Strategies Towards Improving Clinical Outcomes of Peptide Receptor Radionuclide Therapy

Radiation exposure and protection advice after [177Lu]Lu-DOTA-TATE therapy in China

BACKGROUND

We conducted a study on radiation exposure in patients with gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) treated with [177Lu]Lu-DOTA-TATE in China for the first time, aiming to provide guidance and reference for radiation protection in this regard. A total of 30 GEP-NENs patients who received [177Lu]Lu-DOTA-TATE therapy were recruited in the study. We measured the external dose rate (EDR) values of each patient during the injection and 0-6 h post-administration period, as well as the radiation dose (RD) values to healthcare nurses and the surrounding environment. We performed a double exponential curve fitting and estimated the RD to the public from patients discharged at different times after [177Lu]Lu-DOTA-TATE therapy.

RESULTS

Among the 30 patients, 27 patients completed 4 cycles of [177Lu]Lu-DOTA-TATE treatments, the estimated RD to the public indicated that for adult family members, children above 10 years old, children aged 3-10 and coworkers of the patients, patients could begin daily contact at least 24 h, 48 h, 144 h and 192 h after injection to ensure that the total RD values after four treatments not exceed the limit. During the hospitalization of patients receiving [177Lu]Lu-DOTA-TATE, the cumulative dose received by the administering nurses and to the ward environment were both well below the national RD limits.

CONCLUSIONS

This study conducted a fitting analysis of the decay pattern of EDR values in GEP-NENs patients undergoing [177Lu]Lu-DOTA-TATE therapy, in order to establish guidelines for patient discharge timing and provide recommendations for radiation protection for the general public after patient discharge. Trial registration A Study Comparing Treatment With Lutetium[177Lu] Oxodotreotide Injection to Octreotide LAR in Patients With GEP-NETs, NCT05459844. https://clinicaltrials.gov/study/NCT05459844?cond=NCT05459844&rank=1 . Registered 5 July 2022.

Theranostics in Neuroendocrine Tumors: Updates and Emerging Technologies

Advancements in somatostatin receptor (SSTR) targeted imaging and treatment of well-differentiated neuroendocrine tumors (NETs) have revolutionized the management of these tumors. This comprehensive review delves into the current practice, discussing the use of the various FDA-approved SSTR-agonist PET tracers and the predictive imaging biomarkers, and elaborating on Lu177-DOTATATE peptide receptor radionuclide therapy (PRRT) including the evolving areas of post-therapy imaging practices, PRRT retreatment, and the potential role of dosimetry in optimizing patient treatments. The future directions sections highlight ongoing research on investigational PET imaging radiotracers, future prospects in alpha particle therapy, and combination therapy strategies.

Applying HDACis to increase SSTR2 expression and radiolabeled DOTA-TATE uptake: from cells to mice

AIMS

The aim of our study was to determine the effect of histone deacetylase (HDAC) inhibitors (HDACis) on somatostatin type-2 receptor (SSTR2) expression and [111In]In-/[177Lu]Lu-DOTA-TATE uptake in vitro and in vivo.

MATERIALS AND METHODS

The human cell lines NCI-H69 (small-cell lung carcinoma) and BON-1 (pancreatic neuroendocrine tumor) were treated with HDACis (i.e. entinostat, mocetinostat (MOC), LMK-235, CI-994 or panobinostat (PAN)), and SSTR2 mRNA expression levels and [111In]In-DOTA-TATE uptake were measured. Furthermore, vehicle- and HDACi-treated NCI-H69 and BON-1 tumor-bearing mice were injected with radiolabeled DOTA-TATE followed by biodistribution studies. Additionally, SSTR2 and HDAC mRNA expression of xenografts, and of NCI-H69, BON-1, NCI-H727 (human pulmonary carcinoid) and GOT1 (human midgut neuroendocrine tumor) cells were determined.

KEY FINDINGS

HDACi treatment resulted in the desired effects in vitro. However, no significant increase in tumoral DOTA-TATE uptake was observed after HDACi treatment in NCI-H69 tumor-bearing animals, whereas tumoral SSTR2 mRNA and/or protein expression levels were significantly upregulated after treatment with MOC, CI-994 and PAN, i.e. a maximum of 2.1- and 1.3-fold, respectively. Analysis of PAN-treated BON-1 xenografts solely demonstrated increased SSTR2 mRNA expression levels. Comparison of HDACs and SSTR2 expression in BON-1 and NCI-H69 xenografts showed a significantly higher expression of 6/11 HDACs in BON-1 xenografts. Of these HDACs, a significant inverse correlation was found between HDAC3 and SSTR2 expression (Pearson r = -0.92) in the studied cell lines.

