Publications (68) View all
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Article: An Efficient Bioorthogonal Strategy Using CuAAC Click Chemistry for Radiofluorinations of SNEW Peptides and the Role of Copper Depletion.
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ABSTRACT: The EphB2 receptor is known to be overexpressed in various types of cancer and is therefore a promising target for tumor cell imaging by positron emission tomography (PET). In this regard, imaging could facilitate the early detection of EphB2-overexpressing tumors, monitoring responses to therapy directed toward EphB2, and thus improvement in patient outcomes. We report the synthesis and evaluation of several fluorine-18-labeled peptides containing the SNEW amino acid motif, with high affinity for the EphB2 receptor, for their potential as radiotracers in the non-invasive imaging of cancer using PET. For the purposes of radiofluorination, EphB2-antagonistic SNEW peptides were varied at the C terminus by the introduction of L-cysteine, and further by alkyne- or azide-modified amino acids. In addition, two novel bifunctional and bioorthogonal labeling building blocks [(18) F]AFP and [(18) F]BFP were applied, and their capacity to introduce fluorine-18 was compared with that of the established building block [(18) F]FBAM. Copper-assisted Huisgen 1,3-dipolar cycloaddition, which belongs to the set of bioorthogonal click chemistry reactions, was used to introduce both novel building blocks into azide- or alkyne-modified SNEW peptides under mild conditions. Finally, the depletion of copper immediately after radiolabeling is a highly important step of this novel methodology.ChemMedChem 04/2013; · 3.15 Impact Factor -
Article: Synthesis, in silico, in vitro, and in vivo investigation of 5-[(11)C]methoxy-substituted sunitinib, a tyrosine kinase inhibitor of VEGFR-2.
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ABSTRACT: Sunitinib(®) (SU11248) is a highly potent tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR). Radiolabeled inhibitors of receptor tyrosine kinases (RTKs) might be useful tools for monitoring RTKs levels in tumor tissue giving valuable information for anti-angiogenic therapy. Herein we report the synthesis of 5-methoxy-sunitinib 5 and its (11)C-radiolabeled analog [(11)C]-5. The non-radioactive reference compound 5 was prepared by Knoevenagel condensation of 5-methoxy-2-oxindole with the corresponding substituted 5-formyl-1H-pyrrole. A binding constant (K(d)) of 20 nM for 5 was determined by competition binding assay against VEGFR-2. In addition, the binding mode of sunitinib(®) and its 5-methoxy substituted derivative was studied by flexible docking simulations. These studies revealed that the substitution of the fluorine at position 5 of the oxindole scaffold by a methoxy group did not affect the inhibitor orientation, but affected the electrostatic and van der Waals interactions of the ligand with residues near the DFG motif of VEGFR-2. 5-[(11)C]methoxy-sunitinib ([(11)C]-5) was synthesized by reaction of the desmethyl precursor with [(11)C]CH(3)I in the presence of DMF and NaOH in 17 ± 3% decay-corrected radiochemical yield at a specific activity of 162-205 GBq/μmol (EOS). In vivo stability studies of [(11)C]-5 in rat blood showed that more than 70% of the injected compound was in blood stream, 60 min after administration.European journal of medicinal chemistry 10/2012; 58C:272-280. · 3.27 Impact Factor -
Article: Fluorine-18 Radiolabeling and Radiopharmacological Characterization of a Benzodioxolylpyrimidine-based Radiotracer Targeting the Receptor Tyrosine Kinase EphB4.
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ABSTRACT: Members of the Eph receptor tyrosine kinase family play essential roles in the pathogenesis of cancer and are therefore promising candidates for molecular imaging by positron emission tomography (PET), for example. In this regard, radiochemical access to novel PET radiotracers derived from potent inhibitors that target the EphB4 kinase domain and which bear a benzodioxolylpyrimidine structural motif was developed. A synthetic route was established for a new fluorine-18-containing radiotracer and for the desired precursor based on a high-affinity benzodioxolylpyrimidine receptor tyrosine kinase inhibitor lead structure. The radiotracer [(18) F]15 was obtained in 16 % radiochemical yield with a specific activity of ~7 GBq μmol(-1) and >95 % radiochemical purity. Due to the implication of EphB4, particularly in the progression, angiogenesis, and metastasis of melanoma, EphB4-overexpressing human melanoma cells were generated and used as a novel in vitro model for radiopharmacological evaluation of the radiotracer. We demonstrate that the corresponding non-radioactive reference compound regained its functionality as an inhibitor for both EphB4 receptor tyrosine kinase and Src kinase. EphB4 was significantly inhibited at compound concentrations >1 μM. Cellular uptake studies with [(18) F]15 revealed substantial uptake in both EphB4-overexpressing and control cells. Moreover, NMRI nu/nu mice bearing both EphB4-overexpressing tumors and control tumors were used for radiopharmacological characterization by biodistribution studies ex vivo and by dynamic small-animal PET experiments in vivo. Despite the high metabolic stability of the novel radiotracer observed in vivo, no substantial binding or accumulation in EphB4-overexpressing and control tumors was observed. Nevertheless, we point out that the approach presented herein gives convenient access to novel (18) F-labeled benzodioxolylpyrimidines and is a promising strategy for the further development of novel radiotracers for imaging Eph receptor tyrosine kinases in cancer.ChemMedChem 10/2012; 7:1991. · 3.15 Impact Factor -
Article: Cerebral blood flow quantification in the rat: a direct comparison of arterial spin labeling MRI with radioactive microsphere PET.
