Comparison of iodotyrosines and methionine uptake in a rat glioma model.
This study compares brain tumor imaging with 3-[123I]iodo-alpha-methyl-L-tyrosine (IMT) and 3-[123I/125I]iodo-O-methyl-alpha-methyl-L-tyrosine (OMIMT) to that with [methyl-3H]-L-methionine (Met) in a rat glioma model by double-tracer autoradiography.


METHODS
Cells of the glioma clone F-98 were implanted stereotactically into the right basal ganglia of 22 Fischer 344 rats. After 8 days of tumor growth, the animals simultaneously were injected with a mixture of either 123I-IMT and 3H-Met (n=5), 123I-OMIMT and 3H-Met (n=8) or 123I-IMT and 125I-OMIMT (n=9). The animals were killed 15 min after the tracer injection and cryosections of the tumor-bearing brain area were exposed to phosphor-imaging plates both immediately and after the decay of 123I. Tumor-to-brain ratios (T/B) and intratumoral distribution of the different tracers and of the cresyl violet staining of the tissue were compared.


RESULTS
There was a significant correlation of the T/B ratios between all tracers (IMT versus Met: r=0.97, n=5, p < 0.01; OMIMT versus Met: r=0.94, n=8, p < 0.001; OMIMT versus IMT: r=0.95, n=9, p < 0.001). Intratumoral tracer distribution was similar for all tracers and the extent of tumor labeling was identical to that of the histological tumor extent. Mean values of the T/B ratios, however, were lower for IMT (2.81+/-0.78, n=14, mean+/-s.d., p < 0.01 compared with Met) and for OMIMT (2.03+/-0.57, n=17, p < 0.01 compared with Met) than for Met (3.86+/-1.12, n=13).


CONCLUSIONS
This study confirms that tumor imaging with IMT is similar to that of Met but T/B ratios of IMT are lower. OMIMT intratumoral tracer distribution and tumor size are similar to Met and IMT, but the T/B contrast is rather low and makes this amino acid less suitable for clinical application.
Langen
K J
KJ
Institute of Medicine, Research Center Jülich, Germany.
Clauss
R P
RP
Holschbach
M
M
Mühlensiepen
H
H
Kiwit
J C
JC
Zilles
K
K
Coenen
H H
HH
Müller-Gärtner
H W
HW
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D001932:Brain Neoplasms / Q000000981:diagnostic imaging*; D005910:Glioma / Q000000981:diagnostic imaging*; D007457:Iodine Radioisotopes; D008297:Male; D008715:Methionine / Q000493:pharmacokinetics; D008781:Methyltyrosines / Q000493:pharmacokinetics; D009368:Neoplasm Transplantation; D011877:Radionuclide Imaging; D051381:Rats; D011916:Rats, Inbred F344; D014316:Tritium
C090322:3-iodo-O-methyl-alpha-methyltyrosine; D007457:Iodine Radioisotopes; D008781:Methyltyrosines; D014316:Tritium; D008715:Methionine