177Lu‐labeled monomeric,dimeric and multimeric RGD peptides for the therapy of tumors expressing α(ν)β(3) integrins

The conjugation of peptides to gold nanoparticles (AuNPs) produces biocompatible and stable multimeric systems with target‐specific molecular recognition. Peptides based on the cyclic Arg‐Gly‐Asp (RGD) sequence have been reported as high‐affinity agents for the α(ν)β(3) integrin. The aim of this research was to prepare a multimeric system of ¹⁷⁷Lu‐labeled gold nanoparticles conjugated to c(RGDfK)C (cyclo(Arg‐Gly‐Asp‐Phe‐Lys)Cys) and to compare the radiation‐absorbed dose with that of ¹⁷⁷Lu‐labeled monomeric and dimeric RGD peptides to α(ν)β(3) integrin‐positive U87MG tumors in mice. DOTA‐GGC (1,4,7,10‐tetraazacyclododecane‐N‐N′,N″,N?‐tetraacetic acid‐Gly‐Gly‐Cys) and c(RGDfK)C peptides were synthesized and conjugated to AuNPs by a spontaneous reaction of the thiol groups. Transmission electron microscopy, ultraviolet–visible, X‐ray photoelectron spectroscopy, Raman and far‐infrared spectroscopy techniques demonstrated that AuNPs were functionalized with the peptides. For the ¹⁷⁷Lu‐AuNP‐c(RGDfK)C to be obtained, the ¹⁷⁷Lu‐DOTA‐GGC radiopeptide was first prepared and added to a solution of AuNPs followed by c(RGDfK)C (25 µl, 5 µ m ) at 18 °C for 15 min. ¹⁷⁷Lu‐DOTA‐GGC, ¹⁷⁷Lu‐DOTA‐cRGDfK and ¹⁷⁷Lu‐DOTA‐E‐c(RGDfK)₂ were prepared by adding ¹⁷⁷LuCl₃ (370 MBq) to 5 µl (1 mg/ml) of the DOTA derivative diluted with 50 µl of 1 m acetate buffer pH 5. The mixture was incubated at 90 °C in a block heater for 30 min. Radiochemical purity was determined by ultrafiltration and HPLC analyses. Biokinetic studies were accomplished in athymic mice with U87MG‐induced tumors. The radiochemical purity for all ¹⁷⁷Lu‐RGD derivatives was 96 ± 2%. ¹⁷⁷Lu‐absorbed doses per injected activity delivered to U87MG tumors were 0.357 ± 0.052 Gy/MBq (multimer), 0.252 ± 0.027 Gy/MBq (dimer) and 0.102 ± 0.018 Gy/MBq (monomer). ¹⁷⁷Lu‐labeled dimeric and multimeric RGD peptides demonstrated properties suitable for targeted radionuclide therapy of tumors expressing α(ν)β(3) integrins. Copyright © 2012 John Wiley & Sons, Ltd.     

Radiolabeling and in vitro evaluation of a new 5‐fluorouracil derivative with cell culture studies

The clinical impact and accessibility of ^99mTc tracers for cancer diagnosis would be greatly enhanced by the availability of a new, simple, and easy labeling process and radiopharmaceuticals. 5‐Fluorouracil is an antitumor drug, which has played an important role for the treatment of breast carcinoma. In the present study, a new derivative of 5‐Fluorouracil was synthesized as (1‐[{1′‐(1′′‐deoxy‐2′′,3′′:4′′,5′′‐di‐O‐isopropylidene‐β‐D‐fructopyranose‐1′′‐yl)‐1′H‐1′,2′, 3′‐triazol‐4′‐yl}methyl]‐5‐fluorouracil) ( E ) and radiolabeled with ^99mTc. It was analyzed by radio thin layer chromatography for quality control and stability. The radiolabeled complex was subjected to in vitro cell‐binding studies to determine healthy and cancer cell affinity using HaCaT and MCF‐7 cells, respectively. In addition, in vitro cytotoxicity studies of compound E were performed with HaCaT and MCF‐5 cells. The radiochemical purity of the [^99mTc]Tc E was found to be higher than 90% at room temperature up to 6 hours. The radiolabeled complex showed higher specific binding to MCF‐7 cells than HaCaT cells. IC₅₀ values of E were found 31.5 ± 3.4 μM and 20.7 ± 2.77 μM for MCF‐7 and HaCaT cells, respectively. The results demonstrated the potential of a new radiolabeled E with ^99mTc has selective for breast cancer cells.     

