Comparison of [(177)Lu-DOTA(0),Tyr(3)]octreotate and [(177)Lu-DOTA(0),Tyr(3)]octreotide: which peptide is preferable for PRRT?

Comparison of 177Lu-octreotate and 177Lu-octreotide for treatment in human neuroblastoma-bearing mice

Background

Patients with high-risk neuroblastoma (NB) have a 5-year event-free survival of less than 50 %, and novel and improved treatment options are needed. Radiolabeled somatostatin analogs (SSTAs) could be a treatment option. The aims of this work were to compare the biodistribution and the therapeutic effects of 177Lu-octreotate and 177Lu-octreotide in mice bearing the human CLB-BAR NB cell line, and to evaluate their regulatory effects on apoptosis-related genes.

Methods

The biodistribution of 177Lu-octreotide in mice bearing CLB-BAR tumors was studied at 1, 24, and 168 h after administration, and the absorbed dose was estimated to tumor and normal tissues. Further, animals were administered different amounts of 177Lu-octreotate or 177Lu-octreotide. Tumor volume was measured over time and compared to a control group given saline. RNA was extracted from tumors, and the expression of 84 selected genes involved in apoptosis was quantified with qPCR.

Results

The activity concentration was generally lower in most tissues for 177Lu-octreotide compared to 177Lu-octreotate. Mean absorbed dose per administered activity to tumor after injection of 1.5 MBq and 15 MBq was 0.74 and 0.03 Gy/MBq for 177Lu-octreotide and 2.9 and 0.45 Gy/MBq for 177Lu-octreotate, respectively. 177Lu-octreotide treatment resulted in statistically significant differences compared to controls. Fractionated administration led to a higher survival fraction than after a single administration. The pro-apoptotic genes TNSFS8, TNSFS10, and TRADD were regulated after administration with 177Lu-octreotate. Treatment with 177Lu-octreotide yielded regulation of the pro-apoptotic genes CASP5 and TRADD, and of the anti-apoptotic gene IL10 as well as the apoptosis-related gene TNF.

Conclusion

177Lu-octreotide gave somewhat better anti-tumor effects than 177Lu-octreotate. The similar effect observed in the treated groups with 177Lu-octreotate suggests saturation of the somatostatin receptors. Pronounced anti-tumor effects following fractionated administration merited receptor saturation as an explanation. The gene expression analyses suggest apoptosis activation through the extrinsic pathway for both radiopharmaceuticals.

Performance evaluation of Gallium-68 radiopharmaceuticals production using liquid target PETtrace 800 cyclotron

Due to increased demand, cyclotron has an expanding role in producing Gallium-68 (68Ga) radiopharmaceuticals using solid and liquid targets. Though the liquid target produces lower end-of-bombardment activity compared to the solid target, our study presents the performance of 68Ga radiopharmaceuticals production using the liquid target by evaluating the end-of-bombardment activity and the end-of-purification activity of [68Ga]GaCl3. We also present the effect of increasing irradiation time, which significantly improves the end-of-synthesis yield. From the result obtained, the end-of-bombardment activity produced was 4.48 GBq, and the [68Ga]GaCl3 end-of-purification activity produced was 2.51 GBq with below-limit metallic impurities. Increasing the irradiation time showed a significant increase in the end-of-synthesis activity from 1.33 GBq to 1.95 GBq for [68Ga]Ga-PSMA-11 and from 1.13 GBq to 1.74 GBq for [68Ga]Ga-DOTA-TATE. Based on the improvements made, the liquid target production of 68Ga radiopharmaceuticals is feasible and reproducible to accommodate up to 5 patients per production. In addition, this work also discusses the issues encountered, together with the possible corrective and preventative measures.

Image-Guided Precision Medicine in the Diagnosis and Treatment of Pheochromocytomas and Paragangliomas

In this comprehensive review, we aimed to discuss the current state-of-the-art medical imaging for pheochromocytomas and paragangliomas (PPGLs) diagnosis and treatment. Despite major medical improvements, PPGLs, as with other neuroendocrine tumors (NETs), leave clinicians facing several challenges; their inherent particularities and their diagnosis and treatment pose several challenges for clinicians due to their inherent complexity, and they require management by multidisciplinary teams. The conventional concepts of medical imaging are currently undergoing a paradigm shift, thanks to developments in radiomic and metabolic imaging. However, despite active research, clinical relevance of these new parameters remains unclear, and further multicentric studies are needed in order to validate and increase widespread use and integration in clinical routine. Use of AI in PPGLs may detect changes in tumor phenotype that precede classical medical imaging biomarkers, such as shape, texture, and size. Since PPGLs are rare, slow-growing, and heterogeneous, multicentric collaboration will be necessary to have enough data in order to develop new PPGL biomarkers. In this nonsystematic review, our aim is to present an exhaustive pedagogical tool based on real-world cases, dedicated to physicians dealing with PPGLs, augmented by perspectives of artificial intelligence and big data.

Peptides as multifunctional players in cancer therapy

Peptides exhibit lower affinity and a shorter half-life in the body than antibodies. Conversely, peptides demonstrate higher efficiency in tissue penetration and cell internalization than antibodies. Regardless of the pros and cons of peptides, they have been used as tumor-homing ligands for delivering carriers (such as nanoparticles, extracellular vesicles, and cells) and cargoes (such as cytotoxic peptides and radioisotopes) to tumors. Additionally, tumor-homing peptides have been conjugated with cargoes such as small-molecule or chemotherapeutic drugs via linkers to synthesize peptide-drug conjugates. In addition, peptides selectively bind to cell surface receptors and proteins, such as immune checkpoints, receptor kinases, and hormone receptors, subsequently blocking their biological activity or serving as hormone analogs. Furthermore, peptides internalized into cells bind to intracellular proteins and interfere with protein-protein interactions. Thus, peptides demonstrate great application potential as multifunctional players in cancer therapy.

Correlations between [68Ga]Ga-DOTA-TOC Uptake and Absorbed Dose from [177Lu]Lu-DOTA-TATE

PURPOSE

The aim of this paper was to investigate correlations between pre- therapeutic [⁶⁸Ga]Ga-DOTA-TOC uptake and absorbed dose to tumours from therapy with [¹⁷⁷Lu]Lu-DOTA-TATE.

