[⁶⁸Ga]Ga-iPSMA-Lys³-Bombesin: Biokinetics, dosimetry and first patient PET/CT imaging

The prostate-specific membrane antigen (PSMA) and the gastrin-releasing peptide receptor (GRPR) are overexpressed in prostate cancer (PCa). In preclinical studies, the iPSMA-Lys³-Bombesin (iPSMA-BN) heterodimeric ligand has shown a suitable affinity for PSMA and GRPR. This research aimed to assess the biokinetics and radiation dosimetry of [⁶⁸Ga]Ga-iPSMA-BN in four healthy volunteers based on biodistribution data obtained from whole-body PET/CT studies, as well as to visualize the [⁶⁸Ga]Ga-iPSMA-BN tumor uptake in a patient with PCa.

PET/CT images acquired at 5 min, 0.5, 1, and 2 h after radiotracer administration (124.5 ± 2.1 MBq) were corrected for attenuation, scattering, dead-time, and decay. The activity in the segmented volumes of interest (VOIs) in each source organ at different times was adjusted to mono- and bi-exponential biokinetic models (A(t)_VOI), from which the total disintegrations (N) were calculated to assess the internal radiation doses by using the OLINDA V1.1 code.

Images from the patient showed an evident uptake by the metastasis (SUVmax of 4.7) and by the organs expressing GRPR (pancreas) and PSMA (salivary glands). The average effective dose was 2.70 ± 0.05 mSv, which was like those known for most of the ⁶⁸Ga studies, making [⁶⁸Ga]Ga-iPSMA-BN a promising dual-target PET imaging radiotracer for PCa.

[⁶⁸Ga]Ga-iPSMA-BN, capable of detecting both PSMA and GRPR with suitable biokinetics and dosimetric patterns, could be a potential complementary diagnostic tool for the improvement of prostate cancer PET imaging.