Head-to-Head Comparison of 68Ga-DOTA-JR11 and 68Ga-DOTATATE PET/CT in Patients with Metastatic, Well-Differentiated Neuroendocrine Tumors: A Prospective Study

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.

PET imaging of [52 Mn]Mn-DOTATATE and [52 Mn]Mn-DOTA-JR11

Manganese-52 is gaining interest as an isotope for PET imaging due to its desirable decay and chemical properties for radiopharmaceutical development. Somatostatin receptor 2 (SSTR2) is significantly overexpressed by neuroendocrine tumors (NETs) and is an important target for nuclear imaging and therapy. As an agonist, [68Ga]Ga-DOTATATE has demonstrated significant internalization upon interaction with receptor ligands, whereas [68Ga]Ga-DOTA-JR11(as an antagonist) exhibits limited internalization but better pharmacokinetics and increased tumor uptake. The goal of this study was to label both DOTATATE and DOTA-JR11 peptides with 52Mn in high radiochemical yields (RCY) and sufficient specific activity. A comparison of these two compounds was performed in in vitro and in vivo studies in animals with somatostatin receptor-positive xenografts to characterize differences in cell, tumor, and tissue uptake. Radiolabeling of DOTATATE and DOTA-JR11 was carried out by combining varying concentrations of the peptides with [52Mn]MnCl2. In vitro stability of the radiotracers was determined in mouse serum. In vitro cell uptake and internalization assays were performed in SSTR2 + AR42J cells and negative controls. In vivo biodistribution and longitudinal PET imaging was evaluated in mice bearing AR42J tumors. Both [52Mn]Mn-DOTATATE and [52Mn]Mn-DOTA-JR11showed affinity for SSTR2 in AR42J cells. However, the uptake of [52Mn]Mn-DOTATATE was higher (11.95 ± 0.71%/ mg) compared to [52Mn]Mn-DOTA-JR11 (7.31 ± 0.38%/ mg) after 2 h incubation. After 4 h incubation, 53.13 ± 1.83% of the total activity of [52Mn]Mn-DOTATATE was internalized, whereas only 20.85 ± 0.59% of the total activity of [52Mn]Mn-DOTA-JR11 was internalized. The PET images revealed similar biodistribution results, with [52Mn]Mn-DOTATATE showing a significant tumor uptake of 11.16 ± 2.97% ID/g, while [52Mn]Mn-DOTA-JR11 exhibited a lower tumor uptake of 2.11 ± 0.30% ID/g 4 h post-injection. The synthesis of both radiotracers was accomplished with high RCY and purity. The cell uptake and internalization of [52Mn]Mn-DOTATATE showed higher levels compared to [52Mn]Mn-DOTA-JR11. PET images of the radiotracers in AR42J tumor bearing mice demonstrated similar biodistribution in all organs except the tumor, with [52Mn]Mn-DOTATATE showing higher tumor uptake compared to [52Mn]Mn-DOTA-JR11. The variations in properties of these tracers could be used to guide further imaging and treatment studies.

Radiolabeled Somatostatin Analogs for Cancer Imaging

Somatostatin receptors (SSTR) are expressed by many tumours especially those related to neuro-endocrine origin and molecular functional imaging of SSTR expression using radiolabelled somatostatin analogs have revolutionized imaging of patients with these group of malignancies. Coming a long way from the first radiolabelled somatostatin analog 123I-Tyr-3-octreotide, there has been significant developments in terms of radionuclides used, the ligands and somatostatin derivatives. 111In-Pentetreotide extensively employed for imaging NETs at the beginning has now been replaced by 68Ga-SSA based PET-CT. SSA-PET/CT performs superior to conventional imaging modalities and has evolved in the mainframe for NET imaging. The advantages were multiple: (i) superior spatial resolution of PET versus SPECT, (ii) quantitative capabilities of PET aiding in disease activity and treatment response monitoring with better precision, (iii) shorter scan time and (iv) less patient exposure to radiation. The modality is indicated for staging, detecting the primary in CUP-NETs, restaging, treatment planning (along with FDG: the concept of dual-tracer PET-CT) as well as treatment response evaluation and follow-up of NETs. SSA PET/CT has also been incorporated in the guidelines for imaging of Pheochromocytoma-Paraganglioma, Medullary carcinoma thyroid, Meningioma and Tumor induced osteomalacia. At present, there is rising interest on (a) 18F-labelled SSA, (b) 64Cu-labelled SSA, and (c) somatostatin antagonists. 18F offers excellent imaging properties, 64Cu makes delayed imaging feasible which has implications in dosimetry and SSTR antagonists bind with the SST receptors with high affinity and specificity, providing high contrast images with less background, which can be translated to theranostics effectively. SSTR have been demonstrated in non-neuroendocrine tumours as well in the peer-reviewed literature, with studies demonstrating the potential of SSA PET/CT in Neuroblastoma, Nasopharyngeal carcinoma, carcinoma prostate (neuroendocrine differentiation) and lymphoma. This review will focus on the currently available SSAs and their history, different SPECT/PET agents, SSTR antagonists, comparison between the various imaging tracers, and their utility in both neuroendocrine and non-neuroendocrine tumors.

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.

Recent advances and future challenges in the diagnosis of neuroendocrine neoplasms

Neuroendocrine neoplasms (NEN) are a heterogeneous group of malignancies with increasing incidence, whose diagnosis is usually delayed, negatively impacting on patients' prognosis. The latest advances in pathological classifications, biomarker identification and imaging techniques may provide early detection, leading to personalized treatment strategies. In this narrative review the recent developments in diagnosis of NEN are discussed including progresses in pathological classifications, biomarker and imaging. Furthermore, the challenges that lie ahead are investigated. By discussing the limitations of current approaches and addressing potential roadblocks, we hope to guide future research directions in this field. This article is proposed as a valuable resource for clinicians and researchers involved in the management of NEN. Update of pathological classifications and the availability of standardized templates in pathology and radiology represent a substantially improvement in diagnosis and communication among clinicians. Additional immunohistochemistry markers may now enrich pathological classifications, as well as miRNA profiling. New and multi-analytical circulating biomarkers, as liquid biopsy and NETest, are being proposed for diagnosis but their validation and availability should be improved. Radiological imaging strives for precise, non-invasive and less harmful technique to improve safety and quality of life in NEN patient. Nuclear medicine may benefit of somatostatin receptors' antagonists and membrane receptor analogues. Diagnosis in NEN still represents a challenge due to their complex biology and variable presentation. Further advancements are necessary to obtain early and minimally invasive diagnosis to improve patients' outcomes.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

The usefulness of [68 Ga]Ga-DOTA-JR11 PET/CT in patients with meningioma: comparison with MRI

PURPOSE

Clinical studies of PET imaging using SSTR2 agonists have demonstrated high accuracy and correlation with SSTR2 expression in meningiomas. However, the usefulness of the SSTR2 antagonist with [68 Ga]Ga-DOTA-JR11 is uncertain. To evaluate the diagnostic performance of [68 Ga]Ga-DOTA-JR11 PET/CT and to clarify tumor characteristics in patients with suspected meningiomas.

MATERIALS AND METHODS

Patients with suspected de novo or recurrent meningioma in complex locations or atypical images were enrolled from August 2021 to October 2022 in prospective study. All patients underwent contrast-enhanced MRI (CE-MRI), [68 Ga]Ga-DOTA-JR11 PET/CT, and histopathological evaluation. Tumor uptake of [68 Ga]Ga-DOTA-JR11 was measured by SUVmax and tumor-endocranium ratio (TBR). Diagnostic performance was compared between PET and MRI.

RESULTS

Of 36 (50.0 ± 13.0 years of age, 20 women) patients, 32 were histopathologically confirmed meningiomas and four with other tumors. [68 Ga]Ga-DOTA-JR11 uptake was significantly higher in meningioma patients than in those with other tumors (SUVmax: 13.6 ± 7.7 vs. 5.2 ± 3.0, P < 0.001; TBR: 64.2 ± 27.7 vs. 25.0 ± 18.9, P = 0.001). [68 Ga]Ga-DOTA-JR11 PET/CT detected 31 meningiomas, while CE-MRI detected 17 meningiomas of 25 initial diagnosis and 11 recurrent tumors; [68 Ga]Ga-DOTA-JR11 PET had an incremental diagnostic value of 24% (6/25) over MRI in the group of initial diagnosis. There was no statistically significant difference in diagnostic efficacy between PET and MRI (P = 0.45) for all 36 patients. In skull base meningiomas, PET provided a more definitive diagnosis of pituitary involvement (in 12, not in12), compared to MRI (in eight, possible in six, possible not in six, not in four). PET revealed bone involvement in all 14 patients proven by pathology, while MRI identified only 11.

CONCLUSIONS

[68 Ga]Ga-DOTA-JR11 PET/CT provided high image quality and presented an ideal diagnostic performance in detecting meningioma and evaluating the involvement of the pituitary and bone. The study provides valuable evidence for the use of [68 Ga]Ga-DOTA-JR11 PET/CT as a complementary imaging modality to CE-MRI in the evaluation of meningiomas.

Feasibility of acquisitions using total-body PET/CT with a half-dose [68Ga]Ga-FAPI-04 activity in oncology patients

BACKGROUND

[68Ga]Ga-FAPI-04 (gallium-68-labeled fibroblast activation protein inhibitor-04) PET/CT has been widely used in diagnosing malignant tumors. Total-body PET/CT has a long axial field of view and provides higher sensitivity compared to traditional PET/CT. However, whether the reduced injected dose of [68Ga]Ga-FAPI-04 could obtain qualified imaging has not been evaluated.