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ABSTRACT: BACKGROUND: Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognized as a valuable method for non-invasive assessment of cerebral blood flow (CBF) but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. We have conducted the present study with the aim of comparing ASL flow-sensitive alternating inversion recovery (FAIR) derived unidirectional water uptake (K1) and Ga-68 / Cu-64 -microsphere (MS) derived blood flow (f) in the rat brain. METHODS: In 15 animals, K1 and f were determined successively in dedicated small animal positron emission tomography (PET) and MR scanners. The Renkin-Crone model modified by a scaling factor was used for quantification of f and K1. RESULTS: Below about 1 mL/min/mL we obtain an approximately linear relationship between f and K1. At higher flow values the limited permeability of water at the blood brain barrier (BBB) becomes apparent. Within the accessed dynamic flow range (0.2 - 1.9 mL/min/mL) the data are adequately described by the Renkin-Crone model yielding a permeability surface area (PS) product of (1.53 +/- 0.46) mL/min/mL. CONCLUSION: The ASL-FAIR technique is suitable for absolute blood flow quantification in the rat brain when using a one-compartment model including a suitable extraction correction for data evaluation.EJNMMI research. 09/2012; 2(1):47. -
Article: (18)F-Labeled phosphopeptide-cell-penetrating peptide dimers with enhanced cell uptake properties in human cancer cells.
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ABSTRACT: Phosphopeptides represent interesting compounds to study and elucidate cellular protein phosphorylation/dephosphorylation processes underlying various signal transduction pathways. However, studies of phosphopeptide action in cells are severely constrained by the negatively charged phosphate moiety of the phosphopeptide resulting in poor transport through the cell membrane. The following study describes the synthesis and radiopharmacological evaluation of two (18)F-labeled phosphopeptide-cell-penetrating peptide dimers. The polo-like kinase-1-binding hexaphosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH was coupled to cell-penetrating peptides (CPPs), either sC18, a cathelicidin-derived peptide, or the human calcitonin derivative hCT(18-32)-k7. Radiolabeling was accomplished with the prosthetic group N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB) using both, conventional and microfluidic-based bioconjugation of [(18)F]SFB to N-terminal end of phosphopeptide part of the peptide dimers. Cellular uptake studies in human cancer cell lines HT-29 and FaDu cells at 4 °C and 37 °C and small animal PET in BALB/c mice were utilized for radiopharmacological characterization. Isolated radiochemical yields ranged from 2% to 4% for conventional bioconjugation with [(18)F]SFB. Significantly improved isolated radiochemical yields of up to 26% were achieved using microfluidic technology. Cellular uptake studies of radiolabeled phosphopeptide and phosphopeptide-CPP dimers indicate enhanced internalization of 50% ID/mg protein after 2 h for both phosphopeptide dimers compared to the phosphopeptide alone (<1% ID/mg protein). In vivo biodistribution of (18)F-labeled peptide dimers was determined with small animal PET revealing a superior biodistribution pattern of sC18-containing peptide dimer MQSpTPL-sC18 [(18)F]4. ([18)F]SFB labeling of the phosphopeptide-CPP dimers using a microfluidic system leads to an improved chemoselectivity towards the N-terminal NH(2) group compared to the conventional labeling approach. Cell-penetrating peptide sC18 can be considered as an ideal molecular shuttle for intracellular delivery of the Plk1-PBD-binding hexaphosphopeptide as demonstrated by its favourable radiopharmacological profile.Nuclear Medicine and Biology 07/2012; 39(8):1202-12. · 3.02 Impact Factor
