Evaluation of a technetium-99m labeled bombesin homodimer for GRPR imaging in prostate cancer

Multimerization of peptides can improve the binding characteristics of the tracer by increasing local ligand concentration and decreasing dissociation kinetics. In this study, a new bombesin homodimer was developed based on an ε-aminocaproic acid-bombesin(7–14) (Aca-bombesin(7–14)) fragment, which has been studied for targeting the gastrin-releasing peptide receptor (GRPR) in prostate cancer. The bombesin homodimer was conjugated to 6-hydrazinopyridine-3-carboxylic acid (HYNIC) and labeled with ^99mTc for SPECT imaging. The in vitro binding affinity to GRPR, cell uptake, internalization and efflux kinetics of the radiolabeled bombesin dimer were investigated in the GRPR-expressing human prostate cancer cell line PC-3. Biodistribution and the GRPR-targeting potential were evaluated in PC-3 tumor-bearing athymic nude mice. When compared with the bombesin monomer, the binding affinity of the bombesin dimer is about ten times lower. However, the ^99mTc labeled bombesin dimer showed a three times higher cellular uptake at 4 h after incubation, but similar internalization and efflux characters in vitro. Tumor uptake and in vivo pharmacokinetics in PC-3 tumor-bearing mice were comparable. The tumor was visible on the dynamic images in the first hour and could be clearly distinguished from non-targeted tissues on the static images after 4 h. The GRPR-targeting ability of the ^99mTc labeled bombesin dimer was proven in vitro and in vivo. This bombesin homodimer provides a good starting point for further studies on enhancing the tumor targeting activity of bombesin multimers.     

99mTc(N)-DBODC(5), a potential radiolabeled probe for SPECT of multidrug resistance: in vitro study

[^99mTc(N)(DBODC)(PNP5)]⁺ [DBODC is bis(N-ethoxyethyl)dithiocarbamato; PNP5 is bis(dimethoxypropylphosphinoethyl)ethoxyethylamine], abbreviated as ^99mTc(N)-DBODC(5), is a lipophilic cationic mixed compound investigated as a myocardial imaging agent. The findings that this tracer accumulates in mitochondrial structures through a mechanism mediated by the negative mitochondrial membrane potential and that the rapid efflux of ^99mTc(N)-DBODC(5) from nontarget tissues seems to be associated with the multidrug resistance (MDR) P-glycoprotein (P-gp) transport function open up the possibility to extend its clinical applications to tumor imaging and noninvasive MDR studies. The rate of uptake at 4 and 37 °C of ^99mTc(N)-DBODC(5) was evaluated in vitro in selected human cancer cell lines and in the corresponding sublines before and after P-gp and/or MDR-associated protein (MRP) modulator/inhibitor treatment using ^99mTc-sestamibi as a reference. The results indicated that (1) the uptake of both ^99mTc(N)-DBODC(5) and ^99mTc-sestamibi is correlated to metabolic activity of the cells and (2) the cellular accumulation is connected to the level of P-gp/MRP expression; in fact, an enhancement of uptake in resistant cells was observed after treatment with opportune MDR inhibitor/modulator, indicating that the selective blockade of P-gp/MRP prevented efflux of the tracers. This study provides a preliminary indication of the applicability of ^99mTc(N)-DBODC(5) in tumor imaging and in detecting P-gp/MRP-mediated drug resistance in human cancer. In addition, the possibility to control the hydrophobicity and pharmacological activity of this heterocomplex through the variation of the substituents on the ligands backbone without affecting the P₂S₂ coordinating sphere makes ^99mTc(N)-DBODC(5) a suitable scaffold for the preparation of a molecular probe for single photon emission computed tomography of MDR.     

Synthesis and evaluation of 99mTc–2-[(3-carboxy-1-oxopropyl)amino]-2-deoxy-d-glucose as a potential tumor imaging agent

The 2-[(3-carboxy-1-oxopropyl)amino]-2-deoxy-d-glucose (CPADG) was synthesized and radiolabeled with ^99mTcO₄⁻ to obtain the ^99mTc–CPADG complex in high yield. It was stable over 6 h in saline at room temperature and in serum at 37 °C. The partition coefficient and electrophoresis results indicated that the complex was hydrophilic and cationic. In vitro cell studies showed there was an increase in the uptake of ^99mTc–CPADG as a function of incubation time and ^99mTc–CPADG was possibly transported via the glucose transporters. The biodistribution of ^99mTc–CPADG in mice bearing S 180 tumor showed that the complex accumulated in the tumor with high uptake and good retention. The tumor/blood and tumor/muscle ratios increased with time and reached 1.91 and 5.05 at 4 h post-injection. Single photon emission computed tomography (SPECT) image studies showed there was an obvious accumulation in tumor sites, suggesting ^99mTc–CPADG would be a promising candidate for tumor imaging.     