PURPOSE

To explore the effect of half-dose [68Ga]Ga-FAPI-04 on image quality and tumor detectability in oncology patients.

METHODS

A total of twenty-seven patients with tumors or clinically suspected tumors were included, and all patients were scanned with total-body PET/CT after an injected dose of 0.84-1.14 MBq/kg [68Ga]Ga-FAPI-04. All patients obtained superior image quality with 300 s original acquisition time. Images were reconstructed using 180 s, 120 s, 60 s, 40 s, 30 s, 20 s scanning duration by ordered subset expectation maximization algorithm. The subjective image quality of all patients in each time group was scored using 5-point Likert scale. Mediastinal blood pool, liver, spleen, and muscle were analyzed as background using semi-quantitative parameters maximum standardized uptake values (SUVmax), mean standardized uptake values (SUVmean), standard deviation (SD), and signal to noise ratio (SNR). The lesion detection rate, SUVmax, and tumor-to-background ratio (TBR) were calculated for tumors confirmed by pathology.

RESULTS

The subjective image quality score decreased with the shortening of scanning time; however, both 180 s and 120 s images met the diagnostic requirements in terms of overall quality, lesion conspicuity, and image noise. The SUVmax of background increased with the reduction of scanning time, while the SUVmean was relatively stable. With the shortening of scanning time, the SD gradually increased, and the SNR gradually decreased, which was consistent with subjective image quality scores. In 180 s and 120 s images, all 11 primary lesions and 79 metastatic lesions were detected. The SUVmax of tumor focus showed an increasing trend as same as the background. Compared with 300 s, the TBR muscle had no statistical difference in 180 s and 120 s.

CONCLUSIONS

Half-dose [68Ga]Ga-FAPI-04 in total-body PET/CT imaging can shorten the acquisition time to 120 s with acceptable subjective image quality and 100% tumor detection rate. Total-body PET/CT imaging with a half-dose [68Ga]Ga-FAPI-04 and reduced acquisition time can be used in radiation-sensitive and poor tolerant to prolong horizontal positioning and waiting time populations such as children and gravidas.

Inspired by novel radiopharmaceuticals: Rush hour of nuclear medicine

Nuclear medicine plays an irreplaceable role in the diagnosis and treatment of tumors. Radiopharmaceuticals are important components of nuclear medicine. Among the radiopharmaceuticals approved by the Food and Drug Administration (FDA), radio-tracers targeting prostate-specific membrane antigen (PSMA) and somatostatin receptor (SSTR) have held essential positions in the diagnosis and treatment of prostate cancers and neuroendocrine neoplasms, respectively. In recent years, FDA-approved serials of immune-therapy and targeted therapy drugs targeting programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2), and nectin cell adhesion molecule 4 (Nectin 4). How to screen patients suitable for these treatments and monitor the therapy? Nuclear medicine with specific radiopharmaceuticals can visualize the expression level of those targets in systemic lesions and evaluate the efficacy of treatment. In addition to radiopharmaceuticals, imaging equipment is also a key step for nuclear medicine. Advanced equipment including total-body positron emission tomography/computed tomography (PET/CT) and positron emission tomography/magnetic resonance imaging (PET/MRI) has been developed, which contribute to the diagnosis and treatment of tumors, as well as the development of new radiopharmaceuticals. Here, we conclude most recently advances of radiopharmaceuticals in nuclear medicine, and they substantially increase the "arsenal" of clinicians for tumor therapy.

68Ga-SSO-120 PET for Initial Staging of Small Cell Lung Cancer Patients: A Single-Center Retrospective Study

PET imaging using the somatostatin receptor 2 (SSTR2) antagonist satoreotide trizoxetan (SSO-120, previously OPS-202) could offer accurate tumor detection and screening for SSTR2-antagonist radionuclide therapy in patients with SSTR2-expressing small cell lung cancer (SCLC). The aim of this single-center study was to investigate tumor uptake and detection rates of 68Ga-SSO-120 in comparison to 18F-FDG PET in the initial staging of SCLC patients. Methods: Patients with newly diagnosed SCLC who underwent additional whole-body 68Ga-SSO-120 PET/CT during the initial diagnostic workup were retrospectively included. The mean administered activity was 139 MBq, and the mean uptake time was 60 min. Gold-standard staging 18F-FDG PET/CT was evaluated if available within 2 wk before or after 68Ga-SSO-120 PET if morphologic differences in CT images were absent. 68Ga-SSO-120- or 18F-FDG-positive lesions were reported in 7 anatomic regions (primary tumor, thoracic lymph node metastases, and distant metastases including pleural, contralateral pulmonary, liver, bone, and other) according to the TNM classification for lung cancer (eighth edition). Consensus TNM staging (derived from CT, endobronchial ultrasound-guided transbronchial needle aspiration, PET, and brain MRI) by a clinical tumor board served as the reference standard. Results: Thirty-one patients were included, 12 with limited and 19 with extensive disease according to the Veterans Administration Lung Study Group classification. 68Ga-SSO-120-positive tumor was detected in all patients (100%) and in 90 of the 217 evaluated regions (41.5%). Thirteen patients (42.0%) had intense average 68Ga-SSO-120 uptake (region-based mean SUVmax ≥ 10); 28 patients (90.3%) had average 68Ga-SSO-120 uptake greater than liver uptake (region-based mean peak tumor-to-liver ratio > 1). In 25 patients with evaluable 18F-FDG PET, primary tumor, thoracic lymph node metastases, and distant metastases were detected in 100%, 92%, and 64%, respectively, of all investigated patients by 68Ga-SSO-120 and in 100%, 92%, and 56%, respectively, by 18F-FDG PET. 68Ga-SSO-120 PET detected additional contralateral lymph node, liver, and brain metastases in 1, 1, and 2 patients, respectively (no histopathology available), and 18F-FDG PET detected additional contralateral lymph node metastases in 3 patients (1 confirmed, 1 systematic endobronchial ultrasound-guided transbronchial needle aspiration-negative, and 1 without available histopathology). None of these differences altered Veterans Administration Lung Study Group staging. The region-based monotonic correlation between 68Ga-SSO-120 and 18F-FDG uptake was low (Spearman ρ = 0.26-0.33). Conclusion: 68Ga-SSO-120 PET offers high diagnostic precision with comparable detection rates and additional complementary information to the gold standard, 18F-FDG PET. Consistent uptake in most patients warrants exploration of SSTR2-directed radionuclide therapy.

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

The current study aimed to compare 68Ga-NODAGA-Cpa-cyclo(d-Cys-amino-Phe-hydroorotic acid-d-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)-d-Tyr-NH2 (JR11) and 68Ga-DOTATATE PET/CT in patients with metastatic, well-differentiated neuroendocrine tumors. Methods: A prospective bicenter study aimed at enrolling 100 patients with histologically proven, metastatic or unresectable, well-differentiated neuroendocrine tumors was conducted. The first 48 patients represented the study cohort. Each patient received 68Ga-DOTATATE on the first day and 68Ga-NODAGA-JR11 on the second day. Whole-body PET/CT scans were performed at 40-60 min after injection. Normal-organ uptake, lesion numbers, lesion uptake, and sensitivity were compared. The potential impact on clinical management was also determined. Results: Overall, 68Ga-NODAGA-JR11 demonstrated lower background uptake in normal organs. Compared with 68Ga-DOTATATE, 68Ga-NODAGA-JR11 detected significantly more liver lesions (673 vs. 584, P = 0.002). The target-to-background ratio of liver lesions was significantly higher on 68Ga-NODAGA-JR11 (6.4 ± 8.7 vs. 3.1 ±2.6, P = 0.000). Comparable uptake was observed for primary tumors, bone lesions, and lymph node metastases. In total, 180 lesions were detected on conventional imaging in 15 patients; 165 and 139 lesions of them were positive on 68Ga-NODAGA-JR11 and 68Ga-DOTATATE, leading to a sensitivity of 91.7% and 77.2%, respectively. In 14.5% (7/48) of patients, 68Ga-NODAGA-JR11 PET might have a potential impact on clinical management. Conclusion: 68Ga-NODAGA-JR11 shows better sensitivity and a higher target-to-background ratio than 68Ga-DOTATATE. The detection of more lesions by the antagonist may have a potential impact on clinical management in a subgroup of patients.

New horizon of radiopharmaceuticals in management of neuroendocrine tumors

Neuroendocrine neoplasms are rare and heterogenous group of tumors with varying degrees of clinical presentations and involvement of multiple organ systems in the body. In the modern clinical practice somatostatin receptor molecular imaging and targeted radioligand therapy plays a vital role in the diagnosis and management of the disease. Several new and promising radiotracers for NET imaging and theranostics, belonging to various groups and classes are being studied and investigated. This exponential growth of radiotracers poses concerns about the indication, clinical benefit, and safety profile of the agents. We discuss the basis behind these radiotracers clinical use, receptor targeting and intra and inter tumor heterogeneity. Furthermore, role of dual tracer imaging, combination therapy and potential applications of dosimetry in predicting treatment outcome and safety profile is reviewed. Individualized precision medicine with better tumor characterization, maximum therapeutic benefit and minimum toxicity is the way forward for future medicine.

