Synthesis of 99mTc-HYNIC-interleukin-12, a new specific radiopharmaceutical for imaging T lymphocytes.
OBJECTIVE
Few radiopharmaceuticals have been described for the study of lymphocyte trafficking despite its high clinical relevance. The main difficulty resides in the identification of a suitable highly specific probe to target these cells. Interleukin-12 (IL12) is a heterodimeric cytokine which plays a key role in the development of Th(1) lymphocytes. The aims of the present study were to label IL12 with (99m)Tc, to evaluate its ability to bind to activated T lymphocytes in vitro and to study its biodistribution in normal mice and mice affected by autoimmune colitis.


METHODS
IL12 was derivatised with HYNIC-NHS and labelled with( 99m)Tc. An in vitro binding assay was performed on KIT225 cells, an IL12 receptor-positive cell line. (99m)Tc-IL12 biodistribution in normal mice was studied. Targeting experiments were performed in Balb/c mice injected with KIT225 cells and in mice with chemically induced chronic colitis.


RESULTS
(99m)Tc-IL12 labelling efficiency ranged between 75% and 85%. Saturation binding analysis revealed a K (d) of 2.09 nM. Results of biodistribution studies showed a predominant hepatic route of excretion. A significant degree of uptake in the spleen and thymus was also observed. In mice injected with KIT225 cells, (99m)Tc-IL12-specific uptake in these cells increased over time. (99m)Tc-IL12 also accumulated significantly in bowel of mice affected by TNBS-induced colitis showing T lymphocyte infiltration at histology, while accumulation in colon from control animals was negligible.


CONCLUSIONS
We conclude that this radiolabelled cytokine is a suitable candidate for specific in vivo imaging of T lymphocytes: a step forward in molecular imaging of immune-mediated processes.
Annovazzi
Alessio
A
Nuclear Medicine, Ospedale S. Andrea, 2nd Faculty of Medicine La Sapienza, Via di Grottarossa 1035, 00189 Roma, Italy.
D'Alessandria
Calogero
C
Bonanno
Elena
E
Mather
Stephen J
SJ
Cornelissen
Bart
B
van de Wiele
Christophe
C
Dierckx
Rudi A
RA
Mattei
Maurizio
M
Palmieri
Graziana
G
Scopinaro
Francesco
F
Signore
Alberto
A
D000818:Animals; D002460:Cell Line; D003092:Colitis / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D005240:Feasibility Studies; D018664:Interleukin-12; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D009928:Organ Specificity; D015609:Organotechnetium Compounds; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D013601:T-Lymphocytes / Q000737:chemistry / Q000000981:diagnostic imaging* / Q000378:metabolism*; D014018:Tissue Distribution
C513398:99mTc-HYNIC-interleukin-12; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D018664:Interleukin-12