METHODS

This retrospective study included 301 tumours from 54 GEP-NET patients. The tumours were segmented on pre-therapeutic [⁶⁸Ga]Ga-DOTA-TOC PET/CT, and post-therapy [¹⁷⁷Lu]Lu-DOTA-TATE SPECT/CT images, using a fixed 40% threshold. The SPECT/CT images were used for absorbed dose calculations by assuming a linear build-up from time zero to day one, and mono-exponential wash-out after that. Both SUV_mean and SUV_max were measured from the PET images. A linear absorbed-dose prediction model was formed with SUV_mean as the independent variable, and the accuracy was tested with a split 70-30 training-test set.

RESULTS

Mean SUV_mean and SUV_max from [⁶⁸Ga]Ga-DOTA-TOC PET was 24.0 (3.6-84.4) and 41.0 (6.7-146.5), and the mean absorbed dose from [¹⁷⁷Lu]Lu-DOTA-TATE was 26.9 Gy (2.4-101.9). A linear relationship between SUV_mean and [¹⁷⁷Lu]Lu-DOTA-TATE activity concentration at 24 h post injection was found (R² = 0.44, p < 0.05). In the prediction model, a root mean squared error and a mean absolute error of 1.77 and 1.33 Gy/GBq, respectively, were found for the test set.

CONCLUSIONS

There was a high inter- and intra-patient variability in tumour measurements, both for [⁶⁸Ga]Ga-DOTA-TOC SUVs and absorbed doses from [¹⁷⁷Lu]Lu-DOTA-TATE. Depending on the required accuracy, [⁶⁸Ga]Ga-DOTA-TOC PET imaging may estimate the [¹⁷⁷Lu]Lu-DOTA-TATE uptake. However, there could be a high variance between predicted and actual absorbed doses.

Estimation of Absorbed Doses of Indigenously Produced "Direct-route" Lutetium-177-Labeled DOTA-TATE PRRT in Normal Organs and Tumor Lesions in Patients of Metastatic Neuroendocrine Tumors: Comparison with No-Carrier-Added [177Lu]Lu-DOTA-TATE and the Trend with Multiple Cycles

Background: Lutetium-177-labeled somatostatin analogue, [¹⁷⁷Lu]Lu-DOTA-TATE is most commonly used across the world for peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs). The primary objective of this study was to estimate the absorbed doses in organs and tumor lesions in NET patients treated with indigenously produced "direct-route" [¹⁷⁷Lu]Lu-labeled DOTA-TATE and impact of multiple treatment cycles on absorbed doses, and compare with those treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Materials and Methods: Sixty patients of NET were enrolled in this prospective study. These patients received up to 6 cycles of PRRT with [¹⁷⁷Lu]Lu-DOTA-TATE (total 232 cycles) at 10- to 12-week intervals between the two successive therapy cycles. The patients were administered 5.55-7.4 GBq (150-200 mCi) of [¹⁷⁷Lu]Lu-DOTA-TATE in 100 mL of normal saline over a period of 30 min. Postadministration whole-body planar scintigraphy were acquired at five time points 0.5 (prevoid), 2, 12, 24, and 72 h (postvoid) and one SPECT scan at 24 h (postvoid). Number of disintegrations was determined from time-activity curves generated by drawing regions of interests (ROIs) on the images. Tumor masses were derived from computed tomography (CT) data. The absorbed doses for normal organs and tumor lesions were calculated using OLINDA 2.1.1 software. The same were also estimated in a group of 22 patients who were treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Results: The mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.64 ± 0.21, liver 0.10 ± 0.05, spleen 0.88 ± 0.35, bone marrow 0.04 ± 0.02, urinary bladder 0.26 ± 0.06, heart wall 0.04 ± 0.02, and whole-body 0.06 ± 0.02. Tumor dosimetry was performed in a total of 410 tumor lesions, the mean absorbed dose to the tumor lesions was 4.79 ± 4.23 Gy/GBq. Large variations were observed in absorbed doses received by these lesions (range: 0.15-21.26 Gy/GBq). With no-carrier-added [¹⁷⁷Lu]Lu-DOTA-TATE, the mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.76 ± 0.16, liver 0.10 ± 0.05, spleen 1.14 ± 0.31, bone marrow 0.05 ± 0.02, urinary bladder 0.27 ± 0.05, heart wall 0.06 ± 0.02, whole-body 0.07 ± 0.02, and tumor dose 5.87 ± 5.74. Conclusions: There was no statistically significant difference in the dosimetry data of patients treated with no-carrier-added (indirect route) [¹⁷⁷Lu]Lu-labeled DOTA-TATE and the dosimetry data of patients treated with [¹⁷⁷Lu]Lu-labeled with DOTA-TATE formulated using ¹⁷⁷Lu produced through "Direct-route" and were comparable with the data reported.

Theragnostic in neuroendocrine tumors

In the last few decades, the incidence and prevalence of neuroendocrine tumors has been increasing. The theragnostic approach, that allows the diagnosis and treatment of different neoplasms with the same ligand, is a typical nuclear medicine tool. Applied for years, is also pivotal in neuroendocrine tumors (NETs) where it has improved the diagnostic accuracy and the therapeutic efficacy with impact on patient's survival. Theragnostic also allows the identification of important prognostic factors such as tumor location and burden, presence of liver metastases and intensity of somatostatin receptors (SSTR) expression to consider in new and possibly combined studies to ameliorate patient's outcome. Moreover, the possibility to evaluate receptor expression even in non-NET malignancies has de facto widened the possible indications for PRRT. We believe that this innovative therapeutic approach will be implemented in next years by radiomics and biological tumors characterization to better address PRRT applications.

Dosimetry of 177Lu-DOTATOC first circle treatment in patients with advanced metastatic neuroendocrine tumors: A pilot study in China

First cycle dosimetry calculation of ¹⁷⁷Lu-DOTATOC (single activity:1.59-3.49 GBq) was carried out in eight patients with advanced neuroendocrine tumors (NETs) who underwent whole-body planar (0.5, 24, 48, 72 h) and SPECT/CT scans (24 h). Focal uptake of ¹⁷⁷Lu-DOTATOC was found in primary and metastatic tumors. Organs with the highest absorbed doses per injected activity were tumors (1.293 ± 0.862 mGy/MBq) and spleen (0.461 ± 0.408 mGy/MBq), while low absorbed doses were observed in kidneys (0.384 ± 0.112 mGy/MBq) and bone marrow (0.0297 ± 0.0123 mGy/MBq). ¹⁷⁷Lu-DOTATOC is safe, well-tolerated and appropriate in Chinese NETs patients for PRRT.

