Characterization of a radiolabeled small molecule targeting leukocyte function-associated antigen-1 expression in lymphoma and leukemia.
OBJECTIVE
Leukocyte function-associated antigen-1 (LFA-1) is constitutively expressed on leukocytes, including overexpression on lymphomas and leukemias. We have developed a derivative of BIRT 377, an allosteric inhibitor of LFA-1, which may be chemically tagged without affecting binding. In this study, we modified this derivative, (R)-1-(4-aminobutyl)-5-(4-bromobenzyl)-3-(3,5-dichlorophenyl)-5-methylimidazolidine- 2,4-dione (butylamino-NorBIRT), and demonstrated its potential as a noninvasive imaging agent.


METHODS
Specific binding of fluorescein-labeled butylamino-NorBIRT to both human and murine cells was demonstrated using equilibrium binding and dissociation techniques. A radiometal, lutetium-177 (Lu-177), was incorporated into the butylamino-NorBIRT through 1,4,7,10-tetraazacyclododecane-N,N',N",N'''- tetraacetic acid (DOTA) as a chelator.


RESULTS
Equilibrium-binding experiments demonstrated that fluorescein- labeled butylamino-NorBIRT specifically binds human and murine LFA-1 with affinity constants of 135 and 186 nM, respectively. Dissociation kinetic experiments demonstrated an off-rate of 0.168/second(1) on murine cells, consistent with the observed affinity constant. Lutetium-177 was used for labeling, with > or =99.99% radiochemical purity and incorporation yield. This radiolabeled derivative exhibited high stability in fetal bovine serum (FBS) at 37 degrees C over 72 hours. (177)Lu-DOTA-butylamino-NorBIRT showed a binding affinity of 235 nM to human LFA-1 for equilibrium binding and competitive binding experiments.


CONCLUSIONS
The radiolabeled DOTA-butylamino-NorBIRT may have potential as a noninvasive imaging or therapeutic agent in both human and mouse models.
Poria
Rahul B
RB
Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
Norenberg
Jeffrey P
JP
Anderson
Tamara L
TL
Erion
Jack
J
Wagner
Carston R
CR
Arterburn
Jeffrey B
JB
Larson
Richard S
RS
D000818:Animals; D001667:Binding, Competitive; D018922:HL-60 Cells; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006827:Hydantoins / Q000737:chemistry* / Q000378:metabolism*; D048289:Imidazolidines / Q000737:chemistry / Q000378:metabolism; D007553:Isotope Labeling / Q000379:methods; D007700:Kinetics; D007938:Leukemia / Q000000981:diagnostic imaging* / Q000378:metabolism; D008187:Lutetium / Q000737:chemistry* / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D008223:Lymphoma / Q000000981:diagnostic imaging* / Q000378:metabolism; D051379:Mice; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism; D011868:Radioisotopes / Q000737:chemistry* / Q000378:metabolism*; D011877:Radionuclide Imaging
C400461:BIRT 377; C518062:DOTA-1-(4-aminobutyl)-5-(4-bromobenzyl)-3-(3,5-dichlorophenyl)-5-methylimidazolidine-2,4-dione; D006573:Heterocyclic Compounds, 1-Ring; D006827:Hydantoins; D048289:Imidazolidines; D016169:Lymphocyte Function-Associated Antigen-1; D009942:Organometallic Compounds; D011868:Radioisotopes; D008187:Lutetium