Efficacy of radionuclide treatment DOTATATE Y-90 in patients with progressive metastatic gastroenteropancreatic neuroendocrine carcinomas (GEP-NETs): a phase II study

Adverse reactions to therapeutic radiopharmaceuticals

Radiopharmaceuticals are drugs used in treatment or diagnosis that contain a radioactive part, usually a pharmaceutical part in their structure. Adverse drug reactions are harmful and unexpected responses that occur when administered at normal doses. Although radiopharmaceuticals are regarded as safe medical products, adverse reactions should not be ignored. More serious adverse reactions such as myelosuppression, pleural effusion, and death may develop in therapeutic radiopharmaceuticals due to their use at higher doses than those used in diagnosis. Therefore, monitoring adverse reactions and reporting them to health authorities is important. This review aims to provide information about adverse reactions that may be related to radiopharmaceuticals used in treatment.

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.

Carcinoid crisis: The challenge is still there

Carcinoid crisis (CC) has classically been considered the extreme end of the spectrum of carcinoid syndrome (CS). However, this presumption and other aspects of CC remain poorly understood. Consequently, current clinical guidelines are based on a low quality of evidence. There is no standard definition of CC and its incidence is unknown. Patients with florid CS and elevated serotonin (or its derivatives) which develop CC have been reported during decades. Nevertheless, the hypothesis that CC is due to the sudden massive release of serotonin or other vasoactive substances is unproven. Many triggers of CC (surgery, anaesthesia, peptide receptor radionuclide therapy, tumour biopsy or liver-directed treatments) have been proposed. However, data from studies are heterogeneous and even contradictory. Finally, the role of octreotide in the prevention of CC has been questioned. Herein, we report a clinical case and perform a critical review of the evidence available today on this topic.

eTFC-01: a dual-labeled chelate-bridged tracer for SSTR2-positive tumors

BACKGROUND

Integrating radioactive and optical imaging techniques can facilitate the prognosis and surgical guidance for cancer patients. Using a single dual-labeled tracer ensures consistency in both imaging modalities. However, developing such molecule is challenging due to the need to preserve the biochemical properties of the tracer while introducing bulky labeling moieties. In our study, we designed a trifunctional chelate that facilitates the coupling of the targeting vector and fluorescent dye at opposite sites to avoid undesired steric hindrance effects. The synthesis of the trifunctional chelate N3-Py-DOTAGA-(tBu)3 (7) involved a five-step synthetic route, followed by conjugation to the linear peptidyl-resin 8 through solid-phase synthesis. After deprotection and cyclization, the near-infrared fluorescent dye sulfo-Cy.5 was introduced using copper free click chemistry, resulting in eTFC-01. Subsequently, eTFC-01 was labeled with [111In]InCl3. In vitro assessments of eTFC-01 binding, uptake, and internalization were conducted in SSTR2-transfected U2OS cells. Ex-vivo biodistribution and fluorescence imaging were performed in H69-tumor bearing mice.

RESULTS

eTFC-01 demonstrated a two-fold higher IC50 value for SSTR2 compared to the gold standard DOTA-TATE. Labeling of eTFC-01 with [111In]InCl3 gave a high radiochemical yield and purity. The uptake of [111In]In-eTFC-01 in U2OS.SSTR2 cells was two-fold lower than the uptake of [111In]In-DOTA-TATE, consistent with the binding affinity. Tumor uptake in H69-xenografted mice was lower for [111In]In-eTFC-01 at all-time points compared to [111In]In-DOTA-TATE. Prolonged blood circulation led to increased accumulation of [111In]In-eTFC-01 in highly vascularized tissues, such as lungs, skin, and heart. Fluorescence measurements in different organs correlated with the radioactive signal distribution.

CONCLUSION

The successful synthesis and coupling of the trifunctional chelate to the peptide and fluorescent dye support the potential of this synthetic approach to generate dual labeled tracers. While promising in vitro, the in vivo results obtained with [111In]In-eTFC-01 suggest the need for adjustments to enhance tracer distribution.

Advances in Radioligand Theranostics in Oncology

Theranostics with radioligands (radiotheranostics) has played a pivotal role in oncology. Radiotheranostics explores the molecular targets expressed on tumor cells to target them for imaging and therapy. In this way, radiotheranostics entails non-invasive demonstration of the in vivo expression of a molecular target of interest through imaging followed by the administration of therapeutic radioligand targeting the tumor-expressed molecular target. Therefore, radiotheranostics ensures that only patients with a high likelihood of response are treated with a particular radiotheranostic agent, ensuring the delivery of personalized care to cancer patients. Within the last decades, a couple of radiotheranostics agents, including Lutetium-177 DOTATATE (177Lu-DOTATATE) and Lutetium-177 prostate-specific membrane antigen (177Lu-PSMA), were shown to prolong the survival of cancer patients compared to the current standard of care leading to the regulatory approval of these agents for routine use in oncology care. This recent string of successful approvals has broadened the interest in the development of different radiotheranostic agents and their investigation for clinical translation. In this work, we present an updated appraisal of the literature, reviewing the recent advances in the use of established radiotheranostic agents such as radioiodine for differentiated thyroid carcinoma and Iodine-131-labeled meta-iodobenzylguanidine therapy of tumors of the sympathoadrenal axis as well as the recently approved 177Lu-DOTATATE and 177Lu-PSMA for differentiated neuroendocrine tumors and advanced prostate cancer, respectively. We also discuss the radiotheranostic agents that have been comprehensively characterized in preclinical studies and have shown some clinical evidence supporting their safety and efficacy, especially those targeting fibroblast activation protein (FAP) and chemokine receptor 4 (CXCR4) and those still being investigated in preclinical studies such as those targeting poly (ADP-ribose) polymerase (PARP) and epidermal growth factor receptor 2.

[212Pb]Pb-eSOMA-01: A Promising Radioligand for Targeted Alpha Therapy of Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) has been applied to the treatment of neuroendocrine tumors (NETs) for over two decades. However, improvement is still needed, and targeted alpha therapy (TAT) with alpha emitters such as lead-212 (²¹²Pb) represents a promising avenue. A series of ligands based on octreotate was developed. Lead-203 was used as an imaging surrogate for the selection of the best candidate for the studies with lead-212. ^203/212Pb radiolabeling and in vitro assays were carried out, followed by SPECT/CT imaging and ex vivo biodistribution in NCI-H69 tumor-bearing mice. High radiochemical yields (≥99%) and purity (≥96%) were obtained for all ligands. [²⁰³Pb]Pb-eSOMA-01 and [²⁰³Pb]Pb-eSOMA-02 showed high stability in PBS and mouse serum up to 24 h, whereas [²⁰³Pb]Pb-eSOMA-03 was unstable in those conditions. All compounds exhibited a nanomolar affinity (2.5-3.1 nM) for SSTR2. SPECT/CT images revealed high tumor uptake at 1, 4, and 24 h post-injection of [²⁰³Pb]Pb-eSOMA-01/02. Ex vivo biodistribution studies confirmed that the highest uptake in tumors was observed with [²¹²Pb]Pb-eSOMA-01. [²¹²Pb]Pb-eESOMA-01 displayed the highest absorbed dose in the tumor (35.49 Gy/MBq) and the lowest absorbed dose in the kidneys (121.73 Gy/MBq) among the three tested radioligands. [²¹²Pb]Pb-eSOMA-01 is a promising candidate for targeted alpha therapy of NETs. Further investigations are required to confirm its potential.

Imaging and treatment with 68Gallium and 177Lutetium-DOTATATE in a rare SSTR2 and ESWR1-CREM fusion positive undifferentiated round cell tumour of the lung

The authors present a 45-year-old lady with a rare undifferentiated round cell tumour of the lung with a ESWR1-CREM fusion gene that progressed despite multiple lines of therapy. The tumour was Somatostatin Receptors Type 2 (SSTR2) positive and avid on ⁶⁸Gallium-DOTATATE imaging. This allowed for novel treatment with Peptide Receptor Radionuclide Therapy (PRRT) using ¹⁷⁷Lutetium-DOTATATE after all other standard of care options were exhausted.

