Tumor response after [(90)Y-DOTA(0),Tyr(3)]octreotide radionuclide therapy in a transplantable rat tumor model is dependent on tumor size.
A promising application of radiolabeled somatostatin analogs is peptide receptor-targeted radionuclide therapy of somatostatin receptor-expressing tumors. A suitable radionuclide is (90)Y, which emits high-energy beta-particles with a pathlength of several millimeters in tissue, making it especially promising for treatment of large tumors.


METHODS
We investigated the radiotherapeutic effect of different activities (111 and 370 MBq) of [(90)Y-1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA)(0),Tyr(3)]octreotide in Lewis rats bearing somatostatin receptor-positive rat pancreatic CA20948 tumors of different size (0.08-15 cm(2)) in their flank.


RESULTS
Dose-dependent radiotherapeutic effects of (90)Y-labeled octreotide in this rat tumor model were found. Tumor control (100% complete response) was found in animals bearing tumors of 3-9 cm(2) (mean, 7.8 cm(2)) after intravenous injection of the highest activity (370 MBq [(90)Y-DOTA(0),Tyr(3)]octreotide). In rats bearing tumors of < or =1 cm(2) or > or =14 cm(2), the effects were less pronounced (50% and 0% complete response, respectively). In tumors of < or =1 cm(2) the (90)Y radiation energy will not be absorbed completely in the tumor, whereas in tumors of > or =14 cm(2) the increased number of clonogenic and probably hypoxic tumor cells may explain the failure to reach a cure.


CONCLUSIONS
This study shows the ability of [(90)Y-DOTA(0),Tyr(3)]octreotide to control tumor growth, especially in medium-sized tumors. The effect of radionuclide therapy appeared to be dependent on tumor size at the onset of therapy.
de Jong
M
M
Department of Nuclear Medicine, Erasmus University Rotterdam, Rotterdam, The Netherlands.
Breeman
W A
WA
Bernard
B F
BF
Bakker
W H
WH
Visser
T J
TJ
Kooij
P P
PP
van Gameren
A
A
Krenning
E P
EP
D000818:Animals; D004307:Dose-Response Relationship, Radiation; D008297:Male; D009368:Neoplasm Transplantation; D015282:Octreotide / Q000031:analogs & derivatives* / Q000627:therapeutic use*; D010190:Pancreatic Neoplasms / Q000401:mortality / Q000532:radiotherapy*; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D051381:Rats; D011917:Rats, Inbred Lew; D017481:Receptors, Somatostatin / Q000528:radiation effects; D015021:Yttrium Radioisotopes / Q000627:therapeutic use*
D019275:Radiopharmaceuticals; D017481:Receptors, Somatostatin; D015021:Yttrium Radioisotopes; C121107:octreotide, DOTA-Tyr(3)-; D015282:Octreotide