Design of 99mTc‐DTPA‐CLP and Preliminary Evaluation in Rats

Radiopharmaceuticals are localized in (malignant) tumor tissues by different mechanisms. One of these mechanisms, gelatinase enzyme activity, is associated with poor prognosis in cancer patients and potential targets for tumor imaging. There are some gelatinases to be associated with metastatic potential for tumor imaging to possibly predict metastases. In this study, a cyclic decapeptide conjugate, DTPA‐CLP (DTPA‐Cys‐Leu‐Pro‐Gly‐His‐Trp‐Gly‐Phe‐Pro‐Ser‐Cys), was selected as a peptide conjugate because of its selective inhibitory activity toward gelatinases. Peptide‐conjugated DTPA‐CLP was labeled with ^99mTc with a radiolabeling efficiency of 97.0 ± 2.8%. After determining optimization conditions for radiolabeling, a biodistribution study of radiolabeled peptide in albino Wistar rats was performed. According to biodistribution data, ^99mTc‐DTPA‐CLP showed high uptake in the lung, liver, uterus, and spleen. These results show that ^99mTc‐DTPA‐CLP may be used for the imaging of gelatinase activity in metastatic tumors.     

Preparation and comparative evaluation of 99mTc‐HYNIC‐cNGR and 99mTc‐HYNIC‐PEG2‐cNGR as tumor‐targeting molecular imaging probes

The tripeptide sequence asparagine‐glycine‐arginine (NGR) specifically recognizes aminopeptidase N (APN or CD13) receptors highly expressed on tumor cells and vasculature. Thus, NGR peptides can precisely deliver therapeutic and diagnostic compounds to CD13 expressing cancer sites. In this regard, 2 NGR peptide ligands, HYNIC‐c(NGR) and HYNIC‐PEG₂‐c(NGR), were synthesized, radiolabeled with ^99mTc, and evaluated in CD13‐positive human fibrosarcoma HT‐1080 tumor xenografts. The radiotracers, ^99mTc‐HYNIC‐c(NGR) and ^99mTc‐HYNIC‐PEG₂‐c(NGR), could be prepared in approximately 95% radiochemical purity and exhibited excellent in vitro and in vivo stability. The radiotracers were hydrophilic in nature with log P values being ?2.33 ± 0.05 and ?2.61 ± 0.08. The uptake of 2 radiotracers ^99mTc‐HYNIC‐c(NGR) and ^99mTc‐HYNIC‐PEG₂‐c(NGR) was similar in nude mice bearing human fibrosarcoma HT‐1080 tumor xenografts, which was significantly reduced (P < .05) during blocking studies. The 2 radiotracers being hydrophilic cleared rapidly from blood, liver, and intestine and were excreted through renal pathway. The pharmacokinetics of ^99mTc‐labeled HYNIC peptide could not be modulated through introduction of PEG₂ unit, thus posing a challenge for studies with other linkers towards enhanced tumor uptake and retention.     

99mTc‐(EDDA/tricine)‐HYNIC‐GnRH analogue as a potential imaging probe for diagnosis of prostate cancer

Prostate cancer is a serious threat to men's health, so it is necessary to develop the techniques for early detection of this malignancy. Radiolabeled peptides are the useful tools for diagnosis of prostate cancer. In this research, we designed a new HYNIC‐conjugated GnRH analogue and labeled it by ^99mTc with tricine/EDDA as coligands. We used aminohexanoic acid (Ahx) as a hydrocarbon linker to generate ^99mTc‐(tricine/EDDA)‐HYNIC‐Ahx‐[DLys⁶]GnRH. The radiopeptide exhibited high radiochemical purity and stability in solution and serum. Two human prostate cancer cell lines LN‐CaP and DU‐145 were used for cellular experiments. The binding specificity and affinity of radiopeptide for LN‐CaP were superior to DU‐145 cells. The K_d values for LN‐CaP and DU‐145 cells were 41.91 ± 7.03 nM and 55.96 ± 10.56 nM, respectively. High kidney uptake proved that the main excretion route of radiopeptide was through the urinary system. The tumor/muscle ratio of ^99mTc‐HYNIC‐Ahx‐[DLys⁶]GnRH was 4.14 at 1 hr p.i. that decreased to 2.41 at 4 hr p.i. in LN‐CaP tumor‐xenografted nude mice. The blocking experiment revealed that the tumor uptake was receptor‐mediated. The lesion was visualized clearly using ^99mTc‐[DLys⁶]GnRH at 1 hr p.i. Accordingly, this research highlights the capability of ^99mTc‐(tricine/EDDA)‐HYNIC‐Ahx‐[DLys⁶]GnRH peptide as a promising agent for GnRHR‐expressing tumor imaging.     