99mTc-bioorthogonal click chemistry reagent for in vivo pretargeted imaging

Metal-free click chemistry has become an important tool for pretargeted approaches in the molecular imaging field. The application of bioorthogonal click chemistry between a pretargeted trans-cyclooctene (TCO) derivatized monoclonal antibody (mAb) and a ^99mTc-modified 1,2,4,5-tetrazine for tumor imaging was examined in vitro and in vivo. The HYNIC tetrazine compound was synthesized and structurally characterized, confirming its identity. Radiolabeling studies demonstrated that the HYNIC tetrazine was labeled with ^99mTc at an efficiency of >95% and was radiochemically stable. ^99mTc–HYNIC tetrazine reacted with the TCO–CC49 mAb in vitro demonstrating its selective reactivity. In vivo biodistribution studies revealed non-specific liver and GI uptake due to the hydrophobic property of the compound, however pretargeted SPECT imaging studies demonstrated tumor visualization confirming the success of the cycloaddition reaction in vivo. These results demonstrated the potential of ^99mTc–HYNIC–tetrazine for tumor imaging with pretargeted mAbs.     

99mTc标记BmK CT及其胶质瘤荷瘤裸鼠的SPECT成像研究

目的:通过放射性核素~(99m)Tc标记BmK CT多肽制备靶向胶质瘤的显像剂,探讨~(99m)?Tc-BmK CT用于胶质瘤显像的可行性。方法:采用BmK CT多肽游离的氨基与DTPA酸酐反应得到BmK CT-DTPA,经99m Tc标记后通过柱层析分离纯化制备~(99m)?Tc-BmK CT。测定标记物在PBS溶液和血清中不同时间点放射性化学纯度,评价BmK CT-~(99m)?Tc体外稳定性。新西兰白兔耳缘静脉注射~(99m)Tc-BmK CT进行SPECT显像,观察不同时间点体内的放射性分布。皮下胶质瘤裸鼠经尾静脉注射~(99m)Tc-BmK CT,观察不同时间点肿瘤的摄取情况;注射后4 h处死裸鼠,分离肿瘤和主要器官进行离体SPECT显像,并用勾画感兴趣区法分析相对放射性计数。结果:~(99m)Tc标记BmK CT多肽标记率大于80%,经柱层析分离纯化后放射性化学纯度大于99%。标记物在PBS和血清稳定性良好,6 h内放射性化学纯度均大于95%,12 h内放射性化学纯度大于90%。正常白兔SPECT显像表明~(99m)Tc-BmK CT主要浓聚在肝脏、脾脏和肾脏,软组织持续显影微弱,甲状腺区及胃肠未见核素浓聚;显像剂主要通过泌尿系统排泄,24 h肾脏与肝脏显影接近。胶质瘤裸鼠SPECT显像表明,注射后4 h肿瘤显像清楚,ROI分析结果显示肿瘤/肌肉比4.26±0.25,标记物在肿瘤内代谢缓慢,8 h肿瘤部位仍有较高摄取。结论:本研究成功制备了~(99m)Tc标记BmK CT多肽,标记物主要被肝、脾和肾摄取,经泌尿系统排泄;~(99m)Tc-BmK CT能够在皮下胶质瘤中浓聚,注射后4 h肿瘤显影清晰,瘤内代谢缓慢,有潜力成为一种新型胶质瘤分子探针。     

3D image-based dosimetry for Yttrium-90 radioembolization of hepatocellular carcinoma: Impact of imaging method on absorbed dose estimates

