Phase I study of peptide receptor radionuclide therapy with [In-DTPA]octreotide: the Rotterdam experience

Dose escalation of an Evans blue-modified radiolabeled somatostatin analog 177Lu-DOTA-EB-TATE in the treatment of metastatic neuroendocrine tumors

PURPOSE

To evaluate the safety and efficacy of ¹⁷⁷Lu-DOTA-EB-TATE, a radiolabeled somatostatin analog modified by Evans blue, at escalating doses, was used to increase tumor retention in patients with progressive metastatic neuroendocrine tumors (NETs).

METHODS

Thirty-three patients with metastatic NETs were prospectively enrolled into four groups: group A (n = 6, 43 ± 12 years) administered approximately 3.7 GBq (100 mCi) ¹⁷⁷Lu-DOTATATE as controls; group B (n = 7, 55 ± 7 years) administered approximately 1.11 GBq (30 mCi) ¹⁷⁷Lu-DOTA-EB-TATE; group C (n = 6, 55 ± 10 years) administered approximately 1.85 GBq (50 mCi) ¹⁷⁷Lu-DOTA-EB-TATE; group D (n = 14, 50 ± 10 years) administered approximately 3.7 GBq (100 mCi) ¹⁷⁷Lu-DOTA-EB-TATE. Treatment-related adverse events were graded according to the CTCAE v.5.0. ⁶⁸Ga-DOTATATE PET/CT were performed at baseline and 2-3 months after treatment for response evaluation.

RESULTS

Administration was well tolerated. No CTC 3/4 hematotoxicity, nephrotoxicity, or hepatotoxicity was observed during or after treatment in groups A-C. In group D, CTC-3 hematotoxicity was recorded in 2 patients with multicourse chemotherapy previously. After one-cycle treatment, the SUVmax decreased in group C (Δ% = - 17.4 ± 29.3%) and group D (Δ% = - 15.1 ± 39.1%), but greatly increased in group B (Δ% = 30.0 ± 68.0%) and mildly increased in group A (Δ% = 5.4 ± 45.9%). Referring to EORTC criteria, 16.7% (1/6), 0% (0/7), 50% (3/6), and 50% (7/14) were evaluated as partial response in groups A, B, C, and D, respectively. When selecting lesions with comparable baseline SUVmax ranging from 15 to 40, SUVmax showed no significant decrease in group B (Δ% = - 7.3 ± 24.5%) (P = 0.214), significant decrease in group C (Δ% = - 34.9 ± 12.4%) (P = 0.001), and in group D (Δ% = - 17.9 ± 19.7%) (P = 0.012) as compared with group A with increased SUVmax (Δ% = 8.4 ± 48.8%). SUVmax significantly decreased in the EBTATE groups (groups B-D combined) (Δ% = - 19.0 ± 21.5%) as compared with the TATE group (P = 0.045).

CONCLUSION

¹⁷⁷Lu-DOTA-EB-TATE is well tolerated and is more effective than ¹⁷⁷Lu-DOTATATE. Both 1.85 GBq (50 mCi) and 3.7 GBq (100 mCi) doses appear to be more effective than 1.11 GBq (30 mCi) dose. Further investigation with more cycles of ¹⁷⁷Lu-DOTA-EB-TATE treatment and longer follow-up is warranted.

TRIAL REGISTRATION

Treatment Using 177Lu-DOTA-EB-TATE in Patients with Advanced Neuroendocrine Tumors (NCT03478358). URL: https://register.clinicaltrials.gov/prs/app/action/ViewOrUnrelease?uid=U0001JRW&ts=13&sid=S0007RNX&cx=y3yqv4.

Delivery systems exploiting natural cell transport processes of macromolecules for intracellular targeting of Auger electron emitters

The presence of Auger electrons (AE) among the decay products of a number of radionuclides makes these radionuclides an attractive means for treating cancer because these short-range electrons can cause significant damage in the immediate vicinity of the decomposition site. Moreover, the extreme locality of the effect provides a potential for selective eradication of cancer cells with minimal damage to adjacent normal cells provided that the delivery of the AE emitter to the most vulnerable parts of the cell can be achieved. Few cellular compartments have been regarded as the desired target site for AE emitters, with the cell nucleus generally recognized as the preferred site for AE decay due to the extreme sensitivity of nuclear DNA to direct damage by radiation of high linear energy transfer. Thus, the advantages of AE emitters for cancer therapy are most likely to be realized by their selective delivery into the nucleus of the malignant cells. To achieve this goal, delivery systems must combine a challenging complex of properties that not only provide cancer cell preferential recognition but also cell entry followed by transport into the cell nucleus. A promising strategy for achieving this is the recruitment of natural cell transport processes of macromolecules, involved in each of the aforementioned steps. To date, a number of constructs exploiting intracellular transport systems have been proposed for AE emitter delivery to the nucleus of a targeted cell. An example of such a multifunctional vehicle that provides smart step-by-step delivery is the so-called modular nanotransporter, which accomplishes selective recognition, binding, internalization, and endosomal escape followed by nuclear import of the delivered radionuclide. The current review will focus on delivery systems utilizing various intracellular transport pathways and their combinations in order to provide efficient targeting of AE to the cancer cell nucleus.

