Radiochemical Stability Research Articles

Antimicrobial peptide LyeTx I mn∆K labeled with 68Ga is a potential PET radiopharmaceutical for molecular imaging of infections

BackgroundAntimicrobial peptides have been radiolabeled and investigated as molecular diagnostic probes due to their propensity to accumulate in infectious sites rather than aseptic inflammatory lesions. LyeTx I is a cationic peptide from the venom of Lycosa erythrognatha, exhibiting significant antimicrobial activity. LyeTx I mn∆K is a shortened derivative of LyeTx I, with an optimized balance between antimicrobial and hemolytic activities. This study reports the first 68Ga-radiolabeling of the DOTA-modified LyeTx I mn∆K and primarily preclinical evaluations of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a PET radiopharmaceutical for infection imaging. MethodsDOTA(K)-LyeTx I mn∆K was radiolabeled with freshly eluted 68Ga. Radiochemical yield (RCY), radiochemical purity (RCP), and radiochemical stability (in saline and serum) were evaluated using ascending thin-layer chromatography (TLC) and reversed-phase high-performance liquid chromatography (RP-HPLC). The radiopeptide's lipophilicity was assessed by determining the logarithm of the partition coefficient (Log P). Serum protein binding (SBP) and binding to Staphylococcus aureus (S. aureus) cells were determined in vitro. Ex vivo biodistribution studies and PET/CT imaging were conducted in healthy mice (control) and mice with infection and aseptic inflammation to evaluate the potential of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a specific PET radiopharmaceutical for infections. Results[68Ga]Ga-DOTA(K)-LyeTx I mn∆K was obtained with a high RCY (>90 %), and after purification through a Sep-Pak C18 cartridge, the RCP exceeded 99 %. Ascending TLC and RP-HPLC showed that the radiopeptide remained stable for up to 3.0 h in saline solution and up to 1.5 h in murine serum. [68Ga]Ga-DOTA(K)-LyeTx I mn∆K exhibited hydrophilic characteristics (Log P = −2.4 ± 0.1) and low SPB (ranging from 23.3 ± 0.4 % at 5 min of incubation to 10.5 ± 1.1 % at 60 min of incubation). The binding of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K to S. aureus cells was proportional to bacterial concentration, with binding percentages of 8.8 ± 0.5 % (0.5 × 109 CFU.mL−1), 16.2 ± 1.4 % (1.0 × 109 CFU.mL−1), and 62.2 ± 0.6 % (5.0 × 109 CFU.mL−1). Ex vivo biodistribution studies and PET/CT images showed higher radiopeptide uptake at the infection site compared to the aseptic inflammation site; the latter was similar to the control group. Target-to-non-target (T/NT) ratios obtained by ex vivo biodistribution data were approximately 1.0, 1.3, and 3.0 at all investigated time intervals for the control, aseptic inflammation, and infection groups, respectively. Furthermore, T/NT ratios obtained from PET/CT images were 1.1 ± 0.1 for the control group and 1.4 ± 0.1 for the aseptic inflammation group. For the infection group, T/NT ratio was 5.0 ± 0.3, approximately 5 times greater compared to the former groups. ConclusionsThe results suggest the potential of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a PET radiopharmaceutical for molecular imaging of infections.

Synthesis and Biological Evaluation of Novel Cationic Rhenium and Technetium-99m Complexes Bearing Quinazoline Derivative for Epidermal Growth Factor Receptor Targeting.

Background/Objectives: Epidermal growth factor receptor (EGFR) plays a vital role in cell proliferation and survival, with its overexpression linked to various malignancies, including non-small cell lung cancer (NSCLC). Although EGFR tyrosine kinase inhibitors (TKIs) are a key therapeutic strategy, acquired resistance and relapse remain challenges. This study aimed to synthesize and evaluate novel rhenium-based complexes incorporating EGFR TKIs to enhance anticancer efficacy, particularly in radiosensitization. Methods: We synthesized a rhenium tricarbonyl complex (Complex 2) and its 99mTc analog (Complex 2') by incorporating triphenylphosphine instead of bromine as the monodentate ligand and PF6- as the counter-ion, resulting in a positively charged compound that forms cationic structures. Cytotoxicity and EGFR inhibition were evaluated in A431 cells overexpressing EGFR using MTT assays, Western blotting, and flow cytometry. Radiosensitization was tested through MTT and clonogenic assays. The 99mTc complex's radiochemical yield, stability, and lipophilicity were also assessed. Results: Complex 2 exhibited significant cytotoxicity with an IC50 of 2.6 μM and EGFR phosphorylation inhibition with an IC50 of 130.6 nM. Both complex 1 and 2 induced G0/G1 cell cycle arrest, with Complex 2 causing apoptosis. Radiosensitization was observed at doses above 2 Gy. Complex 2' demonstrated high stability and favorable lipophilicity (LogD7.4 3.2), showing 12% cellular uptake after 30 min. Conclusions: Complexes 2 and 2' show promise as dual-function anticancer agents, offering EGFR inhibition, apoptosis induction, and radiosensitization. Their potential as radiopharmaceuticals warrants further in-depth investigation in preclinical models.

