor that is overexpressed in a variety of cancers. B1R is not expressed in healthy tissues, making it an attractive cancer imaging marker. Previously, we reported selective uptake of 68 Ga-P03034 ( 68 Ga-DOTA-dPEG2-LysArg-Pro-Hyp-Gly-Cha-Ser-Pro-Leu) in B1R-positive (B1R1) HEK293T:: hB1R tumor xenografts in mice. In this study, we compare 68 Ga-P03034 with 68 Ga-labeled P04158 ( 68 Ga-DOTA-dPEG2-Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic) and Z02090 ( 68 Ga-DOTAdPEG2-Lys-Lys-Arg-Pro-Hyp-Gly-Cpg-Ser-D-Tic-Cpg) derived from 2 potent B1R antagonists, B9858 and B9958, respectively, for imaging B1R expression with PET. Methods: Peptide sequences were assembled on solid-phase. Cold standards were prepared by incubating DOTA-conjugated peptides with GaCl 3 . Binding affinity was measured via competition binding assays using hB1R-expressing Chinese hamster ovary-K1 cell membranes. 68 Ga labeling was performed in N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) buffer with microwave heating and purified by high-performance liquid chromatography. Imaging/biodistribution studies were performed in mice bearing wild-type HEK293T (B1R−) and B1R1 HEK293T:: hB1R tumors. Results: P03034, P04158, and Z02090 bound B1R with high affinity, with K i values at 16.0 ± 2.9, 1.5 ± 1.9, and 1.1 ± 0.8 nM, respectively. 68 Ga-labeled P03034, P04159, and Z02090 were obtained in greater than 50% decay-corrected radiochemical yields with more than 99% radiochemical purity. Biodistribution studies showed that all three 68 Ga-labeled tracers cleared rapidly from the blood and normal tissues, with excretion mainly via the renal pathway. At 1 h after injection, only the kidneys, bladders, and B1R1 HEK293T::hB1R tumors were clearly visualized in PET images. Uptake values of 68 Ga-labeled P03034, P04158, and Z02090 in B1R1 tumors were 2.17 ± 0.49, 19.6 ± 4.50, and 14.4 ± 1.63 percentage injected dose per gram, respectively. Uptake ratios of B1R1 to B1R− tumor, blood, and muscle were 6.23 ± 1.69, 5.72 ± 2.20, and 25.5 ± 13.1 for 68 Ga-P03034; 34.5 ± 10.5, 19.2 ± 8.21, and 66.1 ± 17.0 for 68 Ga-P04158; and 29.3 ± 9.68, 29.9 ± 5.58, and 124 ± 28.1 for 68 Ga-Z02090, respectively. Conclusion: All three 68 Ga-labeled B1R-targeting peptides generated specific and high-contrasted images of B1R1 tumors xenografted in mice. With significantly higher tumor uptake and target-to-nontarget ratios, 68 Ga-labeled P04158 and Z02090 are superior to P03034 for imaging B1R expression with PET.

Radiolabeled B9958 Derivatives for Imaging Bradykinin B1 Receptor Expression with Positron Emission Tomography: Effect of the Radiolabel–Chelator Complex on Biodistribution and Tumor Uptake

“…[6][7][8] However, the only reported B1R-trageting tracer composed of B9958 and Pip was 18 F-L08060 (Fig. 1).…”

“…By using the sequences of [Leu 9 ,des-Arg 10 ]kallidin and [Hyp 4 ,Cha 6 ,Leu 9 ,des-Arg 10 ]kallidin, the overall charge of these tracers was +1 -+2, and their average kidney uptake ranged 3 -5 %ID/g. [5][6][7] When combining the sequence of B9858/B9958 with 68 Ga-DOTA-dPEG2 or 18 F-AmBF 3 -Mta, the overall charge of these tracers increased to +2 -+3, and their average uptake in kidneys increased to 30 -70 %ID/g. [7][8] The increased kidney uptake among these tracers could be potentially caused by the introduction of additional positive charge(s) by using B9858/B9958 sequence instead of [Hyp 4 ,Cha 6 ,Leu 9 ,des-Arg 10 ]kallidin, and by using the cationic Pip instead of the neutral dPEG2 linker.…”

“…7 The resin was treated with 20% piperidine in N,N-dimethylformamide to remove the N α -Fmoc protecting group. The chelator DOTA tri-t-butyl ester (3 equivalents) was coupled to the N-terminus in N-methyl-2-pyrrolidone with in situ activating reagent N,N'-diisopropylcarbodiimide and N-hydroxysuccinimide (3 equivalents) in the presence of N,N-diisopropylethylamine (20 equivalents …”

Synthesis and evaluation of an 18F‐labeled trifluoroborate derivative of 2‐nitroimidazole for imaging tumor hypoxia with positron emission tomography

“…The stability of 18 F-AmBF 3 -Bu-2NI was measured following literature procedures. 28 Briefly, aliquots of 18 F-AmBF 3 -Bu-2NI (100 μL,~300 μCi) were mixed with 400 μL of BALB/c mouse plasma (Innovative Research) and then incubated at 37°C for pre-determined time points (5,15,30, and 60 minutes). At the end of each incubation period, proteins were precipitated by addition of 0.5-mL acetonitrile.…”

Exploiting cancer’s phenotypic guise against itself: targeting ectopically expressed peptide G-protein coupled receptors for lung cancer therapy

“…Studies on mice lacking each receptor gene and different specific peptidic and non-peptidic antagonists have implied that both B1R and B2R are potential therapeutic targets in various pathophysiological events in the aforementioned diseases [ 17 ]. Due to negligible expression of B1R in healthy tissues, the receptor is very appealing as an imaging marker for tumor diagnosis and for the development of anticancer therapeutic agents [ 80 , 81 ].…”