A Brief History of Nuclear Medicine Imaging of Infection.

For nearly 50 years, nuclear medicine has played an important role in the diagnosis of infection. Gallium citrate Ga 67 was one of the first, if not the first, radionuclide used for this purpose. Unfavorable imaging characteristics, a lack of specificity, and the long interval (2-3 days) between administration and imaging spurred the search for alternatives. At the present time, gallium 67 citrate is used primarily for differentiating acute tubular necrosis from interstitial nephritis and as an alternative for indications including sarcoid, spondylodiscitis, and fever of unknown origin, when 18F-fluorodeoxyglucose (18F-FDG) is not available. The approval, in the mid-1980s, of techniques for in vitro labeling of leukocytes with indium-111 and technetium-99m that subsequently migrate to foci of infection was a significant advance in nuclear medicine imaging of infection and labeled leukocyte imaging still plays an important role in imaging of infection. There are significant disadvantages to in vitro labeled leukocyte imaging. Unfortunately, efforts devoted to developing in vivo leukocyte labeling methods have met with only limited success. Over the past 20 years 18F-FDG has established itself as a valuable imaging agent for musculoskeletal and cardiovascular infections, as well as sarcoidosis and fever of unknown origin. As useful as these agents are, their uptake is based on the host response to infection, not infection itself. Previous attempts at developing infection-specific agents, including radiolabeled antibiotics and vitamins, were limited by poor results and/or lack of availability, so investigators continue to focus on developing infection-specific nuclear medicine imaging agents.

FDG PET in Evaluation of Patients With Fever of Unknown Origin: AJR Expert Panel Narrative Review.

Fever of unknown origin (FUO) is a diagnostic challenge, with its cause remaining undiagnosed in approximately half of patients. Nuclear medicine tests typically are performed after a negative or inconclusive initial workup. Gallium-67 citrate and labeled leukocytes were previous mainstays of radionuclide imaging for FUO, although they had limited diagnostic performance. FDG PET/CT has subsequently emerged as the nuclear medicine imaging test of choice, supported by a growing volume of evidence. A positive FDG PET/CT result contributes useful information by identifying potential causes of fever, localizing sites for further evaluation, and guiding further management; a negative result contributes useful information by excluding focal disease as the cause of fever and predicts a favorable prognosis. In 2021, CMS rescinded a prior national noncoverage determination for FDG PET for infection and inflammation, leading to increasing national utilization of FDG PET/CT for FUO workup. This article reviews the current status of the role of FDG PET/CT in the evaluation of patients with FUO. The literature reporting the diagnostic performance and yield of FDG PET/CT in FUO workup is summarized, with comparison with historically used nuclear medicine tests included. Attention is also given to the test's clinical impact; protocol, cost, and radiation considerations; and application in children.

Usefulness of gallium-67 scintigraphy for evaluating the histopathological activity in interstitial nephritis.

BACKGROUND: Interstitial nephritis is a common cause of renal failure. Gallium-67 scintigraphy is reportedly useful for diagnosing interstitial nephritis; however, its ability to assess disease activity remains unknown. We aimed to analyze the relationship between the renal uptake of gallium-67 and the disease activity in interstitial nephritis. METHODS: We retrospectively analyzed the data of patients who underwent gallium-67 scintigraphy at a hospital in Tokyo. The renal uptake adjusted for the soft tissues beneath the kidneys was semi-quantitatively evaluated. We compared the renal uptake levels between patients clinically diagnosed with and without interstitial nephritis. Among those undergoing renal biopsy, we evaluated the predictive ability of gallium-67 scintigraphy and analyzed the renal uptake levels regarding the disease activity through a histopathological analysis. RESULTS: We included 143 patients; among them, 30, 17, and 96 patients were clinically diagnosed with interstitial nephritis, other kidney diseases, and non-kidney diseases, respectively. The renal uptake of gallium-67 was the highest among patients with interstitial nephritis. Among the 25 patients who underwent renal biopsy, 15 were pathologically diagnosed with interstitial nephritis. The renal uptake levels showed a high discriminative ability (C-statistic: 0.83). Furthermore, net reclassification improvement with the addition of gallium-67 scintigraphy to N-acetyl-ß-D-glucosaminidase for the prediction of interstitial nephritis was 1.14. Histopathological analysis revealed a positive correlation between renal uptake and inflammation in the cortex and peritubular capillaries. CONCLUSIONS: This study confirmed the diagnostic value and potential usefulness of gallium-67 scintigraphy for evaluating interstitial nephritis.