First preclinical evaluation of [225Ac]Ac-DOTA-JR11 and comparison with [177Lu]Lu-DOTA-JR11, alpha versus beta radionuclide therapy of NETs

BACKGROUND

The [¹⁷⁷Lu]Lu-DOTA-TATE mediated peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs) is sometimes leading to treatment resistance and disease recurrence. An interesting alternative could be the somatostatin antagonist, [¹⁷⁷Lu]Lu-DOTA-JR11, that demonstrated better biodistribution profile and higher tumor uptake than [¹⁷⁷Lu]Lu-DOTA-TATE. Furthermore, treatment with alpha emitters showed improvement of the therapeutic index of PRRT due to the high LET offered by the alpha particles compared to beta emitters. Therefore, [²²⁵Ac]Ac-DOTA-JR11 can be a potential candidate to improve the treatment of NETs (Graphical abstract). DOTA-JR11 was radiolabeled with [²²⁵Ac]Ac(NO₃)₃ and [¹⁷⁷Lu]LuCl₃. Stability studies were performed in phosphate buffered saline (PBS) and mouse serum. In vitro competitive binding assay has been carried out in U2OS-SSTR2 + cells for ^natLa-DOTA-JR11, ^natLu-DOTA-JR11 and DOTA-JR11. Ex vivo biodistribution studies were performed in mice inoculated with H69 cells at 4, 24, 48 and 72 h after injection of [²²⁵Ac]Ac-DOTA-JR11. A blocking group was included to verify uptake specificity. Dosimetry of selected organs was determined for [²²⁵Ac]Ac-DOTA-JR11 and [¹⁷⁷Lu]Lu-DOTA-JR11.

RESULTS

[²²⁵Ac]Ac-DOTA-JR11 has been successfully prepared and obtained in high radiochemical yield (RCY; 95%) and radiochemical purity (RCP; 94%). [²²⁵Ac]Ac-DOTA-JR11 showed reasonably good stability in PBS (77% intact radiopeptide at 24 h after incubation) and in mouse serum (~ 81% intact radiopeptide 24 h after incubation). [¹⁷⁷Lu]Lu-DOTA-JR11 demonstrated excellent stability in both media (> 93%) up to 24 h post incubation. Competitive binding assay revealed that complexation of DOTA-JR11 with ^natLa and ^natLu did not affect its binding affinity to SSTR2. Similar biodistribution profiles were observed for both radiopeptides, however, higher uptake was noticed in the kidneys, liver and bone for [²²⁵Ac]Ac-DOTA-JR11 than [¹⁷⁷Lu]Lu-DOTA-JR11.

CONCLUSION

[²²⁵Ac]Ac-DOTA-JR11 showed a higher absorbed dose in the kidneys compared to [¹⁷⁷Lu]Lu-DOTA-JR11, which may limit further studies with this radiopeptide. However, several strategies can be explored to reduce nephrotoxicity and offer opportunities for future clinical investigations with [²²⁵Ac]Ac-DOTA-JR11.

Comparison of the application of 18F-FDG and 68Ga-DOTATATE PET/CT in neuroendocrine tumors: A retrospective study

The present study aimed to compare the efficacy of 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT imaging in the diagnosis, staging, and prognosis evaluation of neuroendocrine tumors (NET). A total of 55 patients (43 were initially evaluated, 12 were evaluated after treatment) who underwent fluorine-18 labeled fluorodeoxyglucose (18F-FDG) and 68Ga DOTATE PET/CT examinations were reviewed retrospectively, and the pathological data were collected. In the initial evaluation, 27/43 were pathologically confirmed as NET patients, as detected by gallium-68 labeld 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraaceticacid-D-Phel-Tyr3-Thr8-OC; among them, 23 were correctly detected by 18F-FDG. In lesion-based comparison, 119/168 focal lesions were depicted on 18F-FDG PET/CT and 68Ga-DOTATATE PET/CT, respectively (P = .0363). Strikingly, gallium-68 labeld 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraaceticacid-D-Phel-Tyr3-Thr8-OC had higher maximum standard uptake value than 18F-FDG but was negatively related to the NET grade for the former, while the latter was positively related to the NET. The value of 68Ga-DOTATATE PET/CT in the diagnosis and staging of NET is higher than that of 18F-FDG PET/CT in NETs, while the value of 18F-FDG PET/CT cannot be ignored in the NET. The combined application of the 2 tracers has major clinical significance in the management of patients with NET.

Direct comparison of [18F]AlF-NOTA-JR11 and [18F]AlF-NOTA-octreotide for PET imaging of neuroendocrine tumors: Antagonist versus agonist

BACKGROUND

[¹⁸F]AlF-NOTA-octreotide is an ¹⁸F-labeled somatostatin analogue which is a good clinical alternative for ⁶⁸Ga-labeled somatostatin analogues. However, radiolabeled somatostatin receptor (SSTR) antagonists might outperform agonists regarding imaging sensitivity of neuroendocrine tumors (NETs). No direct comparison between the antagonist [¹⁸F]AlF-NOTA-JR11 and the agonist [¹⁸F]AlF-NOTA-octreotide as SSTR PET probes is available. Herein, we present the radiosynthesis of [¹⁸F]AlF-NOTA-JR11 and compare its NETs imaging properties directly with the established agonist radioligand [¹⁸F]AlF-NOTA-octreotide preclinically.

METHODS

[¹⁸F]AlF-NOTA-JR11 was synthesized in an automated synthesis module. The in vitro binding characteristics (IC₅₀) of [^natF]AlF-NOTA-JR11 and [^natF]AlF-NOTA-octreotide were evaluated and the in vitro stability of [¹⁸F]AlF-NOTA-JR11 was determined in human serum. In vitro cell binding and internalization was performed with [¹⁸F]AlF-NOTA-JR11 and [¹⁸F]AlF-NOTA-octreotide using SSTR2 expressing cells and the pharmacokinetics were evaluated using μPET/CT in mice bearing BON1.SSTR2 tumor xenografts.

RESULTS

Excellent binding affinity for SSTR2 was found for [^natF]AlF-NOTA-octreotide (IC₅₀ of 25.7 ± 7.9 nM). However, the IC₅₀ value for [^natF]AlF-NOTA-JR11 (290.6 ± 71 nM) was 11-fold higher compared to [^natF]AlF-NOTA-octreotide, indicating lower affinity for SSTR2. [¹⁸F]AlF-NOTA-JR11 was obtained in a good RCY (50 ± 6 %) but with moderate RCP of 94 ± 1 %. [¹⁸F]AlF-NOTA-JR11 demonstrated excellent stability in human serum (>95 % after 240 min). 2.7-fold higher cell binding was observed for [¹⁸F]AlF-NOTA-JR11 as compared to [¹⁸F]AlF-NOTA-octreotide after 60 min. μPET/CT images demonstrated comparable pharmacokinetics and tumor uptake between [¹⁸F]AlF-NOTA-JR11 (SUV_max: 3.7 ± 0.8) and [¹⁸F]AlF-NOTA-octreotide (SUV_max: 3.6 ± 0.4).

CONCLUSIONS

[¹⁸F]AlF-NOTA-JR11 was obtained in good RCY, albeit with a moderate RCP. The cell binding study showed significant higher binding of [¹⁸F]AlF-NOTA-JR11 compared to [¹⁸F]AlF-NOTA-octreotide, despite the higher IC₅₀ value of AlF-NOTA-JR11. However, pharmacokinetics and in vivo tumor uptake was comparable for both radiotracers. Novel Al¹⁸F-labeled derivatives of JR11 with higher SSTR2 affinity should be developed for increased tumor uptake and NET imaging sensitivity.

18F-DOPA PET/CT at the Forefront of Initial or Presurgical Evaluation of Small-Intestine Neuroendocrine Tumors

Our objective was to compare the respective value of ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT for initial staging or presurgical work-up of patients with small-intestine neuroendocrine tumors (SiNETs). Methods: This was a retrospective, multicenter, noninterventional investigation involving 53 non-surgically treated SiNET patients who underwent both ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT within a 6-mo interval without surgical intervention or therapeutic change between the 2 PET/CT studies. Percentage detection rate was calculated according to per-region and per-lesion analyses. Sensitivity for primary tumor detection was assessed in 37 surgically treated patients, taking surgical results (76 SiNETs) as the diagnostic gold standard. Results: ⁶⁸Ga-DOTATOC PET/CT and ¹⁸F-DOPA PET/CT individually identified at least 1 primary SiNET in 92% (34/37) of the patients. Intestinal tumor multifocality was confirmed by histology in 8 patients. ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT were concordantly positive for tumor multifocality in 5 patients, discordantly positive in 2 patients, and concordantly negative in 1 patient. The detection rate for subdiaphragmatic nodal metastases on per-region-based analysis was 91% and 98% for ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT, respectively (P = 0.18). ¹⁸F-DOPA PET/CT detected a higher number of abnormal subdiaphragmatic nodes (P = 0.009). Regarding mesenteric nodes only, ¹⁸F-DOPA PET/CT detected more positive regions (P = 0.005) and nodal lesions (P = 0.003) than ⁶⁸Ga-DOTATOC PET/CT, including nodes at the origin of mesenteric vessels. For detection of distant metastases, ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT performed equally well on a per-region-based analysis. As compared with ⁶⁸Ga-DOTATOC, ¹⁸F-DOPA PET/CT detected more hepatic (P < 0.001), peritoneal (P < 0.001), and lung metastases (P < 0.001). Conclusion: ¹⁸F-DOPA PET/CT detected more lesions than ⁶⁸Ga-DOTATOC PET/CT in the studied patients. The respective roles of the two should be discussed in terms of disease staging and treatment selection.