Assessment of chromatography separation parameters in the quality control of copper-64-labeled neurotensin-like peptides

In recent years, research on the Cu-64 effects on malignant tumours has increased, leading to the development of radiopharmaceuticals with higher selectivity, aiming to target tumour cells while preserving healthy body cells. This work aims to assess the quality of two DOTA-derivatized neuropeptides, NMN and NT (8-13) radiolabelled with Cu-64. An improved analytical radio-HPLC method was developed to evaluate the radiochemical purity and stability. The radiochemical purity is > 99.95% for both 64Cu-DOTA-NMN and 64Cu-DOTA-NT (8-13), the radiolabelled molecules being stable for 72 h after synthesis.

Production, purification and formulation of nanoradiopharmaceutical with 211At: An emerging candidate for targeted alpha therapy

IntroductionAstatine-211 has attained significant interest in the recent times as a promising radioisotope for targeted alpha therapy (TAT) of cancer. In this study, we report the production of 211At via 209Bi (α, 2n) 211At reaction in a cyclotron and development of a facile radiochemical separation procedure to isolate 211At for formulation of nanoradiopharmaceuticals. MethodsNatural bismuth oxide target in pelletized form wrapped in Al foil was irradiated with 30 MeV α-beam in an AVF cyclotron. The irradiated target was dissolved in 2 M HNO3 followed by selective precipitation of Bi as Bi(OH)3 under alkaline condition. The radiochemically separated 211At was used for labeling cyclic RGD peptide conjugated gold nanoparticles (Au-RGD NPs) by surface adsorption. The radiochemical stability of 211At-Au-RGD NPs was evaluated in phosphate buffered saline (PBS) and human serum media. ResultsThe batch yield of 211At at the end of irradiation was ∼6 MBq.μA−1.h−1. After radiochemical separation, ∼80 % of 211At could be retrieved with >99.9 % radionuclidic purity. Au-RGD NPs (particle size 8.4±0.8 nm) could be labeled with 211At with >99 % radiolabeling yield. The radiolabeled nanoparticles retained their integrity in PBS and human serum media over a period of 21 h. ConclusionsThe present strategy simplifies 211At production in terms of purification and would increase affordable access to this radioisotope for TAT of cancer.

Development of Alginate-Based Biodegradable Radioactive Microspheres Labeled with Positron Emitter through Click Chemistry Reaction: Stability and PET Imaging Study.

Biodegradable radioactive microspheres labeled with positron emitters hold significant promise for diagnostic and therapeutic applications in cancers and other diseases, including arthritis. The alginate-based polymeric microspheres offer advantages such as biocompatibility, biodegradability, and improved stability, making them suitable for clinical applications. In this study, we developed novel positron emission tomography (PET) microspheres using alginate biopolymer radiolabeled with gallium-68 (68Ga) through a straightforward conjugation reaction. Polyethylenimine (PEI)-decorated calcium alginate microspheres (PEI-CAMSs) were fabricated and further modified using azadibenzocyclooctyne-N-hydroxysuccinimide ester (ADIBO-NHS). Subsequently, azide-functionalized NOTA chelator (N3-NOTA) was labeled with [68Ga]Ga to obtain [68Ga]Ga-NOTA-N3, which was then reacted with the surface-modified PEI-CAMSs using strain-promoted alkyne-azide cycloaddition (SPAAC) reaction to develop [68Ga]Ga-NOTA-PEI-CAMSs, a novel PET microsphere. The radiolabeling efficiency and radiochemical stability of [68Ga]Ga-NOTA-PEI-CAMSs were determined using the radio-instant thin-layer chromatography-silica gel (radio-ITLC-SG) method. The in vivo PET images were also acquired to study the in vivo stability of the radiolabeled microspheres in normal mice. The radiolabeling efficiency of [68Ga]Ga-NOTA-PEI-CAMSs was over 99%, and the microspheres exhibited high stability (92%) in human blood serum. PET images demonstrated the stability and biodistribution of the microspheres in mice for up to 2 h post injection. This study highlights the potential of biodegradable PET microspheres for preoperative imaging and targeted radionuclide therapy. Overall, the straightforward synthesis method and efficient radiolabeling technique provide a promising platform for the development of theranostic microspheres using other radionuclides such as 90Y, 177Lu, 188Re, and 64Cu.