Effects of chronic immobilization stress on biokinetics and dosimetry of 67Ga in a murine model.

The aim of this work is to determine the effect of chronic immobilization stress on kinetics and dosimetry of 67Ga in a mouse model. A control group (CG) and a stress group (SG), each with 15 mice, were included in the study, and the latter group was subjected to a chronic immobilization stress model 2 h daily for 14 consecutive days. At day 13, 67Ga-citrate was administered intraperitoneally (11.24 ± 0.44 MBq) to each mouse. Then, sets of three mice were obtained sequentially at 24, 36, 48, 60 and 72 h, in which the radionuclide activity was measured with an activity counter. The 67Ga biokinetic data showed a fast blood clearance in the SG, with a mean residence time of 0.06 h. The calculated mean radiation absorbed doses were: liver (2.45 × 10-03 Gy), heart (3.17 × 10-04 Gy) and kidney (1.88 × 10-04 Gy) in the SG. The results show that stress reduced weight gain by approximately 13% and also increased adrenal gland weight by 26%. On the other hand, chronic stress accelerates 67Ga clearance after 24 h compared to normal conditions. It is concluded that murine organisms under chronic immobilization stress have higher gallium-67 clearance rates, decreasing the cumulated activity and absorbed dose in all organs.

Cilostazol-induced acute tubulointerstitial nephritis accompanied by IgA nephropathy: a case report.

BACKGROUND: Cilostazol is an antiplatelet drug that is widely prescribed for the prevention of secondary stroke. Adverse reactions to cilostazol include headaches, palpitations, and diarrhea. Little is known about the nephrotoxicity of cilostazol, such as acute kidney injury. We report a biopsy-proven case of diffuse tubulointerstitial nephritis induced by cilostazol. CASE PRESENTATION: A 69-year-old woman prescribed cilostazol was hospitalized for acute kidney injury. On admission, her renal function deteriorated, with an increased serum creatinine level. Urinalysis showed hematuria, proteinuria, and hyper-beta2-microglobulinuria. A renal biopsy revealed diffuse tubulointerstitial nephritis associated with IgA nephropathy, and gallium-67 scintigraphy showed uptake in the bilateral kidneys. A drug lymphocyte stimulation test for cilostazol was positive, and the patient was diagnosed with cilostazol-induced acute tubulointerstitial nephritis. Despite discontinuation of cilostazol, her renal function rapidly worsened and steroid pulse therapy was initiated, followed by oral high-dose glucocorticoid therapy. After steroid treatment, her serum creatinine level normalized in parallel with urine beta2-microglobulin. CONCLUSION: Cilostazol can induce acute tubulointerstitial nephritis.

A study of radiogallium aqueous chemistry: in vitro and in vivo characterisation of (67) Ga-hydrolysed-stannous fluoride particles.

The objective of this study was to explore the aqueous chemistry of gallium using (67) Ga-chloride starting material, by radiolabelling hydrolysed(h)-stannous fluoride particles and then characterising the optimal formulation for radiochemical purity (RCP) and radioactive particle size distribution in vitro. The pilot reactions determined stannous fluoride was added to (67) Ga-acetate under nitrogen and then heated at 100 °C for 20 min to achieve ≥95% RCP and (67) Ga-particles were >3 µm in diameter. A high radioactive concentration of (67) Ga-h-SnF2 particles could be prepared similarly in ≥97% RCP with 74% as 3-5 µm and 26% >5 µm in diameter. The latter formulation had larger particles than (99m) Tc-h-SnF2 colloid (96% of 1-3 µm), and it resulted in a rat biodistribution of 41% in the lungs, 41% in the liver plus spleen and 18% in the carcass at 20 min after injection. The carcass activity was attributed to bone marrow and some (67) Ga-transferrin formed in blood. Isolated mixed human leucocytes were radiolabelled with (67) Ga-h-SnF2 particles in 100% efficiency, and the (67) Ga-cells did not release soluble (67) Ga(3+) at room temperature over 3 h. The (67) Ga-h-SnF2 particle formulation could find a use in labelling leucocyte cells for in vivo homing studies when delayed animal imaging is required.

Alternatives for the Detection and Diagnosis of Osteoarticular Infections: An Exploratory Review.

The precise diagnosis of osteomyelitis, a bone infection, remains a significant challenge for healthcare professionals. This difficulty stems from the highly variable nature of its clinical presentation and disease course. Patients can exhibit a wide range of symptoms, making it easy to misdiagnose the condition. In turn, inaccurate diagnoses lead to inappropriate treatment regimens, potentially hindering a patient's recovery and causing unnecessary complications. Nuclear medicine offers a ray of hope in this fight against diagnostic ambiguity. It provides valuable tools, such as radiopharmaceutical imaging, that can significantly improve the accuracy of osteomyelitis diagnosis. However, limitations exist. This article explores the need for alternative diagnostic approaches within the specific context of Costa Rica. This exploration is particularly relevant due to the current regional shortage of gallium-67 (67Ga), a radiopharmaceutical commonly used in osteomyelitis diagnosis. The article delves into the nature, function, and limitations of various nuclear medicine techniques, encompassing both independent radiopharmaceuticals like 67Ga and those conjugated with specific targeting molecules to pinpoint areas of infection within the body. Given the scarcity of 67Ga in Costa Rica, it becomes crucial to explore and implement viable alternative diagnostic techniques within the healthcare system. This article emphasizes the need for further investigation into these alternatives, with the goal of improving diagnostic accuracy and ensuring optimal patient care. By implementing these alternatives, healthcare professionals in Costa Rica can effectively combat the challenges posed by osteomyelitis and pave the way for better patient outcomes.

Predictive value of radiologic studies for malignant otitis externa: a systematic review and meta-analysis.

OBJECTIVE: To determine the diagnostic accuracy of Necrotizing Otitis Externa (NOE) based on radiologic studies. METHODS: The PubMed, Cochrane, Embase, Web of Science, SCOPUS, and Google Scholar databases were searched. True-positive and false-negative results were extracted for each study. Methodological quality was evaluated using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. RESULTS: The included studies contained data on 37 studies diagnosed with NOE. The sensitivity of gallium-67, technetium-99m, and Magnetic Resonance Imaging (MRI) was 0.9378 (0.7688-0.9856), 0.9699 (0.8839-0.9927), and 0.9417 (0.6968-0.9913), respectively. For Computed Tomography (CT), the positive criteria consisted of bony erosion alone and bony erosion plus any soft tissue abnormality. The sensitivity of CT based only on bony erosion was 0.7062 (0.5954-0.7971); it was higher 0.9572 (0.9000-0.9823) when based on bony erosion plus any soft tissue abnormality. CONCLUSION: The diagnostic sensitivity of technetium-99m, gallium-67, and MRI was favorable. On CT, the presence of bony erosion may be a useful diagnostic marker of NOE, but the diagnostic sensitivity will be even higher if the criterion of any soft tissue abnormality is also included; however, care should be taken when interpreting the results. Our study demonstrates the potential utility of radiology studies for diagnosing NOE, but their lack of specificity must be considered, and standardized anatomic criteria are still needed. LEVEL OF EVIDENCE: 2A.