Nuclear Medicine and Radiological Imaging of Pancreatic Neuroendocrine Neoplasms: A Multidisciplinary Update

Pancreatic neuroendocrine neoplasms (panNENs) are part of a large family of tumors arising from the neuroendocrine system. PanNENs show low-intermediate tumor grade and generally high somatostatin receptor (SSTR) expression. Therefore, panNENs benefit from functional imaging with ⁶⁸Ga-somatostatin analogues (SSA) for diagnosis, staging, and treatment choice in parallel with morphological imaging. This narrative review aims to present conventional imaging techniques and new perspectives in the management of panNENs, providing the clinicians with useful insight for clinical practice. The ⁶⁸Ga-SSA PET/CT is the most widely used in panNENs, not only fr diagnosis and staging purpose but also to characterize the biology of the tumor and its responsiveness to SSAs. On the contrary, the ¹⁸F-Fluordeoxiglucose (FDG) PET/CT is not employed systematically in all panNEN patients, being generally preferred in G2-G3, to predict aggressiveness and progression rate. The combination of ⁶⁸Ga-SSA PET/CT and ¹⁸F-FDG PET/CT can finally suggest the best therapeutic strategy. Other radiopharmaceuticals are ⁶⁸Ga-exendin-4 in case of insulinomas and ¹⁸F-dopamine (DOPA), which can be helpful in SSTR-negative tumors. New promising but still-under-investigation radiopharmaceuticals include radiolabeled SSTR antagonists and ¹⁸F-SSAs. Conventional imaging includes contrast enhanced CT and multiparametric MRI. There are now enriched by radiomics, a new non-invasive imaging approach, very promising to early predict tumor response or progression.

Detection of Bone Metastases by 68Ga-DOTA-SSAs and 18F-FDG PET/CT: A Two-Center Head-to-Head Study of Gastroenteropancreatic Neuroendocrine Neoplasms

Purpose

This study aimed to assess the efficacy of dual-tracer [⁶⁸Ga-DOTA-somatostatin receptor analogs (SSAs) and ¹⁸F-fluorodeoxyglucose (FDG)] positron emission tomography/computed tomography (PET/CT) imaging for detecting bone metastases (BMs) in patients with gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs).

Methods

We retrospectively enrolled 74 GEP-NEN patients with BMs from two centers, who underwent dual-tracer PET/CT from January 2014 to March 2021. We compared and analyzed effectiveness of the dual PET/CT imaging techniques on the BMs, based on ¹⁸F-FDG and ⁶⁸Ga-DOTA-SSAs. Specifically, we analyzed the imaging results using χ ² tests for classification variables, paired-sample tests for number of BMs, Wilcoxon's signed rank test for number of lesions, and the Kruskal-Wallis test for standard uptake value (SUV) ratio comparison. The correlation of dual-tracer SUVmax with Ki-67 index was analyzed by Spearman's correlation coefficient.

Results

The detection efficiencies of dual-tracer PET/CT imaging in patients with different pathologies showed discordant for detecting liver metastases and BMs in group neuroendocrine tumor (NET) G3, ⁶⁸Ga-DOTA-SSAs was better at detecting BMs for NET G3 (P=0.049 for SUV_T/B and P=0.026 for the number of metastatic lesions). In addition, statistical significance was found among osteogenesis group, osteolysis group, and the no-change group (for bone SUV_T/B value detected by ¹⁸F-FDG and Ki-67 index, osteogenesis group < osteolysis group; for bone SUV_T/B detected by ⁶⁸Ga-DOTA-SSAs, osteogenesis group > the no-change group). What is more, liver and bone SUVmax and Ki-67 index were positively correlated in ¹⁸F-FDG imaging (P < 0.001 for liver; P=0.002 for bone), and negatively correlated in ⁶⁸Ga-DOTA-SSAs imaging (P < 0.001 for liver; P=0.039 for bone).

Conclusions

⁶⁸Ga-DOTA-SSAs was superior to ¹⁸F-FDG for detecting BMs in NET G1/G2 (well and moderately differentiated NETs), as well as in NET G3 (poorly differentiated NETs). Relatively good differentiation was observed in the osteogenesis group. In addition, dual-tracer PET/CT imaging results were observably correlated with tumor differentiation.

Head-to-Head Comparison between Peptide-Based Radiopharmaceutical for PET and SPECT in the Evaluation of Neuroendocrine Tumors: A Systematic Review

We compared head-to-head the most used radiolabeled peptides for single photon computed emission tomography (SPECT) and positron emission tomography (PET) imaging of neuroendocrine tumors (NETs). A comprehensive literature search was performed in PubMed, Web of Science, and Scopus databases. The following words, coupled two by two, were used: 68Ga-DOTATOC; 68Ga-DOTATATE; 68Ga-DOTANOC; 99mTc-EDDA/HYNIC-TOC; 64Cu-DOTATATE; and 111In-DTPA-octreotide. Moreover, a second-step search strategy was adopted by using the following combined terms: "Somatostatin receptor imaging,"; "Somatostatin receptor imaging" and "Functional,"; "Somatostatin receptor imaging" and "SPECT,"; and "Somatostatin receptor imaging" and "PET". Eligible criteria were: (1) original articles focusing on the clinical application of the radiopharmaceutical agents in NETs; (2) original articles in the English language; (3) comparative studies (head-to-head comparative or matched-paired studies). Editorials, letters to the editor, reviews, pictorial essays, clinical cases, or opinions were excluded. A total of 1077 articles were found in the three electronic databases. The full texts of 104 articles were assessed for eligibility. Nineteen articles were finally included. Most articles focused on the comparison between 111In-DTPA-Octreotide and 68Ga-DOTATOC/TATE. Few papers compared 64Cu-DOTATATE and 68Ga-DOTATOC/TATE, or SPECT tracers. The rates of true positivity were 63.7%, 58.5%, 78.4% and 82.4%, respectively, for 111In-DTPA-Octreotide, 99mTc-EDDA/HYNIC-TOC, 68Ga-DOTATATE/TOC and 64Cu-DOTATATE. In conclusion, as highly expected, PET tracers are more suitable for the in vivo identification of NETs. Indeed, in comparative studies, they demonstrated a higher true positive rate than SPECT agents.

Imaging-guided targeted radionuclide tumor therapy: From concept to clinical translation

Since the first introduction of sodium iodide I-131 for use with thyroid patients almost 80 years ago, more than 50 radiopharmaceuticals have reached the markets for a wide range of diseases, especially cancers. The nuclear medicine paradigm also shifts from solely molecular imaging or radionuclide therapy to imaging-guided radionuclide therapy, which is deemed a vital component of precision cancer therapy and an emerging medical modality for personalized medicine. The imaging-guided radionuclide therapy highlights the systematic integration of targeted nuclear diagnostics and radionuclide therapeutics. Regarding this, nuclear imaging serves to "visualize" the lesions and guide the therapeutic strategy, followed by administration of a precise patient specific dose of radiotherapeutics for treatment according to the absorbed dose to different organs and tumors calculated by dosimetry tools, and finally repeated imaging to predict the prognosis. This strategy leads to significantly enhanced therapeutic efficacy, improved patient outcomes, and manageable adverse events. In this review, we provide an overview of imaging-guided targeted radionuclide therapy for different tumors such as advanced prostate cancer and neuroendocrine tumors, with a focus on development of new radioligands and their preclinical and clinical results, and further discuss about challenges and future perspectives.

Positron emission tomography imaging of lung cancer: An overview of alternative positron emission tomography tracers beyond F18 fluorodeoxyglucose

Lung cancer has been the leading cause of cancer-related mortality in China in recent decades. Positron emission tomography-computer tomography (PET/CT) has been established in the diagnosis of lung cancer. ¹⁸F-FDG is the most widely used PET tracer in foci diagnosis, tumor staging, treatment planning, and prognosis assessment by monitoring abnormally exuberant glucose metabolism in tumors. However, with the increasing knowledge on tumor heterogeneity and biological characteristics in lung cancer, a variety of novel radiotracers beyond ¹⁸F-FDG for PET imaging have been developed. For example, PET tracers that target cellular proliferation, amino acid metabolism and transportation, tumor hypoxia, angiogenesis, pulmonary NETs and other targets, such as tyrosine kinases and cancer-associated fibroblasts, have been reported, evaluated in animal models or under clinical investigations in recent years and play increasing roles in lung cancer diagnosis. Thus, we perform a comprehensive literature review of the radiopharmaceuticals and recent progress in PET tracers for the study of lung cancer biological characteristics beyond glucose metabolism.

Molecular Imaging of Neuroendocrine Neoplasms

The key for molecular imaging is the use of a radiotracer with a radioactive and a functional component. While the functional component targets a specific feature of the tumor, the radioactive component makes the target visible. Neuroendocrine neoplasms (NEN) are a diverse group of rare tumors that arise from neuroendocrine cells found mainly in the gastroenteropancreatic system, lung, thyroid, and adrenal glands. They are characterized by the expression of specific hormone receptors on the tumor cell surface, which makes them ideal targets for radiolabeled peptides. The most commonly expressed hormone receptors on NEN cells are the somatostatin receptors. They can be targeted for molecular imaging with various radiolabeled somatostatin analogs, but also with somatostatin antagonists, which have shown improved imaging quality. 18F-DOPA imaging has become a second-line imaging modality in NENs, with the exception of the evaluation of advanced medullary thyroid carcinoma. Alternatives for NENs with insufficient somatostatin receptor expression due to poor differentiation involve targeting glucose metabolism, which can also be used for prognosis. For the localization of the often-small insulinoma, glucagon-like peptide-1 (GLP-1) receptor imaging has become the new standard. Other alternatives involve metaiodobenzylguanidine and the molecular target C-X-C motif chemokine receptor-4. In addition, new radiopeptides targeting the fibroblast activation protein, the glucose-dependent insulinotropic polypeptide receptor and cholecystokinin-2 receptors have been identified in NENs and await further evaluation. This mini-review aims to provide an overview of the major molecular imaging modalities currently used in the field of NENs, and also to provide an outlook on future developments.