Role of Radioembolization in Metastatic Neuroendocrine Tumors

The liver is the most common site of metastasis for neuroendocrine tumors originating from the gastrointestinal tract. Neuroendocrine liver metastases (NELMs) portend a worsening clinical course, making local management important. Local treatment options include surgery, thermal ablation, and trans-catheter intra-arterial therapies, such as radioembolization. Radioembolization is generally preferred over other embolotherapies in patients with colonized biliary systems. Current best practice involves personalized treatment planning, optimizing tumor radiation absorbed dose and minimizing radiation to the normal hepatic parenchyma. As part of a multidisciplinary approach, radioembolization is a versatile embolotherapy offering neoadjuvant, palliative, and ablative treatment options for patients with NELMs.

Health-Related Quality of Life (HRQoL) in Neuroendocrine Tumors: A Systematic Review

Therapeutic advancements in neuroendocrine tumors (NETs) have improved survival outcomes. This study aims to review the impact of the current therapeutics on health-related quality of life (HRQoL) in NET patients. A literature review was performed utilizing PubMed, The Cochrane Library, and EMBASE, using the keywords "Carcinoid", "Neuroendocrine tumor", "NET", "Quality of life", "Chemotherapy", "Chemoembolization", "Radiofrequency ablation", "Peptide receptor radionucleotide therapy", "PRRT", "Surgery", "Everolimus", "Octreotide", "Lanreotide", "Sunitinib", and "Somatostatin analog". Letters, editorials, narrative reviews, case reports, and studies not in English were excluded. Out of 2375 publications, 61 studies met our inclusion criteria. The commonly used instruments were EORTC QLQ-C30, FACT G, and EORTC- QLQ GI.NET-21. HRQoL was assessed in all pivotal trials that led to approvals of systemic therapies. All systemic therapies showed no worsening in HRQoL. The NETTER-1 study was the only study to show a statistically significant improvement in HRQoL in several domains. The trial examining sunitinib versus placebo in pancreatic NETs showed no change in QoL, except for worsening of diarrhea. In addition to clinical outcomes, patient-reported outcomes are a key element in making appropriate treatment decisions. HRQoL data should be readily provided to patients to assist in shared decision-making.

Treatment of Neuroendocrine Neoplasms with Radiolabeled Peptides-Where Are We Now

Peptide receptor radionuclide therapy (PRRT) has been one of the most successful and exciting examples of theranostics in nuclear medicine in recent decades and is now firmly embedded in many treatment algorithms for unresectable or metastatic neuroendocrine neoplasms (NENs) worldwide. It is widely considered to be an effective treatment for well- or moderately differentiated neoplasms, which express high levels of somatostatin receptors that can be selectively targeted. This review article outlines the scientific basis of PRRT in treatment of NENs and describes its discovery dating back to the early 1990s. Early treatments utilizing Indium-111, a γ-emitter, showed promise in reduction in tumor size and improvement in biochemistry, but were also met with high radiation doses and myelotoxic and nephrotoxic effects. Subsequently, stable conjugation of DOTA-peptides with β-emitting radionuclides, such as Yttrium-90 and Lutetium-177, served as a breakthrough for PRRT and studies highlighted their potential in eliciting progression-free survival and quality of life benefits. This article will also elaborate on the key trials which paved the way for its approval and will discuss therapeutic considerations, such as patient selection and administration technique, to optimize its use.

Health-related quality of life and treatment effects in patients with well-differentiated gastroenteropancreatic neuroendocrine neoplasms: A systematic review and meta-analysis

Introduction

Gastroenteropancreatic neuroendocrine neoplasms (GEPNENs) are often diagnosed in an advanced stage. As the optimal sequence of therapy remains largely unclear, all treatment‐related outcomes, including health‐related quality of life (HRQoL) prospects, should be assessed according to patients' preferences.

Methods

A targeted search was performed in PubMed and EMBASE to identify studies on treatment effect and HRQoL, measured using the EORTC QLQ‐C30 tool, in patients with advanced, well‐differentiated GEPNENs. Study quality was assessed, and meta‐analyses were performed for global health status/QOL and tumour response.

Results

The search yielded 1,322 records, and 20 studies were included, examining somatostatin analogues (SSA), peptide receptor radionuclide therapies (PRRT), chemotherapy, SSA‐based combination therapies, and targeted therapies. Global HRQoL was stable, and rates for disease stabilisation were moderate to high across all treatments. Meta‐analyses for global health status/QOL after SSA treatment were not significant (mean difference: –0.3 [95% CI: −1.3 to 0.7]). The highest pooled overall tumour response rate was 33% (95% CI: 24–45%) for PRRT. The highest pooled clinical benefit rate was 94% (95% CI: 65–99%) for chemotherapy.

Conclusion

All treatments appeared beneficial for disease stabilisation while maintaining stable global health status/QOL. High‐quality HRQoL reporting was lacking. HRQoL should be a central outcome next to well‐established outcomes.

PRRT: identikit of the perfect patient

Peptide receptor radionuclide therapy (PRRT) has been strengthened since the publication of NETTER-1. Nevertheless, the correct positioning in the therapeutic algorithm is debated, and no optimal sequence has yet been standardized. Possible criteria to predict the response to PRRT in neuroendocrine tumors (NET) have been proposed. The aim of this review is to define the perfect identity of the eligible patient who can mostly benefit from this therapy. Possible predictive criteria which have been analysed were: primary tumor site, grading, tumor burden, FDG PET and ⁶⁸Ga-PET uptake. Primary tumor site and ⁶⁸Ga-PET uptake do not play a pivotal role in predicting the response, while tumor burden, FDG PET uptake and grading seem to represent predictive/prognostic factors for response to PRRT. The heterogeneity in trial designs, patient populations, type of radionuclides, previous therapies and measurement of outcomes, inevitably limits the strength of our conclusions, therefore care must be taken in applying these results to clinical practice. In conclusion, the perfect patient, selected by ⁶⁸Ga-PET uptake, will likely have a relatively limited liver tumor burden, a ki67 index <20% and will respond to PRRT irrespective to primary tumor. Nevertheless, we have mostly prognostic than predictive factors to predict the efficacy of PRRT in individual patients, while a promising tool could be the NETest. However, to date, the identikit of the perfect patient for PRRT is a puzzle without some pieces and still we cannot disregard a multidisciplinary discussion of the individual case to select the patients who will mostly benefit from PRRT.

Y90 selective internal radiation therapy and peptide receptor radionuclide therapy for the treatment of metastatic neuroendocrine tumors: combination or not?

BACKGROUND

Peptide receptor radionuclide therapy and selective internal radiation therapy are effective radionuclide therapy modalities for unresectable metastatic neuroendocrine tumor patients that cannot be controlled with somatostatin analogs. The present study is intended to evaluate the therapeutic efficacy and toxicity of the combined therapy of selective internal radiation therapy and peptide receptor radionuclide therapy and stand-alone selective internal radiation therapy in patients with neuroendocrine tumor, a liver-dominant disease.

METHODS

This cohort consists of 27 patients with metastatic neuroendocrine tumor and liver-dominant disease. They were grouped as the patients who were treated with selective internal radiation therapy for unresectable liver metastasis (n = 15) and the patients who received a combination of selective internal radiation therapy and peptide receptor radionuclide therapy (n = 12) for hepatic and extrahepatic metastasis. Treatment efficacy and treatment-associated toxicity were retrospectively assessed in both groups.

