Insertion of a lysosomal enzyme cleavage site into the sequence of a radiolabeled neuropeptide influences cell trafficking in vitro and in vivo.

Cancer Biother Radiopharm. 2010 Feb;25(1):89-95

Authors: Raza Naqvi SA, Matzow T, Finucane C, Nagra SA, Ishfaq MM, Mather SJ, Sosabowski J

Abstract Radiolabeled neuropeptides are widely explored for targeting tumours for either imaging or radiotherapeutic purposes. After binding to their receptors, these peptides are rapidly internalized into lysosomes, where they are degraded by proteolytic enzymes, such as cathepsins. The aim of this study was to investigate the effect of the inclusion of specific cleavage sites for cathepsin B into the peptide sequence. The cleavage site, GFLG, together with a series of dipeptides for pharmacokinetic modification of radiometabolites, were, therefore, inserted into a peptide that binds to the gastrin/CCK2 receptor. The receptor binding of the peptides was explored in AR42J cells, rates of internalization, and externalization of the radionuclide were measured and the nature of the radiometabolites explored. The effects of the modifications on biodistribution in tumor-bearing mice was explored by high-resolution single-photon emission computed tomography imaging. Differences in rates of externalization from tumor cells in vitro and in the rates of washout from tumor and kidney in vivo were observed. These results indicate that insertion of an enzymatic cleavage site, such as that for cathepsin B, into a neuropeptide appears to have an influence on the intracellular processing, which results in a change in the rate of egress of radioactivity from target and nontarget tissues.

PMID: 20187801 [PubMed - in process]

A standardised study to compare prostate cancer targeting efficacy of five radiolabelled bombesin analogues.

Eur J Nucl Med Mol Imaging. 2010 Feb 25;

Authors: Schroeder RP, Müller C, Reneman S, Melis ML, Breeman WA, de Blois E, Bangma CH, Krenning EP, van Weerden WM, de Jong M

PURPOSE: Prostate-specific antigen (PSA)-based screening for prostate cancer (PC) has dramatically increased early diagnosis. Current imaging techniques are not optimal to stage early PC adequately. A promising alternative to PC imaging is peptide-based scintigraphy using radiolabelled bombesin (BN) analogues that bind to gastrin-releasing peptide receptors (GRPR) being overexpressed in PC. When labelled to appropriate radionuclides BN targeting of GRPRs may also provide applications for peptide radionuclide receptor therapy (PRRT). Assessment studies under identical experimental conditions allowing a reliable comparison of the potential of such analogues are lacking. This study was performed to evaluate and directly compare five promising radiolabelled BN analogues for their targeting efficacy for PC under standardised conditions. METHODS: The BN agonists [(111)In]DOTA-PESIN, [(111)In]AMBA, [(111)In]MP2346 and [(111)In]MP2653 and one antagonist [(99m)Tc]Demobesin-1 were evaluated in GRPR-overexpressing human PC-3 tumour-bearing mice to determine peptide stability in vivo, biodistribution and GRPR targeting potential by animal SPECT/CT imaging and ex vivo autoradiography. RESULTS: HPLC analysis of blood showed intact Demobesin-1 at 5 and 15 min after injection (64.1 +/- 1.6% and 41.0 +/- 01%, respectively) being much less for the other compounds. AMBA, the second most stable analogue, showed 36.1 +/- 2.7% and 9.8 +/- 1.1% intact peptide after 5 and 15 min. PC-3 tumour uptake at 1 h was comparable for Demobesin-1, AMBA, PESIN and MP2346 (3.0 +/- 0.4, 2.7 +/- 0.5, 2.3 +/- 0.5 and 2.1 +/- 0.9%ID/g, respectively), but very low for MP2653 (0.9 +/- 0.2%ID/g). In addition, MP2346 showed undesirably high uptake in the kidneys (7.9 +/- 1.9%ID/g) being significantly less for the other analogues. AMBA, MP2346 and PESIN revealed favourable increases in tumour to blood ratios over time while changes in tumour to kidney and pancreas ratios for Demobesin-1 from 1 to 24 h after injection were significantly better than for the other analogues. All analogues visualised PC-3 tumours by SPECT/CT and autoradiography. CONCLUSION: In the present study the BN antagonist Demobesin-1 was the best performing analogue showing superior in vivo stability, highest tumour uptake and retention while pancreatic and renal clearance were rapid. PESIN and AMBA were the best GRP agonists with sufficient in vivo stabilities as well as high tumour uptake and retention. Based on these results all three analogues deserve further evaluation for clinical use in PC patients.

