[Cu-64]-labelled trastuzumab: optimisation of labelling by DOTA and NODAGA conjugation and initial evaluation in mice

摘要

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 Cu-64-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. Cu-64-labelling of DOTA-trastuzumab was studied by varying the amount of DOTA-trastuzumab used, reaction temperature and time. Full Cu-64 incorporation could be achieved using a minimum of 10-mu g DOTA-trastuzumab, but the fastest labelling was obtained after 15min at room temperature using 25 mu g of DOTA-trastuzumab. In comparison, 80% incorporation was achieved for Cu-64-labelling of NODAGA-trastuzumab. Both [Cu-64]DOTA-trastuzumab and [Cu-64]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.