Targeting TROP-2 in Prostate Cancer Using Site-Specifically Radiolabeled IMMU-132 with ⁸⁹Zr via 3,4,3-LI(1,2-HOPO)

Abstract

Aim

To develop a site-specifically radiolabeled version of IMMU-132 (sacituzumab govitecan) using zirconium-89 (⁸⁹Zr) with the chelator 3,4,3-LI(1,2-HOPO) and evaluate its stability, specificity, and quantitative targeting ability in TROP-2–positive prostate cancer models.

Methods

IMMU-132 was conjugated to 3,4,3-LI(1,2-HOPO)-maleimide and its integrity was confirmed by SDS-PAGE, SE-HPLC and mass spectrometry. Radiolabeling with ⁸⁹Zr was performed, and radiochemical yield and purity were measured. In vitro stability was assessed in human serum at 37 °C for 120 h. Binding affinity and specificity were evaluated using PC3 (TROP-2⁺) and A549 (TROP-2⁻) cells. Immunoreactivity was determined by Lindmo assay. In vivo PET imaging and ex vivo biodistribution were conducted in PC3-TROP-2⁺ xenograft-bearing mice.

Results

Radiolabeling with ⁸⁹Zr yielded 71.88 ± 0.21% with a radiochemical purity of 98.70 ± 0.55%. The radioconjugate maintained >90% stability in serum over 120 h. High-specific binding was observed in PC3 cells (Bmax ≈ 4750 CPM; Kd = 0.4 × 10⁶ cells/mL), with minimal uptake in A549 cells. The immunoreactive fraction was 88.10%. PET imaging revealed tumor-specific accumulation with a peak SUV mean of 5.8 ± 0.7 at 72 h post-injection. Biodistribution confirmed high tumor uptake (19.4 ± 2.1 %ID/g) and significantly reduced bone uptake (3.2 ± 0.5 %ID/g) compared to conventional ⁸⁹Zr-DFO tracers (p < 0.01).

Conclusion

⁸⁹Zr–IMMU-132–HOPO exhibits excellent in vivo stability, specificity, and selective accumulation in TROP-2–positive prostate tumors, while minimizing off-target bone uptake. These findings support its potential as a next-generation immuno-radiopharmaceutical for quantitative TROP-2 imaging and future theranostic applications in prostate cancer.

Keywords

TROP-2, ⁸⁹Zr Radiolabeling, IMMU-132, Prostate Cancer

Publikationsverlauf

Eingereicht: 14. Juni 2025

Angenommen nach Revision: 14. Oktober 2025

Artikel online veröffentlicht:
26. November 2025

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