Macrocyclic triamine derived glucose analogues for 99m Tc(CO)3 labeling: synthesis and biological evaluation as potential tumor-imaging agents.

[99m Tc(CO)3 (H2 O)3 ]+ has attracted great attention among 99m Tc-labeling techniques, due to its ease of preparation, readily substituted water molecules of the precursor fac-[99m Tc(CO)3 (H2 O)3 ]+ by a variety of functional groups, small size and inertness. Bifunctional chelator based on a macrocyclic polyamine framework shows easy complexation with [99m Tc(CO)3 (H2 O)3 ]+ to produce stable complex. In this study, two novel 1, 5, 9-triazacyclododecane derivatives containing a glucose group (6 and 7) were successfully synthesized by reacting different glucose-azides with alkyne-[12]aneN3 via the so-called click chemistry and radiolabeled with [99m Tc(CO)3 (H2 O)3 ]+ to form 99m Tc(CO)3 -6 (C-1-substituted complex) and 99m Tc(CO)3 -7 (C-2-substituted complex) in high yields. The complexes were stable in vitro over 6 h when incubated in saline at room temperature and in mouse serum at 37 °C. The partition coefficient results showed that they were hydrophilic. The biodistribution studies in Kunming mice bearing S 180 tumor showed both complexes showed accumulation in the tumor. Between them, 99m Tc(CO)3 -7 had the advantages of much higher tumor uptake and tumor/muscle ratio. Compared with other reported 99m Tc-radiolabeled glucose derivatives, 99m Tc(CO)3 -7 also showed a higher tumor uptake and tumor/muscle ratio, suggesting it would be a potential candidate for further development as a tumor-imaging agent.

A biomarker-responsive T2ex MRI contrast agent.

PURPOSE: This study investigated a fundamentally new type of responsive MRI contrast agent for molecular imaging that alters T2 exchange (T2ex ) properties after interacting with a molecular biomarker. METHODS: The contrast agent Tm-DO3A-oAA was treated with nitric oxide (NO) and O2 . The R1 and R2 relaxation rates of the reactant and product were measured with respect to concentration, temperature, and pH. Chemical exchange saturation transfer (CEST) spectra of the reactant and product were acquired using a 7 Tesla (T) MRI scanner and analyzed to estimate the chemical exchange rates and r2ex relaxivities. RESULTS: The reaction of Tm-DO3A-oAA with NO and O2 caused a 6.4-fold increase in the r2 relaxivity of the agent, whereas r1 relaxivity remained unchanged, which demonstrated that Tm-DO3A-oAA is a responsive T2ex agent. The effects of pH and temperature on the r2 relaxivities of the reactant and product supported the conclusion that the product's benzimidazole ligand caused the agent to have a fast chemical exchange rate relative to the slow exchange rate of the reactant's ortho-aminoanilide ligand. CONCLUSIONS: T2ex MRI contrast agents are a new type of responsive agent that have good detection sensitivity and specificity for detecting a biomarker, which can serve as a new tool for molecular imaging. Magn Reson Med 77:1665-1670, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

A Bone-Seeking trans-Cyclooctene for Pretargeting and Bioorthogonal Chemistry: A Proof of Concept Study Using 99mTc- and 177Lu-Labeled Tetrazines.

A high yield synthesis of a novel, small molecule, bisphosphonate-modified trans-cyclooctene (TCO-BP, 2) that binds to regions of active bone metabolism and captures functionalized tetrazines in vivo, via the bioorthogonal inverse electron demand Diels-Alder (IEDDA) cycloaddition, was developed. A 99mTc-labeled derivative of 2 demonstrated selective localization to shoulder and knee joints in a biodistribution study in normal mice. Compound 2 reacted rapidly with a 177Lu-labeled tetrazine in vitro, and pretargeting experiments in mice, using 2 and the 177Lu-labeled tetrazine, yielded high activity concentrations in shoulder and knee joints, with minimal uptake in other tissues. Pretargeting experiments with 2 and a novel 99mTc-labeled tetrazine also produced high activity concentrations in the knees and shoulders. Critically, both radiolabeled tetrazines showed negligible uptake in the skeleton and joints when administered in the absence of 2. Compound 2 can be utilized to target functionalized tetrazines to bone and represents a convenient reagent to test novel tetrazines for use with in vivo bioorthogonal pretargeting strategies.