PMID: 20182713 [PubMed - as supplied by publisher]

Combined optical and single photon emission imaging: preliminary results.

Phys Med Biol. 2009 Dec 7;54(23):L57-62

Authors: Boschi F, Spinelli AE, D'Ambrosio D, Calderan L, Marengo M, Sbarbati A

In vivo optical imaging instruments are generally devoted to the acquisition of light coming from fluorescence or bioluminescence processes. Recently, an instrument was conceived with radioisotopic detection capabilities (Kodak in Vivo Multispectral System F) based on the conversion of x-rays from the phosphorus screen. The goal of this work is to demonstrate that an optical imager (IVIS 200, Xenogen Corp., Alameda, USA), designed for in vivo acquisitions of small animals in bioluminescent and fluorescent modalities, can even be employed to detect signals due to radioactive tracers. Our system is based on scintillator crystals for the conversion of high-energy rays and a collimator. No hardware modifications are required. Crystals alone permit the acquisition of photons coming from an in vivo 20 g nude mouse injected with a solution of methyl diphosphonate technetium 99 metastable (Tc99m-MDP). With scintillator crystals and collimators, a set of measurements aimed to fully characterize the system resolution was carried out. More precisely, system point spread function and modulation transfer function were measured at different source depths. Results show that system resolution is always better than 1.3 mm when the source depth is less than 10 mm. The resolution of the images obtained with radioactive tracers is comparable with the resolution achievable with dedicated techniques. Moreover, it is possible to detect both optical and nuclear tracers or bi-modal tracers with only one instrument.

PMID: 19920307 [PubMed - indexed for MEDLINE]

An Ultrahigh Resolution SPECT System for I-125 Mouse Brain Imaging Studies.

Nucl Instrum Methods Phys Res A. 2009 Mar 1;600(1):498-505

Authors: Meng LJ, Fu G, Roy EJ, Suppe B, Chen CT

This paper presents some initial experimental results obtained with a dual-head prototype single photon emission microscope system (SPEM) that is dedicated to mouse brain studies using I-125 labeled radiotracers. In particular, this system will be used for in vivo tacking of radiolabeled T cells in mouse brain. This system is based on the use of the intensified electron multiplying charge-coupled device (I-EMCCD) camera that offers the combination of an excellent intrinsic spatial resolution, a good signal-to-noise ratio, a large active area and a reasonable detection efficiency over an energy range between 27-140keV. In this study, the dual-head SPEM system was evaluated using both resolution phantoms and a mouse with locally injected T cells labelled with I-125. It was demonstrated that for a relatively concentrated source object, the current dual-head SPEM system is capable of visualizing the tiny amount of radioactivity (~12 nCi) carried by a very small number (<1000) of T cells. The current SPEM system design allows four or six camera heads to be installed in a stationary system configuration that offers a doubled or tripled sensitivity at a spatial resolution similar to that obtained with the dualhead system. This development would provide a powerful tool for in vivo and non-invasive tracking of radiolabeled T cells in mouse brain and potentially for other rodent brain imaging studies.

PMID: 20161174 [PubMed - as supplied by publisher]

Targeting Prostate Cancer Cells In Vivo Using a Rapidly Internalizing Novel Human Single-Chain Antibody Fragment.

J Nucl Med. 2010 Feb 11;

Authors: He J, Wang Y, Feng J, Zhu X, Lan X, Iyer AK, Zhang N, Seo Y, Vanbrocklin HF, Liu B