99mTc‐HYNIC‐(Ser)3‐J18 peptide: A radiotracer for non‐small‐cell lung cancer targeting

Radiolabeled peptide could be a useful tool for the diagnosis of non‐small‐cell lung cancer (NSCLC). In this study, HYNIC‐(Ser)₃‐J18 peptide was labeled with ^99mTc using EDDA/tricine as coligands. The in vitro and in vivo studies of this radiolabeled peptide were performed for cellular‐specific binding and tumor targeting in A‐549 cells and tumor‐bearing mice, respectively. The high radiochemical purity was obtained and this radiolabeled peptide exhibited high stability in buffer and serum. The radiolabeled peptide showed high affinity for the A‐549 cells with a dissociation constant value (K_D) of 4.4 ± 0.8 nm . The tumor–muscles ratios were 2.7 and 4.4 at 1 and 2 hr after injection of ^99mTc‐(EDDA/tricine)‐HYNIC‐(Ser)₃‐J18 in tumor‐bearing mice. The tumor uptake was decreased after preinjection with non‐labeled peptide for this radiolabeled peptide in blocking experiment. The results of this study showed the ^99mTc‐(EDDA/tricine)‐(Ser)₃‐HYNIC‐J18 peptide might be a promising radiolabeled peptide for NSCLC targeting.     

Synthesis and evaluation of 2‐, 4‐, 5‐substituted nitroimidazole‐iminodiacetic acid‐99mTc(CO)3 complexes to target hypoxic tumors

Determination of hypoxia in tumor is an important problem in the clinical management of cancer. Towards this, a series of differently substituted nitroimidazoles, viz. 2‐nitro, 4‐nitro and 5‐nitroimidazole iminodiacetic acid (IDA) derivatives were synthesized and radio‐labeled with a [^99mTc(CO)₃(H₂O)₃]⁺ core. The corresponding ^185/187Re(CO)₃ analogue of 2‐nitroimidazole‐IDA‐^99mTc(CO)₃ complex was also prepared and characterized to elucidate the mode of bonding between the ligand and the M(CO)₃ core (M=^99mTc, ^185/187Re). All the three nitroimidazole‐IDA‐^99mTc(CO)₃ complexes could be prepared in over 95% yield determined by HPLC. The three complexes were then evaluated in a suitable animal model bearing tumor. Though the in vivo accumulation of complexes in hypoxic tissue is governed by factors such as lipophilicity, charge, etc., the variation in accumulation in hypoxic tissue, in the present case, could be explained by considering the reported values of single electron reduction potential of the respective nitroimidazoles. Among the three derivatives studied, the 2‐nitroimidazole‐IDA‐^99mTc(CO)₃ complex produced the best result followed by the 5‐nitroimidazole complex. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of a 99mTc‐labelled meso‐bisphenylporphyrin as a tumour image agent

Porphyrins are excellent agents for photodynamic treatment of various types of cancer and also good metal chelators that form highly stable metallo‐complexes with different radionuclides. Therefore, radiolabelled porphyrins could also be potentially used as tumour imaging agents. In this context, the aim of this work was the radiolabelling of meso‐bis[3,4‐bis(carboxymethyleneoxy)phenyl]porphyrin, 2CPP, with Technetium‐99 m (^99mTc) and the evaluation of its radiochemical and biological properties in vitro and in vivo. The labelling procedure was optimized resulting in an efficiency of 92.52 ± 0.48%. The complex ^99mTC‐2CPP remained stable for more than 4 h. The biodistribution showed that ^99mTc‐2CPP is eliminated by gastrointestinal and urinary pathways. The tumour/muscle ratio increases over time, being 3.33 ± 1.22 and 3.55 ± 1.29 in WiDr‐bearing tumours mice and in H1299‐bearing tumours mice, respectively, 6 h post‐injection, showing the tumour specificity of the ^99mTc‐2CPP complex. The favourable tumour/muscle ratio of ^99mTc‐2CPP shows that this complex could potentially be used as tumour imaging agent. Moreover, it could be used to follow the progression or regression of tumours before, during and after the radiotherapy, chemotherapy and photodynamic therapy. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and evaluation of effect on Escherichia coli and Staphylococcus aureus of radiolabeled ampicillin‐loaded graphene oxide nanoflakes

