99mTc-Labeled Small Peptides as Diagnostic Radiopharmaceuticals

A thiourea-bridged 99mTc(CO)3-dipicolylamine-2-nitroimidazole complex for targeting tumor hypoxia: Utilizing metabolizable thiourea-bridge to improve pharmacokinetics

The 2-nitroimidazole based 99mTc-radiopharmaceuticals are widely explored for imaging tumor hypoxia. Radiopharmaceuticals for targeting hypoxia are often lipophilic and therefore, show significant uptake in liver and other vital organs. In this context, lipophilic radiopharmaceuticals with design features enabling faster clearance from liver may be more desirable. A dipicolylamine-NCS bifunctional chelator that could generate a thiourea-bridge up on conjugation to primary amine bearing molecule was used to synthesize a 2-nitroimidazole-dipicolyl amine ligand for radiolabeling with 99mTc(CO)3 core. Corresponding Re(CO)3-analogue was prepared to establish the structure of 2-nitroimidazole-99mTc(CO)3 complex prepared in trace level. The 2-nitroimidazole-99mTc(CO)3 complex showed a hypoxic to normoxic ratio of ~2.5 in CHO cells at 3 h. In vivo, the complex showed accumulation and retention in tumor with high tumor to blood and tumor to muscle ratio. The study demonstrated the utility of metabolizable thiourea-bridge in 2-nitroimidazole-99mTc(CO)3 complex in inducing faster clearance of the radiotracer from liver. The dipicolylamine-NCS bifunctional chelator reported herein can also be used for radiolabeling other class of target specific molecules with 99mTc(CO)3 core.

Application of 99mTc-Labeled WL12 Peptides as a Tumor PD-L1-Targeted SPECT Imaging Agent: Kit Formulation, Preclinical Evaluation, and Study on the Influence of Coligands

With the development of PD-1/PD-L1 immune checkpoint inhibitor therapy, the ability to monitor PD-L1 expression in the tumor microenvironment is important for guiding therapy. This study was performed to develop a novel radiotracer with optimal pharmacokinetic properties to reflect PD-L1 expression in vivo via single-photon emission computed tomography (SPECT) imaging. [99mTc]Tc-HYNIC-WL12-tricine/M (M = TPPTS, PDA, ISONIC, 4-PSA) complexes with high radiochemical purity (>97%) and suitable molar activity (from 100.5 GBq/μmol to 300 GBq/μmol) were prepared through a kit preparation process. All 99mTc-labeled HYNIC-WL12 radiotracers displayed good in vitro stability for 4 h. The affinity and specificity of the four radiotracers for PD-L1 were demonstrated both in vitro and in vivo. The results of biodistribution studies displayed that the pharmacokinetics of the 99mTc-HYNIC-conjugated radiotracers were significantly influenced by the coligands of the radiotracers. Among them, [99mTc]Tc-HYNIC-WL12-tricine/ISONIC exhibited the optimal pharmacokinetic properties (t1/2α = 8.55 min, t1/2β = 54.05 min), including the fastest clearance in nontarget tissues, highest tumor-to-background contrast (e.g., tumor-to-muscle ratio, tumor-to-blood ratio: 40.42 ± 1.59, 14.72 ± 2.77 at 4 h p.i., respectively), and the lowest estimated radiation absorbed dose, highlighting its potential as a clinical SPECT imaging probe for tumor PD-L1 detection.

Comparative Preclinical Evaluation of HYNIC-Modified Designed Ankyrin Repeat Proteins G3 for the 99mTc-Based Imaging of HER2-Expressing Malignant Tumors

HER2 status determination is a necessary step for the proper choice of therapy and selection of patients for the targeted treatment of cancer. Targeted radiotracers such as radiolabeled DARPins provide a noninvasive and effective way for the molecular imaging of HER2 expression. This study aimed to evaluate tumor-targeting properties of three 99mTc-labeled DARPin G3 variants containing Gly-Gly-Gly-Cys (G3C), (Gly-Gly-Gly-Ser)3-Cys ((G3S)3C), or Glu-Glu-Glu-Cys (E3C) amino acid linkers at the C-terminus and conjugated to the HYNIC chelating agent, as well as to compare them with the clinically evaluated DARPin G3 labeled with 99mTc(CO)3 using the (HE)3-tag at the N-terminus. The labeling of DARPin G3-HYNIC variants provided radiochemical yields in the range of 50-80%. Labeled variants bound specifically to human HER2-expressing cancer cell lines with affinities in the range of 0.5-3 nM. There was no substantial influence of the linker and HYNIC chelator on the binding of 99mTc-labeled DARPin G3 variants to HER2 in vitro; however, [99mTc]Tc-G3-(G3S)3C-HYNIC had the highest affinity. Comparative biodistribution of [99mTc]Tc-G3-G3C-HYNIC, [99mTc]Tc-G3-(G3S)3C-HYNIC, [99mTc]Tc-G3-E3C-HYNIC, and [99mTc]Tc-(HE)3-G3 in healthy CD1 mice showed that there was a strong influence of the linkers on uptake in normal tissues. [99mTc]Tc-G3-E3C-HYNIC had an increased retention of activity in the liver and the majority of other organs compared to the other conjugates. The tumor uptake of [99mTc]Tc-G3-(G3S)3C-HYNIC and [99mTc]Tc-(HE)3-G3 in Nu/j mice bearing SKOV-3 xenografts was similar. The specificity of tumor targeting in vivo was demonstrated for both tracers. [99mTc]Tc-G3-(G3S)3C-HYNIC provided comparable, although slightly lower tumor-to-lung, tumor-to spleen and tumor-to-liver ratios than [99mTc]Tc-(HE)3-G3. Radiolabeling of DARPin G3-HYNIC conjugates with 99mTc provided the advantage of a single-step radiolabeling procedure; however, the studied HYNIC conjugates did not improve imaging contrast compared to the 99mTc-tricarbonyl-labeled DARPin G3. At this stage, [99mTc]Tc-(HE)3-G3 remains the most promising candidate for the clinical imaging of HER2-overexpressing cancers.

Radiosynthesis and Bioevaluation of 99mTc-Labeled Isocyanide Ubiquicidin 29-41 Derivatives as Potential Agents for Bacterial Infection Imaging

To develop a novel 99mTc-labeled ubiquicidin 29-41 derivative for bacterial infection single-photon emission computed tomography (SPECT) imaging with improved target-to-nontarget ratio and lower nontarget organ uptake, a series of isocyanide ubiquicidin 29-41 derivatives (CNnUBI 29-41, n = 5-9) with different carbon linkers were designed, synthesized and radiolabeled with the [99mTc]Tc(I)+ core, [99mTc][Tc(I)(CO)3(H2O)3]+ core and [99mTc][Tc(V)N]2+ core. All the complexes are hydrophilic, maintain good stability and specifically bind Staphylococcus aureus in vitro. The biodistribution in mice with bacterial infection and sterile inflammation demonstrated that [99mTc]Tc-CN5UBI 29-41 was able to distinguish bacterial infection from sterile inflammation, which had an improved abscess uptake and a greater target-to-nontarget ratio. SPECT imaging study of [99mTc]Tc-CN5UBI 29-41 in bacterial infection mice showed that there was a clear accumulation in the infection site, suggesting that this radiotracer could be a potential radiotracer for bacterial infection imaging.