177Lu-DOTATATE for the treatment of gastroenteropancreatic neuroendocrine tumors

Introduction: 177Lutetium-[DOTA°,Tyr3]octreotate (177Lu-DOTATATE) is a type of peptide receptor radionuclide therapy that garnered FDA approval in January 2018 for the treatment of somatostatin receptor-positive gastroenteropancreatic (GEP) neuroendocrine tumor (NET) patients. The therapy approval was based on findings from the randomized international phase III NETTER-1 trial as well as outcome data from a large European registry. The mechanism of the drug stems directly from its structure: a somatostatin analog (octreotate) selectively binding to somatostatin receptor expressing cells and being internalized, along with a chelated beta-emitting isotope 177Lu.Areas Covered: Herein we describe the pharmacology, clinical efficacy and adverse event data from prospective and retrospective studies with 177Lu-DOTATATE. We discuss the role of 177Lu-DOTATATE within the current treatment landscape for GEP NET patients.Expert Opinion: 177Lu-DOTATATE represents a unique addition to the treatment armamentarium for GEP NETs because of its potential to elicit tumor cytoreduction, which is rare among other existing treatment options, and prolonged disease control. Where 177Lu-DOTATATE fits into the treatment sequence for GEP NET patients remains an area of active investigation.

Auger electrons for cancer therapy - a review

Background

Auger electrons (AEs) are very low energy electrons that are emitted by radionuclides that decay by electron capture (e.g. ¹¹¹In, ⁶⁷Ga, ^99mTc, ^195mPt, ¹²⁵I and ¹²³I). This energy is deposited over nanometre-micrometre distances, resulting in high linear energy transfer (LET) that is potent for causing lethal damage in cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for treatment of cancer. In this review, we describe the radiobiological properties of AEs, their radiation dosimetry, radiolabelling methods, and preclinical and clinical studies that have been performed to investigate AEs for cancer treatment.

Results

AEs are most lethal to cancer cells when emitted near the cell nucleus and especially when incorporated into DNA (e.g. ¹²⁵I-IUdR). AEs cause DNA damage both directly and indirectly via water radiolysis. AEs can also kill targeted cancer cells by damaging the cell membrane, and kill non-targeted cells through a cross-dose or bystander effect. The radiation dosimetry of AEs considers both organ doses and cellular doses. The Medical Internal Radiation Dose (MIRD) schema may be applied. Radiolabelling methods for complexing AE-emitters to biomolecules (antibodies and peptides) and nanoparticles include radioiodination (¹²⁵I and ¹²³I) or radiometal chelation (¹¹¹In, ⁶⁷Ga, ^99mTc). Cancer cells exposed in vitro to AE-emitting radiotherapeutic agents exhibit decreased clonogenic survival correlated at least in part with unrepaired DNA double-strand breaks (DSBs) detected by immunofluorescence for γH2AX, and chromosomal aberrations. Preclinical studies of AE-emitting radiotherapeutic agents have shown strong tumour growth inhibition in vivo in tumour xenograft mouse models. Minimal normal tissue toxicity was found due to the restricted toxicity of AEs mostly on tumour cells targeted by the radiotherapeutic agents. Clinical studies of AEs for cancer treatment have been limited but some encouraging results were obtained in early studies using ¹¹¹In-DTPA-octreotide and ¹²⁵I-IUdR, in which tumour remissions were achieved in several patients at administered amounts that caused low normal tissue toxicity, as well as promising improvements in the survival of glioblastoma patients with ¹²⁵I-mAb 425, with minimal normal tissue toxicity.

Conclusions

Proof-of-principle for AE radiotherapy of cancer has been shown preclinically, and clinically in a limited number of studies. The recent introduction of many biologically-targeted therapies for cancer creates new opportunities to design novel AE-emitting agents for cancer treatment. Pierre Auger did not conceive of the application of AEs for targeted cancer treatment, but this is a tremendously exciting future that we and many other scientists in this field envision.

ICRP Publication 140: Radiological Protection in Therapy with Radiopharmaceuticals

Radiopharmaceuticals are increasingly used for the treatment of various cancers with novel radionuclides, compounds, tracer molecules, and administration techniques. The goal of radiation therapy, including therapy with radiopharmaceuticals, is to optimise the relationship between tumour control probability and potential complications in normal organs and tissues. Essential to this optimisation is the ability to quantify the radiation doses delivered to both tumours and normal tissues. This publication provides an overview of therapeutic procedures and a framework for calculating radiation doses for various treatment approaches. In radiopharmaceutical therapy, the absorbed dose to an organ or tissue is governed by radiopharmaceutical uptake, retention in and clearance from the various organs and tissues of the body, together with radionuclide physical half-life. Biokinetic parameters are determined by direct measurements made using techniques that vary in complexity. For treatment planning, absorbed dose calculations are usually performed prior to therapy using a trace-labelled diagnostic administration, or retrospective dosimetry may be performed on the basis of the activity already administered following each therapeutic administration. Uncertainty analyses provide additional information about sources of bias and random variation and their magnitudes; these analyses show the reliability and quality of absorbed dose calculations. Effective dose can provide an approximate measure of lifetime risk of detriment attributable to the stochastic effects of radiation exposure, principally cancer, but effective dose does not predict future cancer incidence for an individual and does not apply to short-term deterministic effects associated with radiopharmaceutical therapy. Accident prevention in radiation therapy should be an integral part of the design of facilities, equipment, and administration procedures. Minimisation of staff exposures includes consideration of equipment design, proper shielding and handling of sources, and personal protective equipment and tools, as well as education and training to promote awareness and engagement in radiological protection. The decision to hold or release a patient after radiopharmaceutical therapy should account for potential radiation dose to members of the public and carers that may result from residual radioactivity in the patient. In these situations, specific radiological protection guidance should be provided to patients and carers.