Ascorbate Preferentially Stimulates Gallium-67 Uptake in Glioblastoma Cells.

Gallium is a tri-valent p-block metal that closely mimics tri-valent iron. Gallium is internalized into cells via transferrin receptor-mediated endocytosis. Both Ga-67 and Ga-68 are radionuclides that can be radiolabeled to various bioactive compounds for clinical imaging procedures to visualize tumors and sites of inflammation. High-dose ascorbate (pharmacological ascorbate) is an emergent glioblastoma therapy that enhances cancer cell-killing through iron-metabolic perturbations. We hypothesized that pharmacological ascorbate treatments might alter Ga-67 uptake in glioblastoma cells. We evaluated the in vitro ability of pharmacological ascorbate to alter gallium uptake in patient-derived glioblastoma cells with variable genetic backgrounds by co-incubating cells with Ga-67 ± pharmacological ascorbate. Surprisingly, we observed increased basal gallium uptake in the glioblastoma cells compared to normal human astrocytes. Further, pharmacological ascorbate treatment stimulated gallium uptake in glioblastoma cells while not affecting uptake in normal human astrocytes. This effect appears to be related to transient increases in transferrin receptor expression. Finally, pharmacological ascorbate treatment appears to stimulate gallium uptake in an iron metabolism-dependent manner. Further mechanistic experiments are required to evaluate the translational utility of ascorbate to impact gallium tumor imaging.

A Comparative Case Study between Gallium-67 Citrate Scintigraphy and Gallium-68 Citrate Positron Emission Tomography-Computed Tomography in Bone Infection.

Bone infections are a common problem, and early diagnosis and intervention can lead to better clinical outcomes and prognoses. Here, we compare the well-known tracers Gallium-67 (Ga-67) citrate versus Ga-68 citrate in the diagnosis of infections.

Tracking Uptake and Metabolism of Xenometallomycins Using a Multi-Isotope Tagging Strategy.

Synthetic and naturally occurring siderophores and their conjugates provide access to the bacterial cytoplasm via active membrane transport. Previously, we displaced iron with the radioactive isotope 67Ga to quantify and track in vitro and in vivo uptake and distribution of siderophore Trojan Horse antibiotic conjugates. Here, we introduce a multi-isotope tagging strategy to individually elucidate the fate of metal cargo and the ligand construct with radioisotopes 67Ga and 124I. We synthesized gallium(III) model complexes of a ciprofloxacin-functionalized linear desferrichrome (Ga-D6) and deferoxamine (Ga-D7) incorporating an iodo-tyrosine linker to enable radiolabeling using the metal-binding (67Ga) and the cargo-conjugation site (124I). Radiochemical experiments with Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa wt strains show that 67Ga-D6/D7 and Ga-D6-124I/D7-124I have comparable uptake, indicating intact complex import and siderophore-mediated uptake. In naive mice, 67Ga-D6/D7 and Ga-D6-124I/D7-124I demonstrate predominantly renal clearance; urine metabolite analysis indicates in vivo dissociation of Ga(III) is a likely mechanism of degradation for 67Ga-D6/D7 when compared to ligand radiolabeled compounds, Ga-D6-124I/D7-124I, which remain >60% intact in urine. Cumulatively, this work demonstrates that a multi-isotope tagging strategy effectively elucidates the in vitro uptake, pharmacokinetics, and in vivo stability of xenometallomycins with modular chemical structures.

Effect of pH Variation on Cross-Linking of Water-Soluble and Acid- Soluble Chitosan with Sodium Tripolyphosphate and Gallium-67.