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

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

Patient Release and Instructions for Lutetium Dotatate Radiopharmaceutical Therapy

ABSTRACT

Lutetium Dotatate radiopharmaceutical therapy (Lutathera) was approved by the United States Food and Drug Administration in 2018 and is used to treat somatostatin receptor positive neuroendocrine tumors. With all new radiopharmaceutical therapies, the radiation exposure to members of the public from the patient who received the therapy must be within regulatory limits and safe. If the patient will expose members of the public to too much radiation, the therapy must be performed on an inpatient basis. This paper shows that the administration of Lutathera can be done on an outpatient basis and provides safety and travel restrictions that should be communicated to the patient prior to leaving. The guidance presented herein serves as a basis for medical institutions looking to use Lutathera to treat patients.

Economic evaluation of orphan drug Lutetium-Octreotate vs. Octreotide long-acting release for patients with an advanced midgut neuroendocrine tumour in the Netherlands

OBJECTIVES

Multiple studies showed positive effects of Lutetium-Octreotate (LO) treatment in neuroendocrine tumours. LO has been used in the Netherlands since the 1980s and recently received the orphan status shortly after the acquisition by Novartis. Since then, the official list price has increased sixfold. From a value-based pricing perspective, we analysed the impact of the increase in price on the incremental cost-effectiveness ratio (ICER) of LO treatment compared to optimal best supportive care, a high dose of Octreotide long-acting release (O-LAR), using the clinical data of the NETTER-1 trial.

METHODS

A Markov model was developed to evaluate the costs per quality-adjusted life-year (QALY) for LO treatment compared to O-LAR from the healthcare perspective. A scenario analysis was conducted to compare the cost-effectiveness with the initial and increased price level of the LO-treatment.

RESULTS

At the increased price level, the cost-effectiveness analysis rendered a deterministic ICER of €53,500 per QALY, while at the initial pricing, the ICER was €19,000 per QALY. The probabilistic sensitivity analysis (PSA) showed that LO had a high probability of being cost-effective at both the increased and initial price level, considering a cost-effectiveness threshold of €80,000.

CONCLUSIONS

Even at the increased price level, LO treatment can still be considered cost-effective using the applicable Dutch willingness-to-pay threshold of 80,000 euro per QALY. Considering the public scrutiny in relation to this price increase, these outcomes raise the question whether traditional cost-effectiveness methods are sufficient in fully capturing the societal acceptance of prices of new medicines.

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.

Preclinical evaluation of [225Ac]Ac-DOTA-TATE for treatment of lung neuroendocrine neoplasms

PURPOSE

There is significant interest in the development of targeted alpha-particle therapies (TATs) for treatment of solid tumors. The metal chelator-peptide conjugate, DOTA-TATE, loaded with the β-particle emitting radionuclide ¹⁷⁷Lu ([¹⁷⁷Lu]Lu-DOTA-TATE) is now standard care for neuroendocrine tumors that express the somatostatin receptor 2 (SSTR2) target. A recent clinical study demonstrated efficacy of the corresponding [²²⁵Ac]Ac-DOTA-TATE in patients that were refractory to [¹⁷⁷Lu]Lu-DOTA-TATE. Herein, we report the radiosynthesis, toxicity, biodistribution (BD), radiation dosimetry (RD), and efficacy of [²²⁵Ac]Ac-DOTA-TATE in small animal models of lung neuroendocrine neoplasms (NENs).

METHODS

[²²⁵Ac]Ac-DOTA-TATE was synthesized and characterized for radiochemical yield, purity and stability. Non-tumor-bearing BALB/c mice were tested for toxicity and BD. Efficacy was determined by single intravenous injection of [²²⁵Ac]Ac-DOTA-TATE into SCID mice-bearing human SSTR2 positive H727 and H69 lung NENs. RD was calculated using the BD data.

RESULTS

[²²⁵Ac]Ac-DOTA-TATE was synthesized with 98% yield, 99.8% purity, and displayed 97% stability after 2 days incubation in human serum at 37 °C. All animals in the toxicity study appeared healthy 5 months post injection with no indications of toxicity, except that animals that received ≥111 kBq of [²²⁵Ac]Ac-DOTA-TATE had chronic progressive nephropathy. BD studies revealed that the primary route of elimination is by the renal route. RD calculations determined pharmacokinetics parameters and absorbed α-emission dosages from ²²⁵Ac and its daughters. For both tumor models, a significant tumor growth delay and time to experimental endpoint were observed following a single administration of [²²⁵Ac]Ac-DOTA-TATE relative to controls.

CONCLUSIONS

These results suggest significant potential for the clinical translation of [²²⁵Ac]Ac-DOTA-TATE for lung NENs.

Evaluation of Ac-Lys0(IRDye800CW)Tyr3-octreotate as a novel tracer for SSTR2-targeted molecular fluorescence guided surgery in meningioma

Purpose

Meningioma recurrence rates can be reduced by optimizing surgical resection with the use of intraoperative molecular fluorescence guided surgery (MFGS). We evaluated the potential of the fluorescent tracer 800CW-TATE for MFGS using in vitro and in vivo models. It targets somatostatin receptor subtype 2 (SSTR₂), which is overexpressed in all meningiomas.

Methods

Binding affinity of 800CW-TATE was evaluated using [¹⁷⁷Lu] Lu-DOTA-Tyr³-octreotate displacement assays. Tumor uptake was determined by injecting 800CW-TATE in (SSTR₂-positive) NCI-H69 or (SSTR₂-negative) CH-157MN xenograft bearing mice and FMT2500 imaging. SSTR₂-specific binding was measured by comparing tumor uptake in NCI-H69 and CH-157MN xenografts, blocking experiments and non-targeted IRDye800CW-carboxylate binding. Tracer distribution was analyzed ex vivo, and the tumor-to-background ratio (TBR) was calculated. SSTR₂ expression was determined by immunohistochemistry (IHC). Lastly, 800CW-TATE was incubated on frozen and fresh meningioma specimens and analyzed by microscopy.

Results

800CW-TATE binding affinity assays showed an IC₅₀ value of 72 nM. NCI-H69 xenografted mice showed a TBR of 21.1. 800CW-TATE detection was reduced after co-administration of non-fluorescent DOTA-Tyr³-octreotate or administration of IRDye800CW. CH-157MN had no tumor specific tracer staining due to absence of SSTR₂ expression, thereby serving as a negative control. The tracer bound specifically to SSTR₂-positive meningioma tissues representing all WHO grades.

