The overexpression of the chemokine receptor CXCR4 plays an important role in oncology, since together with its endogenous ligand, the stromal cell-derived factor (SDF1-a), CXCR4 is involved in tumor development, growth, and organ-specific metastasis. As part of our ongoing efforts to develop highly specific CXCR4-targeted imaging probes and with the aim to assess the suitability of this ligand for first proof-of-concept studies in humans, we further evaluated the new 68 Ga-labeled high-affinity cyclic CXCR4 ligand, 68 Ga-CPCR4-2 (cyclo(D- 68 Ga-DOTA]-Arg 3 -2-Nal 4 -Gly 5 )). Methods: Additional biodistribution and competitions studies in vivo, dynamic PET studies, and investigations on the metabolic stability and plasma protein binding were performed in nude mice bearing metastasizing OH1 human small cell lung cancer xenografts. CXCR4 expression on OH1 tumor sections was determined by immunohistochemical staining. Results: nat Ga-CPCR4-2 exhibits high CXCR4 affinity with a half maximum inhibitory concentration of 4.99 6 0.72 nM. 68 Ga-CPCR4-2 showed high in vivo stability and high and specific tumor accumulation, which was reduced by approximately 80% in competition studies with AMD3100. High CXCR4 expression in tumors was confirmed by immunohistochemical staining. 68 Ga-CPCR4-2 showed low uptake in nontumor tissue and particularly low kidney accumulation despite predominant renal excretion, leading to high-contrast delineation of tumors in small-animal PET studies. Conclusion: The small and optimized cyclic peptide CPCR4-2 labeled with 68 Ga is a suitable tracer for targeting and imaging of human CXCR4 receptor expression in vivo. The high affinity for CXCR4, its in vivo stability, and the excellent pharmacokinetics recommend the further evaluation of 68 Ga-CPCR4-2 in a proof-of-concept study in humans.

The development of biomolecular imprinting over the last decade has raised promising perspectives in replacing natural antibodies with artificial antibodies. A significant number of reports have been dedicated to imprinting of organic and inorganic nanostructures, but very few were performed on nanomaterials with a transduction function. Herein, a relatively fast and efficient plasmonic hot spot‐localized surface imprinting of gold nanorods using reversible template immobilization and siloxane copolymerization is described. The technique enables a fine control of the imprinting process at the nanometer scale and provides a nanobiosensor with high selectivity and reusability. Proof of concept is established by the detection of neutrophil gelatinase‐associated lipocalin (NGAL), a biomarker for acute kidney injury, using localized surface plasmon resonance spectroscopy. The work represents a valuable step towards plasmonic nanobiosensors with synthetic antibodies for label‐free and cost‐efficient diagnostic assays. It is expected that this novel class of surface imprinted plasmonic nanomaterials will open up new possibilities in advancing biomedical applications of plasmonic nanostructures.

The chemokine receptor CXCR4 is a critical regulator of inflammation and immune surveillance, and it is specifically implicated in cancer metastasis and HIV-1 infection. On the basis of the observation that several of the known antagonists remarkably share a C(2) symmetry element, we constructed symmetric dimers with excellent antagonistic activity using a derivative of a cyclic pentapeptide as monomer. To optimize the binding affinity, we investigated the influence of the distance between the monomers and the pharmacophoric sites in the synthesized constructs. The affinity studies in combination with docking computations support a two-site binding model. In a final step, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was introduced as chelator for (radio-)metals, thus allowing to exploit these compounds as a new group of CXCR4-binding peptidic probes for molecular imaging and endoradiotherapeutic purposes. Both the DOTA conjugates and some of their corresponding metal complexes retain good CXCR4 affinity, and one (68)Ga labeled compound was studied as PET tracer.

The synthesis of M(I)(CO)(3)(NNO) (M = Re, (99m)Tc) complexes conjugated to the antitumor agent 2-(4'-aminophenyl)benzothiazole and to its 6-methyl derivative, as well as their in vitro and in vivo biological evaluation as breast cancer radiopharmaceuticals, is reported. The Re complexes displayed under the fluorescence microscope clear uptake by the sensitive to the 2-(4'-aminophenyl)benzothiazole pharmacophore breast cancer cell lines MCF-7 and T47D, while uptake by less sensitive lines and by normal fibroblasts was much weaker. In accordance, uptake of the corresponding radioactive (99m)Tc complexes was clearly higher in the breast cancer cell lines MCF-7 and MDA-231 compared to normal fibroblasts. Biodistribution of the (99m)Tc complexes in SCID mice bearing MCF-7 xenografts showed appreciable tumor uptake. A tumor/muscle ratio of 2.2 was measured for the complex conjugated to 2-(4'-aminophenyl)benzothiazole that led to successful tumor imaging. The results render the 2-(4'-aminophenyl)benzothiazole complexes potential candidates for imaging ((99m)Tc) and targeted radiotherapy ((188)Re) of breast cancer.