Unlocking the Hidden Depths: Multi-Modal Integration of Imaging Mass Spectrometry-Based and Molecular Imaging Techniques

Multimodal imaging (MMI) has emerged as a powerful tool in clinical research, combining different imaging modes to acquire comprehensive information and enabling scientists and surgeons to study tissue identification, localization, metabolic activity, and molecular discovery, thus aiding in disease progression analysis. While multimodal instruments are gaining popularity, challenges such as non-standardized characteristics, custom software, inadequate commercial support, and integration issues with other instruments need to be addressed. The field of multimodal imaging or multiplexed imaging allows for simultaneous signal reproduction from multiple imaging strategies. Intraoperatively, MMI can be integrated into frameless stereotactic surgery. Recent developments in medical imaging modalities such as magnetic resonance imaging (MRI), and Positron Emission Topography (PET) have brought new perspectives to multimodal imaging, enabling early cancer detection, molecular tracking, and real-time progression monitoring. Despite the evidence supporting the role of MMI in surgical decision-making, there is a need for comprehensive studies to validate and perform integration at the intersection of multiple imaging technologies. They were integrating mass spectrometry-based technologies (e.g., imaging mass spectrometry (IMS), imaging mass cytometry (IMC), and Ion mobility mass spectrometry ((IM-IM) with medical imaging modalities, offering promising avenues for molecular discovery and clinical applications. This review emphasizes the potential of multi-omics approaches in tissue mapping using MMI integrated into desorption electrospray ionization (DESI) and matrix-assisted laser desorption ionization (MALDI), allowing for sequential analyses of the same section. By addressing existing knowledge gaps, this review encourages future research endeavors toward multi-omics approaches, providing a roadmap for future research and enhancing the value of MMI in molecular pathology for diagnosis.

[99mTc]Tc-HYNIC-RM2: A potential SPECT probe targeting GRPR expression in prostate cancers

INTRODUCTION

Elevated density of gastrin releasing peptide receptors (GRPR) in prostate cancer has led to exploration of several radiolabeled peptides for imaging and staging of the disease. The GRPR antagonist peptide RM2 has been successfully conjugated with several chelators and radiolabeled with gallium-68. The goal of this study was to synthesize a ^99mTc-labeled probe and investigate its potential for SPECT imaging of prostate cancer. Towards this HYNIC-RM2 peptide conjugate was synthesized, radiolabeled with ^99mTc and evaluated in GRPR-positive PC3 tumor xenografts.

METHODS

HYNIC-RM2 was manually synthesized by standard Fmoc solid phase strategy and radiolabeled with ^99mTc. In vitro cell studies were performed in GRPR-positive human prostate carcinoma (PC3) cells. Metabolic stability studies of [^99mTc]Tc-HYNIC-RM2 were performed in normal mice in the presence as well as absence of neutral endopeptidase (NEP) inhibitor, phosphoramidon (PA). Biodistribution and imaging studies of [^99mTc]Tc-HYNIC-RM2 were performed in SCID mice bearing PC3-xenograft.

RESULTS

[^99mTc]Tc-HYNIC-RM2 exhibited high binding affinity in low nanomolar range (K_d = 1.83 ± 0.31 nM). Metabolic stability studies in mice indicated that in the absence of PA, radiolabeled peptide was about 65 % intact in the blood at 15 min p.i., whereas proportion of intact radiolabeled peptide was enhanced to 90 % on co-administration of PA. Biodistribution studies in PC3 tumor bearing mice demonstrated high tumor uptake (8.02 ± 0.9%ID/g and 6.13 ± 0.44%ID/g at 1 h and 3 h p.i.). Co-administration of PA with the radiolabeled peptide resulted in further enhancement of tumor uptake (14.24 ± 0.76 % ID/g and 11.71 ± 0.59%ID/g at 1 h and 3 h p.i.). SPECT/CT images of [^99mTc]Tc-HYNIC-RM2 could clearly visualize the tumor. Significant (p < 0.001) reduction in the tumor uptake with a co-injected blocking dose of unlabeled peptide ascertained the GRPR specificity of [^99mTc]Tc-HYNIC-RM2.

CONCLUSION

Encouraging results obtained in biodistribution and imaging studies indicate the potential of [^99mTc]Tc-HYNIC-RM2 for further exploration as GRPR targeting agent.

A novel molecular imaging probe [99mTc]Tc-HYNIC-FAPI targeting cancer-associated fibroblasts

Fibroblast activation protein (FAP) is higher expressed on cancer-associated fibroblasts (CAFs) in most malignant epithelial neoplasms, which is lower expressed in normal tissues. As a promising small molecular probe, FAP inhibitor (FAPI) shows the specific binding to FAP. This study aimed to explore a novel molecular probe [^99mTc]Tc-HYNIC-FAPI targeting CAFs. The in vitro characteristics of the probe were also evaluated. The FAPI targeting FAP was designed, synthesized and conjugated with the chelator 6-hydrazinylnicotinic acid (HYNIC) for radiolabeling with ^99mTc. The radiolabeling yield, radiochemical purity and stability were evaluated by Instant thin-layer chromatography (ITLC) and High performance liquid chromatography (HPLC). Lipophilicity was performed by the distribution coefficient test. The binding and migration ability of the probe was assessed using the FAP transfected tumor cell line. The radiolabeling yield of [^99mTc]Tc-HYNIC-FAPI was (97.29 ± 0.46) %. The radiochemical purity was more than 90% and kept stable until 6 h. The radioligand was shown as lower lipophilicity, of which logD7.4 value was - 2.38 [Formula: see text] 0.13. In vitro experiments, the results indicated that the probe showed binding properties, and inhibited the migration of tumor cells. The novel [^99mTc]Tc-HYNIC-FAPI probe was successfully radiosynthesized and exhibited good radiochemical purity, stability and in vitro binding ability to tumor cells. The [^99mTc]Tc-HYNIC-FAPI will be a promising SPECT/CT imaging probe.