BACKGROUND: Chitosan is a cationic biopolymer obtained from deacetylating chitin, a natural compound present in crustacean shell, fungi and exoskeleton of insects. Chitosan involves various applications, including as drug and gene delivery systems, as wound dressing material and scaffolds for tissue engineering, agriculture, textile, food and feed nanotechnology, and in wastewater treatments. Chitosan-TPP particle has been figured out as the most important and stable nanoparticle for chitosan application in various fields. OBJECTIVE: In this study, chitosan was chemically modified by sodium tripolyphosphate (TPP). Afterward, TPP-chitosan was radiolabeled with the gallium-67 radionuclide. The effect of several factors on labeling yield, such as chitosan solubility, acidity and concentration of TPPchitosan solution, and incubation time with gallium-67, were investigated. METHODS: To prepare [67Ga] gallium-chitosan complex, chitosan (0.5 ml) was dissolved in 2.2 mCi of [67Ga] gallium chloride solution. The obtained solution was stirred for 5 min and then kept for 30 min at room temperature. The radiochemical purity and radiolabeling yield were measured via radiochromatography, which was performed by using a radio thin-layer chromatography (TLC) scanner instrument. To investigate the effect of chitosan kind and concentration on the labeling yield, two kinds of chitosan (acid-soluble chitosan and water-soluble chitosan) at two different concentrations (1% and 0.5%) and different pH were used. In addition, labeling efficiency and stability of the 67Ga-TPP-chitosan complex (acidic/water soluble chitosan) at both concentrations (0.5 and 1%) and at room temperature were assessed for 30, 45 and 60 min. RESULTS: The incubation time did not have any significant effect on labeling yield. The acidic soluble chitosan exhibited the highest radiolabeling yield at pH=9.3-10.4, while water-soluble chitosan showed the highest radiolabeling yield at pH > 5. Also, the prepared complex was stable in the final solution at room temperature and could even be used 24 hours after preparation for further application. CONCLUSION: Taken together, the TPP-modified water-soluble chitosan at the concentration of 0.5 % depicted the highest radiochemical yield (>95 %) in the optimized condition (pH= 6.2- 7.6). Therefore, TPP modified water-soluble chitosan can prove to be an effective carrier for therapeutic radionuclides in tumor treatment.

Nuclear model analysis and optimization of production data of the medically interesting 66,67,68 Ga via alpha induced reactions on 63,65 Cu targets.

Evaluation of the 63Cu(α,n)66Ga, 65Cu(α,2n) 67Ga and 65Cu(α,n)68Ga reactions was done to study the production of medical radionuclides 66Ga, 67Ga and 68Ga respectively. 63Cu(α,2n)65Ga and 65Cu(α,3n)66Ga reactions were also evaluated for the estimation of radioisotopic impurities. Cross section data of each reaction were compiled and normalized to the standard values of decay data and monitor reaction. To check the consistency of the literature data, three nuclear model calculations were performed, using nuclear model codes; TAYLS 1.9, ALICE-IPPE, and EMPIRE 3.2. A well-developed evaluation methodology based on the normalized experimental data and nuclear model calculations was used to generate the statistically fitted cross sections. From the fitted cross sections, thick target yields for each reaction were calculated for the estimation of radioisotopic impurities. Finally, a suitable energy region for the production of 66Ga, 67Ga and 68Ga was suggested with a minimum level of radioisotopic impurities.

RetroSPECT: Gallium-67 as a Long-Lived Imaging Agent for Theranostics.

A limitation to the wider introduction of personalised dosimetry in theranostics is the relative paucity of imaging radionuclides with suitable physical and chemical properties to be paired with a long-lived therapeutic partner. As most of the beta-emitting therapeutic radionuclides emit gamma radiation as well they could potentially be used as the imaging radionuclide as well as the therapeutic radionuclide. However, the downsides are that the beta radiation will deliver a significant radiation dose as part of the treatment planning procedure, and the gamma radiation branching ratio is often quite low. Gallium-67 has been in use in nuclear medicine for over 50 years. However, the tremendous interest in gallium imaging in theranostics in recent times has focused on the PET radionuclide gallium-68. In this article it is suggested that the longer-lived gallium-67, which has desirable characteristics for imaging with the gamma camera and a suitably long half-life to match biological timescales for drug uptake and turnover, has been overlooked, in particular, for treatment planning with radionuclide therapy. Gallium-67 could also allow non-PET facilities to participate in theranostic imaging prior to treatment or for monitoring response after therapy. Gallium-67 could play a niche role in the future development of personalised medicine with theranostics.

Is there a role for Gallium-67 SPECT in distinguishing progression and pseudoprogresion in oncologic patients receiving immunotherapy?

Immuno-oncology (IO) with immune checkpoint inhibitors (ICIs) is the new landmark in cancer treatment. However, due to its economical-related burden and the possibility of tumor pseudoprogression with late response patterns, it is imperative to find new ways for early discrimination of patients with IO-sensitive versus IO-resistant disease. ICI-mediated antitumor responses depend on tumor immune infiltration by T-cells capable of recognizing and killing tumor cells. Nevertheless, patients may experience different responses to immunotherapy according to their tumor microenvironment and inflammatory infiltration. T-cell infiltrated tumors are referred to as 'hot' and are potential candidates for a good response to ICIs, whereas 'cold' are those tumors lacking T-cell infiltration and exhibit a narrow likelihood of response to IO therapy. Gallium-67 (67Ga) scintigraphy may hold potential for separating 'hot' from 'cold' tumors, thus providing an imaging tool to distinguish 'hot' ICI-induced pseudoprogression from real early 'cold' progression. Even so, various tumors (lymphomas, lung cancer, breast cancer, hepatoma, malignant melanoma) exhibit an inherent affinity for 67Ga that is independent of the ICI-induced immune infiltration, and this raises issues about false positivity. For that reason, future investigational studies to evaluate the prospective role of this radiotracer in the early prediction of ICI response should be confined to tumors with an inherently low 67Ga affinity (thyroid carcinoma, gastrointestinal and genitourinary tract tumors). We describe our experience with a patient with recurrent metastatic lung adenocarcinoma under ICI therapy that was submitted to 67Ga scanning for a fever of unknown origin and we discuss the aforementioned topics, alongside current imaging trends and future perspectives in the field.

Mucin-1 conjugated polyamidoamine-based nanoparticles for image-guided delivery of gefitinib to breast cancer.

PAMAM dendrimers (PAMs) are a group of polymeric macromolecules with distinctive physicochemical features, which can make them multifunctional theranostic nanoparticles (NPs). This study was designed to examine the impact of mucin-1 aptamer-conjugated NPs which were engineered using PAM for image-guided delivery of gefitinib (GEF) in the breast cancer cells/tumor. For this, PAMAM was conjugated with diethylenetriaminepentaacetic acid (DTPA) and modified with PEG2000 to prepare a multi-functionalized NPs. Subsequently, GEF was loaded onto the DTPA-PAM-PEG NPs, which were then armed with MUC-1 aptamer to form the DTPA-PAM-PEG/GEF@MUC-1 nanosystem. Finally, aptamer-conjugated NPs were radiolabeled by gallium-67 as an imaging agent to construct image-guided nanoplatforms. The prepared NPs were characterized by different techniques. The kinetic release models of gefitinib from radiolabeled NPs offer the sustained-release mechanism of the encapsulated drug for over 7 days. In vitro evaluation showed higher cytotoxicity and enhanced uptake of the mucin-grafted NPs in MCF-7 cells. Nuclear medicine imaging and in vivo investigations revealed significant accumulation of 67Ga-DTPA-PAM-PEG/GEF@MUC-1 in the tumor site of the animal models. These data suggest that the engineered NPs are a promising image-guided nanosystem for mucin-expressing breast cells/tumors with the assistance of nuclear medicine.

Imaging of Acute and Chronic Skull Base Infection.

