Response to Single Low-dose 177Lu-DOTA-EB-TATE Treatment in Patients with Advanced Neuroendocrine Neoplasm: A Prospective Pilot Study

FAP Radioligand Linker Optimization Improves Tumor Dose and Tumor-to-Healthy Organ Ratios in 4T1 Syngeneic Model

Fibroblast activation protein (FAP) has attracted considerable attention as a possible target for the radiotherapy of solid tumors. Unfortunately, initial efforts to treat solid tumors with FAP-targeted radionuclides have yielded only modest clinical responses, suggesting that further improvements in the molecular design of FAP-targeted radiopharmaceutical therapies (RPT) are warranted. In this study, we report several advances on the previously described FAP6 radioligand that increase tumor retention and accelerate healthy tissue clearance. Seven FAP6 derivatives with different linkers or albumin binders were synthesized, radiolabeled, and investigated for their effects on binding and cellular uptake. The radioligands were then characterized in 4T1 tumor-bearing Balb/c mice using both single-photon emission computed tomography (SPECT) and ex vivo biodistribution analyses to identify the conjugate with the best tumor retention and tumor-to-healthy organ ratios. The results reveal an optimized FAP6 radioligand that exhibits efficacy and safety properties that potentially justify its translation into the clinic.

Landscape of Nuclear Medicine in China and Its Progress on Theranostics

Nuclear medicine in China started in 1956 and, with the rapid development of the economy and continuous breakthroughs in precision medicine, has made significant progress in recent years. Almost 13,000 staff members in nearly 1,200 hospitals serve more than 3.9 million patients each year. Over the past decade, the radiopharmaceutical industry has developed rapidly, with the initial formation of a complete industrial chain of production of various radiopharmaceuticals for both clinical use and basic research. Advanced equipment such as PET/CT scanners is being manufactured domestically and even installed abroad. Recently, research into screening and synthesizing new target probes and their translation into the clinic has gained more attention, with various new tracers with potential clinical value being thoroughly studied. Simultaneously, 68Ga- and 177Lu-labeled tumor-targeted probes and others have been implemented for theranostics in an increasing number of hospitals and would be helped by approval from the National Medical Products Administration. Over the next 10-20 y, with the launch of the Mid- and Long-Term Development Plan for Medical Isotopes (2021-2035) by the Chinese government, there is great potential for nuclear medicine in China. With the rise in independent innovation in manufacturing, the shortage of radiopharmaceuticals will be effectively curtailed. We anticipate that the scale of nuclear medicine will at least double by 2035, covering all high-grade hospitals and leading to the aim of "one county, one department" in China.

The crucial role of age and site in incidence and prognosis of female neuroendocrine neoplasms in the United States: a population-based study from 2000 to 2018

BACKGROUND

As the incidence continues to rise, global concern about neuroendocrine neoplasms (NENs) is mounting. However, little is known about how NENs affect women patients.

METHODS

The annual percentage change (APC) was calculated to describe the incidence. Cox proportional hazards multivariable regression was used to identify risk factors. The nomograms were employed to estimate prognosis.

RESULTS

A total of 39,237 female NENs (fNENs) cases were identified. The incidence of fNENs increased annually (APC = 4.5, 95% CI 4.1-4.8, P < 0.05), and the incidence pattern and survival outcomes showed age and site-specificity. Appendiceal, rectal, and pulmonary fNENs were major contributors to the incidence of patients younger than 40, between 40-59, and over 60 years old, respectively. The Cox proportional hazards regression model revealed that age, tumor size, grade, stage, and primary sites were closely related to survival. The worst survival outcomes appeared in breast, reproductive system, and liver fNENs for patients under 40, between 40-49, and over 50 years old, respectively. A nomogram based on these developed with higher predictive accuracy of prognosis, with a C index of 0.906 in the training cohort and 0.901 in the validation cohort.