RESULTS

The objective treatment response and stable disease were found in 13 patients (86.6%) in the selective internal radiation therapy group and eight patients (66.6%) in the selective internal radiation therapy + peptide receptor radionuclide therapy group. The median overall survival rate was found to be 34.9 months, in the selective internal radiation therapy group and 67.5 months in the selective internal radiation therapy + peptide receptor radionuclide therapy group (P = 0.217). The median progression-free survival data was not reached, and the mean values of progression-free survival were 53.1 ± 9.9 months in the selective internal radiation therapy group, and 27.2 ± 5.9 months in the selective internal radiation therapy + peptide receptor radionuclide therapy group (P = 0.561). Temporary lymphopenia was the most common side effect. Grade 1-2 hepatotoxicity was observed to be 6.6% in the selective internal radiation therapy group, while it was not observed in selective internal radiation therapy + peptide receptor radionuclide therapy group.

CONCLUSIONS

In the neuroendocrine tumors with liver-dominant metastatic disease, personalized selective internal radiation therapy and peptide receptor radionuclide therapy and their combinations result in increased survival rates. Selective internal radiation therapy alone could be an effective treatment in patients with liver-limited and -dominant disease.

Radiological and Clinical Efficacy of Intra-Arterial 90Y-DOTATATE in Patients with Unresectable, Progressive, Liver Dominant Neuroendocrine Neoplasms

This study was performed to determine if intra-arterial (i.a.) administration of ⁹⁰Y DOTATATE can provide an effective and safe alternative to the accepted standard for i.v. of peptide receptor radionuclide therapy (PRRT) in liver-dominant metastases of gastrointestinal pancreatic neuroendocrine neoplasm (GEP-NEN). A single site, prospective, preliminary case series study included 39 patients with histologically proven liver-dominant NEN. PRRT in the form of 1.15GBq ⁹⁰Y DOTATATE was given selectively into the liver via radiological catheterization of the hepatic artery, up to four times. The endpoint was radiological response (RECIST). Secondary endpoints assessed clinical well-being post-treatment, progression-free survival (PFS), overall survival (OS), and toxicity. Partial response (PR) was noted in 13% of subjects six weeks post-therapy, increasing to 24% at six months and dropping to 13% at 36 months. Disease progression (DP) was not seen at six weeks, was 5% at six months, and 47% at 36 months. Clinical response based on PS seen in 74% of patients at six weeks, 69% at six months, and 39% at 36 months had PFS and OS, respectively, of 22.7 months and 38.2 months. There was no difference in OS/PFS between those with RECIST PR and SD. One patient had significant toxicity (3%). Use of i.a. PRRT appears to be safe and effective in treating patients with liver-dominant NEN. In addition, the best OS (51 vs. 22 months) was seen when i.a. was used as an upfront treatment of bulky GEP-NEN liver metastases and not after i.v. ⁹⁰Y DOTATATE. The use of i.a. ⁹⁰Y DOTATATE PRRT appears to be safe and effective in treating patients with liver-dominant NEN.

Long-Term Survival and Value of 18F-FDG PET/CT in Patients with Gastroenteropancreatic Neuroendocrine Tumors Treated with Second Peptide Receptor Radionuclide Therapy Course with 177Lu-DOTATATE

Peptide receptor radionuclide therapy (PRRT) has been recognized as a promising therapy against neuroendocrine tumors (NETs). The use of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) in NETs has been a matter of controversy. The purpose of this study was to evaluate the long-term survival and efficacy of a second PRRT course with ¹⁷⁷Lu-DOTATE in patients with advanced gastroenteropancreatic (GEP) NETs. Furthermore, the value of ¹⁸F-FDG PET/CT in these patients was evaluated. 40 patients with GEP NETs who underwent two PRRT courses with ¹⁷⁷Lu-DOTATATE and combined examinations with ⁶⁸Ga-DOTA-TOC and ¹⁸F-FDG PET/CT were evaluated. After the second PRRT course, two patients (5.0%) were in partial remission, 21 patients (52.5%) in stable disease and 17 patients (42.5%) had progressive disease. The median overall survival was 122.10 months. After the second PRRT course, the median overall survival was significantly higher (p = 0.033) in the ¹⁸F-FDG-negative group compared to the ¹⁸F-FDG-positive group (145.50 versus 95.06 months, respectively). The median time to progression was 19.37 months. In conclusion, a second PRRT course with ¹⁷⁷Lu-DOTATE is an effective treatment approach for GEP NET patients with disease progression. A change in ¹⁸F-FDG status after PRRT may predict the disease course and survival. Patients who are ¹⁸F-FDG-negative have a significantly longer overall survival than those who are ¹⁸F-FDG-positive.

Evidence Base for the Use of PRRT

The development of peptide receptor radionuclide therapy (PRRT) in disseminated neuroendocrine tumors (NETs) has been a long and protracted process. The idea was born within nuclear medicine academia but its translation to clinical practice has been marked by misunderstanding of the rigors of the processes used in drug registration. There were several false starts and some of the required basic science did not occur until after first in man studies. The standard process of preclinical, phase 1, 2 and 3 clinical trials were sometimes blurred and the required data including the assurances that patients were studied on protocol was missing from subsequent publications. Despite this there was a growing conviction and increasing evidence that the use of PRRT had a positive benefit in both survival and symptom relief in about 80% of treated patients. After a decade and a half of false starts and incomplete data a formal randomized controlled trial was conducted comparing PRRT with high dose somatostatin which clearly proved that PRRT was both safe, effective and the treatment of choice in hormone refractory NETs.

Non-Pharmacological Therapeutic Options for Liver Metastases in Advanced Neuroendocrine Tumors

The incidence of liver metastasis in digestive neuroendocrine tumors is high. Their presence appears as an important prognostic factor in terms of quality of life and survival. These tumors may be symptomatic because of the tumor burden itself and/or the hormonal hyper-secretion induced by the tumor. Surgery is the treatment of choice for resectable tumors and metastasis. Nevertheless, surgery is only possible in a small number of cases. The management of non-resectable liver metastasis is a challenge. The literature is rich but consists predominantly in small retrospective series with a low level of proof. Thus, the choice of one technique over another could be difficult. Local ablative techniques (radiofrequency) or trans-catheter intra-arterial liver-directed treatments (hepatic artery embolization, chemo-embolization, and radio-embolization) are frequently considered for liver metastasis. In the present review, we focus on these different therapeutic approaches in advanced neuroendocrine tumors, results (clinical and radiological), and overall efficacy, and summarize recommendations to help physicians in their clinical practice.

Therapy of Patients with Neuroendocrine Neoplasia-Evidence-Based Approaches and New Horizons

Neuroendocrine tumors (NETs) show low but increasing incidence and originate in multiple organs, including the pancreas, midgut, caecum, rectum, appendix, colon, and lungs. Due to their stunning genetic, histological, and clinical variability, diagnosis and treatment of NETs are challenging. In addition, low incidence and high variability hamper the implementation of high evidence trials. Therefore, guidelines do not cover the complexity of NETs and, frequently, treatment decisions are taken by interdisciplinary tumor conferences at comprehensive cancer centers. Treatment aims are (i) control of tumor growth, (ii) symptom control, as well as (iii) the improvement of progression-free survival (PFS) and overall survival (OS). Here, we discuss high evidence trials facilitating the achievement of these treatment aims. The majority of the evidence exists for treatment with somatostatin analogue, everolimus, peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE, sunitinib, and telotristat. Among those, PRRT is the only treatment option that has the potential to control symptoms, stop tumor growth, and to improve PFS and OS. In contrast, only a low level of evidence exists for treatment with cytotoxic drugs such as streptozotocin and doxorubicine. Finally, we discuss novel treatment options by a combination of cytotoxic drugs, 177Lu-DOTATATE, and tyrosine kinase inhibitors to be tested in randomized prospective trials in the future. In addition, the application of innovative isotopes, such as 225Ac, for PRRT is discussed.