Conclusion

800CW-TATE demonstrated sufficient binding affinity, specific SSTR₂-mediated tumor uptake, a favorable biodistribution, and high TBR. These features make this tracer very promising for use in MFGS and could potentially aid in safer and a more complete meningioma resection, especially in high-grade meningiomas or those at complex anatomical localizations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11060-021-03739-1.

Development and validation of the HPLC method for quality control of radiolabelled DOTA-TATE and DOTA-TOC preparations

INTRODUCTION

The information on the presence of cold metal complexes in radiolabeled DOTA-TATE or DOTA-TOC is important in assessing the cause of the radiolabeling failure, poor radiolabeling yield and/or low effective molar activity. DOTA-peptide complexes are detectable using UV-Vis detector. The main limitation in the quantitative analysis is the limited availability of standard substances and the lack of data on their molar absorption coefficients. The aim of our study was development and validation of HPLC method enabling RCP analysis and identification and quantification of metal complexes impurities in the radiopharmaceutical preparations of DOTA-chelated peptides.

METHODS

Complexes of DOTA-TATE and DOTA-TOC with several metals, were prepared. Their molar absorption coefficients at 220 nm were determined. The developed HPLC method has been validated in terms of quantitative determination of non-complexed DOTA-TATE and DOTA-TOC and their respective complexes with metallic individuals.

RESULTS

Good chromatographic separation of the individual metal-DOTA-peptide complexes was achieved. The resolution between peaks of interest in radioactive preparations (complexes with: yttrium-90, lutetium-177, gallium-68) and metallic impurities was well above 1.5 (except gallium-68 DOTA-TOC preparations). Limits of detection and quantification were determined based on the parameters of the calibration curves. Based on the spectrophotometric and HPLC-DAD studies and statistical analysis of the results obtained, the average molar absorption coefficient was determined for studied DOTA-TATE and DOTA-TOC complexes, ε_HPLC-DAD = 48 × 10³M^-1 cm^-1. With the use of the determined molar absorption coefficient the method enabled quantitative determination of non-labelled peptide in the radioactive preparation in the linearity range of 0.5-100 μg/mL for DOTA-TATE(net) and 0.5-100 μg/mL for DOTA-TOC(net).

CONCLUSION

The developed HPLC method is suitable for RCP determination of radiolabelled DOTA-TATE and DOTA-TOC preparations. Determination of the average molar absorption coefficient for DOTA-TATE and DOTA-TOC complexes allows assessment of the total content of the peptide in radiopharmaceutical preparation regardless of its chemical form (free ligand, associated with radionuclide, in the form of a complex with metal ions being the impurity) using the HPLC method with UV detection.

Overview of Radiolabeled Somatostatin Analogs for Cancer Imaging and Therapy

Identified in 1973, somatostatin (SST) is a cyclic hormone peptide with a short biological half-life. Somatostatin receptors (SSTRs) are widely expressed in the whole body, with five subtypes described. The interaction between SST and its receptors leads to the internalization of the ligand-receptor complex and triggers different cellular signaling pathways. Interestingly, the expression of SSTRs is significantly enhanced in many solid tumors, especially gastro-entero-pancreatic neuroendocrine tumors (GEP-NET). Thus, somatostatin analogs (SSAs) have been developed to improve the stability of the endogenous ligand and so extend its half-life. Radiolabeled analogs have been developed with several radioelements such as indium-111, technetium-99 m, and recently gallium-68, fluorine-18, and copper-64, to visualize the distribution of receptor overexpression in tumors. Internal metabolic radiotherapy is also used as a therapeutic strategy (e.g., using yttrium-90, lutetium-177, and actinium-225). With some radiopharmaceuticals now used in clinical practice, somatostatin analogs developed for imaging and therapy are an example of the concept of personalized medicine with a theranostic approach. Here, we review the development of these analogs, from the well-established and authorized ones to the most recently developed radiotracers, which have better pharmacokinetic properties and demonstrate increased efficacy and safety, as well as the search for new clinical indications.

tBu4octapa-alkyl-NHS for metalloradiopeptide preparation

The peptide is an important class of biological targeting molecule; herein, a new bifunctional octadentate non-macrocyclic H4octapa, tBu4octapa-alkyl-NHS, which is compatible with solid-phase peptide synthesis and thus useful for radiopeptide preparation, has been synthesized. To preserve denticity, the alkyl-N-hydroxylsuccinimide linker was covalently attached to the methylene-carbon on one of the acetate arms, yielding a chiral carbon center. According to density-functional theory (DFT) calculations using [Lu(octapa-alkyl-benzyl-ester)]- as a simulation model, the chirality has minimal effects on the complex geometry; regardless of the S-/R-stereochemistry, DFT calculations revealed two possible geometric isomers, distorted bicapped trigonal antiprism (DBTA) and distorted square antiprism (DSA), due to the asymmetry in the chelator. To evaluate the biological behavior of the new bifunctionalization, two well-studied PSMA (prostate-specific membrane antigen)-targeting peptidomimetics of varying hydrophobicity were chosen as proof-of-principle targeting vector molecules. Radiolabeling both bioconjugates with lutetium-177 was highly efficient at room temperature in 15 min at micromolar chelator concentration pH = 7. Both the in vitro serum challenge and the lanthanum(iii) challenge studies revealed complex lability, and notably, progressive bone accumulation was only observed with the more hydrophobic linker (i.e. H4octapa-alkyl-PSMA617). This in vivo result informs potential alterations exerted by the linker on the complex geometry and stability, with an appropriate biological targeting vector adopted for such evaluations.

Three-dimensional Monte Carlo-based voxel-wise tumor dosimetry in patients with neuroendocrine tumors who underwent 177Lu-DOTATOC therapy

Background

Patients with advanced neuroendocrine tumors (NETs) of the midgut are suitable candidates for ¹⁷⁷Lu-DOTATOC therapy. Integrated SPECT/CT systems have the potential to help improve the accuracy of patient-specific tumor dosimetry. Dose estimations to target organs are generally performed using the Medical Internal Radiation Dose scheme. We present a novel Monte Carlo-based voxel-wise dosimetry approach to determine organ- and tumor-specific total tumor doses (TTD).

