Head-to-Head Comparison of 68Ga-NODAGA-JR11 and 68Ga-DOTATATE PET/CT in Patients with Metastatic, Well-Differentiated Neuroendocrine Tumors: Interim Analysis of a Prospective Bicenter Study

Beyond fluorodeoxyglucose: Molecular imaging of cancer in precision medicine

Cancer molecular imaging is the noninvasive visualization of a process unique to or altered in neoplasia, such as proliferation, glucose metabolism, and receptor expression, which is relevant to patient management. Several molecular imaging modalities are now available, including magnetic resonance, optical, and nuclear imaging. Nuclear imaging, particularly using fluorine-18-fluorodeoxyglucose positron emission tomography, is widely used in the staging and response assessment of multiple cancer types. However, at this writing, new nuclear medicine probes, especially positron emission tomography tracers, are increasingly used or are being investigated for cancer evaluation. This review focuses on these probes, their biologic targets, and the applications or potential applications for their use in the assessment of various neoplasms, including both probes available for commercial use-such as somatostatin receptor ligands in neuroendocrine tumors, prostate-specific membrane antigen ligands in prostate cancer, norepinephrine analogs in neural crest tumors like neuroblastoma, and estrogen analogs in breast cancer-and others in clinical development, such as fibroblast-activating protein inhibitors, C-X-C chemokine receptor type 4 ligands, and monoclonal antibodies targeting receptor tyrosine kinases, CD4-positive or CD8-positive tumor-infiltrating lymphocytes, tumor-associated macrophages, and cancer stem cell biomarkers. These developments represent a major step toward the integration of molecular imaging as a powerful tool in precision medicine, with an expectedly significant impact on patient management and outcome.

Cancer Targeting Radiopeptidomimetics in Molecular Nuclear Medicine

Peptides are highly receptor-affine molecules exhibiting suitable pharmacokinetics. Additionally, low-cost production, simple protocols allowing easy modifications, and tolerance toward harsh reaction conditions make peptides ideal ligands for preparation of radiopharmaceuticals for cancer detection and treatment. However, natural peptides being substrates for enzymes are susceptible to proteolysis, which limits the in vivo lifetime and the target uptake. Therefore, the majority of peptides are not able to progress beyond preclinical research. Advancement of peptides for clinical analysis needs modification to instill improved features. Continuous increase and further expected rise in cancer cases in the next decade require development of more disease-directed and promising radiopharmaceuticals. Redesigned peptide, mimicking the original peptide with similar or improved affinity and high metabolic stability, shall have significant edge. This review outlines the design of peptidomimetics by incorporation of D-amino acids (inverso); reversal of D-amino acid sequence (retro-inverso), and reversal of L-amino acid sequence (retro). Clinically successful radiopeptidomimetics prepared using the three approaches have been elaborated to elucidate the important role of peptidomimetics in cancer management.

Development of Novel Peptide-Based Radiotracers for Detecting FGL1 Expression in Tumors