Prognostic Significance of Somatostatin Receptor Heterogeneity in Progressive Neuroendocrine Tumor Treated with Lu-177 DOTATOC or Lu-177 DOTATATE

AIM

One of the primary prerequisites for peptide receptor radionuclide therapy (PRRT) in patients with neuroendocrine tumors (NET) is the presence of somatostatin receptors (SSTR) on NET cells. NET are highly heterogeneous and an individual patient as well as separate metastases can harbor cells with different clones, which influence the SSTR expression on NET cells. With this background we looked into our institutional database to assess the prognostic significance of quality of SSTR expression on SSTR PET/CT imaging in patients treated with at least two cycles of Lu-177 DOTATOC or Lu-177 DOTATATE.

METHOD

Clinical reports and images from 65 (25 females, 40 males; 65 ± 11 years old) patients with progressive grade 1 or grade 2 NET with 2-5 therapy cycles of PRRT with an average administered dose of 6.6 ± 0.97 GBq Lu-177 DOTATOC or Lu-177 DOTATATE were analyzed. All patients were examined with baseline Ga-68 DOTATATE or Ga-68 DOTATOC PET/CT (PET). Quality of SSTR expression as a measure of heterogeneity on indexed lesions was assessed visually. Patients were followed for a median duration of 25 months after the first PRRT (range 5-77 months).

RESULTS

A total of 70% of the patients received three or more therapy cycles. Twenty-six patients (40%) were treated with PRRT as first or second line while 39 (60%) as third line or more. SSTR expression was heterogeneous in 28 (44.4%) and homogeneous in 35 (55.6%) patients. Disease stabilization could be achieved in 23 patients (35.4%), whereas 17 (26.1%) showed partial remission and 25 patients (38.5%) had disease progression. Median OS was not reached. The 24-month survival rate of the whole study cohort was 83%. In univariate analyses, factors influencing OS were carcinoid heart disease, carcinoid syndrome and quality of SSTR expression (p < 0.05). Patients with heterogeneous SSTR expression on target lesions had a significantly lower OS (p = 0.01). Median time to progression in total patient population was found to be 40 months. Patients with heterogeneous SSTR expression on target lesions had significantly lower TTP (26 months vs 54 months log Rank p = 0.013). By multivariate analyses, quality of SSTR was found to be the only prognostic factor for OS (p = 0.04; HR = 3.68) and also for TTP (p = 0.03; HR = 3.09).

CONCLUSION

Visual assessment of SSTR heterogeneity has both predictive and prognostic value in progressive grade 1 or grade 2 NET patients undergoing PRRT.

Neurotheranostics as personalized medicines

The discipline of neurotheranostics was forged to improve diagnostic and therapeutic clinical outcomes for neurological disorders. Research was facilitated, in largest measure, by the creation of pharmacologically effective multimodal pharmaceutical formulations. Deployment of neurotheranostic agents could revolutionize staging and improve nervous system disease therapeutic outcomes. However, obstacles in formulation design, drug loading and payload delivery still remain. These will certainly be aided by multidisciplinary basic research and clinical teams with pharmacology, nanotechnology, neuroscience and pharmaceutic expertise. When successful the end results will provide "optimal" therapeutic delivery platforms. The current report reviews an extensive body of knowledge of the natural history, epidemiology, pathogenesis and therapeutics of neurologic disease with an eye on how, when and under what circumstances neurotheranostics will soon be used as personalized medicines for a broad range of neurodegenerative, neuroinflammatory and neuroinfectious diseases.

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.

Systemic treatment for lung carcinoids: from bench to bedside

In the huge spectrum of lung neuroendocrine neoplasms, typical and atypical carcinoids should be considered as a separate biological entity from poorly differentiated forms, harboring peculiar molecular alterations. Despite their indolent behavior, lung carcinoids correlate with a worse survival. To date, only limited therapeutic options are available and novel drugs are strongly needed. In this work, we extensively reviewed scientific literature exploring available therapeutic options, new molecular targets and future perspectives in the management of well differentiated neoplasms of bronchopulmonary tree. Systemic therapy represents the main option in advanced and unresectable disease; accepted choices are somatostatin analogs, peptide receptor radionuclide therapy, everolimus and chemotherapy. To date, an univocal treatment strategy has not been identified yet, thus tailored therapeutic algorithms should consider treatment efficacy as well as safety profiles. Several molecular alterations found in carcinoid tumors might act as molecular targets leading to development of new therapeutic options. Further studies are necessary to identify new potential “druggable” molecular targets in the selected subset of low-grade lung carcinoids. Furthermore, evaluating the available therapies in more homogeneous population might improve their efficacy through a perfect tailoring of treatment options.

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.

The Inflammation-Based Index Can Predict Response and Improve Patient Selection in NETs Treated With PRRT: A Pilot Study

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) is an effective treatment of certain patients with metastatic neuroendocrine tumors (NETs). Tumor response is highly variable; no biomarker in clinical practice has been demonstrated to reliably predict outcome. The inflammation-based index (IBI), derived from serum C-reactive protein and albumin levels, predicts survival and response to treatment in patients in several cancer types and was therefore explored in this setting.

MATERIALS AND METHODS

Clinico-pathological data from patients undergoing PRRT for metastatic NETs were collected at baseline and during treatment. The primary endpoint was progression-free survival (PFS) with a secondary endpoint of overall survival (OS). Cox regression analysis tested associations between baseline variables and their dynamic changes and PFS and OS. Decision curve analysis (DCA) was used to determine the net benefit associated with a treatment strategy determined by the baseline IBI and nonresponse to PRRT.