BackgroundTo improve therapy outcome of Yttrium-90 selective internal radiation therapy (⁹⁰Y SIRT), patient-specific post-therapeutic dosimetry is required. For this purpose, various dosimetric approaches based on different available imaging data have been reported. The aim of this work was to compare post-therapeutic 3D absorbed dose images using Technetium-99m (^99mTc) MAA SPECT/CT, Yttrium-90 (⁹⁰Y) bremsstrahlung (BRS) SPECT/CT, and ⁹⁰Y PET/CT.MethodsTen SIRTs of nine patients with unresectable hepatocellular carcinoma (HCC) were investigated. The ^99mTc SPECT/CT data, obtained from ^99mTc-MAA-based treatment simulation prior to ⁹⁰Y SIRT, were scaled with the administered ⁹⁰Y therapy activity. 3D absorbed dose images were generated by dose kernel convolution with scaled ^99mTc/⁹⁰Y SPECT/CT, ⁹⁰Y BRS SPECT/CT, and ⁹⁰Y PET/CT data of each patient. Absorbed dose estimates in tumor and healthy liver tissue obtained using the two SPECT/CT methods were compared against ⁹⁰Y PET/CT.ResultsThe percentage deviation of tumor absorbed dose estimates from ⁹⁰Y PET/CT values was on average −2 ± 18% for scaled ^99mTc/⁹⁰Y SPECT/CT, whereas estimates from ⁹⁰Y BRS SPECT/CT differed on average by −50 ± 13%. For healthy liver absorbed dose estimates, all three imaging methods revealed comparable values.ConclusionThe quantification capabilities of the imaging data influence ⁹⁰Y SIRT tumor dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. When no ⁹⁰Y PET/CT image data are available, the proposed scaled ^99mTc/⁹⁰Y SPECT/CT dosimetry method was found to be more appropriate for HCC tumor dosimetry than ⁹⁰Y BRS SPECT/CT based dosimetry.     

Synthesis and biological evaluation of a novel 99mTc(CO)3 complex of ciprofloxacin dithiocarbamate as a potential agent to target infection

The ciprofloxacin dithiocarbamate (CPFXDTC) was radiolabeled with [^99mTc(CO)₃(H₂O)₃]⁺ intermediate to form the ^99mTc(CO)₃–CPFXDTC complex in high yield. The ^99mTc(CO)₃–CPFXDTC complex was characterized by HPLC and its stability in serum was studied. Its partition coefficient indicated that it was a lipophilic complex. The bacterial binding efficiency of ^99mTc(CO)₃–CPFXDTC was almost the same as that of ^99mTcN–CPFXDTC, and was higher than that of ^99mTc–ciprofloxacin. Biodistribution results in induced infection mice showed ^99mTc(CO)₃–CPFXDTC had higher uptake at the sites of infection and better abscess/blood and abscess/muscle ratios than those of ^99mTc–ciprofloxacin and ^99mTcN–CPFXDTC. Single photon emission computed tomography (SPECT) static imaging study in infected rabbits demonstrated the uptake in the left thigh infection lesion was observable, while no accumulation in the right thigh muscle was found. These results suggested ^99mTc(CO)₃–CPFXDTC would be a promising candidate for further evaluation as infection imaging agent.     

99mTc- and Re-labeled 6-dialkylamino-2-naphthylethylidene derivatives as imaging probes for β-amyloid plaques

Based on the conjugate strategy, two neutral ^99mTc labeled 2-(1-(6-(dialkylamino)naphthalen-2-yl)ethylidene)malononitrile (DDNP) and 1-(6-(dialkylamino)naphthalen-2-yl)ethanone (ENE) derivatives, and their corresponding rhenium complexes were synthesized. In vitro fluorescent staining indicated that the corresponding rhenium derivatives selectively stained the β-amyloid (Aβ) plaques in the brain sections of AD model mice with low background. Compared with FDDNP and FENE, the affinities of the corresponding rhenium derivatives to Aβ aggregates decreased about 10-14-fold. In vivo biodistribution experiments in normal mice showed that ^99mTc-MAMA-ENE displayed medium initial brain uptake (0.65 %ID/g at 2 min) with a reasonable washout from the brain (0.19 %ID/g at 2 h) while ^99mTc-MAMA-DDNP showed a low brain uptake (0.28 %ID/g at 2 min). Further optimize these ^99mTc-labeled tracers in order to improve their binding affinities to Aβ plaques and diffusion through the blood brain barrier may generate useful imaging agents for SPECT.     

