Purpose
Fibroblast activation protein (FAP), which has high expression in cancer-associated fibroblasts of epithelial cancers, can be used as a theranostic target. Our previous study used
64
Cu and
...225
Ac-labelled FAP inhibitors (FAPI-04) for a FAP-expressing pancreatic cancer xenograft imaging and therapy. However, the optimal therapeutic radionuclide for FAPI needs to be investigated further. In this study, we evaluated the therapeutic effects of beta-emitter (
177
Lu)-labelled FAPI-46 and alpha-emitter (
225
Ac)-labelled FAPI-46 in pancreatic cancer models.
Methods
PET scans (1 h post injection) were acquired in PANC-1 xenograft mice (
n
= 9) after the administration of
18
FFAPI-74 (12.4 ± 1.7 MBq) for the companion imaging. The biodistribution of
177
LuFAPI-46 and
225
AcFAPI-46 were evaluated in the xenograft model (total
n
= 12). For the determination of treatment effects,
177
LuFAPI-46 and
225
AcFAPI-46 were injected into PANC-1 xenograft mice at different doses: 3 MBq (
n
= 6), 10 MBq (
n
= 6), 30 MBq (
n
= 6), control (
n
= 4) for
177
LuFAPI-46, and 3 kBq (
n
= 3), 10 kBq (
n
= 2), 30 kBq (
n
= 6), control (
n
= 7) for
225
AcFAPI-46. Tumour sizes and body weights were followed.
Results
18
FFAPI-74 showed rapid clearance by the kidneys and high accumulation in the tumour and intestine 1 h after administration.
177
LuFAPI-46 and
225
AcFAPI-46 also showed rapid clearance by the kidneys and relatively high accumulation in the tumour at 3 h. Both
177
LuFAPI-46 and
225
AcFAPI-46 showed tumour-suppressive effects, with a mild decrease in body weight. The treatment effects of
177
LuFAPI-46 were relatively slow but lasted longer than those of
225
AcFAPI-46.
Conclusion
This study suggested the possible application of FAPI radioligand therapy in FAP-expressing pancreatic cancer. Further evaluation is necessary to find the best radionuclide with shorter half-life, as well as the combination with therapies targeting tumour cells directly.
Objective
Astatine (
211
At) is a promising alpha emitter as an alternative to iodine (
131
I). We are preparing the first-in-human (FIH) clinical trial of targeted alpha therapy for differentiated ...thyroid cancer in consultation with Pharmaceuticals and Medical Devices Agency. Here, we performed an extended single-dose toxicity examination under a reliability standard, as a preclinical safety assessment of
211
AtNaAt to determine the FIH dose.
Methods
211
AtNaAt solution was injected into normal 6-week-old mice (male (
n
= 50) and female (
n
= 50), body weight: male 33.2 ± 1.7 g, female 27.3 ± 1.5 g), which were then divided into four groups: 5 MBq/kg (
n
= 20), 20 MBq/kg (
n
= 20), 50 MBq/kg (
n
= 30), saline control (
n
= 30). The mice were followed up for 5 days (primary evaluation point for acute toxicity:
n
= 80) or 14 days (
n
= 20: evaluation point for recovery) to monitor general condition and body weight change. At the end of the observation period, necropsy, blood test, organ weight measurement, and histopathological examination were performed. For body weight, blood test, and organ weight, statistical analyses were performed to compare data between the control and injected groups.
Results
No abnormal findings were observed in the general condition of mice. In the 50 MBq/kg group, males (days 3 and 5) showed a significant decrease in body weight compared with the control. However, necropsy did not differ significantly beyond the range of spontaneous lesions. In the blood test, males (50 MBq/kg) and females (50 MBq/kg) showed a decrease in white blood cell and platelet counts on day 5, and recovery on day 14. In the testis, a considerable weight decrease was observed on day 14 (50 MBq/kg), and multinucleated giant cells were observed in all mice, indicating a significant change related to the administration of
211
AtNaAt.
Conclusions
In the extended single-dose toxicity study of
211
AtNaAt, administration of high doses resulted in weight loss, transient bone marrow suppression, and pathological changes in the testis, which require consideration in the FIH clinical trial.
Astatine-211 (
At)-labeled phenylalanine is expected to be a promising agent for targeted alpha-particle therapy for the treatment of patients with glioma. The existing reactions to prepare the ...labeled compound usually require organic solvents and metals that are toxic and hazardous to the environment. In this study, we developed a novel method wherein astatination was realized via the substitution of
At for a dihydroxyboryl group coupled to phenylalanine.
