GRP Receptor Imaging of Prostate Cancer Using [ 99m Tc]Demobesin 4: a First-in-Man Study

Purpose We explored the imaging of bombesin receptors and evaluated the clinical use of [ 99m Tc]Demobesin 4 ([ 99m Tc]DB4) in prostate cancer patients. Procedures [ 99m Tc]DB4 was prepared according to Good Manufacturing Practice. Patients with prostate cancer underwent serial planar and SPECT imaging up to 3 h after administration. Blood and urine samples were taken to assess pharmacokinetics. Results [ 99m Tc]DB4 is safe and clears rapidly from the bloodstream via the kidneys resulting in low background activity. The tracer binds strongly to the gastrin-releasing peptide receptor (GRPR) in vivo as indicated by the high uptake in the pancreas seen in all patients. In patients who had undergone hormone therapy, [ 99m Tc]DB4 did not efficiently image metastatic prostate cancer. In contrast, in newly diagnosed patients local disease was visualised. Conclusions The GRPR is an unsuitable target for imaging refractory prostate cancer but may be useful in untreated disease. [ 99m Tc]DB4 is a promising radiopharmaceutical which merits further exploration in this specific group of patients.