Synthesis and Bioevaluation of Novel Technetium-99m-Labeled Complexes with Norfloxacin HYNIC Derivatives for Bacterial Infection Imaging

To seek a novel ^99mTc-labeled quinolone derivative for bacterial infection SPECT imaging that aims to lower nontarget organ uptake, a novel norfloxacin 6-hydrazinoicotinamide (HYNIC) derivative (HYNICNF) was designed and synthesized. It was radiolabeled with different coligands, such as tricine, trisodium triphenylphosphine-3,3',3″-trisulfonate (TPPTS), sodium triphenylphosphine-3-monosulfonate (TPPMS), and ethylenediamine-N,N'-diacetic acid (EDDA), to obtain three ^99mTc-labeled norfloxacin HYNIC complexes, namely, [^99mTc]Tc-tricine-TPPTS-HYNICNF, [^99mTc]Tc-tricine-TPPMS-HYNICNF, and [^99mTc]Tc-EDDA-HYNICNF. These complexes were purified (RCP > 95%) and evaluated in vitro and in vivo for targeting bacteria. All three complexes are hydrophilic, maintain good stability, and specifically bind Staphylococcus aureus in vitro. The biodistribution in mice with bacterial infection demonstrated that [^99mTc]Tc-EDDA-HYNICNF showed a higher abscess uptake and lower nontarget organ uptake and was able to distinguish bacterial infection and sterile inflammation. Single photon emission computed tomography (SPECT) image study in bacterial infection mice showed there was a visible accumulation in the infection site, suggesting that [^99mTc]Tc-EDDA-HYNICNF is a potential radiotracer for bacterial infection imaging.

99mTc- Anionic dendrimer targeted vascular endothelial growth factor as a novel nano-radiotracer for in-vivo breast cancer imaging

Since breast cancer is the commonly cause of death among women around the world, diagnosis at the early stages is significantly important to prevent the metastasis of the cancer. Among the various growth factors that are involved in angiogenesis, vascular endothelial growth factor (VEGF) is believed to be the most important factor. Overexpressed VEGF receptor on tumors surface, is particularly interesting for cancer cells targeting purposes. In this study, citric acid dendrimer conjugated with VEGF antagonist peptide was synthesized. The obtained product was confirmed by FT-IR, TEM, DLS, and EDS. In vitro cytotoxicity assay showed no toxicity on normal cells and indicated the notably dose-dependence toxicity on cancer cells. Box-Behnken software as a computational method was used to determine the optimum amount of radiolabeling parameters. Optimized parameters for reducing agent, dendrimer-anti-VEGF, and time were 1.4 mg, 17.5 mg, and about 30 min respectively. Radiochemical purity of radio-labeled conjugated dendrimer was determined about 90 percent. SPECT imaging was done to observe the in vivo accumulation of dendrimer-anti-VEGF in the tumor site. Images showed high accumulation of radio-tracer in the tumor region. All in all, obtained results confirmed our hypothesis that the dendrimer-anti-VEGF can be a good radio-tracer for diagnosis of cancer.

Radiopharmaceutical Labelling for Lung Ventilation/Perfusion PET/CT Imaging: A Review of Production and Optimization Processes for Clinical Use

Lung ventilation/perfusion (V/Q) positron emission tomography-computed tomography (PET/CT) is a promising imaging modality for regional lung function assessment. The same carrier molecules as a conventional V/Q scan (i.e., carbon nanoparticles for ventilation and macro aggregated albumin particles for perfusion) are used, but they are labeled with gallium-68 (⁶⁸Ga) instead of technetium-99m (^99mTc). For both radiopharmaceuticals, various production processes have been proposed. This article discusses the challenges associated with the transition from ^99mTc- to ⁶⁸Ga-labelled radiopharmaceuticals. The various production and optimization processes for both radiopharmaceuticals are reviewed and discussed for optimal clinical use.

Homomultimer strategy for improvement of radiolabeled peptides and antibody fragments in tumor targeting

A homomultimeric radioligand is composed of multiple identical ligands connected to the linker and radionuclide to detect a variety of overexpressed receptors on cancer cells. Multimer strategy holds great potential for introducing new radiotracers based on peptide and monoclonal antibody (mAb) derivatives in molecular imaging and therapy. It offers a reliable procedure for the preparation of biological-based targeting with diverse affinities and pharmacokinetics. In this context, we provide a useful summary and interpretation of the main results by a comprehensive look at multimeric radiopharmaceuticals in nuclear oncology. Therefore, there will be explanations for the strategy mechanisms and the main variables affecting the biodistribution results. The discussion is followed by highlights of recent work in the targeting of various types of receptors. The consequences are expressed based on comparing some parameters between monomer and multimer counterparts in each relevant section.

Bifunctional chelators for radiorhenium: past, present and future outlook

Targeted radionuclide therapy (TRNT) is an ever-expanding field of nuclear medicine that provides a personalised approach to cancer treatment while limiting toxicity to normal tissues. It involves the radiolabelling of a biological targeting vector with an appropriate therapeutic radionuclide, often facilitated by the use of a bifunctional chelator (BFC) to stably link the two entities. The radioisotopes of rhenium, 186Re (t 1/2 = 90 h, 1.07 MeV β-, 137 keV γ (9%)) and 188Re (t 1/2 = 16.9 h, 2.12 MeV β-, 155 keV γ (15%)), are particularly attractive for radiotherapy because of their convenient and high-abundance β--particle emissions as well as their imageable γ-emissions and chemical similarity to technetium. As a transition metal element with multiple oxidation states and coordination numbers accessible for complexation, there is great opportunity available when it comes to developing novel BFCs for rhenium. The purpose of this review is to provide a recap on some of the past successes and failings, as well as show some more current efforts in the design of BFCs for 186/188Re. Future use of these radionuclides for radiotherapy depends on their cost-effective availability and this will also be discussed. Finally, bioconjugation strategies for radiolabelling biomolecules with 186/188Re will be touched upon.

Development of a hydroxamamide-based bifunctional chelating agent to prepare technetium-99m-labeled bivalent ligand probes

Hydroxamamide (Ham) is a thiol-free chelating agent that forms technetium-99m (^99mTc)-complexes with a metal-to-ligand ratio of 1:2 under moderate reaction conditions. Therefore, Ham-based chelating agents will produce ^99mTc-labeled compounds with a bivalent targeting scaffold. For their universal usage, we developed a novel Ham-based bifunctional chelating agent, “Ham-Mal”, with a maleimide group that can easily conjugate with a thiol group, for to preparing ^99mTc-labeled bivalent ligand probes. Ham-Mal was synthesized by a four-step reaction, and then reacted with cysteine or c(RGDfC) to produce Ham-Cys or Ham-RGD. These precursors were reacted with ^99mTcO₄^- for 10 min under room temperature to obtain ^99mTc-(Ham-Cys)₂ and ^99mTc -(Ham-RGD)₂. The cellular uptake level of ^99mTc-(Ham-RGD)₂ by U87MG (high Integrin ɑ_vβ₃ expression) cells was significantly higher than that by PC3 (low Integrin ɑ_vβ₃ expression) cells at 60 min after the incubation, and the uptake was significantly suppressed by pre-treatment for 15 min with excess c(RGDfK) peptide. In the in vivo study with U87MG/PC3 dual xenografted BALB/c-nu mice, the radioactivity of U87MG tumor tissue was significantly higher than that of PC3 tumor tissue at 360 min after the administration of ^99mTc-(Ham-RGD)₂. These results suggest Ham-Mal may have potential as a bifunctional chelating agent for ^99mTc-labeled bivalent ligand probes.

