Synthesis and biological evaluation of a 99mTc-labelled sulfonamide conjugate for in vivo visualization of carbonic anhydrase IX expression in tumor hypoxia.
BACKGROUND
Carbonic anhydrase (CA) IX is a transmembrane protein overexpressed in many frequently occurring tumors associated with tumor hypoxia. Sulfonamides and their bioisosteres are known to inhibit CA IX activity. In this study, 4-(2-aminoethyl)benzenesulfonamide was conjugated to a tridentate ligand, N-2-picolyl-N-acetic acid and labeled with a (99m)Tc(I)-tricarbonyl moiety resulting in [(99m)Tc(CO)(3) (L)] (L=N-(pyridin-2-yl-methyl)-N[2-(4-sulfamoylphenyl)-ethyl]aminoethyl acetate) complex, [(99m)Tc]-5. Similarly the corresponding rhenium congener (Re-4) was synthesized. The in vitro CA IX affinity and inhibitory activity of Re-4 were determined and [(99m)Tc]-5 was evaluated as a tracer for in vivo visualisation of CA IX expression.


METHODS
Evaluation of the in vitro affinity (inhibition constant, K(i)) of Re-4 for CA isozymes I, II, IX and XII was carried out by assaying the CA catalyzed CO(2) hydration activity and efficacy studies were performed in HT 29 cell lines expressing CA IX under normoxia or hypoxia. Biodistribution studies of [(99m)Tc]-5 were performed in xenograft mice bearing CA IX expressing tumors.


RESULTS
The in vitro affinity of Re-4 for CA IX was 58 nM and CA IX induced acidification of extracellular medium was efficiently reduced (P<.05) in the presence of 1 mM Re-4. Biodistribution studies indicated a maximal tumor uptake of [(99m)Tc]-5 of 0.1% ID/g at 30 min post injection.


CONCLUSIONS
[(99m)Tc]-5 and its rhenium congener were synthesized and characterized. In vitro studies showed that the rhenium compound has a high affinity for CA IX and effectively inhibits CA IX activity. In vivo studies revealed a limited tracer accumulation in a CA IX expressing tumor but with increasing tumor-to-blood activity ratios as a function of time.
Akurathi
Vamsidhar
V
Laboratory for Radiopharmacy, Katholieke Universiteit Leuven, 3000 Leuven, Belgium.
Dubois
Ludwig
L
Lieuwes
Natasja G
NG
Chitneni
Satish K
SK
Cleynhens
Bernard J
BJ
Vullo
Daniela
D
Supuran
Claudiu T
CT
Verbruggen
Alfons M
AM
Lambin
Philippe
P
Bormans
Guy M
GM
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D015609:Organotechnetium Compounds / Q000737:chemistry*; D013449:Sulfonamides / Q000138:chemical synthesis* / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology
D000951:Antigens, Neoplasm; D015609:Organotechnetium Compounds; D013449:Sulfonamides; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases