First in-human evaluation of [1-13C]pyruvate in D2O for hyperpolarized MRI of the brain: A safety and feasibility study

PURPOSE

To investigate the safety and value of hyperpolarized (HP) MRI of [1-13C]pyruvate in healthy volunteers using deuterium oxide (D2O) as a solvent.

METHODS

Healthy volunteers (n = 5), were injected with HP [1-13C]pyruvate dissolved in D2O and imaged with a metabolite-specific 3D dual-echo dynamic EPI sequence at 3T at one site (Site 1). Volunteers were monitored following the procedure to assess safety. Image characteristics, including SNR, were compared to data acquired in a separate cohort using water as a solvent (n = 5) at another site (Site 2). The apparent spin-lattice relaxation time (T1) of [1-13C]pyruvate was determined both in vitro and in vivo from a mono-exponential fit to the image intensity at each time point of our dynamic data.

RESULTS

All volunteers completed the study safely and reported no adverse effects. The use of D2O increased the T1 of [1-13C]pyruvate from 66.5 ± 1.6 s to 92.1 ± 5.1 s in vitro, which resulted in an increase in signal by a factor of 1.46 ± 0.03 at the time of injection (90 s after dissolution). The use of D2O also increased the apparent relaxation time of [1-13C]pyruvate by a factor of 1.4 ± 0.2 in vivo. After adjusting for inter-site SNR differences, the use of D2O was shown to increase image SNR by a factor of 2.6 ± 0.2 in humans.

CONCLUSIONS

HP [1-13C]pyruvate in D2O is safe for human imaging and provides an increase in T1 and SNR that may improve image quality.

Position paper to facilitate patient access to radiopharmaceuticals: considerations for a suitable pharmaceutical regulatory framework

BACKGROUND

Nuclear medicine has made enormous progress in the past decades. However, there are still significant inequalities in patient access among different countries, which could be mitigated by improving access to and availability of radiopharmaceuticals.

MAIN BODY

This paper summarises major considerations for a suitable pharmaceutical regulatory framework to facilitate patient access to radiopharmaceuticals. These include the distinct characteristics of radiopharmaceuticals which require dedicated regulations, considering the impact of the variable complexity of radiopharmaceutical preparation, personnel requirements, manufacturing practices and quality assurance, regulatory authority interfaces, communication and training, as well as marketing authorisation procedures to ensure availability of radiopharmaceuticals. Finally, domestic and regional supply to ensure patient access via alternative regulatory pathways, including in-house production of radiopharmaceuticals, is described, and an outlook on regulatory challenges faced by new developments, such as the use of alpha emitters, is provided.

CONCLUSIONS

All these considerations are an outcome of a dedicated Technical Meeting organised by the IAEA in 2023 and represent the views and opinions of experts in the field, not those of any regulatory authorities.

Paradigms for Precision Medicine in Epichaperome Cancer Therapy

Alterations in protein-protein interaction networks are at the core of malignant transformation but have yet to be translated into appropriate diagnostic tools. We make use of the kinetic selectivity properties of an imaging probe to visualize and measure the epichaperome, a pathologic protein-protein interaction network. We are able to assay and image epichaperome networks in cancer and their engagement by inhibitor in patients' tumors at single-lesion resolution in real time, and demonstrate that quantitative evaluation at the level of individual tumors can be used to optimize dose and schedule selection. We thus provide preclinical and clinical evidence in the use of this theranostic platform for precision medicine targeting of the aberrant properties of protein networks.

Imaging-assisted nanoimmunotherapy for atherosclerosis in multiple species

Nanomedicine research produces hundreds of studies every year, yet very few formulations have been approved for clinical use. This is due in part to a reliance on murine studies, which have limited value in accurately predicting translational efficacy in larger animal models and humans. Here, we report the scale-up of a nanoimmunotherapy from mouse to large rabbit and porcine atherosclerosis models, with an emphasis on the solutions we implemented to overcome production and evaluation challenges. Specifically, we integrated translational imaging readouts within our workflow to both analyze the nanoimmunotherapeutic's in vivo behavior and assess treatment response in larger animals. We observed our nanoimmunotherapeutic's anti-inflammatory efficacy in mice, as well as rabbits and pigs. Nanoimmunotherapy-mediated reduction of inflammation in the large animal models halted plaque progression, supporting the approach's translatability and potential to acutely treat atherosclerosis.

Biodistribution and Dosimetry of 18F-Meta-Fluorobenzylguanidine: A First-in-Human PET/CT Imaging Study of Patients with Neuroendocrine Malignancies

