Purpose
Fibroblast activation protein-α (FAP)-targeting radioligands have recently demonstrated high diagnostic potential. However, their therapeutic value is impaired by the short tumor residence ...time. Several strategies have been tested to overcome this limitation, but a head-to-head comparison has never been done. With the aim to identify strengths and limitations of the suggested strategies, we compared the monomer FAPI-46 versus (a) its dimer (FAPI-46-F1D), (b) two albumin binders conjugates (FAPI-46-Ibu (ibuprofen) and FAPI-46-EB (Evans Blue)), and (c) cyclic peptide FAP-2286.
Methods
177
Lu-labeled ligands were evaluated in vitro in cell lines with low (HT-1080.hFAP) and high (HEK-293.hFAP) humanFAP expression. SPECT/CT imaging and biodistribution studies were conducted in HT-1080.hFAP and HEK-293.hFAP xenografts. The areas under the curve (AUC) of the tumor uptake and tumor-to-critical-organs ratios and the absorbed doses were estimated.
Results
Radioligands showed IC
50
in the picomolar range. Striking differences were observed in vivo regarding tumor uptake, residence, specificity, and total body distribution. All
177
LuLu-FAPI-46-based radioligands showed similar uptake between the two tumor models.
177
LuLu-FAP-2286 showed higher uptake in HEK-293.hFAP and the least background. The AUC of the tumor uptake and absorbed dose was higher for
177
LuLu-FAPI-46-F1D and the two albumin binder conjugates,
177
LuLu-FAPI-46-Ibu and
177
LuLu-FAPI-46-EB, in HT1080.hFAP xenografts and for
177
LuLu-FAPI-46-EB and
177
LuLu-FAP-2286 in HEK293.hFAP xenografts. The tumor-to-critical-organs AUC values and the absorbed doses were in favor of
177
LuLu-FAP-2286, but tumor-to-kidneys.
Conclusion
The study indicated dimerization and cyclic peptide structures as promising strategies for prolonging tumor residence time, sparing healthy tissues. Albumin binding strategy outcome depended on the albumin binding moiety. The peptide showed advantages in terms of tumor-to-background ratios, besides tumor-to-kidneys, but its tumor uptake was FAP expression–dependent.
Radiolabeled peptides can deliver radiation selectively to tumors via targeting peptide receptors that are overexpressed on the surface of cancer cells. The radiation is used either for detection ...(imaging) or for destruction (therapy) of these tumors. The Division of Radiopharmaceutical
Chemistry at the University Hospital Basel has conducted pioneering work on the development of peptide-based radiopharmaceuticals. Our research covers the entire spectrum of such developments, from bench-to-bedside, and it is illustrated in this article by selective cases.
Somatostatin-based radiolabeled peptides have been successfully introduced into the clinic for targeted imaging and radionuclide therapy of somatostatin receptor (sst)-positive tumors, especially of ...subtype 2 (sst2). The clinically used peptides are exclusively agonists. Recently, we showed that radiolabeled antagonists may be preferable to agonists because they showed better pharmacokinetics, including higher tumor uptake. Factors determining the performance of radioantagonists have only scarcely been studied. Here, we report on the development and evaluation of four (64)Cu or (68)Ga radioantagonists for PET of sst2-positive tumors.
The novel antagonist p-Cl-Phe-cyclo(D-Cys-Tyr-D-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)D-Tyr-NH(2) (LM3) was coupled to 3 macrocyclic chelators, namely 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo6.6.2hexadecane (CB-TE2A), 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), and DOTA. (64/nat)Cu- and (68/nat)Ga-NODAGA-LM3 were prepared at room temperature, and (64/nat)Cu-CB-TE2A-LM3 and (68/nat)Ga-DOTA-LM3 were prepared at 95°C. Binding affinity and antagonistic properties were determined with receptor autoradiography and immunofluorescence microscopy using human embryonic kidney (HEK)-sst2 cells. In vitro internalization and dissociation was evaluated using the same cell line. Biodistribution and small-animal PET studies were performed with HEK-sst2 xenografts.
