In this article, we present the synthesis and characterization of three macrocyclic chelators, HPATA, PATAM, and HPATPA, based on a pyridine-azacrown compound. Their complexation with Ga and Lu has been thoroughly investigated using MALDI TOF MS, H NMR spectroscopy, radiolabeling studies, and experiments in vitro with fetal bovine serum and a 1000-fold molar excess of HEDTA. Our studies have shown that the chelators HPATA and HPATPA form complexes at room temperature with both radionuclides (RCY > 80 % and > 90 % for complexes with HPATA and HPATPA after 30 min, respectively). The chelator PATAM requires high temperature (95 °C) for complexation. In vitro stability assays in fetal bovine serum as well as HEDTA-challenge revealed that transchelation occurs for all complexes with Ga. However, complexes of the ligands HPATA and PATAM with Lu were found stable. Thus, taking into account the radiolabeling at room temperature and in vitro stability of the complex [Lu]Lu·PATA, our investigations revealed the chelator HPATA is a candidate for radiopharmaceutical use with Lu.

Intranasal (IN) administration, often referred to as nose-to-brain (N2B) drug delivery, is an attractive approach for delivering drugs to the central nervous system. However, the efficacy of this method is limited because of the small size of the nasal olfactory region, which limits the drug dosage. Using permeation enhancers could improve drug delivery from this region to the brain, though their effects are not fully understood. We therefore investigated the effects of co-administration of permeation enhancers on N2B drug delivery of a model drug domperidone, a peripherally acting dopamine D2 receptor (D2R) blocker.

Our objective was to study convection enhanced delivery (CED) of Lu-labeled metal chelating polymer (MCP) conjugated to gold nanoparticles ([Lu]Lu-MCP-AuNP) alone or combined with anti-PD1 immune checkpoint inhibition (ICI) for improving the survival of immunocompetent C57BL/6J mice with orthotopic GL261 murine glioma tumors.

Elevated levels of HER2 receptor in breast cancer can be targeted through receptor-specific peptides for precise detection and therapy by nuclear medicine approach. Previously reported retro analogue of A9 peptide had shown HER2-specificity with promising pharmacokinetic features. Hence, with an aim of further improving the circulation time of rL-A9 radiopeptide, long polyethylene glycol chain (PEG) was introduced at the N-terminus of the peptide during solid phase synthesis and influence of PEGylation on biological profile was studied. [Lu]Lu-DOTA-PEG-rL-A9 demonstrated high specific cellular uptake (5.94 ± 0.09 %) in HER2-expressing human breast carcinoma SKBR3 cells and low nanomolar binding affinity (K = 34.58 ± 12.78 nM). Uptake in SKBR3 tumors induced in female SCID mice was higher at all the time points investigated (3, 24, 48 h) in comparison to the non-PEGylated radiopeptide, [Lu]Lu-DOTA-rL-A9. Blocking studies led to 51 % reduction in accumulation of radioactivity in the tumor indicating specificity of the radiopeptide. Improved tumor-to-stomach and tumor-to-intestine ratios for [Lu]Lu-DOTA-PEG-rL-A9 compared to [Lu]Lu-DOTA-rL-A9 at 48 h shall pave the way for better contrast and delineation of metastatic sites.

Monitoring β-cell mass and function would provide a better understanding of diabetes, setting the stage for truly individualized therapies. We applied a combined PET/MRI protocol to monitor engrafted islets mass and function without pre-labeling of isolated cells. A PET tracer binding to GLP-1R quantifies β-cell mass, while Mn-CA characterizes β-cell function. Both parameters were assessed in transplanted and native β-cells in vivo and validated with autoradiography and mass spectrometry imaging.

Antimicrobial 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 Ga-radiolabeling of the DOTA-modified LyeTx I mn∆K and primarily preclinical evaluations of [Ga]Ga-DOTA(K)-LyeTx I mn∆K as a PET radiopharmaceutical for infection imaging.

Ketone metabolism has been studied using positron emission tomography (PET) with the radiotracers [C]acetoacetate and [C]β-hydroxybutyrate. However, whether these two radiotracers actually yield equivalent estimates of cerebral and myocardial ketone metabolism has not yet been investigated. This study aimed to investigate and compare the kinetics of both tracers in the brain and heart of healthy rats under varying levels of circulating ketones at baseline and after a single-dose exogenous ketone ester (KE) supplement.