Ampicillin is a one of effective antibiotics against Gram‐positive and Gram‐negative bacteria. This study aimed to label ampicillin‐loaded graphene oxide nanoflake (AMP‐GO) with ^99mTc and evaluate of its in vitro binding to Staphylococcus aureus and Escherichia coli. Firstly, ampicillin was loaded into graphene oxide nanoflake prepared. AMP‐GO was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques, and the amount of loaded ampicillin onto GO was determined by UV‐Vis absorption spectroscopy. AMP and AMP‐GO were labeled with ^99mTc using stannous chloride reducing agent. Labeling efficiency of ^99mTc‐AMP‐GO was found to be 97.66 ± 2.06%. ^99mTc‐AMP‐GO has higher binding efficiencies to both S. aureus and E. coli than ^99mTc‐AMP. ^99mTc‐AMP‐GO could be promising candidate as agent infection nuclear imaging. Furthermore, in vivo studies of ^99mTc‐AMP‐GO with infected rats are planned to be performed.     

99mTc‐labeled NGR‐chlorambucil conjugate, 99mTc‐HYNIC‐CLB‐c(NGR) for targeted chemotherapy and molecular imaging

Targeted delivery of chemotherapeutic drug at the tumor site enhances the efficacy with minimum systemic exposure. Towards this, drugs conjugated with peptides having affinity towards a particular molecular target are recognized as affective agents for targeted chemotherapy. Thus, in the present study, tumor‐homing asparagine‐glycine‐arginine (NGR) peptide ligand was conjugated to DNA alkylating nitrogen mustard, chlorambucil (CLB). The peptide‐drug conjugate (PDC), CLB‐c(NGR), was radiolabeled with ^99mTc‐HYNIC core to trace its pharmacokinetics and biodistribution pattern. In vitro cell‐binding studies of ^99mTc‐HYNIC‐CLB‐c(NGR) were conducted in murine melanoma B16F10 cells. The cytotoxicity studies conducted by incubation of the peptide/drug/PDC with B16F10 cells demonstrated enhanced cytotoxic effect of PDC in comparison to either the peptide or the drug alone. In vivo biodistribution studies in C57BL6 mice bearing melanoma tumor showed maximum tumor uptake at 30 minutes pi (2.45 ± 0.28% ID/g), which reduced to 0.77 ± 0.1% ID /g at 3 hours pi. The radiotracer being hydrophilic cleared rapidly from the heart, lungs, liver, and muscle. The tumor‐to‐blood and tumor‐to‐muscle ratios improved with time. This study opens avenues for conjugation of other targeting peptides with the drug CLB for enhanced toxicity at the diseased site.     

N‐[3‐[4‐(2‐methoxyphenyl) piperaziny‐1‐yl]propyl]cyclam: synthesized as a potential 5‐HT1A receptor ligand and labelled with 99mTc‐nitrido core

This paper reports the synthesis of new potential 5‐HT_1A receptor ligand N‐[3‐[4‐(2‐methoxyphenyl)piperaziny‐1‐yl]propyl]cyclam (MPPC) and radiolabelling of it with ^99mTc‐nitrido core. The novel neutral complex ^99mTcN‐MPPC combines 1,4,8,11‐tetraazacyclotetradecane (cyclam) ligand as chelate moiety for ^99mTc‐nitrido with a 1‐(2‐methoxyphenyl)piperazine moiety derived from WAY 100635 via a 3‐carbon alkyl chain. This provided a reliable and reproducible method for attaching the technetium to the pharmacophore moiety of WAY 100635. ^99mTcN‐MPPC was prepared by a two‐step procedure and the radiochemical purity was found to be greater than 95%. It was hydrophilic and stable for at least 4 h at room temperature. In vivo stability study in normal rats showed that no degradation of ^99mTcN‐MPPC was found in deproteinated blood samples at 2 h post‐injection. This effective ^99mTc‐labelling strategy for obtaining neutral ^99mTc nitrido complexes would be a useful tool to prepare new SPECT agents to image 5‐HT_1A receptor with cyclam conjugated ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