All metallopeptides demonstrated antagonistic properties. The affinities depend on chelator and radiometal and vary about 10-fold; (68/nat)Ga-NODAGA-LM3 has the lowest half maximal inhibitory concentration (1.3 ± 0.3 nmol/L). The biodistribution studies show impressive tumor uptake at 1 h after injection, particularly of (64)Cu- and (68)Ga-NODAGA-LM3 (∼40 percentage injected dose per gram of tissue %ID/g), which were proven to be specific. Background clearance was fast and the tumor washout relatively slow for (64)Cu-NODAGA-LM3 (∼15 %ID/g, 24 h after injection) and almost negligible for (64)Cu-CB-TE2A-LM3 (26.9 ± 3.3 %ID/g and 21.6 ± 2.1 %ID/g, 4 and 24 h after injection, respectively). Tumor-to-normal-tissue ratios were significantly higher for (64)Cu-NODAGA-LM3 than for (64)Cu-CB-TE2A-LM3 (tumor-to-kidney, 12.8 ± 3.6 and 1.7 ± 0.3, respectively; tumor-to-muscle, 1,342 ± 115 and 75.2 ± 8.5, respectively, at 24 h, P < 0.001). Small-animal PET shows clear tumor localization and high image contrast, especially for (64)Cu- and (68)Ga-NODAGA-LM3.
This article demonstrates the strong dependence of the affinity and pharmacokinetics of the somatostatin-based radioantagonists on the chelator and radiometal. (64)Cu- and (68)Ga-NODAGA-LM3 and (64)Cu-CB-TE2A-LM3 are promising candidates for clinical translation because of their favorable pharmacokinetics and the high image contrast on PET scans.
Our primary aim was to compare the therapeutic index (tumor-to-bone marrow and tumor-to-kidney absorbed-dose ratios) of the new radiolabeled somatostatin receptor antagonist
LuLu-DOTA-JR11 with the ...established radiolabeled somatostatin receptor agonist
LuLu-DOTATOC in the same patients with progressive, standard therapy-refractory meningioma.
In this prospective, single-center, open-label phase 0 study (NCT04997317), 6 consecutive patients were included: 3 men and 3 women (mean age, 63.5 y). Patients received 6.9-7.3 GBq (standard injected radioactivity) of
LuLu-DOTATOC followed by 3.3-4.9 GBq (2 GBq/m
× body surface area) of
LuLu-DOTA-JR11 at an interval of 10 ± 1 wk. In total, 1
LuLu-DOTATOC and 2-3
LuLu-DOTA-JR11 treatment cycles were performed. Quantitative SPECT/CT was done at approximately 24, 48, and 168 h after injection of both radiopharmaceuticals to calculate meningioma and organ absorbed doses as well as tumor-to-organ absorbed-dose ratios (3-dimensional segmentation approach for meningioma, kidneys, liver, bone marrow, and spleen).
The median of the meningioma absorbed dose of 1 treatment cycle was 3.4 Gy (range, 0.8-10.2 Gy) for
LuLu-DOTATOC and 11.5 Gy (range, 4.7-22.7 Gy) for
LuLu-DOTA-JR11. The median bone marrow and kidney absorbed doses after 1 treatment cycle were 0.11 Gy (range, 0.05-0.17 Gy) and 2.7 Gy (range, 1.3-5.3 Gy) for
LuLu-DOTATOC and 0.29 Gy (range, 0.16-0.39 Gy) and 3.3 Gy (range, 1.6-5.9 Gy) for
LuLu-DOTA-JR11, resulting in a 1.4 (range, 0.9-1.9) times higher median tumor-to-bone marrow absorbed-dose ratio and a 2.9 (range, 2.0-4.8) times higher median tumor-to-kidney absorbed-dose ratio with
LuLu-DOTA-JR11. According to the Common Terminology Criteria for Adverse Events version 5.0, 2 patients developed reversible grade 2 lymphopenia after 1 cycle of
LuLu-DOTATOC. Afterward, 2 patients developed reversible grade 3 lymphopenia and 1 patient developed reversible grade 3 lymphopenia and neutropenia after 2-3 cycles of
LuLu-DOTA-JR11. No grade 4 or 5 adverse events were observed at 15 mo or more after the start of therapy. The disease control rate was 83% (95% CI, 53%-100%) at 12 mo or more after inclusion.