At4-astato-L-phenylalanine was obtained as the carrier-free product in aqueous medium in high radiochemical yields (98.1 ± 1.9%, n = 5). The crude reaction mixture was purified by solid-phase extraction, and the radiochemical purity of the product was 99.3 ± 0.7% (n = 5). The high yield and purity were attributed to the formation of
AtAtI and AtI
as the reactive intermediates in the astatination reaction. The reaction did not require any organic solvents or toxic reagents, suggesting that this method is suitable for clinical applications.
The high
stability of 2,2-dihydroxymethyl-3-
Ffluoropropyl-2-nitroimidazole (
FDiFA) prompted us to evaluate neopentyl as a scaffold to prepare a radiotheranostic system with radioiodine and ...astatine. Three DiFA analogues with one, two, or without a hydroxyl group were synthesized. While all
I-labeled compounds remained stable against nucleophilic substitution, only a
I-labeled neopentyl glycol was stable against cytochrome P450 (CYP)-mediated metabolism and showed high stability against
deiodination.
At-labeled neopentyl glycol also remained stable against both nucleophilic substitution and CYP-mediated metabolism.
At-labeled neopentyl glycol showed the biodistribution profiles similar to those of its radioiodinated counterpart in contrast to the
I/
At-labeled benzoate pair. The urine analyses confirmed that
At-labeled neopentyl glycol was excreted in the urine as a glucuronide conjugate with the absence of free
AtAt
. These findings indicate that neopentyl glycol would constitute a promising scaffold to prepare a radiotheranostic system with radioiodine and
At.
Some types of dioxetanes are called chemiluminophores because they produce luminescence light without the use of enzymes. Here, we designed and synthesized a novel carboxy group‐containing ...chemiluminophore derivative, which enabled the simple introduction of such a chemiluminophore to the molecule of interest. Furthermore, we demonstrate that the in vivo imaging system (IVIS imaging system) can recognize tagged chemicals, indicating that such a chemiluminophore could be employed as a tracer molecule for biological studies.
A novel carboxy group‐containing chemiluminophore derivative, which enabled the simple introduction of a chemiluminophore to the molecule of interest, was developed. This chemiluminophore cast luminescence light without enzymes, such as luciferase. Chemiluminophore‐containing probes thus obtained could be visualized by in vivo imaging system.
This study confirmed the effect of sodium/iodine symporter (NIS) expression on existing drugs by in vitro and in vivo tests using cultured cell lines. The tumor growth inhibitory effect of sodium ...astatide (
AtNaAt) was evaluated by in vitro and in vivo tests using human thyroid cancer cells (K1, K1/NIS and K1/NIS-DOX). NIS expression in cancer cells was controlled using the Tet-On system.
INaI was used as control existing drug. From the results of the in vitro studies, the mechanism of
AtNaAt uptake into thyroid cancer cells is mediated by NIS, analogous to
INaI, and the cellular uptake rate correlates with the expression level of NIS.
AtNaAt's ability to inhibit colony formation was more than 10 times that of
INaI per becquerel (Bq), and
AtNaAt's DNA double-strand breaking (DSB) induction was more than ten times that of
INaI per Bq, and
AtNaAt was more than three times more cytotoxic than
INaI (at 1000 kBq each). In vivo studies also showed that the tumor growth inhibitory effect of
AtNaAt depended on NIS expression and was more than six times that of
INaI per Bq.
Astatine (211At) is an alpha-emitter with a better treatment efficacy against differentiated thyroid cancer compared with iodine (131I), a conventional beta-emitter. However, its therapeutic ...comparison has not been fully evaluated. In this study, we compared the therapeutic effect between 211AtNaAt and 131INaI. In vitro analysis of a double-stranded DNA break (DSB) and colony formation assay were performed using K1-NIS cells. The therapeutic effect was compared using K1-NIS xenograft mice administered with 211AtNaAt (0.4 MBq (n = 7), 0.8 MBq (n = 9), and 1.2 MBq (n = 4)), and 131INaI (1 MBq (n = 4), 3 MBq (n = 4), and 8 MBq (n = 4)). The 211AtNaAt induced higher numbers of DSBs and had a more reduced colony formation than 131INaI. In K1-NIS mice, dose-dependent therapeutic effects were observed in both 211AtNaAt and 131INaI. In 211AtNaAt, a stronger tumour-growth suppression was observed, while tumour regrowth was not observed until 18, 25, and 46 days after injection of 0.4, 0.8, and 1.2 MBq of 211AtNaAt, respectively. While in 131INaI, this was observed within 12 days after injection (1, 3, and 8 MBq). The superior therapeutic effect of 211AtNaAt suggests the promising clinical applicability of targeted alpha therapy using 211AtNaAt in patients with differentiated thyroid cancer refractory to standard 131INaI treatment.