Small peptide-based GLP-1R ligands: an approach to reduce the kidney uptake of radiolabeled GLP-1R-targeting agents?

Aim

Elevated kidney uptake in insulinoma patients remains a major limitation of radiometallated exendin-derived ligands of the glucagon-like peptide 1 receptor (GLP-1R). Based on the previously published potent GLP-1R-activating undecapeptide 1, short-chained GLP-1R ligands were developed to investigate whether kidney uptake can be reduced by means of direct ¹⁸F-labeling (nuclide-based accelerated renal excretion) or the reduction of the overall ligand charge (ligand-based reduced kidney uptake).

Materials & methods

GLP-1R ligands were prepared according to optimized standard protocols via solid-phase peptide synthesis (SPPS) or, when not practicable, via fragment coupling in solution. Synthesis of (2‘-Et, 4‘-OMe)4, 4’-L-biphenylalanine ((2′-Et, 4′-OMe)BIP), required for the preparation of 1, was accomplished by Suzuki-Miyaura cross-coupling. In vitro experiments were performed using stably transfected GLP-1R⁺ HEK293-hGLP-1R cells.

Results

In contrast to the three reference ligands glucagon-like peptide 1 (GLP-1, IC₅₀ = 23.2 ± 12.2 nM), [Nle¹⁴, Tyr(3-I)⁴⁰]exendin-4 (IC₅₀ = 7.63 ± 2.78 nM) and [Nle¹⁴, Tyr⁴⁰]exendin-4 (IC₅₀ = 9.87 ± 1.82 nM), the investigated GLP-1R-targeting small peptides (9–15 amino acids), including lead peptide 1, exhibited only medium to low affinities (IC₅₀ > 189 nM). Only SiFA-tagged undecapeptide 5 (IC₅₀ = 189 ± 35 nM) revealed a higher affinity than 1 (IC₅₀ = 669 ± 242 nM).

Conclusion

The investigated small peptides, including lead peptide 1, could not compete with favorable in vitro characteristics of glucagon-like peptide 1 (GLP-1), [Nle¹⁴, Tyr(3-I)⁴⁰]exendin-4 and [Nle¹⁴, Tyr⁴⁰]exendin-4. The auspicious EC₅₀ values of 1 provided by the literature could not be transferred to competitive binding experiments. Therefore, the use of 1 as a basic scaffold for the design of further GLP-1R-targeting radioligands cannot be recommended. Further investigations might include the scaffold of 5, although substantial optimizations concerning affinity and lipophilicity would be required. In sum, GLP-1R-targeting radioligands with reduced kidney uptake could not be obtained in this work, which emphasizes the need for further ligands addressing this particular issue.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41181-021-00136-x.

A Combined Study of Tc Redox Speciation in Complex Aqueous Systems: Wet-Chemistry, Tc K-/L3-Edge X-ray Absorption Fine Structure, and Ab Initio Calculations

The combination of wet-chemistry experiments (measurements of pH, E_h, and [Tc]) and advanced spectroscopic techniques (K- and L₃-edge X-ray absorption fine structure spectroscopy) confirms the formation of a very stable Tc(V)-gluconate complex under anoxic conditions. In the presence of gluconate and an excess of Sn(II) (at pe + pH ≈ 2), technetium forms a very stable Tc(IV)-gluconate complex significantly enhancing the solubility defined by TcO₂(s) in hyperalkaline gluconate-free systems. A new setup for "tender" X-ray spectroscopy (spectral range, ∼2-5 keV) in transmission or total fluorescence yield detection mode based on a He flow cell has been developed at the INE Beamline for radionuclide science (KIT light source). This setup allows handling of radioactive specimens with total activities up to one million times the exemption limit. For the first time, Tc L₃-edge measurements (∼2.677 keV) of Tc species in liquid (aqueous) media are reported, clearly outperforming conventional K-edge spectroscopy as a tool to differentiate Tc oxidation states and coordination environments. The coupling of L₃-edge X-ray absorption near-edge spectroscopy measurements and relativistic multireference ab initio methods opens new perspectives in the definition of chemical and thermodynamic models for systems of relevance in the context of nuclear waste disposal, environmental, and pharmaceutical applications.

Radiolabeling and evaluation of a novel [99mTcN]2+ complex with deferoxamine dithiocarbamate as a potential agent for bacterial infection imaging

In order to find a ^99mTc-labeled deferoxamine radiotracer for bacterial infection imaging, deferoxamine dithiocarbamate (DFODTC) was successfully synthesized and it was radiolabeled with [^99mTcN]²⁺ core to prepare the ^99mTcN(DFODTC)₂ complex. ^99mTcN(DFODTC)₂ was obtained with high radiochemical purity without further purification. The complex was lipophilic and exhibited good in vitro stability. According to the result of bacterial binding study, the binding of ^99mTcN(DFODTC)₂ to bacteria was specific. Biodistribution in mice study indicated that ^99mTcN(DFODTC)₂ had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses at 120 min after injection, which showed that the radiotracer could differentiate between bacterial infection and sterile inflammation. SPECT/CT images showed that there was a clear accumulation in infection sites, suggesting that ^99mTcN(DFODTC)₂ could be a potential bacterial infection imaging radiotracer.

MUC1-Targeted Radiopharmaceuticals in Cancer Imaging and Therapy

Mucin 1 (MUC1) is a large, transmembrane mucin glycoprotein overexpressed in most adenocarcinomas and plays an important role in tumor progression. Regarding its cellular distribution, biochemical features, and function, tumor-related MUC1 varies from the MUC1 expressed in normal cells. Therefore, targeting MUC1 for cancer immunotherapy and imaging can exploit the difference between cancerous and normal cells. Radiopharmaceuticals have a potential use as carriers for the delivery of radionuclides to tumors for a diagnostic imaging and radiotherapy. Several radiolabeled targeting molecules like peptides, antibodies, and aptamers have been efficiently demonstrated in detecting and treating cancer by targeting MUC1. This review provides a brief overview of the current status of developments and applications of MUC1-targeted radiopharmaceuticals in cancer imaging and therapy.