Preparation and biodistribution of a 99mTc tricarbonyl complex with deoxyglucose dithiocarbamate as a tumor imaging agent for SPECT

The deoxyglucose dithiocarbamate (DGDTC) was successfully labeled with the ^99mTc(CO)₃ core to provide the corresponding ^99mTc(CO)₃–DGDTC complex in good yields. The radiochemical purity of the ^99mTc(CO)₃–DGDTC complex was over 90%, as measured by high performance liquid chromatography (HPLC). The complex possessed good stability in saline at room temperature and in mouse plasma at 37 °C. Its partition coefficient result indicated that it was a hydrophilic complex. The electrophoresis results showed the complex was neutral. The biodistribution of ^99mTc(CO)₃–DGDTC in mice bearing S 180 tumor showed that the complex clearly accumulated in tumor, exhibiting high tumor/blood and tumor/muscle ratios and good tumor retention. Single photon emission computed tomography (SPECT) image studies showed there was a visible uptake in tumor sites, suggesting ^99mTc(CO)₃–DGDTC could be considered as a potential tumor imaging agent.     

Near-infrared fluorescence imaging of CD13 receptor expression using a novel Cy5.5-labeled dimeric NGR peptide

In this study, we synthesized a novel Cy5.5-labeled dimeric NGR peptide (Cy5.5-NGR2) via bioorthogonal click chemistry, and evaluated the utility of Cy5.5-NGR2 for near-infrared fluorescence imaging of CD13 receptor expression in vivo. The dimeric NGR peptide (NGR2) was conjugated with an alkyne-containing PEG unit followed by mixing with an azide-terminated Cy5.5 fluorophore (Cy5.5-N₃) to afford Cy5.5-NGR2. The probe was subject to in vitro and in vivo evaluations. The bioorthogonal click chemistry provided a rapid conjugation of the alkyne-containing NGR2 with Cy5.5-N₃ in a quantitative yield within 15 min. The laser confocal microscopy revealed that binding of Cy5.5-NGR2 to CD13 receptor is target-specific as demonstrated in CD13-positive HT-1080 cells, CD13-negative MCF-7 cells, and a blocking study in HT-1080 cells. For in vivo optical imaging, Cy5.5-NGR2 exhibited rapid HT-1080 tumor targeting at 0.5 h postinjection (pi), and highest tumor-to-background contrast at 2 h pi. The CD13-specific tumor accumulation of Cy5.5-NGR2 was accomplished by a blocking study with unlabeled NGR peptide in HT-1080 tumor bearing mice. The tumor-to-muscle ratio of Cy5.5-NGR2 at 2 h pi reached 2.65 ± 0.13 in the non-blocking group vs. 1.05 ± 0.06 in the blocking group. The results from ex vivo imaging were consistent with the in vivo findings. We concluded that Cy5.5-NGR2 constructed by bioorthogonal click chemistry is a promising molecular probe, not only allowing the NIR optical imaging of CD13 overexpressed tumors, but also having the potential to facilitate noninvasive monitoring of CD13-targeted tumor therapy.     

Comparison of 90Y SIRT predicted and delivered absorbed doses using a PSF conversion method

PurposeThe aims of this study were to develop and apply a method to correct for the differences in partial volume effects of pre-therapy Technetium-99 m (^99mTc)-MAA SPECT and post-therapy Yttrium-90 (⁹⁰Y) bremsstrahlung SPECT imaging in selective internal radiation therapy, and to use this method to improve quantitative comparison of predicted and delivered ⁹⁰Y absorbed doses.MethodsThe spatial resolution of ^99mTc SPECT data was converted to that of ⁹⁰Y SPECT data using a function calculated from ^99mTc and ⁹⁰Y point spread functions. This resolution conversion method (RCM) was first applied to ^99mTc and ⁹⁰Y SPECT phantom data to validate the method, and then to clinical data to assess the power of ^99mTc SPECT imaging to predict the therapeutic absorbed dose.ResultsThe maximum difference between absorbed doses to phantom spheres was 178%. This was reduced to 27% after the RCM was applied.The clinical data demonstrated differences within 38% for mean absorbed doses delivered to the normal liver, which were reduced to 20% after application of the RCM. Analysis of clinical data showed that therapeutic absorbed doses delivered to tumours greater than 100 cm³ were predicted to within 52%, although there were differences of up to 210% for smaller tumours, even after the RCM was applied.ConclusionsThe RCM was successfully verified using phantom data. Analysis of the clinical data established that the ^99mTc pre-therapy imaging was predictive of the ⁹⁰Y absorbed dose to the normal liver to within 20%, but had poor predictability for tumours smaller than 100 cm³.     