Tricarbonyl (99m)Tc(i) and Re(i)-thiosemicarbazone complexes: synthesis, characterization and biological evaluation for targeting bacterial infection.

Methyl, ethyl and phenyl nitrofuryl thiosemicarbazone ligands (, and respectively) were radiolabeled with freshly prepared aqueous solution of a fac[(99m)Tc(CO)3(H2O)3](+) precursor. The radiochemical yield was around 98% as determined by thin layer chromatography and HPLC. The complexes exhibited substantial stability. The corresponding Re(i) complexes were prepared from a Re(CO)5Br precursor to understand the coordination behavior of the ligands against a tricarbonyl rhenium(i) precursor. The rhenium(i) complexes were characterized by means of IR, NMR and mass spectroscopic studies as well as by X-ray crystallography, and correlated with the technetium complexes by means of HPLC studies. Electrochemical reduction of monomeric Re(CO)3-complexes of nitrofuryl ethyl thiosemicarbazone was also studied using cyclic voltammetry. Biodistribution studies of (99m)Tc(CO)3-labeled thiosemicarbazones in rats intramuscularly infected with S. aureus exhibited substantial in vivo stability of the complex and moderate accumulation at the site of focal infection.

99mTc(CO)3-Labeled Benzothiazole Derivatives Preferentially Bind Cerebrovascular Amyloid: Potential Use as Imaging Agents for Cerebral Amyloid Angiopathy.

Cerebral amyloid angiopathy (CAA) is a disorder affecting the elderly that is characterized by amyloid-ß (Aß) deposition in blood vessel walls of the brain. A series of 99mTc(CO)3-labeled benzothiazole derivatives as potential SPECT imaging probes for cerebrovascular Aß deposition is reported. Rhenium surrogate displayed high affinities to Aß aggregates with Ki values ranging from 106 to 42 nM, and they strongly stained Aß deposits in transgenic mice (Tg) and Alzheimer's disease (AD) patients. In vitro autoradiography on brain sections of Tg and AD patients confirmed that [99mTc]24 possessed sufficient affinity for Aß plaques, and [99mTc]24 could only label Aß deposition in blood vessels but not Aß plaques in the parenchyma of the brain of AD patients. Moreover, [99mTc]24 possessed favorable initial uptake (1.21% ID/g) and fast blood washout (blood2 min/blood60 min=23) in normal mice. These preliminary results suggest that [99mTc]24 may be used as an Aß imaging probe for the detection of CAA.

Size Control of (99m)Tc-tin Colloid Using PVP and Buffer Solution for Sentinel Lymph Node Detection.

Colloidal particle size is an important characteristic that allows mapping sentinel nodes in lymphoscintigraphy. This investigation aimed to introduce different ways of making a (99m)Tc-tin colloid with a size of tens of nanometers. All agents, tin fluoride, sodium fluoride, poloxamer-188, and polyvinylpyrrolidone (PVP), were mixed and labeled with (99m)Tc. Either phosphate or sodium bicarbonate buffers were used to adjust the pH levels. When the buffers were added, the size of the colloids increased. However, as the PVP continued to increase, the size of the colloids was controlled to within tens of nanometers. In all samples, phosphate buffer added PVP (30 mg) stabilized tin colloid ((99m)Tc-PPTC-30) and sodium bicarbonate solution added PVP (50 mg) stabilized tin colloid ((99m)Tc-BPTC-50) were chosen for in vitro and in vivo studies. (99m)Tc-BPTC-50 (<20 nm) was primarily located in bone marrow and was then secreted through the kidneys, and (99m)Tc-PPTC-30 (>100 nm) mainly accumulated in the liver. When a rabbit was given a toe injection, the node uptake of (99m)Tc-PPTC-30 decreased over time, while (99m)Tc-BPTC-50 increased. Therefore, (99m)Tc-BPTC-50 could be a good candidate radiopharmaceutical for sentinel node detection. The significance of this study is that nano-sized tin colloid can be made very easily and quickly by PVP.

