%0 Journal Article
%T Straightforward thiol-mediated protein labelling with DTPA: Synthesis of a highly active 111In-annexin A5-DTPA tracer
%A Harald Kratz
%A Akvile Haeckel
%A Roger Michel
%A Lena Sch£¿nzart
%A Uli Hanisch
%A Bernd Hamm
%A Eyk Schellenberger
%J EJNMMI Research
%D 2012
%I Springer
%R 10.1186/2191-219x-2-17
%X Here, we report an optimised two-step synthesis of annexin A5-diethylene triamine pentaacetic acid (DTPA) (anxA5-DTPA) for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging with a single purification step. The use of a recombinant annexin A5 (cys-anxA5) with a single thiol group allowed regionally specific coupling, without affecting the binding domain of cys-anxA5.The metal complexing capacity of anxA5-DTPA was investigated by labelling with 111In3+ and Eu3+. Binding of modified anxA5-DTPA to apoptotic cells was tested in competition experiments with a fluorescent anxA5 derivative (anxA5-FITC) using flow cytometry and compared with that of wildtype anxA5 or non-binding anxA5-DTPA (M1234-anxA5-DTPA). The binding affinity to apoptotic cells of the anxA5-DTPA conjugate does not differ from that of wildtype anxA5.This two-step synthesis of annexin A5-DTPA resulted in biologically active anxA5-DTPA, which can be labelled with radionuclides for use in SPECT and PET imaging.Targeting of externalised phosphatidylserines (PS) using annexin A5 (anxA5) is relatively unspecific because it will detect not only apoptotic cells but also, for instance, necrotic cells, ageing cells, hypoxic cardiomyocytes [1], tumour blood vessels and intravascular thrombi [2]. Nevertheless, imaging using radiolabeled anxA5 can be used very sensitively and flexibly as a damage marker in a variety of clinical applications, for instance for monitoring the response to chemotherapy [3-6], where it is not important to differentiate apoptotic from necrotic cells. Moreover, it is possible to visualise purely apoptotic processes [7] with high sensitivity.Modifications are necessary before annexin can be used as a molecular probe. This is frequently done with amine-reactive linkers (usually N-hydroxysuccinimide ester), which randomly react with one or more of the 21 amino groups localised at lysines in anxA5. Since it has been shown that this modification redu
%K Annexin A5
%K Apoptosis imaging
%K PET
%K SPECT
%K DTPA
%K Indium
%U http://www.ejnmmires.com/content/2/1/17