Fibroblast activation proteins (FAP) are overexpressed in the tumor stroma and have received attention as target molecules for radionuclide therapy. The FAP inhibitor (FAPI) is used as a probe to ...deliver nuclides to cancer tissues. In this study, we designed and synthesized four novel
At-FAPI(s) possessing polyethylene glycol (PEG) linkers between the FAP-targeting and
At-attaching moieties.
At-FAPI(s) and piperazine (PIP) linker FAPI exhibited distinct FAP selectivity and uptake in FAPII-overexpressing HEK293 cells and the lung cancer cell line A549. The complexity of the PEG linker did not significantly affect selectivity. The efficiencies of both linkers were almost the same. Comparing the two nuclides,
At was superior to
I in tumor accumulation. In the mouse model, the antitumor effects of the PEG and PIP linkers were almost the same. Most of the currently synthesized FAPI(s) contain PIP linkers; however, in our study, we found that PEG linkers exhibit equivalent performance. If the PIP linker is inconvenient, a PEG linker is expected to be an alternative.
Astatine (211At) is a cyclotron-produced alpha emitter with a physical half-life of 7.2 h. In our previous study, the 211At-labeled prostate-specific membrane antigen (PSMA) compound (211AtPSMA-5) ...exhibited excellent tumor growth suppression in a xenograft model. We conducted preclinical biodistribution and toxicity studies for the first-in-human clinical trial. 211AtPSMA-5 was administered to both normal male ICR mice (n = 85) and cynomolgus monkeys (n = 2). The mice were divided into four groups for the toxicity study: 5 MBq/kg, 12 MBq/kg, 35 MBq/kg, and vehicle control, with follow-ups at 1 day (n = 10 per group) and 14 days (n = 5 per group). Monkeys were observed 24 h post-administration of 211AtPSMA-5 (9 MBq/kg). Blood tests and histopathological examinations were performed at the end of the observation period. Blood tests in mice indicated no significant myelosuppression or renal dysfunction. However, the monkeys displayed mild leukopenia 24 h post-administration. Despite the high accumulation in the kidneys and thyroid, histological analysis revealed no abnormalities. On day 1, dose-dependent single-cell necrosis/apoptosis was observed in the salivary glands of mice and intestinal tracts of both mice and monkeys. Additionally, tingible body macrophages in the spleen and lymph nodes indicated phagocytosis of apoptotic B lymphocytes. Cortical lymphopenia (2/10) in the thymus and a decrease in the bone marrow cells (9/10) were observed in the 35 MBq/kg group in mice. These changes were transient, with no irreversible toxicity observed in mice 14 days post-administration. This study identified no severe toxicities associated with 211AtPSMA-5, highlighting its potential as a next-generation targeted alpha therapy for prostate cancer. The sustainable production of 211At using a cyclotron supports its applicability for clinical use.
Currently, targeted alpha therapy (TAT) is a new therapy involving the administration of a therapeutic drug that combines a substance of α-emitting nuclides that kill cancer cells and a drug that ...selectively accumulates in cancer cells. It is known to be effective against cancers that are difficult to treat with existing methods, such as cancer cells that are widely spread throughout the whole body, and there are high expectations for its early clinical implementation. The nuclides for TAT, including
Tb,
At,
Bi,
Pb (for
Bi),
Ra,
Ac,
Th, and
U, are known. However, some nuclides encounter problems with labeling methods and lack sufficient preclinical and clinical data. We labeled the compounds targeting prostate specific membrane antigen (PSMA) with
At and
Ac. PSMA is a molecule that has attracted attention as a theranostic target for prostate cancer, and several targeted radioligands have already shown therapeutic effects in patients. The results showed that
At, which has a much shorter half-life, is no less cytotoxic than
Ac. In
At labeling, our group has also developed an original method (
). We have succeeded in obtaining a highly purified labeled product in a short timeframe using this method.
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![Synthesis of [ 211 At]4-ast...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2045-2322/small "Synthesis of [ 211 At]4-astato-L-phenylalanine by dihydroxyboryl-astatine substitution reaction in aqueous solution")