Size Control of 99mTc-tin Colloid Using PVP and Buffer Solution for Sentinel Lymph Node Detection

Colloidal particle size is an important characteristic that allows mapping sentinel nodes in lymphoscintigraphy. This investigation aimed to introduce different ways of making a 99mTc-tin colloid with a size of tens of nanometers. All agents, tin fluoride, sodium fluoride, poloxamer-188, and polyvinylpyrrolidone (PVP), were mixed and labeled with 99mTc. Either phosphate or sodium bicarbonate buffers were used to adjust the pH levels. When the buffers were added, the size of the colloids increased. However, as the PVP continued to increase, the size of the colloids was controlled to within tens of nanometers. In all samples, phosphate buffer added PVP (30 mg) stabilized tin colloid (99mTc-PPTC-30) and sodium bicarbonate solution added PVP (50 mg) stabilized tin colloid (99mTc-BPTC-50) were chosen for in vitro and in vivo studies. 99mTc-BPTC-50 (100 nm) mainly accumulated in the liver. When a rabbit was given a toe injection, the node uptake of 99mTc-PPTC-30 decreased over time, while 99mTc-BPTC-50 increased. Therefore, 99mTc-BPTC-50 could be a good candidate radiopharmaceutical for sentinel node detection. The significance of this study is that nano-sized tin colloid can be made very easily and quickly by PVP.

Oxidative remobilization of technetium sequestered by sulfide-transformed nano zerovalent iron.

Our previous study showed that formation of TcS2-like phases is favored over TcO2 under sulfidic conditions stimulated by nano zerovalent iron. This study further investigates the stability of Tc(IV) sulfide upon reoxidation by solution chemistry, solid phase characterization, and X-ray absorption spectroscopy. Tc dissolution data showed that Tc(VII) reduced by sulfide-transformed nZVI has substantially slower reoxidation kinetics than Tc(VII) reduced by nZVI only. The initial inhibition of Tc(IV) dissolution at S/Fe = 0.112 is due to the redox buffer capacity of FeS, which is evidenced by the parallel trends in oxidation-reduction potentials (ORP) and Tc dissolution kinetics. The role of FeS in inhibiting Tc oxidation is further supported by the Mössbauer spectroscopy and micro X-ray diffraction data at S/Fe = 0.112, showing persistence of FeS after 24-h oxidation but complete oxidation after 120-h oxidation. X-ray absorption spectroscopy data for S/Fe = 0.011 showed significantly increasing percentages of TcS2 in the solid phase after 24-h oxidation, indicating stronger resistance of TcS2 to oxidation. At S/Fe = 0.112, the XAS results revealed significant transformation of Tc speciation from TcS2 to TcO2 after 120-h oxidation. Given that no apparent Tc dissolution occurred during this period, the speciation transformation might play a secondary role in hindering Tc oxidation. Collectively, the results indicate that sequestrating Tc as TcS2 under stimulated sulfate reduction is a promising strategy to improve the long-term stability of reduced Tc in subsurface remediation.

Possibilities of optical imaging of the (99m)Tc-based radiopharmaceuticals.

In vivo optical imaging is widely used in preclinical studies. Recently, the application of optical imaging systems for preclinical visualization of gamma-emitting isotopes has become of interest since the evaluation of various organs relies on (99m)Tc-based radiopharmaceuticals (RPs). In vitro radioluminescence of (99m)Tc-based RPs, including pertechnetate, albumin macroaggregates, dimercaptosuccinic acid, phytate colloid, and ethylenediamine tetramethylene phosphonic acid, was studied with IVIS Spectrum CT™ optical imaging system. The distribution of phytate colloid was also studied in vivo with and without scintillating materials and the results were compared with those obtained with a conventional scintigraphy. The visible light emission appeared to be due to the radioluminescence of water and luminophores contained in RPs rather than from Cherenkov radiation. Weak air luminescence affected the background. The radioluminescence of fluids induced by (99m)Tc-based tracers could be detected using charge-coupled device optical imaging systems. The radioluminescence intensity and its spectral distribution depend on the surrounding fluid and known luminophores present. Thus, in some cases the in vivo optical imaging is possible but the use of scintillator, e.g., borosilicate glass or bismuth germanate, is preferred.

Synthesis and biological evaluation of technetium-99m labeled galactose derivatives as potential asialoglycoprotein receptor probes in a hepatic fibrosis mouse model.

