[89Zr]Zr-PSMA-617 PET/CT in biochemical recurrence of prostate cancer: first clinical experience from a pilot study including biodistribution and dose estimates

PSMA PET/CT in biochemical recurrence of prostate cancer with PSA levels ≤ 0.2 ng/mL: a German multicenter analysis of conventional PSMA tracers, including [68Ga]Ga-PSMA-11, [68Ga]Ga-PSMA I&T, and [18F]PSMA-1007

BACKGROUND

Prostate-specific membrane antigen (PSMA)-directed positron emission tomography/computed tomography (PET/CT) has emerged as a highly accurate imaging modality for detecting tumor lesions in patients with biochemical recurrence (BCR) of prostate cancer (PC). While detection rates of lesions suspicious for PC relapse are known to increase with rising prostate-specific antigen (PSA) levels, data on the efficacy of PSMA PET/CT at very low PSA values (≤ 0.2 ng/mL) remain limited.

METHODS

In this multicenter study, we analyzed 321 patients with BCR and a PSA value ≤ 0.2 ng/mL across five German academic centers, using three different PSMA-targeted radiotracers: [68Ga]Ga-PSMA-11, [68Ga]Ga-PSMA I&T, and [18F]PSMA-1007 and analyzed the detection rates and potential predictive parameters.

RESULTS

The overall pooled detection rate was 29.6%. No statistically significant differences in detection rates were observed between the three radiotracers ([68Ga]Ga-PSMA-11 29.4% vs. [68Ga]Ga-PSMA I&T, 22.5% vs. [18F]PSMA-1007 32.4%, p ≥ 0.314). Detection rates were significantly higher in patients with a PSA level > 0.15 ng/mL (p = 0.029, φ = 0.122), in those with an initial Gleason score > 7 (p = 0.018, φ = 0.141) and in those receiving androgen deprivation therapy (p = 0.031, φ = 0.120).

CONCLUSION

All three radiotracers demonstrated comparable diagnostic performance, with no significant superiority observed between the 68Ga- and 18F-labeled tracers in the patient sample investigated (overall pooled detection rate: 29.6%). This positivity rate can serve as an expectation horizon for both the attending physician and the patient in the case of low PSA values. Further studies with larger cohorts, preferably conducted in a prospective setting, are needed to confirm and expand upon our findings.

Diffuse Peritoneal Carcinomatosis of Prostate Cancer Unveiled by [89Zr]Zr-PSMA-617 PET/CT

ABSTRACT

We report an interesting case of a 64-year-old man with a history of radical prostatectomy for prostate cancer. The patient presented with steady increasing prostate-specific antigen levels, but with negative findings on previous multiple conventional prostate-specific membrane antigen (PSMA) PET/CT (with [68Ga]Ga-PSMA-11) and [18F]FDG PET/CT. A recently introduced PSMA tracer using long-lived 89Zr (half-life 3.3 days), [89Zr]Zr-PSMA-617, was administered in attempt to localize potential local recurrence or metastasis. [89Zr]Zr-PSMA-617 PET/CT clearly revealed diffuse peritoneal carcinomatosis and local recurrence of the prostate cancer, which were unidentified on previous conventional PET/CT scans. This case highly demonstrates the potential of PET imaging with the novel PSMA tracer [89Zr]Zr-PSMA-617.

A whole gamma imaging prototype for higher quantitative imaging of89Zr-labeled antibodies in a tumor mouse model

