Preclinical characterisation of 111In-DTPA-trastuzumab

Trastuzumab (Herceptin(R)) is a recombinant humanised IgG1 monoclonal antibody against the human epidermal growth factor receptor 2 (HER2), used for metastatic breast cancer treatment. Radiolabelled trastuzumab may have several future applications for diagnostic use. The aim of the present study was to develop clinical grade (111)Indium (In-111) radiolabelled trastuzumab, to evaluate the stability and immunoreactivity of the tracer and to perform a biodistribution study in human tumour-bearing mice. Trastuzumab was radiolabelled with In-111 using DTPA as a chelator. In-111-DTPA-trastuzumab ( labelling yield 92.3 +/- 2.3%, radiochemical purity 97.0 +/- 1.5%) is stable in PBS when stored at 4degreesC for more than 14 days. The immunoreactive fraction determined by cell-binding assays, using the HER2-overexpressing human ovarian SK-OV-3 tumour cell line, was 0.87 +/- 0.06. Biodistribution and tumour targeting were studied in HER2 receptor-positive and - negative tumour-bearing athymic mice. The HER2-positive tumour showed (9.77 +/- 1.14% injected dose per gram ( ID g(-1))) substantial uptake of the labelled antibody already after 5 h. The difference in uptake between HER2-positive versus - negative tumours was even more pronounced 3 days after injection (16.30 +/- 0.64% ID g(-1)), and was visualised by radioimmunoscintigraphy. Liver, spleen and kidney showed marked tracer uptake. In summary, trastuzumab can be efficiently radiolabelled with In-111 with high labelling yields and high stability. In-111-DTPA-trastuzumab selectively binds to the human HER2 receptor both in vitro and in vivo in animals. Therefore, In-111-DTPA-trastuzumab appears suitable for clinical use.