Cationic radionuclides and ligands for targeted therapeutic radiopharmaceuticals

This review considers the already used and potential α- and β-emitting cationic radionuclides for targeted radionuclide therapy. Recent results of laboratory, preclinical and clinical applications of these radionuclides are discussed. As opposed to β-emitters, which are already used in nuclear medicine, α-emitters involved in targeted radiopharmaceuticals were subjected to clinical trials only recently and were found to be therapeutically effective. The review summarizes recent trends in the development of ligands as components of radiopharmaceuticals addressing specific features of short-lived cationic radionuclides applied in medicine. Despite a steadily growing number of chelating ligands, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and diethylenetriaminepentaacetic acid (DTPA) remain the most widely used agents in nuclear medicine. The drawbacks of these compounds restrict the application of radionuclides in medicine. Variations in the macrocycle size, the introduction and modification of substituents can significantly improve the chelating ability of ligands, enhance stability of radionuclide complexes with these ligands and eliminate the influence of ligands on the affinity of biological targeting vectors.

The bibliography includes 189 references.

Peptide Receptor Radionuclide Therapy for Pancreatic Neuroendocrine Tumours

Background:

The incidence of pancreatic Neuroendocrine Tumours (pNETs) has increased considerably in the last few decades. The characteristic features of this tumour and the development of new investigative and therapeutic methods had a great impact on its management.

Objective:

The aim of this review is to investigate the outcome of Peptide Receptor Radionuclide Therapy (PRRT) in the treatment of pancreatic neuroendocrine tumours.

Methods:

A comprehensive literature search strategy was used based on two databases (SCOPUS, and PubMed). We considered all studies published in English, evaluating the use of PRRT (177Luteciuim- DOTA-conjugated peptides and 90Yetrium- DOTA- conjugated peptides) in the treatment of pancreatic neuroendocrine tumours as a standalone entity or as a subgroup within the wider category of Gastroenteropancreatic Neuroendocrine Tumours (GEP NETs).

Results:

PRRT was found to be an effective treatment modality as a monotherapy or in combination with other therapies in the treatment of non-operable and metastatic pNETs where other options are limited. Complete response was reported to be between 2-6% while partial response was achieved in up to 60% of cases. Survival analysis was also impressive. Progression Free Survival (PFS) reached a mean of 34 months and Overall Survival (OS) of 53 months. PRRT also proved to improve patients’ Quality of Life (QoL). Acute and sub-acute side effects like nephrotoxicity and haematotoxicity are usually mild and reversible.

Conclusion:

PRRT is well tolerated and effective treatment option for non-operable and/or metastatic pNETs. Side effects are usually mild and reversible. Larger randomized controlled trails need to be done to compare PRRT with other treatment modalities and to provide more detailed guidelines regarding patient selections, the choice of PRRT, follow up and response assessment to maximum potential benefit.

A Clinical Efficacy of PRRT in Patients with Advanced, Nonresectable, Paraganglioma-Pheochromocytoma, Related to SDHx Gene Mutation

Paragangliomas and pheochromytomas (PPGLs) exhibit variable malignancy, advanced/hormonally active/progressive need therapy. PRRT (Peptide Receptor Radionuclide Therapy) could be an option for these patients. To evaluate the effectiveness of PRRT (90Y DOTATATE), based on overall survival (OS) and progression-free survival (PFS), in patients with PPGLs, related to SDHx gene mutation, we conducted a prospective open-label, single-center, phase II study. Thirteen patients were observed, eight PGL1 and five PGL4, all with advanced, non-resectable tumors, and eight had metastases. All were treated with 90Y DOTATATE. Efficacy was based on OS and PFS, and radiological response was based on RECIST. Hormonal activity was evaluated using serum-fractionated free catecholamines. Eight subjects had a clinical response, three were stable, and two exhibited disease progression. Among four patients with hormonally-active PPGLs, three showed a reduction and one showed normalization. OS for all was 68.0 months; PFS was 35.0 months. OS in PGL4 = 25.0 vs. N.R. (not reached) in PGL1. PFS in PGL4 = 12.0 vs. N.R. in PGL1. A difference was seen in the OS and PFS in patients who did not respond clinically, compared to those who did, OS = 22.0 vs. N.R. PFS = 7.0 vs. N.R. A difference in the OS and PFS was noted in patients with liver and bone involvement compared to those without. PRRT is an effective therapy in selected population of patients with SDHx, in those with locally-advanced, non-resectable tumors. Furthermore, it is effective regardless of the secretory status.

Somatostatin Analogues in the Treatment of Neuroendocrine Tumors: Past, Present and Future

In recent decades, the incidence of neuroendocrine tumors (NETs) has steadily increased. Due to the slow-growing nature of these tumors and the lack of early symptoms, most cases are diagnosed at advanced stages, when curative treatment options are no longer available. Prognosis and survival of patients with NETs are determined by the location of the primary lesion, biochemical functional status, differentiation, initial staging, and response to treatment. Somatostatin analogue (SSA) therapy has been a mainstay of antisecretory therapy in functioning neuroendocrine tumors, which cause various clinical symptoms depending on hormonal hypersecretion. Beyond symptomatic management, recent research demonstrates that SSAs exert antiproliferative effects and inhibit tumor growth via the somatostatin receptor 2 (SSTR2). Both the PROMID (placebo-controlled, prospective, randomized study in patients with metastatic neuroendocrine midgut tumors) and the CLARINET (controlled study of lanreotide antiproliferative response in neuroendocrine tumors) trial showed a statistically significant prolongation of time to progression/progression-free survival (TTP/PFS) upon SSA treatment, compared to placebo. Moreover, the combination of SSA with peptide receptor radionuclide therapy (PRRT) in small intestinal NETs has proven efficacy in the phase 3 neuroendocrine tumours therapy (NETTER 1) trial. PRRT is currently being tested for enteropancreatic NETs versus everolimus in the COMPETE trial, and the potential of SSTR-antagonists in PRRT is now being evaluated in early phase I/II clinical trials. This review provides a synopsis on the pharmacological development of SSAs and their use as antisecretory drugs. Moreover, this review highlights the clinical evidence of SSAs in monotherapy, and in combination with other treatment modalities, as applied to the antiproliferative management of neuroendocrine tumors with special attention to recent high-quality phase III trials.

Molecular imaging and therapy of somatostatin receptor positive tumors

Somatostatin receptors (SSTR) are upregulated in the cells of origin that define numerous neuroendocrine neoplasms. PET imaging with ⁶⁸Ga-DOTATATE allows specific targeting of SSTR2A, a single species of SSTR receptor, which is commonly overexpressed in a variety of gastroenteropancreatic neuroendocrine tumors, as well as pulmonary carcinoid and head and neck tumors. Due to more specific targeting of SSTR2 as well as lower radiation dose, shorter study length, ability to quantify uptake, and lower cost, ⁶⁸Ga-DOTATATE has demonstrated superior imaging attributes when compared to ¹¹¹In-pentetreotide. As with any novel imaging modality, dedicated training, increasing experience and staying up-to-date with scientific publications are required to provide optimal patient care. The purpose of this review is to summarize the current state of the art in SSTR-targeted molecular imaging and discuss ongoing and future potential diagnostic and therapeutic applications.

Targeted Alpha Particle Therapy for Neuroendocrine Tumours: The Next Generation of Peptide Receptor Radionuclide Therapy

Neuroendocrine tumours (NETs) are being seen increasingly frequently, but to date only complete surgical resection is curative. However, among the various therapeutic options, peptide receptor radionuclide therapy, linking a radioactive moiety to an octreotide derivative, has been shown to be highly efficacious and a well-tolerated therapy, improving progression-free survival and probably overall survival. Nevertheless, the current radionuclides in use are beta particle emitters with non-optimal radiobiological properties. A new generation of alpha particle-emitting radionuclides is being developed, with advantages in terms of very high energy and a short path length, which should theoretically show higher efficacy. We survey the current developments in this field, emphasising the exciting potential of this novel form of therapy for NETs.