Human antibodies targeting prostate cancer cell surface epitopes may be useful for imaging and therapy. The objective of this study was to evaluate the tumor targeting of an internalizing human antibody fragment, a small-size platform, to provide high contrast in a mouse model of human prostate carcinoma. METHODS: A prostate tumor-targeting single-chain antibody fragment (scFv), UA20, along with a nonbinding control scFv, N3M2, were labeled with (99m)Tc and evaluated for binding and rapid internalization into human prostate tumor cells in vitro and tumor homing in vivo using xenograft models. For the in vitro studies, the labeled UA20 scFv was incubated at 37 degrees C for 1 h with metastatic prostate cancer cells (DU145) to assess the total cellular uptake versus intracellular uptake. For the animal studies, labeled UA20 and N3M2 scFvs were administered to athymic mice implanted subcutaneously with DU145 cells. Mice were imaged with small-animal SPECT/CT with concomitant biodistribution at 1 and 3 h after injection. RESULTS: The UA20 scFv was labeled in 55%-65% yield and remained stable in phosphate buffer within 24 h. The labeled UA20 scFv was taken up specifically by prostate tumor cells. Internalization was rapid, because incubation at 37 degrees C for less than 1 h resulted in 93% internalization of total cell-associated scFvs. In animal studies, SPECT/CT showed significant tumor uptake as early as 1 h after injection. At 3 h after injection, tumor uptake was 4.4 percentage injected dose per gram (%ID/g), significantly greater than all organs or tissues studied (liver, 2.7 %ID/g; other organs or tissues, <1 %ID/g), except the kidneys (81.4 %ID/g), giving tumor-to-blood and tumor-to-muscle ratios of 12:1 and 70:1, respectively. In contrast, the control antibody exhibited a tumor uptake of only 0.26 %ID/g, similar to that of muscle and fat. Tumor-specific targeting was evidenced by reduced tumor uptake of nearly 70% on administration of a 10-fold excess of unlabeled UA20 scFv. Kidney uptake was nonspecific, consistent with the route of excretion by scFvs. CONCLUSION: The UA20 scFv showed rapid and specific internalization in prostate tumor cells in vitro and accumulation in prostate tumor xenografts in vivo, demonstrating the potential for future development for prostate cancer imaging and targeted therapy.

PMID: 20150269 [PubMed - as supplied by publisher]

Production and radioimmunoimaging of novel fully human phage display recombinant antibodies and growth inhibition of lung adenocarcinoma cell line overexpressing Prx I.

Cancer Biol Ther. 2009 Jul;8(14):1369-77

Authors: Luo Y, Pang H, Li S, Cao H, Peng Z, Fan C, Li S

The Peroxiredoxin I (Prx I) is a member of the Peroxiredoxin family, which is overexpressed in many diverse tumor types and is an anti-apoptosis protein for tumor cell proliferation and survival. Therapeutic strategies targeting the Prx I may therefore be effective broad-spectrum anticancer agents. We constructed a phage display single-chain variable fragment (scFv) antibody library and sieve out the fully human, lung adenocarcinoma-sepcific monoclonal antibodies. The selection on Prx I was performed using above-mentioned lung adenocarcinoma-sepcific monoclonal antibodies with high affinity to Prx I overexpressing lung adenocarcinoma cells. The candidate scFv sequences, based on enzyme-linked immunosorbent assay (ELISA) screening data, were chosen for soluble expression, and a 30 kDa band was observed on polyacrylamide gel electrophoresis as predicted. The purified antibodies were characterized by immunoblotting and showed high specificity to Prx I-overexpressing lung adenocarcinoma cells A549. Radioimmunoimaging was taken to evaluate specificity and distribution of antibodies in vivo. The radiolocalization index (RI) of tumor/serum and tumor/muscle gradually increased, reaching its peak (4.06 +/- 0.13 and 5.17 +/- 0.97, respectively) at 48 h postadministration. Single photon emission computed tomography (SPECT) imaging showed the radioactivity was aggregated in tumor locations and tumor imaging was clearly observed. The internalized scFv resulted in antibody-mediated cell apoptosis and downregulation of Prx I expression. These results demonstrate that the scFv possesses strong antitumor activity on lung adenocarcinoma and may therefore be an effective therapeutic candidate for the treatment of cancers that are dependent on Prx I for growth and survival.

PMID: 19556853 [PubMed - indexed for MEDLINE]

Assessment of the Na/I symporter as a reporter gene to visualize oncolytic adenovirus propagation in peritoneal tumours.

Eur J Nucl Med Mol Imaging. 2010 Feb 6;

Authors: Merron A, Baril P, Martin-Duque P, de la Vieja A, Tran L, Briat A, Harrington KJ, McNeish IA, Vassaux G

PURPOSE: In vivo imaging of the spread of oncolytic viruses using the Na/I symporter (NIS) has been proposed. Here, we assessed whether the presence of NIS in the viral genome affects the therapeutic efficacy of the oncolytic adenovirus dl922-947 following intraperitoneal administration, in a mouse model of peritoneal ovarian carcinoma. METHODS: We generated AdAM7, a dl922-947 oncolytic adenovirus encoding the NIS coding sequence. Iodide uptake, NIS expression, infectivity and cell-killing activity of AdAM7, as well as that of relevant controls, were determined in vitro. In vivo, the propagation of this virus in the peritoneal cavity of tumour-bearing mice was determined using SPECT/CT imaging and its therapeutic efficacy was evaluated. RESULTS: In vitro infection of ovarian carcinoma IGROV-1 cells with ADAM7 led to functional expression of NIS. However, the insertion of NIS into the viral genome resulted in a loss of efficacy of the virus in terms of replication and cytotoxicity. In vivo, on SPECT/CT imaging AdAM7 was only detectable in the peritoneal cavity of animals bearing peritoneal ovarian tumours for up to 5 days after intraperitoneal administration. Therapeutic experiments in vivo demonstrated that AdAM7 is as potent as its NIS-negative counterpart. CONCLUSION: This study demonstrated that despite the detrimental effect observed in vitro, insertion of the reporter gene NIS in an oncolytic adenovirus did not affect its therapeutic efficacy in vivo. We conclude that NIS is a highly relevant reporter gene to monitor the fate of oncolytic adenovectors in live subjects.