RESULTS

Fifty-five patients were recruited. Baseline IBI > 0 was associated with inferior PFS (hazard ratio, 14.2; 95% CI, 5.25 to 38.5; P < 0.001) and OS (P < 0.001). Multivariate analysis confirmed an independent association between IBI and PFS (P = 0.001). DCA indicated a net clinical benefit at risk thresholds between 0.03 and 0.58.

CONCLUSION

Baseline IBI score and its dynamic change through treatment are associated with both PFS and OS. At a risk threshold equivalent to the currently accepted rate of nonresponse to therapy, implementation of this easily derived score could avoid a substantial number of futile treatments. These findings should be validated in additional independent cohorts.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

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.

Antitumor Activity of Auger Electron Emitter 111In Delivered by Modular Nanotransporter for Treatment of Bladder Cancer With EGFR Overexpression

Gamma-ray emitting ¹¹¹In, which is extensively used for imaging, is also a source of short-range Auger electrons (AE). While exhibiting negligible effect outside cells, these AE become highly toxic near DNA within the cell nucleus. Therefore, these radionuclides can be used as a therapeutic anticancer agent if delivered precisely into the nuclei of tumor target cells. Modular nanotransporters (MNTs) designed to provide receptor-targeted delivery of short-range therapeutic cargoes into the nuclei of target cells are perspective candidates for specific intracellular delivery of AE emitters. The objective of this study was to evaluate the in vitro and in vivo efficacy of ¹¹¹In attached MNTs to kill human bladder cancer cells overexpressing epidermal growth factor receptor (EGFR). The cytotoxicity of ¹¹¹In delivered by the EGFR-targeted MNT (¹¹¹In-MNT) was greatly enhanced on EJ-, HT-1376-, and 5637-expressing EGFR bladder cancer cell lines compared with ¹¹¹In non-targeted control. In vivo microSPECT/CT imaging and antitumor efficacy studies revealed prolonged intratumoral retention of ¹¹¹In-MNT with t½ = 4.1 ± 0.5 days as well as significant dose-dependent tumor growth delay (up to 90% growth inhibition) after local infusion of ¹¹¹In-MNT in EJ xenograft-bearing mice.

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.

Modular Nanotransporters for Nuclear-Targeted Delivery of Auger Electron Emitters

This review describes artificial modular nanotransporters (MNTs) delivering their cargos into target cells and then into the nuclei – the most vulnerable cell compartment for most anticancer agents and especially for radionuclides emitting short-range particles. The MNT strategy uses natural subcellular transport processes inherent in practically all cells including cancer cells. The MNTs use these processes just as a passenger who purchased tickets for a multiple-transfer trip making use of different kinds of public transport to reach the desired destination. The MNTs are fusion polypeptides consisting of several parts, replaceable modules, accomplishing binding to a specific receptor on the cell and subsequent internalization, endosomal escape and transport into the cell nucleus. Radionuclides emitting short-range particles, like Auger electron emitters, acquire cell specificity and significantly higher cytotoxicity both in vitro and in vivo when delivered by the MNTs into the nuclei of cancer cells. MNT modules are interchangeable, allowing replacement of receptor recognition modules, which permits their use for different types of cancer cells and, as a cocktail of several MNTs, for targeting several tumor-specific molecules for personalized medicine.

Neuroendocrine neoplasms of rectum: A management update

The estimated annual incidence of R-NENs is 1.04 per 100,000 persons although the real incidence may be underestimated, as not all R-NEN are systematically reported in registers. Also the prevalence has increased substantially, reflecting the rising incidence and indolent nature of R-NENs, showing the highest prevalence increase among all site of origin of NENs. The size of the tumor reveals the behavior of R-NENs where the risk for metastatic spread increases for lesions > 10 mm. Applying the WHO 2010 grading system to whole NENs originating in the gastroenteropancreatic system, R-NENs are classified as Well-Differentiated Neuroendocrine Tumors (WD-NET), which contain NET G1 and NET G2, and Poorly-Differentiated Carcinomas (PD-NEC) enclosing only G3 neoplasms for which the term carcinoma is applied. The treatment is endoscopic resection in most cases: conventional polypectomy or endoscopic mucosal resection (EMR) for smaller lesions or endoscopic submucosal resection with a ligation device (ESMR-L), cap-assisted EMR (EMR-C) and endoscopic submucosal dissection (ESD). However it is important to know when the endoscopic treatment is not enough, and surgical treatment is indicated, or when the latter could be unnecessary. For PD-NECs, it has recently been demonstrated that chemoradiotherapy is associated with a similar long-term survival to that obtained with surgery. As well, new targeted-agents chemotherapy may be indicated for metastatic WD-NETs.

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.

Refractory thyroid carcinoma: which systemic treatment to use?

The incidence of thyroid cancer has increased markedly in recent decades, but has been stable in terms of mortality rates. For the most part, these cancers are treated with surgery, which may or may not be followed by radioactive iodine depending on the tumor subtype. Still, many of these cancers will recur and may be treated with radioactive iodine or another surgery. It is unclear what treatment is best for cases of locally advanced or metastatic thyroid cancer that are refractory to radioactive iodine. Chemotherapy has a very low response rate. However, in the past few years, several systemic therapies, primarily targeted, have emerged to improve the overall survival of these patients. Alternative treatments are also of interest, namely peptide receptor radionuclide therapy or immunotherapy.

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.