A prospective head-to-head comparison of 68 Ga-NOTA-3P-TATE-RGD and 68 Ga-DOTATATE in patients with gastroenteropancreatic neuroendocrine tumours

PURPOSE

The aim of this study was to compare ⁶⁸ Ga-NOTA-3P-TATE-RGD, a dual somatostatin receptor 2- and integrin α_Vβ₃-targeting tracer, to ⁶⁸ Ga-DOTATATE in a single group of patients with gastroenteropancreatic (GEP)-neuroendocrine tumours (NETs).

METHODS

Thirty-five patients with histologically confirmed GEP-NETs (5 grade 1, 28 grade 2, and 2 grade 3 tumours) were prospectively enrolled with informed consent. The primary tumour mainly originated from the pancreas and rectum. All patients were scanned with both ⁶⁸ Ga-NOTA-3P-TATE-RGD PET/CT and ⁶⁸ Ga-DOTATATE PET/CT within a week and compared on a head-to-head basis. Sixteen patients also had conventional ¹⁸F-FDG PET/CT. Images were evaluated semi-quantitatively using maximum standardized uptake values (SUVmax) of tumour and tumour-to-background ratio.

RESULTS

All patients had at least one positive lesion on each of the two scans. A total of 1190 and 1106 lesions were detected on ⁶⁸ Ga-NOTA-3P-TATE-RGD images and ⁶⁸ Ga-DOTATATE images, respectively (P = 0.152). ⁶⁸ Ga-NOTA-3P-TATE-RGD PET/CT revealed significantly more lesions in the liver than ⁶⁸ Ga-DOTATATE PET/CT (634 vs. 532, P = 0.021). Both tracers produced comparable results for detecting primary tumours (20 vs. 20, P = 1.000), lymph node metastases (101 vs. 102, P = 0.655), and bone metastases (381 vs. 398, P = 0.244). The tumour SUVmax in 12 patients was significantly higher for ⁶⁸ Ga-NOTA-3P-TATE-RGD than for ⁶⁸ Ga-DOTATATE (27.2 ± 13.6 vs. 19.5 ± 10.0, P < 0.001); among them, 9 had ¹⁸F-FDG PET/CT and all were found to be FDG-positive. The remaining 23 patients had significantly higher ⁶⁸ Ga-DOTATATE uptake than ⁶⁸ Ga-NOTA-3P-TATE-RGD uptake (22.3 ± 16.4 vs. 11.9 ± 7.5, P < 0.001); among them, 7 had ¹⁸F-FDG PET/CT and 6 were FDG-negative. Generally, ⁶⁸ Ga-DOTATATE demonstrated higher tumour SUVmax than ⁶⁸ Ga-NOTA-3P-TATE-RGD (20.8 ± 16.0 vs. 14.2 ± 8.9, P < 0.001), including primary tumours, liver lesions, lymph node lesions, and bone lesions. However, the tumour-to-background ratio of liver lesions was significantly higher when using ⁶⁸ Ga-NOTA-3P-TATE-RGD compared with that when using ⁶⁸ Ga-DOTATATE (8.4 ± 5.5 vs. 4.7 ± 3.7, P < 0.001).

CONCLUSION

⁶⁸ Ga-NOTA-3P-TATE-RGD performed better than ⁶⁸ Ga-DOTATATE in detection of liver metastases with a higher tumour-to-background ratio. Moreover, ⁶⁸ Ga-NOTA-3P-TATE-RGD tended to demonstrate higher uptake over ⁶⁸ Ga-DOTATATE in FDG-avid NETs.

TRIAL REGISTRATION

Dual SSTR2 and Integrin αvβ3 Targeting PET/CT Imaging (NCT02817945, registered 5 November 2018). URL OF REGISTRY: https://clinicaltrials.gov/ct2/show/NCT02817945.

Molecular imaging phenotyping for selecting and monitoring radioligand therapy of neuroendocrine neoplasms

Neuroendocrine neoplasia (NEN) is an umbrella term that includes a widely heterogeneous disease group including well-differentiated neuroendocrine tumours (NETs), and aggressive neuroendocrine carcinomas (NECs). The site of origin of the NENs is linked to the intrinsic tumour biology and is predictive of the disease course. It is understood that NENs demonstrate significant biologic heterogeneity which ultimately translates to widely varying clinical presentations, disease course and prognosis. Thus, significant emphasis is laid on the pre-therapy evaluation of markers that can help predict tumour behavior and dynamically monitors the response during and after treatment. Most well-differentiated NENs express somatostatin receptors (SSTRs) which make them appropriate for peptide receptor radionuclide therapy (PRRT). However, the treatment outcomes of PRRT depend heavily on the adequacy of patient selection by molecular imaging phenotyping not only utilizing pre-treatment SSTR PET but ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) PET to provide insights into the intra- or inter-tumoural heterogeneity of the metastatic disease. Molecular imaging phenotyping may go beyond patient selection and provide useful information during and post-treatment for monitoring of temporal heterogeneity of the disease and dynamically risk-stratify patients. In addition, advances in the understanding of genomic-phenotypic classifications of pheochromocytomas and paragangliomas led to an archetypical example in precision medicine by utilizing molecular imaging phenotyping to guide radioligand therapy. Novel non-SSTR based peptide receptors have also been explored diagnostically and therapeutically to overcome the tumour heterogeneity. In this paper, we review the current molecular imaging modalities that are being utilized for the characterization of the NENs with special emphasis on their role in patient selection for radioligand therapy.

New PET Radiotracers for the Imaging of Neuroendocrine Neoplasms

OPINION STATEMENT

Neuroendocrine neoplasms (NEN) are a heterogeneous group of tumours derived from cells of neuroendocrine origin and can potentially arise everywhere in the human body. The diagnostic assessment of NEN can be performed using a variety of PET radiopharmaceuticals. Well-differentiated NEN (NET) present a high expression of SSTR (somatostatin receptors) and can therefore be studied with 68Ga-DOTA-peptides ([68Ga]Ga-DOTANOC, [68Ga]Ga-DOTATOC, [68Ga]Ga-DOTATATE). Current guidelines recommend the use of SSTR imaging to assess disease extension at staging/restaging, follow-up, assessment of response to therapy and selection of patients who may benefit from radionuclide therapy (PRRT). [18F]F-FDG is used for the assessment of high-grade tumours (high-grade G2, G3 and NEC) and in every case, there is one or more mismatched lesions between diagnostic CT (positive) and SSTR-PET/CT (negative). [18F]F-DOPA is currently used for the assessment of medullary thyroid carcinoma, neuroblastoma, primary pheochromocytoma and abdominal paraganglioma. In recent years, however, several new tracers were designed exploiting the many potential targets of the neuroendocrine cell and were employed in clinical trials for both imaging and therapy. Currently, the real-life clinical impact of these tracers is still mostly not known; however, the favourable biodistribution (e.g. [68Ga]Ga-FAPI, SSTR antagonists) and the possibility to use new theranostic pairs may provide novel diagnostic as well as therapeutic options (e.g. [68Ga]Ga-PSMA, [64Cu]Cu-SARTATE, [68Ga]Ga-CXCR4) for NEN patients.

Head-to-Head Comparison of 68Ga-DOTA-TATE and 68Ga-DOTA-JR11 PET/CT in Patients With Tumor-Induced Osteomalacia: A Prospective Study

Background

The purpose of this study is to compare the sensitivity of ⁶⁸Ga-DOTA-JR11 and ⁶⁸Ga-DOTA-TATE PET/CT for detecting the responsible tumor of tumor-induced osteomalacia (TIO) and investigate if ⁶⁸Ga-DOTA-JR11 PET/CT can identify the culprit tumor of TIO in multiple suspicious lesions in ⁶⁸Ga-DOTA-TATE PET/CT.

Methods

A total of 19 patients with suspected TIO were prospectively recruited in this study. Each patient underwent whole-body PET/CT scan 40–60 min postinjection using ⁶⁸Ga-DOTA-TATE and ⁶⁸Ga-DOTA-JR11 on the same PET/CT, respectively in sequence, and on consecutive days. The diagnosis of TIO was confirmed by the combination of the postsurgical pathological results of the tumor and clinical information.

Results

Among the 19 patients with TIO who were included in this study, culprit tumors from all patients were confirmed pathologically. ⁶⁸Ga-DOTA-TATE PET/CT positively identified the causative tumor in 18/19 patients, whereas ⁶⁸Ga-DOTA-JR11 PET/CT was positive in 11/19 patients (94.7% vs. 57.9%, respectively; p < 0.05). ⁶⁸Ga-DOTA-TATE PET/CT demonstrated more than one increased focal activity in 7 patients for a total of 16 lesions (3 lesions each in 2 patients and 2 lesions each in the rest 5 patients). However, seven of these 16 lesions showed concordant results on ⁶⁸Ga-DOTA-JR11 PET/CT by demonstrating increased activity (one lesion in each of the 7 patients). The surgical specimens of the lesions in these 7 patients confirmed the phosphaturic mesenchymal tumor. A total of 11 culprit tumors were positive in both ⁶⁸Ga-DOTA-TATE and ⁶⁸Ga-DOTA-JR11 PET/CT. The SUVmax of 11 culprit tumors was significantly higher on ⁶⁸Ga-DOTA-TATE PET/CT compared with that on ⁶⁸Ga-DOTA-JR11 PET/CT (17.8 ± 12.5 vs. 6.8 ± 6.2; p < 0.05).

