-labelled trastuzumab: Optimisation of labelling by DOTA and NODAGA conjugation and initial evaluation in mice

Abstract

The human epidermal growth factor receptor-2 (HER2) is overexpressed in 20-30% of all breast cancer cases, leading to increased cell proliferation, growth and migration. The monoclonal antibody, trastuzumab, binds to HER2 and is used for treatment of HER2-positive breast cancer. Trastuzumab has previously been labelled with copper-64 by conjugation of a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator. The aim of this study was to optimise the 64Cu-labelling of DOTA-trastuzumab and as the first to produce and compare with its 1,4,7-triazacyclononane, 1-glutaric acid-5,7 acetic acid (NODAGA) analogue in a preliminary HER2 tumour mouse model. The chelators were conjugated to trastuzumab using the activated esters DOTA mono-N-hydroxysuccinimide (NHS) and NODAGA-NHS. 64Cu-labelling of DOTA-trastuzumab was studied by varying the amount of DOTA-trastuzumab used, reaction temperature and time. Full 64Cu incorporation could be achieved using a minimum of 10-μg DOTA-trastuzumab, but the fastest labelling was obtained after 15 min at room temperature using 25 μg of DOTA-trastuzumab. In comparison, 80% incorporation was achieved for 64Cu-labelling of NODAGA-trastuzumab. Both [64Cu]DOTA-trastuzumab and [64Cu]NODAGA-trastuzumab were produced after purification with radiochemical purities of >97%. The tracers were injected into mice with HER2 expressing tumours. The mice were imaged by positron emission tomography and showed high tumour uptake of 3-9% ID/g for both tracers. The monoclonal antibody trastuzumab, with high affinity to HER2, was labelled with copper-64 using DOTA and NODAGA as chelator. 64Cu-labelling was optimised, and full incorporation was achieved after 15 min at room temperature using 25-μg DOTA-trastuzumab. Both [64Cu]DOTA-trastuzumab and [64Cu]NODAGA-trastuzumab were produced after purification with radiochemical purities of >97% and displayed tumour uptakes of 3-9% ID/g in mice with HER2 expressing tumours.