A novel immune checkpoint, FGL1, is a potentially viable target for tumor immunotherapy. The development of FGL1-targeted PET probes could provide significant insights into the immune system's status and the evaluation of treatment efficacy. A ClusPro 2.0 server was used to analyze the interaction between FGL1 and LAG3, and the candidate peptides were identified by using the Rosetta peptide derivate protocol. Three candidate peptides targeting FGL1, named FGLP21, FGLP22, and FGLP23, with a simulated affinity of -9.56, -8.55, and -8.71 kcal/mol, respectively, were identified. The peptides were readily conjugated with p-NCS-benzyl-NODA-GA, and the resulting compounds were successfully labeled with 68Ga in approximately 70% yields and radiochemical purity greater than 95%. In vitro competitive cell-binding assay demonstrated that all probes bound to FGL1 with IC50 ranging from 100 nM to 160 nM. Among the probes, PET imaging revealed that 68Ga-NODA-FGLP21 exhibited the best tumor imaging performance in mice bearing FGL1 positive Huh7 tumor. At 60 min p.i., the tumor uptake of 68Ga-NODA-FGLP21 was significantly higher than those of 68Ga-NODA-FGLP22 and 68Ga-NODA-FGLP23, respectively (2.51 ± 0.11% ID/g vs 1.00 ± 0.16% ID/g and 1.49 ± 0.05% ID/g). Simultaneously, the tumor-to-muscle uptake ratios of the former were also higher than those of the latter, respectively (19.40 ± 2.30 vs 9.65 ± 0.62 and 12.45 ± 0.72). In the presence of unlabeled FGLP21, the uptake of 68Ga-NODA-FGLP21 in Huh7 xenograft decreased to 0.81 ± 0.09% ID/g at 60 min p.i., which is similar to that observed in the FGL1 negative U87 MG tumor (0.46 ± 0.03% ID/g). The results were consistent with the immunohistochemical analysis and ex vivo autoradiography. No significant radioactivity was accumulated in normal organs, except for kidneys. In summary, a preclinical study confirmed that the tracer 68Ga-NODA-FGLP21 has the potential to specifically detect FGL1 expression in tumors with good contrast to the background.

Research process of PET tracers for neuroendocrine tumors diagnosis

Neuroendocrine tumors (NETs) can affect several organ systems and present a variety of clinical symptoms, which are difficult to diagnose by conventional methods. Somatostatin receptor (SSTR) is a group of specific receptors expressed on the well-differentiated NET cell membrane. [68Ga]-labeled somatostatin analogues (SSAs) PET/CT, endogenous ligands targeting SSTR, is widely used in currently clinical NETs diagnosis. The dual-tracer strategy ([68Ga]Ga-SSAs + [18F]FDG) allows for a more detailed evaluation of tumor metabolism and receptor expression. The NETPET score, integrating [68Ga]Ga-SSAs PET/CT and [18F]FDG PET/CT results, enhances the accuracy of predicting treatment response and prognosis. In addition, novel isotopes ([18F]/[64Cu]) labeled SSAs and SSTR antagonists outperformed [68Ga]-SSAs in lesion detection, tumor uptake, and tumor-to-background ratio. Due to undifferentiated or dedifferentiated NETs, SSTR may not be expressed. [68Ga]Ga-Pentixafor and [18F]-FDG PET/CT are applicable for SSTR-negative NET diagnosis. [18F]-MFBG and [18F]-DOPA have a higher sensitivity for identifying non-metastatic pheochromocytoma and paraganglioma (PPGL) than other radiotracers. This review addressed NET diagnosis with conventional imaging techniques, the clinical application of novel radiotracers, and the merits and limitations of the various radiotracers.

Synthesis and preclinical evaluation of [18F]AlF-NOTA-Asp2-PEG2-JR11 as a novel antagonist radioligand for PET imaging of somatostatin receptor

PURPOSE

Somatostatin receptor (SSTR) antagonists have recently emerged as preferable radiotracers for SSTR-targeted imaging and therapy. This study aimed to design a novel SSTR antagonist, [18F]AlF-NOTA-Asp2-PEG2-JR11, and compare its preclinical performance with the previously reported antagonist, [18F]AlF-NOTA-JR11, and the agonist [68Ga]Ga-DOTA-TATE.

METHODS

[18F]AlF-NOTA-Asp2-PEG2-JR11 was synthesized via a one-step radiolabeling process involving [18F]AlF chelation. The binding affinity, internalization, and cellular uptake were evaluated using AR42J/SSTR + cells. Biodistribution and PET/CT imaging were conducted in mice bearing xenografted AR42J/SSTR + or HCT116/SSTR- tumor xenografts.