Methods

A cohort of 14 patients with histologically confirmed metastasized NETs of the midgut (11 men, 3 women, 62.3 ± 11.0 years of age) underwent a total of 39 cycles of ¹⁷⁷Lu-DOTATOC therapy (mean 2.8 cycles, SD ± 1 cycle). After the first cycle of therapy, regions of interest were defined manually on the SPECT/CT images for the kidneys, the spleen, and all 198 tracer-positive tumor lesions in the field of view. Four SPECT images, taken at 4 h, 24 h, 48 h and 72 h after injection of the radiopharmaceutical, were used to determine their effective half-lives in the structures of interest. The absorbed doses were calculated by a three-dimensional dosimetry method based on Monte Carlo simulations. TTD was calculated as the sum of all products of single tumor doses with single tumor volumes divided by the sum of all tumor volumes.

Results

The average dose values per cycle were 3.41 ± 1.28 Gy (1.91–6.22 Gy) for the kidneys, 4.40 ± 2.90 Gy (1.14–11.22 Gy) for the spleen, and 9.70 ± 8.96 Gy (1.47–39.49 Gy) for all ¹⁷⁷Lu-DOTATOC-positive tumor lesions. Low- and intermediate-grade tumors (G 1–2) absorbed a higher TTD compared to high-grade tumors (G 3) (signed-rank test, p =  < 0.05). The pre-therapeutic chromogranin A (CgA) value and the TTD correlated significantly (Pearson correlation:  = 0.67, p = 0.01). Higher TTD resulted in a significant decrease of CgA after therapy.

Conclusion

These results suggest that Monte Carlo-based voxel-wise dosimetry is a very promising tool for predicting the absorbed TTD based on histological and clinical parameters.

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.

Accuracy of kidney dosimetry performed using simplified time activity curve modelling methods: a 177Lu-DOTATATE patient study

¹⁷⁷Lu-DOTATATE therapy has been shown to produce encouraging results in treatment of neuroendocrine tumours (NETs). Unfortunately, since dosimetry for radionuclide therapy is considered to be challenging, typically similar amount of radiopharmaceutical is administered to every patient. There is growing evidence that the efficacy of this therapy can be significantly improved by employing personalized protocols, based on the organ-at-risk dosimetry. The aim of this study is to propose a practical and accurate dosimetry protocol based on the simplified acquisition schedules. Data from fifty-three therapy cycles in thirty-nine NET patients were analyzed. Three SPECT/CT scans, acquired at 4 h (D0), 23 h (D1) and 70 h (D3) after injection, were performed. The kidney volume was determined using CT and the activity was determined from quantitative SPECT using an iterative thresholding method. For each dataset, four methods were used to model the time-activity-curves (TAC): M1-two trapezoid segments (0 to D0 and D0 to D1), followed by monoexponential fit to D1  +  D3 data; M2-monoexponential fit to D0  +  D1  +  D3 data; M3 and M4-monoexponential fit to D0  +  D3 and D1  +  D3 data, respectively. Additionally, kidney doses obtained from single time point method using a monoexponential curve with the population mean effective half-life, normalized to activities at D0 or D1 or D3 points, were calculated. The accuracy of simplified dosimetry methods was assessed as the percentage difference relative to doses calculated from M1. The major contribution to the absorbed dose estimate comes from the area under the late time portion of the TAC (D1 to infinity). Therefore, information from the late scan (D3) is crucial for the determination of kidney absorbed doses. Single time point method using monoexponential TAC, with the population mean effective half-life normalized to the late data point (48-72 h for kidneys) produces  <10% deviation in the absorbed dose estimation, thus is recommended for clinical use.

Production and characterization of no-carrier-added 161Tb as an alternative to the clinically-applied 177Lu for radionuclide therapy

BACKGROUND

161Tb is an interesting radionuclide for cancer treatment, showing similar decay characteristics and chemical behavior to clinically-employed 177Lu. The therapeutic effect of 161Tb, however, may be enhanced due to the co-emission of a larger number of conversion and Auger electrons as compared to 177Lu. The aim of this study was to produce 161Tb from enriched 160Gd targets in quantity and quality sufficient for first application in patients.

METHODS

No-carrier-added 161Tb was produced by neutron irradiation of enriched 160Gd targets at nuclear research reactors. The 161Tb purification method was developed with the use of cation exchange (Sykam resin) and extraction chromatography (LN3 resin), respectively. The resultant product (161TbCl3) was characterized and the 161Tb purity compared with commercial 177LuCl3. The purity of the final product (161TbCl3) was analyzed by means of γ-ray spectrometry (radionuclidic purity) and radio TLC (radiochemical purity). The radiolabeling yield of 161Tb-DOTA was assessed over a two-week period post processing in order to observe the quality change of the obtained 161Tb towards future clinical application. To understand how the possible drug products (peptides radiolabeled with 161Tb) vary with time, stability of the clinically-applied somatostatin analogue DOTATOC, radiolabeled with 161Tb, was investigated over a 24-h period. The radiolytic stability experiments were compared to those performed with 177Lu-DOTATOC in order to investigate the possible influence of conversion and Auger electrons of 161Tb on peptide disintegration.

RESULTS

Irradiations of enriched 160Gd targets yielded 6-20 GBq 161Tb. The final product was obtained at an activity concentration of 11-21 MBq/μL with ≥99% radionuclidic and radiochemical purity. The DOTA chelator was radiolabeled with 161Tb or 177Lu at the molar activity deemed useful for clinical application, even at the two-week time point after end of chemical separation. DOTATOC, radiolabeled with either 161Tb or 177Lu, was stable over 24 h in the presence of a stabilizer.

CONCLUSIONS

In this study, it was shown that 161Tb can be produced in high activities using different irradiation facilities. The developed method for 161Tb separation from the target material yielded 161TbCl3 in quality suitable for high-specific radiolabeling, relevant for future clinical application.

Radiolabelled Aptamers for Theranostic Treatment of Cancer

Cancer has a high incidence and mortality rate worldwide, which continues to grow as millions of people are diagnosed annually. Metastatic disease caused by cancer is largely responsible for the mortality rates, thus early detection of metastatic tumours can improve prognosis. However, a large number of patients will also present with micrometastasis tumours which are often missed, as conventional medical imaging modalities are unable to detect micrometastases due to the lack of specificity and sensitivity. Recent advances in radiochemistry and the development of nucleic acid based targeting molecules, have led to the development of novel agents for use in cancer diagnostics. Monoclonal antibodies may also be used, however, they have inherent issues, such as toxicity, cost, unspecified binding and their clinical use can be controversial. Aptamers are a class of single-stranded RNA or DNA ligands with high specificity, binding affinity and selectivity for a target, which makes them promising for molecular biomarker imaging. Aptamers are presented as being a superior choice over antibodies because of high binding affinity and pH stability, amongst other factors. A number of aptamers directed to cancer cell markers (breast, lung, colon, glioblastoma, melanoma) have been radiolabelled and characterised to date. Further work is ongoing to develop these for clinical applications.