PMID: 20140612 [PubMed - as supplied by publisher]

Effects of Pluronic and Doxorubicin on Drug Uptake, Cellular Metabolism, Apoptosis and Tumor Inhibition in Animal Models of MDR Cancers.

J Control Release. 2010 Jan 11;

Authors: Batrakova EV, Li S, Brynskikh AM, Sharma AK, Li Y, Boska M, Gong N, Mosley RL, Alakhov VY, Gendelman HE, Kabanov AV

Cancer chemotherapy is believed to be impeded by multidrug resistance (MDR). Pluronic (triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), PEO-b-PPO-b-PEO) were previously shown to sensitize MDR tumors to antineoplastic agents. This study uses animal models of Lewis lung carcinoma (3LL-M27) and T-lymphocytic leukemia (P388/ADR and P388) derived solid tumors to delineate mechanisms of sensitization of MDR tumors by Pluronic P85 (P85) in vivo. First, non-invasive single photon emission computed tomography (SPECT) and tumor tissue radioactivity sampling demonstrate that intravenous co-administration of P85 with a Pgp-substrate, (99)Tc-sestamibi, greatly increases the tumor uptake of this substrate in the MDR tumors. Second, (31)P magnetic resonance spectroscopy ((31)P-MRS) in live animals and tumor tissue sampling for ATP suggest that P85 and doxorubicin (Dox) formulations induce pronounced ATP depletion in MDR tumors. Third, these formulations are shown to increase tumor apoptosis in vivo by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and reverse transcription polymerase chain reaction (RT-PCR) for caspases 8 and 9. Altogether, formulation of Dox with P85 results in increased inhibition of the growth solid tumors in mice and represents novel and promising strategy for therapy of drug resistant cancers.

PMID: 20074598 [PubMed - as supplied by publisher]

Small-animal SPECT and SPECT/CT: application in cardiovascular research.

Eur J Nucl Med Mol Imaging. 2010 Jan 13;

Authors: Golestani R, Wu C, Tio RA, Zeebregts CJ, Petrov AD, Beekman FJ, Dierckx RA, Boersma HH, Slart RH

Preclinical cardiovascular research using noninvasive radionuclide and hybrid imaging systems has been extensively developed in recent years. Single photon emission computed tomography (SPECT) is based on the molecular tracer principle and is an established tool in noninvasive imaging. SPECT uses gamma cameras and collimators to form projection data that are used to estimate (dynamic) 3-D tracer distributions in vivo. Recent developments in multipinhole collimation and advanced image reconstruction have led to sub-millimetre and sub-half-millimetre resolution SPECT in rats and mice, respectively. In this article we review applications of microSPECT in cardiovascular research in which information about the function and pathology of the myocardium, vessels and neurons is obtained. We give examples on how diagnostic tracers, new therapeutic interventions, pre- and postcardiovascular event prognosis, and functional and pathophysiological heart conditions can be explored by microSPECT, using small-animal models of cardiovascular disease.

PMID: 20069298 [PubMed - as supplied by publisher]

Quinoline-n-butylcyanoacrylate-based nanoparticles for brain targeting for the diagnosis of Alzheimer's disease.

Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2010 Jan;2(1):35-47

Authors: Kulkarni PV, Roney CA, Antich PP, Bonte FJ, Raghu AV, Aminabhavi TM

A survey of research activity on nanoparticles (NPs) based on polymeric devices that could cross the blood-brain barrier (BBB) is given along with the presentation of our own data on the development of NPs of n-butyl-2-cyanoacrylate (BCA) for brain delivery to aid the early diagnosis of Alzheimer's disease (AD), a neurodegenerative disorder of the elderly people, the most prevalent form of dementia. Typical data are presented on in vivo detection of amyloid peptides (A beta) (amyloid plaques) that are used as targets for developing the biological markers for the diagnosis of AD. In order to develop efficient in vivo probes, polymeric n-butyl-2-cyanoacrylate (PBCA) NPs have been prepared and encapsulated with the radio-labeled amyloid affinity drug (125)I-clioquinol (CQ, 5-chloro-7-iodo-8-hydroxyquinoline) to improve the transport to brain and amyloid plaque retention of (125)I-CQ using the NPs of PBCA. The (125)I-CQ discriminately binds to the AD post-mortem brain tissue homogenates versus control. (125)I-CQ-PBCA NPs labeled the A beta plaques from the AD human post-mortem frontal cortical sections on paraffin-fixed slides. Storage phosphor imaging verified preferential uptake by AD brain sections compared to cortical control sections. The (125)I-CQ-PBCA NPs crossed the BBB in wild type mouse, giving an increased brain uptake measured in terms of % ID/g i.e., injected dose compared to (125)I-CQ. Brain retention of (125)I-CQ-PBCA NPs was significantly increased in the AD transgenic mice (APP/PS1) and in mice injected with aggregated A beta 42 peptide versus age-matched wild type controls. The results of this study are verified by in vivo storage phosphor imaging and validated by histopathological staining of plaques and select metal ions, viz. Fe(2+) and Cu(2+). The (125)I-CQ-PBCA NPs had more efficient brain entry and rapid clearance in normal mice and enhanced the retention in AD mouse brain demonstrating the ideal in vivo imaging characteristics. The (125)I-CQ-PBCA NPs exhibited specificity for A beta plaques both in vitro and in vivo. This combination offered radio-iodinated CQ-PBCA NPs as the promising delivery vehicle for in vivo single photon emission tomography (SPECT) ((123)I) or PET ((124)I) amyloid imaging agent. The importance of the topic in relation to brain delivery and other similar type of work published in this area are covered to highlight the importance of this research to medical disciplines.

PMID: 20049829 [PubMed - in process]

Synthesis and Characterization of Iodinated Tetrahydroquinolines Targeting the G Protein-Coupled Estrogen Receptor GPR30.

J Med Chem. 2009 Dec 30;

Authors: Ramesh C, Nayak TK, Burai R, Dennis MK, Hathaway HJ, Sklar LA, Prossnitz ER, Arterburn JB

A series of iodo-substituted tetrahydro-3H-cyclopenta[c]quinolines was synthesized as potential targeted imaging agents for the G protein-coupled estrogen receptor GPR30. The affinity and specificity of binding to GPR30 versus the classical estrogen receptors ERalpha/beta and functional responses associated with ligand-binding were determined. Selected iodo-substituted tetrahydro-3H-cyclopenta[c]quinolines exhibited IC(50) values lower than 20 nM in competitive binding studies with GPR30-expressing human endometrial cancer cells. These compounds functioned as antagonists of GPR30 and blocked estrogen-induced PI3K activation and calcium mobilization. The tributylstannyl precursors of selected compounds were radiolabeled with (125)I using the iodogen method. In vivo biodistribution studies in female ovariectomized athymic (NCr) nu/nu mice bearing GPR30-expressing human endometrial tumors revealed GPR30-mediated uptake of the radiotracer ligands in tumor, adrenal, and reproductive organs. Biodistribution and quantitative SPECT/CT studies revealed structurally related differences in the pharmacokinetic profiles, target tissue uptake, and metabolism of the radiolabeled compounds as well as differences in susceptibility to deiodination. The high lipophilicity of the compounds adversely affects the in vivo biodistribution and clearance of these radioligands and suggests that further optimization of this parameter may lead to improved targeting characteristics.

PMID: 20041667 [PubMed - as supplied by publisher]

Covalently combining carbon nanotubes with anticancer agent: preparation and antitumor activity.

ACS Nano. 2009 Sep 22;3(9):2740-50

Authors: Wu W, Li R, Bian X, Zhu Z, Ding D, Li X, Jia Z, Jiang X, Hu Y

A multiwalled carbon nanotube (MWNT)-based drug delivery system was developed by covalently combining carbon nanotubes with the antitumor agent 10-hydroxycamptothecin (HCPT) using hydrophilic diaminotriethylene glycol as the spacer between nanotube and drug moieties. The surface functionalizations of the nanotube were carried out by enrichment of carboxylic groups with optimized oxidization treatment, followed by covalently linking hydrophilic diaminotriethylene glycol via amidation reaction, and then HCPT was chemically attached to carbon nanotubes through a cleavable ester linkage. It is demonstrated that the obtained MWNT-HCPT conjugates are superior in antitumor activity both in vitro and in vivo to clinical HCPT formulation. In vivo single photon emission computed tomography (SPECT) imaging and ex vivo gamma scintillation counting analyses reveal that MWNT-HCPT conjugates have relatively long blood circulation and high drug accumulation in the tumor site. These properties together with the enhanced cell uptake and multivalent presentation of HCPT on a single nanotube benefit substantially the antitumor effects and would boost significantly the applications of carbon nanotubes in the biomedicine field.