Clinical History of the Theranostic Radionuclide Approach to Neuroendocrine Tumors and Other Types of Cancer: Historical Review Based on an Interview of Eric P. Krenning by Rachel Levine

In nuclear medicine, the term theranostics describes the combination of therapy and diagnostic imaging. In practice, this concept dates back more than 50 years; however, among the most successful examples of theranostics are peptide receptor scintigraphy and peptide receptor radionuclide therapy of neuroendocrine tumors. The development of these modalities through the radiolabeling of somatostatin analogs with various radionuclides has led to a revolution in patient management and established a foundation for expansion of the theranostic principle into other oncology indications. This article provides a review of the evolution and development of the theranostic radionuclide approach to the management of neuroendocrine tumors, as described by the inventor of this technique, Eric P. Krenning, in an interview with Rachel Levine.

Radionuclide Therapy for Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is a form of systemic radiotherapy that allows targeted delivery of radionuclides to tumor cells expressing high levels of somatostatin receptors. The two radiopeptides most commonly used for PRRT, ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE, have been successfully employed for more than a decade for the treatment of advanced neuroendocrine tumors (NETs). Recently, the phase III, randomized NETTER-1 trial has compared ¹⁷⁷Lu-DOTATATE versus high-dose octreotide LAR in patients with progressive, metastatic midgut NETs, demonstrating exceptional tolerability and efficacy. This review summarizes recent developments in the field of radionuclide therapy for gastroenteropancreatic and lung NETs and considers possible strategies to further enhance its clinical efficacy.

Treatment Strategies for Metastatic Neuroendocrine Tumors of the Gastrointestinal Tract

OPINION STATEMENT

The therapeutic landscape of gastroenteropancreatic-neuroendocrine tumors (GEP-NETs) has evolved significantly in recent years. Current and emerging treatment options include somatostatin analogs, radiolabeled somatostatin analogs, the mTOR inhibitor everolimus, and the tyrosine kinase inhibitor sunitinib. Although high-quality data from phase III trials are lacking, cytotoxic agents are commonly used for the treatment of poorly differentiated neuroendocrine carcinomas and well-differentiated NETs originating in the pancreas. Hepatic-directed therapies are recommended for patients with slow-growing, liver-predominant disease but have never been compared to systemic agents. Telotristat ethyl, a novel serotonin synthesis inhibitor, has recently demonstrated efficacy in palliating diarrhea in patients with poorly controlled carcinoid syndrome. In the absence of definite predictive biomarkers, therapeutic decisions in most cases rely on clinical and pathological criteria. However, navigating the current therapeutic algorithm may be challenging, and future trials need to address several important questions: what is the best sequence of treatment? Is there a role for combination therapies in GEP-NETs? Are neoadjuvant, adjuvant, or maintenance strategies safe and effective? Do all NET patients require active treatment? What new molecular targets can be clinically exploited? A tight integration between basic and clinical research is needed to further advance the field of NETs.

Persistent Hematologic Dysfunction after Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE: Incidence, Course, and Predicting Factors in Patients with Gastroenteropancreatic Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) may induce long-term toxicity to the bone marrow (BM). The aim of this study was to analyze persistent hematologic dysfunction (PHD) after PRRT with ¹⁷⁷Lu-DOTATATE in patients with gastroenteropancreatic neuroendocrine tumors (GEP NETs). Methods: The incidence and course of PHD were analyzed in 274 GEP NET patients from a group of 367 patients with somatostatin receptor-positive tumors. PHD was defined as diagnosis of myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), myeloproliferative neoplasm (MPN), MDS/MPN, or otherwise unexplained cytopenia (for >6 mo). Using data from The Netherlands Cancer Registry, the expected number of hematopoietic neoplasms (MDS, AML, MPN, and MDS/MPN) was calculated and adjusted for sex, age, and follow-up period. The following risk factors were assessed: sex, age over 70 y, bone metastasis, prior chemotherapy, prior external-beam radiotherapy, uptake on the [¹¹¹In-DTPA⁰]octreotide scan, tumor load, grade 3-4 hematologic toxicity during treatment, estimated absorbed BM dose, elevated plasma chromogranin A level, baseline blood counts, and renal function. Results: Eleven (4%) of the 274 patients had PHD after treatment with ¹⁷⁷Lu-DOTATATE: 8 patients (2.9%) developed a hematopoietic neoplasm (4 MDS, 1 AML, 1 MPN, and 2 MDS/MPN) and 3 patients (1.1%) developed BM failure characterized by cytopenia and BM aplasia. The median latency period at diagnosis (or first suspicion of a PHD) was 41 mo (range, 15-84 mo). The expected number of hematopoietic neoplasms based on The Netherlands Cancer Registry data was 3.0, resulting in a relative risk of 2.7 (95% confidence interval, 0.7-10.0). No risk factors for PHD could be identified for the GEP NET patients, not even bone metastasis or estimated BM dose. Seven patients with PHD developed anemia in combination with a rise in mean corpuscular volume. Conclusion: The prevalence of PHD after PRRT with ¹⁷⁷Lu-DOTATATE was 4% in our patient population. The median time at which PHD developed was 41 mo after the first PRRT cycle. The relative risk for developing a hematopoietic neoplasm was 2.7. No risk factors were found for the development of PHD in GEP NET patients.