RESULTS

[18F]AlF-NOTA-Asp2-PEG2-JR11 was manually synthesized within 30 min with an uncorrected radiochemical yield of 39.56 ± 3.25% (n > 5) and radiochemical purity (RCP) exceeding 99% (n > 5). [18F]AlF-NOTA-Asp2-PEG2-JR11 demonstrated excellent in vivo stability over 2 h (RCP > 95%). Among AR42J cells, [18F]AlF-NOTA-Asp2-PEG2-JR11 exhibited high affinity, specific uptake, and low internalization, similar to [18F]AlF-NOTA-JR11. Biodistribution and micro-PET/CT imaging studies revealed comparable tumor uptake between [18F]AlF-NOTA-Asp2-PEG2-JR11 and [18F]AlF-NOTA-JR11 (9.26 ± 0.49 vs. 10.18 ± 0.82%ID/g, p = 0.147) at 60 min post-injection (p.i), both were significantly higher than [68Ga]Ga-DOTA-TATE (6.79 ± 0.29%ID/g, p = 0.001). Co-injecting the corresponding inhibitor significantly reduced the tumor uptake of all three tracers. Notably, [18F]AlF-NOTA-Asp2-PEG2-JR11 reached peak tumor uptake at 30 min p.i. and exhibited the lowest uptake and fastest clearance in most normal organs, including the kidney, bone, liver, and muscle, resulting in the highest and increasing tumor-to-background ratios (TBR) over time among the three tracers.

CONCLUSION

The synthesis of [18F]AlF-NOTA-Asp2-PEG2-JR11 is efficient, with high radiochemical yield and RCP. [18F]AlF-NOTA-Asp2-PEG2-JR11 exhibits excellent in vivo stability, high tumor uptake, and superior TBR, making it a promising potential tracer for imaging SSTR-positive tumors.

Ectopic Cushing Syndrome Localized by 68 Ga-DOTA-LM3 PET/CT

ABSTRACT

A 53-year-old woman presented with signs of Cushing syndrome with challenges in diagnosis and localization. A novel somatostatin receptor (SSTR)-targeted PET/CT with 68 Ga-DOTA-LM3, an SSTR antagonist, revealed a suspicious focal finding in the pancreatic head, proven to be ectopic Cushing syndrome after surgical resection. This interesting image clearly shows the potential of PET imaging with SSTR antagonists as 68 Ga-DOTA-LM3 in the diagnosis of ectopic Cushing syndrome.

Theranostics in Neuroendocrine Tumors: Updates and Emerging Technologies

Advancements in somatostatin receptor (SSTR) targeted imaging and treatment of well-differentiated neuroendocrine tumors (NETs) have revolutionized the management of these tumors. This comprehensive review delves into the current practice, discussing the use of the various FDA-approved SSTR-agonist PET tracers and the predictive imaging biomarkers, and elaborating on Lu177-DOTATATE peptide receptor radionuclide therapy (PRRT) including the evolving areas of post-therapy imaging practices, PRRT retreatment, and the potential role of dosimetry in optimizing patient treatments. The future directions sections highlight ongoing research on investigational PET imaging radiotracers, future prospects in alpha particle therapy, and combination therapy strategies.

Evaluation of the safety, biodistribution, dosimetry of [18F]AlF-NOTA-LM3 and head-to-head comparison with [68Ga]Ga-DOTATATE in patients with well-differentiated neuroendocrine tumors: an interim analysis of a prospective trial

PURPOSE

18F-labelled somatostatin receptor (SSTR) analogs offer several advantages over 68Ga in terms of yield, cost, spatial resolution and detection rate. This study presents an interim analysis of a prospective trial designed to assess the safety, biodistribution and dosimetry of [18F]AlF-NOTA-LM3, and compare its diagnostic efficacy and clinical management outcomes with [68Ga]Ga-DOTATATE or [68Ga]Ga-NODAGA-LM3 in patients with well-differentiated NETs.