Recent Advances in Radiometals for Combined Imaging and Therapy in Cancer

Nuclear medicine is defined as the use of radionuclides for diagnostic and therapeutic applications. The imaging modalities positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are based on γ-emissions of specific energies. The therapeutic technologies are based on β^- -particle-, α-particle-, and Auger electron emitters. In oncology, PET and SPECT are used to detect cancer lesions, to determine dosimetry, and to monitor therapy effectiveness. In contrast, radiotherapy is designed to irreparably damage tumor cells in order to eradicate or control the disease's progression. Radiometals are being explored for the development of diagnostic and therapeutic radiopharmaceuticals. Strategies that combine both modalities (diagnostic and therapeutic), referred to as theranostics, are promising candidates for clinical applications. This review provides an overview of the basic concepts behind therapeutic and diagnostic radiopharmaceuticals and their significance in contemporary oncology. Select radiometals that significantly impact current and upcoming cancer treatment strategies are grouped as clinically suitable theranostics pairs. The most important physical and chemical properties are discussed. Standard production methods and current radionuclide availability are provided to indicate whether a cost-efficient use in a clinical routine is feasible. Recent preclinical and clinical developments and outline perspectives for the radiometals are highlighted in each section.

Radiolabeled Peptide Probes for Liver Cancer Imaging

Liver cancer/Hepatocellular Carcinoma (HCC) is a leading cause of cancer death and represents an important cause of mortality worldwide. Several biomarkers are overexpressed in liver cancer, such as Glypican 3 (GPC3) and Epidermal Growth Factor Receptor (EGFR). These biomarkers play important roles in the progression of tumors and could serve as imaging and therapeutic targets for this disease. Peptides with adequate stability, receptor binding properties, and biokinetic behavior have been intensively studied for liver cancer imaging. A great variety of them have been radiolabeled with clinically relevant radionuclides for liver cancer diagnosis, and many are promising imaging and therapeutic candidates for clinical translation. Herein, we summarize the advancement of radiolabeled peptides for the targeted imaging of liver cancer.

Radiosynthesis, molecular modeling and biodistribution of 99mTc-Protoporphyrin as a preclinical model for tumor diagnosis

Porphyrins are among the most important and widely used compounds involved in a variety of chemical and biochemical applications. These molecules exhibit very special properties that encourage researchers to label many derivatives with diagnostic or therapeutic radionuclides for medical applications. This study reports the radiolabeling and biodistribution of [Formula: see text]Tc-protoporphyrin IX ([Formula: see text]Tc-PPIX) as a novel potential solid-tumor imaging agent. The factors affecting the radiolabeling process were varied to achieve maximum radiochemical yield. [Formula: see text]Tc-PPIX was obtained in high yield of 97.34 ± 0.21% and high stability in serum up to 24 h. The radiochemical yield of [Formula: see text]Tc-PPIX was assessed by a combination of a paper chromatographic technique and HPLC. A computational analysis for all the potential structures that may be formed due to the interaction between protoporphyrin IX and technetium was performed via the DFT method of calculations in gas phase to predict the most likely structure. Molecular docking was further employed to shed light on the nature of the interaction between the most stable complexes with the target protein. Finally, the in-vivo biodistribution of [Formula: see text]Tc-PPIX complex was evaluated in solid-tumor-bearing mice and high tumor/tissue ratio of 5.17 ± 0.34 at 60 min post injection was obtained. Our finding clearly suggests [Formula: see text]Tc-PPIX as a potential SPECT agent for tumor imaging.

The Effects of the Spacer on Radiochemical and Biological Properties of New Radiolabeled Bombesin(7-14) Derivative

OBJECTIVE

The aim of this study was to develop 99mTc-[HYNIC-X-D-Phe13]-BBN(7-14)NH2 derivatives using two different tripeptidic spacer groups (X=GGG and X=SSS) in order to improve its pharmacokinetics, in vitro stability, specific binding, and affinity.

BACKGROUND

Bombesin (BBN), a 14-aminoacid amphibian peptide homolog of mammalian gastrinreleasing peptide (GRP), has demonstrated the ability to bind with high affinity and specificity to GRP receptor, which is overexpressed on a variety of human cancers.

METHODS

Peptide conjugates labeled with 99mTc using tricine-EDDA and radiochemical purity was assessed by TLC and HPLC. The stability of radio conjugates was evaluated in the presence of saline and human serum. Affinity, internalization, and also dissociation Constant was evaluated using MDAMB- 231 and PC-3 cell line. Biodistribution study was performed in BALB/C mice.

RESULTS

Labeling yield of ˃95% was obtained. The change introduced in the BBN sequence increased plasma stability. In vitro blocking studies showed that binding and internalization of both radiolabeled peptides are mediated by their receptors on the surface of MDA-MB-231 and PC-3 cells. Biodistribution results demonstrated a rapid blood clearance, with predominantly renal excretion. Specific binding in GRP receptor-positive tissues, such as pancreas was confirmed with a blocking study.

CONCLUSION

The introduction of the spacer sequence between chelator and BBN(7-14) led to improved bidistribution. Analog with tri-Gly spacer is the more promising radiopeptide for targeting GRP receptors than Ser conjugates. Therefore, these analogs can be considered as a candidate for the identification of bombesin-positive tumors.

Manipulating Pharmacokinetics of Purification-Free 99mTc-Labeled Bivalent Probes for In Vivo Imaging of Saturable Targets

