Imaging Bradykinin B1 Receptor with⁶⁸Ga-Labeled [des-Arg¹⁰]Kallidin Derivatives: Effect of the Linker on Biodistribution and Tumor Uptake

Abstract

Bradykinin B1 receptor (B1R) that is overexpressed in cancers but minimally expressed in normal healthy tissues represents an attractive biomarker for the development of cancer imaging agents. The goal of this study was to evaluate the effect of different linkers on the pharmacokinetics and tumor uptake of a B1R-targeting radio-peptide sequence, 68Ga-DOTA-linker-Lys-Arg-Pro-Hyp-Gly-Cha-Ser-Pro-Leu. Four peptides, SH01078, P03034, P04115, and P04168, with 6-aminohexanoic acid, 9-amino-4,7-dioxanonanoic acid, Gly-Gly, and 4-amino-(1-carboxymethyl)piperidine, respectively, as the linker were synthesized and evaluated. In vitro competition binding assays showed that the Ki values of SH01078, P03034, P04115, and P04168 were 27.8±4.9, 16.0±1.9, 11.4±2.5, and 3.6±0.2 nM, respectively. Imaging and biodistribution studies were performed in mice bearing both B1R-positive HEK293T::hB1R and B1R-negative HEK293T tumors. All tracers showed mainly renal excretion with excellent tumor visualization and minimal background activity except for kidneys and bladder. The average uptake of 68Ga-labeled SH01078, P03034, and P04115 in HEK293T::hB1R tumor was similar (1.96-2.17%ID/g) at 1 h postinjection. 68Ga-P04168 generated higher HEK293T::hB1R tumor uptake (4.15±1.13%ID/g) and lower background activity, leading to a >2-fold improvement in HEK293T::hB1R tumor-to-background (HEK293T tumor, blood, muscle, and liver) contrasts over those of 68Ga-labeled SH01078, P03034, and P04115. Our results indicate that the choice of linker affects binding affinity, pharmacokinetics, and tumor targeting. The use of the cationic 4-amino-(1-carboxymethyl)piperidine linker improved tumor visualization, and the resulting 68Ga-P04168 might be promising for clinical application for imaging B1R-expressing tumors with positron emission tomography.

Preclinical Melanoma Imaging with 68Ga-Labeled α-Melanocyte-Stimulating Hormone Derivatives Using PET

“…In vivo stability was characterized according to previously published procedures 22. Briefly, mice were sedated with 2% isoflurane, and 8-12 MBq of 68 Ga-labeled peptide was injected via tail vein.…”

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

“…Table 1). 6 The increase in B1R+ tumor uptake could be partly due to improved binding affinity of these B9958 derivatives (K i = 1.4 -2.6 nM) over previously reported 68 Ga-labeled [Hyp 4 ,Cha 6 ,Leu 9 ,des-Arg 10 ]kallidin derivatives (K i = 3.6 -28 nM, Table 1). Another possible factor for the increased uptake in B1R+ tumor is the enhanced in vivo stability of radiolabeled B9958 derivatives.…”

“…In comparison, only 8 -17% of 68 Ga-[Hyp 4 ,Cha 6 ,Leu 9 ,des-Arg 10 ]kallidin remained intact under the same assay conditions. 6 The four radiolabeled Pip-B9958 derivatives ( Fig. 1) showed comparable high binding affinity to B1R (K i = 0.5 -2.6 nM).…”

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

Design, synthesis and evaluation of18F-labeled cationic carbonic anhydrase IX inhibitors for PET imaging

“…Stability in plasma was performed following published procedures 47,48 . Aliquots (100 lL) of 18 F-labeled 2 were incubated with 400 lL of balb/c mouse plasma (Innovative Research, Novi, MI) for upwards of 60 min at 37 C. At the end of each incubation period, samples were quenched by addition of acetonitrile (0.5 mL), centrifuged to remove proteins, and finally passed through a 0.2 micron filter.…”