Neuroendocrine Tumor Therapy: 177Lu-DOTATATE

OBJECTIVE

The purposes of this article are to increase understanding of the concepts of theranostics and peptide receptor radionuclide therapy (PRRT) as they apply to neuroendocrine tumors (NETs); review the key 1, 2, and 3 clinical trial data leading to the approval of ¹⁷⁷Lu-tetraazacyclododecanetetraacetic acid-octreotide (¹⁷⁷Lu-DOTATATE); and foster understanding of the practical aspects and future directions of PRRT for NETs.

CONCLUSION

In January 2018, ¹⁷⁷Lu-DOTATATE therapy was approved in the United States (previously approved in Europe in September 2017) for adult patients with somatostatin receptor-positive gastroenteropancreatic neuroendocrine tumors, including those of the foregut, midgut, and hindgut. The results of the phase 3 Neuroendocrine Tumors Therapy (NETTER-1) trial show favorable outcomes with respect to the primary endpoint of progression-free survival and a host of secondary objectives, including overall survival, objective response rate, and quality of life measures. Patient selection is based on a number of specific factors and should be sequenced carefully with respect to other available therapies, ideally in multidisciplinary cancer conferences. Establishing the therapy at a new institution can be somewhat involved, but once it is established, the therapy is fairly straightforward to administer and is well tolerated with limited side-effects and toxicity. A number of approaches and issues are still to be worked out, and this therapy will continue to be studied and optimized.

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.

External radiation exposure, excretion, and effective half-life in 177Lu-PSMA-targeted therapies

Background

Prostate-specific membrane antigen (PSMA)-targeted therapy with ¹⁷⁷Lu-PSMA-617 is a therapeutic option for patients with metastatic castration-resistant prostate cancer (mCRPC). To optimize the therapy procedure, it is necessary to determine relevant parameters to define radiation protection and safety necessities. Therefore, this study aimed at estimating the ambient radiation exposure received by the patient. Moreover, the excreted activity was quantified.

Results

In total, 50 patients with mCRPC and treated with ¹⁷⁷Lu-PSMA-617 (mean administered activity 6.3 ± 0.5 GBq) were retrospectively included in a bi-centric study. Whole-body dose rates were measured at a distance of 2 m at various time points after application of ¹⁷⁷Lu-PSMA-617, and effective half-lives for different time points were calculated and compared. Radiation exposure to the public was approximated using the dose integral. For the estimation of the excreted activity, whole body measurements of 25 patients were performed at 7 time points.

Unbound ¹⁷⁷Lu-PSMA-617 was rapidly cleared from the body. After 4 h, approximately 50% and, after 12 h, approximately 70% of the administered activity were excreted, primarily via urine. The mean dose rates were the following: 3.6 ± 0.7 μSv/h at 2 h p. i., 1.6 ± 0.6 μSv/h at 24 h, 1.1 ± 0.5 μSv/h at 48 h, and 0.7 ± 0.4 μSv/h at 72 h. The mean effective half-life of the cohort was 40.5 ± 9.6 h (min 21.7 h; max 85.7 h). The maximum dose to individual members of the public per treatment cycle was ~ 250 ± 55 μSv when the patient was discharged from the clinic after 48 h and ~ 190 ± 36 μSv when the patient was discharged after 72 h.

Conclusions

In terms of the radiation exposure to the public, ¹⁷⁷Lu-PSMA is a safe option of radionuclide therapy. As usually four (sometimes more) cycles of the therapy are performed, it must be conducted in a way that ensures that applicable legal requirements can be followed. In other words, the radiation exposure to the public and the concentration of activity in wastewater must be sub-marginal. Therefore, in certain countries, hospitalization of these patients is mandatory.

Paradigm shift in theranostics of neuroendocrine tumors: conceptual horizons of nanotechnology in nuclear medicine

We present a comprehensive review of Neuroendocrine Tumors (NET) and the current and developing imaging and therapeutic modalities for NET with emphasis on Nuclear Medicine modalities. Subsequently, nanotechnology and its emerging role in cancer management, especially NET, are discussed. The article is both educative and informative. The objective is to provide an insight into the developments made in nuclear medicine and nanotechnology towards management of NET, individually as well as combined together.

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.

Twins in spirit part IV - [177Lu] high affinity DOTATATE. A promising new tracer for peptide receptor radiotherapy?

AIM

Besides the use of somatostatin analogues, small molecules like sunitinib and everolimus as well as conventional chemotherapy, peptide receptor radiotherapy (PRRT) using radiolabelled somatostatin analogues has gained an important role in the treatment of inoperable, metastasized neuroendocrine tumours (NET). There are various radiotracers in use. Based on our experience with the PET tracer [⁶⁸Ga]DOTA-3-iodo-Tyr³-octreotate ([⁶⁸Ga]HA-DOTATATE), a DOTATATE derivative with an increased binding affinity to hsst5, the current retrospective analysis is exploring the therapeutic potential of [¹⁷⁷Lu]HA-DOTATATE.

METHODS

Eighteen patients with metastatic NET (G1/G2) were treated using [¹⁷⁷Lu]DOTATATE and/or [¹⁷⁷Lu]HA-DOTATATE, and dosimetric results of both tracers were compared.

RESULTS

Using [¹⁷⁷Lu]HA-DOTATATE, a mean tumour dose of 5.34 Gy/GBq (median 2.53 Gy/GBq; range 0.89-33.3 Gy/GBq) was achieved, while [¹⁷⁷Lu]DOTATATE delivered a tumour dose of 5.53 Gy/GBq (median 2.70 Gy/GBq; range 0.44-15.3 Gy/GBq). Organ doses for [¹⁷⁷Lu]HA-DOTATATE vs. [¹⁷⁷Lu]DOTATATE were as follows: kidney 2.31 ± 0.85 vs. 2.03 ± 0.96 Gy/GBq, liver 1.06 ± 0.79 vs. 1.67 ± 1.73 Gy/GBq, spleen 3.89 ± 4.04 vs. 4.50 ± 3.69 Gy/GBq and whole body 0.16 ± 0.10 Gy/GBq vs. 0.15 ± 0.08 Gy/GBq. Tumour-to-kidney dose ratio was slightly higher for [¹⁷⁷Lu]DOTATATE (2.4 ± 5.6) compared to [¹⁷⁷Lu]HA-DOTATATE (1.5 ± 3.6).