METHODS

Twenty-one patients with histologically confirmed well-differentiated neuroendocrine tumors (G1 and G2) were prospectively recruited. The first eight patients underwent serial PET scans at 5, 15, 30, 45, 60, and 120 min after [18F]AlF-NOTA-LM3 injection to assess biodistribution and dosimetry. The remaining patients underwent whole-body PET/CT scans. [18F]AlF-NOTA-LM3 and [68Ga]Ga-DOTATATE PET/CT were done within a week, with a minimum 24-hour interval between the two scans. Focal uptake above the surrounding background activity and could not be explained by physiologic uptake was considered lesions of NETs. Lesion number, tumor uptake, and tumor-to-background ratio (TBR) were compared. In patients with discrepant findings, the size of the smallest lesions (measured on coregistered CT) detected on [68Ga]Ga-DOTATATE and [18F]AlF-NOTA-LM3 was compared.

RESULTS

[18F]AlF-NOTA-LM3 was safe and well-tolerated. Physiological uptake of [18F]AlF-NOTA-LM3 was significantly lower than that of [68Ga]Ga-DOTATATE in abdominal organs and bone marrow, but higher in blood pool and lung. The mean effective dose was 0.024 ± 0.014 mSv/MBq. [18F]AlF-NOTA-LM3 detected significantly more liver lesions (457 vs. 291, P = 0.006) and lymph node lesions (30 vs. 22, P = 0.011) compared to [68Ga]Ga-DOTATATE. The tumor uptake was comparable, but TBR was significantly higher with [18F]AlF-NOTA-LM3 for lesions from all sites except for the duodenum. The size of the minimum liver lesions (0.54 ± 0.15 vs. 1.01 ± 0.49, P<0.001) and lymph node lesions (0.50 ± 0.19 vs. 1.26 ± 0.86, P = 0.024) detected on [18F]ALF-NOTA-LM3 were significantly smaller than those detected on [68Ga]Ga-DOTATATE.

CONCLUSION

[18F]AlF-NOTA-LM3 shows favorable biodistribution, higher spatial resolution and superior performance than [68Ga]Ga-DOTATATE in detecting liver and lymph node metastases, with higher TBR. Notably, it is the first SSTR analog to show superiority in detecting lymph node lesions when compared to [68Ga]Ga-DOTATATE.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT06056362.

A head-to-head comparison of [68Ga]Ga-DOTATATE and [68Ga]Ga-FAPI PET/CT in patients with nasopharyngeal carcinoma: a single-center, prospective study

PURPOSE

We aimed to compare the staging efficiency of [68Ga]Ga-DOTATATE and [68Ga]Ga-FAPI PET/CT in nasopharyngeal carcinoma (NPC) patients.

METHODS

Thirty-nine patients with pathologically confirmed NPC were enrolled in this prospective study. Each patient underwent paired [68Ga]Ga-DOTATATE and [68Ga]Ga-FAPI PET/CT on 2 successive days. The accuracy of two PET/CT for assessing T, N, and M stages was compared by using head-and-neck MRI, histopathologic diagnosis and follow-up results as reference standards. The radiotracer uptake derived from two PETs was also compared.

RESULTS

For treatment-naïve patients, [68Ga]Ga-DOTATATE PET/CT showed identical sensitivity for the primary tumours but clearer tumor delineation induced by higher tumour-to-background (TBR) ratio (19.1 ± 8.7 vs. 12.4 ± 7.7, P = 0.003), compared with [68Ga]Ga-FAPI PET/CT. Regarding cervical lymph node (CLN) metastases, [68Ga]Ga-DOTATATE PET had significantly better sensitivity and accuracy based on neck sides (98% vs. 82%, P < 0.001; 99% vs. 88% P = 0.008), neck levels (98% vs. 78%, 99% vs. 97%; both P < 0.001) and individual nodes (89% vs. 56%, 91% vs. 76%; both P < 0.001), and higher TBR (8.1 ± 4.1 vs. 6.3 ± 3.7, P < 0.001). Additionally, [68Ga]Ga-DOTATATE PET/CT revealed higher sensitivity and accuracy for distant metastases (96% vs. 53%, 95% vs. 52%; both P < 0.001), particularly in bone metastases (99% vs. 49%, 97% vs. 49%; both P < 0.001). For post-treatment patients, [68Ga]Ga-DOTATATE PET/CT identified one more true-negative case than [68Ga]Ga-FAPI PET/CT.