Objective.Positron emission tomography (PET) has become an important clinical modality, but it is limited to imaging the annihilation radiation from positron-electron collisions. Recently, PET imaging with89Zr, which has a half-life of 3 d, has attracted much attention in immuno-PET to visualize immune cells and cancer cells by targeting specific antibodies on the cell surface. However,89Zr emits a single gamma ray at 909 keV four times more frequently than positrons, causing image quality (IQ) degradation in conventional PET. To overcome this drawback, use of such single gamma rays for imaging was previously proposed as whole gamma imaging (WGI). In WGI, a single gamma ray is detected by Compton imaging; by inserting a scatter detector ring inside the PET ring, WGI can realize both PET imaging and Compton imaging in one modality. A prototype for WGI was developed and Compton imaging of a mouse after intravenous administration of89Zr oxalate was demonstrated. However, the Compton imaging of the single gamma ray still presented a challenge due to its low IQ compared to PET.Approach.In this study, the scatter detector insert of the earlier WGI prototype was redesigned with the aim of improving Compton imaging performance. The new prototype produced WGI images by additive averaging of PET and Compton images after optimizing the ratio of each iteration in the image reconstruction. WGI IQ was then evaluated using the NEMA NU4 IQ phantom, and a tumor-burdened mouse was imaged with WGI up to 12 d after89Zr labeled antibody injection.Main results.Consequently, the Compton imaging performance was improved by lowering the angular resolution measure from 6.7 degrees to 6.4 degrees and the sensitivity from 0.11% to 0.18% compared to the previous prototype WGI. The phantom images with WGI showed a 15% reduction in noise and a 3% increase in contrast recovery under low-statistical conditions compared to images reconstructed by PET data alone.Significance. In-vivomouse imaging with the new prototype WGI was successfully performed. This successful imaging leads to the expectation that future whole-body WGI imaging will enable more sensitive and better quantitative89Zr antigen-antibody reaction imaging to be obtained.

Human Biodistribution and Radiation Dosimetry of the Targeting Fibroblast Growth Factor Receptor 1-Positive Tumors Tracer [68Ga]Ga-DOTA-FGFR1-Peptide

Objective: [68Ga]Ga-DOTA-FGFR1-peptide is a novel positron emission tomography (PET) radiotracer targeting fibroblast growth factor receptor 1 (FGFR1). This study evaluated the safety, biodistribution, radiation dosimetry, and imaging potential of [68Ga]Ga-DOTA-FGFR1-peptide. Methods: The FGFR1-targeting peptide DOTA-(PEG2)-KAEWKSLGEEAWHSK was synthesized by manual solid-phase peptide synthesis with high-performance liquid chromatography purification, and labeled with 68Ga with DOTA as chelating agent. We recruited 14 participants and calculated the radiation dose of 4 of these pathologically confirmed nontumor subjects using OLINDA/EXM 2.2.0 software. At the same time, the imaging potential in 10 of these lung cancer patients was evaluated. Results: The biodistribution of [68Ga]Ga-DOTA-FGFR1-peptide in 4 subjects showed the highest uptake in the bladder and kidney. Dosimetry analysis indicated that the bladder wall received the highest effective dose (3.73E-02 mSv/MBq), followed by the lungs (2.36E-03 mSv/MBq) and red bone marrow (2.09E-03 mSv/MBq). No normal organs were found to have excess specific absorbed doses. The average systemic effective dose was 4.97E-02 mSv/MBq. The primary and metastatic tumor lesions were clearly visible on PET/computed tomography (CT) images in 10 patients. Conclusion: Our results indicate that [68Ga]Ga-DOTA-FGFR1-peptide has a good dosimetry profile and can be used safely in humans, and it has significant potential value for clinical PET/CT imaging.

Highlighting New Research Trends on Zirconium-89 Radiopharmaceuticals Beyond Antibodies

Zirconium-89 (89Zr) is a cyclotron-produced positron-emitting radioisotope with a half-life of 3.27 days, which makes delayed or longitudinal imaging possible. It is a superior isotope for tracking particles over several days at a high sensitivity, resolution, and specificity. 89Zr-monoclonal antibodies (89Zr-mAb) have gained significant attention in the field of molecular imaging. However, the past decade has shown an avid increase in research concerning 89Zr-radiopharmaceuticals apart from 89Zr-mAb. In this article we highlight and discuss the status and challenges attributed to current preclinical and clinical investigations of 89Zr-radiopharmaceuticals developed beyond 89Zr-mAb, e.g., mAb-derived variants and macro-biomolecules, proteins, peptides, nanoparticles, and living cells.

Outstanding increase in tumor-to-background ratio over time allows tumor localization by [89Zr]Zr-PSMA-617 PET/CT in early biochemical recurrence of prostate cancer

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) using prostate-specific membrane antigen (PSMA)-targeted radiotracers labeled with zirconium-89 (89Zr; half-life ~ 78.41 h) showed promise in localizing biochemical recurrence of prostate cancer (BCR) in pilot studies.