CONCLUSION

Both tracers showed marked inter-patient variation in their dosimetry, and no significant differences in dosimetry of [¹⁷⁷Lu]HA-DOTATATE and [¹⁷⁷Lu]DOTATATE were observed when taking all patients into account. Thus, [¹⁷⁷Lu]HA-DOTATATE appears viable for PRRT, although it was marginally inferior regarding kidney dose and tumour-to-kidney dose ratio compared to the established [¹⁷⁷Lu]DOTATATE.

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.

177Lu-DOTATATE treatment in neuroendocrine tumours. A preliminary study

Therapy with radiolabelled somatostatin analogue peptides is a promising new therapy to treat neuroendocrine tumours. The aim of this preliminary study is to present our experience with ¹⁷⁷Lu-DOTATATE therapy, and evaluate tolerability and short-term efficacy in patients with tumours expressing somatostatin receptors. A total of 7 patients with metastatic neuroendocrine tumours were treated, each with 4 doses of ¹⁷⁷Lu-DOTATATE. The treatment response was evaluated in the form of biochemical response (tumour markers), imaging methods (somatostatin receptor scintigraphy, computed tomography, and magnetic resonance), and functional and quality of life responses using the Karnofsky performance status scale. Treatment toxicity was also evaluated. The results obtained were as follows: Biochemical response: 60% of patients showed tumour marker levels returning to normal, while they decreased significantly in the remaining 40%. Imaging response: 85.7% had a partial response, while 14.3% showed stable disease. All (100%) patients showed a significant improvement in quality of life, with increased Karnofsky scale scores. No patient had acute or chronic toxicity, and subacute transient haematological toxicity was observed in 42.8% of patients. Despite being a preliminary study, it was found that treatment with ¹⁷⁷Lu-DOTATATE is a safe treatment with few side effects, and an objective response was achieved in most patients.

[(177)Lu-DOTA](0)-D-Phe(1)-Tyr(3)-Octreotide ((177)Lu-DOTATOC) For Peptide Receptor Radiotherapy in Patients with Advanced Neuroendocrine Tumours: A Phase-II Study

PURPOSE

To characterise efficacy and safety of (177)Lu-DOTATOC as agent for peptide receptor radiotherapy (PRRT) of advanced neuroendocrine tumours (NET).

PATIENTS AND METHODS

Fifty-six subjects with metastasized and progressive NET (50% gastroenteral, 26.8% pancreatic, 23.2% other primary sites) treated consecutively with (177)Lu-DOTATOC were analysed retrospectively. Subjects were administered (177)Lu-DOTATOC (mean 2.1 cycles; range 1-4) as 7.0GBq (median) doses at three-monthly intervals. Efficacy was analysed using CT and/or MRI according to RECIST 1.1 criteria and results were stratified for the number of administered cycles and the primary tumour origin.

RESULTS

In the total NET population (A), median progression-free (PFS) and overall survival (OS) were 17.4 and 34.2 months, respectively, assessed in a follow-up time (mean ± SD) of 16.1 ± 12.4 months. In patients receiving more than one cycle, mean follow-up time was 22.4 ± 11.0 months for all NETs (B) and PFS was 32.0 months for all NETs (B), 34.5 months for GEP-NET (C), and 11.9 months for other NETs (D). Objective response rates (Complete/Partial Responses) were 33.9%, 40.6%, 54.2%, and 0% for A, B, C, and D groups, respectively, while disease control rates in the same were 66.1%, 93.8%, 100%, and 75%. Complete responses (16.1%, 18.8% and 25.0% for groups A, B and C) were high, 78% of which were maintained throughout the follow up. There were no serious adverse events. One case of self-limiting grade 3 myelotoxicity was reported. Although 20% of patients had mild renal insufficiency at baseline, there was no evidence of exacerbated or de novo renal toxicity after treatment.

CONCLUSION

(177)Lu-DOTATOC is a novel agent for PRRT with major potential to induce objective tumour responses and sustained disease control in progressive neuroendocrine tumours, even when administered in moderate activities. The observed safety profile suggests a particularly favourable therapeutic index, including in patients with impaired bone marrow or renal function, which reflects a uniquely low uptake of (177)Lu-DOTATOC by normal organs.

[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.

177Lu-labeled carbon nanospheres: a new entry in the field of targeted radionanomedicine

¹⁷⁷Lu-labeled carbon nanospheres loaded with cRGDfK peptide have been developed as radionanoprobes with favorable pharmacokinetics for integrin α_vβ₃-mediated active targeting.

Subacute haematotoxicity after PRRT with (177)Lu-DOTA-octreotate: prognostic factors, incidence and course

PURPOSE

In peptide receptor radionuclide therapy (PRRT), the bone marrow (BM) is one of the dose-limiting organs. The accepted dose limit for BM is 2 Gy, adopted from (131)I treatment. We investigated the incidence and duration of haematological toxicity and its risk factors in patients treated with PRRT with (177)Lu-DOTA(0)-Tyr(3)-octreotate ((177)Lu-DOTATATE). Also, absorbed BM dose estimates were evaluated and compared with the accepted 2 Gy dose limit.

METHODS

The incidence and duration of grade 3 or 4 haematological toxicity (according to CTCAE v3.0) and risk factors were analysed. Mean BM dose per unit (gigabecquerels) of administered radioactivity was calculated and the correlations between doses to the BM and haematological risk factors were determined.

RESULTS

Haematological toxicity (grade 3/4) occurred in 34 (11 %) of 320 patients. In 15 of the 34 patients, this lasted more than 6 months or blood transfusions were required. Risk factors significantly associated with haematological toxicity were: poor renal function, white blood cell (WBC) count <4.0 × 10(9)/l, age over 70 years, extensive tumour mass and high tumour uptake on the OctreoScan. Previous chemotherapy was not associated. The mean BM dose per administered activity in 23 evaluable patients was 67 ± 7 mGy/GBq, resulting in a mean BM dose of 2 Gy in patients who received four cycles of 7.4 GBq (177)Lu-DOTATATE. Significant correlations between (cumulative) BM dose and platelet and WBC counts were found in a selected group of patients.