Two galactose derivatives, a monovalent (99m)Tc-MAMA-MGal galactoside and a divalent (99m)Tc-MAMA-DGal galactoside, were synthesized and radiolabeled in high radiochemical purity (>98%). Dynamic microSPECT imaging and biodistribution study of two traces in normal and liver fibrosis mice showed that the (99m)Tc-MAMA-DGal revealed higher specific binding to asialoglycoprotein receptors in liver and then rapidly excreted via both hepatobiliary system and renal clearance. The results suggest that (99m)Tc-MAMA-DGal may be used as SPECT probes for noninvasive evaluation of asialoglycoprotein receptor-related liver dysfunction.

ß-Technetium dichloride: solid-state modulated structure, electronic structure, and physical properties.

A second polymorph of technetium dichloride, ß-TcCl2, has been synthesized from the reaction of Tc metal and chlorine in a sealed tube at 450 °C. The crystallographic structure and physical properties of ß-TcCl2 have been investigated. The structure of ß-TcCl2 consists of infinite chains of face sharing [Tc2Cl8] units; within a chain, the Tc≡Tc vectors of two adjacent [Tc2Cl8] units are ordered in the long-range where perpendicular and/or parallel arrangement of Tc≡Tc vectors yields a modulated structure. Resistivity and Seebeck measurements performed on a ß-TcCl2 single crystal indicate the compound to be a p-type semiconductor while a magnetic susceptibility measurement shows technetium dichloride to be diamagnetic. A band gap of 0.12(2) eV was determined by reflectance spectroscopy measurements. Theoretical calculations at the density functional level were utilized for the investigation of other possible stable forms of TcCl2.

99mTc-(Me)FGCDEVD, a potential tracer for apoptosis detection.

(Me)FGC(Bz)DEVD was radiolabeled with technetium-99m in high yield. This tracer was preferentially accumulated in apoptotic cells in the in vitro studies. Tumor uptake occurred in vivo after cisplatin injection due to the apoptosis induction, which not observed in the untreated tumors. Therefore, (99m)Tc-(Me)FGCDEVD is a potential tracer for apoptosis detection.

Synthetic precursors for TCNQF4(2-) compounds: synthesis, characterization, and electrochemical studies of (Pr4N)2TCNQF4 and Li2TCNQF4.

Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF(4) and Li(2)TCNQF(4) to be achieved. Reaction of LiI with TCNQF(4), in a 4:1 molar ratio, in boiling acetonitrile yields Li(2)TCNQF(4). However, deviation from this ratio or the reaction temperature gives either LiTCNQF(4) or a mixture of Li(2)TCNQF(4) and LiTCNQF(4). This is the first report of the large-scale chemical synthesis of Li(2)TCNQF(4). Attempts to prepare a single crystal of Li(2)TCNQF(4) have been unsuccessful, although air-stable (Pr(4)N)(2)TCNQF(4) was obtained by mixing Pr(4)NBr with Li(2)TCNQF(4) in aqueous solution. Pr(4)NTCNQF(4) was also obtained by reaction of LiTCNQF(4) with Pr(4)NBr in water. Li(2)TCNQF(4), (Pr(4)N)(2)TCNQF(4), and Pr(4)NTCNQF(4) have been characterized by UV-vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr(4)N)(2)TCNQF(4) and Pr(4)NTCNQF(4) have been determined by X-ray crystallography. These TCNQF(4)(2-) salts will provide useful precursors for the synthesis of derivatives of the dianions.

[Re(CO)(3)](+) labelling of a novel cysteine/hexahistidine tag: insights into binding mode by liquid chromatography-mass spectrometry.

We recently described a novel amino acid sequence, KCKLAAALEHHHHHH, for site-specific radiolabelling of proteins with [(99m)Tc(CO)(3)(OH(2))(3)](+) or [Re(CO)(3)(OH(2))(3)](+) with improved efficiency compared to conventional hexahistidine tags (His-tag). C2AH, a modification of the protein C2A (the phosphatidylserine (PS)-binding domain of rat synaptotagmin I) engineered to contain this novel C-terminal tag, was produced. Rhenium tricarbonyl conjugates of C2AH were analysed post tryptic digest by liquid chromatography-electrospray mass spectrometry (LC-MS), giving rise to a peak with the molecular weight corresponding to M(+)=[Re(CO)(3)+CK+LAAALEHHHHHH](+). This species arises as a result of trypsin cleavage on the C-terminus of both the lysine (Lys) residues on either side of the Cys while both fragments still remain bound to the rhenium. This confirmed that cysteine (Cys) was directly involved in the coordination of the rhenium tricarbonyl. To demonstrate the superiority of the cysteine containing His-tag sequences for binding [Re(CO)(3)](+), two peptides CKLAAALEHHHHHH and LAAALEHHHHHH were synthesised. In a competition experiment the mixed peptides were incubated with one molar equivalent of [Re(CO)(3)(H(2)O)(3)](+), and LC-ESMS demonstrated that 92% and 9% of CKLAAALEHHHHHH and LAAALEHHHHHH respectively were co-ordinated by one [Re(CO)(3)](+).