A five-compartment biokinetic model for 90 Y-DOTATOC therapy

PURPOSE

Neuroendocrine tumors (NETs) are now routinely treated by radiopeptide targeted therapy using somatostatin receptor-binding peptides such as ⁹⁰ Y- and ¹⁷⁷ Lu-DOTATOC. The objective of this work was to develop a biokinetics model of ⁹⁰ Y labelled DOTATOC, which is applied in the therapy of NETs to estimate doses in kidney and tumor.

METHODS

A multi-compartment model described by two sets of differential equations, one set for the actual 30-min infusion and the other set for the post-infusion period was developed and activities were measured by liquid scintillation counting in blood (compartment 1) and the urine (compartment 3). The inter-compartment transfer coefficients, λ_ij , were varied to yield the best fit of the calculated to the measured time-activity data and the ⁹⁰ Y-DOTATOC time-activity data in the five-compartments comprising the human body were thus determined. The resulting time-activity curves were integrated over the interval from 0 to 72 h post administration to obtain the number of radioactive decays in each compartment and, in case of the kidneys and tumor, then multiplied by the self-dose ⁹⁰ Y beta particle absorbed fraction, determined by Monte Carlo (MC) simulation, the kidney and tumor absorbed doses.

RESULTS

Transfer coefficients λ_ij , were determined for five-compartments for all patients. Time- activity curves of ⁹⁰ Y-DOTATOC in 14 patients were determined, and two typical ones are shown graphically. Absorbed doses in the tumor and kidneys, obtained by the developed method, were determined. The mean absorbed dose in a kidney per unit of administered activity is 1.43 mGy/MBq (range 0.73-2.42 mGy/MBq). The tumor dose was determined as 30.94 mGy/MBq (range 20.05-42.31 mGy/MBq).

CONCLUSION

Analytical solution of a biokinetic model for ⁹⁰ Y-DOTATOC therapy enabled determination of the transfer coefficients and derivation of time-activity curves and kidney and tumor absorbed doses for 14 treated patients. The model can be applied to other radionuclides where elimination is predominantly through urine, which is often the case in radiopharmaceuticals.

177Lu-DOTATATE therapy in patients with neuroendocrine tumours including high-grade (WHO G3) neuroendocrine tumours: response to treatment and long-term survival update

PURPOSE

Upon diagnosis, distant metastases are encountered in 21-50% of neuroendocrine tumours (NETs). However, few systemic treatment options are available for the well-differentiated NETs in the metastatic stage. Lu-DOTATATE is one of the most effective treatments in this limited patient group. We retrospectively investigated its efficacy and effect on the survival in patients with both well-differentiated and grade III NETs who had high uptake in pretherapeutic Ga-DOTATATE PET/computed tomography scans.

PATIENTS AND METHODS

Patients with metastatic NETs treated with Lu-DOTATATE between January 2010 and November 2015 in our department were included in this retrospective cohort. Toxicity and adverse effects were evaluated according to SWOG criteria. Progression-free survival (PFS) and overall survival (OS) rates were calculated considering the first date of treatment. Response was evaluated according to RECIST criteria. Potential predictors of survival and response were analysed.

RESULTS

Patients (n=186) with metastatic NETs originating from various primary sites (bronchial, pancreatic, nonpancreatic gastroenteropancreatic-NETs, pheochromocytoma-paraganglioma and unknown primary) were treated with 1107 courses of Lu-DOTATATE treatment (median: 6; range: 3-12). Among 160 patients whose responses to treatment could be evaluated according to the RECIST criteria, 28.1% (n=45) had a progressive disease, 21.9% (n=35) had a stable disease, 46.9% (n=75) had a partial response and 3.1% (n=5) had a complete response. Median follow-up was 30.6 months. The Kaplan-Meier estimated median PFS was 36.4 months, mean PFS was 38 months and the mean OS was 55 months. The disease control rates in patients with WHO grades I, II and III were 74, 73 and 60%, respectively, and the OS rates were 61.9, 52.2 and 38.4 months, respectively. We observed no major renal toxicity except a minor increase (11.1%) in average serum creatinine levels. In 33.9% (n=56) of the patients, grade I toxicity; in 9.1% (n=15), grade II; and in 1.2% (n=2), grade III toxicity were observed.

CONCLUSION

Lu-DOTATATE therapy is an important treatment option in somatostatin receptor type-2-positive pancreatic, nonpancreatic gastroenteropancreatic-NETs, and lung NETs including metastatic NETs with an unknown primary site and significantly contributed to patients' OS. Additionally, peptide receptor radionuclide therapy may have a role in a selected subgroup of patients with grade III NET with high somatostatin receptor type-2 expression.

New Treatments for the Carcinoid Syndrome

Neuroendocrine tumors, including carcinoids, are rare and insidiously growing tumors. Related to their site of origin, tumors can be functional, causing various forms of the carcinoid syndrome, owing to the overproduction of serotonin, histamine, or other bioactive substances. They often invade adjacent structures or metastasize to the liver and elsewhere. Treatment includes multimodal approaches, including cytoreductive surgery, locoregional embolization, cytotoxic therapy, peptide receptor radionuclide therapy, and various targeted therapies with goals of symptom relief and control of tumor growth. This article summarizes current and emerging approaches to management and reviews several promising future therapies.

Peptide Receptor Radiotherapy Comes of Age

Peptide receptor radionuclide therapy is a form of systemic radiotherapy shown to be effective in treating neuroendocrine tumors expressing somatostatin receptors. The NETTER-1 trial was the first randomized phase III clinical trial evaluating a radiolabeled somatostatin analog, and demonstrated significant improvement in progression-free survival among patients with midgut neuroendocrine tumors treated with ¹⁷⁷Lu-DOTATATE versus high-dose octreotide. This article discusses the evolution of peptide receptor radionuclide therapy, side effects, and potential future treatment approaches.

Twelve-Year Follow-up After Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been used for more than 20 y as a systemic treatment approach in inoperable or metastatic somatostatin receptor-positive tumors. The purpose of this study was to analyze the long-term outcome of PRRT with regard to the most commonly used radiopharmaceuticals, ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE. Methods: This retrospective clinical study included a total of 44 consecutive patients (27 men) with advanced tumors and enhanced somatostatin receptor expression. Mean age at initial diagnosis was 60 y (SD, 11.3 y; range, 40-84 y). Median follow-up was 80 mo. For ¹⁷⁷Lu-PRRT, the mean number of cycles administered was 5.3 ± 2.5 and the mean activity was 27.2 ± 14.9 GBq per patient. For ⁹⁰Y-PRRT, the mean number of cycles administered was 5.5 ± 2.6 and the mean activity was 14.7 ± 7.3 GBq per patient. Overall, 378 cycles were administered (mean, 8.6 ± 3.4 cycles per patient), with an overall cumulative activity of 1,514.1 GBq. Results: Median overall survival was 79 mo. Twenty-one (77.8%) of the 27 men and 9 (52.9%) of the 17 women had died 12 y after commencement of PRRT. The shortest duration of illness was 8 mo and the longest 155 mo. Severe side effects (World Health Organization grades III and IV) were seen in 9 of the 14 patients still alive. Chronic kidney disease in combination with anemia was the most common finding in the 9 patients with severe side effects. A poor prognosis was found for those patients who showed progressive disease, in comparison with patients with cumulative disease control after initial PRRT (log rank, P < 0.001), whereas women and patients with no more than 2 tumor sites seemed to especially benefit from PRRT (not reaching significance levels). Conclusion: PRRT is encouraging in terms of long-term outcome. Thirty-two percent (14/44 patients) of the patients with metastatic or inoperable disease were still alive more than 12 y after the beginning of radionuclide therapy. Possible predictors for favorable outcome are having an initial response to PRRT, having a low number of affected sites, and being female.