99mTc‐Doxycycline hyclate: a new radiolabeled antibiotic for bacterial infection imaging

Radiolabeled antibiotics are promising radiopharmaceuticals for the precise diagnosis and detection of infectious lesions. Doxycycline Hyclate (DOX) was chosen to investigate new ^99mTc‐labeled antibacterial agent. Ready to use freeze dry kits were formulated with optimum labeling conditions. Human serum stability, sterility, and pyrogenicity of kits were estimated, and gamma scintigraphy, in vivo biodistribution, and histopathological studies with bacterial infected rats were performed. DOX were successfully labeled by ^99mTc with high radiochemical purity, and the labeled compound was stable in human serum. Kits were sterile, pyrogen‐free, and stable up to 6 months. Static images depicted rapid distribution throughout the body and high uptake in bacterial infected thigh muscle. The uptake ratios of radiopharmaceuticals in infected thigh muscle were found above 2 up to 5 h. Five hours after injection, the rats were sacrificed, and biodistribution was determined. Samples of bacterial infected muscle, healthy muscle, blood, liver, spleen, lung, kidney, stomach, intestine, urine and heart were weighed, and the radioactivity was measured by using a gamma counter. The %ID/g of ^99mTc‐DOX was found 0.23 ± 0.06 for infected thigh muscle. According to the imaging, biodistribution, and histopathological studies, the promising characteristics of ^99mTc‐DOX make the new radiopharmaceutical valuable to examine for future studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,radiolabeling and in vitro and in vivo characterization of a technetium‐99m‐labeled alpha‐M2 peptide as a tumor imaging agent

Abstract: In an effort to develop a peptide‐based radiopharmaceutical for the detection of breast cancer, we have prepared an analog of αM2 peptide, modified to incorporate an N₃S chelate system. Mercaptoacetyltriglycine (MAG)₃‐derivatized αM2 peptide was prepared by solid‐phase synthesis and radiolabeled with ^99mTc by an exchange method. In vitro cell‐binding on human breast cancer cell lines, MDA‐MB‐231 and MCF‐7, indicated the affinity and specificity of ^99mTc‐MAG₃‐αM2 toward breast cancer cells. Additionally, the radiolabeled peptide showed rapid internalization into human breast cancer cells. In vivo biodistribution in mice showed that the radiolabeled peptide cleared rapidly from the blood and most non‐target tissues and was excreted significantly via the kidneys. Uptake of ^99mTc‐MAG₃‐αM2 in the tumor was moderate. The radiochemical and in vitro and in vivo characterization indicates that the radiolabeled peptide has certain favorable properties and it might be a useful radiopharmaceutical for the detection of breast cancer in vivo.     

Synthesis and preliminary evaluation of a 99mTc‐labeled folate‐PAMAM dendrimer for FR imaging

Folate receptor is an ideal target for tumor‐specific diagnostic and therapeutic. The aim of this study was to synthesize ^99mTc‐labeled folate‐polyamidoamine dendrimer modified with 2‐hydrazinonicotinic acid (^99mTc‐HP ₃FA ) for FR imaging. The ^99mTc‐HP ₃FA conjugate was prepared using N‐tris‐(hydroxymethyl)‐methylglycine and trisodium triphenylphosphine‐3,3′,3″‐trisulfonate as coligands. Physicochemical properties, in vitro cell uptake study, and in vivo micro‐single‐photon emission computed tomography/CT imaging were performed. The radiolabeled ^99mTc‐HP ₃FA conjugate was prepared with high radiolabeling yield, good stability, and water solubility (logP  = ?1.70 ± 0.21). In cell uptake study, the radiolabeled conjugate showed high uptakes in the FR ‐abundant KB cells and could be blocked significantly by excess folic acid. The 7721 cells which served as control group substantially had no uptakes. The results of micro‐single‐photon emission computed tomography/CT imaging exhibited that high accumulation of activity was found in FR ‐overexpressed KB tumor, and the tumor‐to‐muscle ratio was approximately 25.78, while, using free FA as inhibitor, the uptakes of ^99mTc‐HP ₃FA in KB tumor and kidney were obviously inhibited. In summary, a new radiocompound was synthesized successfully with specific FR targeting ability. The feasibility of ^99mTc‐HP ₃FA for early diagnosis of FR ‐positive tumors with non‐invasive single‐photon emission computed tomography imaging was demonstrated and the possibility of imaging‐guided drug delivery based on multifunctional polyamidoamine will be studied in the future.     