Lead-212/Bismuth-212 InVivo Generator Based on Ultrasmall Silver Telluride Nanoparticles.

Radionuclide therapy employing alpha emitters holds great potential for personalized cancer treatment. However, certain challenges remain when designing alpha radiopharmaceuticals, including the lack of stability of used radioconjugates due to nuclear decay events. In this work, ultrasmall silver telluride nanoparticles with a core diameter of 2.1 nm were prepared and radiolabeled with lead-212 using a chelator-free method with a radiolabeling efficiency of 75%. The results from the invitro radiochemical stability assay indicated a very high retention of bismuth-212 despite the internal conversion effects originating from the decay of 212Pb. To further evaluate the potential of the nanoparticles, they were radiolabeled with indium-111, and their cell uptake and subcellular distribution were determined in 2D U87 cells, showing accumulation in the nucleus. Although not intentional, it was observed that the indium-111-radiolabeled nanoparticles induced efficient tumor cell killing, which was attributed to the Auger electrons emitted by indium-111. Combining the results obtained in this work with other favorable properties such as fast renal clearance and the possibility to attach targeting vectors on the surface of the nanoparticles, all well-known from the literature, these ultra-small silver telluride nanoparticles provide exciting opportunities for the design of theragnostic radiopharmaceuticals.

Claudin18.2-Targeted SPECT/CT Imaging for Gastric Cancer: Preclinical Evaluation and Clinical Translation of the 99mTc-Labeled Nanobody (PHG102) Radiotracer.

Claudin18.2 (CLDN18.2) has emerged as a significant target in the treatment of advanced gastric cancer. The screening of patients positive for CLDN18.2 is crucial for the effective application of targeted therapies specific to CLND18.2. In this study, we developed a novel nanobody-based probe, [99mTc]Tc-PHG102, for use in nuclear medicine. We analyzed its radiochemical yield and stability to ensure accurate probe characterization. Additionally, we assessed the probe's affinity and specificity toward the CLDN18.2 target and evaluated its efficacy in the BGC82318.2 xenograft model for SPECT/CT imaging of gastric cancer. The binding of [99mTc]Tc-PHG102 to HEK-293T18.2 and BGC82318.2 cells was notably higher than its binding to HEK-293T18.1, HEK-293T, and BGC823 cells, with bound values of 12.87 ± 1.46%, 6.16 ± 0.34%, 1.25 ± 0.22%, 1.14 ± 0.26%, and 1.32 ± 0.07% AD, respectively. The binding ability of [99mTc]Tc-PHG102 was significantly different between CLDN18.2-positive and negative cells (P < 0.001). Imaging results demonstrated a time-dependent tumor accumulation of the radiotracer. Notably, at 0.5 h postinjection, rapid accumulation was observed with an average tumor uptake of 4.63 ± 0.81% ID/cc (n = 3), resulting in clear tumor visualization. By 1 h postinjection, as [99mTc]Tc-PHG102 was rapidly metabolized, a decrease in uptake by other organs was noted. Preliminary clinical imaging trials further confirmed the safety and effectiveness of the probe, indicating specificity for lesions expressing CLDN18.2 in gastric cancer and favorable in vivo metabolic properties. In conclusion, the nanobody-based probe [99mTc]Tc-PHG102 proves to be a safe and effective tool for detecting CLDN18.2 expression levels in gastric cancer tumors and for screening CLDN18.2-positive patients.

Peptide-based immuno-PET/CT monitoring of dynamic PD-L1 expression during glioblastoma radiotherapy