CONCLUSION

[68Ga]Ga-DOTATATE PET/CT performed better than [68Ga]Ga-FAPI PET/CT in visualizing the primary tumours, detecting the metastatic lesions and identifying the local recurrence, suggesting [68Ga]Ga-DOTATATE PET/CT may be superior to [68Ga]Ga-FAPI PET/CT for NPC staging.

Neuroendocrine Tumors: Diagnostics

Neuroendocrine neoplasms (NEN) are rare tumors arising from neuroendocrine cells. NEN are ideally suited for a theragnostic approach due to their specific expression of somatostatin receptors (SSTR). SSTR imaging of NEN dates back to the 1980s, but has evolved recently due to the introduction of more sensitive SSTR PET radiotracers. SSTR PET is a primary imaging modality for identifying NEN and characterizing SSTR expression. SSTR PET is complementary to anatomic imaging for assessing tumor response to treatment. SSTR PET is mandated to determine eligibility for peptide receptor radionuclide therapy. Here, the role of imaging to aid management of NEN is reviewed.

Clinical Intricacies and Advances in Neuroendocrine Tumors: An Organ-Based Multidisciplinary Approach

ABSTRACT

Neuroendocrine neoplasms (NENs) are rare neoplasms originating from neuroendocrine cells, with increasing incidence due to enhanced detection methods. These tumors display considerable heterogeneity, necessitating diverse management strategies based on factors like organ of origin and tumor size. This article provides a comprehensive overview of therapeutic approaches for NENs, emphasizing the role of imaging in treatment decisions. It categorizes tumors based on their locations: gastric, duodenal, pancreatic, small bowel, colonic, rectal, appendiceal, gallbladder, prostate, lung, gynecological, and others. The piece also elucidates the challenges in managing metastatic disease and controversies surrounding MEN1-neuroendocrine tumor management. The article underscores the significance of individualized treatment plans, underscoring the need for a multidisciplinary approach to ensure optimal patient outcomes.

Gallium-68 labeled somatostatin receptor antagonist PET/CT in over 500 patients with neuroendocrine neoplasms: experience from a single center in China

PURPOSE

Somatostatin receptor antagonists have shown promising performance for imaging neuroendocrine neoplasms. However, there is a lack of studies exploring the diagnostic performance of SSTR antagonists or comparing them with agonists in a large cohort of patients with NENs. This study aimed to retrospectively review all SSTR antagonist PET/CT scans conducted at Peking Union Medical College Hospital since November 2018 in patients with confirmed or suspected NENs.

METHODS

Four types of SSTR antagonists were utilized, including [68Ga]Ga-NODAGA-LM3, [68Ga]Ga-DOTA-LM3, [68Ga]Ga-NODAGA-JR11, and [68Ga]Ga-DOTA-JR11. The reference standard was based on a combination of histopathology, clinical evaluation, imaging results, and follow-up. Patient-based sensitivity, specificity, and accuracy were evaluated. The SUVmax and tumor-to-liver ratio (TLR) of the hottest lesions was recorded and compared between antagonists and [68Ga]Ga-DOTATATE.