The accumulation of ^99mTc-labeled probes targeting saturable systems of the body is hindered by the presence of a large excess of unlabeled ligands needed to ensure high radiochemical yields in a short reaction time. To address the issue, we recently reported a novel concept of a metal-coordination-mediated synthesis of a bivalent ^99mTc-labeled probe from a monovalent ligand using d-penicillamine (Pen) as a chelating molecule and c(RGDfK) as a model targeting device. The Pen-conjugated c(RGDfK) via a hexanoate linkage (Pen-Hx-c(RGDfK)) provided a bivalent [^99mTc]Tc-[(Pen-Hx-c(RGDfK))₂ that possessed much higher integrin α_vβ₃ binding affinity than Pen-Hx-c(RGDfK) and visualized a murine tumor without purification. However, high radioactivity levels were observed in the abdominal regions, which necessitated improved pharmacokinetics of the probes for practical applications. In this study, a pharmacokinetic (PK) modifier was introduced to manipulate the pharmacokinetics of the ^99mTc-Pen₂-based bivalent probe. The Hx linkage in Pen-Hx-c(RGDfK) was replaced with acetyl-d-serine-d-serine-glycine (Ac-ssG) or hexanoyl-d-serine-d-serine-d-serine (Hx-sss) to prepare Pen-Ac-ssG-c(RGDfK) or Pen-Hx-sss-c(RGDfK). Pen-Ac-ssG-c(RGDfK) impaired the complexation ability of Pen-Hx-c(RGDfK), and a monovalent ^99mTc-labeled compound was generated at low ligand concentration. However, Pen-Hx-sss-c(RGDfK) provided the objective bivalent ^99mTc-labeled probe in high radiochemical yields at a concentration similar to that of Pen-Hx-c(RGDfK). [^99mTc]Tc-[Pen-Hx-sss-c(RGDfK)]₂ also possessed stability and integrin α_vβ₃ binding affinity similar to those of [^99mTc]Tc-[Pen-Hx-c(RGDfK)]₂. As a result, [^99mTc]Tc-[Pen-Hx-sss-c(RGDfK)]₂ exhibited tumor and abdominal radioactivity levels similar to and significantly lower than those of [^99mTc]Tc-[Pen-Hx-c(RGDfK)]₂. These findings indicate the incorporation of a tripeptide PK modifier to Pen-Hx-c(RGDfK) preserved the complexation ability and improved the pharmacokinetics of the resulting ^99mTc-labeled bivalent probe without impairing the targeting ability. Thus, the [Pen-Hx-(PK modifier)-(targeting device)] would constitute a basic formulation for preparing the ^99mTc-Pen₂-based bivalent probes for imaging saturable targets of the body.

Single Photon Emission Computed Tomography Tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g., peptide, antibody fragment) and a γ-radiation-emitting radionuclide (e.g., ^99mTc, ¹²³I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design, these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

Rhenium and technetium-complexed silicon rhodamines as near-infrared imaging probes for bimodal SPECT- and optical imaging

The first technetium-99m tricarbonyl core labelled fluorescent Si-rhodamine and its rhenium analogue for bimodal SPECT- and near-infrared fluorescence imaging is presented.

Synthesis and biological evaluation of RGD conjugated with Ketoprofen/Naproxen and radiolabeled with [99mTc] via N4(GGAG) for αVβ3 integrin-targeted drug delivery

BACKGROUND

Integrins are interesting targets in oncology. RGD sequence has high affinity for α_Vβ₃ integrin receptors. Diagnostic/therapeutic agents can be selectively delivered into cancer cells overexpressing α_Vβ₃ integrin by using RGD as a carrier. Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown anticancer properties in in vitro and in vivo studies. The anti-cancer properties of NSAIDs occur though COX-2 inhibition. Regarding the anti-cancer properties of NSAIDs and overexpression of COX-2 enzyme in cancer cells, targeted delivery of NSAIDs into cancer cells to maximize their efficiency and minimize their side effects may gain increased clinical interest.

OBJECTIVES

In this study, RGD was conjugated to ketoprofen/Naproxen to selectively transfer these non-selective COX inhibitors into cancer cells.

METHODS

Keto/Nap-RGD-N4 peptides were synthesized based on solid phase fmoc peptide synthesis. Radiolabeling with [^99mTc] via N4 (GGAG) ligand was done for biological evaluation. Affinity and specificity of Keto/Nap-RGD-N4 to integrin was determined using A2780, OVCAR-3, SKOV-3 and HT-1080 cell lines. Percentage of Intenalization was measured in A2780 cells. Biodistriburion was studied in normal and tumor model mice.

RESULTS

Radiolabeled compounds showed high affinity to cells expressing α_Vβ₃ integrin in comparison to cells not expressing α_Vβ₃. The affinity to A2780 was significantly higher than OVCAR-3 cells. The %internalization into A2780 cells was quite low. Compounds showed more than 50% inhibition on A2780 and OVCAR-3 cells, less than 10% on MCF-7 and HT-1080 cells and no cytotoxicity on fibroblast cells after 48 h incubation. Although uptake of radiolabeled compounds in tumor was high at 1 h post-injection, the tumor/blood ratio was less than 1.5 which made SPECT imaging impossible.

CONCLUSION

Provided that NSAID drugs are conjugated to RGD, there will be a selective delivery to target tissues as well as synergetic anti-tumor effects which reduce systemic doses and toxicity. Graphical abstract.

Preparation and clinical translation of 99mTc-PSMA-11 for SPECT imaging of prostate cancer

This study explores the feasibility of radiolabeling the HBED-CC-PSMA (PSMA-11) ligand with Tc-99m for SPECT imaging of prostate cancer patients. ⁶⁸Ga-HBED-CC-PSMA (PSMA-11) is used clinically for PET/CT imaging of prostate cancer (PCa) patients. However, a PET/CT facility may not be affordable and/or accessible to remotely located health centers. Thus, economic considerations require development of a SPECT-based tracer to provide low cost effective health care to the entire global population. Hence, radiochemical parameters were varied and optimized to obtain the maximum radiochemical yield of ^99mTc-PSMA-11. ^99mTc-PSMA-11 could be prepared in 60 ± 5% radiochemical yield and >98% radiochemical purity with a specific activity of 15 ± 5 GBq μmol^-1. The radiotracer exhibited high stability in vitro in human serum after 24 h. A cell uptake of 15.2 ± 1.2% was observed for ^99mTc-PSMA-11 in PSMA-positive prostate carcinoma LNCaP cells. Rapid clearance from blood, liver, intestine, lungs and other major organs was observed during normal biodistribution studies. The radiotracer, ^99mTc-PSMA-11, exhibited physiological distribution in salivary and lacrimal glands similar to that of ⁶⁸Ga-PSMA-11 in mice and successfully identified primary tumors as well as metastatic lesions in human patients. This study thus highlights successful radiolabeling of HBED-CC-PSMA with Tc-99m and the potential of ^99mTc-PSMA-11 as a SPECT imaging agent for PCa.

Peptide-Conjugated Nanoparticles as Targeted Anti-angiogenesis Therapeutic and Diagnostic in Cancer

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Targeting angiogenesis in the microenvironment of a tumor can enable suppression of tumor angiogenesis and delivery of anticancer drugs into the tumor. Anti-angiogenesis targeted delivery systems utilizing passive targeting such as Enhanced Permeability and Retention (EPR) and specific receptor-mediated targeting (active targeting) should result in tumor-specific targeting. One targeted anti-angiogenesis approach uses peptides conjugated to nanoparticles, which can be loaded with anticancer agents. Anti-angiogenesis agents can suppress tumor angiogenesis and thereby affect tumor growth progression (tumor growth arrest), which may be further reduced with the targetdelivered anticancer agent. This review provides an update of tumor vascular targeting for therapeutic and diagnostic applications, with conventional or long-circulating nanoparticles decorated with peptides that target neovascularization (anti-angiogenesis) in the tumor microenvironment.