METHODS

Retrospective analysis of 38 consecutive men with BCR (median [minimum-maximum] prostate-specific antigen 0.52 (0.12-2.50 ng/mL) undergoing [89Zr]Zr-PSMA-617 PET/CT post-negative [68Ga]Ga-PSMA-11 PET/CT. PET/CT acquisition 1-h, 24-h, and 48-h post-injection of a median (minimum-maximum) [89Zr]Zr-PSMA-617 tracer activity of 123 (84-166) MBq.

RESULTS

[89Zr]Zr-PSMA-617 PET/CT detected altogether 57 lesions: 18 local recurrences, 33 lymph node metastases, 6 bone metastases in 30/38 men with BCR (78%) and prior negative conventional PSMA PET/CT. Lesion uptake significantly increased from 1-h to 24-h and, in a majority of cases, from 24-h to 48-h. Tumor-to-background ratios significantly increased over time, with absolute increases of 100 or more. No side effects were noted. After [89Zr]Zr-PSMA-617 PET/CT-based treatment, prostate-specific antigen concentration decreased in all patients, becoming undetectable in a third of patients.

LIMITATIONS

retrospective, single center design; infrequent histopathological and imaging verification.

CONCLUSION

This large series provides further evidence that [89Zr]Zr-PSMA-617 PET/CT is a beneficial imaging modality to localize early BCR. A remarkable increase in tumor-to-background ratio over time allows localization of tumor unidentified on conventional PSMA PET/CT.

Preclinical studies and absorbed dose estimation of [89Zr]Zr-DFO-Bevacizumab for PET imaging of VEGF-expressing tumors

This study aimed to carry out the preclinical studies of [89Zr]Zr-DFO-Bevacizumab. The radiolabeled compound was prepared with radiochemical purity >99% (ITLC), and a specific activity of 74 GBq/g. Cellular studies indicated the great capability of [89Zr]Zr-DFO-Bevacizumab for binding to SKOV3 cell lines. High accumulation was observed in the tumor. The liver and spleen received the highest absorbed dose with 1.12 and 0.72 mGy/MBq, respectively. This radiopharmaceutical can be considered as a suitable PET agent for VEGF-expressing ovarian cancer imaging.

[68Ga]PSMA-11 for positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer

INTRODUCTION

Theranostics targeting prostate-specific membrane antigen (PSMA) represent a new targeted approach for prostate cancer care that combines diagnostic and therapeutic radiopharmaceuticals to diagnose and treat the disease. Positron emission tomography (PET) is the imaging method of choice and several diagnostic radiopharmaceuticals for quantifying PSMA have received FDA approval and are in clinical use. [68Ga]Ga-PSMA-11 is one such imaging agent and the focus of this article. One beta-emitting radioligand therapy ([177Lu]Lu-PSMA-617) has also received FDA approval for prostate cancer treatment, and several other alpha- and beta-emitting radioligand therapies are in clinical trials.

AREAS COVERED

Theranostics targeting PSMA in men with prostate cancer are discussed with a focus on use of [68Ga]Ga-PSMA-11 for imaging PSMA-positive lesions in men with prostate cancer. The review covers [68Ga]Ga-PSMA-11 manufacture, current regulatory status, comparison of [68Ga]Ga-PSMA-11 to other imaging techniques, clinical updates, and emerging applications of artificial intelligence for [68Ga]Ga-PSMA-11 PET.

EXPERT OPINION

[68Ga]Ga-PSMA-11 is used in conjunction with a PET/CT scan to image PSMA positive lesions in men with prostate cancer. It is manufactured by chelating precursor with68Ga, either from a generator or cyclotron, and has regulatory approval around the world. It is widely used clinically in conjunction with radioligand therapies like [177Lu]Lu-PSMA-617.

Potential of PSMA-targeting radioligand therapy for malignant primary and secondary brain tumours using super-selective intra-arterial administration: a single centre, open label, non-randomised prospective imaging study

BACKGROUND

The aim of this study was to provide quantitative evidence for the potential of PSMA-targeting radioligand therapy (RLT) as treatment approach for malignant brain tumours, and to explore whether tumour uptake could be enhanced by super-selective intra-arterial (ssIA)-administration.

