Peptide receptor therapies in neuroendocrine tumors

Appendiceal Neuroendocrine Neoplasms: A Comprehensive Review

ABSTRACT

Appendiceal neuroendocrine neoplasm (NEN) is the most common adult appendiceal malignant tumor, constituting 16% of gastrointestinal NENs. They are versatile tumors with varying morphology, immunohistochemistry, secretory properties, and cancer genomics. They are slow growing and clinically silent, to begin with, or present with features of nonspecific vague abdominal pain. Most acute presentations are attributed clinically to appendicitis, with most cases detected incidentally on pathology after an appendectomy. Approximately 40% of them present clinically with features of hormonal excess, which is likened to the functional secretory nature of their parent cell of origin. The symptoms of carcinoid syndrome render their presence clinically evident. However, slow growing and symptomatically silent in its initial stages, high-grade neuroendocrine tumors and neuroendocrine carcinomas of the appendix are aggressive and usually have hepatic and lymph node metastasis at presentation. This review article focuses on imaging characteristics, World Health Organization histopathological classification and grading, American Joint Committee on Cancer/Union or International Cancer Control, European Neuroendocrine Tumor Society staging, European Neuroendocrine Tumor Society standardized guidelines for reporting, data interpretation, early-stage management protocols, and advanced-stage appendiceal NENs. Guidelines are also set for the follow-up and reassessment. The role of targeted radiotherapy, chemotherapy, and high-dose somatostatin analogs in treating advanced disease are discussed, along with types of ablative therapies and liver transplantation for tumor recurrence. The search for newer location-specific biomarkers in NEN is also summarized. Regarding the varying aggressiveness of the tumor, there is a scope for research in the field, with plenty of data yet to be discovered.

Comparison of [18F]DOPA and [68Ga]DOTA-TOC as a PET imaging tracer before peptide receptor radionuclide therapy

Background

In treatment of neuroendocrine neoplasms (NENs), confirmation of somatostatin receptor expression with 68Ga-DOTA somatostatin analogues is mandatory to determine eligibility for peptide receptor radionuclide therapy (PRRT). [18F]DOPA can detect additional lesions compared to [68Ga]DOTA-TOC. The aim of this study was to explore differences in tumour detection of both tracers and their relevance for selecting patients for PRRT. We retrospectively studied eight patients with NENs who underwent both [68Ga]DOTA-TOC and carbidopa-enhanced [18F]DOPA PET/CT, before first-time PRRT with [177Lu]DOTA-TATE. Tracer order was influenced due to stock availability or to detect suspected metastases with a second tracer. On CT, disease control was defined as a lesion showing complete response, partial response, or stable disease, according to RECIST 1.1. criteria.

Results

Seven patients with in total 89 lesions completed four infusions of 7.4 GBq [177Lu]DOTA-TATE, one patient received only two cycles. Before treatment, [18F]DOPA PET/CT detected significantly more lesions than [68Ga]DOTA-TOC PET/CT (79 vs. 62, p < .001). After treatment, no difference in number of lesions with disease control was found for [18F]DOPA-only (5/27) and [68Ga]DOTA-TOC-only lesions (4/10, p = .25). [18F]DOPA detected more liver metastases (24/27) compared to [68Ga]DOTA-TOC (7/10, p = .006). Six patients showed inpatient heterogeneity in treatment response between [18F]DOPA-only and [68Ga]DOTA-TOC-only lesions.

Conclusions

Response to PRRT with [177Lu]DOTA-TATE was comparable for both [68Ga]DOTA-TOC- and [18F]DOPA-only NEN lesions. [18F]DOPA may be capable of predicting response to PRRT while finding more lesions compared to [68Ga]DOTA-TOC, although these additional lesions are often small of size and undetected by diagnostic CT.

Early Complications of Radioisotope Therapy with Lutetium-177 and Yttrium-90 in Patients with Neuroendocrine Neoplasms-A Preliminary Study

Neuroendocrine neoplasms (NENs) constitute a heterogenous group of tumors originating from neuroendocrine cells scattered throughout the body. Peptide Receptor Radionuclide Therapy (PRRT) is a treatment of choice of unresectable metastasized progressive and well-differentiated NENs. The aim of the study was to assess early bone marrow and kidney injury after administration of Lutetium-177 or Lutetium-177 combined with Yttrium-90. Thirty-one patients received treatment with [¹⁷⁷Lu]Lu-DOTATATE with the activity of 7.4 GBq. Eleven patients received tandem treatment with [⁹⁰Y]Y-DOTATATE with the activity of 1.85 GBq + [¹⁷⁷Lu]Lu-DOTATATE with the activity of 1.85 GBq. After PRRT a significant decrease in leukocyte, neutrophil, and lymphocyte counts was noted. Tandem treatment demonstrated a more marked decrease in white blood cell count compared to Lutetium-177 therapy only. Conversely, no significant influence on glomerular filtration was found in this assessment. However, PRRT triggered acute renal tubule dysfunction, regardless of the treatment type. Regarding the acute complications, PRRT appeared to be a safe modality in the treatment of patients with NEN.

Synergism of Checkpoint Inhibitors and Peptide Receptor Radionuclide Therapy in the Treatment of Pituitary Carcinoma

Context

Aggressive pituitary tumors that have progressed following temozolomide have limited treatment options. Peptide receptor radionuclide therapy and immunotherapy may have a complementary role in the management of these tumors.

Methods

We provide follow-up data on a previously reported patient with a hypermutated recurrent tumor. The patient in this report provided written informed consent for tumor sequencing and review of medical records on an institutional review board–approved research protocol (NCT01775072).

Results

This patient with a corticotroph pituitary carcinoma with alkylator-induced somatic hypermutation has remained on treatment with ipilimumab and nivolumab for 3.5 years and remains clinically well. After an initial partial response to checkpoint inhibitors, she has had several recurrences that have undergone immunoediting of subclonal mutations, which have been effectively treated with continuation of immunotherapy, surgery, external beam radiation, and ¹⁷⁷Lu-DOTATATE. Following external beam radiotherapy (RT), she had radiographic evidence of an abscopal response at a distant site of disease suggesting a synergism between checkpoint inhibitors and RT. Following treatment with ¹⁷⁷Lu-DOTATATE, the patient had a partial response with a 61% reduction in volume of the target lesion.

Conclusion

In patients with aggressive pituitary tumors, treatment with checkpoint inhibitors may trigger an abscopal response from RT. With appropriate selection, an additional efficacious treatment, ¹⁷⁷Lu-DOTATATE, may be available for a limited number of patients with aggressive pituitary tumors, including patients who have progressed on temozolomide and exhibit increased somatostatin receptor expression on ⁶⁸Ga-DOTATATE positron emission tomography.