CONCLUSIONS

Our findings revealed distinct site-specific tendencies in the incidence and survival patterns among fNEN patients across various age groups. Thus, reasonable patient screening and stratification strategies should be implemented, especially for young patients.

Towards the Magic Radioactive Bullet: Improving Targeted Radionuclide Therapy by Reducing the Renal Retention of Radioligands

Targeted radionuclide therapy (TRT) is an emerging field and has the potential to become a major pillar in effective cancer treatment. Several pharmaceuticals are already in routine use for treating cancer, and there is still a high potential for new compounds for this application. But, a major issue for many radiolabeled low-to-moderate-molecular-weight molecules is their clearance via the kidneys and their subsequent reuptake. High renal accumulation of radioactive compounds may lead to nephrotoxicity, and therefore, the kidneys are often the dose-limiting organs in TRT with these radioligands. Over the years, different strategies have been developed aiming for reduced kidney retention and enhanced therapeutic efficacy of radioligands. In this review, we will give an overview of the efforts and achievements of the used strategies, with focus on the therapeutic potential of low-to-moderate-molecular-weight molecules. Among the strategies discussed here is coadministration of compounds that compete for binding to the endocytic receptors in the proximal tubuli. In addition, the influence of altering the molecular design of radiolabeled ligands on pharmacokinetics is discussed, which includes changes in their physicochemical properties and implementation of cleavable linkers or albumin-binding moieties. Furthermore, we discuss the influence of chelator and radionuclide choice on reabsorption of radioligands by the kidneys.

Evaluation of Safety, Biodistribution, and Dosimetry of a Long-Acting Radiolabeled Somatostatin Analog 177 Lu-DOTA-EB-TATE With and Without Amino Acid Infusion

PURPOSE

Kidney is considered to be one of the dose-limiting organs in peptide receptor radionuclide therapy (PRRT). Amino acid cocktail infusion has been applied to reduce renal absorbed dose by inhibiting the proximal tubular reabsorption of the radiopeptide. An Evans blue-modified 177 Lu-labeled octreotate ( 177 Lu-DOTA-EB-TATE) has an extended circulation in the blood, which may make the amino acid infusion unnecessary. The aim of this study was to evaluate the safety, biodistribution, and dosimetry of 177 Lu-DOTA-EB-TATE with and without amino acid infusion.

PATIENTS AND METHODS

Ten patients with metastatic neuroendocrine tumors were randomly divided into 2 groups. The effect of amino acid infusion on renal uptake was assessed in a crossover randomized setting. Group A received 177 Lu-DOTA-EB-TATE at a dose of 3.7 GBq without amino acid infusion for the first cycle and with amino acid infusion for the second cycle; group B received 177 Lu-DOTA-EB-TATE at a dose of 3.7 GBq with amino acid infusion for the first cycle and without amino acid infusion for the second cycle. All patients underwent serial whole-body planar imaging at 1, 24, 96, and 168 hours and SPECT scan at 24 hours after radioligand administration. Abdominal CT was performed 2 days before PRRT for SPECT/CT fusion. The dosimetry was calculated using the HERMES software. Dosimetry evaluation was compared on a between-group and intrapatient basis.

RESULTS

Administrations of 177 Lu-DOTA-EB-TATE with or without amino acids were well tolerated. No grade 4 hematotoxicity was observed in any of the patients. Grade 3 thrombocytopenia was reported in 1 patient. No nephrotoxicity of any grade was recorded. No significant difference was observed in creatinine (75.1 ± 21.7 vs 67.5 ± 18.1 μmol/L, P = 0.128), blood urea nitrogen (4.5 ± 0.8 vs 5.1 ± 1.4 mmol/L, P = 0.612), or GFR (109.3 ± 25.2 vs 100.9 ± 24.9 mL/min, P = 0.398) before and after PRRT. For each cycle, there was no significant difference in whole-body effective dose, kidney effective dose, as well as residence time of the kidneys between group A and B ( P > 0.05). By intrapatient comparison, without and with amino acid infusion also did not show significant difference in whole-body effective dose (0.14 ± 0.05 vs 0.12 ± 0.04 mSv/MBq, P = 0.612), kidney effective dose (1.09 ± 0.42 vs 0.73 ± 0.31 mSv/MBq, P = 0.093), and residence time of the kidneys (2.95 ± 1.58 vs 3.13 ± 1.11 hours, P = 0.674).