METHODS

Ten patients (n = 5 high-grade glioma, n = 5 brain metastasis) received 1.5 MBq/kg [68Ga]Ga-PSMA-11 intravenously and, within 7 days, intra-arterially (i.e., selectively in tumour-feeding arteries), followed twice by PET-MRI at 90, 165 and 240 min post-injection. Patient safety was monitored for each procedure. Standardised uptake values (SUVs) were obtained for tumour, healthy-brain, salivary glands and liver. Tumour-to-salivary-gland (T/SG) and tumour-to-liver (T/L) uptake-ratios were calculated.

FINDINGS

No adverse events requiring study termination occurred. All patients showed uptake of [68Ga]Ga-PSMA-11 at the tumour site. Uptake was a median 15-fold higher following ssIA-administration (SUVmax median: 142.8, IQR: 102.8-245.9) compared to IV-administration (10.5, IQR:7.5-13.0). According to the bootstrap analysis, mean SUVmax after ssIA (168.8, 95% CI: 110.6-227.0) was well beyond the 95% confidence-interval of IV administration (10.5, 95% CI: 8.4-12.7). Uptake in healthy-brain was negligible, independent of administration route (SUVmean <0.1-0.1). Off-target uptake was comparable, resulting in more favourable T/SG- and T/L-ratios of 8.4 (IQR: 4.4-11.5) and 26.5 (IQR: 14.0-46.4) following ssIA, versus 0.5 (IQR: 0.4-0.7) and 1.8 (IQR: 1.0-2.7) for IV-administration.

INTERPRETATION

ssIA-administration is safe and leads to a median fifteen-fold higher radioligand uptake at the tumour site, therewith qualifying more patients for treatment and enhancing the potential of therapy. These results open new avenues for the development of effective RLT-based treatment strategies for patients with brain tumours.

FUNDING

Semmy Foundation.

Long-Term Tumor-Targeting Effect of E. coli as a Drug Delivery System

To overcome the limitations of current nano/micro-scale drug delivery systems, an Escherichia coli (E. coli)-based drug delivery system could be a potential alternative, and an effective tumor-targeting delivery system can be developed by attempting to perform chemical binding to the primary amine group of a cell membrane protein. In addition, positron emission tomography (PET) is a representative non-invasive imaging technology and is actively used in the field of drug delivery along with radioisotopes capable of long-term tracking, such as zirconium-89 (89Zr). The membrane proteins were labeled with 89Zr using chelate (DFO), and not only was the long-term biodistribution in tumors and major organs evaluated in the body, but the labeling stability of 89Zr conjugated to the membrane proteins was also evaluated through continuous tracking. E. coli accumulated at high levels in the tumor within 5 min (initial time) after tail intravenous injection, and when observed after 6 days, 89Zr-DFO on the surface of E. coli was found to be stable for a long period of time in the body. In this study, we demonstrated the long-term biodistribution and tumor-targeting effect of an E. coli-based drug delivery system and verified the in vivo stability of radioisotopes labeled on the surface of E. coli.

[89Zr]Zr-PSMA-617 PET/CT characterization of indeterminate [68Ga]Ga-PSMA-11 PET/CT findings in patients with biochemical recurrence of prostate cancer: lesion-based analysis

BACKGROUND

The state-of-the-art method for imaging men with biochemical recurrence of prostate cancer (BCR) is prostate-specific membrane antigen (PSMA)-targeted positron emission tomography/computed tomography (PET/CT) with tracers containing short-lived radionuclides, e.g., gallium-68 (68Ga; half-life: ∼67.7 min). However, such imaging not infrequently yields indeterminate findings, which remain challenging to characterize. PSMA-targeted tracers labeled with zirconium-89 (89Zr; half-life: ∼78.41 h) permit later scanning, which may help in classifying the level of suspiciousness for prostate cancer of lesions previously indeterminate on conventional PSMA-targeted PET/CT.

