Preparation and preclinical evaluation of 131I-trastuzumab for breast cancer

Trastuzumab that targets the human epidermal growth factor receptor type 2 (HER2) is known to benefit patients with HER2+ metastatic breast cancer. The objective was to explore the potential of I-131-trastuzumab for treatment of breast cancers. Radioiodination of trastuzumab was carried out by chloramine-T method, purified by using PD-10 column, and characterized by size exclusion high-performance liquid chromatography on a gel column. In vitro studies were carried out in HER2+ cells to determine the specificity of the radioimmunoconjugate. Uptake and retention of I-131-trastuzumab were determined by biodistribution studies in tumor-bearing non-obese diabetic/severe combined immunodeficiency and normal severe combined immunodeficiency mice. The radiochemical purity (RCP) of I-131-trastuzumab was 98 +/- 0.4% with retention time of 17minutes by high-performance liquid chromatography. In vitro stability studies exhibited RCP of more than 90% in serum at 37 degrees C after 120hours of radioiodination. In vitro cell binding with I-131-trastuzumab in HER2+ cells showed binding of 28% to 35% which was inhibited significantly, with unlabeled trastuzumab confirming its specificity. K-d value of I-131-trastuzumab was 0.5nM, while its immunoreactivity was more than 80%. Uptake of more than 12% and retention were observed in the tumors up to 120hours p.i. I-131-trastuzumab prepared in-house-exhibited RCP of more than 98%, excellent immunoreactivity, affinity to HER2+ cell lines and good tumor uptake thereby indicating its potential for further evaluation in HER2+ breast cancers.