Accumulation Of Radioactivity Research Articles

Improving the In Vivo Stability of [52Mn]Mn(II) Complexes with 18-Membered Macrocyclic Chelators for PET Imaging.

We report the [natMn/52Mn]Mn(II) complexes of the macrocyclic chelators PYAN [3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane] and CHXPYAN [(41R,42R,101R,102R)-3,5,9,11-tetraaza-1,7(2,6)-dipyridina-4,10(1,2)-dicyclohexanacyclododecaphane]. The X-ray crystal structures of Mn-PYAN and Mn-CHXPYAN evidence distorted octahedral geometries through coordination of the nitrogen atoms of the macrocycles. Cyclic voltammetry studies evidence reversible processes due to the Mn(II)/Mn(III) pair, indicating that the complexes are resistant to oxidation. CHXPYAN forms a more thermodynamically stable and kinetically inert Mn(II) complex than PYAN. Radiochemical studies with the radioactive isotope manganese-52 (52Mn, t1/2 = 5.6 days) evidenced better radiochemical yields for CHXPYAN than for PYAN. Both [52Mn]Mn(II) complexes remained stable in mouse and human serum, so in vivo stability studies were carried out. Positron emission tomography/computed tomography scans and biodistribution assays indicated that [52Mn]Mn-PYAN has a distribution pattern similar to that of [52Mn]MnCl2, showing persistent radioactivity accumulation in the kidneys. Conversely, [52Mn]Mn-CHXPYAN remained stable in vivo, clearing quickly from the liver and kidneys.

PET/CT with <sup>18</sup>F-FDG for TENIS Syndrome in a Patient with Bone Metastasis of Hurthle Cell Thyroid Cancer: a Clinical Case Report

A significant role in improving the prognosis of differentiated thyroid cancer (DTC) in the presence of bone metastases is determined by early diagnosis of metastases, timely and correctly selected treatment tactics for the patient. During dynamic follow-up of patients with DTC after combined treatment (thyroidectomy with radioiodine therapy) are determination of the level of oncomarkers (serum thyroglobulin and antibodies to thyroglobulin) and ultrasound diagnostic of the neck, scanning with radioactive iodine (if clinically indicated). In some cases, patients have TENIS-syndrome (Thyroglobulin Elevated Negative Iodine Scintigraphy, hereinafter TENIS-syndrome), characterized by high serum thyroglobulin level in blood and absence of radioactive iodine accumulation on post therapeutic scintigraphy. According to the research studies, PET/CT with 18F-FDG has high sensitivity and specificity (89 % and 72 %, respectively) in visualization of metastatic radioiodine refractory foci in TENIS-syndrome.This article presents a clinical case of a patient, a 52-year-old woman with Gurtle cell thyroid cancer (pT3aN0M0, stage I) with established TENIS syndrome. Thyroidectomy was performed in September 2019 and radioiodine therapy was performed in January 2022 due to suspected disease progression given high thyroglobulin levels. Given the absence of pathologic accumulation of 131I according to post-therapy radioiodine scanning, PET/CT with 18F-FDG was performed, which revealed a solitary metastasis in the left iliac bone (41×35×42 mm with SUVmax 17.25). In November 2022, radical treatment of the solitary bone metastasis was performed in the scope of resection of the left iliac bone with reconstructive-plastic component. According to the data of control examinations in June 2023, the patient has a complete biochemical and radiologic remission of the disease.

Synthesis and biological evaluation of radioiodinated benzoxazole and benzothiazole derivatives for imaging myelin in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system that results from destruction of the myelin sheath. Due to heterogeneity of the symptoms and course of MS, periodic monitoring of disease activity is important for diagnosis and treatment. In the present study, we synthesized four radioiodinated benzoxazole (BO) and benzothiazole (BT) derivatives, and evaluated their utility as novel myelin imaging probes for single photon emission computed tomography (SPECT). In a biodistribution study using normal mice, three compounds ([125I]BO-1, [125I]BO-2, and [125I]BT-2) displayed moderate brain uptake (2.7, 2.9, and 2.8% ID/g, respectively) at 2 min postinjection. On ex vivo autoradiography using normal mice, [125I]BO-2 showed the most preferable ratio of radioactivity accumulation in white matter (myelin-rich region) versus gray matter (myelin-deficient region). In addition, the radioactivity of [125I]BO-2 was reduced in the lysophosphatidylcholine-induced demyelination region. In conclusion, [123I]BO-2 demonstrated the fundamental characteristics of a myelin imaging probe for SPECT.

89Zr-ImmunoPET for the Specific Detection of EMP2-Positive Tumors.