Skull base infections are uncommon but can be life threatening without timely recognition. Imaging plays a crucial role because symptoms can be vague and nonlocalizing. Necrotizing otitis externa in diabetic or immunocompromised patients is the commonest cause of skull base osteomyelitis (SBO), followed by sinogenic infections and idiopathic central SBO. Multiparametric magnetic resonance (MR) and high-resolution CT are the mainstays for establishing a diagnosis and estimating disease extent, with MR being superior in ascertaining marrow and soft tissue involvement. Monitoring treatment response, of which imaging is a fundamental part, is challenging, with emerging promising imaging tools.

Prognosis and Outcomes of Clinically Diagnosed Cardiac Sarcoidosis Without Positive Endomyocardial Biopsy Findings.

Background: Diagnosis of cardiac sarcoidosis (CS) is sometimes difficult due to a low positive rate of epithelioid granulomas by endomyocardial biopsy (EMB). Accordingly, Japanese guidelines can allow the CS diagnosis using clinical data alone without EMB results (clinical CS) since 2006. However, little is known about prognosis and outcome of clinical CS. Objectives: Purpose of this study was to analyze the prognosis, outcomes, and response to corticosteroid of clinical CS using large-scale cohort survey. Methods: Overall, 422 CS patients (mean age 60 ± 13 years, 68% female, median follow-up period of 5 years), including 345 clinical CS and 77 EMB-positive patients, histologically diagnosed CS (histological CS) by Japanese guidelines, were enrolled and examined. Results: Clinical profile (age, sex, initial cardiac arrhythmias, and abnormal uptake of gallium-67 scintigraphy or 18F-fluorodeoxyglucose positron emission tomography in heart) was similar in both groups. Although clinical CS had better prognosis (P = 0.018) and outcome (all-cause death, appropriate defibrillator therapy, and heart transplantation; P = 0.008), multivariate Cox hazard analysis revealed that left ventricular ejection fraction (LVEF) and sustained ventricular tachycardia history were independently associated with outcome (P < 0.001 and P = 0.002, respectively), but not with the diagnosed CS category. Moreover, similar LVEF recovery after corticosteroid was observed in both groups with low LVEF (≤35%) at the 1-year follow-up period (P < 0.001). Conclusions: In clinical CS according to the Japanese guideline, prophylactic implantable-cardioverter-defibrillator and immunosuppressive therapy are important in patients with low LVEF or ventricular tachycardia history, similar to histological CS.

Biodistribution and imaging of an hsp90 ligand labelled with 111In and 67Ga for imaging of cell death.

BACKGROUND: 4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid (GSAO) when conjugated at the γ-glutamyl residue with fluorophores and radio-isotopes is able to image dead and dying cells in vitro and in vivo by binding to intracellular 90-kDa heat shock proteins (hsp90) when cell membrane integrity is compromised. The ability to image cell death has potential clinical impact especially for early treatment response assessment in oncology. This work aims to assess the biodistribution and tumour uptake of diethylene triamine pentaacetic acid GSAO labelled with 111In ([111In]In-DTPA-GSAO) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid GSAO labelled with 67Ga ([67Ga]Ga-DOTA-GSAO) in a murine subcutaneous tumour xenograft model and estimate dosimetry of [67Ga]Ga-DOTA-GSAO. RESULTS: There was good tumour uptake of both [111In]In-DTPA-GSAO and [67Ga]Ga-DOTA-GSAO (2.44 ± 0.26% injected activity per gramme of tissue (%IA/g) and 2.75 ± 0.34 %IA/g, respectively) in Balb c nu/nu mice bearing subcutaneous tumour xenografts of a human metastatic prostate cancer cell line (PC3M-luc-c6). Peak tumour uptake occurred at 2.7 h post injection. [111In]In-DTPA-GSAO and [67Ga]Ga-DOTA-GSAO demonstrated increased uptake in the liver (4.40 ± 0.86 %IA/g and 1.72 ± 0.27 %IA/g, respectively), kidneys (16.54 ± 3.86 %IA/g and 8.16 ± 1.33 %IA/g) and spleen (6.44 ± 1.24 %IA/g and 1.85 ± 0.44 %IA/g); however, uptake in these organs was significantly lower with [67Ga]Ga-DOTA-GSAO (p = 0.006, p = 0.017 and p = 0.003, respectively). Uptake of [67Ga]Ga-DOTA-GSAO into tumour was higher than all organs except the kidneys. There was negligible uptake in the other organs. Excretion of [67Ga]Ga-DOTA-GSAO was more rapid than [111In]In-DTPA-GSAO. Estimated effective dose of [67Ga]Ga-DOTA-GSAO for an adult male human was 1.54 × 10- 2 mSv/MBq. CONCLUSIONS: [67Ga]Ga-DOTA-GSAO demonstrates higher specific uptake in dead and dying cells within tumours and lower uptake in normal organs than [111In]In-DTPA-GSAO. [67Ga]Ga-DOTA-GSAO may be potentially useful for imaging cell death in vivo. Dosimetry estimates for [67Ga]Ga-DOTA-GSAO are acceptable for future human studies. This work also prepares for development of 68Ga GSAO radiopharmaceuticals.