RESULTS

A total of 622 antagonist scans from 549 patients were included in the analysis. The patient-level sensitivity, specificity, and accuracy of antagonist imaging (all tracers combined) were 91.0% (443/487), 91.9% (57/62), and 91.1% (500/549), respectively. In 181 patients with a comparative [68Ga]Ga-DOTATATE PET/CT scan, the patient-level sensitivity, specificity, and accuracy were 87.5% (147/168), 76.9% (10/13), and 86.7% (157/181), respectively. For the hottest lesions, SSTR antagonists all tracers combined demonstrated an overall comparable SUVmax to [68Ga]Ga-DOTATATE (40.1 ± 32.5 vs. 39.4 ± 23.8, p = 0.772). While [68Ga]Ga-NODAGA-LM3 showed significantly higher uptake than [68Ga]Ga-DOTATATE (57.4 ± 38.5 vs. 40.0 ± 22.8, p<0.001), [68Ga]Ga-NODAGA-JR11 (39.7 ± 26.5 vs. 34.3 ± 23.9, p = 0.108) and [68Ga]Ga-DOTA-LM3 (38.9 ± 32.1 vs. 37.2 ± 22.1, p = 0.858) showed comparable uptake to [68Ga]Ga-DOTATATE, and [68Ga]Ga-DOTA-JR11 showed lower uptake (28.9 ± 26.1 vs. 44.0 ± 25.7, p = 0.001). All antagonists exhibited significantly higher TLR than [68Ga]Ga-DOTATATE (12.1 ± 10.8 vs. 5.2 ± 4.5, p<0.001).

CONCLUSION

Gallium-68 labeled SSTR antagonists could serve as alternatives to SSTR agonists for imaging of NENs. Among various antagonists, [68Ga]Ga-NODAGA-LM3 seems to have the best imaging profile.

Radionuclide Theranostics in Neuroendocrine Neoplasms: An Update

PURPOSE OF REVIEW

This paper aims to address the latest findings in neuroendocrine tumor (NET) theranostics, focusing on new evidence and future directions of combined diagnosis with positron emission tomography (PET) and treatment with peptide receptor radionuclide therapy (PRRT).

RECENT FINDINGS

Following NETTER-1 trial, PRRT with [177Lu]Lu-DOTATATE was approved by FDA and EMA and is routinely employed in advanced G1 and G2 SST (somatostatin receptor)-expressing NET. Different approaches have been proposed so far to improve the PRRT therapeutic index, encompassing re-treatment protocols, combinations with other therapies and novel indications. Molecular imaging holds a potential added value in characterizing disease biology and heterogeneity using different radiopharmaceuticals (e.g., SST and FDG) and may provide predictive and prognostic parameters. Response assessment criteria are still an unmet need and new theranostic pairs showed preliminary encouraging results. PRRT for NET has become a paradigm of modern theranostics. PRRT holds a favorable toxicity profile, and it is associated with a prolonged time to progression, reduction of symptoms, and improved patients' quality of life. In light of further optimization, different new strategies have been investigated, along with the development of new radiopharmaceuticals.

Scalable droplet-based radiosynthesis of [18F]fluorobenzyltriphenylphosphonium cation ([18F]FBnTP) via a "numbering up" approach

The [18F]fluorobenzyltriphenylphosphonium cation ([18F]FBnTP) has emerged as a highly promising positron emission tomography (PET) tracer for myocardial perfusion imaging (MPI) due to its uniform distribution in the myocardium and favorable organ biodistribution demonstrated in preclinical studies. However, a complex and low-efficiency radiosynthesis procedure has significantly hindered its broader preclinical and clinical explorations. Recently, Zhang et al. developed a pinacolyl arylboronate precursor, enabling a one-step synthesis process that greatly streamlines the production of [18F]FBnTP. Building upon this progress, our group successfully adapted the approach to a microdroplet reaction format and demonstrated improved radiosynthesis performance in a preliminary optimization study. However, scaling up to clinical dose amounts was not explored. In this work, we demonstrate that scale-up can be performed in a straightforward manner using a "numbering up" strategy (i.e. performing multiple droplet reactions in parallel and pooling the crude products). The resulting radiochemical yield after purification and formulation was high, up to 66 ± 1% (n = 4) for a set of experiments involving pooling of 4 droplet reactions, accompanied by excellent radiochemical purity (>99%) and molar activity (339-710 GBq μmol-1). Notably, we efficiently achieved sufficient activity yield (0.76-1.84 GBq) for multiple clinical doses from 1.6 to 3.7 GBq of [18F]fluoride in just 37-47 min.