Synthesis and biological evaluation of a 99mTc-labelled sulfonamide conjugate for in vivo visualization of carbonic anhydrase IX expression in tumor hypoxia

Akurathi, Vamsidhar; Dubois, Ludwig; Lieuwes, Natasja G.; Chitneni, Satish K.; Cleynhens, Bernard J.; Vullo, Daniela; Supuran, Claudiu T.; Verbruggen, Alfons M.; Lambin, Philippe; Bormans, Guy M.

doi:10.1016/j.nucmedbio.2010.02.006

« Previous Next »Nuclear Medicine and Biology
Volume 37, Issue 5 , Pages 557-564, July 2010

Synthesis and biological evaluation of a ^99mTc-labelled sulfonamide conjugate for in vivo visualization of carbonic anhydrase IX expression in tumor hypoxia

Vamsidhar Akurathi
- Laboratory for Radiopharmacy, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Ludwig Dubois
- Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, University of Maastricht, 6200 Maastricht, The Netherland
Natasja G. Lieuwes
- Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, University of Maastricht, 6200 Maastricht, The Netherland
Satish K. Chitneni
- Department of Radiology, Duke University Medical Centre, Durham, NC 27710, USA
Bernard J. Cleynhens
- Laboratory for Radiopharmacy, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Daniela Vullo
- Universita degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, 50019 Sesto Fiorentino, Florence, Italy
Claudiu T. Supuran
- Universita degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, 50019 Sesto Fiorentino, Florence, Italy
Alfons M. Verbruggen
- Laboratory for Radiopharmacy, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Philippe Lambin
- Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, University of Maastricht, 6200 Maastricht, The Netherland
Guy M. Bormans
- Laboratory for Radiopharmacy, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
- Corresponding author. Post box 821, O&N2, Herestraat 49, BE-3000 Leuven, Belgium. Tel.: +32 0 16 330447; fax: +32 0 16 330449.

Received 26 October 2009; received in revised form 23 February 2010; accepted 28 February 2010. published online 26 April 2010.

Abstract

Introduction

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 ^99mTc(I)-tricarbonyl moiety resulting in [^99mTc(CO)₃ (L)] (L=N-(pyridin-2-yl-methyl)-N[2-(4-sulfamoylphenyl)-ethyl]aminoethyl acetate) complex, [^99mTc]-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 [^99mTc]-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 CO₂ hydration activity and efficacy studies were performed in HT 29 cell lines expressing CA IX under normoxia or hypoxia. Biodistribution studies of [^99mTc]-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 [^99mTc]-5 of 0.1% ID/g at 30 min post injection.

Conclusion

[^99mTc]-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.

Keywords: Carbonic anhydrase IX, Sulfonamides, Technetium-99m tricarbonyls, Tumor hypoxia