Synthesis and biodistribution of a new class of 99mTc-labeled fatty acid analogs for myocardial imaging

A series of ^99mTc-bis(aminoethanethiol)-fatty acid (^99mTc-BAT-fatty acid) analogs were synthesized and evaluated as potential tracers of myocardial metabolism. The BAT-fatty acid precursors were prepared using a new synthetic route that avoids the use of strong reducing agents such as lithium aluminum hydride. Biodistribution studies of the no-carrier-added ^99mTc-complexes were conducted in rats using [¹²⁵I]IPPA as an internal standard. The myocardial uptake of the ^99mTc-BAT-fatty acid analogs was significantly less than that of [¹²⁵I]IPPA and indicates the ^99mTc analogs are not suitable candidates for SPECT-based myocardial imaging studies.     

Preparation,radiolabeling and biodistribution of a new class of bisaminothiol (BAT) ligands as possible imaging agents

In developing new ligands as potential brain and heart perfusion imaging agents two ligands based upon N₂S₂ donor atoms with the biphenyl backbone were synthesized. Biphenyl-2,2′-bis(N-1-amino-2-methyl-propane-2-thiol) (BP-BAT-TM) and biphenyl-2,2′-bis(N-1-amino-2-ethyl-butane-2-thiol) (BP-BAT-TE) form stable, neutral and lipid soluble complexes with [^99mTc]pertechnetate in the presence of tin(II) tartarate as a reducing agent. The [^99mTc]BP-BAT-TM complex penetrates the blood-brain barrier following i.v. injection into rats. Washout from the brain is fast, indicating no retention. The biodistribution of [^99mTc]BP-BAT-TE in rats showed an intitial heart uptake (0.8% /organ, at 2 min) and a slow washout (0.74% at 15 min). No brain uptake was found (0.05%). Significant uptake and retention in liver was observed. An imaging study of [^99mTc]BP-BAT-TE in a monkey showed no brain uptake and a clear indication of liver uptake and gall bladder clearance. These results indicate that this ligand system may be suitable as the basic core structure for the development of new imaging agents. Further studies with structural variations in the biphenyl backbone are warranted to develop new ^99mTc imaging agents for clinical applications.     

Synthesis and biological evaluation of 99mTc(CO)3(His–CB) as a tumor imaging agent

The chlorambucil l-histidine conjugate was synthesized and radiolabeled with [^99mTc(CO)₃]⁺ core to form the ^99mTc(CO)₃(His–CB) complex. The radiochemical purity of the complex was over 90%. It had good hydrophilicity and was stable at room temperature. The high initial tumor uptake with certain retention, fast clearance from background, good tumor/non-tumor ratios and satisfactory scintigraphic images highlighted the potential of ^99mTc(CO)₃(His–CB) as a tumor imaging agent.     

A Novel 99mTc-Labeled Molecular Probe for Tumor Angiogenesis Imaging in Hepatoma Xenografts Model: A Pilot Study

Introduction

Visualization of tumor angiogenesis using radionuclide targeting provides important diagnostic information. In previous study, we proved that an arginine-arginine-leucine (RRL) peptide should be a tumor endothelial cell specific binding sequence. The overall aim of this study was to evaluate whether ^99mTc-radiolabeled RRL could be noninvasively used for imaging of malignant tumors in vivo, and act as a new molecular probe targeting tumor angiogenesis.

Methods

The RRL peptide was designed and radiosynthesized with ^99mTc by a one-step method. The radiolabeling efficiency and radiochemical purity were then characterized in vitro. ^99mTc-RRL was injected intravenously in HepG2 xenograft-bearing BALB/c nude mice. Biodistribution and in vivo imaging were performed periodically. The relationship between tumor size and %ID uptake of ^99mTc-RRL was also explored.