CONCLUSIONS

177 Lu-DOTA-EB-TATE PRRT with and without amino acid infusion demonstrated a favorable safety profile in neuroendocrine tumor patients. Administration of 177 Lu-DOTA-EB-TATE without amino acid infusion has acceptable slightly increased kidney absorbed dose and residence time of the kidneys, and does not affect kidney function. Further investigation in a larger cohort and long-term follow-up are warranted.

Wnt/β-catenin modulating drugs regulate somatostatin receptor expression and internalization of radiolabelled octreotide in neuroendocrine tumor cells

BACKGROUND

Differentiated neuroendocrine tumors (NETs) express somatostatin receptors (SSTRs), targets for therapy with either unlabeled or radioactively labeled somatostatin analogs (SSA). Associated with worse prognosis, dedifferentiated NET loose SSTR expression, which may be linked to deregulation of Wnt/β-catenin signaling on an intracellular level. The aim of the present study was to investigate the effect of Wnt/β-catenin signaling pathway alterations on SSTR expression and its function in NET.

METHODS

The NET cell lines BON-1 and QGP-1 were incubated with the Wnt-inhibitors 5-aza-2'-deoxycytidine (5-aza-CdR), Quercetin, or Niclosamide, or the Wnt activator lithium chloride (LiCl). Expression of SSTR1, SSTR2, and SSTR5 was determined by quantitative RT-PCR (qRT-PCR), immunocytomicroscopy and western blot. Changes in the Wnt pathway were analyzed by qRT-PCR of selected target genes and the TaqMan Array Human WNT Pathway. Receptor-associated function was determined by measuring the cellular uptake of [125I-Tyr3] octreotide.

RESULTS

The mRNAs of SSTRs 1-5 were expressed in both cell lines. Wnt inhibitors caused downregulation of Wnt target genes, while 5-aza-CdR had the highest inhibitory effect. LiCl lead to an upregulation of Wnt genes, which was more marked in QGP-1 cells. SSTR expression increased in both cell lines upon Wnt inhibition. All three Wnt inhibitors lead to a marked increase in the specific uptake of [125I-Tyr3]octreotide, with 5-aza-CdR showing the greatest effect (increase by more than 50% in BON-1 cells), while a decreased uptake of [125I-Tyr3]octreotide was seen upon activation of Wnt signaling by LiCl.

CONCLUSIONS

We demonstrate here that Wnt signaling orchestrates SSTR expression and function in a preclinical NET model. Wnt inhibition increases [125I-Tyr3]octreotide uptake offering an opportunity to enhance the efficacy of SSTR-targeted theranostic approaches.

Rare earth-doped nanocrystals for bioimaging in the near-infrared region

Rare earth-doped nanocrystals are widely used in medical diagnostics and bioimaging due to their narrow luminescence emission spectra (10-20 nm), long lifetime, and no photobleaching properties. Especially in the near-infrared (NIR) region, deeper tissue imaging can be achieved with low background luminescence and high spatial resolution. Further precise image-guided diagnosis and treatment can be achieved by using multimodal imaging such as MRI/CT/NIR/PA. Here, we focus on the construction of rare earth-doped nanocrystals, optical properties, and progress of such nanocomposites for bioimaging in the NIR region. In addition, the limitations at this stage in the field of bioimaging and the prospects for future technological development of rare earth-doped nanocrystals are present.