Radiochemical and biological characteristics of 99mTc‐difloxacin and 99mTc‐pefloxacin for detecting sites of infection

The optimization of the radiolabeling yield of ciprofloxacin analogous, difloxacin and pefloxacin, with ^99mTc was described. At pH 4, difloxacin was labeled with ^99mTc with a labeling yield of 95.6% by adding ^99mTc to 5 mg difloxacin in the presence of 100 µg SnCl₂·2H₂O whereas ^99mTc‐pefloxacin was labeled (98.1%) by adding ^99mTc to 4 mg pefloxacin in the presence of 50 µg SnCl₂·2H₂O. The radiochemical purity for both labeled compounds was evaluated with ITLC and HPLC system. Biological distribution of ^99mTc‐difloxacin and ^99mTc‐pefloxacin was carried out in experimentally induced infection rats, in the left thigh, using Staphylococcus aureus. Both thighs of the rats were dissected and counted and the ratio of bacterial infected thigh/contralateral thigh was then evaluated. T/NT for both ^99mTc‐difloxacin and ^99mTc‐pefloxacin was found to be 5.5±0.5 and 4.9±0.3, respectively, which was higher than that of the commercially available ^99mTc‐ciprofloxacin. Copyright © 2010 John Wiley & Sons, Ltd.     

Labeling and evaluation of 99mTc‐tricarbonyl‐meloxicam as a preferential COX‐2 inhibitor for inflammation imaging

Imaging of inflammation has an important role in dissolving problems in diagnosis and therapy of patients with inflammatory disorders. In this study meloxican as a nonsteroidal anti‐inflammatory drug (NSAID) has been labeled with thechnetium‐99m‐tricarbonyl core ([^99mTc (CO)₃ (H₂O)₃]⁺) in order to evaluate its feasibility as an inflammation imaging agent for in vivo use. ^99mTc‐tricabonyl labeling of meloxicam was performed by its incubation with prepared precursor ^99mTc‐tricabonyl and heating in a boiling water bath for 30 min while various range of pH (1–9) was adjusted. The stability of ^99mTc‐tricarbonyl‐Meloxicam was checked in human serum at 37 °C, and biodistribution was studied in mice. Labeling yield of 98.1 ± 0.4% was obtained corresponding to a specific activity of 0.14 GBq/µmol. The radioconjugate showed good stability in human serum. Our main achievement was high accumulation of ^99mTc‐tricarbonyl‐Meloxicam in the inflammated muscle in mice (T/NT = 3.90 at 4 h post injection) which may diagnostically be beneficial for distinguish sites of inflammation.     

Kit with technetium‐99m labelled antimicrobial peptide UBI 29‐41 for specific infection detection

The purpose of this study was to investigate radiochemical and biological characteristics of an instant kit for the preparation of ^99mTc‐labelled UBI 29‐41 for specific detection of infections. The kit is based on ^99mTc‐labelling via HYNIC conjugated to the terminal amine of the peptide, producing a well‐understood labelled compound. One hour after the addition of fresh ^99mTcO to the kit ITLC and HPLC reverse‐phase analysis was performed. Stability of the labelled complex was challenged and the binding to bacterial pellets was assessed. Finally, the biodistribution and accumulation in MRSA‐infected tissues were studied using scintigraphy and ex vivo countings. Data were compared to a non‐kit control method. Radiochemical analysis indicated >96% labelling, stability for 24 h and the preparation was used without purification. In vitro studies showed 41% of radioactivity was bound to bacteria. After injection into mice with a bacterial infection the site of infection was visualized within 30 min. Kit prepared ^99mTc‐HYNIC‐UBI 29‐41 was rapidly (half‐life 113 min) cleared via the kidneys and urinary bladder, essentially slower than control peptide (half‐life 74 min). This slower clearance results in higher activities in blood and other tissues. Nevertheless, ^99mTc‐HYNIC‐UBI 29‐41 shows favourable radiochemical characteristics and deserves further evaluation in a clinical setting. Copyright © 2005 John Wiley & Sons, Ltd.     