In vitro cytotoxicity of Auger electron-emitting [67Ga]Ga-trastuzumab.

INTRODUCTION: Molecular radiotherapy exploiting short-range Auger electron-emitting radionuclides has potential for targeted cancer treatment and, in particular, is an attractive option for managing micrometastatic disease. Here, an approach using chelator-trastuzumab conjugates to target radioactivity to breast cancer cells was evaluated as a proof-of-concept to assess the suitability of 67Ga as a therapeutic radionuclide. METHODS: THP-trastuzumab and DOTA-trastuzumab were synthesised and radiolabelled with Auger electron-emitters 67Ga and 111In, respectively. Radiopharmaceuticals were tested for HER2-specific binding and internalisation, and their effects on viability (dye exclusion) and clonogenicity of HER2-positive HCC1954 and HER2-negative MDA-MB-231 cell lines was measured. Labelled cell populations were studied by microautoradiography. RESULTS: Labelling efficiencies for [67Ga]Ga-THP-trastuzumab and [111In]In-DOTA-trastuzumab were 90% and 98%, respectively, giving specific activities 0.52 ± 0.16 and 0.61 ± 0.11 MBq/µg (78-92 GBq/µmol). At 4 nM total antibody concentration and 200 × 103 cells/mL, [67Ga]Ga-THP-trastuzumab showed higher percentage of cell association (10.7 ± 1.3%) than [111In]In-DOTA-trastuzumab (6.2 ± 1.6%; p = 0.01). The proportion of bound activity that was internalised did not differ significantly for the two tracers (62.1 ± 1.4% and 60.8 ± 15.5%, respectively). At 100 nM, percentage cell binding of both radiopharmaceuticals was greatly reduced compared to 4 nM and did not differ significantly between the two (1.2 ± 1.0% [67Ga]Ga-THP-trastuzumab and 0.8 ± 0.9% for [111In]In-DOTA-trastuzumab). Viability and clonogenicity of HER2-positive cells decreased when each radionuclide was incorporated into cells by conjugation with trastuzumab, but not when the same level of radioactivity was confined to the medium by omitting the antibody conjugation, suggesting that 67Ga needs to be cell-bound or internalised for a therapeutic effect. Microautoradiography showed that radioactivity bound to individual cells varied considerably within the population. CONCLUSIONS: [67Ga]Ga-THP-trastuzumab reduced cell viability and clonogenicity only when cell-bound, suggesting 67Ga holds promise as a therapeutic radionuclide as part of a targeted radiopharmaceutical. The causes and consequences of non-homogeneous uptake among the cell population should be explored.