Deciphering albumin-directed drug delivery by imaging

Albumin is the most abundant plasma protein, exhibits extended circulating half-life, and its properties have long been exploited for diagnostics and therapies. Many drugs intrinsically bind albumin or have been designed to do so, yet questions remain about true rate limiting factors that govern albumin-based transport and their pharmacological impacts, particularly in advanced solid cancers. Imaging techniques have been central to quantifying - at a molecular and single-cell level - the impact of mechanisms such as phagocytic immune cell signaling, FcRn-mediated recycling, oncogene-driven macropinocytosis, and albumin-drug interactions on spatial albumin deposition and related pharmacology. Macroscopic imaging of albumin-binding probes quantifies vessel structure, permeability, and supports efficiently targeted molecular imaging. Albumin-based imaging in patients and animal disease models thus offers a strategy to understand mechanisms, guide drug development and personalize treatments.

Albumin Binder-Conjugated Fibroblast Activation Protein Inhibitor Radiopharmaceuticals for Cancer Therapy

Fibroblast activation protein (FAP) has become an attractive target for diagnosis and therapy, and a series of FAP inhibitor (FAPI)-based radiotracers has been developed and had excellent performance for diagnosis outcomes in clinical applications. Yet, their fast clearance and insufficient tumor retention have hampered their further clinical application in cancer treatment. In this study, we developed 2 albumin binder-conjugated FAPI radiotracers, TEFAPI-06 and TEFAPI-07. They were derived from FAPI-04 and were optimized by conjugating 2 types of well-studied albumin binders, 4-(p-iodophenyl) butyric acid moiety (TEFAPI-06) and truncated Evans blue moiety (TEFAPI-07), to try to overcome the above limitations at the expense of prolonging the blood circulation. Methods: TEFAPI-06 and TEFAPI-07 were synthesized and labeled with 68Ga, 86Y, and 177Lu successfully. A series of cell assays was performed to identify the binding affinity and FAP specificity in vitro. PET imaging, SPECT imaging, and biodistribution studies were performed to evaluate the pharmacokinetics in pancreatic cancer patient-derived xenograft (PDX) animal models. The cancer treatment efficacy of 177Lu-TEFAPI-06 and 177Lu-TEFAPI-07 were evaluated in pancreatic cancer PDX-bearing mice. Results: The binding affinities (dissociation constants) to FAP of 68Ga-TEFAPI-06 and 68Ga-TEFAPI-07 were 10.16 ± 2.56 nM and 7.81 ± 2.28 nM, respectively, which were comparable with that of 68Ga-FAPI-04. Comparative PET imaging of HT-1080-FAP and HT-1080 tumor-bearing mice and a blocking study showed the FAP-targeting ability in vivo of these 2 tracers. Compared with 177Lu-FAPI-04, PET imaging, SPECT imaging, and biodistribution studies of TEFAPI-06 and TEFAPI-07 demonstrated their remarkably enhanced tumor accumulation and retention, respectively. Notable tumor growth inhibition by 177Lu-TEFAPI-06 and 177Lu-TEFAPI-07 were observed, whereas the control group and the group treated by 177Lu-FAPI-04 showed a slight therapeutic effect. Conclusion: Two albumin binder-conjugated FAPI radiopharmaceuticals have been developed and evaluated in vitro and in vivo. Significantly improved tumor uptake and retention were observed, compared with the original FAPI tracer. Both 177Lu-TEFAPI-06 and 177Lu-TEFAPI-07 showed remarkable growth inhibition of PDX tumors, whereas the side effects were almost negligible, demonstrating that these radiopharmaceuticals are promising for further clinical translational studies.

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.

Somatostatin receptor radionuclide therapy in neuroendocrine tumors

Peptide receptor radionuclide therapy (PRRT) using 177Lu-DOTATATE has been approved for the treatment of gastroenteropancreatic NETs. An understanding of benefits and risks is important for the appropriate implementation of this therapy. This review summarizes study data supporting the use of radiolabeled somatostatin analogs for the treatment of advanced NETs and highlights risks, including potential toxicities in specific populations. Key ongoing clinical trials, including randomized studies, are designed to better define the position of PRRT within the broader therapeutic landscape. Preclinical and early-phase human studies are focused on the development of novel somatostatin-receptor agonists and antagonists, new radionuclides, and radiosensitizing combination therapies.