Treatment with 1 cycle of
LuLu-DOTA-JR11 showed 2.2-5.7 times higher meningioma absorbed doses and a favorable therapeutic index compared with
LuLu-DOTATOC after injection of 1.4-2.1 times lower activities. The first efficacy results demonstrated a high disease control rate with an acceptable safety profile in the standard therapy for refractory meningioma patients. Therefore, larger studies with
LuLu-DOTA-JR11 are warranted in meningioma patients.
The peptide fragment of human serum albumin that was identified as an inhibitor of C–X–C motif chemokine receptor 4 (CXCR4), termed EPI-X4, was investigated as a scaffold for the development of ...CXCR4-targeting radio-theragnostics. Derivatives of its truncated version JM#21 (ILRWSRKLPCVS) were conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and tested in Jurkat and Ghost-CXCR4 cells. Ligand-1, -2, -5, -6, -7, -8, and -9 were selected for radiolabeling. Molecular modeling indicated that 177Lu-DOTA incorporation C-terminally did not interfere with the CXCR4 binding. Lipophilicity, in vitro plasma stability, and cellular uptake hinted 177Lu-7 as superior. In Jurkat xenografts, all radioligands showed >90% washout from the body within an hour, with the exception of 177Lu-7 and 177Lu-9. 177Lu-7 demonstrated best CXCR4-tumor targeting. Ex vivo biodistribution and single-photon emission computed tomography (SPECT)/positron emission tomography (PET)/CT imaging of 177Lu-7/68Ga-7 showed the same distribution profile for both radioligands, characterized by very low uptake in all nontargeted organs except the kidneys. The data support the feasibility of CXCR4-targeting with EPI-X4-based radioligands and designate ligand-7 as a lead candidate for further optimization.
Our primary aim was to compare the therapeutic index (tumor–to–bone marrow and tumor-to-kidney absorbed-dose ratios) of the new radiolabeled somatostatin receptor antagonist 177LuLu-DOTA-JR11 with ...the established radiolabeled somatostatin receptor agonist 177LuLu-DOTATOC in the same patients with progressive, standard therapy-refractory meningioma. Methods: In this prospective, single-center, open-label phase 0 study ( NCT04997317 ), 6 consecutive patients were included: 3 men and 3 women (mean age, 63.5 y). Patients received 6.9–7.3 GBq (standard injected radioactivity) of 177LuLu-DOTATOC followed by 3.3–4.9 GBq (2 GBq/m2 × body surface area) of 177LuLu-DOTA-JR11 at an interval of 10 ± 1 wk. In total, 1 177LuLu-DOTATOC and 2–3 177LuLu-DOTA-JR11 treatment cycles were performed. Quantitative SPECT/CT was done at approximately 24, 48, and 168 h after injection of both radiopharmaceuticals to calculate meningioma and organ absorbed doses as well as tumor-to-organ absorbed-dose ratios (3-dimensional segmentation approach for meningioma, kidneys, liver, bone marrow, and spleen). Results: The median of the meningioma absorbed dose of 1 treatment cycle was 3.4 Gy (range, 0.8–10.2 Gy) for 177LuLu-DOTATOC and 11.5 Gy (range, 4.7–22.7 Gy) for 177LuLu-DOTA-JR11. The median bone marrow and kidney absorbed doses after 1 treatment cycle were 0.11 Gy (range, 0.05–0.17 Gy) and 2.7 Gy (range, 1.3–5.3 Gy) for 177LuLu-DOTATOC and 0.29 Gy (range, 0.16–0.39 Gy) and 3.3 Gy (range, 1.6–5.9 Gy) for 177LuLu-DOTA-JR11, resulting in a 1.4 (range, 0.9–1.9) times higher median tumor–to–bone marrow absorbed-dose ratio and a 2.9 (range, 2.0–4.8) times higher median tumor-to-kidney absorbed-dose ratio with 177LuLu-DOTA-JR11. According to the Common Terminology Criteria for Adverse Events version 5.0, 2 patients developed reversible grade 2 lymphopenia after 1 cycle of 177LuLu-DOTATOC. Afterward, 2 patients developed reversible grade 3 lymphopenia and 1 patient developed reversible grade 3 lymphopenia and neutropenia after 2–3 cycles of 177LuLu-DOTA-JR11. No grade 4 or 5 adverse events were observed at 15 mo or more after the start of therapy. The disease control rate was 83% (95% CI, 53%–100%) at 12 mo or more after inclusion. Conclusion: Treatment with 1 cycle of 177LuLu-DOTA-JR11 showed 2.2–5.7 times higher meningioma absorbed doses and a favorable therapeutic index compared with 177LuLu-DOTATOC after injection of 1.4–2.1 times lower activities. The first efficacy results demonstrated a high disease control rate with an acceptable safety profile in the standard therapy for refractory meningioma patients. Therefore, larger studies with 177LuLu-DOTA-JR11 are warranted in meningioma patients.
