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Updated: Jun 13, 2025
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An Automated Radiosynthesis of [68Ga]Ga-FAPI-46 for Routine Clinical Use
Published on: May 24, 2024
Radiosynthesis and in-vitro identification of a molecular probe 131I-FAPI targeting cancer-associated fibroblasts
Yaxin Tian1,2, Yanghongyan Jiang3, Ping Ma1
1Department of Nuclear Medicine, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, China.
Purpose:
Fibroblast activation protein (FAP) is highly expressed in the mesenchyme of most malignant epithelial tumors, while its expression is low in normal tissues. FAP inhibitors (FAPIs) bind specifically to FAP and are used for tumor-targeted diagnosis and therapy. The aim of this study was to radiosynthesize a novel molecular probe 131I-FAPI and evaluate its in-vitro targeting and biological characteristics.
Methods:
The structurally modified FAPI was labelled with 131I through the chloramine-T method. The radiolabeling rate was then detected by thin-layer chromatography (TLC). The stability of 131I-FAPI was determined at PBS (room temperature) and serum (37°C). Its hydrophilicity was calculated by measuring its lipid-water partition coefficient. Pancreatic cancer PANC-1 cell line and glioma U87 cell line were cultured in vitro. Cell uptake assay was used to show the binding ability of 131I-FAPI. The CCK-8 assay was used to calculate the inhibitory effects of 131I-FAPI at different time points (4h, 8h, 12h, 24h, 48h) after comparing with the 131I and FAPI. The before-and-after-24h scratch areas of the two cells were determined in order to verify the effect of 131I-FAPI on the migration ability of the cells.
Results:
The radiolabeling rate was (84.9 ± 1.02) %. The radiochemical purity of 131I-FAPI remained over 80% in both 25°C PBS and 37°C serum. The value of the lipid-water partition coefficient was -0.869 ± 0.025, indicating the hydrophilic of the probe. The cellular uptake assay showed that U87 cells had a specific binding capacity for 131I-FAPI. In cell inhibition assays, the inhibitory effect of 131I-FAPI on U87 cells increased with time. The results of cell scratch assay showed that 131I-FAPI had the strongest inhibitory effect on the migratory ability of U87 cells compared with 131I and FAPI (P<0.001).
Conclusion:
131I-FAPI was synthesized with good in-vitro stability and hydrophilic properties. It can be specifically bound by U87 cells. The proliferation and migration of U87 cells can be effectively inhibited. 131I-FAPI is promising to become a therapeutic probe.
Insights
A novel radioactive tracer, 131I-FAPI, effectively targets cancer cells in vitro. This fibroblast activation protein inhibitor shows promise for cancer diagnosis and therapy by inhibiting tumor cell proliferation and migration.
Area of Science:
- Nuclear Medicine
- Radiochemistry
- Oncology
Background:
- Fibroblast activation protein (FAP) is a key marker overexpressed in various malignant epithelial tumors but minimally in healthy tissues.
- FAP inhibitors (FAPI) are crucial for targeted cancer diagnosis and therapy due to their specific binding to FAP.
- Developing novel radiolabeled FAPI probes enhances their utility in molecular imaging and therapeutic applications.
Purpose of the Study:
- To synthesize a novel molecular probe, 131I-FAPI, through radiosynthesis.
- To evaluate the in vitro targeting capabilities and biological characteristics of the newly developed 131I-FAPI probe.
- To assess the potential of 131I-FAPI as a diagnostic and therapeutic agent for FAP-expressing tumors.
Main Methods:
- Radiosynthesis of 131I-FAPI using the chloramine-T method.
- Assessment of radiolabeling yield and purity via thin-layer chromatography (TLC).
- Evaluation of in vitro stability in PBS and serum, hydrophilicity via lipid-water partition coefficient, and cell uptake in PANC-1 and U87 cell lines.
- Inhibition assays (CCK-8) and cell migration assays (scratch assay) to determine biological effects on U87 cells.
Main Results:
- Successful radiosynthesis of 131I-FAPI with a radiolabeling rate of (84.9 ± 1.02)% and radiochemical purity over 80%.
- The probe exhibited good in vitro stability and hydrophilic properties (lipid-water partition coefficient: -0.869 ± 0.025).
- 131I-FAPI demonstrated specific binding to U87 cells, effectively inhibiting their proliferation and migration in vitro (P<0.001).
Conclusions:
- The synthesized 131I-FAPI probe possesses favorable in vitro stability and hydrophilic characteristics.
- 131I-FAPI exhibits specific binding to U87 glioma cells and effectively inhibits their proliferation and migration.
- 131I-FAPI shows significant promise as a novel therapeutic probe for FAP-expressing cancers.
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