(177)Lu-OPS201 targeting somatostatin receptors: in vivo biodistribution and dosimetry in a pig model.
BACKGROUND
(177)Lu is used in peptide receptor radionuclide therapies for the treatment of neuroendocrine tumors. Based on the recent literature, SST2 antagonists are superior to agonists in tumor uptake. The compound OPS201 is the novel somatostatin antagonist showing the highest SST2 affinity. The aim of this study was to measure the in vivo biodistribution and dosimetry of (177)Lu-OPS201 in five anesthetized Danish Landrace pigs as an appropriate substitute for humans to quantitatively assess the absorbed doses for future clinical applications.


RESULTS
(177)Lu-OPS201 was obtained with a specific activity ranging from 10 to 17 MBq/μg. Prior to administration, the radiochemical purity was measured as s > 99.7 % in all cases. After injection, fast clearance of the compound from the blood stream was observed. Less than 5 % of the injected activity was presented in blood 10 min after injection. A series of SPECT/CT and whole-body scans conducted until 10 days after intravenous injection showed uptake mostly in the liver, spine, and kidneys. There was no visible uptake in the spleen. Blood samples were taken to determine the time-activity curve in the blood. Time-activity curves and time-integrated activity coefficients were calculated for the organs showing visible uptake. Based on these data, the absorbed organ dose coefficients for a 70-kg patient were calculated with OLINDA/EXM. For humans after an injection of 5 GBq (177)Lu-OPS201, the highest predicted absorbed doses are obtained for the kidneys (13.7 Gy), the osteogenic cells (3.9 Gy), the urinary bladder wall (1.8 Gy), and the liver (1.0 Gy). No metabolites of (177)Lu-OPS201 were found by radio HPLC analysis. None of the absorbed doses calculated will exceed organ toxicity levels.


CONCLUSIONS
The (177)Lu-OPS201 was well tolerated and caused no abnormal physiological or behavioral signs. In vivo distributions and absorbed doses of pigs are comparable to those observed in other publications. According to the biodistribution data in pigs, presented in this work, the expected radiation exposure in humans will be within the acceptable range.
Department of Nuclear Medicine, University of Würzburg, Oberdürrbacher Str. 6, 97080, Würzburg, Germany. beykan_s@ukw.de.
Seval
S
Beykan
Department of Nuclear Medicine, Aalborg University Hospital, Aalborg, Denmark.
Jan S
JS
Dam
Department of Nuclear Medicine, University of Würzburg, Oberdürrbacher Str. 6, 97080, Würzburg, Germany.
Uta
U
Eberlein
Octreopharm Science GmbH, Ipsen Group, Berlin, Germany.
Jens
J
Kaufmann
Biomedical Research Laboratory, Department of Clinical Medicine, Aalborg University Hospital, Aalborg, Denmark.
Benedict
B
Kjærgaard
Department of Nuclear Medicine, Aalborg University Hospital, Aalborg, Denmark.
Lars
L
Jødal
Octreopharm Science GmbH, Ipsen Group, Berlin, Germany.
Hakim
H
Bouterfa
Octreopharm Science GmbH, Ipsen Group, Berlin, Germany.
Romain
R
Bejot
Department of Nuclear Medicine, University of Würzburg, Oberdürrbacher Str. 6, 97080, Würzburg, Germany.
Michael
M
Lassmann
Department of Nuclear Medicine, Aalborg University Hospital, Aalborg, Denmark.|Department of Chemistry and Biochemistry, Aalborg University, Aalborg, Denmark.
Svend Borup
SB
Jensen
Antagonist; Dosimetry; JR11; Lutetium-177; Neuroendocrine tumor (NET); OPS201; PRRT; Pig model