Therapeutic 188Re-lanreotide: determination of radiopharmacokinetic parameters in rats.

Objectives: The radiopharmacokinetic parameters of the therapeutic radiopharmaceutical (188)Re-lanreotide were compared in rats implanted with hepatocarcinoma tumours (n= 18) and healthy rats (n= 18).

Methods: Rats were injected with approximately 1.8 MBq (188)Re-lanreotide (0.1 ml) via the tail vein and blood samples were obtained. The activity per gram of tissue (%IA/g) was calculated and the radiopharmacokinetic parameters determined. Data were fitted using a two-compartment model.

Key Findings: Significant differences were found between healthy and hepatoma rats for beta elimination half-life (22.56 vs 48.14 h); transference constants K(10) (k(e)) (6.44 vs 3.05 h(-1)) and K(12) (2.76 vs 7.09 h(-1)); volume of distribution (2.06 vs 5.45 ml); mean residence time (66.58 vs 95.50 h) and apparent volume of distribution at steady state (131.30 vs 810.37 ml). The tumour/organ ratios after 24 h were 11.20 for tumour/muscle, 8.00 for tumour/liver and 7.72 for tumour/bone. The scintigraphic images obtained therefore had high resolution.

Conclusions: (188)Re-lanreotide had a prolonged beta elimination half-life and increased volume of distribution in rats with hepatocellular carcinoma. This may be beneficial in the diagnosis and therapy of metastatic lesions in patients with cancer.