Conclusions

⁶⁸Ga-DOTA-TATE PET/CT is more sensitive to ⁶⁸Ga-DOTA-JR11 PET/CT in the detection of the culprit tumor of TIO. However, ⁶⁸Ga-DOTA-JR11 PET/CT might be helpful to identify the tumor in multiple suspicious lesions in ⁶⁸Ga-DOTA-TATE PET/CT.

Clinical Trial Registration

clinicaltrials.gov, identifier NCT 04689893.

Radiolabeled Somatostatin Analogs-A Continuously Evolving Class of Radiopharmaceuticals

Somatostatin receptors (SSTs) are recognized as favorable molecular targets in neuroendocrine tumors (NETs) and neuroendocrine neoplasms (NENs), with subtype 2 (SST₂) being the predominantly and most frequently expressed. PET/CT imaging with ⁶⁸Ga-labeled SST agonists, e.g., ⁶⁸Ga-DOTA-TOC (SomaKit TOC^®) or ⁶⁸Ga-DOTA-TATE (NETSPOT^®), plays an important role in staging and restaging these tumors and can identify patients who qualify and would potentially benefit from peptide receptor radionuclide therapy (PRRT) with the therapeutic counterparts ¹⁷⁷Lu-DOTA-TOC or ¹⁷⁷Lu-DOTA-TATE (Lutathera^®). This is an important feature of SST targeting, as it allows a personalized treatment approach (theranostic approach). Today, new developments hold promise for enhancing diagnostic accuracy and therapeutic efficacy. Among them, the use of SST₂ antagonists, such as JR11 and LM3, has shown certain advantages in improving image sensitivity and tumor radiation dose, and there is evidence that they may find application in other oncological indications beyond NETs and NENs. In addition, PRRT performed with more cytotoxic α-emitters, such as ²²⁵Ac, or β^- and Auger electrons, such as ¹⁶¹Tb, presents higher efficacy. It remains to be seen if any of these new developments will overpower the established radiolabeled SST analogs and PRRT with β^--emitters.

Radiolabeled Somatostatin Analogues for Diagnosis and Treatment of Neuroendocrine Tumors

Neuroendocrine neoplasms (NENs) are rare and heterogeneous tumors that require multidisciplinary discussion for optimal care. The theranostic approach (DOTA peptides labelled with 68Ga for diagnosis and with 90Y or 177Lu for therapy) plays a crucial role in the management of NENs to assess disease extension and as a criteria for peptide receptor radionuclide therapy (PRRT) eligibility based on somatostatin receptor (SSTR) expression. On the diagnostic side, [68Ga]Ga-DOTA peptides PET/CT (SSTR PET/CT) is the gold standard for imaging well-differentiated SSTR-expressing neuroendocrine tumors (NETs). [18F]FDG PET/CT is useful in higher grade NENs (NET G2 with Ki-67 > 10% and NET G3; NEC) for more accurate disease characterization and prognostication. Promising emerging radiopharmaceuticals include somatostatin analogues labelled with 18F (to overcome the limits imposed by 68Ga), and SSTR antagonists (for both diagnosis and therapy). On the therapeutic side, the evidence gathered over the past two decades indicates that PRRT is to be considered as an effective and safe treatment option for SSTR-expressing NETs, and is currently included in the therapeutic algorithms of the main scientific societies. The positioning of PRRT in the treatment sequence, as well as treatment personalization (e.g., tailored dosimetry, re-treatment, selection criteria, and combination with other alternative treatment options), is warranted in order to improve its efficacy while reducing toxicity. Although very preliminary (being mostly hampered by lack of methodological standardization, especially regarding feature selection/extraction) and often including small patient cohorts, radiomic studies in NETs are also presented. To date, the implementation of radiomics in clinical practice is still unclear. The purpose of this review is to offer an overview of radiolabeled SSTR analogues for theranostic use in NENs.

A prospective randomized, double-blind study to evaluate the diagnostic efficacy of 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3 in patients with well-differentiated neuroendocrine tumors: compared with 68Ga-DOTATATE

PURPOSE

The purpose of this study is to evaluate the diagnostic efficacy of ⁶⁸ Ga-NODAGA-LM3 and ⁶⁸ Ga-DOTA-LM3 and compare them with ⁶⁸ Ga-DOTATATE in patients with well-differentiated neuroendocrine tumors.

METHODS

Patients were prospectively recruited and equally randomized into two arms: Arm A, patients would undergo a whole-body ⁶⁸ Ga-NODAGA-LM3 PET/CT scan on the 1st day and ⁶⁸ Ga-DOTATATE PET/CT scan on the 2nd day; Arm B, patients would undergo a whole-body ⁶⁸ Ga-DOTA-LM3 PET/CT scan on the 1st day and ⁶⁸ Ga-DOTATATE PET/CT scan on the 2nd day. Biodistribution in normal organs, lesion detection ability, and tumor uptake were compared between antagonist and agonist in each arm.

RESULTS

A total of 40 patients with well-differentiated NETs, 20 in each arm, were recruited in the study. ⁶⁸ Ga-NODAGA-LM3 showed a similar pattern as ⁶⁸ Ga-DOTATATE, while ⁶⁸ Ga-DOTA-LM3 demonstrated significantly lower uptake in almost all normal organs compared to ⁶⁸ Ga-DOTATATE. Both ⁶⁸ Ga-NODAGA-LM3 and ⁶⁸ Ga-DOTA-LM3 showed superiority in lesion detection compared to ⁶⁸ Ga-DOTATATE on lesion-based and patient-based comparison. ⁶⁸ Ga-NODAGA-LM3 showed a significantly higher tumor uptake (median SUVmax 29.1 versus 21.6, P < 0.05) and tumor-to-background ratio (median tumor-to-liver ratio 5.0 versus 2.9, P < 0.05) compared to ⁶⁸ Ga-DOTATATE. ⁶⁸ Ga-DOTA-LM3 showed comparable uptake (median SUVmax 16.1 versus 17.8, P = 0.714) and higher tumor-to-background ratio (median tumor-to-liver ratio 5.2 versus 2.1, P < 0.05).

CONCLUSION

Both ⁶⁸ Ga-NODAGA-LM3 and ⁶⁸ Ga-DOTA-LM3 are promising SSTR2 antagonists for neuroendocrine tumors. They demonstrated superiority in diagnostic efficacy compared to agonist ⁶⁸ Ga-DOTATATE.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04318561.

Use of 18F-FDG PET/CT to Differentiate Ectopic Adrenocorticotropic Hormone-Secreting Lung Tumors From Tumor-Like Pulmonary Infections in Patients With Ectopic Cushing Syndrome

Background

Ectopic adrenocorticotropic hormone (ACTH)-secreting lung tumors represent the most common cause of ectopic Cushing syndrome (ECS). Pulmonary opportunistic infections are associated with ECS. The present study aimed to evaluate the usefulness of ¹⁸F-FDG PET/CT for differentiating ectopic ACTH-secreting lung tumors from tumor-like pulmonary infections in patients with ECS.

Methods

We retrospectively reviewed the imaging data of 24 patients with ECS who were suspected to have ACTH-secreting lung tumors and underwent ¹⁸F-FDG PET/CT between 2008 and 2019. Eleven patients with lung tumors and 4 with pulmonary infections also had additional somatostatin receptor imaging (^99mTc-HYNIC-TOC SPECT/CT or ⁶⁸Ga-DOTATATE PET/CT).

Results

In total, 18 patients had lung tumors and six had pulmonary infections. The primary source of ECS remained occult in the six patients with pulmonary infections. The maximum standardized uptake value (SUV_max) for pulmonary infections was significantly higher than that for tumors (P = 0.008). Receiver operating characteristic analysis revealed that a cut-off SUV_max of 4.95 helped in differentiating ACTH-secreting lung tumors from infections with 75% sensitivity and 94.4% specificity. For the 11 patients with ACTH-lung tumors, somatostatin receptor imaging (SRI) was positive in 6; while for the 4 with pulmonary infections, SRI was positive in 2. The sensitivity and specificity of somatostatin receptor imaging (SRI) for detecting ACTH-secreting lung tumor was 54.5% and 50%.

Conclusions

Our findings suggest that pulmonary infections exhibit significantly higher FDG uptake than ACTH-secreting lung tumors in ¹⁸F-FDG PET/CT. An SUV_max cut-off value of 4.95 may be useful for differentiating the two conditions. Our results also suggested that SRI may not be an effective tool for differentiating the two conditions given the relatively low specificity.

68Ga-DOTATATE and 68Ga-NODAGA-JR11 PET/CT Images in a Patient With Gastric Neuroendocrine Tumor

ABSTRACT

A 52-year-old man with newly diagnosed gastric neuroendocrine tumor (NET) underwent 68Ga-NODAGA-JR11 and 68Ga-DOTATATE imaging. 68Ga-DOTATATE PET/CT showed no 68Ga-DOTATATE uptake in the lesion, where 68Ga-NODAGA-JR11 showed intense uptake. The patient subsequently received endoscopic submucosal dissection and en bloc resection of the lesion, which was pathologically confirmed as gastric NET (G2). The positive findings of 68Ga-NODAGA-JR11 in the current case highlighted that 68Ga-NODAGA-JR11 PET/CT may be a promising molecular imaging technique for the detection of NETs with high sensitivity.