PMID: 19702292 [PubMed - indexed for MEDLINE]

Targeted radionuclide therapy using a Wnt-targeted replicating adenovirus encoding the Na/I symporter.

Clin Cancer Res. 2009 Nov 1;15(21):6595-601

Authors: Peerlinck I, Merron A, Baril P, Conchon S, Martin-Duque P, Hindorf C, Burnet J, Quintanilla M, Hingorani M, Iggo R, Lemoine NR, Harrington K, Vassaux G

PURPOSE: The Na/I symporter (hNIS) promotes concentration of iodine in cells. In cancer gene therapy, this transgene has potential as a reporter gene for molecular imaging of viral biodistribution and as a therapeutic protein promoting (131)I-mediated radiotherapy. Here, we combined the imaging and therapeutic potential of hNIS in an oncolytic adenoviruses targeting colorectal cancer cells. EXPERIMENTAL DESIGN: We generated an adenovirus (AdIP2) encoding hNIS and capable of selective replication in colorectal carcinoma cells. The selectivity of this virus was verified in vitro and in vivo. Its spread in tumors was monitored in vivo using single-photon emission computed tomography/CT imaging upon (99m)TcO(4)(-) injection and confirmed by immunohistochemistry. Metabolic radiotherapy was done through injection of therapeutic doses of (131)I(-). RESULTS: We showed in vitro and in vivo the selectivity of AdIP2 and that hNIS expression is restricted to the target cells. Imaging and immunohistochemical data showed that viral spread is limited and that the point of maximal hNIS expression is reached 48 hours after a single intratumoral injection. Administration of a single therapeutic dose of (131)I at this time point led to a dramatic reduction in tumor size not observed in hNIS-negative viruses. CONCLUSIONS: This report showed for the first time that the combination of the imaging and therapeutic potentials of hNIS can be applied to oncolytic adenoviruses in experimental models of cancer.

PMID: 19861465 [PubMed - indexed for MEDLINE]

Novel anilinophthalimide derivatives as potential probes for beta-amyloid plaque in the brain.

Bioorg Med Chem. 2009 Dec 24;

Authors: Duan XH, Qiao JP, Yang Y, Cui MC, Zhou JN, Liu BL

A group of novel 4,5-dianilinophthalimide derivatives has been synthesized in this study for potential use as beta-amyloid (Abeta) plaque probes. Staining of hippocampus tissue sections from Alzheimer's disease (AD) brain with the representative compound 9 indicated selective labeling of it to Abeta plaques. The binding affinity of radioiodinated [(125)I]9 for AD brain homogenates was 0.21nM (K(d)), and of other derivatives ranged from 0.9 to 19.7nM, except for N-methyl-4,5-dianilinophthalimide (K(i)>1000nM). [(125)I]9 possessed the optimal lipophilicity with LogP value of 2.16, and its in vivo biodistribution in normal mice exhibited excellent initial brain uptake (5.16% ID/g at 2min after injection) and a fast washout rate (0.56% ID/g at 60min). The encouraging results suggest that this novel derivative of [(123)I]9 may have potential as an in vivo SPECT probe for detecting amyloid plaques in the brain.

PMID: 20036557 [PubMed - as supplied by publisher]

Targeting of CCK-2 receptor-expressing tumors using a radiolabeled divalent gastrin peptide.

