To enhance tumor uptake and retention, we designed and developed bi-specific heterodimeric radiotracers targeting both FAP and αvβ3, [68Ga]Ga-FAPI-RGD. The present study aimed to evaluate the specificity, pharmacokinetics, and dosimetry of [68Ga]Ga-FAPI-RGD by preclinical and preliminary clinical studies. Methods: FAPI-RGD was designed and synthesized with the quinoline-based FAPI-02 and the cyclic RGDfK peptide. Preclinical pharmacokinetics were determined in Panc02 xenograft model using microPET and biodistribution experiments. The safety and effective dosimetry of [68Ga]Ga-FAPI-RGD was evaluated in 6 cancer patients, and compared with 2-[18F]FDG imaging. Results: The [68Ga]Ga-FAPI-RGD had good stability in saline for at least 4 h, and showed favorable binding affinity and specificity in vitro and in vivo. Compared to [68Ga]Ga-FAPI-02 and [68Ga]Ga-RGDfK, the tumor uptake and retention of [68Ga]Ga-FAPI-RGD were very much enhanced than its monomeric counterparts at all the time points examined by microPET imaging. A total of 6 patients with various malignant tumors were prospectively enrolled. The effective dose of [68Ga]Ga-FAPI-RGD was 1.94E-02 mSv/MBq. The biodistribution of [68Ga]Ga-FAPI-RGD from 0 to 2 h after injection demonstrated rapid and high tumor uptake, prolonged tumor retention, and high tumor-to-background ratios (TBRs) which further increased over time. No significant difference in mean SUVmax of [68Ga]Ga-FAPI-RGD and 2-[18F]FDG was present in primary tumors (8.9±3.2 vs. 10.3 ± 6.9; p = 0.459). Conclusion: The dual targeting PET tracer [68Ga]Ga-FAPI-RGD showed significantly improved tumor uptake and retention, as well as cleaner background over 68Ga-labeled FAPI and RGD monospecific tracers. The first-in-human biodistribution study showed high TBRs over time, suggesting high diagnostic performance and favorable tracer kinetics for potential therapeutic applications.
Keywords: 68Ga; FAPI-RGD; fibroblast activation protein; heterodimer; integrin αvβ3.
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