Peptide receptor radionuclide therapy in the management of gastrointestinal neuroendocrine tumors: efficacy profile, safety, and quality of life

Peptide receptor radionuclide therapy (PRRT), developed over the last two decades, is carried out using radiopharmaceuticals such as 90Y-DOTA-Tyr3-octreotide and 177Lu-DOTA-Tyr3-octreotate (177Lu-Dotatate). These radiocompounds are obtained by labeling a synthetic somatostatin analog with a β-emitting radioisotope. The compounds differ from each other in terms of their energetic features (due to the radionuclide) and peptide receptor affinity (due to the analog) but share the common characteristic of binding specific membrane somatostatin receptors that are (generally) overexpressed in neuroendocrine neoplasms (NENs) and their metastases. NENs are tumors arising from diffuse neuroendocrine system cells that are classified according to grading based on Ki67 percentage values (Grades 1 and 2 are classed as neuroendocrine tumors [NETs]) and to the anatomical site of occurrence (in this paper, we only deal with gastroenteropancreatic [GEP]-NETs, which account for 60%–70% of all NENs). They are also characterized by specific symptoms such as diarrhea and flushing (30% of cases). Despite substantial experience gained in the area of PRRT and its demonstrable effects in terms of efficacy, safety, and improvement in quality of life, these compounds are still not registered (registration of 177Lu-Dotatate for the treatment of midgut NETs is expected soon). Thus, PRRT can only be used in experimental protocols. We provide an overview of the work of leading groups with wide-ranging experience and continuity in data publication in the area of GEP-NET PRRT and report our own personal experience of using different dosage schedules based on the presence of kidney and bone marrow risk factors. Our results on the retreatment of patients previously administered 90Y-DOTA-Tyr3-octreotide with a low dosage of 177Lu-Dotatate are also included. A comment on potential future developments of PRRT in GEP-NETs is provided.

ENETS Consensus Guidelines for the Standards of Care in Neuroendocrine Neoplasia: Peptide Receptor Radionuclide Therapy with Radiolabeled Somatostatin Analogues

The purpose of these guidelines is to assist physicians caring for patients with neuroendocrine neoplasia in considering eligibility criteria for peptide receptor radionuclide therapy (PRRT) and in defining the minimum requirements for PRRT. It is not these guidelines' aim to give recommendations on the use of specific radiolabelled somatostatin analogues for PRRT as different analogues are being used, and their availability is governed by varying international regulations. However, a recent randomized controlled trial, NETTER-1, has provided evidence that may establish ¹⁷⁷Lu-DOTA-octreotate (LutaThera®) as the first widely approved agent. It also makes recommendations on what minimal patient, tumour, and treatment outcome characteristics should be reported for PRRT to facilitate robust comparisons between studies.

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.

Peptide Receptor Radionuclide Therapy in the Treatment of Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is a promising new treatment modality for inoperable or metastasized gastroenteropancreatic neuroendocrine tumors patients. Most studies report objective response rates in 15% to 35% of patients. Progression-free (PFS) and overall survival (OS) compare favorably with that for somatostatin analogues, chemotherapy, or newer, "targeted" therapies. Prospective, randomized data regarding the potential PFS and OS benefit of PRRT compared with standard therapies is anticipated.

Systemic treatment of gastroenteropancreatic neuroendocrine tumors (GEP-NETS): current approaches and future options

OBJECTIVE

To describe recent advances in the treatment of gastroenteropancreatic neuroendocrine tumors (GEP-NETs).

METHODS

A review of the published English language literature on GEP-NET therapy with a focus on practice-changing clinical trials.

RESULTS

Somatostatin analog (SSA) treatment remains a cornerstone of GEP-NET therapy, primarily for patients with hormonally functional tumors and midgut carcinoids. The biologic agents everolimus and sunitinib have similar tumor-stabilizing effects in pancreatic NETs and are both approved to treat progressive low-intermediate-grade tumors. Their role in nonpancreatic NETs remains controversial. Cytotoxic chemotherapy is effective against pancreatic NETs, but modern prospective data is lacking. Radiolabeled SSAs will likely become more widely available once phase III randomized studies are completed.

CONCLUSIONS

New treatment options for GEP-NETs have become available and highlight the necessity of developing predictive biomarkers that will allow for appropriate and individualized therapy selection.

Management of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (pNETs) are rare tumors that have a better prognosis than their exocrine counterpart, but frequently present with advanced disease. Management of pNETs has evolved considerably over the past decade. Surgical resection remains the only potentially curative option for patients with pNETs. Patients who have locoregionally advanced and/or metastatic pNETs require additional treatments. These include liver-directed (transarterial (chemo)-embolization, selective intraarterial radio therapy) and systemic therapies (somatostatin analogs, targeted therapy such as tyrosine-kinase inhibitors and mammalian target of rapamycin inhibitor, peptide receptor radionuclide therapy and cytotoxic chemotherapy). The aim of this article is to review the current treatment options as well as potential future therapeutic perspectives for patients with pNETs.

Peptide receptor radionuclide therapy: focus on bronchial neuroendocrine tumors

Well-differentiated bronchial neuroendocrine tumors (B-NETs) are rare. They represent 1-5 % of all lung cancers. The incidence of these neoplasms has risen over the past 30 years and, especially for advanced or metastatic disease, management is complex and requires a multidisciplinary approach. Treatment with somatostatin analogs (SSAs) is the most important first-line therapy, in particular in well-differentiated NETs with high somatostatin type receptor (SSTR) expression. In these tumors, the role of mammalian target of rapamycin (m-TOR) inhibitors and the potential utility of other target therapies remain unclear while chemotherapy represents the gold standard treatment only for aggressive forms with low SSTR expression. Peptide receptor radionuclide therapy (PRRT) is an emerging treatment modality for advanced NETs. There are many cumulative evidences about the effectiveness and tolerability of this therapeutic approach, especially in gastro-entero-pancreatic (GEP)-NETs. For B-NETs, scientific research is moving more slowly. Here, we performed a review in order to evaluate the efficacy and toxicity of PRRT with a focus on patients with inoperable or metastatic well-differentiated B-NETs.