Intraindividual comparison of [177Lu]Lu-DOTA-EB-TATE and [177Lu]Lu-DOTA-TOC

Purpose

The radiolabelled somatostatin analogue [¹⁷⁷Lu]Lu-DOTA-EB-TATE binds to albumin via Evans blue, thereby increasing the residence time in the blood and potentially allowing more therapeutic agent to be absorbed into the target tissue during peptide receptor radionuclide therapy. It was tested in selected patients whether the substance is superior to [¹⁷⁷Lu]Lu-DOTA-TOC.

Methods

Activity kinetics in organs and tumours after [¹⁷⁷Lu]Lu-DOTA-EB-TATE and [¹⁷⁷Lu]Lu-DOTA-TOC were compared intraindividually in five patients with progressive somatostatin receptor-positive disease scheduled for radionuclide therapy.

Results

In comparison to [¹⁷⁷Lu]Lu-DOTA-TOC, tumour doses per administered activity were higher for [¹⁷⁷Lu]Lu-DOTA-EB-TATE in 4 of 5 patients (median ratio: 1.7; range: 0.9 to 3.9), kidney doses (median ratio: 3.2; range: 1.6 to 9.8) as well as spleen doses (median ratio: 4.7; range 1.2 to 6.2) in all patients, and liver doses in 3 of 4 evaluable patients (median ratio: 4.0; range: 0.7 to 4.9). The tumour to critical organs absorbed dose ratios were higher after [¹⁷⁷Lu]Lu-DOTA-TOC in 4 of 5 patients.

Conclusions

Prior to a treatment with [¹⁷⁷Lu]Lu-DOTA-EB-TATE, it should be assessed individually whether the compound is superior to established substances.

177Lu-DOTA-EB-TATE, a Radiolabeled Analogue of Somatostatin Receptor Type 2, for the Imaging and Treatment of Thyroid Cancer

PURPOSE

The goal of this study was to analyze the role of somatostatin receptor type 2 (SSTR2) as a molecular target for the imaging and treatment of thyroid cancer through analysis of SSTR2 expression and its epigenetic modulation and testing tumor uptake of different radiolabeled SSTR2 analogues.

EXPERIMENTAL DESIGN

We analyzed SSTR2 expression by immunostaining of 92 thyroid cancer tissue samples and quantified standard uptake values (SUV_max) of SSTR2 analogue, ⁶⁸Ga-DOTA-TATE, by PET/CT imaging in 25 patients with metastatic thyroid cancer. We utilized human thyroid cancer cell lines characterized by differential SSTR2 expression (TT, BCPAP, and FTC133) and rat pancreatic cell line (AR42J) with intrinsically high SSTR2 expression for functional in vitro studies. SSTR2-high (AR42J) and SSTR2-low (FTC133) xenograft mouse models were used to test the uptake of radiolabeled SSTR2 analogues and their therapeutic efficacy in vivo.

RESULTS

Thyroid cancer had a higher SSTR2 expression than normal thyroid. Hurthle cell thyroid cancer was characterized by the highest ⁶⁸Ga-DOTA-TATE uptake [median SUV_max, 16.5 (7.9-29)] than other types of thyroid cancers. In vivo studies demonstrated that radiolabeled DOTA-EB-TATE is characterized by significantly higher tumor uptake than DOTA-TATE (P < 0.001) and DOTA-JR11 (P < 0.001). Treatment with ¹⁷⁷Lu-DOTA-EB-TATE extended survival and reduced tumor size in a mouse model characterized by high somatostatin (SST) analogues uptake (SUV_max, 15.16 ± 4.34), but had no effects in a model with low SST analogues uptake (SUV_max, 4.8 ± 0.27).