90Y/177Lu-DOTATOC: From Preclinical Studies to Application in Humans

The PRRT (Peptide Receptor Radionuclide Therapy) is a promising modality treatment for patients with inoperable or metastatic neuroendocrine tumors (NETs). Progression-free survival (PFS) and overall survival (OS) of these patients are favorably comparable with standard therapies. The protagonist in this type of therapy is a somatostatin-modified peptide fragment ([Tyr3] octreotide), equipped with a specific chelating system (DOTA) capable of creating a stable bond with β-emitting radionuclides, such as yttrium-90 and lutetium-177. In this review, covering twenty five years of literature, we describe the characteristics and performances of the two most used therapeutic radiopharmaceuticals for the NETs radio-treatment: [90Y]Y-DOTATOC and [177Lu]Lu-DOTATOC taking this opportunity to retrace the most significant results that have determined their success, promoting them from preclinical studies to application in humans.

[18F]FDG-PET/CT and long-term responses to everolimus in advanced neuroendocrine neoplasia

PURPOSE

This study aims to identify in patients with neuroendocrine neoplasia (NEN) the potential correlation between FDG-PET findings and responses to everolimus therapy to identify predictors of long-term efficacy.

METHODS

Retrospective analysis of patients with sporadic, advanced, progressive NEN treated with everolimus was performed based on the available data on FDG-PET patients obtained before commencing therapy. Data are expressed as the median (25-75th IQR). Risk factor analysis and survival analysis were performed by logistic regression and Cox proportional hazard regression and the determination of Kaplan-Meier curves, as appropriate.

RESULTS

Sixty-six patients were evaluated (NET G1 19.7%, NET G2 75.7%, and NET G3 4.6%), including 45.4% with positive FDG-PET findings. Overall, disease stabilization and a partial response were achieved for 71.2% and 6% of patients, respectively. A long-term response (> 24 months) was observed in 33% of patients. Ki67 was the only predictor of tumor progression (p = 0.03). No significant difference in clinical outcomes was observed between patients with positive or negative FDG-PET findings (median PFS was 24 months and 18 months, respectively, p = 0.337; the disease control rate was 83.3% and 70%, respectively, p = 0.245).

CONCLUSIONS

Everolimus is a valid therapeutic option for advanced, progressive, well-differentiated NEN, even in patients with positive FDG-PET findings.

The Safety and Efficacy of the Repeated PRRT with [90Y]Y/[177Lu]Lu-DOTATATE in Patients with NET

PURPOSE

The peptide receptor radionuclide therapy (PRRT) is a treatment option for patients with disseminated, inoperable G1 and G2 neuroendocrine tumours (NETs). The study aims to evaluate the safety, efficacy, and progression-free survival (PFS) of patients after retreatment (R-PRRT) and re-retreatment (RR-PRRT) with tandem isotopes [⁹⁰Y]Y/[¹⁷⁷Lu]Lu-DOTATATE. Material and Methods. Out of 99 treated patients with G1 and G2 NETs, 26 were included in the study and treated with the repeated PRRT (with 5 undergoing the re-repeated PRRT treatment) after an initial positive response to four PRRT cycles and later progression of the disease. [⁶⁸Ga]Ga-DOTATATE PET/CT and CT/MRI procedures were performed before and after the treatment. Patients were treated with [⁹⁰Y]Y/[¹⁷⁷Lu]Lu-DOTATATE (1 : 1) with mixed amino acid infusion for kidney protection. Toxicity was evaluated using the CTCAE 3.0 criteria.

RESULTS

The median follow-up was 88 months (the range: 42-164). The median cumulative administered activity was 22.2 GBq (the range: 17.8-30.7 GBq). Myelodysplastic syndrome occurred in one patient (3.8%), and grade 4 renal toxicity was also detected in one patient (3.8%). No other cases of grade 3 or 4 bone marrow and renal toxicity were observed. The median PFS rate was 31 months after the PRRT and 23 months following the R-PRRT. The OS rate from the diagnosis (OS-d) was 109 months and from the start of the PRRT (OS-t)-92.4 months. During the restaging, 3-6 months after the PRRT, PR, SD, and PD were observed in 19.2%, 80.8%, and 0% of the patients, respectively. After the R-PRRT, PR, SD, and PD were observed in 50%, 42.3%, and 7.7% of the patients, respectively.

CONCLUSIONS

The repeated therapy with [⁹⁰Y]Y/[¹⁷⁷Lu]Lu-DOTATATE is safe and effective for patients with disseminated, inoperable G1 and G2 neuroendocrine tumours.

Evolving role of biomaterials in diagnostic and therapeutic radiation oncology

Radiation therapy to treat cancer has evolved significantly since the discovery of x-rays. Yet, radiation therapy still has room for improvement in reducing side effects and improving control of cancer. Safer and more effective delivery of radiation has led us to novel techniques and use of biomaterials. Biomaterials in combination with radiation and chemotherapy have started to appear in pre-clinical explorations and clinical applications, with many more on the horizon. Biomaterials have revolutionized the field of diagnostic imaging, and now are being cultivated into the field of theranostics, combination therapy, and tissue protection. This review summarizes recent development of biomaterials in radiation therapy in several application areas.

99mTc-EDDA/HYNIC-TOC is a New Opportunity in Neuroendocrine Tumors of the Lung (and in other Malignant and Benign Pulmonary Diseases)

Neuroendocrine tumors (NETs) consist of a relatively rare spectrum of malignancies that can arise from neuroendocrine cells; lung NETs (L-NETs) represent about 25% of primary lung neoplasm and 10% of all carcinoid tumors. Diagnostic algorithm usually takes into consideration chest Xray, contrast-enhanced CT and MRI. Nuclear medicine plays a crucial role in the detection and correct assessment of neoplastic functional status as it provides in vivo metabolic data related to the overexpression of Somatostatin Receptors (SSTRs) and also predicting response to peptide receptor radionuclide therapy (PRRT). 111In-Pentreotide (Octreoscan®) is commercially available for imaging of neuroendocrine tumors, their metastases and the management of patients with NETs. More recently, 99mTc-EDDA/HYNIC-TOC(Tektrotyd®) was introduced into the market and its use has been approved for imaging of patients with L-NETs and other SSTR-positive tumors. 99mTc-EDDA/HYNIC-TOC could also represent a good alternative to 68Ga-DOTA-peptides (DOTA-TOC, DOTA-NOC, DOTATATE) in hospitals or centers where PET/CT or 68Ge/68Ga generators are not available. When compared to 111In-Pentetreotide, Tektrotyd® showed slightly higher sensitivity, in the presence of higher imaging quality and lower radiation exposure for patients. Interesting perspectives depending on the kinetic analysis allowed by Tektrotyd® may be obtained in differential diagnosis of non-small cells lung cancer (NSCLC) versus small cells lung cancer (SCLC) and NETs. An interesting perspective could be also associated with a surgery radio-guided by Tektrotyd® in operable lung tumors, including either NETs and NSCLC.

Physiopathological Premises to Nuclear Medicine Imaging of Pancreatic Neuroendocrine Tumours

Background:

Pancreatic Neuroendocrine Tumors (P-NETs) are a challenge in terms of both diagnosis and therapy; morphological studies need to be frequently implemented with nonstandard techniques such as Endoscopic Ultrasounds, Dynamic CT, and functional Magnetic Resonance.

Discussion:

The role of nuclear medicine, being scarcely sensitive F-18 Fluorodeoxyglucose, is mainly based on the over-expression of Somatostatin Receptors (SSTR) on neuroendocrine tumor cells surface. Therefore, SSTR can be used as a target for both diagnosis, using radiotracers labeled with gamma or positron emitters, and therapy. SSTRs subtypes are capable of homo and heterodimerization in specific combinations that alter both the response to ligand activation and receptor internalization.