Myelotoxicity of Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors: A Decade of Experience

AIM

This review of the literature, and the authors' own decade of experience with lutetium-177-octreotate-capecitabine±temozolomide peptide receptor radionuclide therapy (PRRT)-chemotherapy of GEPNETs, analyses the risk of both short- and long-term hematotoxicity.

BACKGROUND

Myelodysplastic syndrome (MDS) and acute leukemia (AL) have been associated with PRRT in heavily pretreated patients with a history of exposure to alkylating agents. Commenced 15 years ago, PRRT is now becoming established as first- and second-line therapy for gastroentero pancreatic neuroendocrine tumors (GEPNETs), and early treatment minimizes myelotoxicity, which is the most significant potential adverse event following PRRT.

RESULTS

Sixteen key articles involving primary research were identified. A total of 2225 patients were treated (2104 treated with PRRT monotherapy and 121 with PRRT combined with chemotherapy). The average age of patients in these studies ranged from 53 to 64 years with median duration of follow-up ranging from 6 to 62 months. Short-term myelotoxicity was observed in 221 patients (10%), occurring in 213 of 2104 patients treated with PRRT monotherapy and 8 of 121 patients treated with PRRT combined with chemotherapy. Acute toxicity manifested as modest self-limited grade 3/4 toxicity (CTCAE or WHO), most often affecting platelets during the first cycle of treatment. Toxicity manifesting early was easily managed with dose modification or therapy cessation and was ameliorated by appropriate patient selection. MDS/AL was a rare stochastic event occurring in 32 (1.4%) patients. Where bone marrow biopsy was performed, cases of MDS displayed cytogenetic abnormalities, consistent with secondary MDS. Factors associated with myelotoxicity included age >70 years, impaired renal function, baseline cytopenias, prior number of therapies, prior chemotherapy (alkylating agents), and prior radiotherapy.

CONCLUSION

Early therapy with PRRT-containing regimens improves outcomes, minimizes myelotoxicity, and renders the risk of MDS and AL negligible.

Comparison of 111In-[DTPA0]Octreotide Versus Non Carrier Added 177Lu- [DOTA0,Tyr3]-Octreotate Efficacy in Patients With GEP-NET Treated Intra-arterially for Liver Metastases

AIM

In patients with progressive, metastatic neuroendocrine tumors (NET), intra-arterial radionuclide infusions with high activities of In-[DTPA]-octreotide and more recently with non-carrier added (nca) Lu-[DOTA,Tyr]-octreotate have been performed with encouraging results. However, the affinity profiles (IC50) of these radiopeptides for human sst2 receptors are markedly different (In-[DTPA]-octreotide, 22 ± 3.6 nM and nca Lu-[DOTA,Tyr]-octreotate, 1.5 ± 4.0 nM). The total administered activity is determined by organ dose limits (kidneys and bone marrow), and our aim therefore was to compare and evaluate the therapeutic efficacy of both radiopeptides in metastatic NETs.

METHODS

Thirty patients with gastroenteropancreatic (GEP) somatostatin-positive NETs with liver metastases confirmed on biopsy and In-pentetreotide scan were included. They were treated with In-[DTPA]-octreotide (n = 17) or nca Lu-[DOTA,Tyr]-octreotate (n = 13). Blood samples were collected 2, 4, 8, and 24 hours postadministration to calculate residence time in blood and in red marrow. The maximum percentage uptake in organs and tumors was estimated by region of interest analysis, and tumor dosimetry calculations were performed using OLINDA/EXM/ 1.0 software.

RESULTS

ncaLu-[DOTA,Tyr3]-octreotate blood radioactivity, expressed as a percentage of the injected dose, was significantly lower than In-[DTPA]-octreotide (P < 0.05), as clearly depicted from the time-activity curves; the background-corrected tumor uptake was significantly higher than In-[DTPA]-octreotide but without any significant difference in other organs (spleen, kidneys, and liver).

CONCLUSIONS

Using Lu-[DOTA,Tyr]-octreotate, a 3-fold higher absorbed dose to tumor tissue was achieved compared with In-[DTPA] octreotide. Residence time of nca Lu-[DOTA,Tyr]-octreotate results in a significantly higher absorbed dose to bone marrow compared with In-[DTPA]-octreotide. However, a drawback of In-[DTPA]-octreotide therapy is that the number of administrations would need to be almost doubled to achieve an equal therapeutic outcome as compared with Lu-[DOTA,Tyr]-octreotate.

Contribution of Auger/conversion electrons to renal side effects after radionuclide therapy: preclinical comparison of (161)Tb-folate and (177)Lu-folate

Background

The radiolanthanide ¹⁶¹Tb has, in recent years, attracted increasing interest due to its favorable characteristics for medical application. ¹⁶¹Tb exhibits similar properties to the widely-used therapeutic radionuclide ¹⁷⁷Lu. In contrast to ¹⁷⁷Lu, ¹⁶¹Tb yields a significant number of short-ranging Auger/conversion electrons (≤50 keV) during its decay process. ¹⁶¹Tb has been shown to be more effective for tumor therapy than ¹⁷⁷Lu if applied using the same activity. The purpose of this study was to investigate long-term damage to the kidneys after application of ¹⁶¹Tb-folate and compare it to the renal effects caused by ¹⁷⁷Lu-folate.