Prostate cancer is one of the most common malignancies for which great progress has been made in identifying appropriate molecular targets that would enable efficient in vivo targeting for imaging and therapy. The type II integral membrane protein, prostate specific membrane antigen (PSMA) is overexpressed on prostate cancer cells in proportion to the stage and grade of the tumor progression, especially in androgen-independent, advanced and metastatic disease, rendering it a promising diagnostic and/or therapeutic target. From the perspective of nuclear medicine, PSMA-based radioligands may significantly impact the management of patients who suffer from prostate cancer. For that purpose, chelating-based PSMA-specific ligands have been labeled with various diagnostic and/or therapeutic radiometals for single-photon-emission tomography (SPECT), positron-emission-tomography (PET), radionuclide targeted therapy as well as intraoperative applications. This review focuses on the development and further applications of metal-based PSMA radioligands.

Gastrin-releasing peptide receptors (GRPrs) are overexpressed on a variety of human cancers, providing the opportunity for peptide receptor targeting via radiolabeled bombesin-based peptides. As part of our ongoing investigations into the development of improved GRPr antagonists, this study aimed at verifying whether and how Nterminal modulations improve the affinity and pharmacokinetics of radiolabeled GRPr antagonists. Methods: The potent GRPr antagonist MJ9, Pip-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH 2 (Pip, 4-amino-1-carboxymethyl-piperidine), was conjugated to 1,4,7-triazacyclononane, 1-glutaric acid-4,7 acetic acid (NODAGA), and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and radiolabeled with 68 Ga and 64 Cu. The GRPr affinity of the corresponding metalloconjugates was determined using 125 I-Tyr 4 -BN as a radioligand. The labeling efficiency of 68 Ga 31 was compared between NODAGA-MJ9 and NOTA-MJ9 in acetate buffer, at room temperature and at 95°C. The 68 Ga and 64 Cu conjugates were further evaluated in vivo in PC3 tumor xenografts by biodistribution and PET imaging studies. Results: The half maximum inhibitory concentrations of all the metalloconjugates are in the high picomolar-low nanomolar range, and these are the most affine-radiolabeled GRPr antagonists we have studied so far in our laboratory. NODAGA-MJ9 incorporates 68 Ga 31 nearly quantitatively (.98%) at room temperature within 10 min and at much lower peptide concentrations (1.4 · 10 −6 M) than NOTA-MJ9, for which the labeling yield was approximately 45% under the same conditions and increased to 75% at 95°C for 5 min. Biodistribution studies showed high and specific tumor uptake, with a maximum of 23.3 ± 2.0 percentage injected activity per gram of tissue (%IA/g) for 68 Ga-NOTA-MJ9 and 16.7 ± 2.0 %IA/g for 68 Ga-NODAGA-MJ9 at 1 h after injection. The acquisition of PET images with the 64 Cu-MJ9 conjugates at later time points clearly showed the efficient clearance of the accumulated activity from the background already at 4 h after injection, whereas tumor uptake still remained high. The high pancreas uptake for all radiotracers at 1 h after injection was rapidly washed out, resulting in an increased tumor-to-pancreas ratio at later time points. Conclusion: We have developed 2 GRPr antagonistic radioligands, which are improved in terms of binding affinity and overall biodistribution profile. Their promising in vivo pharmacokinetic performance may contribute to the improvement of the diagnostic imaging of tumors overexpressing GRPr.

No abstract

The gastrin-releasing peptide receptor (GRPr) is an important molecular target for the visualization and therapy of tumors and can be targeted with radiolabeled bombesin derivatives. The present study aims to develop statine-based bombesin receptor antagonists suitable for labeling with 64Cu for imaging by positron emission tomography (PET). The potent GRPr antagonist D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 was conjugated to the sarcophagine (3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane=Sar) derivative 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid (MeCOSar) via PEG4 (LE1) and PEG2 (LE2) spacers and radiolabeled with 64Cu2+ with >95% yield and specific activities of about 100 MBq/nmol. Both Cu(II) conjugates have high affinity for GRPr (IC50: natCu-LE1, 1.4±0.1 nM; natCu-LE2, 3.8±0.6 nM). The antagonistic properties of both conjugates were confirmed by Ca2+-flux measurements. Biodistribution studies of Cu-64-LE1 exhibited specific targeting of the tumor (19.6±4.7% IA/g at 1 h p.i.) and GRPr-positive organs. Biodistribution and PET images at 4 and 24 h postinjection showed increasing tumor-to-background ratios with time. This was illustrated by the acquisition of PET images showing high tumor-to-normal tissue contrast. This study demonstrates the high affinity of the MeCOSar-PEGx-bombesin conjugates to GRPr. The stability of 64Cu complexes of MeCOSar, the long half-life of 64Cu, and the suitable biodistribution profile of the 64Cu-labeled peptides lead to PET images of high contrast suitable for potential translation into the clinic.