Tumor targeting with 99mTc radiolabeled peptides: Clinical application and recent development

Targeting overexpressed receptors on the cancer cells with radiolabeled peptides has become very important in nuclear oncology in the recent years. Peptides are small and have easy preparation and easy radiolabeling protocol with no side‐effect and toxicity. These properties made them a valuable tool for tumor targeting. Based on the successful imaging of neuroendocrine tumors with ¹¹¹In‐octreotide, other receptor‐targeting peptides such as bombesin (BBN), cholecystokinin/gastrin analogues, neurotensin analogues, glucagon‐like peptide‐1, and RGD peptides are currently under development or undergoing clinical trials. The most frequently used radionuclides for tumor imaging are ^99mTc and ¹¹¹In for single‐photon emission computed tomography and ⁶⁸Ga and ¹⁸F for positron emission tomography imaging. This review presents some of the ^99mTc‐labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.     

A 99mTc(CO)3‐labeled benzylguanidine with persistent heart uptake

We describe the synthesis and biological evaluation of the cationic ^99mTc–tricarbonyl complex fac‐[^99mTc(CO)₃(κ³‐L1)]⁺ (Tc1) anchored by a pyrazole‐diamine‐methylbenzylguanidine‐based ligand (L1), as potentially useful for myocardial imaging. The rhenium complex fac‐[Re(CO)₃(κ³‐L1)]⁺ (Re1) was prepared and characterized as a ‘cold’ surrogate of the radioactive complex. Cell uptake studies in a neuroblastoma cell line suggest that Tc1 uptake mechanism is related to the norepinephrine transporter (NET). Tissue distribution studies in CD1 mice showed that Tc1 presents high initial heart uptake and a slow washout from the heart (7.8 ± 1.3% injected dose per gram (ID/g), 30‐min post‐injection (p.i.); 6.3 ± 1.3% ID/g, 60‐min p.i.), with heart to blood ratios of 11.8 and 9.0 at 30‐ and 60‐min p.i., respectively. The uptake mechanism of Tc1 appears to be similar to that of metaiodobenzylguanidine (MIBG), as it can be reduced by coinjection with nonradioactive MIBG. The biodistribution profile of Tc2, where the benzylguanidine pharmacophore is absent, corroborates the fact that Tc1 does not accumulate in the heart by a simple diffusion mechanism but rather by a NET‐mediated mechanism. The results confirm those obtained in the cell assays. Despite the persistent heart uptake found for Tc1, the high hepatic and renal uptake remains to be improved.     

Synthesis and evaluation of a new 99mTc(I)‐tricarbonyl complex bearing the 5‐nitroimidazol‐1‐yl moiety as potential hypoxia imaging agent

The objective of this work was to develop a novel ^99mTc complex bearing the 5‐nitroimidazol‐1‐yl moiety with recognised selectivity towards hypoxic tissue, as a potential radiopharmaceutical for imaging tumour hypoxia. The new metronidazole derivative (2‐amine‐3‐[2‐(2‐methyl‐5‐nitro‐1H‐imidazol‐1‐yl)ethylthio]propanoic acid) (L) containing adequate groups to coordinate technetium through the formation of a Tc(I)‐tricarbonyl complex was synthesised with adequate yield (33%) and characterised by spectroscopy. Labelling was performed by substitution of three labile water molecules of the technetium tricarbonyl precursor, fac‐[^99mTc(CO)₃(H₂O)₃]⁺ with the ligand. A radiochemical purity higher than 90% was achieved and remained unchanged for more than 4 h. The complex has a high stability in plasma, a moderate plasma protein binding and a moderate hydrophilicity. In vitro cell uptake studies showed a ratio between the activity taken up by cells in hypoxia/normoxia of 1.6 ± 0.4 (p < 0.5). Biodistribution in normal mice showed rapid depuration and low uptake in all organs and tissues except liver. Biodistribution in mice bearing induced tumours showed a low tumour uptake, but tumour/muscle ratio was favourable thanks to depuration. Comparison with biological results of other metronidazole derivatives clearly shows that modifications of the chelator are very important and contribute to improve the biological behaviour.