CONCLUSIONS

A novel SST analogue, ¹⁷⁷Lu-DOTA-EB-TATE, has the potential to be translated from bench to bedside for the targeted therapy of patients characterized by high uptake of SST analogues in metastatic lesions.

Advances in Molecular Imaging and Radionuclide Therapy of Neuroendocrine Tumors

Neuroendocrine neoplasms make up a heterogeneous group of tumors with inter-patient and intra-patient variabilities. Molecular imaging can help to identify and characterize neuroendocrine tumors (NETs). Furthermore, imaging and treatment with novel theranostics agents offers a new, tailored approach to managing NETs. Recent advances in the management of NETs aim to enhance the effectiveness of targeted treatment with either modifications of known substances or the development of new substances with better targeting features. There have been several attempts to increase the detectability of NET lesions via positron emission tomography (PET) imaging and improvements in pretreatment planning using dosimetry. Especially notable is PET imaging with the radionuclide Copper-64. Increasing interest is also being paid to theranostics of grade 3 and purely differentiated NETs, for example, via targeting of the C-X-C motif chemokine receptor 4 (CXCR4). The aim of this review is to summarize the most relevant recent studies, which present promising new agents in molecular imaging and therapy for NETs, novel combination therapies and new applications of existing molecular imaging modalities in nuclear medicine.

Targeted Radionuclide Therapy in Patient-Derived Xenografts Using 177Lu-EB-RGD

Currently, most patients with non-small cell lung cancer (NSCLC) are diagnosed in advanced stages with a poor five-year survival rate. Therefore, intensive research aimed at finding novel therapeutic strategies has been ongoing; experimental models that reliably emulate NSCLC disease are greatly needed to predict responses to novel therapeutics. Therefore, we developed patient-derived xenograft (PDX) models of NSCLC, which we then used to evaluate the therapeutic efficacy of ¹⁷⁷Lu-EB-RGD, a peptide-based radiopharmaceutical with improved pharmacokinetics that targets integrin α_vβ₃ In this study, three different groups of NSCLC-PDXs were successfully established, all of which maintained the same IHC and genetic characteristics of the human primary tumor. The two NSCLC-PDX groups with intense and low expression of integrin α_vβ₃ (denoted as PDX_αvβ3+ and PDX_αvβ3-) were chosen as the experimental models to evaluate the in vivo biological behavior of ¹⁷⁷Lu-EB-RGD. In SPECT imaging and biodistribution studies, ¹⁷⁷Lu-EB-RGD showed significantly higher accumulation in PDX_αvβ3+ and PDX_αvβ3- models than its corresponding monomer ¹⁷⁷Lu-RGD. A single dose of 18.5 MBq ¹⁷⁷Lu-EB-RGD was enough to completely eradicate the tumors in PDX_αvβ3+, with no sign of tumor recurrence during the observation period. Such treatment was also efficacious in PDX_αvβ3-: a single dose of 29.6 MBq ¹⁷⁷Lu-EB-RGD led to a significant delay in tumor growth as compared with that in the control or ¹⁷⁷Lu-RGD group. The preclinical data from the use of this model suggest that ¹⁷⁷Lu-EB-RGD may be an effective treatment option for NSCLC and should be further evaluated in human trials.

Peptide Receptor Radionuclide Therapy of Late-Stage Neuroendocrine Tumor Patients with Multiple Cycles of 177Lu-DOTA-EB-TATE