SIGNIFICANCE

To conclude, tumoral uptake levels of radiolabeled DOTA-TATE were not enhanced after HDACi treatment in vivo, but, depending on the applied inhibitor, increased SSTR2 expression levels were observed.

Peptide Radioligands in Cancer Theranostics: Agonists and Antagonists

The clinical success of radiolabeled somatostatin analogs in the diagnosis and therapy-"theranostics"-of tumors expressing the somatostatin subtype 2 receptor (SST₂R) has paved the way for the development of a broader panel of peptide radioligands targeting different human tumors. This approach relies on the overexpression of other receptor-targets in different cancer types. In recent years, a shift in paradigm from internalizing agonists to antagonists has occurred. Thus, SST₂R-antagonist radioligands were first shown to accumulate more efficiently in tumor lesions and clear faster from the background in animal models and patients. The switch to receptor antagonists was soon adopted in the field of radiolabeled bombesin (BBN). Unlike the stable cyclic octapeptides used in the case of somatostatin, BBN-like peptides are linear, fast to biodegradable and elicit adverse effects in the body. Thus, the advent of BBN-like antagonists provided an elegant way to obtain effective and safe radiotheranostics. Likewise, the pursuit of gastrin and exendin antagonist-based radioligands is advancing with exciting new outcomes on the horizon. In the present review, we discuss these developments with a focus on clinical results, commenting on challenges and opportunities for personalized treatment of cancer patients by means of state-of-the-art antagonist-based radiopharmaceuticals.

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

Background

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

Results

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

Conclusions

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

Peptide Receptor Radionuclide Therapy

The concept of using a targeting molecule labeled with a diagnostic radionuclide for using positron emission tomography or single photon emission computed tomography imaging with the potential to demonstrate that tumoricidal radiation can be delivered to tumoral sites by administration of the same or a similar targeting molecule labeled with a therapeutic radionuclide termed "theranostics." Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs (SSAs) is a well-established second/third-line theranostic treatment for somatostatin receptor-positive well-differentiated (neuro-)endocrine neoplasms (NENs). PRRT with 177Lu-DOTATATE was approved by the regulatory authorities in 2017 and 2018 for selected patients with low-grade well-differentiated gastroenteropancreatic (GEP) NENs. It improves progression-free survival as well as quality of life of GEP NEN patients. Favorable symptomatic and biochemical responses using PRRT with 177Lu-DOTATATE have also been reported in patients with functioning metastatic GEP NENs like metastatic insulinomas, Verner Morrison syndromes (VIPomas), glucagonomas, and gastrinomas and patients with carcinoid syndrome. This therapy might also become a valuable therapeutic option for inoperable low-grade bronchopulmonary NENs, inoperable or progressive pheochromocytomas and paragangliomas, and medullary thyroid carcinomas. First-line PRRT with 177Lu-DOTATATE and combinations of this therapy with cytotoxic drugs are currently under investigation. New radiolabeled somatostatin receptor ligands include SSAs coupled with alpha radiation emitting radionuclides and somatostatin receptor antagonists coupled with radionuclides.

"Clickable" Albumin Binders for Modulating the Tumor Uptake of Targeted Radiopharmaceuticals

The intentional binding of radioligands to albumin gains increasing attention in the context of radiopharmaceutical cancer therapy as it can lead to an enhanced radioactivity uptake into the tumor lesions and, thus, to a potentially improved therapeutic outcome. However, the influence of the radioligand's albumin-binding affinity on the time profile of tumor uptake has been only partly addressed so far. Based on the previously identified N^ε-4-(4-iodophenyl)butanoyl-lysine scaffold, we designed "clickable" lysine-derived albumin binders (cLABs) and determined their dissociation constants toward albumin by novel assay methods. Structure-activity relationships were derived, and selected cLABs were applied for the modification of the somatostatin receptor subtype 2 ligand (Tyr³)octreotate. These novel conjugates were radiolabeled with copper-64 and subjected to a detailed in vitro and in vivo radiopharmacological characterization. Overall, the results of this study provide an incentive for further investigations of albumin binders for applications in endoradionuclide therapies.