Epithelial membrane protein-2 (EMP2) is upregulated in a number of tumors and therefore remains a promising target for mAb-based therapy. In the current study, image-guided therapy for an anti-EMP2 mAb was evaluated by PET in both syngeneic and immunodeficient cancer models expressing different levels of EMP2 to enable a better understanding of its tumor uptake and off target accumulation and clearance. The therapeutic efficacy of the anti-EMP2 mAb was initially evaluated in high- and low-expressing tumors, and the mAb reduced tumor load for the high EMP2-expressing 4T1 and HEC-1-A tumors. To create an imaging agent, the anti-EMP2 mAb was conjugated to p-SCN-Bn-deferoxamine (DFO) and radiolabeled with 89Zr. Tumor targeting and tissue biodistribution were evaluated in syngeneic tumor models (4T1, CT26, and Panc02) and human tumor xenograft models (Ramos, HEC-1-A, and U87MG/EMP2). PET imaging revealed radioactive accumulation in EMP2-positive tumors within 24 hours after injection, and the signal was retained for 5 days. High specific uptake was observed in tumors with high EMP2 expression (4T1, CT26, HEC-1-A, and U87MG/EMP2), with less accumulation in tumors with low EMP2 expression (Panc02 and Ramos). Biodistribution at 5 days after injection revealed that the tumor uptake ranged from 2 to approximately 16%ID/cc. The results show that anti-EMP2 mAbs exhibit EMP2-dependent tumor uptake with low off-target accumulation in preclinical cancer models. The development of improved anti-EMP2 Ab fragments may be useful to track EMP2-positive tumors for subsequent therapeutic interventions.

18F]pFBC, a Covalent CLIP-Tag Radiotracer for Detection of Viral Reporter Gene Transfer in the Murine Brain.

Preclinical models of neurological diseases and gene therapy are essential for neurobiological research. However, the evaluation of such models lacks reliable reporter systems for use with noninvasive imaging methods. Here, we report the development of a reporter system based on the CLIP-tag enzyme and [18F]pFBC, an 18F-labeled covalent CLIP-tag-ligand synthesized via a DoE-optimized and fully automated process. We demonstrated its specificity using a subcutaneous xenograft model and a model of viral vector-mediated brain gene transfer by engineering HEK293 cells and striatal neurons to express membrane-tethered CLIP-tag protein. After in vitro characterization of the reporter, mice carrying either CLIP-tag expressing or control subcutaneous xenografts underwent dynamic [18F]pFBC PET imaging. The CLIP-tag expressing xenografts showed a significantly higher uptake than control xenografts (tumor-to-muscle ratio 5.0 vs 1.7, p = 0.0379). In vivo, metabolite analysis by radio-HPLC from plasma and brain homogenates showed only one radio-metabolite in plasma and none in the brain. In addition, [18F]pFBC showed fast uptake and rapid clearance from the brain in animals injected with adeno-associated virus (AAV)-CLIP in the right striatum but no right-to-left (R-L) uptake difference in the striata in the acquired PET data. In contrast, autoradiography showed a clear accumulation of radioactivity in the AAV-CLIP-injected right striatum compared to the sham-injected left striatum control. CLIP-tag expression and brain integrity were verified by immunofluorescence and light sheet microscopy. In conclusion, we established a novel reporter gene system for PET imaging of gene expression in the brain and periphery and demonstrated its potential for a wide range of applications, particularly for neurobiological research and gene therapy with viral vectors.

Synthesis and biological evaluation of novel 18F-labeled 2,4-diaminopyrimidine derivatives for detection of ghrelin receptor in the brain

The ghrelin receptor (GHSR) is known to regulate various physiological processes including appetite, food intake, and growth hormone release. Its expression is mainly observed in the brain, pancreas, stomach, and intestine. However, the functions of the receptor have not been fully elucidated. GHSR imaging with positron emission tomography (PET) is expected to further understanding of the functions and pathologies of the receptor. In this study, we newly designed and synthesized diaminopyrimidine derivatives ([18F]BPP-1 and [18F]BPP-2) and evaluated their utility as novel PET probes targeting GHSR. In in vitro competitive binding assays, the binding affinity of BPP-2 for GHSR (Ki = 274 nM) was comparable to that of the diaminopyimidine lead compound Abb8a (Ki = 109 nM). In a biodistribution study using normal mice, [18F]BPP-2 displayed low uptake in the brain and moderate uptake in the pancreas, but high radioactivity accumulation in bone was observed due to its defluorination in vivo. Taken together, although further improvement of the pharmacokinetics is needed, the diaminopyrimidine scaffold has potential for the development of useful GHSR-targeting PET probes.

First-in-human validation of enzymolysis clearance strategy for decreasing renal radioactivity using modified [68Ga]Ga-HER2 Affibody.

Enzymolysis clearance strategy, characterized by releasing the non-reabsorbable radioactive fragment under the specific cleavage of enzymes, is confirmed to be a safe and effective way to reduce the renal radioactivity accumulation in mice. However, the effectiveness of this strategy in humans remains unknown. Human epidermal growth factor receptor 2 (HER2) is overexpressed in various types of tumors, and radiolabeled HER2 Affibody is believed to be an attractive tool for HER2-targeted theranostics. However, its wide application is limited by the high and persistent renal uptake. In this study, we intend to validate the effectiveness of enzymolysis clearance strategy in reducing renal accumulation by using a modified HER2 Affibody. A new HER2 Affibody ligand, NOTA-MVK-ZHER2:2891, containing a cleavable Met-Val-Lys (MVK) linker was synthesized and labeled with 68Ga. The microPET imaging study was performed in SKOV-3 tumor mice to assess the uptakes of the control ligand and the MVK one in tumors and kidneys. Seven healthy volunteers were included for biodistribution and dosimetric studies with both the control and MVK ligands performed 1week apart. Urine and blood samples from healthy volunteers were collected for in vivo metabolism study of the two ligands. Four HER2-positive and two HER2-negative patients were recruited for [68Ga]Ga-NOTA-MVK-ZHER2:2891 PET/CT imaging at 2 and 4h post-injection (p.i.). [68Ga]Ga-NOTA-MVK-ZHER2:2891 was stable both in PBS and in mouse serum. MicroPET images showed that the tumor uptake of [68Ga]Ga-NOTA-MVK-ZHER2:2891 was comparable to that of [68Ga]Ga-NOTA-ZHER2:2891 at all the time points, while the kidney uptake was significantly reduced 40min p.i. (P < 0.05). The biodistribution study in healthy volunteers showed that the kidney uptake of MVK ligand was significantly lower than that of the control ligand at 1h p.i. (P < 0.05), with the SUVmean of 34.3 and 45.8, respectively, while the uptakes of the two ligands in the other organs showed negligible difference. The effective doses of the MVK ligand and the control one were 26.1 and 28.7 µSv/MBq, respectively. The enzymolysis fragment of [68Ga]Ga-NOTA-Met-OH was observed in the urine samples of healthy volunteers injected with the MVK ligand, indicating that the enzymolysis clearance strategy worked in humans. The PET/CT study of patients showed that the range of SUVmax of HER2-positive lesions was 9.4-21, while that of HER2-negative lesions was 2.7-6.2, which suggested that the MVK modification did not affect the ability of ZHER2:2891 structure to bind with HER2. We for the first time demonstrated that enzymolysis clearance strategy can effectively reduce renal radioactivity accumulation in humans. This strategy is expected to decrease renal radiation dose of peptide and small protein-based radiotracers, especially in the field of radionuclide therapy.

Chemical Species Change of Radionuclides by Microorganisms: Effects of Exudated Siderophores

Microbial exudates including siderophore, which changes chemical species of actinides and lanthanides. We have investigated effects of desferrioxamine B (DFOB; one of the siderophores) and siderophore-like organic molecules (SLOM) on the adsorption of lanthanides by microbial cells, aluminium oxide (Al2O3), and manganese (Mn) oxides. When DFOB was present, the distribution coefficients of cerium (Ce) were measured to be lower than those of neighboring elements of lanthanum (La) and praseodymium (Pr) (Negative anomaly of Ce adsorption). Even though initial oxidation state of Ce in the solution was III, that was changed to IV after the addition of DFOB, indicating that Ce(III) was oxidized by forming complex with DFOB. When lanthanides were adsorbed by biogenic Mn(IV) oxides, negative anomaly of Ce adsorption was observed in the sorption in alkaline solution. Ce(III) was oxidized to forme the complexes of Ce(IV) with SLOM in the solution. These results show that siderophore possesses high performance of oxidation of Ce(III) to Ce(IV) during association, affectiong the adsorption behavior of Ce. After Fukushima accident, radioactive Cs accumulation by Eleutherococcus sciadophylloides (Koshiabura) caused by the dissolution of Fe from soil around the roots, that was dominated by siderophore releasing microorganisms (SB). These SBs may enhance dissolution of iron (Fe) and uranium (U) phases in the nuclear fuel debris formed in the nuclear reactors in Fukushima Daiichi nuclear power plant. Thus, in the interaction between microorganisms and radionuclides, SLOMs discharged by microorganisms are deeply involved in the chemical state change of radionuclides.

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.

A Proof-of-Concept Study on the Theranostic Potential of 177 Lu-labeled Biocompatible Covalent Polymer Nanoparticles for Cancer Targeted Radionuclide Therapy.

Theranostic nanomedicine combined bioimaging and therapy probably rises more helpful and interesting opportunities for personalized medicine. In this work, 177 Lu radiolabeling and surface PEGylation of biocompatible covalent polymer nanoparticles (CPNs) have generated a new theranostic nanoformulation (177 Lu-DOTA-PEG-CPNs) for targeted diagnosis and treatment of breast cancer. The in vitro anticancer investigations demonstrate that 177 Lu-DOTA-PEG-CPNs possess excellent bonding capacity with breast cancer cells (4T1), inhibiting the cell viability, leading to cell apoptosis, arresting the cell cycle, and upregulating the reactive oxygen species (ROS), which can be attributed to the good targeting ability of the nanocarrier and the strong relative biological effect of the radionuclide labelled compound. Single photon emission computed tomography/ computed tomography (SPECT/CT) imaging and in vivo biodistribution based on 177 Lu-DOTA-PEG-CPNs reveal that notable radioactivity accumulation at tumor site in murine 4T1 models with both intravenous and intratumoral administration of the prepared radiotracer. Significant tumor inhibition has been observed in mice treated with 177 Lu-DOTA-PEG-CPNs, of which the median survival was highly extended. More strikingly, 50 % of mice intratumorally injected with 177 Lu-DOTA-PEG-CPNs was cured and showed no tumor recurrence within 90 days. The outcome of this work can provide new hints for traditional nanomedicines and promote clinical translation of 177 Lu radiolabeled compounds efficiently.

Preclinical In Vivo Imaging of Multiple Myeloma with [ 18f]Fluorohomoleucine (FHL) PET/CT

Purpose: Imaging of patients with multiple myeloma (MM) remains challenging due to its multi-focal nature affecting bone marrow, bone structures and soft tissue. As a result, current diagnostic methods like X-rays, CT and MRI scans only provide a partial understanding of disease activity and treatment response, lacking a comprehensive overview. Although 2-deoxy-2-[ 18F]fluoro-D-glucose (FDG) positron emission tomography (PET) has become the standard for detecting multifocal cancer spread, its use in MM patients is limited due to metabolic heterogeneity of MM and limited sensitivity in detecting extramedullary disease leading to false negative and false positive scans. To overcome these limitations, we developed a novel radiopharmaceutical L-[ 18F]Fluorohomoleucine (FHL) targeting LAT1 amino acid transporter. LAT1 has been significantly correlated with the proliferative activity of MM cells, poor prognosis and response to treatment in MM patients, presenting an appealing molecular target for assessing disease activity. Methods: FHL was synthesized as described by Nodwell et al. (J Nucl Med, 2019) and FDG was obtained from BC Cancer. LAT1 expression in multiple myeloma (MM) cell lines was confirmed by flow cytometry. Cell uptake assays were conducted using luciferase-transfected MM1S, L363, NCI H929 and AMO1 MM cells, and 2-amino-bicyclo[2.2.1]heptanes-2-carboxylic acid (BCH) was used as a blocking agent. For in vivo studies, male NRG mice were injected either with 1 x 10 6 MM cells intravenously (i.v.) via the caudal vein or subcutaneously (SQ) with 1 x 10 7 cells. Tumor engraftment was monitored weekly on an in vivo bioluminescence imager Perkin Elmer's IVIS Ilumina 5, starting at 2 weeks post-injection (p.i.). Biodistribution and PET/CT imaging studies were conducted at 4-6 weeks p.i. Results: All MM cells tested exhibited LAT1-specific FHL uptake in vitro with L363 and NCI H929 demonstrating the highest tracer uptake and average blocking efficacy over 83% and 93%, respectively. We were able to observe weekly progression of disease in the i.v. cohort using IVIS imaging. Biodistribution and PET imaging studies revealed FHL accumulation in the SQ xenografts, pancreas and excretion via the urinary tract. The SQ tumor uptake values were 4.53±0.82 %ID/g in AMO1 xenografts, 5.55±0.82 %ID/g in NCI H929, and 6.37±0.70 %ID/g in L363 tumors. In the i.v. cohort, the mouse intravenously injected with L363 cells demonstrated accumulation of radioactivity in the skull and vertebrae, as anticipated from the IVIS images. Furthermore, preliminary data suggests that FHL was able to detect a more extensive bone and lymphatic involvement than FDG in MM xenografts. Conclusion: We have demonstrated the ability of FHL for in vivo imaging of three human multiple myeloma tumors in SQ murine models, with the tumor uptake ranging from 4.53±0.82 %ID/g in AMO1 xenografts to 6.37±0.70 %ID/g in L363 tumors. Work is underway to establish the utility of this tracer in detecting disease dissemination in the orthotopic murine models of multiple myeloma, with promising preliminary results presented herein.

Radiometal Complexes as Pharmacokinetic Modifiers: A Potent 68Ga-Labeled Gastrin-Releasing Peptide Receptor Antagonist Based on the Macrocyclic Metal Chelator NODIA-Me.

The gastrin-releasing peptide receptor (GRPr) is overexpressed in various cancer types including prostate and breast carcinomas, making it an attractive target for molecular imaging and therapy. In this work, we designed a novel GRPr antagonistic probe comprising metal chelator NODIA-Me. This 1,4,7-triazacyclononane-based chelator forms positively charged metal complexes due to its neutral methylimidazole arms. Because a positive charge at the N-terminus of GRPr conjugates is responsible for high receptor affinity as exemplified by the current gold standard DOTA-RM2, we investigated if a positively charged radiometal complex can be used as a pharmacokinetic modifier to also produce high-affinity GRPr conjugates. In this respect, the bioconjugate NODIA-Me-Ahx-JMV594 was prepared by a combination of solid-phase peptide synthesis and solution-based reactions in a 94% yield. Radiolabeling provided the 68Ga-labeled conjugate in radiochemical yields of >95% and radiochemical purities of >98% with mean molar activities of Am ∼17 MBq nmol-1. The competitive GRPr affinity of the metal-free and 69/71Ga-labeled conjugate was determined to be IC50 = 0.41 ± 0.06 and 1.45 ± 0.06 nM, respectively. The metal-free GRPr antagonist DOTA-RM2 and its corresponding 69/71Ga complex had IC50 values of 1.42 ± 0.07 and 0.98 ± 0.19 nM, respectively. Small-animal PET imaging of mice bearing GRPr(+) PC-3 tumors revealed high radioactivity accumulation in the tumors and in the pancreas as an organ with high levels of GRPr expression. These findings were corroborated by the corresponding ex vivo biodistribution data, in which the tumors and the pancreas exhibited the highest radioactivity accumulation. By coinjection of an excess of NODIA-Me-Ahx-JMV594, uptake in the tumors and GRPr(+) organs was significantly reduced, confirming specific receptor-mediated uptake. The estrogen receptor-positive tumor of a female breast cancer patient was clearly visualized by PET imaging using 68Ga-labeled NODIA-Me-Ahx-JMV594. To summarize, the positive charge at the N-terminus of the conjugate induced by the Ga(NODIA-Me) complex resulted in high GRPr affinity comparable to that of the potent antagonist DOTA-RM2. The conjugate NODIA-Me-Ahx-JMV594 is a promising probe for imaging of GRPr tumors that warrants further evaluation in larger patient cohorts as well as in combination with other radiometals.

Synthetic Control of Thorium Metal‐Organic Frameworks for Sequencing and Sensing of Radioiodine Species

Comprehensive SummaryExploring the physiochemical properties and expanding the applications of actinide‐containing materials is paramount to address the escalating challenge of radioactive waste accumulation. However, unlocking the full potential of these materials is largely crippled by the radiotoxicity of the actinides. We report here two porous and luminescent thorium‐based metal‐organic frameworks (Th‐BITD‐1 and Th‐BITD‐2) that serve as a bifunctional platform for sequencing and sensing of radioiodine, a much more radioactive fission product discharged during the nuclear fuel reprocessing. In particular, Th‐BITD‐1 displays better iodine uptake performance than Th‐BITD‐2 via the solution‐based process and vapor diffusion with the maximum adsorption capacities of 831 and 1099 mg/g, respectively. Furthermore, Th‐BITD‐1 can function as a highly sensitive luminescence sensor for iodate with a quenching constant (KSV) of 6.6(5) × 103 M−1 and a detection limit of 2.02 μM, respectively, outperforming 2.96(6) × 103 M−1 and 10.5 μM of Th‐BITD‐2. Moreover, a positive correlation between the sensing efficacy and the iodate adsorption capacity has been revealed. This work highlights the opportunity in designing novel actinide‐based MOFs for their potential applications in radiological fields, e.g., radionuclide separation and detection.

Head-to-Head Comparison of 68Ga-PSMA-11 with 68Ga-P137 in Patients with Suspected Prostate Cancer.

P137 is a novel oxalyldiaminopropionic acid-urea-based prostate-specific membrane antigen (PSMA) targeting agent. This study compared the uptake patterns of 68Ga-P137 and the FDA-approved PET tracer 68Ga-PSMA-11 for diagnosing prostate cancer (PCa). Sixteen patients suspected of PCa were scanned by 68Ga-PSMA-11 and 68Ga-P137 PET/CT, respectively, followed by prospective analysis. The tumor-to-background ratio was calculated using normal prostate tissue, blood pool, muscle, and urine as backgrounds. Pathology or follow-up results were used to analyze uptake patterns of benign/malignant lesions and various organs. Thirteen patients were diagnosed with PCa and three with benign prostate diseases (BPD). The number and location of primary lesions, lymph node metastasis (LNM) (n = 25), bone metastasis (n = 30), and liver metastasis (n = 3) detected by the two tracers were identical. Maximum standardized uptake value (SUVmax), tumor/normal prostate ratio, as well as semiquantitative miPSMA-ES and PRIMARY diagnostic scores (P all >0.05) showed similar uptake levels of primary lesions between 68Ga-P137 and 68Ga-PSMA-11. Compared to 68Ga-P137, the SUVmax of 68Ga-PSMA-11 was significantly higher for bone metastasis, LNM, and liver metastasis (14.9 ± 7.2 vs 9.1 ± 4.4, 14.4 ± 5.0 vs 7.5 ± 2.4, 13.9 ± 2.0 vs 8.8 ± 2.4, P all <0.05). One-hour postinjection, SUVmax of the duodenum (9.4 ± 2.1 vs 16.2 ± 6.1), kidney (19.4 ± 4.3 vs 45.6 ± 20.9), and urine (14.1 ± 7.1 vs 42.1 ± 25.9) were significantly lower for 68Ga-P137 than for 68Ga-PSMA-11 (P all <0.05), whereas the radioactivity accumulation of blood pool and muscle (3.9 ± 0.5 vs 1.6 ± 0.4, 1.0 ± 0.1 vs 0.6 ± 0.1, P all <0.05) of 68Ga-P137 was significantly higher than 68Ga-PSMA-11. The uptake level of 68Ga-P137 has no significant difference from that of 68Ga-PSMA-11 in prostate primary lesions, and their imaging performances are visually equivalent for both primary and metastatic lesions, despite a higher blood pool and muscle background and a lower uptake in metastatic lesions. Due to the lower urine excretion of 68Ga-P137, primary prostate lesions near the urine can potentially be displayed clearer than 68Ga-PSMA-11.

Synthesis and evaluation of a novel PET ligand, a GSK’963 analog, aiming at autoradiography and imaging of the receptor interacting protein kinase 1 in the brain

BackgroundReceptor interacting protein kinase 1 (RIPK1) is a serine/threonine kinase, which regulates programmed cell death and inflammation. Recently, the involvement of RIPK1 in the pathophysiology of Alzheimer’s disease (AD) has been reported; RIPK1 is involved in microglia’s phenotypic transition to their dysfunctional states, and it is highly expressed in the neurons and microglia in the postmortem brains in AD patients. They prompt neurodegeneration leading to accumulations of pathological proteins in AD. Therefore, regulation of RIPK1 could be a potential therapeutic target for the treatment of AD, and in vivo imaging of RIPK1 may become a useful modality in studies of drug discovery and pathophysiology of AD. The purpose of this study was to develop a suitable radioligand for positron emission tomography (PET) imaging of RIPK1.Results(S)-2,2-dimethyl-1-(5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)propan-1-one (GSK’963) has a high affinity, selectivity for RIPK1, and favorable physiochemical properties based on its chemical structure. In this study, since 11C-labeling (half-life: 20.4 min) GSK’963 retaining its structure requiring the Grignard reaction of tert-butylmagnesium halides and [11C]carbon dioxide was anticipated to give a low yield, we decided instead to 11C-label a GSK’963 analog ((S)-2,2-dimethyl-1-(5-(m-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)propan-1-one, GG502), which has a high RIPK1 inhibitory activity equivalent to that of the original compound GSK’963. Thus, we successfully 11C-labeled GG502 using a Pd-mediated cross-coupling reaction in favorable yields (3.6 ± 1.9%) and radiochemical purities (> 96%), and molar activity (47–115 GBq/μmol). On autoradiography, radioactivity accumulation was observed for [11C]GG502 and decreased by non-radioactive GG502 in the mouse spleen and human brain, indicating the possibility of specific binding of this ligand to RIPK1. On brain PET imaging in a rhesus monkey, [11C]GG502 showed a good brain permeability (peak standardized uptake value (SUV) ~3.0), although there was no clear evidence of specific binding of [11C]GG502. On brain PET imaging in acute inflammation model rats, [11C]GG502 also showed a good brain permeability, and no significant increased uptake was observed in the lipopolysaccharide-treated side of striatum. On metabolite analysis in rats at 30 min after administration of [11C]GG502, ~55% and ~10% of radioactivity was from unmetabolized [11C]GG502 in the brain and the plasma, respectively.ConclusionsWe synthesized and evaluated a 11C-labeled PET ligand based on the methylated analog of GSK’963 for imaging of RIPK1 in the brain. Although in autoradiography of the resulting [11C]GG502 indicated the possibility of specific binding, the actual PET imaging failed to detect any evidence of specific binding to RIPK1 despite its good brain permeability. Further development of radioligands with a higher binding affinity for RIPK1 in vivo and more stable metabolite profiles compared with the current compound may be required.

The cycle effect quantified: reduced tumour uptake in subsequent cycles of [177Lu]Lu-HA-DOTATATE during peptide receptor radionuclide therapy.