METHODS

To assess the ability of [89Zr]Zr-PSMA-617 PET/CT to characterize such lesions, we retrospectively analyzed altogether 20 lesions that were indeterminate on prior [68Ga]Ga-PSMA-11 PET/CT, in 15 men with BCR (median prostate-specific antigen: 0.70 ng/mL). The primary endpoint was the lesions' classifications, and secondary endpoints included [89Zr]Zr-PSMA-617 uptake (maximum standardized uptake value [SUVmax]), and lesion-to-background ratio (tumor-to-liver ratio of the SUVmax [TLR]). [89Zr]Zr-PSMA-617 scans were performed 1 h, 24 h, and 48 h post-injection of 123 ± 19 MBq of radiotracer, 35 ± 35 d post-[68Ga]Ga-PSMA-11 PET/CT.

RESULTS

Altogether, 6/20 previously-indeterminate lesions (30%) were classified as suspicious (positive) for prostate cancer, 14/20 (70%), as non-suspicious (negative). In these two categories, [89Zr]Zr-PSMA-617 uptake and lesional contrast showed distinctly different patterns. In positive lesions, SUVmax and TLR markedly rose from 1 to 48 h, with SUVmax essentially plateauing at high levels, and TLR further steeply increasing, from 24 to 48 h. In negative lesions, uptake, when present, was very low, and decreasing, while contrast was minimal, from 1 to 48 h. No adverse events or clinically-relevant vital signs changes related to [89Zr]Zr-PSMA-617 PET/CT were noted during or ~ 4 weeks after the procedure.

CONCLUSIONS

In men with BCR, [89Zr]Zr-PSMA-617 PET/CT may help characterize as suspicious or non-suspicious for prostate cancer lesions that were previously indeterminate on [68Ga]Ga-PSMA-11 PET/CT.

TRIAL REGISTRATION

Not applicable.

Whole Gamma Imaging: Challenges and Opportunities

Compton imaging has been recognized as a possible nuclear medicine imaging method following the establishment of SPECT and PET. Whole gamma imaging (WGI), a combination of PET and Compton imaging, could be the first practical method to bring out the potential of Compton imaging in nuclear medicine. With the use of such positron emitters as 89Zr and 44Sc, WGI may enable highly sensitive imaging of antibody drugs for early tumor detection and quantitative hypoxia imaging for effective tumor treatment. Some of these concepts have been demonstrated preliminarily in physics experiments and small animal imaging tests with a developed WGI prototype.

From Bench to Bedside: Patient-Oriented Radiopharmaceutical Development in Nuclear Medicine Based on the Example of [89Zr]Zr-PSMA-DFO

The interdisciplinary possibilities inherent in nuclear medicine offer an opportunity for the patient-centered development of radioactive pharmaceuticals based on specific research questions. This approach provides radiopharmaceutical manufacturers with a robust scientific foundation on which to navigate the regulatory requirements for drug approval laid down by the law. A vivid illustration of this interdisciplinary cooperation has been the development of a Zr-89-labeled PSMA ligand where reliable results have been obtained across various domains, including chemistry, radiochemistry, biochemistry, and preclinical research. This comprehensive process extended to feasibility studies conducted with carefully selected patients from a single nuclear medicine clinic. The approach demonstrates how far close collaboration between different disciplines within nuclear medicine can further the move towards patient-oriented radiopharmaceutical treatments while simultaneously meeting regulatory demands. With such a strategy, innovative radiopharmaceutical solutions can be brought to the market more swiftly and efficiently, in line with the needs of patients.

Detection efficacy of [89Zr]Zr-PSMA-617 PET/CT in [68Ga]Ga-PSMA-11 PET/CT-negative biochemical recurrence of prostate cancer

RATIONALE

In patients with biochemical recurrence of prostate cancer (BCR), preliminary data suggest that prostate-specific membrane antigen (PSMA) ligand radiotracers labeled with zirconium-89 (89Zr; half-life ~ 78.41 h), which allow imaging ≥ 24 h post-injection, detect suspicious lesions that are missed when using tracers incorporating short-lived radionuclides.