CONCLUSION

The incidence of subacute haematological toxicity after PRRT with (177)Lu-DOTATATE is acceptable (11 %). Patients with impaired renal function, low WBC count, extensive tumour mass, high tumour uptake on the OctreoScan and/or advanced age are more likely to develop grade 3/4 haematological toxicity. The BM dose limit of 2 Gy, adopted from (131)I, seems not to be valid for PRRT with (177)Lu-DOTATATE.

Pharmacokinetic digital phantoms for accuracy assessment of image-based dosimetry in (177)Lu-DOTATATE peptide receptor radionuclide therapy

Patient-specific image-based dosimetry is considered to be a useful tool to limit toxicity associated with peptide receptor radionuclide therapy (PRRT). To facilitate the establishment and reliability of absorbed-dose response relationships, it is essential to assess the accuracy of dosimetry in clinically realistic scenarios. To this end, we developed pharmacokinetic digital phantoms corresponding to patients treated with (177)Lu-DOTATATE. Three individual voxel phantoms from the XCAT population were generated and assigned a dynamic activity distribution based on a compartment model for (177)Lu-DOTATATE, designed specifically for this purpose. The compartment model was fitted to time-activity data from 10 patients, primarily acquired using quantitative scintillation camera imaging. S values for all phantom source-target combinations were calculated based on Monte-Carlo simulations. Combining the S values and time-activity curves, reference values of the absorbed dose to the phantom kidneys, liver, spleen, tumours and whole-body were calculated. The phantoms were used in a virtual dosimetry study, using Monte-Carlo simulated gamma-camera images and conventional methods for absorbed-dose calculations. The characteristics of the SPECT and WB planar images were found to well represent those of real patient images, capturing the difficulties present in image-based dosimetry. The phantoms are expected to be useful for further studies and optimisation of clinical dosimetry in (177)Lu PRRT.

Yttrium-based therapy for neuroendocrine tumors

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

Single vial kit formulation of DOTATATE for preparation of (177) Lu-labeled therapeutic radiopharmaceutical at hospital radiopharmacy

The clinical applications of radiolabeled somatostatin analogue (177) Lu-DOTA-Tyr(3) -Thr(8) -Octreotide ((177) Lu-DOTATATE) constitute a promising treatment option for patients with disseminated and inoperable neuroendocrine (NET) tumors. Formulation of (177) Lu-DOTATATE in hospital radiopharmacy under aseptic conditions in a safe and reliable manner is a major constraint for its extensive use. The present work was intended to develop a kit for the safe preparation of the therapeutic radiopharmaceutical, viz. (177) Lu-DOTATATE of high quality that can be easily adapted at conventional hospital radiopharmacies. Single vial kits of DOTATATE were formulated and evaluated for suitability for radiolabeling as well as stability on its storage. Patient dose of (177) Lu-DOTATATE (7.4 GBq) could be successfully prepared using semi-automated in-house setup that assures safe handling and high yields of product of pharmaceutical purity suitable for clinical use. Fast clearance of activity via renal route was observed in preclinical biodistribution studies of (177) Lu-DOTATATE carried out in normal Swiss mice. Deployment of in-house produced (177) LuCl3 , cold kits and easy adaptability of synthesis setup at hospital radiopharmacy for preparation is likely to expand applications of peptide receptor radionuclide therapy.

Production of (177)Lu for Targeted Radionuclide Therapy: Available Options

BACKGROUND

This review provides a comprehensive summary of the production of (177)Lu to meet expected future research and clinical demands. Availability of options represents the cornerstone for sustainable growth for the routine production of adequate activity levels of (177)Lu having the required quality for preparation of a variety of (177)Lu-labeled radiopharmaceuticals. The tremendous prospects associated with production of (177)Lu for use in targeted radionuclide therapy (TRT) dictate that a holistic consideration should evaluate all governing factors that determine its success.

METHODS

While both "direct" and "indirect" reactor production routes offer the possibility for sustainable (177)Lu availability, there are several issues and challenges that must be considered to realize the full potential of these production strategies.

RESULTS

This article presents a mini review on the latest developments, current status, key challenges and possibilities for the near future.

CONCLUSION

A broad understanding and discussion of the issues associated with (177)Lu production and processing approaches would not only ensure sustained growth and future expansion for the availability and use of (177)Lu-labeled radiopharmaceuticals, but also help future developments.

Prediction of clinically relevant hyperkalemia in patients treated with peptide receptor radionuclide therapy

Background

Peptide receptor radionuclide therapy (PRRT) is applied in patients with advanced neuroendocrine tumors. Co-infused amino acids (AA) should prevent nephrotoxicity. The aims of this study were to correlate the incidence of AA-induced hyperkalemia (HK) (≥5.0 mmol/l) and to identify predictors of AA-induced severe HK (>6.0).

Methods

In 38 patients, standard activity of ¹⁷⁷Lu-labelled somatostatin analogs was administered. Pre-therapeutic kidney function was assessed by renal scintigraphy and laboratory tests. For kidney protection, AA was co-infused. Biochemical parameters (potassium, glomerular filtration rate, creatinine, blood urea nitrogen (BUN), sodium, phosphate, chloride, and lactate dehydrogenase (LDH)) were obtained prior to 4 and 24 h after the AA infusion. Incidence of HK (≥5.0) was correlated with pre-therapeutic kidney function and serum parameters. Formulas for the prediction of severe hyperkalemia (>6.0) were computed and prospectively validated.

Results

At 4 h, HK (≥5.0) was present in 94.7% with severe HK (>6.0) in 36.1%. Values normalized after 24 h in 84.2%. Pre-therapeutic kidney function did not correlate with the incidence of severe HK.

Increases in K⁺ were significantly correlated with decreases in phosphate (r = −0.444, p < 0.005) and increases in BUN (r = 0.313, p = 0.056). A baseline BUN of >28 mg/dl had a sensitivity of 84.6% and a specificity of 60.0% (AUC = 0.75) in predicting severe HK of >6.0 (phosphate, AUC = 0.37).

Computing of five standard serum parameters (potassium, BUN, sodium, phosphate, LDH) resulted in a sensitivity of 88.9% and a specificity of 79.3% for the prediction of severe HK >6.0 (accuracy = 81.6%).

Conclusions

A combination of serum parameters predicted prospectively the occurrence of relevant HK with an accuracy of 81.6% underlining its potential utility for identifying ‘high-risk’ patients prone to PRRT.