Radiopharmacokinetic and dosimetric parameters of 188Re-lanreotide in athymic mice with induced human cancer tumors

Radiolabeled peptides, like the somatostatin analogs, have been used for peptide receptor-mediated radionuclide therapy (PRMRT) in metastatic neuroendocrine tumors.The eight amino acid peptide 3-(2-naphthalenyl)-d-alanyl-l-cysteinyl-l-tyrosyl-d-tryptophyl-l-lysyl-l-valyl-l-cysteinyl-l-threoninamide,cyclic(2 ? 7)-disulfide (9Cl) (lanreotide) was found to bind to the five somatostatin tumor receptors. Lanreotide has been labeled via the bifunctional chelating agent, DOTA, to 111In, and 90Y. A direct labeling method was used to label lanreotide with 188Re. Athymic mice with implanted human cancer tumors (uterine-cervix, renal, and neuroblastoma) were injected with radiochemically pure 188Re-lanreotide (1.11 MBq). The percent injected activity (%IA/g) from serial blood samples was the input data for the WinNonlin computer program to obtain radiopharmacokinetic parameters. The organs percent injected activity per gram of tissue (%IA/g) was extrapolated to the weights of a 70 kg male model organs and the number of nuclear transitions (N) were the input for the OLINDA/EXM program to obtain dosimetry estimates. Induced uterine-cervix tumors (HeLa cells) show a mean 2.4 %IA/g uptake up to 24 h and the tumor/blood ratio was over 1.85 (1.524 h post-injection) confirming 188Re-lanreotide remains bound to the tumor. The estimated tumor absorbed dose was 460 mGy/MBq. Human effective dose was 0.0182 mSv/MBq. Therefore, 188Re-lanreotide is a good candidate for PRMRT and a clinical trial is being planned in order to acquire individual dosimetric data.