Real-time, noninvasive programmed death-ligand 1 (PD-L1) testing using molecular imaging has enhanced our understanding of the immune environments of neoplasms and has served as a guide for immunotherapy. However, the utilization of radiotracers in the imaging of human brain tumors using positron emission tomography/computed tomography (PET/CT) remains limited. This investigation involved the synthesis of [18F]AlF-NOTA-PCP2, which is a novel peptide-based radiolabeled tracer that targets PD-L1, and evaluated its imaging capabilities in orthotopic glioblastoma (GBM) models. Using this tracer, we could noninvasively monitor radiation-induced PD-L1 changes in GBM. [18F]AlF-NOTA-PCP2 exhibited high radiochemical purity (>95%) and stability up to 4 hours after synthesis. It demonstrated specific, high-affinity binding to PD-L1 in vitro and in vivo, with a dissociation constant of 0.24 nM. PET/CT imaging, integrated with contrast-enhanced magnetic resonance imaging, revealed significant accumulation of [18F]AlF-NOTA-PCP2 in orthotopic tumors, correlating with blood–brain barrier disruption. After radiotherapy (15 Gy), [18F]AlF-NOTA-PCP2 uptake in tumors increased from 9.51% ± 0.73% to 12.04% ± 1.43%, indicating enhanced PD-L1 expression consistent with immunohistochemistry findings. Fractionated radiation (5 Gy × 3) further amplified PD-L1 upregulation (13.9% ± 1.54% ID/cc) compared with a single dose (11.48% ± 1.05% ID/cc). Taken together, [18F]AlF-NOTA-PCP2 may be a valuable tool for noninvasively monitoring PD-L1 expression in brain tumors after radiotherapy.

Effects of PEGylation on Imaging Contrast of 68Ga-Labeled Bicyclic Peptide PET Probes Targeting Nectin-4.

Nectin cell adhesion molecule 4 (Nectin-4) is overexpressed in various malignant tumors and has emerged as a promising target for tumor imaging. Bicyclic peptides, known for their conformational rigidity, metabolic stability, and membrane permeability, are ideal tracers for positron emission tomography (PET) imaging. In this study, we evaluated the feasibility of visualizing Nectin-4-positive tumors using radiolabeled bicyclic peptide derivatives and optimized the pharmacokinetics of radiotracers by introducing PEG chains of different lengths. Five PEGylated radiotracers radiolabeled with 68Ga3+ exhibited high radiochemical purity and stability. As the chain length increased, the Log D values decreased from -2.32 ± 0.13 to -2.50 ± 0.16, indicating a gradual increase in the hydrophilicity of the radiotracers. In vitro cell-binding assay results showed that the PEGylated bicyclic peptide exhibits nanomolar affinity, and blocking experiments confirmed the specific binding of the tracers to the Nectin-4 receptor. In vivo PET imaging and biodistribution studies in SW780 and 5637 xenograft mice showed that [68Ga]Ga-NOTA-PEG12-BP demonstrated optimal pharmacokinetics, characterized by rapid and good tumor uptake, faster background clearance, and improved tumor-to-tissue contrast. Finally, compared with 18F-FDG, PET imaging, in vivo blocking assays of [68Ga]Ga-NOTA-PEG12-BP and histological staining confirmed that specific tumor uptake was mediated by Nectin-4 receptors. The results indicated that [68Ga]Ga-NOTA-PEG12-BP was a promising PET radiotracer for Nectin-4 targeting, with applications for clinical translation.

Peptide derived from plant defensins: A promising 68Ga radiolabelled agent for diagnostic of infection foci in PET.

The development of new radiopharmaceuticals for the detection of hidden infection foci has great relevance for early detection and the selection of the correct treatment, particularly in immunosuppressed patients. In that sense, the labelling of antimicrobial peptides (AMPs) that are capable of binding specifically to the pathogenic microorganism which causes the infection, should provide a sufficiently specific agent, able to distinguish an infection from a sterile inflammation. Defensins are particularly interesting molecules with antimicrobial activity, the EcgDf1 defensin was identified from the genome of a Uruguayan native plant, Erythrina crista-galli, the 'Ceibo' tree. Our group has previously reported a synthetic biologically active short analogue EcgDf21 (ERFTGGHCRGFRRRCFCTKHC) successfully labelled with 99mTc. Herein we present a shorter analogue which also preserves the γ-core domain, as a pharmacophore for a potential infection detection agent. This peptide was derivatized with the bifunctional chelating agent 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) through a lysine linker in the amino-terminal group (NOTA-KGHCRGFRRRC) and radiolabelled with 68Ga ([68Ga]Ga-NOTA-K-EcgDf1(10)). The [68Ga]Ga-NOTA-K-EcgDf1(10) labelling procedure rendered a product with high radiochemical purity and stability in the labelling milieu. The Log P value indicated that the complex has a hydrophilic behaviour, confirmed by the biodistribution profile. The [68Ga]Ga-NOTA-K-EcgDf1(10) complex demonstrated specific binding to cultures of Candida albicans and Aspergillus niger. Its biodistribution showed renal elimination and low accumulation in the rest of the body. It was possible to successfully differentiate sterile inflammation from infection by PET images in nude mice with a target/non-target ratio of 3.3 for C. albicans and 3.7 for A. niger, respectively.