This study aimed to evaluate the safety and efficacy of multiple cycles of ¹⁷⁷Lu-DOTA-Evans blue (EB)-TATE peptide receptor radionuclide therapy (PRRT) at escalating doses in neuroendocrine tumors (NETs). Methods: Thirty-two NET patients were randomly divided into 3 groups and treated with escalating doses. Group A received 1.17 ± 0.09 GBq/cycle; group B, 1.89 ± 0.53 GBq/cycle; and group C, 3.97 ± 0.84 GBq/cycle. The treatment was planned for up to 3 cycles. Treatment-related adverse events were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 5.0. Treatment response was evaluated according to the European Organisation for Research and Treatment of Cancer criteria and modified PERCIST. Results: Administration of PRRT was well tolerated, without life-threatening adverse events (CTCAE grade 4). CTCAE grade 3 hematotoxicity was recorded in 1 patient (16.6%) in group B (thrombocytopenia) and 3 patients (21.4%) in group C (thrombocytopenia in 3, anemia in 1). CTCAE grade 3 hepatotoxicity (elevated aspartate aminotransferase) was recorded in 1 patient in group A (8.3%) and 1 patient in group C (7.1%). No nephrotoxicity was observed. According to the criteria of the European Organisation for Research and Treatment of Cancer, the overall disease response rates were similar in groups A, B, and C (50.0%, 50.0%, and 42.9%, respectively), and the overall disease control rates were higher in groups B (83.3%) and C (71.5%) than in group A (66.7%). According to modified PERCIST, a lower disease response rate but a similar disease control rate were found. When a comparable baseline SUV_max ranging from 15 to 40 was selected, the percentage change in SUV_max increased slightly in group A (2.1% ± 40.8%) but decreased significantly in groups B and C (-38.7% ± 10.0% and -14.7% ± 20.0%, respectively) after the first PRRT (P = 0.001) and decreased in all 3 groups after the third PRRT (groups A, B, and C: -6.9% ± 42.3%, -49.2% ± 30.9%, -11.9% ± 37.9%, respectively; P = 0.044). Conclusion: Dose escalations of up to 3.97 GBq/cycle seem to be well tolerated for ¹⁷⁷Lu-DOTA-EB-TATE. ¹⁷⁷Lu-DOTA-EB-TATE doses of 1.89 and 3.97 GBq/cycle were effective in tumor control and more effective than 1.17 GBq/cycle.

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.

Molecular imaging and radionuclide therapy of pheochromocytoma and paraganglioma in the era of genomic characterization of disease subgroups

In recent years, advancement in genetics has profoundly helped to gain a more comprehensive molecular, pathogenic, and prognostic picture of pheochromocytomas and paragangliomas (PPGLs). Newly discovered molecular targets, particularly those that target cell membranes or signaling pathways have helped move nuclear medicine in the forefront of PPGL precision medicine. This is mainly based on the introduction and increasing experience of various PET radiopharmaceuticals across PPGL genotypes quickly followed by implementation of novel radiotherapies and revised imaging algorithms. Particularly, 68Ga-labeled-SSAs have shown excellent results in the diagnosis and staging of PPGLs and in selecting patients for PRRT as a potential alternative to 123/131I-MIBG theranostics. PRRT using 90Y/177Lu-DOTA-SSAs has shown promise for treatment of PPGLs with improvement of clinical symptoms and/or disease control. However, more well-designed prospective studies are required to confirm these findings, in order to fully exploit PRRT's antitumoral properties to obtain the final FDA approval. Such an approval has recently been obtained for high-specific-activity 131I-MIBG for inoperable/metastatic PPGL. The increasing experience and encouraging preliminary results of these radiotherapeutic approaches in PPGLs now raises an important question of how to further integrate them into PPGL management (e.g. monotherapy or in combination with other systemic therapies), carefully taking into account the PPGLs locations, genotypes, and growth rate. Thus, targeted radionuclide therapy (TRT) should preferably be performed at specialized centers with an experienced interdisciplinary team. Future perspectives include the introduction of dosimetry and biomarkers for therapeutic responses for more individualized treatment plans, α-emitting isotopes, and the combination of TRT with other systemic therapies.

Mini-review: Targeted radiopharmaceuticals incorporating reversible, low molecular weight albumin binders

The combination of low molecular weight, reversible human serum albumin (HSA) binders with targeted radiopharmaceuticals in dual-targeted radioconjugates holds great promise, in particular for endoradiotherapy. Attachment of HSA-binders to radiopharmaceuticals extends their blood circulation time and results in an enhanced tumour uptake as well as often in an improved pharmacokinetic profile. In this mini-review, an overview of currently pursued approaches of this novel strategy is provided.