Results

The labeling efficiencies of ^99mTc-RRL reached 76.9%±4.5% (n = 6) within 30–60 min at room temperature, and the radiochemical purity exceeded 96% after purification. In vitro stability experiment revealed the radiolabeled peptide was stable. Biodistribution data showed that ^99mTc-RRL rapidly cleared from the blood and predominantly accumulated in the kidneys and tumor. The specific uptake of ^99mTc-RRL in tumor was significantly higher than that of unlabeled RRL blocking and free pertechnetate control test after injection (p<0.05). The ratio of the tumor-to-muscle exceeded 6.5, tumor-to-liver reached 1.98 and tumor-to-blood reached 1.95. In planar gamma imaging study, the tumors were imaged clearly at 2–6 h after injection of ^99mTc-RRL, whereas the tumor was not imaged clearly in blocking group. The tumor-to-muscle ratio of images with ^99mTc-RRL was comparable with that of ¹⁸F-FDG PET images. Immunohistochemical analysis verified the excessive vasculature of tumor. There was a linear relationship between the tumor size and uptake of ^99mTc-RRL with R² = 0.821.

Conclusion

^99mTc-RRL can be used as a potential candidate for visualization of tumor angiogenesis in malignant carcinomas.     

Metastatic melanoma imaging using a novel Tc-99m-labeled lactam-cyclized alpha-MSH peptide

The purpose of this study was to determine the metastatic melanoma imaging property of ^99mTc(EDDA)-HYNIC-Aoc-Nle-CycMSH_hex {hydrazinonicotinamide-8-aminooctanoic acid-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH₂}. HYNIC-Aoc-Nle-CycMSH_hex was synthesized using fluorenylmethyloxy carbonyl (Fmoc) chemistry. The IC₅₀ value of HYNIC-Aoc-Nle-CycMSH_hex was 0.78?±?0.13?nM for B16/F10 melanoma cells. ^99mTc(EDDA)-HYNIC-Aoc-Nle-CycMSH_hex displayed significantly higher uptake (14.26?±?2.74 and 10.45?±?2.31%?ID/g) in B16/F10 metastatic melanoma-bearing lung than that in normal lung (0.90?±?0.15 and 0.53?±?0.14%?ID/g) at 2 and 4?h post-injection, respectively. B16/F10 pulmonary metastatic melanoma lesions were clearly visualized by SPECT/CT using ^99mTc(EDDA)-HYNIC-Aoc-Nle-CycMSH_hex as an imaging probe at 2?h post-injection, underscoring its potential as an imaging probe for metastatic melanoma detection.     

Tetraamine‐modified octreotide and octreotate: labeling with 99mTc and preclinical comparison in AR4‐2J cells and AR4‐2J tumor‐bearing mice

Two somatostatin analogues, [^99mTc]Demotide and [^99mTc]Demotate 4, were compared with [^99mTc]Demotate 1, a previously reported somatostatin receptor subtype 2 (sst₂) targeting tracer. Conjugates were prepared by coupling an open‐chain tetraamine chelator to D ‐Phe¹ of [Tyr³]‐octreotide or [Tyr³]‐octreotate, respectively, via a p‐benzylaminodiglycolic acid spacer adopting solid‐phase peptide synthesis techniques. Peptide conjugates were collected in a highly pure form after chromatographic purification. Eventually, [^99mTc]Demotide and [^99mTc]Demotate 4 were obtained in ～1 Ci/µmol specific activity and >96% purity after labeling under alkaline conditions. Demotide and Demotate 4 exhibited similar high binding affinities for the sst₂ expressed in AR4‐2J cells with IC₅₀ values 0.16 and 0.10 nM, respectively. The (radio)metallated analogues [^99mTc]Demotide and [^99mTc]Demotate 4 showed equally high affinities to the sst₂ during saturation binding assays in AR4‐2J cell membranes (K_ds 0.08 and 0.07 nM, respectively). During incubation at 37 °C with AR4‐2J cells, the radiopeptides internalized effectively via a receptor‐mediated process, with [^99mTc]Demotate 4 exhibiting a faster internalization rate than [^99mTc]Demotide. After injection in athymic mice bearing sst₂‐expressing AR4‐2J tumors, the radiotracers showed high and specific uptake in the tumor (>25%ID/g at 1 h) and in the sst₂–positive organs. However, both [^99mTc]Demotide and [^99mTc]Demotate 4 showed unfavorably higher background activity, especially in the abdomen, in comparison to [^99mTc]Demotate 1 and are, therefore, less suited than [^99mTc]Demotate 1 for sst₂‐targeted tumor imaging in man. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd.     