A Prospective, Randomized, Double-Blind Study to Evaluate the Safety, Biodistribution, and Dosimetry of 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3 in Patients with Well-Differentiated Neuroendocrine Tumors

68Ga-NODAGA-LM3 (where LM3 is p-Cl-Phe-cyclo(d-Cys-Tyr-d-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)d-Tyr-NH2) and 68Ga-DOTA-LM3 are somatostatin receptor subtype 2 (SSTR2)-specific antagonists used for PET/CT imaging. The purpose of this study was to evaluate the safety, biodistribution, and dosimetry of 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3 in patients with well-differentiated neuroendocrine tumors. Methods: Patients were equally randomized into 2 arms, with arm A receiving 68Ga-NODAGA-LM3 and arm B receiving 68Ga-DOTA-LM3. Serial PET scans were acquired at 5, 15, 30, 45, 60, and 120 min after 68Ga-NODAGA-LM3 (200 MBq ± 11 MBq/40 μg of total peptide mass) or 68Ga-DOTA-LM3 (172 MBq ± 21 MBq/40 μg of total peptide mass) injection. The biodistribution in normal organs, tumor uptake, and safety were assessed. Radiation dosimetry was calculated using OLINDA/EXM (version 1.0). Results: Sixteen patients, 8 in each arm, were recruited in the study. Both tracers were well tolerated in most patients. Two patients in arm B had nausea (grade 2), and one of them had vomiting (grade 1). The PET images of the other 14 patients were further analyzed. Significantly lower organ uptake was observed in the pituitary, parotids, liver, spleen, pancreas, adrenal, stomach, small intestine, and kidneys with 68Ga-DOTA-LM3 than with 68Ga-NODAGA-LM3. In total, 38 lesions were analyzed, including 18 with 68Ga-NODAGA-LM3 and 20 with 68Ga-DOTA-LM3. Both tracers showed good tumor uptake and retention. With 68Ga-NODAGA-LM3, the tracer accumulation in tumor lesions increased by 138%, from an average SUVmax of 31.3 ± 19.7 at 5 min to 74.6 ± 56.3 at 2 h. With 68Ga-DOTA-LM3, the tumor uptake rapidly reached a high level at 5 min after injection, with an average SUVmax of 36.6 ± 23.6, and continued to increase to 45.3 ± 29.3 until 30 min after injection. The urinary bladder wall was the organ receiving the highest absorbed dose in both arms. The mean effective dose was 0.026 ± 0.003 mSv/MBq for 68Ga-NODAGA-LM3 and 0.025 ± 0.002 mSv/MBq for 68Ga-DOTA-LM3. Conclusion: Both 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3 show favorable biodistribution, high tumor uptake, and good tumor retention, resulting in high image contrast. The dosimetric data are comparable to those for other 68Ga-labeled SSTR2 antagonists. Further studies are required to look into the potential antagonistic effects of 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3.

Positive Somatostatin Receptor Expression Demonstrated on 68Ga-NODAGA-LM3 PET/CT in a Neuroendocrine Tumor Patient With Negative Immunohistochemical Staining: Conflict or Heterogeneity

ABSTRACT

We present a case with pulmonary atypical carcinoid and multiple hepatic metastases. Immunohistochemical staining of liver biopsy sample was negative for somatostatin receptor subtype 2, but 68Ga-NODAGA-LM3 PET/CT scan revealed multiple positive lesions. The mismatch was actually caused by heterogeneous expression of somatostatin receptor in liver lesions.

Small bowel radiology

PURPOSE OF REVIEW

Recent advances in computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), and nuclear radiology have improved the diagnosis and characterization of small bowel pathology. Our purpose is to highlight the current status and recent advances in multimodality noninvasive imaging of the small bowel.

RECENT FINDINGS

CT and MR enterography are established techniques for small bowel evaluation. Dual-energy CT is a novel technique that has shown promise for the mesenteric ischemia and small bowel bleeding. Advanced US techniques and MRI sequences are being investigated to improve assessment of bowel inflammation, treatment response assessment, motility, and mural fibrosis. Novel radiotracers and scanner technologies have made molecular imaging the new reference standard for small bowel neuroendocrine tumors. Computational image analysis and artificial intelligence (AI) have the potential to augment physician expertise, reduce errors and variability in assessment of the small bowel on imaging.

SUMMARY

Advances in translational imaging research coupled with progress in imaging technology have led to a wider adoption of cross-sectional imaging for the evaluation and management of small bowel entities. Ongoing developments in image acquisition and postprocessing techniques, molecular imaging and AI have the strongest potential to transform the care and outcomes of patients with small bowel diseases.

Targeted Cancer Therapy: What's New in the Field of Neuroendocrine Neoplasms?

Neuroendocrine tumors (NETs) are a heterogeneous family of neoplasms of increasing incidence and high prevalence due to their relatively indolent nature. Their wide anatomic distribution and their characteristic ability to secrete hormonally active substances pose unique challenges for clinical management. They are also characterized by the common expression of somatostatin receptors, a target that has been extremely useful for diagnosis and treatment (i.e., somatostatin analogues (SSAs) and peptide-receptor radionuclide therapy (PRRT)). Chemotherapy is of limited use for NETs of non-pancreatic origin, and the only approved targeted agents for advanced progressive NETs are sunitinib for those of pancreatic origin, and everolimus for lung, gastrointestinal and pancreatic primaries. Despite recent therapeutic achievements, thus, systemic treatment options remain limited. In this review we will discuss the state-of-the-art targeted therapies in the field of NETs, and also future perspectives of novel therapeutic drugs or strategies in clinical development, including recently presented results from randomized trials of yet unapproved antiangiogenic agents (i.e., pazopanib, surufatinib and axitinib), PRRT including both approved radiopharmaceuticals (177Lu-Oxodotreotide) and others in development (177Lu-Edotreotide, 177Lu-Satoreotide Tetraxetan), immunotherapy and other innovative targeted strategies (antibody-drug conjugates, bites,…) that shall soon improve the landscape of personalized treatment options in NET patients.

Somatostatin Receptor Imaging PET in Neuroendocrine Neoplasm

PET/computed tomography (CT) imaging increasingly is used in neuroendocrine neoplasms (NENs) for diagnosis, staging, monitoring, prognostication, and choosing treatment. Somatostatin PET analog tracers have added to the specificity by obtaining higher affinity to somatostatin receptors with ⁶⁸Ga-labeled or ⁶⁴Cu-labeled DOTA peptides compared with single-photon emission CT imaging isotopes. PET uptake correlates to tumor grade and is an essential part of theranostics with peptide receptor radionuclide treatment. This article focuses on the literature on head-to-head studies and meta-analyses of different combinations of peptide agonists and a few antagonists. Overall, the published data support the diagnostic capability of PET/CT imaging in NENs.

Synthesis, preclinical evaluation, and a pilot clinical imaging study of [18F]AlF-NOTA-JR11 for neuroendocrine neoplasms compared with [68Ga]Ga-DOTA-TATE

PURPOSE

A [¹⁸F]AlF-labeled somatostatin receptor (SSTR) antagonist was developed for imaging of neuroendocrine neoplasms (NENs), evaluated and compared with [⁶⁸Ga]Ga-DOTA-TATE.

METHOD

[¹⁸F]AlF-NOTA-JR11 was synthesized manually and qualified with high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). The cellular uptake, internalization, and saturation binding were performed with HEK293-SSTR2 cells. Biodistribution and micro-PET imaging were carried out with HEK293-SSTR2 tumor-bearing mice. [¹⁸F]AlF-NOTA-JR11 PET/MR imaging and [⁶⁸Ga]Ga-DOTA-TATE PET/CT were performed with ten patients of NEN at 50~60 min post-injection (p.i.). Normal organ biodistribution and tumor detectability were evaluated.

RESULT

[¹⁸F]AlF-NOTA-JR11(24~36 GBq/μmol) was prepared within 30 min and 51.35 ± 3.30% (n > 10)of radiochemical yield. The radiochemical purity was 98.74 ± 1.24% (n > 10). Two stereoisomers were found and confirmed by LC-MS. The cellular uptake of [¹⁸F]AlF-NOTA-JR11 and [⁶⁸Ga]Ga-DOTA-TATE were 4.50 ± 0.31 and 4.50 ± 0.13 %AD/10⁵ cells at 30 min, and the internalization at 37 °C of [¹⁸F]AlF-NOTA-JR11 (5.47 ± 0.32% at 60 min) was significantly lower than [⁶⁸Ga]Ga-DOTA-TATE (66.89 ± 1.62% at 60 min). The affinity of [¹⁸F]AlF-NOTA-JR11 (K_d = 11.59 ± 1.31 nM) was slightly lower than [⁶⁸Ga]Ga-DOTA-TATE (K_d = 7.36 ± 1.02 nM); [¹⁸F]AlF-NOTA-JR11 showed high uptake in tumor (9.02 ± 0.92 %ID/g at 60 min p.i.) which can be blocked by 50 μg of NOTA-JR11 (3.40 ± 1.64 %ID/g at 60 min p.i.); the result was coincident with micro-PET imaging. Imaging study of NEN patients showed that more lesions were found only by [¹⁸F]AlF-NOTA-JR11 (n = 67 vs. 1 only by [⁶⁸Ga]Ga-DOTA-TATE), and the uptakes of [¹⁸F]AlF-NOTA-JR11 in majority normal organs were significantly lower than [⁶⁸Ga]Ga-DOTA-TATE. The target to nontarget of maximum of standard uptake value (SUVmax) of [¹⁸F]AlF-NOTA-JR11 in liver lesions were significantly higher than those of [⁶⁸Ga]Ga-DOTA-TATE.

CONCLUSION

Qualitied [¹⁸F]AlF-NOTA-JR11 is prepared conveniently with reasonable yield, and it can bind SSTR2 specifically with high affinity. Excellent imaging capability of [¹⁸F]AlF-NOTA-JR11 for NENs is superior to [⁶⁸Ga]Ga-DOTA-TATE, especially in digestive system. It has a great potential for imaging of NENs.

Knowns and unknowns of bone metastases in patients with neuroendocrine neoplasms: A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aimed to develop an evidence-based summary of current knowledge of bone metastases (BMs) in neuroendocrine neoplasms (NENs), inform diagnosis and treatment and standardise management between institutions.

METHODS

PubMed, Medline, EMBASE and meeting proceedings were searched for eligible studies reporting data on patients with BMs and NENs of any grade of differentiation and site; poorly-differentiated large/small cell lung cancer were excluded. Data were extracted and analysed using STATA v.12. Meta-analysis of proportions for calculation of estimated pooled prevalence of BM and calculation of weighted pooled frequency and weighted pooled mean for other variables of interest was performed .

RESULTS

A total of 149 studies met the eligibility criteria. Pooled prevalence of BMs was 18.4% (95% CI 15.4-21.5). BMs were mainly metachronous with initial diagnosis of NEN (61.2%) and predominantly osteoblastic; around 61% were multifocal, with a predisposition in axial skeleton. PET/CT seemed to provide (together with MRI) the highest sensitivity and specificity for BM detection. Almost half of patients (46.4%) reported BM-related symptoms: pain (66%) and skeletal-related events (SREs, fracture/spinal cord compression) (26.2%; weightedweighted mean time-to-SRE 9.9 months). Management of BMs was multimodal [bisphosphonates and bone-modifying agents (45.2%), external beam radiotherapy (34.9%), surgery (14.8%)] and supported by little evidence. Overall survival (OS) from the time of diagnosis of BMs was long [weighted mean 50.9 months (95% CI 40.0-61.9)]. Patients with BMs had shorter OS [48.8 months (95% CI 37.9-59.6)] compared to patients without BMs [87.4 months (95% CI 74.9-100.0); p = 0.001]. Poor performance status and BM-related symptoms were also associated with worse OS.

CONCLUSIONS

BMs in patients with NENs remain underdiagnosed and undertreated. Recommendations for management of BMs derived from current knowledge are provided. Prospective studies to inform management are required.

177Lu-DOTA-EB-TATE, a Radiolabeled Analogue of Somatostatin Receptor Type 2, for the Imaging and Treatment of Thyroid Cancer

PURPOSE

The goal of this study was to analyze the role of somatostatin receptor type 2 (SSTR2) as a molecular target for the imaging and treatment of thyroid cancer through analysis of SSTR2 expression and its epigenetic modulation and testing tumor uptake of different radiolabeled SSTR2 analogues.

EXPERIMENTAL DESIGN

We analyzed SSTR2 expression by immunostaining of 92 thyroid cancer tissue samples and quantified standard uptake values (SUV_max) of SSTR2 analogue, ⁶⁸Ga-DOTA-TATE, by PET/CT imaging in 25 patients with metastatic thyroid cancer. We utilized human thyroid cancer cell lines characterized by differential SSTR2 expression (TT, BCPAP, and FTC133) and rat pancreatic cell line (AR42J) with intrinsically high SSTR2 expression for functional in vitro studies. SSTR2-high (AR42J) and SSTR2-low (FTC133) xenograft mouse models were used to test the uptake of radiolabeled SSTR2 analogues and their therapeutic efficacy in vivo.

RESULTS

Thyroid cancer had a higher SSTR2 expression than normal thyroid. Hurthle cell thyroid cancer was characterized by the highest ⁶⁸Ga-DOTA-TATE uptake [median SUV_max, 16.5 (7.9-29)] than other types of thyroid cancers. In vivo studies demonstrated that radiolabeled DOTA-EB-TATE is characterized by significantly higher tumor uptake than DOTA-TATE (P < 0.001) and DOTA-JR11 (P < 0.001). Treatment with ¹⁷⁷Lu-DOTA-EB-TATE extended survival and reduced tumor size in a mouse model characterized by high somatostatin (SST) analogues uptake (SUV_max, 15.16 ± 4.34), but had no effects in a model with low SST analogues uptake (SUV_max, 4.8 ± 0.27).

CONCLUSIONS

A novel SST analogue, ¹⁷⁷Lu-DOTA-EB-TATE, has the potential to be translated from bench to bedside for the targeted therapy of patients characterized by high uptake of SST analogues in metastatic lesions.

Role of PET/CT and Therapy Management of Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine neoplasms (panNENs) are heterogeneous neoplasms with neuroendocrine differentiation that show peculiar clinical and histomorphological features, with variable prognosis. In recent years, advances in knowledge regarding the pathophysiology and heterogeneous clinical presentation, as well as the availability of different diagnostic procedures for panNEN diagnosis and novel therapeutic options for patient clinical management, has led to the recognition of the need for an active multidisciplinary discussion for optimal patient care. Molecular imaging with positron emission tomography/computed tomography (PET/CT) has become indispensable for the management of panNENs. Several PET radiopharmaceuticals can be used to characterize either panNEN receptor expression or metabolism. The aim of this review is to offer an overview of all the currently used radiopharmaceuticals and of the new upcoming tracers for pancreatic neuroendocrine tumors (panNETs), and their clinical impact on therapy management. [68Ga]Ga-DOTA-peptide PET/CT (SSA-PET/CT) has high sensitivity, specificity, and accuracy and is recommended for the staging and restaging of any non-insulinoma well-differentiated panNEN cases to carry out detection of unknown primary tumor sites or early relapse and for evaluation of in vivo somatostatin receptors expression (SRE) to select patient candidates for peptide receptor radiometabolic treatment (PRRT) with 90Y or 177Lu and/or cold analogs. SSA-PET/CT also has a strong impact on clinical management, leading to a change in treatment in approximately a third of the cases. Its role for treatment response assessment is still under debate due to the lack of standardized criteria, even though some semiquantitative parameters seem to be able to predict response. [18F]FDG PET/CT generally shows low sensitivity in small growing and well-differentiated neuroendocrine tumors (NET; G1 and G2), while it is of utmost importance in the evaluation and management of high-grade NENs and also provides important prognostic information. When positive, [18F]FDG PET/CT impacts therapeutical management, indicating the need for a more aggressive treatment regime. Although FDG positivity does not exclude the patient from PRRT, several studies have demonstrated that it is certainly useful to predict response, even in this setting. The role of [18F]FDOPA for the study of panNET is limited by physiological uptake in the pancreas and is therefore not recommended. Moreover, it provides no information on SRE that has crucial clinical management relevance. Early acquisition of the abdomen and premedication with carbidopa may be useful to increase the accuracy, but further studies are needed to clarify its utility. GLP-1R agonists, such as exendin-4, are particularly useful for benign insulinoma detection, but their accuracy decreases in the case of malignant insulinomas. Being a whole-body imaging technique, exendin-PET/CT gives important preoperative information on tumor size and localization, which is fundamental for surgical planning as resection (enucleation of the lesion or partial pancreatic resection) is the only curative treatment. New upcoming tracers are under study, such as promising SSTR antagonists, which show a favorable biodistribution and higher tumor-to-background ratio that increases tumor detection, especially in the liver. [68Ga]pentixafor, an in vivo marker of CXCR4 expression associated with the behavior of more aggressive tumors, seems to only play a limited role in detecting well-differentiated NET since there is an inverse expression of SSTR2 and CXCR4 in G1 to G3 NETs with an elevation in CXCR4 and a decrease in SSTR2 expression with increasing grade. Other tracers, such as [68Ga]Ga-PSMA, [68Ga]Ga-DATA-TOC, [18F]SiTATE, and [18F]AlF-OC, are also under investigation.

Advances in Molecular Imaging and Radionuclide Therapy of Neuroendocrine Tumors

Neuroendocrine neoplasms make up a heterogeneous group of tumors with inter-patient and intra-patient variabilities. Molecular imaging can help to identify and characterize neuroendocrine tumors (NETs). Furthermore, imaging and treatment with novel theranostics agents offers a new, tailored approach to managing NETs. Recent advances in the management of NETs aim to enhance the effectiveness of targeted treatment with either modifications of known substances or the development of new substances with better targeting features. There have been several attempts to increase the detectability of NET lesions via positron emission tomography (PET) imaging and improvements in pretreatment planning using dosimetry. Especially notable is PET imaging with the radionuclide Copper-64. Increasing interest is also being paid to theranostics of grade 3 and purely differentiated NETs, for example, via targeting of the C-X-C motif chemokine receptor 4 (CXCR4). The aim of this review is to summarize the most relevant recent studies, which present promising new agents in molecular imaging and therapy for NETs, novel combination therapies and new applications of existing molecular imaging modalities in nuclear medicine.