Bench to Bedside: Albumin Binders for Improved Cancer Radioligand Therapies

Radioligand therapy (RLT) relies on the use of pharmacophores to selectively deliver ionization energy to cancers to exert its tumoricidal effects. Cancer cells that are not directly targeted by a radioconjugate remain susceptible to RLT because of the crossfire effect. This is significant given the inter- and intra-heterogeneity of tumors. In recent years, reversible albumin binders have been used as simple "add-ons" for radiopharmaceuticals to modify pharmacokinetics and to enhance therapeutic efficacy. In this Review, we discuss recent advances in albumin binder platforms used in RLT, with an emphasis on 4-( p-iodophenyl)butyric acid and Evans blue derivatives. We focus on four biological systems pertinent to oncology that utilize this class of compounds: folate receptor, integrin αvβ3, somatostatin receptor, and prostate-specific membrane antigen. Finally, we offer our perspectives on albumin binders for RLT, highlighting future areas of research that will help propel the technology further for clinical use.

The theranostic promise for Neuroendocrine Tumors in the late 2010s - Where do we stand, where do we go?

More than 25 years after the first peptide receptor radionuclide therapy (PRRT), the concept of somatostatin receptor (SSTR)-directed imaging and therapy for neuroendocrine tumors (NET) is seeing rapidly increasing use. To maximize the full potential of its theranostic promise, efforts in recent years have expanded recommendations in current guidelines and included the evaluation of novel theranostic radiotracers for imaging and treatment of NET. Moreover, the introduction of standardized reporting framework systems may harmonize PET reading, address pitfalls in interpreting SSTR-PET/CT scans and guide the treating physician in selecting PRRT candidates. Notably, the concept of PRRT has also been applied beyond oncology, e.g. for treatment of inflammatory conditions like sarcoidosis. Future perspectives may include the efficacy evaluation of PRRT compared to other common treatment options for NET, novel strategies for closer monitoring of potential side effects, the introduction of novel radiotracers with beneficial pharmacodynamic and kinetic properties or the use of supervised machine learning approaches for outcome prediction. This article reviews how the SSTR-directed theranostic concept is currently applied and also reflects on recent developments that hold promise for the future of theranostics in this context.

Novel Structural Modification Based on Evans Blue Dye to Improve Pharmacokinetics of a Somastostatin-Receptor-Based Theranostic Agent

The development of somastatin (SS) peptide analogues for the detection and treatment of neuroendocrine tumors has been successful with the recent FDA approval of ⁶⁸Ga-DOTA-TATE and ¹⁷⁷Lu-DOTA-TATE. The structure of these peptide constructs contains the peptide binding motif that binds to the receptor with high affinity, a chelator to complex the radioactive metal, and a linker between the peptide and chelator. However, these constructs suffer from rapid blood clearance, which limits their tumor uptake. In this study, this design has been further improved by incorporating a modification to control the in vivo pharmacokinetics. Adding a truncated Evans Blue (EB) dye molecule into the construct provides a prolonged half-life in blood as a result of its low micromolar affinity to albumin. We compared ¹⁷⁷Lu-DOTA-TATE to the modified ¹⁷⁷Lu Evans Blue compound (¹⁷⁷Lu-DMEB-TATE), in vitro and in vivo in mice bearing A427-7 xenografts. The tumor uptake of ¹⁷⁷Lu-DMEB-TATE was significantly greater than the uptake of ¹⁷⁷Lu-DOTA-TATE in the biodistribution and SPECT-imaging studies. The therapeutic effect of the ¹⁷⁷Lu-DMEB-TATE construct was superior to the that of the ¹⁷⁷Lu-DOTA-TATE construct at the doses evaluated.