Development and Synthesis of Bombesin-Based Radiopharmaceutical Precursors Modified with Knottin.

The work analyzed the chemical and radiochemical stability of the synthesized peptide labeled with a lutetium radioisotope using high-performance liquid chromatography. A fluorescent-labeled peptide, obtained by a solid-phase peptide synthesis, was used to analyze binding to cultures expressing bombesin receptors. The analysis has shown increased chemical and radiochemical stability of the knottin-modified peptide, as compared to the commercial analog, and maintenance of a high ability to bind to receptors on the surface of cancer cells. The structure created on the basis of a short bombesin peptide and knottin possesses increased stability and retains the ability to bind to cancer cells. All this allows us to consider the creation of these structures as a strategy for fabricating stabilizing scaffolds for short peptides for a peptide-receptor therapy.

Preclinical characterisation of gallium-68 labeled ferrichrome siderophore stereoisomers for PET imaging applications

BackgroundSiderophores are small iron-binding molecules produced by microorganisms to facilitate iron acquisition from the environment. Radiolabelled siderophores offer a promising solution for infection imaging, as they can specifically target the pathophysiological mechanisms of pathogens. Gallium-68 can replace the iron in siderophores, enabling molecular imaging with positron emission tomography (PET). Stereospecific interactions play a crucial role in the recognition of receptors, transporters, and iron utilisation. Furthermore, these interactions have an impact on the host environment, affecting pharmacokinetics and biodistribution. This study examines the influence of siderophore stereoisomerism on imaging properties, with a focus on ferrirubin (FR) and ferrirhodin (FRH), two cis–trans isomeric siderophores of the ferrichrome type.ResultsTested siderophores were labelled with gallium-68 with high radiochemical purity. The resulting complexes differed in their in vitro characteristics. [68Ga]Ga-FRH showed less hydrophilic properties and higher protein binding values than [68Ga]Ga-FR. The stability studies confirmed the high radiochemical stability of both [68Ga]Ga-siderophores in all examined media. Both siderophores were found to be taken up by S. aureus, K. pneumoniae and P. aeruginosa with similar efficacy. The biodistribution tested in normal mice showed rapid renal clearance with low blood pool retention and fast clearance from examined organs for [68Ga]Ga-FR, whereas [68Ga]Ga-FRH showed moderate retention in blood, resulting in slower pharmacokinetics. PET/CT imaging of mice injected with [68Ga]Ga-FR and [68Ga]Ga-FRH confirmed findings from ex vivo biodistribution studies. In a mouse model of S. aureus myositis, both radiolabeled siderophores showed radiotracer accumulation at the site of infection.ConclusionsThe 68Ga-complexes of stereoisomers ferrirubin and ferrirhodin revealed different pharmacokinetic profiles. In vitro uptake was not affected by isomerism. Both compounds had uptake with the same bacterial culture with similar efficacy. PET/CT imaging showed that the [68Ga]Ga-complexes accumulate at the site of S. aureus infection, highlighting the potential of [68Ga]Ga-FR as a promising tool for infection imaging. In contrast, retention of the radioactivity in the blood was observed for [68Ga]Ga-FRH. In conclusion, the stereoisomerism of potential radiotracers should be considered, as even minor structural differences can influence their pharmacokinetics and, consequently, the results of PET imaging.

Assessment of bioactive peptides derived from laminin-111 as prospective breast cancer-targeting agents

Breast cancer remains a pressing public health issue primarily affecting women. Recent research has spotlighted bioactive peptides derived from laminin-111, implicated in breast tumor development. Remarkably, the sequences IKVAV, YIGSR, and KAFDITYVRLKF from the α1, β1, and γ1 chains, respectively, have garnered significant attention. This study aims to assess the potential of these radiolabeled peptides as targeting agents for breast cancer. The three peptides were synthesized using the Fmoc strategy, purified via reversed-phase high-performance liquid chromatography (RP-HPLC), and characterized through mass spectrometry. Iodine-131 (131I) radiolabeling was performed using the chloramine T method, exhibiting high radiochemical yield and stability for [131I]I-YIKVAV and [131I]I-YIGSR. Conversely, [131I]I-KAFDITYVRLKF demonstrated low radiochemical yield and stability and was excluded from the biological studies. The lipophilicity of the compounds ranged from − 2.12 to − 1.10. Serum protein binding assay for [131I]I-YIKVAV and [131I]I-YIGSR reached ≅ 48% and ≅ 25%, respectively. Affinity for breast cancer cells was evaluated using MDA-MB-231 and MCF-7 tumor cell lines, indicating the affinity of the radiopeptides with these tumor cells. Ex vivo biodistribution profiles of the radiopeptides were assessed in the MDA-MB-231 breast tumor animal model, revealing tumor tissue accumulation, supported by a high tumor-to-contralateral muscle ratio and autoradiography. These results signify the effective penetration of YIKVAV and YIGSR into tumor tissue. Therefore, the synthesized α1 and β1 peptide fragments exhibit favorable characteristics as potential breast cancer-targeting agents, promising future exploration as radiopharmaceuticals for breast cancer.