Development of 99mTc-labeled asymmetric urea derivatives that target prostate-specific membrane antigen for single-photon emission computed tomography imaging

Prostate-specific membrane antigen (PSMA) is expressed strongly in prostate cancers and is, therefore, an attractive diagnostic and radioimmunotherapeutic target. In contrast to previous reports of PMSA-targeting ^99mTc-tricarbonyl complexes that are cationic or lack a charge, no anionic ^99mTc-tricarbonyl complexes have been reported. Notably, the hydrophilicity conferred by both cationic and anionic charges leads to rapid hepatobiliary clearance, whereas an anionic charge might better enhance renal clearance relative to a cationic charge. Therefore, an improvement in rapid clearance would be expected with either cationic or anionic charges, particularly anionic charges. In this study, we designed and synthesized a novel anionic ^99mTc-tricarbonyl complex ([^99mTc]TMCE) and evaluated its use as a single-photon emission computed tomography (SPECT) imaging probe for PSMA detection. Direct synthesis of [^99mTc]TMCE from dimethyl iminodiacetate, which contains both the asymmetric urea and succinimidyl moiety important for PSMA binding, was performed using our microwave-assisted one-pot procedure. The chelate formation was successfully achieved even though the precursor included a complicated bioactive moiety. The radiochemical yield of [^99mTc]TMCE was 12–17%, with a radiochemical purity greater than 98% after HPLC purification. [^99mTc]TMCE showed high affinity in vitro, with high accumulation in LNCaP tumors and low hepatic retention in biodistribution and SPECT/CT studies. These findings warrant further evaluation of [^99mTc]TMCE as an imaging agent and support the benefit of this strategy for the design of other PSMA imaging probes.     

Synthesis of Tc-99m labeled glucosamino-Asp-cyclic(Arg-Gly-Asp-d-Phe-Lys) as a potential angiogenesis imaging agent

Angiogenesis imaging agents for single photon emission computed tomography (SPECT) play a role in diagnosing tumor-induced angiogenesis as well as tumor metastasis. We synthesized and evaluated radiolabeled RGD glycopeptides by incorporation of the [^99mTc(CO)₃(H₂O)₃]⁺. ^99mTc labeled glucosamino-D-c(RGDfK) ([^99mTc]2) was prepared in 90–93% radiochemical yields (decay corrected). In vitro cell binding assays demonstrated selective binding [^99mTc]2 to human umbilical vein endothelial (HUVE) cells, with inhibition of binding to 37.3% of control levels by 10 μM of cold authentic compounds. In addition, [^99mTc]2 was shown to have high binding affinity to purified α_vβ₃ integrin (IC₅₀ = 1.5 nM). These results suggest that these radiolabeled RGD glycopeptides may have value for non-invasive assessment of angiogenesis.     

Development of a Radiolabeled Peptide-Based Probe Targeting MT1-MMP for Breast Cancer Detection

Breast cancer is one of the most frequent and aggressive primary tumors among women of all races. Matrix metalloproteinase (MMPs), a family of zinc- and calcium-dependent secreted or membrane anchored endopeptidases, is overexpressed in varieties of diseases including breast cancer. Therefore, noninvasive visualization and quantification of MMP in vivo are of great interest in basic research and clinical application for breast cancer early diagnosis. Herein, we developed a ^99mTc labeled membrane type I matrix metalloproteinase (MT1-MMP) specific binding peptide, [^99mTc]-(HYNIC-AF7p)(tricine)(TPPTS), for in vivo detection of MDA-MB-231 breast tumor by single photon emission computed tomography (SPECT). [^99mTc]-(HYNIC-AF7p)(tricine)(TPPTS) demonstrated nice biostability and high MT1-MMP binding affinity in vitro and in vivo. Tumor-to-muscle ratio was found to reach to the highest (4.17±0.49) at 2 hour after intravenously administration of [^99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) into MDA-MB-231 tumor bearing mice. Overall, [^99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) demonstrated great potential for MT1-MMP targeted detection in vivo and it would be a promising molecular imaging probe that are probably beneficial to breast cancer early diagnoses.