J Nucl Med. 2009 Dec;50(12):2082-9

Authors: Sosabowski JK, Matzow T, Foster JM, Finucane C, Ellison D, Watson SA, Mather SJ

Gastrin/cholecystokinin subtype 2 receptors (CCK-2Rs) are overexpressed in several tumor types and are, thus, a potential target for peptide receptor radionuclide therapy (PRRT) of cancer. To improve the in vivo performance of CCK-2R binding peptides, we have previously synthesized and screened a series of divalent gastrin peptides for improved biochemical and biologic characteristics. In this study, we explore in more detail the most promising of these compounds and compare its performance with a previously described monomeric peptide. METHODS: From six (111)In-labeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-conjugated divalent gastrin peptides based on the C-terminal sequence of minigastrin, the maleimide-linked compound DOTA-GSC(succinimidopropionyl-EAYGWNleDF-NH(2))-EAYGWNleDF-NH(2) (MGD5) was selected. The in vitro stability, receptor binding, and internalization of (111)In-MGD5 were studied and compared with those of monomer compound (111)In-APH070. In vivo biodistribution and imaging using a SPECT/CT camera were also performed. RESULTS: More than 90% of the labeled divalent peptide remained intact after 20 h of incubation in plasma. The inhibitory concentration of 50% of the divalent peptide was 1.0 versus 5.6 nM for the monomer, and the dissociation constant was 0.7 versus 2.9 nM. The rate of internalization of the divalent peptide was twice that of the monomer. Tumor uptake of the divalent peptide in vivo was about 6 times that of the monomer. The rate of washout of the divalent peptide from the tumor was lower than that of the monomer. CONCLUSION: Dimerization of the CCK-2R binding site results in an increase in binding affinity and an increase in tumor uptake both in vitro and in vivo. It is likely that these increases would result in improved tumor-targeting efficiency in patients with CCK-2R-positive tumors.

PMID: 19910426 [PubMed - indexed for MEDLINE]

Study on biodistribution and imaging of radioiodinated arginine-arginine-leucine peptide in nude mice bearing human prostate carcinoma.

Ann Nucl Med. 2009 Dec 9;

Authors: Yu M, Zhou H, Liu X, Huo Y, Zhu Y, Chen Y

OBJECTIVE: To investigate the biodistribution and imaging of (131)I-labeled arginine-arginine-leucine (RRL) peptide in human prostate carcinoma bearing nude mice. METHODS: The 10-mer cyclic peptide containing the RRL sequence (YCGGRRLGGC) was synthesized by the solid-phase method. Disulfide bonds between the cysteines maintain the cyclic structure. Radioiodination of the RRL peptide was performed by the chloramine-T method. (131)I-labeled peptides were injected into the nude mice bearing human prostate carcinoma via a tail vein. Biodistribution and imaging results in vivo were obtained. RESULTS: The (131)I-labeling rate of RRL peptide was about 60%. The radiochemical purity was 96.5%. The radiochemical purity of the labeled compound remained 90.3% at 24 h in human blood serum at 37 degrees C. In the biodistribution studies, radiolabeled RRL peptide probe accumulated in the tumor to a level of approximately 2.52 and 0.65% injected dose per gram of tissue at 6 and 24 h after administration. The data for the (131)I-labeled control peptide were 0.73 and 0.06% ID/g at 6 and 24 h after administration. The ratios of radioactivity in tumors to radioactivity in blood at 1, 6, and 24 h after injection were about 0.32, 1.12, 1.30 for RRL peptide and 0.30, 0.37, 0.22 for control peptide. The ratios of radioactivity in tumors to radioactivity in muscle at 1, 6, 24 h after injection were about 1.40, 3.94, 9.08 for RRL peptide and 1.98, 2.89, 1.78 for control peptide. At 24 h after administration, the SPECT imaging obtained clearly showed a contrasting tumor on the right armpit of mice with high concentrations of radioactivity, and the surrounding background was very low. CONCLUSIONS: The results suggest that radioiodination of RRL peptide is feasible and that the labeled compound is stable in human blood serum. The (131)I-labeled RRL peptide shows high tumor uptake and good tumor-to-organ ratios that allow noninvasive visualization of tumors. The (131)I-labeled compound is valuable to detect tumors as molecular probe.

PMID: 19997991 [PubMed - as supplied by publisher]

Endogenous competition against binding of [(18)F]DMFP and [(18)F]fallypride to dopamine D(2/3) receptors in brain of living mouse.

Synapse. 2009 Dec 2;64(4):313-322

Authors: Rominger A, Wagner E, Mille E, Böning G, Esmaeilzadeh M, Wängler B, Gildehaus FJ, Nowak S, Bruche A, Tatsch K, Bartenstein P, Cumming P