Radiometals play an important role in nuclear medicine, both for imaging and therapy. Binding studies represent an important step in the development of new radiolabeled ligands, as valuable insights into the binding properties can be gained. However, this technique requires high radiochemical purity, otherwise results may lead to wrong assumptions or misinterpretations of affinities or uptake rates. Therefore, this in vitro study aimed at investigating the cell binding and internalization characteristics of different radiometal chlorides ([In]InCl, [Ga]GaCl and [Lu]LuCl) commonly applied in nuclear medicine, as well as the clinically applied [Lu]Lu-PSMA-I&T in comparison, by using prostate cancer cells. PC-3 and LNCaP cells were incubated with 100 kBq of the respective radiometal chloride or [Lu]Lu-PSMA-I&T for 1 h. For [Lu]LuCl, nuclei isolations and colloid determinations in saline and cell medium were also performed. Results showed that [In]InCl and [Ga]GaCl bind and are internalized up to 3 % to PC-3 and LNCaP cells, whereas [Lu]LuCl showed cell binding of up to 25 %, internalization up to 2.5 % and a nuclear uptake below 0.3 %. In comparison, [Lu]Lu-PSMA-I&T showed only 3 % total cell binding to LNCaP cells. Further analysis of [Lu]LuCl stability in NaCl and cell medium showed only low amounts of colloids, which are not increasing over time, and negligible unspecific binding to the used cell culture plates. In conclusion, the results demonstrate the importance of high radiochemical purity, especially with regard to Lu-177 labeled compounds. Even if radiopharmaceuticals comply with common release-criteria, significant uptake can be derived from [Lu]LuCl impurities and lead to wrong estimations of a compound's uptake behavior. Assuming an experimental result of 2 % membrane binding of the applied product, and 5 % residual [Lu]LuCl in the final product (thereof 25 % membrane binding, as described above), would lead to 1.25 % membrane binding resulting from [Lu]LuCl and only 0.75 % from the radiopharmaceutical.

M2-type tumor-associated macrophages (TAM) residing in the tumor microenvironment (TME) have been linked to tumor invasiveness, metastasis and poor prognosis. M2 TAMs suppress T cell activation, silencing the recognition of the cancer by the immune system. Targeting TAMs in anti-cancer therapy may support the immune system and immune-checkpoint inhibitor therapies to fight the cancer cells. We aimed to develop a PET tracer for the imaging of M2 TAM infiltration of cancer, using activated legumain as the imaging target.

The selection for either primary or interval cytoreductive surgery (CRS) in patients with epithelial ovarian cancer (EOC) is currently based on imaging techniques like computed tomography (CT), [F]fluorodeoxyglucose-positron emission tomography ([F]FDG-PET), diffusion-weighted magnetic resonance imaging (DW-MRI) and/or diagnostic laparoscopy, but these have limitations. Folate receptor (FR)-targeted PET/CT imaging, using [F]fluoro-PEG-folate, could improve preoperative assessment, potentially reducing unnecessary laparotomies. This paper presents the first experience with [F]fluoro-PEG-folate PET/CT imaging in advanced stage EOC, focusing on safety, tolerability, and feasibility for reflecting the extent of disease.

Patients with advanced metastatic estrogen receptor-positive breast cancer often develop resistance to standard treatments, leading to uncontrolled progression. Thus, innovative therapies are urgently needed. The gastrin-releasing peptide receptor (GRPR) is overexpressed in various cancers, including breast cancer, making it an interesting theranostic target. RM26, a GRPR-targeting antagonist, has demonstrated promising in vivo kinetics in prostate cancer models. This study evaluated the theranostic capabilities of [Co]Co-/[Lu]Lu-DOTA-RM26 in vitro in estrogen receptor-positive breast cancer cells and assessed the diagnostic potential of [Co]Co-DOTA-RM26 in vivo in a breast cancer mouse model.

Direct fluorination of a tosylate or mesylate precursor has been a wide-spread and reliable way for radio-fluorination. This approach can be difficult to achieve when the precursor cannot be easily obtained or is chemically unstable. A possible alternative method is to radiolabel ethylene ditosylate or 1,3-propanediol di-p-tosylate to form a radiofluorinated synthon. Here we present the automation of a simplified and reliable approach for the two-step fluorination using [F]FP-TMP, an analog of antibacterial agent trimethoprim. We demonstrate the feasibility of purifying the fluorinated synthon via filtration, and one final HPLC purification on a commercially available Trasis AllinOne module. The overall reaction time for the two-step reaction is around 90 min andthe decay-corrected yield for more than fifty preparations of [F]FP-TMP is 22 ± 5 % with high radiochemical purity (≥ 90 %) and specific activities (147 ± 107 GBq/μmol). All batches passed pre-established quality control specifications, demonstrating the utility of using this method in tracer syntheses that meet good manufacturing practice (GMP) requirement. This method can be adopted to the syntheses of other radiotracers, such as [F]FE-TMP, (+)-[F]F-PHNO and [F]FFMZ.

Heterotopic ossification (HO) is the formation of bone within soft tissue where bone normally does not exist. In general, it is characterized by highly active tissue with high bone turnover and rapid bone formation. It is of an utmost importance to precisely identify and accurately diagnose the maturity of HO as early surgical intervention may result in its recurrence. The objective of this work is the experimental evaluation of HO maturity stage using advanced noninvasive nuclear medicine techniques. The use of PET radiopharmaceuticals may result in a more specific diagnosis between the phases due to their higher sensitivity and better resolution compared to bone scan.

Positron emission tomography (PET) can provide information about tumor-associated macrophage (TAM) infiltration, as long as a suitable tracer is available. This study aimed to evaluate the radiolabeled peptide [F]AlF-NODA-MP-C6-CTHRSSVVC as a potential PET tracer for imaging of the CD163 receptor, which is expressed on M2-type tumor-associated macrophages. The conjugated peptide NODA-MP-C6-CTHRSSVVC was labeled with aluminum [F]fluoride. Tracer binding and its biodistribution were evaluated in an in vitro binding assay and in healthy BALB/c mice, respectively. In addition, different treatments with cyclophosphamide in tumor-bearing mice were used to assess whether the tracer could detect differences in CD163 expression caused by differential TAM infiltration. After 7 days of treatment, animals were injected with [F]AlF-NODA-MP-C6-CTHRSSVVC, and a 60-min dynamic PET scan was performed, followed by an ex vivo biodistribution study. [F]AlF-NODA-MP-C6-CTHRSSVVC was prepared in 23 ± 6 % radiochemical yield and showed approximately 50 % of specific receptor-mediated binding in an in vitro binding assay on human CD163-expressing tissue homogenates. No CD163-mediated binding of [F]AlF-NODA-MP-C6-CTHRSSVVC was detected by PET under normal physiological conditions in healthy BALB/c mice. On the other hand, CD163-positive xenograft tumors were clearly visualized with PET and a positive correlation was found between CD163 levels and the [F]AlF-NODA-MP-C6-CTHRSSVVC tumor-to-muscle ratio (TMR) obtained from the PET images (Pearson r = 0.76, p = 0.002). No significant differences in the CD163 protein level and in the tracer uptake between treatment groups were found in the tumors. Taken together, [F]AlF-NODA-MP-C6-CTHRSSVVC appears a promising candidate PET tracer for M2-type TAM, as it binds specifically to CD163 in vitro and its tumor uptake correlates well with CD163 expression in vivo.

Prostate-specific membrane antigen (PSMA) is a promising target for treating metastatic castration-resistant prostate cancer. Our previous report presented In- or Ac-labeled PSMA-NAT-DA1 (PNT-DA1) as a PSMA-targeted ligand. To improve its therapeutic efficiency, PNT-DA1 contains 4-(p-iodophenyl)butyric acid (IPBA), which is known as an albumin binder (ALB) moiety. However, few reports have examined the relationship between the chemical modification of the ALB moiety and pharmacokinetics of PSMA-targeted radioligands. To assess this relationship, we designed, synthesized, and evaluated four [In]In-PNT-DA1 analogues with ALB moieties different from IPBA.

Astatine-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 At via Bi (α, 2n) At reaction in a cyclotron and development of a facile radiochemical separation procedure to isolate At for formulation of nanoradiopharmaceuticals.

[F]F13640 is a new PET radiopharmaceutical for brain molecular imaging of serotonin 5-HT receptors. Since we intend to use this radiopharmaceutical in psychiatric studies, it is crucial to establish possible sensitivity modification of 5-HT receptors availability during an acute stress exposure. In this study, we first assessed the cerebrometabolic effects of a new animal model of stress with [F]FDG and then proceeded to test for effects of this model on the cerebral binding of [F]F13640, a 5-HT receptors PET radiopharmaceutical.

Targeted alpha therapy (TAT) of somatostatin receptor-2 (SSTR2) positive neuroendocrine tumors (NETs) involving Ac-225 ([Ac]Ac-DOTA-TATE) has previously demonstrated improved therapeutic efficacy over conventional beta particle-emitting peptide receptor radionuclide therapy agents. DOTA-TATE requires harsh radiolabeling conditions for chelation of [Ac]Ac, which can limit the achievable molar activities and thus therapeutic efficacy of such TAT treatments. Macropa-TATE was recently highlighted as a potential alternative to DOTA-TATE, owing to the mild radiolabeling conditions and high affinity toward [Ac]Ac; however, elevated liver and kidney uptake were noted as a major limitation and a suitable imaging radionuclide is yet to be reported, which will be required for patient dosimetry studies and assessment of therapeutic benefit. Previously, [Tb]Tb-crown-TATE has shown highly effective imaging of NETs in preclinical SPECT/CT studies, with high tumor uptake and low non-target accumulation; these favourable properties and the versatile coordination behavior of the crown chelator may therefore show promise for combination with Ac-225 for TAT.

Great strides have been made identifying molecular and genetic changes expressed by various tumor types. These molecular and genetic changes are used as pharmacologic targets for precision treatment using large molecule (LM) proteins with high specificity. Theranostics exploits these LM biomolecules via radiochemistry, creating sensitive diagnostic and therapeutic agents. Intravenous (i.v.) LM drugs have an extended biopharmaceutical half-life thus resulting in an insufficient therapeutic index, permitting only palliative brachytherapy due to unacceptably high rates of systemic nontarget radiation doses to normal tissue. We employ tumor arteriole embolization isolating a tumor from the systemic circulation, and local intra-arterial (i.a.) infusion to improve uptake of a LM drug within a porcine renal tumor (RT).

Prostate cancer affects 1 in 6 men, and it is the second‑leading cause of cancer-related death in American men. Surgery is one of the main treatment modalities for prostate cancer, but it often results in incomplete resection margins or complete resection that leads to nerve damage and undesirable side effects. In the present work, we have developed a new bimodal tracer, NODAGA-sCy7.5 PSMAi (prostate-specific membrane antigen inhibitor), labeled with the true matched theranostic pair Cu/Cu and a near-infrared fluorescent dye. This agent could potentially be used for concomitant PET imaging, optical surgical navigation, and targeted radiopharmaceutical therapy.

Zirconium-89 (Zr) is a positron emitter with several advantages over other shorter-lived positron emission tomography (PET) compatible radiometals such as gallium-68 or copper-64. These include practically unlimited availability, extremely low cost, greatly facilitated distribution logistics, positron energy fit for medical PET imaging, and sufficiently long physical half-life to enable PET imaging at later time points for patient-specific dosimetry estimations. Despite these apparent benefits, the reception of Zr in the nuclear medicine community has been tepid. The driving factor for the absence of broader adaptation is mostly routed in its final formulation - [Zr]zirconium oxalate. While serving as a suitable precursor solution for the gold standard chelator deferoxamine (DFO), [Zr]Zr-oxalate is inaccessible for the most commonly used chelators, such as the macrocyclic DOTA, due to its pre-chelated state. Consequently, pioneering work has been conducted by multiple research groups to create oxalate-free forms of [Zr]Zr, either via chemical conversion of oxalate into other counterion forms or via direct radiochemical isolation of [Zr]ZrCl, showing that [Zr]Zr-DOTA complexes are possible and stable. However, this success was accompanied by challenges, including complex and labor-intensive radiochemical processing and radiolabeling procedures as well as the relatively minuscule conversion rates. Here, we report on the direct production of [Zr]ZrCl avoiding oxalate and metal contaminants to enable efficient radiolabeling of DOTA constructs.