MATERIALS AND METHODS

To confirm [89Zr]Zr-PSMA-617 positron emission tomography/computed tomography (PET/CT) detection efficacy regarding such lesions, and compare quality of 1-h, 24-h, and 48-h [89Zr]Zr-PSMA-617 scans, we retrospectively analyzed visual findings and PET variables reflecting lesional [89Zr]Zr-PSMA-617 uptake and lesion-to-background ratio. The cohort comprised 23 men with BCR post-prostatectomy, median (minimum-maximum) prostate-specific antigen (PSA) 0.54 (0.11-2.50) ng/mL, and negative [68Ga]Ga-PSMA-11 scans 40 ± 28 d earlier. Primary endpoints were percentages of patients with, and classifications of, suspicious lesions.

RESULTS

Altogether, 18/23 patients (78%) had 36 suspicious lesions (minimum-maximum per patient: 1-4) on both 24-h and 48-h scans (n = 33 lesions) or only 48-h scans (n = 3 lesions). Only one lesion appeared on a 1-h scan. Lesions putatively represented local recurrence in 11 cases, and nodal or bone metastasis in 21 or 4 cases, respectively; 1/1 lesion was histologically confirmed as a nodal metastasis. In all 15 patients given radiotherapy based on [89Zr]Zr-PSMA-617 PET/CT, PSA values decreased after this treatment. Comparison of PET variables in 24-h vs 48-h scans suggested no clear superiority of either regarding radiotracer uptake, but improved lesion-to-background ratio at 48 h.

CONCLUSIONS

In men with BCR and low PSA, [89Zr]Zr-PSMA-617 PET/CT seems effective in finding prostate malignancy not seen on [68Ga]Ga-PSMA-11 PET/CT. The higher detection rates and lesion-to-background ratios of 48-h scans versus 24-h scans suggest that imaging at the later time may be preferable. Prospective study of [89Zr]Zr-PSMA-617 PET/CT is warranted.

Histologically Confirmed Testicular Metastasis Revealed by [89Zr]Zr-PSMA-617 PET/CT in a Patient with Biochemical Recurrence of Prostate Cancer and Negative Conventional PSMA PET/CT Imaging

We present an interesting image of a testicular metastasis from prostate cancer revealed by [⁸⁹Zr]Zr-PSMA-617 PET/CT imaging in a 70-year-old man with biochemical recurrence and negative conventional [⁶⁸Ga]Ga-PSMA-11 PET/CT imaging. This case should encourage the consideration of [⁸⁹Zr]Zr-PSMA-617 PET/CT if conventional PSMA PET/CT imaging had failed to localize biochemical recurrence, and may remind colleagues of this rare but potential metastatic localization in this setting.

Detection Efficacy of 68Ga-PSMA-11 PET/CT in Biochemical Recurrence of Prostate Cancer with Very Low PSA Levels: A 7-Year, Two-Center "Real-World" Experience

In biochemical recurrence of prostate cancer (BCR), prompt tumor localization guides early treatment, potentially improving patient outcomes. Gallium-68 prostate-specific membrane antigen-11 positron emission tomography/computed tomography (⁶⁸Ga-PSMA-11 PET/CT) detection rates of lesions suspicious for prostate cancer are well known to rise along with prostate-specific antigen (PSA) concentration. However, published data are limited regarding very low values (≤0.2 ng/mL). We retrospectively analyzed ~7-year "real-world" experience in this setting in a large post-prostatectomy cohort (N = 115) from two academic clinics. Altogether 44 lesions were detected in 29/115 men (25.2%) (median [minimum-maximum] 1 [1-4]/positive scan). The apparent oligometastatic disease was found in nine patients (7.8%) at PSA as low as 0.03 ng/mL. Scan positivity rates were highest when PSA was >0.15 ng/mL, PSA doubling time was ≤12 months, or the Gleason score was ≥7b (in 83 and 107 patients, respectively, with available data); these findings were statistically significant (p ≤ 0.04), except regarding PSA level (p = 0.07). Given the benefits of promptly localizing recurrence, our observations suggest the potential value of ⁶⁸Ga-PSMA-11 PET/CT in the very low PSA BCR setting, especially in cases with more rapid PSA doubling time or with high-risk histology.