Avidin–biotin system: a small library of cysteine biotinylated derivatives designed for the [99mTc(N)(PNP)]2+ metal fragment

Bolzati, Cristina; Caporale, Andrea; Agostini, Stefania; Carta, Davide; Cavazza-Ceccato, Mario; Refosco, Fiorenzo; Tisato, Francesco; Schievano, Elisabetta; Bandoli, Giuliano

doi:10.1016/j.nucmedbio.2007.04.006

« Previous Next »Nuclear Medicine and Biology
Volume 34, Issue 5 , Pages 511-522, July 2007

Avidin–biotin system: a small library of cysteine biotinylated derivatives designed for the [^99mTc(N)(PNP)]²⁺ metal fragment

Cristina Bolzati
- ICIS-CNR, Corso Stati Uniti, 4, 35127 Padova, Italy
- Corresponding author. Tel.: +39 049 8275352; fax: +39 049 8275366.
Andrea Caporale
- Department of Chemical Sciences, University of Padua, 35131 Padova, Italy
Stefania Agostini
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Davide Carta
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Mario Cavazza-Ceccato
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Fiorenzo Refosco
- ICIS-CNR, Corso Stati Uniti, 4, 35127 Padova, Italy
Francesco Tisato
- ICIS-CNR, Corso Stati Uniti, 4, 35127 Padova, Italy
Elisabetta Schievano
- Department of Chemical Sciences, University of Padua, 35131 Padova, Italy
Giuliano Bandoli
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy

Received 2 October 2006; received in revised form 5 April 2007; accepted 6 April 2007. published online 13 June 2007.

Abstract

Using the avidin–biotin system as model, we investigate here the effective application of [Tc(N)L(PNP)]^+/0 technology (L=N-functionalized cysteine [O⁻,S⁻]; PNP=aminodiphosphine) to the preparation of target-specific radiopharmaceuticals.

A series of ^99mTc-nitrido complexes containing functionalized biotin ligands was prepared and their biological profile was determined. To minimize the steric and the electronic influences of the Tc-carrying complex on the biotin–avidin receptor interaction, the following N-functionalized cysteine–biotin derivatives were synthesized: (1) Biot-CysOSH; (2) Biot-Abu-CysOSH; (3) Biot-Abz-CysOSH; (4) Biot-l-(Ac)Lys-CysOSH; (5) Biot-d-(Ac)Lys-CysOSH; (6) Biot-Glu-CysOSH.

The asymmetrical nitrido-Tc(V) ^99g/99mTc(N)(Biot-X-CysOS)(PNP3) (X=spacer) complexes, where PNP3 was N,N-bis-[(dimethoxypropyl)phosphinoethyl] methoxy-ethylamine, were obtained by simultaneous addition of PNP3 and the relevant biotinylated ligand to a solution containing a ^99mTc-nitrido precursor (yields >95%). In all cases, a mixture of syn- and anti isomers was observed. In vitro challenge experiments with glutathione and cysteine indicated that no transchelation reactions occurred. Assessment of the in vitro binding to avidin of the complexes revealed that only the complexes containing Biot-Abu-CysOS and Biot-Glu-CysOS ligand maintained a good affinity for the concentrator. Stability studies carried out in human and mouse plasma as well as in rat and mouse liver homogenate evidenced a rapid enzymatic degradation for the ^99mTc(N)(Biot-Abu-CysOS)(PNP3) complex, whereas the ^99mTc(N)(Biot-Glu-CysOS)(PNP3) one was stable in all conditions. Tissue biodistribution in normal Balb/C mice of the most stable candidate showed a rapid clearance both from the blood and the other tissues. The activity was eliminated both through the hepatobiliary system and the urinary tract.

Keywords: Avidin–biotin system, Cysteine biotinylated derivative, Technetium