Methods

Renal side effects were investigated in nude mice after the application of different activities of ¹⁶¹Tb-folate (10, 20, and 30 MBq per mouse) over a period of 8 months. Renal function was monitored by the determination of ^99mTc-DMSA uptake in the kidneys and by measuring blood urea nitrogen and creatinine levels in the plasma. Histopathological analysis was performed by scoring of the tissue damage observed in HE-stained kidney sections from euthanized mice.

Results

Due to the co-emitted Auger/conversion electrons, the mean absorbed renal dose of ¹⁶¹Tb-folate (3.0 Gy/MBq) was about 24 % higher than that of ¹⁷⁷Lu-folate (2.3 Gy/MBq). After application of ¹⁶¹Tb-folate, kidney function was reduced in a dose- and time-dependent manner, as indicated by the decreased renal uptake of ^99mTc-DMSA and the increased levels of blood urea nitrogen and creatinine. Similar results were obtained when ¹⁷⁷Lu-folate was applied at the same activity. Histopathological investigations confirmed comparable renal cortical damage after application of the same activities of ¹⁶¹Tb-folate and ¹⁷⁷Lu-folate. This was characterized by collapsed tubules and enlarged glomeruli with fibrin deposition in moderately injured kidneys and glomerulosclerosis in severely damaged kidneys.

Conclusions

Tb-folate induced dose-dependent radionephropathy over time, but did not result in more severe damage than ¹⁷⁷Lu-folate when applied at the same activity. These data are an indication that Auger/conversion electrons do not exacerbate overall renal damage after application with ¹⁶¹Tb-folate as compared to ¹⁷⁷Lu-folate, even though they result in an increased dose deposition in the renal tissue. Global toxicity affecting other tissues than kidneys remains to be investigated after ¹⁶¹Tb-based therapy, however.

[177Lu-DOTA0,Tyr3]-octreotate in the treatment of midgut neuroendocrine tumors

Midgut neuroendocrine tumors (NETs) are relatively rare and remarkably heterogeneous. Although recent developments for pancreatic NETs have brought multiple new therapies to patients who need them, there has been little observed efficacy against midgut NETs. Peptide receptor radionuclide therapy utilizes somatostatin analogs conjugated to radioactive isotopes in order to deliver high doses of radiation directly to tumor cells, which express somatostatin receptors. Peptide receptor radionuclide therapy with [(177)Lu-DOTA(0),Tyr(3)]-octreotate (DOTATATE) has been reported and investigated for more than a decade, and the randomized controlled NETTER-1 study of this agent has recently been reported to show promising results. In this article, we will summarize and evaluate the rationale and existing clinical data for the activity of DOTATATE in midgut NETs, to give context for the interpretation of NETTER-1 results when they are fully available.

Peptide receptor radionuclide therapy of neuroendocrine tumours

In the past decades, the number of neuroendocrine tumours that are detected is increasing. A relative new and promising therapy for patients with metastasised or inoperable disease is peptide receptor radionuclide therapy (PRRT). This therapy involves an infusion of somatostatin analogues linked to radionuclides like Yttrium-90 or Lutetium-177. Objective response rates are reported in 15-35%. Response rates may vary between type of tumour and radionuclide. Besides the objective response rate, overall survival and progression free survival increase significantly. Also, the quality of life improves as well. Serious side-affects are rare. PRRT is usually well tolerated, also in patients with extensive metastasised disease. Recent studies combined PRRT with other types of therapies. Unfortunately no randomised trials comparing these strategies are available. In the future, more research is needed to evaluate the best therapy combinations or sequence of therapies.

Human Anti-Oxidation Protein A1M--A Potential Kidney Protection Agent in Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been in clinical use for 15 years to treat metastatic neuroendocrine tumors. PRRT is limited by reabsorption and retention of the administered radiolabeled somatostatin analogues in the proximal tubule. Consequently, it is essential to develop and employ methods to protect the kidneys during PRRT. Today, infusion of positively charged amino acids is the standard method of kidney protection. Other methods, such as administration of amifostine, are still under evaluation and show promising results. α₁-microglobulin (A1M) is a reductase and radical scavenging protein ubiquitously present in plasma and extravascular tissue. Human A1M has antioxidation properties and has been shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. It has recently been shown in mice that exogenously infused A1M and the somatostatin analogue octreotide are co-localized in proximal tubules of the kidney after intravenous infusion. In this review we describe the current situation of kidney protection during PRRT, discuss the necessity and implications of more precise dosimetry and present A1M as a new, potential candidate for renal protection during PRRT and related targeted radionuclide therapies.

SPECT- and PET-based patient-tailored treatment in neuroendocrine tumors: a comprehensive multidisciplinary team approach

The overexpression of somatostatin receptors on the tumor cell surface of neuroendocrine tumors (NETs) detected by multimodal functional imaging modalities such as SPECT and PET tracers constitutes a therapeutic option using targeting radiolabeled compounds. We will introduce the theranostic concept in general, explain in more detail its development in NETs, and discuss available SPECT and PET tracers regarding their potential for diagnostic imaging, visualization of target expression, and treatment tailoring. Moreover, we will discuss the currently available peptide receptor radionuclide therapy principles and compare them to previously published studies. Finally, we will discuss which new concepts will most likely influence the theranostic treatment approach in NETs in the future.