Quality of Life in Patients with Metastatic Gastroenteropancreatic Neuroendocrine Tumors Receiving Peptide Receptor Radionuclide Therapy: Information from a Monitoring Program in Clinical Routine

In patients with metastatic gastroenteropancreatic neuroendocrine tumors (NETs), we evaluated health-related quality of life (HRQoL) from the first peptide receptor radionuclide therapy (PRRT) to the first restaging and compared the scores with general-population (GP) norms. Methods: The data were from routine HRQoL monitoring using the core quality-of-life questionnaire of the European Organization for Research and Treatment of Cancer (EORTC QLQ-C30). Patients received 4-6 cycles of ¹⁷⁷Lu-DOTATATE or ⁹⁰Y-DOTATOC. To be eligible for analysis, patients had to have at least one HRQoL assessment before PRRT and at least one HRQoL assessment at the end of or after treatment completion. Linear mixed models were used to consider HRQoL changes over time. Results: In total, 61 gastroenteropancreatic NET patients (small-intestine NETs, n = 37; pancreatic NETs, n = 24) were eligible for analysis. Clear improvements from baseline to the first restaging were found for diarrhea in small-intestine NET patients, showing a decrease of 16 points, which represents a moderately large change. We observed a clinically relevant decrease in appetite loss (17 points), but for female small-intestine NET patients only. Other HRQoL changes were also restricted to sociodemographic or clinical subgroups and mainly reflected improvements, except for physical and social functioning, which showed decreasing scores in older small-intestine NET patients. Compared with HRQoL GP norms, patients had impairments consisting of diarrhea; fatigue; appetite loss; reduced physical, social, and role functioning; and reduced global HRQoL. Except for diarrhea and appetite loss, patient scores at the first restaging did not reach GP levels. Conclusion: Our analyses support previous findings of overall stable HRQoL under PRRT. Yet, significant HRQoL impairments compared with the GP and potentially specific subgroup patterns need to be considered.

Chemical aspects of metal ion chelation in the synthesis and application antibody-based radiotracers

Radiometals are becoming increasingly accessible and are utilized frequently in the design of radiotracers for imaging and therapy. Nuclear properties ranging from the emission of γ-rays and β+ -particles (imaging) to Auger electron and β- and α-particles (therapy) in combination with long half-lives are ideally matched with the relatively long biological half-life of monoclonal antibodies in vivo. Radiometal labeling of antibodies requires the incorporation of a metal chelate onto the monoclonal antibody. This chelate must coordinate the metal under mild conditions required for the handling of antibodies, as well as provide high kinetic, thermodynamic, and metabolic stability once the metal ion is coordinated to prevent release of the radionuclide before the target site is reached in vivo. Herein, we review the role of different radiometals that have found applications of the design of radiolabeled antibodies for imaging and radioimmunotherapy. Each radionuclide is described regarding its nuclear synthesis, coordinative preference, and radiolabeling properties with commonly used and novel chelates, as well as examples of their preclinical and clinical applications. An overview of recent trends in antibody-based radiopharmaceuticals is provided to spur continued development of the chemistry and application of radiometals for imaging and therapy.

Correlation of dose with toxicity and tumour response to 90Y- and 177Lu-PRRT provides the basis for optimization through individualized treatment planning

PURPOSE

Peptide receptor radionuclide therapy (PRRT) with ⁹⁰Y-labelled and ¹⁷⁷Lu-labelled peptides is an effective strategy for the treatment of metastatic/nonresectable neuroendocrine tumours (NETs). Dosimetry provides important information useful for optimizing PRRT with individualized regimens to reduce toxicity and increase tumour responses. However, this strategy is not applied in routine clinical practice, despite the fact that several dosimetric studies have demonstrated significant dose-effect correlations for normal organ toxicity and tumour response that can better guide therapy planning. The present study reviews the key relationships and the radiobiological models available in the literature with the aim of providing evidence that optimization of PRRT is feasible through the implementation of dosimetry.

METHODS

The MEDLINE database was searched combining specific keywords. Original studies published in the English language reporting dose-effect outcomes in patients treated with PRRT were chosen.

RESULTS

Nine of 126 studies were selected from PubMed, and a further five were added manually, reporting on 590 patients. The studies were analysed and are discussed in terms of weak and strong elements of correlations.

CONCLUSION

Several studies provided evidence of clinical benefit from the implementation of dosimetry in PRRT, indicating the potential contribution of this approach to reducing severe toxicity and/or reducing undertreatment that commonly occurs. Prospective trials, possibly multicentre, with larger numbers of patients undergoing quantitative dosimetry and with standardized methodologies should be carried out to definitively provide robust predictive paradigms to establish effective tailored PRRT.

Concomitant 177Lu-DOTATATE and Capecitabine Therapy in Patients With Advanced Neuroendocrine Tumors: A Long-term-Outcome, Toxicity, Survival, and Quality-of-Life Study

PURPOSE

The purpose of this study was to evaluate the outcome, toxicity, survival, and quality of life in patients with advanced neuroendocrine tumors.

METHODS

One hundred sixty-seven patients were enrolled in the study. All patients underwent baseline Ga-DOTANOC PET/CT scans. Lu-DOTATATE therapy was administered quarterly along with oral capecitabine therapy in group 1 patients (n = 88), whereas group 2 patients (n = 79) were treated only with Lu-DOTATATE. Hematologic, kidney function, liver function tests and chromogranin A levels were recorded before and after therapy at 2-week, 4-week, and 3-month intervals. Biochemical and morphological responses were assessed with the trend in chromogranin A levels and Response Evaluation Criteria in Solid Tumors 1.1 criteria, respectively.

RESULTS

There was no significant difference in the hemoglobin levels after Lu-DOTATATE therapy (P = 0.4892). In most patients, there was a decrease in the platelet levels; however, all the patients had platelet counts greater than 100,000/μL with no platelet toxicity. There was no toxicity related to leukocytes. Two patients showed renal insufficiencies. No hepatotoxicity was observed in any of the patients. According to Response Evaluation Criteria in Solid Tumors 1.1 criteria, in group 1 patients, the response was partial response in 34% of the patients, stable disease in 50.2%, and progressive disease in 6.8% versus partial response in 6.3%, stable disease in 60.9%, and progressive disease in 26.5% among group 2 patients. The median overall survival (OS) and progression-free survival (PFS) was not reached in group 1 patients. The median OS and PFS in group 2 patients were 48 months. Ki-67 tumor proliferation index was significantly associated with increased risk of disease progression.

CONCLUSIONS

Addition of capecitabine therapy with Lu-DOTATATE therapy lengthens the OS and PFS. Patients with aggressive disease may benefit from this synergetic therapeutic approach.

Peptide Receptor Radionuclide Therapy and the Treatment of Gastroentero-pancreatic Neuroendocrine Tumors: Current Findings and Future Perspectives

Purpose and Methods

Patients with inoperable and metastasized neuroendocrine tumors (NETs), particularly those with grades 1 and 2, usually receive treatment with somatostatin analogues (SSAs). Peptide receptor radionuclide therapy (PRRT) has gained momentum over the past two decades in patients who progress on SSAs. 177Lu-DOTATATE is currently the most widely used radiopeptide for PRRT. We reviewed the recent evidence on PRRT and the treatment of gastroentero-pancreatic neuroendocrine tumors (GEP-NETs).

Results

¹⁷⁷Lu-DOTATATE can be used as neoadjuvant treatment in patients with inoperable GEP-NETs, who might be candidate for surgery after treatment and as adjuvant therapy after surgical intervention. Combination treatments of PRRT with chemotherapy or targeted agents as well as combinations of radionuclides in patients with NETs have been explored over the last few years. The majority of patients with NETs experience partial response or have disease stabilization, a small percentage has complete response, while some 30% of patients, however, will have disease progression. The safety and efficacy of retreatment with extra cycles of PRRT as salvage therapy have been evaluated in small retrospective series.

