Molecular imaging of reduced renal uptake of radiolabelled [DOTA(0),Tyr(3)]octreotate by the combination of lysine and Gelofusine in rats

Aim: In peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues, kidney uptake of radiolabelled compound is the major dose-limiting factor. We studied the effects of Gelofusine (20 mg) and lysine (100 mg) and the combination of both after injection of therapeutic doses of radiolabelled [DOTA(0),Tyr(3)]octreotate (60 MBq In-111 or 555 MBq Lu-177 labelled to 15 mu g peptide) in male Lewis rats. Methods: Kidney uptake was measured by single photon emission computed tomography (SPECT) scans with a four-headed multi-pinhole camera (NanoSPECT) at 24 h, 5 and 7 days p. i. and was quantified by volume of interest analysis. For validation the activity concentration in the dissected kidneys was also determined ex vivo using a gamma counter and a dose calibrator. Results: Gelofusine and lysine both reduced kidney uptake of [Lu-177-DOTA(0),Tyr(3)]octreotate significantly by about 40% at all time points. The combination of Gelofusine and lysine resulted in a 62% inhibition of kidney uptake (p < 0.01 vs. lysine alone). A weak but significant dose-response relationship for Gelofusine, but not for lysine, was found. In a study with [In-111-DOTA(0),Tyr(3)]octreolate, conclusions drawn from NanoSPECT data were confirmed by biodistribution data. Conclusions: We conclude that rat kidney uptake of radiolabelled somatostatin analogues can be monitored for a longer period in the same animal using animal SPECT. Gelofusine and lysine had equal potential to reduce kidney uptake of therapeutic doses of [Lu-177-DOTA(0),Tyr(3)]octreotate. The combination of these compounds caused a significantly larger reduction than lysine or Gelofusine alone and may therefore offer new possibilities in PRRT. The NanoSPECT data were validated by standard biodistribution experiments