Clear evidence regarding the effect of reduced tumour accumulation in later peptide receptor radionuclide therapy (PRRT) cycles is lacking. Therefore, we aimed to quantify potential cycle effects for patients treated with [177Lu]Lu-HA-DOTATATE using a population pharmacokinetic (PK) modelling approach. A population PK model was developed using imaging data from 48 patients who received multiple cycles of [177Lu]Lu-HA-DOTATATE. The five-compartment model included a central, kidney, spleen, tumour and lumped rest compartment. Tumour volume and continued use of long-acting somatostatin analogues (SSAs) were tested as covariates in the model. In addition, the presence of a cycle effect was evaluated by relating the uptake rate in a specific cycle as a fraction of the (tumour or organ) uptake rate in the first cycle. The final PK model adequately captured observed radioactivity accumulation in kidney, spleen and tumour. A higher tumour volume was identified to increase the tumour uptake rate, where a twofold increase in tumour volume resulted in a 2.3-fold higher uptake rate. Also, continued use of long-acting SSAs significantly reduced the spleen uptake rate (68.4% uptake compared to SSA withdrawal (10.5% RSE)). Lastly, a cycle effect was significantly identified, where tumour uptake rate decreased to 86.9% (5.3% RSE) in the second cycle and even further to 79.7% (5.6% RSE) and 77.6% (6.2% RSE) in the third and fourth cycle, respectively, compared to cycle one. Using a population PK modelling approach, the cycle effect of reduced tumour uptake in subsequent PRRT cycles was quantified. Our findings implied that downregulation of target receptors is probably not the major cause of the cycle effect, due to a plateau in the decrease of tumour uptake in the fourth cycle.

Selection and Use of Antioxidants-radioprotectors in the Composition of Therapeutic Radiopharmaceuticals (Review)

Introduction. The use of radiopharmaceuticals for targeted radionuclide therapy (TRT), the efficacy of which was established during clinical trials, is safe and effective for various pathological conditions, including cancer. The main feature of therapeutic radiopharmaceuticals (RPs) is the use of β–- and α-emitting radionuclides (RNs) in the finished dosage form (FD). Among the radionuclides used for radionuclide therapy, lutetium-177 is currently one of the most popular in clinical practice because of its chemical and nuclear characteristics. The list of RPs based on lutetium-177 is constantly expanding, and Lutathera® ([177Lu]Lu-DOTA-TATE) and Pluvicto™ ([177Lu]Lu-PSMA-617) have been approved for clinical use in several countries.Text. Because of the high activity of RNs in a single dose of therapeutic RPs (up to 8 GBq in a monodose for 177Lu), ionizing radiation of the used RNs leads to a decrease in RPs quality owing to radiolytic degradation of the vector molecule. This leads to a decreased specific accumulation of radioactivity in the foci of pathology, reduced therapeutic effect, and potentially increases the risk of radiotoxicity to non-target organs and tissues. The degree and intensity of radiolytic degradation of the vector molecule and, consequently, the shelf life of RPs depend on many factors, among which the activity concentration of the radionuclide in the preparation, its half-life, and the energy of the emitted particles are the most important. To suppress the effects of radiolysis, various excipients with antioxidant (radioprotective) properties were introduced into the compositions of the finished dosage forms. Among the substances studied, the most popular were gentisic acid, ascorbic acid, and ethanol. In this work, the advantages and disadvantages of various antioxidants and their combinations used in therapeutic RPs were considered in lutetium-177 preparations.Conclusion. Selection of the optimal composition of the dosage form is an urgent task, as it will ensure high-quality RPs both at the time of preparation and during the shelf life and delivery to the end user, which will greatly facilitate the use and centralized supply of therapeutic RPs. The necessity of creating a unified approach for the selection of antioxidants at the pharmaceutical development stage of radiopharmaceuticals is shown. For this purpose, an approach combining studies of radical reaction kinetics with studies of radiation-chemical yields of radiolysis products under identical or maximally similar conditions with subsequent verification of the stability of RPs dosage form seems to be very promising and has proven to be effective. In contrast, the empirical approach, which implies the selection of radioprotectors based on a direct study of their influence on the preservation of the level of radiochemical purity, is suboptimal because of the high market value of both radionuclides and non-radioactive precursors.

Preliminary PET imaging of [11C]evobrutinib in mouse models of colorectal cancer, SARS-CoV-2, and lung damage: Radiosynthesis via base-aided palladium-NiXantphos-mediated 11C-carbonylation.

Evobrutinib is a second-generation, highly selective, irreversible Bruton's tyrosine kinase (BTK) inhibitor that has shown efficacy in the autoimmune diseases arthritis and multiple sclerosis. Its development as a positron emission tomography (PET) radiotracer has potential for in vivo imaging of BTK in various disease models including several cancers, severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), and lipopolysaccharide (LPS)-induced lung damage. Herein, we report the automated radiosynthesis of [11C]evobrutinib using a base-aided palladium-NiXantphos-mediated 11C-carbonylation reaction. [11C]Evobrutinib was reliably formulated in radiochemical yields of 5.5 ± 1.5% and a molar activity of 34.5 ± 17.3 GBq/μmol (n =12) with 99% radiochemical purity. Ex vivo autoradiography studies showed high specific binding of [11C]evobrutinib in HT-29 colorectal cancer mouse xenograft tissues (51.1 ± 7.1%). However, in vivo PET/computed tomography (CT) imaging with [11C]evobrutinib showed minimal visualization of HT-29 colorectal cancer xenografts and only a slight increase in radioactivity accumulation in the associated time-activity curves. In preliminary PET/CT studies, [11C]evobrutinib failed to visualize either SARS-CoV-2 pseudovirus infection or LPS-induced injury in mouse models. In conclusion, [11C]evobrutinib was successfully synthesized by 11C-carbonylation and based on our preliminary studies does not appear to be a promising BTK-targeted PET radiotracer in the rodent disease models studied herein.

