[⁶⁴Cu]‐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.

Towards integration of 64Cu-DOTA-trastuzumab PET-CT and MRI with mathematical modeling to predict response to neoadjuvant therapy in HER2 + breast cancer

“…Another consideration regarding the PET data, concerns the debate over which radiolabeled version of trastuzumab is most appropriate for clinical application, 64 Cu or 89 Zr labelled trastuzumab. The longer half-life of 89 Zr (78 h) makes it more appealing from an imaging perspective, but this does expose patients to roughly 2.5 × the radiation dose associated with (for example) a standard 18 F-FDG-PET scan 60,61 . While 64 Cu has a shorter half-life (12.7 h), it is still sufficiently long for imaging up to 48 h. Therefore, the copper isotope is attractive for PET imaging as well as patient safety 62,63 .…”

Towards integration of 64Cu-DOTA-Trasztusumab PET-CT and MRI with mathematical modeling to predict response to neoadjuvant therapy in HER2+ breast cancer

“…Another consideration regarding the PET data, concerns the debate over which radiolabeled version of trastuzumab is most appropriate for clinical application, 64 Cu or 89 Zr labelled trastuzumab. The longer half-life of 89 Zr (78 hours) makes it more appealing from an imaging perspective, but this does expose patients to roughly 2.5× the radiation dose associated with (for example) a standard 18 F-FDG-PET scan [56,57]. While 64 Cu has a shorter half-life (12.7 hours), it is still sufficiently long for imaging up to 48 hours.…”

Comparison between Fractionated Dose and Single Dose of Cu-64 Trastuzumab Therapy in the NCI-N87 Gastric Cancer Mouse Model

“…Cu-64-TRZ could be used for both diagnosis and therapy. Previously, an antigen-responsive molecular sensor study with TRZ [24], a comparison study of chelator [25], dosimetry studies of Cu-64-TRZ PET [13,26], and a study of I-131 TRZ using a HER2+ NCI N87 xenograft mouse model [27] were conducted. However, tumor microenvironments such as angiogenesis, fibrosis, and proliferation were not considered in those previous studies [13,24,25,26,27].…”