Evaluation of New 99mTc(CO)3 + Radiolabeled Glycylglycine In Vivo

BACKGROUND

Peptide-based agents are used in molecular imaging due to their unique properties, such as rapid clearance from the circulation, high affinity and target selectivity. Many of the radiolabeled peptides have been clinically experienced with diagnostic accuracy. The aim of this study was to investigate in vivo biological behavior of [^99mTc(CO)₃(H₂O)₃]+ radiolabeled glycylglycine (GlyGly).

METHODS

Glycylglycine was radiolabeled with a high radiolabeling yield of 94.69±2%, and quality control of the radiolabeling process was performed by thin layer radiochromatography (TLRC) and High-Performance Liquid Radiochromatography (HPLRC). Lipophilicity study for radiolabeled complex (^99mTc(CO)₃-Gly-Gly) was carried out using solvent extraction. The in vivo evaluation was performed by both biodistribution and SPECT imaging.

RESULTS

The high radiolabelling yield of ^99mTc(CO)₃-GlyGly was obtained and verified by TLRC and HPLRC as well. According to the in vivo results, SPECT images and biodistribution data are in good accordance. The excretion route from the body was both hepatobiliary and renal.

CONCLUSION

This study shows that ^99mTc(CO)₃-GlyGly has the potential to be used as a peptide-based imaging agent. Further studies, ^99mTc(CO)₃-GlyGly can be performed on tumor-bearing animals.

Comparison of prostate-specific membrane antigen ligands in clinical translation research for diagnosis of prostate cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA), overexpressed on prostate cancer (PCa), is a well-characterized cell surface protein to selectively diagnose PCa. PSMA's unique characteristics and its 1000-fold higher expression in PCa compared with other tissues renders it as a suitable biomarker for detection of PCa in its early stage. In this report, we critically analyze and recommend the requirements needed for the development of variety of PSMA-targeted molecular imaging agents based on antibodies, small molecule ligands, peptides, and aptamers. The targeting moieties are either conjugated to radionuclear isotopes or near-infrared agents for efficient diagnosis of PCa.

RECENT FINDINGS

From the analysis, it was found that several small molecule-derived PCa imaging agents are approved for clinical trials in Europe and the United States, and few are already in the clinical use for diagnosis of PCa. Even though ¹¹¹In-labeled capromab pendetide was approved by the Food and Drug Administration (FDA) and other engineered antibodies are available for detection of PCa, but high production cost, low shelf life (less than 1 month at 4°C), possibility of human immuno reactions, and low blood clearance rate necessitated a need for developing new imaging agents, which are serum stable, cost-effective, and possesses longer shelf life (6 months), have fast clearance rate from nontargeted tissues during the diagnosis process. It is found that small molecule ligand-derived imaging agents possesses most of the desired properties expected for an ideal diagnostic agent when compared with other targeting moieties.

CONCLUSION

This report discusses in detail the homing moieties used in the development of targeted diagnostic tools for detection of PCa. The merits and demerits of monoclonal antibodies, small molecule ligands, peptides, and aptamers for imaging of PCa and intraoperative guided surgery are extensively analyzed. Among all, urea-based ligands were found to be most successful in preclinical and clinical trials and show a major promise for future commercialization.

Preparation and evaluation of 99mTc-labeled porphyrin complexes prepared using PNP and HYNIC cores: studying the effects of core selection on pharmacokinetics and tumor uptake in a mouse model

Porphyrins are tetrapyrrolic macrocyclic ligands known for their affinity towards neoplastic tissues and once radiolabeled with a suitable diagnostic radioisotope could potentially be used for the imaging of tumorous lesions. In the present study, an unsymmetrically substituted porphyrin derivative namely 5-(p-amino-propyloxyphenyl)-10,15,20-tris(carboxymethyleneoxyphenyl)-porphyrin was synthesized and modified further to enable radiolabeling with ^99mTc using two different ^99mTc-cores viz. ^99mTc-HYNIC (hydrazino nicotinic acid) and ^99mTc(N)PNP2 (PNP2 = bis-[(2-dimethylphosphino)ethyl]-methoxy-ethylamine) in order to study the effect of employing different ^99mTc-cores on tumor affinity and pharmacokinetic behavior of the resultant ^99mTc-labeled porphyrin complexes. ^99mTc-Porphyrin complexes were characterized by reversed phase HPLC studies and could be prepared with >95% radiochemical purity under optimized radiolabeling conditions. Both ^99mTc-complexes were found to be adequately stable in human blood serum till 3 h post-preparation. Bio-distribution studies, carried out in Swiss mice bearing fibrosarcoma tumors, revealed relatively higher tumor uptake for the ^99mTc-HYNIC-porphyrin complex (3.95 ± 1.42 and 3.28 ± 0.27% IA per g) compared to that exhibited by the ^99mTc(N)PNP-DTC-porphyrin complex (1.52 ± 0.53 and 1.56 ± 0.10% IA per g) at 1.5 and 3 h post-administration, although the former complex exhibited comparatively lower lipophilicity in the octanol-water system. Higher uptake and longer retention in the blood were observed for the ^99mTc-HYNIC-porphyrin complex (6.63 ± 0.75 and 4.36 ± 0.25% IA per g) compared to that exhibited by the ^99mTc(N)PNP-DTC-porphyrin complex (2.41 ± 0.54 and 2.30 ± 0.16% IA per g) at both 1.5 and 3 h post-administration. However, relatively lower liver uptake was observed for the former complex (19.26 ± 3.48 and 18.45 ± 1.05% IA per g) than that exhibited by the latter one (39.37 ± 3.88 and 34.15 ± 8.25% IA per g) at both 1.5 and 3 h post-administration. This study indicates that the in vivo behavior exhibited by the ^99mTc-labeled porphyrins not only depends on their lipophilicity/hydrophilicity but is also governed by the Tc-cores employed for radiolabeling.

Pharmacokinetics of protein and peptide conjugates

Protein and peptide conjugates have become an important component of therapeutic and diagnostic medicine. These conjugates are primarily designed to improve pharmacokinetics (PK) of those therapeutic or imaging agents, which do not possess optimal disposition characteristics. In this review we have summarized preclinical and clinical PK of diverse protein and peptide conjugates, and have showcased how different conjugation approaches are used to obtain the desired PK. We have classified the conjugates into peptide conjugates, non-targeted protein conjugates, and targeted protein conjugates, and have highlighted diagnostic and therapeutic applications of these conjugates. In general, peptide conjugates demonstrate very short half-life and rapid renal elimination, and they are mainly designed to achieve high contrast ratio for imaging agents or to deliver therapeutic agents at sites not reachable by bulky or non-targeted proteins. Conjugates made from non-targeted proteins like albumin are designed to increase the half-life of rapidly eliminating therapeutic or imaging agents, and improve their delivery to tissues like solid tumors and inflamed joints. Targeted protein conjugates are mainly developed from antibodies, antibody derivatives, or endogenous proteins, and they are designed to improve the contrast ratio of imaging agents or therapeutic index of therapeutic agents, by enhancing their delivery to the site-of-action.