Clinical Utility of 18F-FDG PET in Neuroendocrine Tumors Prior to Peptide Receptor Radionuclide Therapy: A Systematic Review and Meta-Analysis

Simple Summary

Functional imaging with ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) has evolved into a major clinical tool in cancer diagnosis and management for many malignancies in diverse clinical settings, providing valuable information on tumor behavior and aggressiveness. In the field of neuroendocrine tumors (NETs), recent advances in molecular imaging and targeted treatments with novel theranostic agents favor a more patient-tailored approach. Although peptide receptor radionuclide therapy (PRRT) has recently become an established therapy for progressive NETs, the role of ¹⁸F-FDG PET prior to PRRT in patients with NETs of different origins and grades remains to be determined. Herein, we provide a comprehensive summary of available evidence in contemporary literature by means of a systematic review and meta-analysis, demonstrating that dual-functional imaging with ⁶⁸Ga-DOTA-peptides and ¹⁸F-FDG prior to PRRT appears to be a useful tool in NET management by delineating tumor somatostatin receptor expression and glycolytic metabolic activity, and predicting tumor response and survival outcomes.

Abstract

The role of ¹⁸F-FDG PET in patients with variable grades of neuroendocrine tumors (NETs) prior to peptide receptor radionuclide therapy (PRRT) has not been adequately elucidated. We aimed to evaluate the impact of ¹⁸F-FDG PET status on disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) in neuroendocrine tumor (NET) patients receiving PRRT. We searched the MEDLINE, Embase, Cochrane Library, and Web of Science databases up to July 2020 and used the Newcastle-Ottawa scale (NOS) criteria to assess quality/risk of bias. A total of 5091 articles were screened. In 12 studies, 1492 unique patients with NETs of different origins were included. The DCR for patients with negative ¹⁸F-FDG PET status prior to PRRT initiation was 91.9%, compared to 74.2% in patients with positive ¹⁸F-FDG PET status (random effects odds ratio (OR): 4.85; 95% CI: 2.27–10.36). Adjusted analysis of pooled hazard ratios (HRs) confirmed longer PFS and OS in NET patients receiving PRRT with negative ¹⁸F-FDG PET (random effects HR:2.45; 95%CIs: 1.48–4.04 and HR:2.25; 95% CIs:1.55–3.28, respectively). In conclusion, ¹⁸F-FDG PET imaging prior to PRRT administration appears to be a useful tool in NET patients to predict tumor response and survival outcomes and a negative FDG uptake of the tumor is associated with prolonged PFS and OS.

Neuroendocrine Carcinoma as an Independent Prognostic Factor for Patients With Prostate Cancer: A Population-Based Study

BACKGROUND

Neuroendocrine carcinoma (NEC) is a rare and highly malignant variation of prostate adenocarcinoma. We aimed to investigate the prognostic value of NEC in prostate cancer.

METHODS

A total of 530440 patients of prostate cancer, including neuroendocrine prostate cancer (NEPC) and adenocarcinoma from 2004 to 2018 were obtained from the national Surveillance, Epidemiology, and End Results (SEER) database. Propensity score matching (PSM), multivariable Cox proportional hazard model, Kaplan-Meier method and subgroup analysis were performed in our study.

RESULTS

NEPC patients were inclined to be older at diagnosis (Median age, 69(61-77) vs. 65(59-72), P< 0.001) and had higher rates of muscle invasive disease (30.9% vs. 9.2%, P < 0.001), lymph node metastasis (32.2% vs. 2.2%, P < 0.001), and distal metastasis (45.7% vs. 3.6%, P < 0.001) compared with prostate adenocarcinoma patients. However, the proportion of NEPC patients with PSA levels higher than 4.0 ng/mL was significantly less than adenocarcinoma patients (47.3% vs. 72.9%, P<0.001). NEPC patients had a lower rate of receiving surgery treatment (28.8% vs. 43.9%, P<0.001), but they had an obviously higher rate of receiving chemotherapy (57.9% vs. 1.0%, P<0.001). A Cox regression analysis demonstrated that the NEPC patients faced a remarkably worse OS (HR = 2.78, 95% CI = 2.34-3.31, P < 0.001) and CSS (HR = 3.07, 95% CI = 2.55-3.71, P < 0.001) compared with adenocarcinoma patients after PSM. Subgroup analyses further suggested that NEPC patients obtained significantly poorer prognosis across nearly all subgroups.

CONCLUSION

The prognosis of NEPC was worse than that of adenocarcinoma among patients with prostate cancer. The histological subtype of NEC is an independent prognostic factor for patients with prostate cancer.