Aim. Molecular imaging studies with benzamide radioligands can reveal competition from endogenous binding at D(2/3)-receptors in living brain. However, single photon emission computed tomography (SPECT) methods suffer from limited spatial resolution, and [(11)C]-labeled ligands are only available at positron emission tomography (PET) research sites with cyclotron-radiochemistry facilities, whereas [(18)F] can be transported, due to its longer physical half-life. Therefore, we endeavored to characterize the vulnerabilities of the benzamide antagonist [(18)F]desmethoxyfallypride (DMFP) and its high-affinity congener [(18)F]fallypride (FP) to competition from endogenous dopamine in living mouse brain. Methods. Groups of awake mice were pretreated with saline, amphetamine (10 mg/kg), or reserpine (5 mg/kg), followed by i.v. tracer injections. Mice were killed at 2.5-90 min (DMFP) or 2.5-180 min (FP) circulation times. Brains were dissected and regional radioactivity concentration measured by gamma counting. Other groups of mice were anesthetized for dynamic microPET recordings with DMFP or FP. Binding potentials (BP(ND)) were calculated using cerebellum as reference region. Results. With 90-min circulation, DMFP BP(ND) in striatum was 2.4 by dissection and 2.2 by microPET, which showed a 62% decrease in response to amphetamine-evoked dopamine release and a 33% increase after reserpine-evoked dopamine depletion. With 120-min circulation, FP BP(ND) in striatum was 24.1 by dissection and 9.2 by microPET, which showed a 31% decrease in the amphetamine group, but no effect of reserpine. Dissection showed similar sensitivities for FP binding, but only a 29% amphetamine-evoked reduction for DMFP. Conclusions. Relative to gold standard ex vivo results, microPET estimates of DMFP BP(ND) were unbiased, whereas FP BP(ND) in striatum was substantially underestimated. Both tracers proved suitable for revealing pharmacologically evoked changes in competition at D(2/3)-receptors in striatum of living mice. Synapse 64:313-322, 2010. (c) 2009 Wiley-Liss, Inc.

PMID: 19957365 [PubMed - as supplied by publisher]

Single Photon Emission Computed Tomography (SPECT) for Functional Investigation of the Proximal Tubule in Conscious Mice.

Am J Physiol Renal Physiol. 2009 Dec 2;

Authors: Jouret F, Walrand S, Parreira KS, Courtoy PJ, Pauwels S, Devuyst O, Jamar F

Non-invasive analysis of renal function in conscious mice is necessary to optimize the use of mouse models. In this study, we evaluated whether single photon emission computed tomography (SPECT) using specific radionuclear tracers can be used to analyze changes in renal proximal tubule functions. The tracers included dimercaptosuccinic acid ((99m)Tc-DMSA), which is used for cortex imaging; 99mTc-mercaptoacetyltriglycine ((99m)Tc-MAG3), used for dynamic renography; and (123)I-beta2-microglobulin, which monitors receptor mediated endocytosis. (99m)Tc-DMSA SPECT imaging was shown to delineate the functional renal cortex with a ~1 mm spatial resolution and accumulated in the cortex reaching a plateau 5h after injection. The cortical uptake of (99m)Tc-DMSA was abolished in Clcn5 knock-out mice, a model of proximal tubule dysfunction. Dynamic renography with (99m)Tc-MAG3 in conscious mice demonstrated rapid extraction from blood, renal accumulation and subsequent tubular secretion. Anesthesia induced a significant delay in the (99m)Tc-MAG3 clearance. The tubular reabsorption of (123)I-beta2-microglobulin was strongly impaired in the Clcn5 knock-out mice, with defective tubular processing and loss of the native tracer in urine, reflecting proximal tubule dysfunction. Longitudinal studies in a model of cisplatin-induced acute tubular injury revealed a correlation between tubular recovery and (123)I-beta2-microglobulin uptake. These data show that SPECT imaging with well-validated radiotracers allows in vivo investigations of specific proximal tubule functions in conscious mice. Key words: Receptor-mediated endocytosis, Tubular secretion, ClC-5, Radionuclear tracers.

PMID: 19955188 [PubMed - as supplied by publisher]

MicroPET, MicroSPECT, and NIR fluorescence imaging of biomolecules in vivo.

Methods Mol Biol. 2009;544:461-81

Authors: Li ZB, Chen X

Molecular imaging is a newly merged multidisciplinary subject that requires contributions from biology, medical physics, and chemistry/radiochemistry. Integrin alpha(v)beta(3), a cell adhesion molecule, plays pivotal roles in regulating tumor angiogenesis and the growth of new blood vessels. In this chapter, we use the cell adhesion molecule integrin alpha(v)beta(3) as an example to demonstrate how one can synthesize appropriate arginine-glycine-aspartic acid (RGD) peptide-containing probes for visualizing and quantifying the receptor expression in vivo by means of microPET, microSPECT, and NIR fluorescence.

PMID: 19488719 [PubMed - indexed for MEDLINE]