Improved synthesis on solid phase of dithiocarbamic cRGD-derivative and 99m Tc-radiolabelling

In the field of angiogenesis, small cyclic pentapeptides containing the RGD motif are playing a relevant role for their high affinity and specificity for integrin receptors and for the possibility to act at both therapeutic and diagnostic level by inhibiting pathological angiogenesis and by serving as shuttles to deliver imaging-probe including SPECT/PET radionuclides to specific tissues. In the last decade, several new protocols were reported in literature for the direct synthesis of cyclic RDG either in solution or by SPPS. Here, we have elaborated and tested some alternative approaches using different resins and different protective groups. The introduction of the dithiocarbamate function, useful to complex radio-metals suitable for nuclear medicine applications, has also been considered and achieved.

Docking, synthesis, in-vitro evaluation, and optimization of reaction conditions for direct radiolabeling of CGPRPPC with technetium-99m through the GAGG sequence

OBJECTIVE

With respect to the reported promising results of cyclic peptide CGPRPPC in early detection of thrombotic lesions, we developed a practical approach for technetium-99m labeling of this peptide using the Glycine-Alanine-Glycine-Glycine (GAGG) sequence as a chelating moiety.

MATERIALS AND METHODS

The peptide conjugated to GAGG was prepared using the solid-phase method. The optimization of radiolabeling conditions was performed on the basis of such variables as incubation time, reaction temperature, pH, and concentration of peptide and stannous chloride. Moreover, the stability and fibrin-binding affinity of the radiolabeled peptide were measured. The peptide-fibrin interactions were analyzed by docking studies using HEX and Auto dock 4.2. Softwares.

RESULTS

The amounts of synthesized peptide and stannous chloride required for optimal radiolabeling through GAGG were 10 µmol/l and 5 µg, respectively. The best radiochemical purity% (>93%) was achieved at pH 7-8 within 15 min and a reaction temperature of 37°C. On the basis of in silico and in-vitro results, the GAGG-conjugated CGPRPPC peptide showed better binding affinity versus the HYNIC-conjugated one.

CONCLUSION

We could radiolabel the fibrin-targeting peptide with high radiochemical purity% and stability during a short incubation period without a boiling step. Compared with the HYNIC-conjugated peptide, a higher binding affinity was found. Therefore, the GAGG chelating moiety possesses a considerable potentiality in Technetium 99m labeling of peptides while CGPRPPC maintains its binding properties to thrombotic lesions.

Tumor targeting with 99m Tc 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 ¹¹¹ In-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 ^99m Tc and ¹¹¹ In for single-photon emission computed tomography and ⁶⁸ Ga and ¹⁸ F for positron emission tomography imaging. This review presents some of the ^99m Tc-labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.

Synthesis of 99m Tc-roxithromycin: A novel diagnostic agent to discriminate between septic and aseptic inflammation

Roxithromycin is a second-generation macrolide antibiotic derived from erythromycin. In the current study, roxithromycin (ROX) was successfully labeled with technetium-99m for early diagnosis of bacterial infection and discrimination between septic and aseptic inflammation. The highest radiochemical purity of ≥95% was achieved by investigating different labeling parameters such as pH, ligand/reducing agent concentration, temperature, and amount of stabilizing agent. For this purpose, 0.3-0.5 mg ligand, 2-6 μg SnCl₂ ·2H₂ O as a reducing agent at basic pH (8-10 pH) and 2 mg mannitol used as a stabilizing agent, in the end, 370 MBq ^99m Tc added into the reaction vials and incubated for a wide range of temperature (-4 to 65°C). The percent radiochemical purity of ^99m Tc-roxithromycin was assessed with the help of the radio-thin-layer chromatography technique. The characterization studies were carried out using electrophoresis and Radio-HPLC techniques as well as saline stability and serum stability studies were also performed. Furthermore, biodistribution study was also performed in an inflamed animal model to discriminate between septic (heat-killed Staphylococcus aureus) and aseptic (turpentine oil) inflammatory lesions. The results were elaborated that ^99m Tc-roxithromycin (^99m Tc-ROX) was clearly bounded at the septic inflammation site (T/NT ratio of 7.08 ± 1.14) at 30 min postadministration, and maximum accumulation was seen in heart, lungs, liver, stomach, kidneys, and intestine. The results were suggested that ^99m Tc-ROX might be used to discriminate between septic and aseptic inflammatory lesions at an early stage.

Technetium-99m chelator-free radiolabeling of specific glutamine tumor imaging nanoprobe: in vitro and in vivo evaluations

Introduction

Nowadays, molecular imaging radiopharmaceuticals', nanoparticles', and/or small-molecule biomarkers' applications are increasing rapidly worldwide. Thus, researchers focus on providing the novel, safe, and cost-effective ones.

Materials and methods

In the present experiment, technetium-99m (^99mTc)-labeled PEG-citrate dendrimer-G₂ conjugated with glutamine (nanoconjugate) was designed and assessed as a novel tumor imaging probe both in vitro and in vivo. Nanoconjugate was synthesized and the synthesis was confirmed by Fourier transform infrared, proton nuclear magnetic resonance, liquid chromatography-mass spectrometry, dynamic light scattering, and static light scattering techniques. The toxicity was assessed by XTT and apoptosis and necrosis methods.

Results

Radiochemical purity indicates that the anionic dendrimer has a very high potential to complex formation with ^99mTc and is also very stable in the human serum in different times. Results from the imaging procedures showed potential ability of nanoconjugates to detect tumor site.

Conclusion

Suitable features of the anionic dendrimer show that it is a promising agent to improve nanoradiopharmaceuticals.

Technetium Complexes and Radiopharmaceuticals with Scorpionate Ligands

Scorpionate ligands have played a crucial role in the development of technetium chemistry and, recently, they have also fueled important advancements in the discovery of novel diagnostic imaging agents based on the γ-emitting radionuclide technetium-99m. The purpose of this short review is to provide an illustration of the most general and relevant results in this field, however without being concerned with the details of the analytical features of the various compounds. Thus, emphasis will be given to the description of the general features of technetium complexes with scorpionate ligands including coordination modes, structural properties and an elementary bonding description. Similarly, the most relevant examples of technetium-99m radiopharmaceuticals derived from scorpionate ligands and their potential interest for nuclear imaging will be summarized.