Preparation and Evaluation of [18F]AlF-NOTA-PBB for PET Imaging of Cyclin-dependent Kinase 4/6 in Tumors.

Cyclin-dependent kinases (CDKs), especially cyclin-dependent kinase 4/6 (CDK4/6), have been targets for the development of specific tumor imaging agents. Palbociclib is a highly selective CDK4/6 inhibitor. In this study, to develop a novel 18F-labeled palbociclib derivative for specific tumor imaging, we designed and synthesized a ligand (NOTA-PBB) consisting of palbociclib as the targeted pharmacophore and NOTA as the macrocyclic bifunctional chelator. The corresponding [18F]AlF-NOTA-PBB complex was prepared with high radiochemical purity (98.4 ± 0.15%) and yield (58.7 ± 4.5%) within 35 min without requiring HPLC purification through a simple one-step 18F-labeling strategy of NOTA-AlF chelation chemistry. The radiotracer was lipophilic (log P = 0.095 ± 0.003) and had good stability in vitro and in vivo. The cellular uptake studies performed on the MCF-7 breast cancer cell line (ER-positive and HER2-negative) showed that radioactive uptake was blocked by preincubating with a molar dose of palbociclib and it had a nanomolar binding affinity to CDK4/6 (IC50 = 16.23 ± 1.84 nM), demonstrating a CDK4/6-mediated uptake mechanism. Its ex vivo biodistribution in nude mice-bearing MCF-7 tumors showed obvious tumor uptake and a high tumor/muscle ratio of [18F]AlF-NOTA-PBB, and tumor uptake was inhibited with 100 μg of palbociclib, demonstrating specific binding to CDK4/6. Radioactivity accumulation in MCF-7 tumors was observed in PET imaging with [18F]AlF-NOTA-PBB. Based on the results of this work, [18F]AlF-NOTA-PBB has the promising capability as a CDK4/6-targeted tumor imaging agent.

Synthesis and Radiolabeling of Glu-Urea-Lys with 99mTc-Tricarbonyl-Imidazole-Bathophenanthroline Disulfonate Chelation System and Biological Evaluation as Prostate-Specific Membrane Antigen Inhibitor.

Background: The Glu-Urea-Lys (EUK) pharmacophore as prostate-specific membrane antigen (PSMA)-targeted ligand was synthesized, radiolabeled with 99mTc-tricarbonyl-imidazole-BPS chelation system, and biological activities were evaluated. The strategy [2 + 1] ligand is applied for tricarbonyl labeling. (5-imidazole-1-yl)pentanoic acid as a monodentate ligand and bathophenanthroline disulfonate (BPS) as a bidentate ligand formed a chelate system with 99mTc-tricarbonyl. EUK-pentanoic acid-imidazole and EUK were evaluated for PSMA active site using AutoDock 4 software. Materials and Methods: EUK-pentanoic acid-imidazole was synthesized in two steps. BPS was radiolabeled with 99mTc-tricarbonyl at 100°C for 30 min. The purified 99mTc(CO)3(H2O)BPS was used to radiolabel EUK-pentanoic acid-imidazole at 100°C, 30 min. Radiochemical purity, Log P, and stability studies were carried out within 24 h. Affinity of 99mTc(CO)3BPS-imidazole-EUK was performed in the saturation binding studies using LNCaP cells at 37°C for 1 h with a range of 0.001-1000 nM radiolabeled compound range. Internalization studies were performed in LNCaP cells with 1000 nM radiolabeled compound incubated for (0-2) h at 37°C. Biodistribution was studied in normal male Balb/c mice. The artificial intelligence predicts the uptake of radiolabeled compound in tumor. Results: The structures of synthesized compounds were confirmed by mass spectroscopy. Radiochemical purity, Log P, and protein binding were ≥95%, -0.2%, and 23%, respectively. The radiolabeled compound was stable in saline and human plasma within 24 h with radiochemical purity ≥90%. There was no release of 99mTc within 4 h in competition with histidine. The affinity was 82 ± 26.38 nM, and the activity increased inside the cells over time. Biodistribution studies showed radioactivity accumulation in kidneys less than 99mTc-HYNIC-PSMA. There was a moderate accumulation of radioactivity in the liver and intestine. Conclusion: Based on the results, 99mTc(CO)3BPS-imidazole-EUK can potentially be used as an imaging agent for studies at prostate bed and distal areas. The chelate system can be potentially labeled with rhenium for imaging studies (fluorescent or scintigraphy) and therapy.