Conclusion:

Although agonists usually provide efficient internalization, also somatostatin antagonists (SS-ANTs) could be used for imaging and therapy. Peptide Receptor Radionuclide Therapy (PRRT) represents the most successful option for targeted therapy. The theranostic model based on SSTR does not work in insulinoma, in which different radiotracers such as F-18 FluoroDOPA or tracers for the glucagon-like peptide-1 receptor have to be preferred.

Surgical resection of neuroendocrine tumors of the pancreas (pNETs) by minimally invasive surgery: the laparoscopic approach

Neuroendocrine tumors of the pancreas (pNETs) are a rare group of neoplasms that originate from the endocrine portion of the pancreas. Tumors that either secrete or do not secrete compounds, resulting in symptoms, can be classified as functioning and non-functioning pNETs, respectively. The prevalence of such tumors has recently increased due to the use of more sensitive imaging techniques, such as multidetector computed tomography, magnetic resonance imaging and endoscopic ultrasound. The biological behavior of pNETs varies widely from indolent, well-differentiated tumors to those that are far more aggressive. The most effective and radical treatment for pNETs is surgical resection. Over the last decade, minimally invasive surgery has been increasingly used in pancreatectomy, with laparoscopic pancreatic surgery (LPS) emerging as an alternative to open pancreatic surgery (OPS) in patients with pNETs. Non-comparative studies have shown that LPS is safe and effective. In well-selected groups of patients with pancreatic lesions, LPS was found to results in good perioperative outcomes, including reduced intraoperative blood loss, postoperative pain, time to recovery, and length of hospital stay. Despite the encouraging results of studies from highly specialized centers with extensive experience, no randomized trials to date have conclusively validated these findings. Indications for minimally invasive LPS for patients with pNETs remain unclear. This review presents the current state of LPS for pNETs.

Lu-177-Based Peptide Receptor Radionuclide Therapy for Advanced Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is a systemic cytotoxic radiation therapy using a compound of β-emitting radionuclide chelated to a peptide for the treatment of tumor with overexpressed specific cell receptor such as somatostatin receptor subtype 2 (SSTR2) of neuroendocrine tumor (NET). Surgical resection should be performed for the curative treatment for NETs when it is feasible; however, a multi-disciplinary approach is needed when locally advanced or metastasized disease. PRRT with lutetium-177 (Lu-177)-labeled somatostatin analogues, as a new treatment modality targeting metastatic or inoperable NETs expressing the SSTR2, have been developed and successfully used for the past two decades. As Lu-177 emits both β- and γ-radiation, it has the ability as a theragnostic agent for NETs compared with only β-emitting yttrium-90 labeled PRRT. Several recent studies reported that Lu-177 gave an overall positive response and improved the patients' quality of life. To fully exploit its potential, large comparative studies are needed for the assessment of distinct efficacies of Lu-177 labeled PRRT. Additionally, for extending the indications and developing new regimens of Lu-177-based PRRT, more dedicated clinical research is required.

The role of peptide receptor radionuclide therapy in advanced/metastatic thoracic neuroendocrine tumors

Bronchopulmonary (BP) neuroendocrine tumors (NETs) comprise a spectrum of tumors that develop from respiratory neuroendocrine cells and represent ~20% of all lung neoplasia and ~30% of all NETs. The only curative treatment is surgical resection. For well-differentiated forms (typical and atypical carcinoids), medical therapy ranges from bioactive agents (e.g., somatostatin analogs), to biotherapy (e.g., everolimus), standard chemotherapy and peptide receptor radionuclide therapy (PRRT). PRRT with radiolabeled somatostatin analogs is an innovative treatment for inoperable or metastasized, well/moderately differentiated, NET. Initially developed for gastroenteropancreatic tumors, it is also used in BP-NET because these tumors express the target receptor. Two decades of clinical trials with either ⁹⁰Y-octreotide or ¹⁷⁷Lu-octreotate, have demonstrated the efficacy of PRRT, as measured by tumor response, symptom relief and quality of life (QoL) improvement. PRRT with ⁹⁰Y- and ¹⁷⁷Lu-peptides is generally well-tolerated and adverse events (kidney and bone marrow) are modest. The paper illustrates the history, technique and results of this treatment in the few dedicated studies and the many BP NET cases embedded within larger NET series. The limitations of the present body of information are addressed, and the future perspectives, in terms of prospective studies required to define the position of PRRT in the therapeutic algorithm of BP-NETs and the need for predictive molecular biomarkers to guide future studies, are discussed.

Theranostics of Neuroendocrine Tumors

Somatostatin receptor positron emission tomography/computed tomography using ⁶⁸Ga-labeled somatostatin analogs is the mainstay for the evaluation of receptor status in neuroendocrine tumors (NETs). This translates towards better therapy options, with increasing evidence of peptide receptor radionuclide therapy (PRRT) as the treatment of choice for advanced or progressive NETs. There are benefits in progression-free and overall survival as well as a significant improvement in clinical condition. In patients with progressive NETs, fractionated, personalized PRRT results in good therapeutic responses with no significant severe hematological and/or renal toxicity, thus improving quality of life.

Evaluation of somatostatin and nucleolin receptors for therapeutic delivery in non-small cell lung cancer stem cells applying the somatostatin-analog DOTATATE and the nucleolin-targeting aptamer AS1411

Cancer stem cells represent the putative tumor-driving subpopulation thought to account for drug resistance, relapse, and metastatic spread of epithelial and other cancer types. Accordingly, cell surface markers for therapeutic delivery to cancer stem cells are subject of intense research. Somatostatin receptor 2 and nucleolin are known to be overexpressed by various cancer types, which have elicited comprehensive efforts to explore their therapeutic utilization. Here, we evaluated somatostatin receptor 2 targeting and nucleolin targeting for therapeutic delivery to cancer stem cells from lung cancer. Nucleolin is expressed highly but not selectively, while somatostatin receptor 2 is expressed selectively but not highly by cancer cells. The non-small cell lung cancer cell lines A549 and H1299, displayed average levels of both surface molecules as judged based on analysis of a larger cell line panel. H1299 compared to A549 cells showed significantly elevated sphere-forming capacity, indicating higher cancer stem cell content, thus qualifying as suitable test system. Nucleolin-targeting 57Co-DOTA-AS1411 aptamer showed efficient internalization by cancer cells and, remarkably, at even higher efficiency by cancer stem cells. In contrast, somatostatin receptor 2 expression levels were not sufficiently high in H1299 cells to confer efficient uptake by either non-cancer stem cells or cancer stem cells. The data provides indication that the nucleolin-targeting AS1411 aptamer might be used for therapeutic delivery to non-small cell lung cancer stem cells.

Advances in the Diagnosis of Neuroendocrine Neoplasms

Somatostatin receptor PET/CT using (68)Ga-labeled somatostatin analogs, is a mainstay for the evaluation of the somatostatin receptor status in neuroendocrine neoplasms. In addition, the assessment of glucose metabolism by (18)F-FDG PET/CT at diagnosis can overcome probable shortcomings of histopathologic grading. This offers a systematic theranostic approach for the management of neuroendocrine neoplasms, that is, patient selection for the appropriate treatment-surgery, somatostatin analogs, peptide receptor radionuclide therapy, targeted therapies like everolimus and sunitinib, or chemotherapy-and also for therapy response monitoring. Novel targets, for example, the chemokine receptor CXCR4 in higher-grade tumors and glucagon like peptide-1 receptor in insulinomas, appear promising for imaging. Scandium-44 and Copper-64, especially on account of their longer half-life (for pretherapeutic dosimetry) and cyclotron production (which favors mass production), might be the potential alternatives to (68)Ga for PET/CT imaging. The future of molecular imaging lies in Radiomics, that is, qualitative and quantitative characterization of tumor phenotypes in correlation with tumor genomics and proteomics, for a personalized cancer management.

Targeted Radionuclide Therapy: An Evolution Toward Precision Cancer Treatment

OBJECTIVE

This article reviews recent developments in targeted radionuclide therapy (TRT) approaches directed to malignant liver lesions, bone metastases, neuroendocrine tumors, and castrate-resistant metastatic prostate cancer and discusses challenges and opportunities in this field.

CONCLUSION

TRT has been employed since the first radioiodine thyroid treatment almost 75 years ago. Progress in the understanding of the complex underlying biology of cancer and advances in radiochemistry science, multimodal imaging techniques including the concept of "see and treat" within the framework of theranostics, and universal traction with the notion of precision medicine have all contributed to a resurgence of TRT.

Is there still a role for the hepatic locoregional treatment of metastatic neuroendocrine tumors in the era of systemic targeted therapies?

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) frequently present with distant metastases at the time of diagnosis and the liver is the most frequent site of spreading. The early identification of metastatic disease represents a major prognostic factor for GEP-NENs patients. Radical surgical resection, which is feasible for a minority of patients, is considered the only curative option, while the best management for patients with unresectable liver metastases is still being debated. In the last few years, a number of locoregional and systemic treatments has become available for GEP-NEN patients metastatic to the liver. However, to date only a few prospective studies have compared those therapies and the optimal management option is based on clinical judgement. Additionally, locoregional treatments appear feasible and safe for disease control for patients with limited liver involvement and effective in symptoms control for patients with diffuse liver metastases. Considering the lack of randomized controlled trials comparing the locoregional treatments of liver metastatic NEN patients, clinical judgment remains key to set the most appropriate therapeutic pathway. Prospective data may ultimately lead to more personalized and optimized treatments. The present review analyzes all the locoregional therapy modalities (i.e., surgery, ablative treatments and transarterial approach) and aims to provide clinicians with a useful algorithm to best treat GEP-NEN patients metastatic to the liver.

Radiolabeled Somatostatin Analogue Therapy Of Gastroenteropancreatic Cancer

Peptide receptor radionuclide therapy (PRRT) has been utilized for more than two decades and has been accepted as an effective therapeutic modality in the treatment of inoperable or metastatic gastroenteropancreatic neuroendocrine neoplasms (NENs) or neuroendocrine tumors (NETs). The two most commonly used radiopeptides for PRRT, (90)Y-octreotide and (177)Lu-octreotate, produce disease-control rates of 68%-94%, with progression-free survival rates that compare favorably with chemotherapy, somatostatin analogues, and newer targeted therapies. In addition, biochemical and symptomatic responses are commonly observed. In general, PRRT is well tolerated with only low to moderate toxicity in most individuals. In line with the need to place PRRT in the therapeutic sequence of gastroenteropancreatic NENs, a recently sponsored phase III randomized trial in small intestine NENs treated with (177)Lu-octreotate vs high-dose octreotide long-acting release demonstrated that (177)Lu-octreotate significantly improved progression-free survival. Other strategies that are presently being developed include combinations with targeted therapies or chemotherapy, intra-arterial PRRT, and salvage treatments. Sophisticated molecular tools need to be incorporated into the management strategy to more effectively define therapeutic efficacy and for an early identification of adverse events. The strategy of randomized controlled trials is a key issue to standardize the treatment and establish the position of PRRT in the therapeutic algorithm of NENs.

Effectiveness of radiolabelled somatostatin analogues (90Y-DOTATOC and 177Lu-DOTATATE) in patients with metastatic neuroendocrine tumours: a single centre experience in Mexico

OBJECTIVE

To determine the effectiveness of therapy with the radiolabelled somatostatin analogues, ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE, in the treatment of metastatic neuroendocrine tumours with progression to first-line treatment.

MATERIAL AND METHODS

A study was conducted on 30 patients diagnosed with neuroendocrine tumours (gastroenteropancreatic, bronchopulmonary, MEN2A, MEN2B, phaeochromocytoma, and paraganglioma) with metastatic disease diagnosed by the pathology department, with progression to first-line treatment, and recruited from December 2014 to February 2016. Efficacy was analysed using computed tomography (CT) according RECIST 1.1 criteria, and the molecular changes using the SUVmax of PET/CT with ⁶⁸Ga-DOTATOC. Safety was carried out with a renal scan with ^99mTc-MAG3.

RESULTS

The 30 patients received a total of 49 cycles ⁹⁰Y-DOTATOC (21 doses) and ¹⁷⁷ Lu-DOTATATE (28 doses), with a mean of 1.5 cycles per patient. Of these, 17 (56.7%) showed a partial morphological response, 22 (73.3%) molecular and biochemical response, and 23 (76.6%) clinical response. One patient died during the median follow-up of 13 months. The median overall survival from diagnosis was 54 months (95% CI; 31.18-76.81), and median progression-free survival was 32 months (95% CI; 15.00-48.99).

CONCLUSION

Therapy with ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE is a promising therapy for patients with well and moderately differentiated neuroendocrine tumours. The efficacy is better the larger the number of cycles administered, inversely proportional to the number of metastases (<10), and is associated with the level of uptake according to the SUVmax by the metastases, regardless of metabolically active tumour volume.

Myeloid neoplasms after chemotherapy and PRRT: myth and reality

Peptide receptor radionuclide therapy (PRRT) with (90)Y-octreotide or (177)Lu-octreotate is an effective treatment for inoperable or metastatic neuroendocrine tumors (NETs), particularly well-differentiated gastroenteropancreatic or bronchopulmonary NETs. PRRT is generally extremely well tolerated, with modest toxicity to target organs, kidney and bone marrow. Nevertheless, a priori concerns regarding long-term effects lead clinicians such as Brieau and coworkers, in this ERC issue, to ascribe to the combination of alkylating agents and PRRT the apparently high occurrence (n=4) of myeloproliferative events (therapy-related myeloid neoplasms (t-MNs)) in a small cohort of 20 progressive, advanced digestive NETs treated with PRRT after chemotherapy. Anecdotal reports of myelotoxic events should be placed in the correct perspective of larger series, where the reported incidence of these events is ~2%, with the aim of promoting a balanced awareness of the issue and unbiased and reasonable overall conclusions. For a comprehensive definition of the issue, we provide an evaluation of the occurrence of t-MN in patients treated with various myelotoxic treatments.

Therapeutic radionuclides in nuclear medicine: current and future prospects

The potential use of radionuclides in therapy has been recognized for many decades. A number of radionuclides, such as iodine-131 ((131)I), phosphorous-32 ((32)P), strontium-90 ((90)Sr), and yttrium-90 ((90)Y), have been used successfully for the treatment of many benign and malignant disorders. Recently, the rapid growth of this branch of nuclear medicine has been stimulated by the introduction of a number of new radionuclides and radiopharmaceuticals for the treatment of metastatic bone pain and neuroendocrine and other malignant or non-malignant tumours. Today, the field of radionuclide therapy is enjoying an exciting phase and is poised for greater growth and development in the coming years. For example, in Asia, the high prevalence of thyroid and liver diseases has prompted many novel developments and clinical trials using targeted radionuclide therapy. This paper reviews the characteristics and clinical applications of the commonly available therapeutic radionuclides, as well as the problems and issues involved in translating novel radionuclides into clinical therapies.

Long-term results of PRRT in advanced bronchopulmonary carcinoid

PURPOSE

Peptide receptor radionuclide therapy (PRRT) for the treatment of neuroendocrine tumours (NET) has been explored for almost two decades, but there are still few trials that have exclusively investigated well-differentiated and moderately differentiated NET arising from the respiratory tree. Thus, the aim of this study was to explore the outcome in patients affected by bronchopulmonary carcinoid (BPC) following PRRT.

METHODS

We retrospectively analysed 114 patients with advanced stage BPC consecutively treated with PRRT at the European Institute of Oncology, Milan, from 1997 to 2012 and followed until October 2014. The objective responses, overall survival (OS) and progression-free survival (PFS) were rated, and three different PRRT protocols ((90)Y-DOTATOC vs. (177)Lu-DOTATATE vs. (90)Y-DOTATOC + (177)Lu-DOTATATE) were compared with regard to their efficacy and tolerability.

RESULTS

The median OS (evaluated in 94 of the 114 patients) was 58.8 months. The median PFS was 28.0 months. The (177)Lu-DOTATATE protocol resulted in the highest 5-year OS (61.4%). Morphological responses (partial responses + minor responses) were obtained in 26.5% of the cohort and were associated with longer OS and PFS. The (90)Y-DOTATOC + (177)Lu-DOTATATE protocol provided the highest response rate (38.1%). Adverse events were mild in the majority of patients. However, haematological toxicity negatively affected survival. No severe (grade 3/4) serum creatinine increase was observed. Patients treated with (90)Y-DOTATOC alone more frequently showed a mild/moderate decrease in renal function. In patients treated with chemotherapy before PRRT had a shorter OS and PFS, and a higher risk of developing nephrotoxicity.

CONCLUSION

In a large cohort of patients with advanced BPC treated in a "real-world" scenario and followed up for a median of 45.1 months (range 2-191 months), PRRT proved to be promising in prolonging survival and delaying disease progression. Despite the potential selection biases, considering the risk-benefit ratio, (177)Lu-DOTATATE monotherapy seems the best option for PRRT. Our results indicate that the use of PRRT in earlier stages of the disease could provide a more favorable outcome.

Metastatic Bone Pain Palliation using (177)Lu-Ethylenediaminetetramethylene Phosphonic Acid

¹⁷⁷Lu-ethylenediaminetetramethylene phosphonic acid (EDTMP) is presently suggested as an excellent bone seeking radionuclide for developing metastatic bone pain (MBP) palliation agent owing to its suitable nuclear decay characteristics. To find the exact dosage and its efficiency, this clinical study was performed on the human being, using ¹⁷⁷Lu-EDTMP for MBP palliation. ¹⁷⁷Lu-EDTMP was prepared by Iran, atomic energy organization. Thirty consecutive patients with determined tumors, incontrollable MBP, and positive bone scan at 4 weeks before the beginning of the study participated in this study in the nuclear medicine ward. ¹⁷⁷Lu-EDTMP in the form of sterile slow IV injection was administered with a dose of 29.6 MBq/kg. Short form of brief pain inventory questionnaire was used to evaluate the efficiency of the intervention. Questionnaires were filled out by an expert nuclear physician every 2 weeks while the cell blood count was also checked every 2 weeks up to 12 weeks for evaluation of bone marrow suppression and hematological toxicity. Furthermore, whole body scan was done at days 1, 3, and 7. Twenty-five patients showed a significant pain relief since 2 weeks after the injection, and continued until the end of the follow up period (12 weeks). There were no significant early complications such as bone marrow suppression, hematological toxicity, and no systemic adverse effects. No complication was observed in renal function. Twenty one patients showed flare phenomenon that was started after the 12.2 ± 1.78 h lasting for 38.4 ± 23.08. Sixteen patients (53%) were completely treated; nine patients (30%) showed a partial response, and five patients (17%) had no response to treatment. Total response to treatment was achieved in 25 patients (83%). At the end of the evaluation, no bone marrow suppression or hematologic toxicity was observed. ¹⁷⁷Lu-EDTMP has shown suitable physical and biological properties with good results in long term bone pain relief for patients with bone metastasis.

Production, quality control, biodistribution assessment and preliminary dose evaluation of [177Lu]-tetra phenyl porphyrin complex as a possible therapeutic agent

<p>Due to interesting therapeutic properties of ¹⁷⁷Lu and tumor avidity of tetraphenyl porphyrins (TPPs), ¹⁷⁷Lu-tetraphenyl porphyrin was developed as a possible therapeutic compound. ¹⁷⁷Lu of 2.6-3 GBq/mg specific activity was obtained by irradiation of natural Lu₂O₃sample with thermal neutron flux of 4 × 10¹³ n.cm^-2.s^-1. Tetraphenyl porphyrin was synthetized and labeled with ¹⁷⁷Lu. Radiochemical purity of the complex was studied using Instant thin layer chromatography (ITLC) method. Stability of the complex was checked in final formulation and human serum for 48 h. The biodistribution of the labeled compound in vital organs of wild-type rats was studied up to 7 d. The absorbed dose of each human organ was calculated by medical internal radiation dose (MIRD) method. A detailed comparative pharmacokinetic study was performed for ¹⁷⁷Lu cation and [¹⁷⁷Lu]-TPP. The complex was prepared with a radiochemical purity: >97±1% and specific activity: 970-1000 MBq/mmol. Biodistribution data and dosimetric results showed that all tissues receive approximately an insignificant absorbed dose due to rapid excretion of the complex through the urinary tract. [¹⁷⁷Lu]-TPP can be an interesting tumor targeting agent due to low liver uptake and very low absorbed dose of approximately 0.036 to the total body of human.</p>

Peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors: current state and future perspectives

The heterogeneous nature of neuroendocrine tumors, their indolent course and lack of therapeutic options for the management of advanced cases – together form the Achilles heel for oncologists. Somatostatin receptor-specific imaging with Ga-68 labeled peptides has provided an opportunity for management of advanced cancers with their therapeutic radionuclide counterparts (Lu-177/Y-90 labeled peptides). Molecular imaging with positron emission tomography/computed tomography is accepted technique for treatment response assessment, since the radiolabels for imaging and therapy are same, thereby depicting accurate response. We have compiled and reviewed our experience of last 8–10 years in the use of these novel radiolabeled peptides in the treatment of neuroendocrine tumors, focusing on the survival, toxicity profiles and the recent advances and improvements.