PEGylation and biodistribution of an anti-MUC1 aptamer in MCF-7 tumor-bearing mice.

Aptamers are characterized by a rapid renal clearance leading to a short in vivo circulating half-life. In order to use aptamers as anticancer therapeutic agents, their exposure time to the tumor has to be enhanced via increasing residency in the bloodstream. A way to achieve this goal is by conjugating the aptamer to poly(ethylene glycol) (PEG). Herein, we present the conjugation of a bifunctionalized anti-MUC1 aptamer (NH(2)-AptA-SR) with the (99m)Tc coordinating moiety MAG2 and either a conventional branched PEG or the comb-shaped PolyPEG via a two-step synthesis. The isolated products were radiolabeled with (99m)Tc and their biodistribution and tumor-targeting properties in MCF-7 tumor bearing mice were analyzed and compared.

Radiotracers for different angiogenesis receptors in a melanoma model.

Early and reliable diagnosis of melanoma, a skin tumor with a poor prognosis, is extremely important. Phage display peptide libraries are a convenient screening resource for identifying bioactive peptides that interact with cancer targets. The aim of this study was to evaluate two technetium-99m tracers for angiogenesis detection in a melanoma model, using cyclic pegylated pentapeptide with RGD and NGR motifs conjugated with the bifunctional chelator mercaptoacetyltriglycine (MAG(3)). The conjugated peptides (10 µl of a µg/µl solution) were labeled with technetium-99m using a sodium tartrate buffer. Radiochemical evaluation was carried out by instant thin-layer chromatography and confirmed by high-performance liquid chromatography. The partition coefficient was determined and internalization assays were performed in two melanoma cell lines (B16F10 and SKMEL28). Biodistribution evaluation of the tracers was carried out in healthy animals at different time points and also in tumor-bearing mice, 120 min post injection. Blocking studies were also conducted by coinjection of cold peptides. The conjugates displayed a rather similar pharmacokinetic profile. They were radiolabeled with high radiochemical purity (>97%) and both were hydrophilic with preferential renal excretion. Yet, tumor uptake was higher for human than for murine melanoma cells, especially for [(99m)Tc]-MAG(3)-PEG(8)-c(RGDyk) (7.85±2.34%injected dose/g 120 min post injection). The performance of [(99m)Tc]-MAG(3)-PEG(8)-c(RGDyk) was better than the NGR tracer with regard to human melanoma uptake. In this sense, it should be considered for future radiotracer studies of tumor diagnosis.

Selective polarographic determination of stannous ion in technetium radiopharmaceutical cold kits.

UNLABELLED: The aim of this work was to develop a selective method for quantification of Sn(II) and Sn(IV) in dimercaptosuccinic acid (DMSA), ethylcysteinate dimer (ECD), methylenediphosphonic acid (MDP), and pyrophosphate radiopharmaceutical cold kits by differential pulse polarography. METHODS: A dripping mercury electrode 150 polarographic/stripping analyzer with a conventional 3-electrode configuration was used with 3 M H(2)SO(4) and 3 M HCl supporting electrolytes for Sn(II) and Sn(IV), respectively. The polarographic analysis was performed using a 1-s drop time, 50-mV·s(-1) scan rate, -50-mV pulse amplitude, 40-ms pulse time, and 10-mV step amplitude. To quantify Sn(IV), oxidation of Sn(II) by H(2)O(2) was performed. The calibration curves for Sn(II) and Sn(IV) were obtained in the range of 0-10 µg·mL(-1). RESULTS: The analytic curves for Sn(II) in 3 M H(2)SO(4) and Sn(IV) in 3 M HCl were represented by the following equations: i (µA) = 0.098 [Sn(II)] + 0.018 (r(2) = 0.998) and i (µA) = 0.092 [Sn(IV)] + 0.016 (r(2) = 0.998), respectively. The detection limits were 0.21 µg·mL(-1) for Sn(II) and 0.15 µg·mL(-1) for Sn(IV). In DMSA, ECD, MDP, and pyrophosphate, 90.0%, 64.9%, 93.2%, and 87.5%, respectively, of the tin was present as Sn(II). In this work, selective determination of Sn(II) and Sn(IV) was achieved using 2 supporting electrolytes (H(2)SO(4) and HCl). In 3 M H(2)SO(4), only Sn(II) produced a polarographic wave with the maximum current in -370 mV. Under the same conditions, no current could be determined for Sn(IV). In 3 M HCl, Sn(II) and Sn(IV) were electroactive and the maximum currents of the 2 waves appeared in -250 and -470 mV. No other components of the lyophilized reagents had any influence. CONCLUSION: The developed polarographic method was adequate to quantify Sn(II) and Sn(IV) in DMSA, ECD, MDP, and pyrophosphate cold kits.