Brachytherapy at the nanoscale with protein functionalized and intrinsically radiolabeled [169Yb]Yb2O3 nanoseeds.

Classical brachytherapy of solid malignant tumors is an invasive procedure which often results in an uneven dose distribution, while requiring surgical removal of sealed radioactive seed sources after a certain period of time. To circumvent these issues, we report the synthesis of intrinsically radiolabeled and gum Arabic glycoprotein functionalized [169Yb]Yb2O3 nanoseeds as a novel nanoscale brachytherapy agent, which could directly be administered via intratumoral injection for tumor therapy. 169Yb (T½ = 32days) was produced by neutron irradiation of enriched (15.2% in 168Yb) Yb2O3 target in a nuclear reactor, radiochemically converted to [169Yb]YbCl3 and used for nanoparticle (NP) synthesis. Intrinsically radiolabeled NP were synthesized by controlled hydrolysis of Yb3+ ions in gum Arabic glycoprotein medium. In vivo SPECT/CT imaging, autoradiography, and biodistribution studies were performed after intratumoral injection of radiolabeled NP in B16F10 tumor bearing C57BL/6 mice. Systematic tumor regression studies and histopathological analyses were performed to demonstrate therapeutic efficacy in the same mice model. The nanoformulation was a clear solution having high colloidal and radiochemical stability. Uniform distribution and retention of the radiolabeled nanoformulation in the tumor mass were observed via SPECT/CT imaging and autoradiography studies. In a tumor regression study, tumor growth was significantly arrested with different doses of radiolabeled NP compared to the control and the best treatment effect was observed with ~ 27.8MBq dose. In histopathological analysis, loss of mitotic cells was apparent in tumor tissue of treated groups, whereas no significant damage in kidney, lungs, and liver tissue morphology was observed. These results hold promise for nanoscale brachytherapy to become a clinically practical treatment modality for unresectable solid cancers.

A PEG-assisted membrane coating to prepare biomimetic mesoporous silicon for PET/CT imaging of triple-negative breast cancer

Triple-negative breast cancer (TNBC) diagnosis remains challenging without expressing critical receptors. Cancer cell membrane (CCm) coating has been extensively studied for targeted cancer diagnostics due to attractive features such as good biocompatibility and homotypic tumor-targeting. However, the present study found that widely used CCm coating approaches, such as extrusion, were not applicable for functionalizing irregularly shaped nanoparticles (NPs), such as porous silicon (PSi). To tackle this challenge, we proposed a novel approach that employs polyethylene glycol (PEG)-assisted membrane coating, wherein PEG and CCm are respectively functionalized on PSi NPs through chemical conjugation and physical absorption. Meanwhile, the PSi NPs were grafted with the bisphosphonate (BP) molecules for radiolabeling. Thanks to the good chelating ability of BP and homotypic tumor targeting of cancer CCm coating, a novel PSi-based contrast agent (CCm-PEG-89Zr-BP-PSi) was developed for targeted positron emission tomography (PET)/computed tomography (CT) imaging of TNBC. The novel imaging agent showed good radiochemical purity (∼99 %) and stability (∼95 % in PBS and ∼99 % in cell medium after 48 h). Furthermore, the CCm-PEG-89Zr-BP-PSi NPs had efficient homotypic targeting ability in vitro and in vivo for TNBC. These findings demonstrate a versatile biomimetic coating method to prepare novel NPs for tumor-targeted diagnosis.

Size-dependent therapeutic efficiency of 223Ra-labeled calcium carbonate carriers for internal radionuclide therapy of breast cancer.