Preclinical and clinical studies have indicated that somatostatin receptor (sst)-expressing tumors demonstrate higher uptake of radiolabeled sst antagonists than of sst agonists. In 4 consecutive ...patients with advanced neuroendocrine tumors, we evaluated whether treatment with (177)Lu-labeled sst antagonists is feasible.
After injection of approximately 1 GBq of (177)Lu-DOTA-Cpa-c(DCys-Aph(Hor)-DAph(Cbm)-Lys-Thr-Cys)-DTyr-NH2 ((177)Lu-DOTA-JR11) and (177)Lu-DOTATATE, 3-dimensional voxel dosimetry analysis based on SPECT/CT was performed. A higher tumor-to-organ dose ratio for (177)Lu-DOTA-JR11 than for (177)Lu-DOTATATE was the prerequisite for treatment with (177)Lu-DOTA-JR11.
Reversible minor adverse effects of (177)Lu-DOTA-JR11 were observed. (177)Lu-DOTA-JR11 showed a 1.7-10.6 times higher tumor dose than (177)Lu-DOTATATE. At the same time, the tumor-to-kidney and tumor-to-bone marrow dose ratio was 1.1-7.2 times higher. All 4 patients were treated with (177)Lu-DOTA-JR11, resulting in partial remission in 2 patients, stable disease in 1 patient, and mixed response in the other patient.
Treatment of neuroendocrine tumors with radiolabeled sst antagonists is clinically feasible and may have a significant impact on peptide receptor radionuclide therapy.
Context: Surgical intervention is advised in patients with multiple endocrine neoplasia type-1 (MEN-1) and nonfunctioning pancreatic neuroendocrine tumors (PanNETs) with a size greater than or equal ...to20 mm. Functioning PanNETs, such as in patients with endogenous hyperinsulinemic hypoglycemia (EHH) due to (one or multiple) insulinomas, should be treated surgically independent of size. Preoperative localization of insulinomas is critical for surgery. Objective: To evaluate the feasibility and sensitivity of .sup.68Ga-DOTA-exendin-4 positron emission tomography (PET)/CT in the detection of clinically relevant lesions in patients with MEN-1 and EHH in combination with MRI. Design: Post hoc subgroup analysis of a larger prospective imaging study with 52 patients with EHH. Patients: Six of 52 consecutive patients with EHH and genetically proven MEN-1 mutation were included. Interventions: All patients received one .sup.68Ga-DOTA-exendin-4 PET/CT and one MRI scan within 3 to 4 days. Thereafter, surgery was performed based on all imaging results. Main Outcome Measures: Lesion-based sensitivity of PET/CT and MRI for detection of clinically relevant lesions was calculated. Readers were unaware of other results. The reference standard was surgery with histology and treatment outcome. True positive (i.e., clinically relevant lesions) was defined as PanNETs greater than or equal to20 mm or insulinoma. Results: In six patients, 37 PanNETs were confirmed by histopathology. Sensitivity (95% CI) in the detection of clinically relevant lesions for combined PET/CT plus MRI, MRI, and PET/CT was 92.3% (64% to 99.8%), 38.5% (13.9% to 68.4%), and 84.6% (54.6% to 98.1%), respectively (P = 0.014 for the comparison of PET/CT plus MRI vs MRI). Postsurgery, EHH resolved in all patients. Conclusion: .sup.68Ga-DOTA-exendin-4 PET/CT is feasible in patients with MEN-1 and EHH. The combination with MRI is superior to MRI alone in the detection of insulinomas and may guide the surgical strategy. (J Clin Endocrinol Metab 104: 5843-5852, 2019)
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