Technetium dichloride: a new binary halide containing metal-metal multiple bonds.

Technetium dichloride has been discovered. It was synthesized from the elements and characterized by several physical techniques, including single crystal X-ray diffraction. In the solid state, technetium dichloride exhibits a new structure type consisting of infinite chains of face sharing [Tc(2)Cl(8)] rectangular prisms that are packed in a commensurate supercell. The metal-metal separation in the prisms is 2.127(2) Å, a distance consistent with the presence of a Tc≡Tc triple bond that is also supported by electronic structure calculations.

Dissolution of technetium(IV) oxide by natural and synthetic organic ligands under both reducing and oxidizing conditions.

Technetium-99 (Tc) in nuclear waste is a significant environmental concern due to its long half-life and high mobility in the subsurface. Reductive precipitation of technetium(IV) oxides [TcO(2)(s)] is an effective means of immobilizing Tc, thereby impeding its migration in groundwater. However, technetium(IV) oxides are subject to dissolution by oxidants and/or complexing agents. In this study we ascertain the effects of a synthetic organic ligand, ethylenediaminetetraacetate (EDTA), and two natural humic isolates on the dissolution and solubility of technetium(IV) oxides. Pure synthetic technetium(IV) oxide (0.23 mM) was used in batch experiments to determine dissolution kinetics at pH ∼6 under both reducing and oxidizing conditions. All organic ligands were found to enhance the dissolution of technetium(IV) oxides, increasing their solubility from ∼10(-8) M (without ligands) to 4 × 10(-7) M under strictly anoxic conditions. Reduced Tc(IV) was also found to reoxidize rapidly under oxic conditions, with an observed oxidative dissolution rate approximately an order of magnitude higher than that of ligand-promoted dissolution under reducing conditions. Significantly, oxidative dissolution was inhibited by EDTA but enhanced by humic acid compared to experiments without any complexing agents. The redox functional properties of humics, capable of facilitating intramolecular electron transfer, may account for this increased oxidation rate under oxic conditions. Our results highlight the importance of complex interactions for the stability and mobility of Tc and thus for the long-term fate of Tc in contaminated environments.

Metal complex mediated conjugation of peptides to nucleus targeting acridine orange: a modular concept for dual-modality imaging agents.

To target the nucleus of specific cells, trifunctional radiopharmaceuticals are required. We have synthesized acridine orange derivatives which comprise an imidazole-2-carbaldehyde function for coordination to the [Re(CO)3](+) or [(99m)Tc(CO)3](+) core. Upon coordination, this aldehyde is activated and rapidly forms imines with amines from biological molecules. This metal-mediated imine formation allows for the conjugation of a nuclear targeting portion with a specific cell receptor binding function directly on the metal. With this concept, we have conjugated the acridine orange part to a bombesin peptide directly on the (99m)Tc core and in one step. In addition, a linker containing an integrated disulfide has been coupled to bombesin. LC/MS study showed that the disulfide was reductively cleaved with a 60 min half-life time. This concept enables the combination of a nucleus targeting agent with a specific cell receptor molecule directly on the metal without the need of separate conjugation prior to labeling, thus, a modular approach. High uptake of the BBN conjugate into PC-3 cells was detected by fluorescence microscopy, whereas uptake into B16BL6 cells was negligible.