The size of drug carriers strongly affects their biodistribution, tissue penetration, and cellular uptake in vivo. As a result, when such carriers are loaded with therapeutic compounds, their size can influence the treatment outcomes. For internal α-radionuclide therapy, the carrier size is particularly important, because short-range α-emitters should be delivered to tumor volumes at a high dose rate without any side effects, i.e. off-target irradiation and toxicity. In this work, we aim to evaluate and compare the therapeutic efficiency of calcium carbonate (CaCO3) microparticles (MPs, >2 μm) and nanoparticles (NPs, <100 nm) labeled with radium-223 (223Ra) for internal α-radionuclide therapy against 4T1 breast cancer. To do this, we comprehensively study the internalization and penetration efficiency of these MPs and NPs, using 2D and 3D cell cultures. For further therapeutic tests, we develop and modify a chelator-free method for radiolabeling of CaCO3 MPs and NPs with 223Ra, improving their radiolabeling efficiency (>97%) and radiochemical stability (>97%). After intratumoral injection of 223Ra-labeled MPs and NPs, we demonstrate their different therapeutic efficiencies against a 4T1 tumor. In particular, 223Ra-labeled NPs show a tumor inhibition of approximately 85%, which is higher compared to 60% for 223Ra-labeled MPs. As a result, we can conclude that 223Ra-labeled NPs have a more suitable biodistribution within 4T1 tumors compared to 223Ra-labeled MPs. Thus, our study reveals that 223Ra-labeled CaCO3 NPs are highly promising for internal α-radionuclide therapy.

Mechanisms of inclusion of thallium-201 into Prussian blue nanoparticles for nuclear medicine applications.

Prussian blue is known for its high affinity for thallium and other univalent metal cations and has been used as a treatment for radiocaesium and thallium/radiothallium poisoning. While Prussian blue nanoparticles (PBNPs) show potential for binding radioactive thallium for further use in nuclear medicine applications, the inclusion mechanism remains elusive. Understanding the interaction between PBNPs and 201Tl is essential for identifying the physicochemical and radiochemical properties required for optimal in vivo performance. In this work, we evaluated the binding mechanism between Tl and PBNPs with different coatings and core shapes. Combining PBNPs with [201Tl] thallium(I) chloride provided high radiolabelling yields and radiochemical stabilities under physiological conditions. Comprehensive characterisation by different X-ray techniques confirmed that Tl ions are located in the interstitial sites within the crystal structure, maintaining the integrity of the iron (Fe) 4p electronic distribution and inducing local modifications in the nearby C-N ligands. Additionally, this inclusion does not impact the core or the shell of the nanoparticles but does alter their ionic composition. The PB ionic network undergoes significant changes, with a substantial drop in K+ content, confirming that Tl+ ions replace K+ and occupy additional spaces within the crystal structure. These results open new opportunities in nuclear medicine applications with 201Tl-PBNPs where the size, shape and composition of the particles can be specifically tuned depending on the desired biological properties without affecting the radiochemical performance as a vehicle for 201Tl.

68Ga labeled EphA2-targeted cyclic peptide: a novel positron imaging tracer for triple-negative breast cancer?

The absence of better biomarkers currently limits early diagnosis and treatment of triple-negative breast cancer (TNBC). Our previously published study reported that the cyclic-peptide SD01 exhibited specific binding to EphA2 (Ephrin type-A receptor 2) on TNBC. To develop a novel PET imaging agent, we prepared gallium-68 (68Ga) labeled-DOTA-SD01 and evaluated its specificity and effectiveness through micro PET/CT imaging in a TNBC-bearing mouse model. SD01 and a control linear peptide YSA were conjugated to DOTA and subsequently labeled with 68Ga, obtaining 68Ga-DOTA-SD01 and 68Ga-DOTA-YSA. Both showed high radiochemical purity, stability, good hydrophilicity, and high binding affinity to 4T1 cells. Micro PET/CT imaging showed high radioactivity accumulation in tumors; SUVmean (mean standardized uptake value) of tumors in the group of 68Ga-DOTA-SD01 was 3.34 ± 0.25 and 2.65 ± 0.32 in the group of 68Ga-DOTA-YSA; T/NT ratios (target to non-target, SUVmean ratios of tumor to muscle) were 3.12 ± 0.06 and 2.77 ± 0.11 at 30 min, respectively (p < 0.05). The biodistribution study showed that tumor uptake % ID per g (percentage of injected dose per gram of tissue) in the group of 68Ga-DOTA-SD01 was 2.73 ± 0.34, and 1.77 ± 0.38 in the group of 68Ga-DOTA-YSA; T/NT ratios (radioactivity of tumor to muscle) were 3.55 ± 0.12 and 3.05 ± 0.10 for both groups at 30 min, respectively (p < 0.05). All these suggest that 68Ga-DOTA-SD01 may act as a better novel PET imaging agent for EphA2 positive tumors, such as TNBC.