Conclusion

Overall, there is evidence that disease control and quality of life improve significantly after 117Lu PRRT therapy. Clinical trials on this therapy are scarce, and there is a need for further studies to establish proper management guidelines.

Retreatment with peptide receptor radionuclide therapy in patients with progressing neuroendocrine tumours: efficacy and prognostic factors for response

OBJECTIVE:

To evaluate the efficacy and toxicity of a repeat peptide receptor radionuclide therapy (PRRT) course in neuroendocrine tumour patients who have progressed following previous PRRT and to identify factors contributing to retreatment outcomes.

METHODS:

This was a retrospective analysis of 47 consecutive patients who had been treated with PRRT (PRRT1) and following disease progression were retreated with a second course of PRRT (PRRT2). We reviewed patient, tumour and treatment characteristics, time to progression after PRRT1 and PRRT2, overall survival and toxicity. We evaluated Kaplan-Meier survival plots, multiple regression analysis on factors predictive of time to progression and toxicity.

RESULTS:

PRRT1: 45/47 patients were initially were treated with ⁹⁰Y-DOTATATE, with two patients treated with ¹⁷⁷Lu-DOTATATE. The median progression free survival (PFS) following PRRT1 was 30 months [95% confidence interval (CI) (26.9-36.6 months)]. Two patients developed Grade 1 renal toxicity. 3/47 patients had bone marrow toxicity, with 1 of these patients having Grade 3 toxicity. PRRT2: At the second course of treatment, 29 patients were treated with ⁹⁰Y-DOTATATE and 18 patients with ¹⁷⁷Lu-DOTATATE. Of the 44 patients with evaluable survival data, 41 patients developed disease progression. The median PFS after PRRT2 was 17.5 months [95% CI (11-23.8 months)]. There was no statistically significant difference in median PFS dependent on the choice of radiopharmaceutical: median PFS for ¹⁷⁷Lu-DOTATATE = 17.2 months, median PFS for ⁹⁰Y-DOTATATE = 17.3 months. Male sex and high burden of liver metastases were associated with shorter PFS following a PRRT retreatment course. 17/41 (41%) patients had bone marrow toxicity (2/17 had Grade 3 toxicity; no Grade 4 toxicity was seen). One patient developed myelodysplastic syndrome. 6/41 (14.6%) developed Grade 1 renal toxicity and 1/41 (2.4%) had Grade 4 renal toxicity. The median overall survival from commencement of first PRRT cycle was 71 months.

CONCLUSION:

PRRT retreatment is safe and offers patients, who had progressed following initial PRRT course, a reasonably good PFS. Extra consideration is needed in patients with multiple comorbidities, as they may be at greater risk of renal and haematological toxicity. Male sex and high burden of liver metastases seem to be associated with shorter PFS following PRRT retreatment.

ADVANCES IN KNOWLEDGE:

The majority of studies on PRRT have shown that it is effective as an initial treatment. This study with long-term follow-up demonstrates that PRRT is safe and effective retreatment option in patients that have progressed following initial PRRT course.

Prevention and management of carcinoid crises in patients with high-risk neuroendocrine tumours undergoing peptide receptor radionuclide therapy (PRRT): Literature review and case series from two Australian tertiary medical institutions

Peptide receptor radionuclide therapy (PRRT) is an important therapeutic option for somatostatin receptor (SSTR) positive metastatic and/or inoperable neuroendocrine tumours (NETs). However, in patients with poorly controlled carcinoid syndrome, it may lead to an acute flare of carcinoid symptoms or even carcinoid crisis. We report seven patients who received PRRT with (¹⁷⁷Lu-DOTA⁰, Tyr³) octreotate (¹⁷⁷Lu-octreotate-LuTate) across two Australian tertiary medical institutions who developed acute flare of carcinoid symptoms/carcinoid crisis during/after PRRT. Cases were identified as high-risk due to previous history of carcinoid crises, high tumour burden and markedly elevated tumour markers. We propose a protocol to prevent and manage severe carcinoid symptoms in high-risk patients treated with PRRT.

Prospective observational study of 177Lu-DOTA-octreotate therapy in 200 patients with advanced metastasized neuroendocrine tumours (NETs): feasibility and impact of a dosimetry-guided study protocol on outcome and toxicity

PURPOSE

Peptide receptor radionuclide therapy in patients with neuroendocrine tumours has yielded promising results. This prospective study investigated the feasibility of dosimetry of the kidneys and bone marrow during therapy and its impact on efficacy and outcome.

METHODS

The study group comprised 200 consecutive patients with metastasized somatostatin receptor-positive neuroendocrine tumours progressing on standard therapy or not suitable for other therapeutic options. A treatment cycle consisted of 7.4 GBq ¹⁷⁷Lu-DOTA-octreotate with co-infusion of a mixed amino acid solution, and cycles were repeated until the absorbed dose to the kidneys reached 23 Gy or there were other reasons for stopping therapy. The Ki-67 index was ≤2% in 47 patients (23.5%), 3-20% in 121 (60.5%) and >20% in 16 (8%).

RESULTS

In 123 patients (61.5%) the absorbed dose to the kidneys reached 23 Gy with three to nine cycles during first-line therapy; in no patient was a dose to the bone marrow of 2 Gy reached. The best responses (according to RECIST 1.1) were a complete response (CR) in 1 patient (0.5%), a partial response (PR) in 47 (23.5%), stable disease (SD) in 135 (67.5%) and progressive disease (PD) in 7 (3.5%). Median progression-free survival was 27 months (95% CI 22-30 months) in all patients, 33 months in those in whom the absorbed dose to the kidneys reached 23 Gy and 15 months in those in whom it did not. Median overall survival (OS) was 43 months (95% CI 39-53 months) in all patients, 54 months in those in whom the absorbed dose to the kidneys reached 23 Gy and 25 months in those in whom it did not. Median OS was 60 months in patients with a best response of PR or CR, 42 months in those with SD and 16 months in those with PD. Three patients (1.5%) developed acute leukaemia, 1 patient (0.5%) chronic leukaemia (unconfirmed) and 30 patients (15%) grade 3 or 4 bone marrow toxicity. Eight patients (4%) developed grade 2 kidney toxicity and one patient (0.5%) grade 4 kidney toxicity.

CONCLUSIONS

Dosimetry-based therapy with ¹⁷⁷Lu-DOTA-octreotate is feasible. Patients in whom the absorbed dose to the kidneys reached 23 Gy had a longer OS than those in whom it did not. Patients with CR/PR had a longer OS than those with SD. Bone marrow dosimetry did not predict toxicity.

Theranostics in nuclear medicine practice

The importance of personalized medicine has been growing, mainly due to a more urgent need to avoid unnecessary and expensive treatments. In nuclear medicine, the theranostic approach is an established tool for specific molecular targeting, both for diagnostics and therapy. The visualization of potential targets can help predict if a patient will benefit from a particular treatment. Thanks to the quick development of radiopharmaceuticals and diagnostic techniques, the use of theranostic agents has been continually increasing. In this article, important milestones of nuclear therapies and diagnostics in the context of theranostics are highlighted. It begins with a well-known radioiodine therapy in patients with thyroid cancer and then progresses through various approaches for the treatment of advanced cancer with targeted therapies. The aim of this review was to provide a summary of background knowledge and current applications, and to identify the advantages of targeted therapies and imaging in nuclear medicine practices.

Molecular radiotheranostics for neuroendocrine tumours

This article discusses the important role of nuclear medicine imaging and therapy in the management of neuroendocrine tumours (NETs). Somatostatin receptor scintigraphy has a high impact on patient management versus conventional imaging. Molecular radiotherapy is an important part of the management of patients with NETs. Selection of patients for molecular radiotherapy in NETs is based on uptake on their radionuclide imaging study. The imaging agent has the same mechanism of uptake as the therapeutic agent. Thus, the imaging study preselects patients that are likely to concentrate radiation within their tumours.