Yttrium-based therapy for neuroendocrine tumors

Peptide receptor radionuclide therapy with (90)Y-peptides is generally well tolerated. Acute side effects are usually mild; some are related to the coadministration of amino acids and others to the radiopeptide itself. Chronic and permanent effects on target organs, particularly kidneys and bone marrow, are generally mild if necessary precautions are taken. The potential risk to kidney and red marrow limits the amount of radioactivity that may be administered. However, when tumor masses are irradiated with adequate doses, volume reduction may be observed. (90)Y-octreotide has been the most used radiopeptide in the first 8 to 10 years of experience.

Long-term tolerability of PRRT in 807 patients with neuroendocrine tumours: the value and limitations of clinical factors

PURPOSE

Peptide receptor radionuclide therapy (PRRT) with (90)Y and (177)Lu provides objective responses in neuroendocrine tumours, and is well tolerated with moderate toxicity. We aimed to identify clinical parameters predictive of long-term renal and haematological toxicity (myelodysplastic syndrome and acute leukaemia).

METHODS

Of 807 patients studied at IEO-Milan (1997-2013), 793 (98 %) received (177)Lu (278, 34.4 %), (90)Y (358, 44.4 %) or (177)Lu and (90)Y combined (157. 19.5 %), and 14 (2 %) received combinations of PRRT and other agents. Follow-up was 30 months (1-180 months). The parameters evaluated included renal risk factors, bone marrow toxicity and PRRT features. Data analysis included multiple regression, random forest feature selection, and recursive partitioning and regression trees.

RESULTS

Treatment with (90)Y and (90)Y + (177)Lu was more likely to result in nephrotoxicity than treatment with (177)Lu alone (33.6 %, 25.5 % and 13.4 % of patients, respectively; p < 0.0001). Nephrotoxicity (any grade), transient and persistent, occurred in 279 patients (34.6 %) and was severe (grade 3 + 4) in 12 (1.5 %). In only 20-27 % of any nephrotoxicity was the disease modelled by risk factors and codependent associations (p < 0.0001). Hypertension and haemoglobin toxicity were the most relevant factors. Persistent toxicity occurred in 197 patients (24.3 %). In only 22-34 % of affected patients was the disease modelled by the clinical data (p < 0.0001). Hypertension (regression coefficient 0.14, p < 0.0001) and haemoglobin toxicity (regression coefficient 0.21, p < 0.0001) were pertinent factors. Persistent toxicity was associated with shorter PRRT duration from the first to the last cycle (mean 387 vs. 658 days, p < 0.004). Myelodysplastic syndrome occurred in 2.35 % of patients (modelled by the clinical data in 30 %, p < 0.0001). Platelet toxicity grade (2.05 ± 1.2 vs. 0.58 ± 0.8, p < 0.0001) and longer PRRT duration (22.6 ± 24 vs. 15.5 ± 9 months, p = 0.01) were relevant. Acute leukaemia occurred in 1.1 % of patients (modelled by the clinical data in 18 %, p < 0.0001).

CONCLUSION

Identified risk factors provide a limited (<30 %) risk estimate even with target tissue dosimetry. These data strongly suggest the existence of unidentified individual susceptibilities to radiation-associated disease.

Preparation and evaluation of Lu-(177) phytate Complex for Radiosynovectomy

Lu-(177) of 2.6-3 GBq/mg specific activity was obtained by irradiation of natural Lu2O3 sample with thermal neutron flux of 4 × 10(13) n/cm/s. The product was converted into chloride form which was further used for labeling of Lu(-177) phytate complex successfully with high radiochemical purity (>99.9%, instant thin layer chromatography, MeOH: H2O: Acetic acid, 4:4:2, as mobile phase). The complex stability and viscosity were checked in the final solution up to 7 days. The prepared complex solution (100 μCi/100 μl) was injected intra-articularly to the male rat knee joint. Leakage of radioactivity from the injection site and its distribution in organs were investigated up to 7 days. Approximately, all injected dose has remained in injection site 7 days after injection. The complex was proved to be a feasible agent for cavital radiotherapy in oncology and rheumatology.

(99m)Tc-labeled-rhTSH analogue (TR1401) for imaging poorly differentiated metastatic thyroid cancer

BACKGROUND

Differentiated thyroid carcinomas originating from thyroid follicular cells are frequent tumors of the thyroid with relatively good prognosis due to improved surgical techniques and follow-up procedures. Poorly differentiated thyroid cancers, which lose iodine uptake ability, in most cases still express thyrotropin (TSH) receptors (TSHR). Therefore, the aim of this study was to radiolabel a superagonist recombinant human TSH (rhTSH) analogue for imaging poorly differentiated thyroid cancer.

METHODS

The TSHR superagonist, TR1401, was labeled with (99m)Tc using an indirect method via succinimidyl-6-hydrazinonicotinate hydrochloride conjugation. In vitro quality controls included SDS-PAGE, cysteine challenge, and cell-binding assay on TSHR positive cell lines (JP09 and ML-1). In vivo studies included tumor targeting experiments in athymic nude CD-1 mice xenografted with several different TSHR positive cells (JP09, K1, and ML-1) and TSHR negative cells (JP02) as control.

RESULTS

The superagonist rhTSH analogue TR1401 was labeled with high labeling efficiency (>95%) and high specific activity (9250 MBq/mg). The labeled molecule retained its biologic activity and structural integrity. In tumor targeting experiments, a focal uptake of radiolabeled TR1401 was observed in TSHR positive cells but not in TSHR negative cells. The same observation was made in a dog with spontaneous intraglandular thyroid cancer.

CONCLUSIONS

We were able to radiolabel the rhTSH superagonist analogue TR1401 with (99m)Tc efficiently with retention of in vitro and in vivo binding capacity to TSHR. The relative role of such novel radiopharmaceutical versus (131)I scanning of thyroid cancer will require future histopathologic and clinical studies, but it may open new perspectives for presurgical staging of thyroid cancer, and diagnosis of radioiodine negative local relapses and/or distant metastases.

Down-regulation of pancreatic and duodenal homeobox-1 by somatostatin receptor subtype 5: a novel mechanism for inhibition of cellular proliferation and insulin secretion by somatostatin

Somatostatin (SST) is a regulatory peptide and acts as an endogenous inhibitory regulator of the secretory and proliferative responses of target cells. SST’s actions are mediated by a family of seven transmembrane domain G protein-coupled receptors that comprise five distinct subtypes (SSTR1-5). SSTR5 is one of the major SSTRs in the islets of Langerhans. Homeodomain-containing transcription factor pancreatic and duodenal homeobox-1 (PDX-1) is essential for pancreatic development, β cell differentiation, maintenance of normal β cell functions in adults and tumorigenesis. Recent studies show that SSTR5 acts as a negative regulator for PDX-1 expression and that SSTR5 mediates somatostatin’s inhibitory effect on cell proliferation and insulin expression/excretion through down-regulating PDX-1 expression. SSTR5 exerts its inhibitory effect on PDX-1 expression at both the transcriptional level by down-regulating PDX-1 mRNA and the post-translational level by enhancing PDX-1 ubiquitination. Identification of PDX-1 as a transcriptional target for SSTR5 may help in guiding the choice of therapeutic cancer treatments.

Peptide receptor radionuclide therapy for advanced neuroendocrine tumors

Peptide receptor radionuclide therapy (PRRT) consists of the systemic administration of a synthetic peptide, labeled with a suitable β-emitting radionuclide, able to irradiate tumors and their metastases via internalization through a specific receptor (usually somatostatin S2), over-expressed on the cell membrane. After almost 2 decades of experience, PRRT, with either (90)Y-octreotide or (177)Lu-octreotate, has established itself to be an efficient and effective therapeutic modality. As a treatment, it is relatively safe up to the known thresholds of absorbed and bio-effective isotope dosages and the renal and hematological toxicity profiles are acceptable if adequate protective measures are undertaken.

Peptide receptor radionuclide therapy of neuroendocrine tumors with (90)Y-DOTATOC: is treatment response predictable by pre-therapeutic uptake of (68)Ga-DOTATOC?

PURPOSE

PET with (68)Ga-DOTATOC allows for imaging and quantitative assessment of somatostatin receptor expression in neuroendocrine tumors (NET). The aim of this retrospective study was to analyze whether pre-therapeutic (68)Ga-DOTATOC PET/CT is able to predict response to Peptide Receptor Radionuclide Therapy (PRRT).

PATIENTS AND METHODS

Forty patients with advanced stage NET were treated with a fixed dose of (90)Y-DOTATOC (5550 or 3700MBq). Prior to PRRT, each patient received (68)Ga-DOTATOC PET/CT. Treatment results were evaluated after 3months by CT, tumor marker levels and clinical course and correlated with (68)Ga-DOTATOC uptake (SUVmax) and the assumed uptake of (90)Y-DOTATOC in tumor manifestations (MBq/g). ROC analysis and pairwise comparison of area under the curve (AUC) were performed with pre-treatment uptake of (68)Ga-DOTATOC, assumed uptake of (90)Y-DOTATOC and treatment activity alone and in relation to body weight as continuous variables, and response/no response as classification variable.

RESULTS

According to conventional criteria (tumor shrinkage, decrease of tumor markers, improved or stable clinical condition), 20 patients were classified as responders, 16 as non-responders and in four patients findings were equivocal. Using a SUV more than 17.9 as cut-off for favorable outcome, PET was able to predict treatment response of all responders and 15 out of 16 non-responders. All four patients with equivocal findings showed SUV less than or equal to 17.9 and soon experienced tumor progression. The assumed uptake of (90)Y-DOTATOC in tumor manifestations using a cut-off more than 1.26MBq/g as predictor of response was able to correctly classify 19 out of 20 responders, and 14 out of 16 non-responders. In all patients with equivocal findings, the assumed uptake of (90)Y-DOTATOC was below 1.26MBq/g.

CONCLUSION

Pre-therapeutic (68)Ga-DOTATOC tumor uptake as well as assumed uptake of (90)Y-DOTATOC are strongly associated with the results of subsequent PRRT. The defined cut-off values should be confirmed by prospective studies and may then provide the rationale for individual dosing and selecting patients with high likelihood of favorable treatment outcome.

Divergent role of (68)Ga-labeled somatostatin analogs in the workup of patients with NETs: AIIMS experience

Neuroendocrine tumors (NETs) encompass a wide range of rare and heterogeneous neoplasms arising from the neural crest. Diagnosis of NETs is conventionally done by a combination of common clinical symptoms and biochemical evidence of hormonal excess, which these tumors are known to secrete. After a diagnosis of NET is established, a search for its localization is carried out using common morphologic imaging methods such as ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). The main problem with structural imaging is, however, its inability to distinguish between endocrine and exocrine lesions. Functional imaging of NETs started with use of iodine-131-meta-iodobenzylguanidine ((131)I-MIBG) and has come a long way since. From accurate demonstration of functioning tumors to detection of small and occult lesions, functional imaging has penetrated almost every aspect of NET management. Procedures such as (131/123)I-MIBG, (111)In-Octreoscan and others are rapidly giving way to use of PET/CT based on the superior resolution of the system and the availability of target-specific positron-emitting radiotracers. The availability of (68)Ga from generator-based radionuclide systems, namely (68)Ge/(68)Ga generators, opened up a new era of molecular imaging for NETs. A multitude of somatostatin analogs can be easily radioliganded with (68)Ga using heterocyclic macromolecular bifunctional chelating systems for targeted diagnosis of somatostatin receptor-expressing tumors, used most effectively to date for detection of NETs. This chapter focuses on our experience at the All India Institute of Medical Sciences, New Delhi regarding the divergent roles of (68)Ga-labeled somatostatin analogs in the workup of patients with NETs.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.

An evidence-based review of quantitative SPECT imaging and potential clinical applications

SPECT has traditionally been regarded as nonquantitative. Advances in multimodality γ-cameras (SPECT/CT), algorithms for image reconstruction, and sophisticated compensation techniques to correct for photon attenuation and scattering have, however, now made quantitative SPECT viable in a manner similar to quantitative PET (i.e., kBq cm(-3), standardized uptake value). This review examines the evidence for quantitative SPECT and demonstrates clinical studies in which the accuracy of the reconstructed SPECT data has been assessed in vivo. SPECT reconstructions using CT-based compensation corrections readily achieve accuracy for (99m)Tc to within ± 10% of the known concentration of the radiotracer in vivo. Quantification with other radionuclides is also being introduced. SPECT continues to suffer from poorer photon detection efficiency (sensitivity) and spatial resolution than PET; however, it has the benefit in some situations of longer radionuclide half-lives, which may better suit the biologic process under examination, as well as the ability to perform multitracer studies using pulse height spectroscopy to separate different radiolabels.

Distribution, elimination, and renal handling of (99m)technetium-Demogastrin 1

Radiolabeled cholecystokinin/gastrin (CCK) receptor-targeting peptides are promising compounds for radiodiagnosis and radiotherapy of certain malignancies. This study evaluated the pharmacokinetic profile of a CCK-2 receptor-specific peptide, Demogastrin 1, labeled with technetium-99m ((99m)Tc-Demogastrin 1), in rats. To investigate the fate of (99m)Tc-Demogastrin 1 in the rat, biodistribution and elimination studies in vivo were performed, and elimination parameters in perfused rat liver and kidney were determined. Biodistribution studies showed that (99m)Tc-Demogastrin 1 was rapidly cleared from the blood and most organs. A significant amount of radioactivity was detected in the CCK-2 receptor-rich organs, such as the stomach. Low radioactivity was found in the CCK-1 receptor-rich organs. Radioactivity in bowels and stomach declined relatively slowly. High and long-term retention of radioactivity in the kidneys was observed. Elimination of (99m)Tc-Demogastrin 1 via the bile was negligible. A high and rapid renal excretion was observed in elimination experiments in vivo. In the perfused kidney, glomerular filtration was found to be the main renal excretion mechanism of (99m)Tc-Demogastrin 1. Demogastrin 1 was distributed preferentially to the organs expressing CCK-2 receptors. The decisive elimination route of (99m)Tc-Demogastrin 1 in rats was urinary excretion. A high and prolonged renal retention may limit potential clinical use of the compound.

Radiolabeled somatostatin analogues therapy in advanced neuroendocrine tumors: a single centre experience

The aim of this study was to assess the efficacy of PRRT in patients with advanced neuroendocrine tumors (NETs). Patients and Methods. From January 2007 to August 2011, we enrolled 65 patients (m/f 38/27; mean age 65 years, range 33–83) with advanced NETs having enhanced SSTR expression, treated with PRRT. The enhanced expression of SSTR was assessed using ⁶⁸Ga-DOTATOC/DOTATATE PET/CT. Among all the enrolled patients, 6 of them were excluded from the present analysis since they voluntarily interrupted treatment. Mean activity/cycle of 2.6 GBq (⁹⁰Y-DOTATOC/DOTATATE) or 6.0 GBq (¹⁷⁷Lu-DOTATOC/DOTATATE) was administrated intravenously (max 9 cycles). Results. Complete response (CR) was found in 1/59 (2%) patients, partial remission (PR) in 24/59 (40.5%) patients, stable disease (SD) in 24/59 (40.5%), and progression (PD) in 10/59 (17%) patients. The overall tumor response rate (CR + PR) was 42.5%. In 40.5% of patients, the disease could be stabilized. Overall, 49 out of 59 patients had no tumor progression (83%). Twelve patients out of 59 (20%) had grade 2-3 hematological side effects including anemia, thrombocytopenia, and leukopenia. Long-term nephrotoxicity was observed in 3 patients (2 moderate, 1 severe). Conclusions. PRRT is a promising perspective for patients with advanced NETs.

Yttrium-labelled peptides for therapy of NET

Peptide receptor radionuclide therapy (PRRT) consists in the systemic administration of a synthetic peptide, labelled with a suitable beta-emitting radionuclide, able to irradiate tumours and their metastases via the internalization through a specific receptor, overexpressed on the cell membrane. After 15 years of experience, we can state that PRRT with (90)Y-labelled peptides is generally well tolerated. Acute side effects are usually mild, some of which are related to the co-administration of amino acids, such as nausea. Others are related to the radiopeptide, such as fatigue or the exacerbation of an endocrine syndrome, which rarely occurs in functioning tumours. Chronic and permanent effects on target organs, particularly the kidneys and the bone marrow, are generally mild if the necessary precautions are taken. Currently, the potential risk to kidney and red marrow limits the amount of radioactivity that may be administered. However, when tumour masses are irradiated with adequate doses, volume reduction may be observed. (90)Y-octreotide has been the most widely used radiopeptide in the first 8-10 years of experience. Unfortunately, all of the published results derive from different and inhomogeneous phase I/II studies. Hence, a direct comparison is virtually impossible to date. Nevertheless, even with these limitations, objective responses are registered in 10-34% of patients. The optimal timing of (90)Y-DOTATOC in the management of somatostatin receptor (SSTR)-positive tumours and the way in which it should be integrated with other treatments have yet to be defined, and prospective phase II/III trials comparing the efficacy and toxicity of different schemes of (90)Y-DOTATOC administration are still warranted.

Negative regulation of pancreatic and duodenal homeobox-1 by somatostatin receptor subtype 5

Somatostatin receptor subtype 5 (SSTR5) mediates the inhibitory effect of somatostatin and its analogs on insulin expression/secretion and islet cell proliferation. We provide biochemical and genetic evidence that SSTR5 exerted its physiological actions via down-regulating pancreatic and duodenal homeobox-1 (PDX-1), a β-cell-specific homeodomain-containing transcription factor. Cotransfection of SSTR5 with PDX-1 resulted in dose-dependent inhibition of PDX-1 expression in human embryonic kidney 293 cells. SSTR5 agonist RPL-1980 inhibited PDX-1 expression and abolished glucagon-like peptide 1-stimulated PDX-1 expression in mouse insulinoma β-TC-6 cells. SSTR5 knockdown by short hairpin RNA led to increased PDX-1 expression that was accompanied by enhanced insulin secretion stimulated by high glucose in β-TC6 cells and alternated expressions of cell cycle proteins that favor cell proliferation in mouse insulinoma MIN6 cells. Quantitative RT-PCR analysis showed that cotransfected SSTR5 inhibited PDX-1 mRNA expression, whereas knockdown of SSTR5 increased PDX-1 mRNA expression. In addition, we found that cotransfected wild-type SSTR5 increased PDX-1 ubiquitination in human embryonic kidney 293 cells, whereas SSTR5 P335L, a hypofunctional single nucleotide polymorphism of SSTR5, inhibited PDX-1 ubiquitination. SSTR5 knockout resulted in increased expression of PDX-1, insulin, and proliferating cell nuclear antigen in the islets of sstr(-/-) mice. Immunohistochemistry analysis showed that SSTR5 P335L was associated with elevated expression of PDX-1 in human pancreatic neuroendocrine tumor. Taken together, our studies demonstrated that SSTR5 is a negative regulator for PDX-1 expression and that SSTR5 may mediate the inhibitory effects of somatostatin and its analogs on insulin expression/secretion and cell proliferation via down-regulating PDX-1 at both transcriptional and posttranslational levels.

Pregnant with metastatic neuroendocrine tumour of the ovary: what now?

Neuroendocrine tumours (NET) are a heterogeneous group of neoplasms commonly occurring in the gastrointestinal tract or lungs but can occur in other regions. Primary ovarian NET account for 5% of all NET and 0.1% of all ovarian malignancies. In metastatic disease, the therapeutic goal is to extend survival and to improve quality of life. As these tumours express somatostatin receptors, somatostatin analogues are frequently used to control symptoms. Here we present a case of a pregnant woman with an ovarian NET with liver metastases and carcinoid syndrome who was treated with the somatostatin analogue, Octreotide LAR. We also summarize reported data of the use of somatostatin analogues during pregnancy.

Clinical molecular imaging with radiotracers: current status

Molecular imaging is defined as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Most clinical molecular imaging is currently done using radioisotope-labeled agents to define the activity of various metabolic pathways in vivo or to determine the distribution and density of various receptors relevant to human disease. This paper briefly reviews most of the commonly used radiopharmaceuticals in nuclear medicine, as well as newer agents that are likely to become available in the near future. The metabolic pathways include those relevant to the thyroid, parathyroid, heart, brain, bones, kidneys, liver, pancreas, adrenals and tumor. The receptor systems include agents useful in evaluating movement disorders, dementia, cardiac sympathetic enervation and neoangiogenesis. Receptor systems relevant to tumors include somatostatin receptors (neuroendocrine tumors), prostate-specific membrane antigen, carbonic anhydrase IX (renal cancer), and CD-20 (lymphoma). These agents, and newer agents that are being developed, are likely to become critical in the development of personalized medicine, where it will become increasingly important to determine whether a treatment that is targeted to a specific metabolic pathway or receptor is likely to be successful.