Early Development and Pre-Clinical Evaluation of a Fluorine-18 Labeled Peptide p5+14 for PET/CT Imaging of Cardiac Amyloidosis

Background:Systemic amyloidosis is a rare protein misfolding disorder, where patients can present with varied symptoms due to the diverse organ involvement. This is particularly true of patients with light chain associated (AL) amyloidosis, which makes early and accurate diagnosis challenging. Currently there are no FDA-approved methods that allow visualization of amyloidosis in patients. Nuclear imaging is a promising method for early detection of amyloid. We have developed a novel amyloid-reactive peptide, designated p5+14, capable of binding AL, as well as other types of amyloid, via multivalent electrostatic interactions. Peptide p5+14 has been successfully radiolabeled with radioiodine and technetium-99m and evaluated clinically, labeled with iodine-124, in a PET/CT imaging study of patients with amyloidosis (NCT03678259). While there are numerous advantages to using I-124 as the radionuclide for amyloid imaging, fluorine is a viable alternative for detecting cardiac amyloidosis. Fluorine-18 has a shorter half-life (108 min as compared to 4.2 days) thus reducing the internal radiation dose to patients. Moreover, F-18 is the most common nuclide used in PET imaging. We have previously generated a 18F-labeled variant of p5+14; however, the reaction was inefficient and not translatable. Here we present a novel development strategy for generating 18F labeled p5+14 using a commercially available precursor that can bind AL amyloid and perform initial characterization of the reagent in a murine model of inflammation-associated systemic AA amyloidosis. Methods: Isotopic exchange chemistry using a silicon-fluoride-acceptor (SiFA) method was used to label peptide p5+14 with F-18. The peptide precursor was purchased from Almac Life Sciences (Penicuik, UK). 18F was purchased from PetNet (Siemens Healthineers, Knoxville, TN) and prepared for reaction according to standard methods. After drying, F-18 (1000 - 1900 MBq ) was dissolved in anhydrous acetonitrile and the pH neutralized before the addition of peptide precursor. Radiolabeling was performed at room temperature for 5 min. After standard purification of the product, radiochemical purity studies demonstrated that it was stable, with no significant loss of F-18 for at least 5 hours. Radiofluorinated p5+14 was assessed in bioactivity “pulldown” assays to ensure binding to synthetic AL amyloid-like fibrils and human AL amyloid extracts. The radiolabeled peptide was also diluted in PBS and injected IV in the lateral tail vein of mice with severe systemic AA amyloidosis. After 1 h, mice were euthanized small animal PET/CT imaging performed and tissue biodistribution measurements were conducted using an automated Wizard 3 gamma counter (1480 Wallac Gamma Counter, Perkin-Elmer). Results: Using optimized synthesis conditions, the non-decay corrected radiochemical yield was 55±4.5%. Radiochemical purity was 99±1% at end of synthesis. Peptide purity was shown to be 93.7±4.9% by assessed using HPLC. Radiochemical stability was similarly evaluated using an HLPC method and remained &amp;gt;97.5% radiochemical purity at 5 hours after synthesis. The binding of 18F-p5+14 to synthetic AL amyloid like fibrils composed of a l6 variable domain was 96.2%, mimicking data using the radioiodinated peptide, and 87.2% to human AL amyloid extracts. Background binding to control beads was 17.4%. In mice, accumulation of 18F-peptide in the liver and spleen, the organs with most AA amyloid deposits in this mouse model, was readily evident in PET images taken 1 h post injection. There was also evidence of hepatic clearance of the peptide, manifest as a prominent gall bladder in the images. There was no accumulation of F-18 in bone, indicating positive in vivo stability. Imaging of amyloid-free wild type mice showed rapid clearance with radioactivity in the urinary bladder, gall bladder and gastrointestinal tract with little or no hepatosplenic radiotracer retention. Conclusion: Radiofluorination of peptides, such as p5+14, has been made more efficient through the use of novel precursors amenable to isotopic exchange. 18F-peptide binds amyloid effectively and may serve as a next generation radiotracer for the detection of cardiac amyloid by PET/CT imaging. Acknowledgments: EW is a doctoral student in the Comparative and Experimental Medicine Program. This study was supported by the Amyloidosis and Cancer Theranostics Program and the UTGSM.

P-290 - Analysis of radiochemical stability and in vivo distribution of recoiled 213Bi from [225Ac]Ac-DOTATATE in preclinical model

P-290 - Analysis of radiochemical stability and in vivo distribution of recoiled 213Bi from [225Ac]Ac-DOTATATE in preclinical model