The safety of available treatments options for neuroendocrine tumors

INTRODUCTION

Neuroendocrine neoplasms (NEN) represent a heterogeneous group of malignancies generally characterized by low proliferation and indolent course. However, about half of the newly diagnosed cases are metastatic and require long-term systemic therapies. Areas covered: This review revises the literature to summarize the current knowledge upon safety of all systemic treatment options available. Thirty three different clinical studies have been considered, including 4 on somatostatin analogues (SSA), 5 on targeted therapies, 10 on peptide receptor radionuclide therapy (PRRT), and 14 on chemotherapy. Expert opinion: SSA are safe and well tolerated without any relevant severe adverse event and very low treatment discontinuation rate. Targeted therapies show a satisfying safety profile. Most adverse events are grade 1-2 and easy manageable with dose reduction or temporary interruption. PRRT is manageable and safe with a low rate of grade 3-4 adverse events. However, severe renal and hematologic toxicity may occur. Chemotherapy is usually considered after previous therapeutic lines. Therefore, these subjects are more susceptible to experience adverse events due to cumulative toxicities or poor performance status. The available systemic treatment options are generally well tolerated and suitable for long-term administration. Cumulative toxicity should be taken in account for the definition of therapeutic sequence.

111In-DTPA-d-Phe-1-Asp0-d-Phe1-octreotide exhibits higher tumor accumulation and lower renal radioactivity than 111In-DTPA-d-Phe1-octreotide

INTRODUCTION

¹¹¹In-DTPA-d-Phe¹-octreotide scintigraphy is an important method of detecting neuroendocrine tumors. We previously reported that a new derivative of ¹¹¹In-DTPA-d-Phe¹-octreotide, ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide, accomplished the reduction of prolonged renal accumulation of radioactivity. The aim of this study was to evaluate the tumor accumulation of ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide in vitro and in vivo by comparing it with ¹¹¹In-DTPA-d-Phe¹-octreotide.

METHODS

The tumor accumulation of this octreotide derivative was determined by measuring its uptake using cultured AR42J cells in vitro and biodistribution studies in vivo. The distribution of the radiotracer and the extent of somatostatin receptor-specific uptake in the tumor were estimated by a counting method using AR42J tumor-bearing mice. The radioactive metabolite species in the tumor and kidney were identified by HPLC analyses at 3 and 24h post-injection of the ¹¹¹In-DTPA-conjugated peptide.

RESULTS

In both cases, in vitro and in vivo, the tumor radioactivity levels of ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide were approximately 2-4 times higher than those of ¹¹¹In-DTPA-d-Phe¹-octreotide. On in vitro cellular uptake inhibition and radioreceptor assay, ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide exhibited a binding affinity to somatostatin receptor highly similar to that of ¹¹¹In-DTPA-d-Phe¹-octreotide. As the additional cellular uptake of ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide was significantly lower at low temperature than at 37°C, it was considered that a cellular uptake pathway is involved in energy-dependent endocytotic processes. In the radiometabolite analysis of ¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide, ¹¹¹In-DTPA-d-Phe-Asp-OH was a major metabolite in the tumor at 24h post-injection.

CONCLUSION

¹¹¹In-DTPA-d-Phe^-1-Asp⁰-d-Phe¹-octreotide exhibited higher tumor accumulation and persistence of tumor radioactivity than ¹¹¹In-DTPA-d-Phe¹-octreotide. We reasoned that this higher tumor accumulation would not be based on the receptor affinity but on a receptor-mediated endocytotic process involved in temperature-dependent cellular uptake. The present study demonstrated the great potential of the pharmaceutical development of a new radiolabeled peptide with high tumor accumulation and low renal radioactivity by the chemical modification of ¹¹¹In-DTPA-d-Phe¹-octreotide.

Management Options for Advanced Low or Intermediate Grade Gastroenteropancreatic Neuroendocrine Tumors: Review of Recent Literature

Our understanding of the biology, genetics, and natural history of neuroendocrine tumors (NETs) of the gastrointestinal tract and pancreas has improved considerably in the last several decades and the spectrum of available therapeutic options is rapidly expanding. The management of patients with metastatic low or intermediate grade NETs has been revolutionized by the development of new treatment strategies such as molecular targeting therapies with everolimus and sunitinib, somatostatin analogs, tryptophan hydroxylase inhibitors, and peptide receptor radionuclide therapy that can be used alone or as a multimodal approach with or without surgery. To further define and clarify the utility, appropriateness, and the sequence of the growing list of available therapies for this patient population will require more high level evidence; however, data from well-designed randomized phase III clinical trials is rapidly accumulating that will further stimulate development of new management strategies. It is therefore important to thoroughly review emerging evidence and report major findings in frequent updates, which will expand our knowledge and contribute to a better understanding, characterization, and management of advanced NETs.

Renal Function Assessment During Peptide Receptor Radionuclide Therapy

Theranostics labeled with Y-90 or Lu-177 are highly efficient therapeutic approaches for the systemic treatment of various cancers including neuroendocrine tumors and prostate cancer. Peptide receptor radionuclide therapy (PRRT) has been used for many years for metastatic or inoperable neuroendocrine tumors. However, renal and hematopoietic toxicities are the major limitations for this therapeutic approach. Kidneys have been considered as the "critical organ" because of the predominant glomerular filtration, tubular reabsorption by the proximal tubules, and interstitial retention of the tracers. Severe nephrotoxity, which has been classified as grade 4-5 based on the "Common Terminology Criteria on Adverse Events," was reported in the range from 0%-14%. There are several risk factors for renal toxicity; patient-related risk factors include older age, preexisting renal disease, hypertension, diabetes mellitus, previous nephrotoxic chemotherapy, metastatic lesions close to renal parenchyma, and single kidney. There are also treatment-related issues, such as choice of radionuclide, cumulative radiation dose to kidneys, renal radiation dose per cycle, activity administered, number of cycles, and time interval between cycles. In the literature, nephrotoxicity caused by PRRT was documented using different criteria and renal function tests, from serum creatinine level to more accurate and sophisticated methods. Generally, serum creatinine level was used as a measure of kidney function. Glomerular filtration rate (GFR) estimation based on serum creatinine was preferred by several authors. Most commonly used formulas for estimation of GFR are "Modifications of Diet in Renal Disease" (MDRD) equation and "Cockcroft-Gault" formulas. However, more precise methods than creatinine or creatinine clearance are recommended to assess renal function, such as GFR measurements using Tc-99m-diethylenetriaminepentaacetic acid (DTPA), Cr-51-ethylenediaminetetraacetic acid (EDTA), or measurement of Tc-99m-MAG3 clearance, particularly in patients with preexisting risk factors for long-term nephrotoxicity. Proximal tubular reabsorption and interstitial retention of tracers result in excessive renal irradiation. Coinfusion of positively charged amino acids, such as l-lysine and l-arginine, is recommended to decrease the renal retention of the tracers by inhibiting the proximal tubular reabsorption. Furthermore, nephrotoxicity may be reduced by dose fractionation. Patient-specific dosimetric studies showed that renal biological effective dose of <0Gy was safe for patients without any risk factors. A renal threshold value <28Gy was recommended for patients with risk factors. Despite kidney protection, renal function impairment can occur after PRRT, especially in patients with risk factors and high single or cumulative renal absorbed dose. Therefore, patient-specific dosimetry may be helpful in minimizing the renal absorbed dose while maximizing the tumor dose. In addition, close and accurate renal function monitoring using more precise methods, rather than plasma creatinine levels, is essential to diagnose the early renal functional changes and to follow-up the renal function during the treatment.