¹²³I-meta-iodobenzylguanidine (¹²³I-MIBG) imaging is currently a mainstay in the evaluation of many neuroendocrine tumors, especially neuroblastoma. ¹²³I-MIBG imaging has several limitations that can be overcome by the use of a PET agent. ¹⁸F-meta-fluorobenzylguanidine (¹⁸F-MFBG) is a PET analog of MIBG that may allow for single-day, high-resolution quantitative imaging. We conducted a first-in-human study of ¹⁸F-MFBG PET imaging to evaluate the safety, feasibility, pharmacokinetics, and dosimetry of ¹⁸F-MFBG in neuroendocrine tumors (NETs). Methods: Ten patients (5 with neuroblastoma and 5 with paraganglioma/pheochromocytoma) received 148-444 MBq (4-12mCi) of ¹⁸F-MFBG intravenously followed by serial whole-body imaging at 0.5-1, 1-2, and 3-4 after injection. Serial blood samples (a total of 6) were also obtained starting at 5 min after injection to as late as 4 h after injection; whole-body distribution and blood clearance data, lesion uptake, and normal-tissue uptake were determined, and radiation-absorbed doses to normal organs were calculated using OLINDA. Results: No side effects were seen in any patient after ¹⁸F-MFBG injection. Tracer distribution showed prominent activity in the blood pool, liver, and salivary glands that decreased with time. Mild uptake was seen in the kidneys and spleen, which also decreased with time. Urinary excretion was prominent, with an average of 45% of the administered activity in the bladder by 1 h after injection; whole-body clearance was monoexponential, with a mean biologic half-life of 1.95 h, whereas blood clearance was biexponential, with a mean biologic half-life of 0.3 h (58%) for the rapid α phase and 6.1 h (42%) for the slower β phase. The urinary bladder received the highest radiation dose with a mean absorbed dose of 0.186 ± 0.195 mGy/MBq. The mean total-body dose was 0.011 ± 0.011 mGy/MBq, and the effective dose was 0.023 ± 0.012 mSv/MBq. Both skeletal and soft-tissue lesions were visualized with high contrast. The SUVmax (mean ± SD ) of lesions at 1-2 h after injection was 8.6 ± 9.6. Conclusion: Preliminary data show that ¹⁸F-MFBG imaging is safe and has favorable biodistribution and kinetics with good targeting of lesions. PET imaging with ¹⁸F-MFBG allows for same-day imaging of NETs. ¹⁸F-MFBG appears highly promising for imaging of patients with NETs, especially children with neuroblastoma.

Glutamine-based PET imaging facilitates enhanced metabolic evaluation of gliomas in vivo

Glucose and glutamine are the two principal nutrients that cancer cells use to proliferate and survive. Many cancers show altered glucose metabolism, which constitutes the basis for in vivo positron emission tomography (PET) imaging with (18)F-fluorodeoxyglucose ((18)F-FDG). However, (18)F-FDG is ineffective in evaluating gliomas because of high background uptake in the brain. Glutamine metabolism is also altered in many cancers, and we demonstrate that PET imaging in vivo with the glutamine analog 4-(18)F-(2S,4R)-fluoroglutamine ((18)F-FGln) shows high uptake in gliomas but low background brain uptake, facilitating clear tumor delineation. Chemo/radiation therapy reduced (18)F-FGln tumor avidity, corresponding with decreased tumor burden. (18)F-FGln uptake was not observed in animals with a permeable blood-brain barrier or neuroinflammation. We translated these findings to human subjects, where (18)F-FGln showed high tumor/background ratios with minimal uptake in the surrounding brain in human glioma patients with progressive disease. These data suggest that (18)F-FGln is avidly taken up by gliomas, can be used to assess metabolic nutrient uptake in gliomas in vivo, and may serve as a valuable tool in the clinical management of gliomas.

A prospective pilot study of (89)Zr-J591/prostate specific membrane antigen positron emission tomography in men with localized prostate cancer undergoing radical prostatectomy

PURPOSE

In this pilot study we explored the feasibility of (89)Zr labeled J591 monoclonal antibody positron emission tomography of localized prostate cancer.

MATERIALS AND METHODS

Before scheduled radical prostatectomy 11 patients were injected intravenously with (89)Zr-J591, followed 6 days later by whole body positron emission tomography. Patients underwent surgery the day after imaging. Specimens were imaged by ex vivo micro positron emission tomography and a custom 3 Tesla magnetic resonance scanner coil. Positron emission tomography images and histopathology were correlated.

RESULTS

Median patient age was 61 years (range 47 to 68), median prostate specific antigen was 5.2 ng/ml (range 3.5 to 12.0) and median biopsy Gleason score of the 11 index lesions was 7 (range 7 to 9). On histopathology 22 lesions were identified. Median lesion size was 5.5 mm (range 2 to 21) and median Gleason score after radical prostatectomy was 7 (range 6 to 9). Eight of 11 index lesions (72.7%) were identified by in vivo positron emission tomography. Lesion identification improved with increasing lesion size for in vivo and ex vivo positron emission tomography (each p <0.0001), and increasing Gleason score (p = 0.14 and 0.01, respectively). Standardized uptake values appeared to correlate with increased Gleason score but not significantly (p = 0.19).

CONCLUSIONS

To our knowledge this is the first report of (89)Zr-J591/prostate specific membrane antigen positron emission tomography in localized prostate cancer cases. In this setting (89)Zr-J591 bound to tumor foci in situ and positron emission tomography identified primarily Gleason score 7 or greater and larger tumors, likely corresponding to clinically significant disease warranting definitive therapy. A future, larger clinical validation trial is planned to better define the usefulness of (89)Zr-J591 positron emission tomography for localized prostate cancer.