Preparation and preclinical evaluation of 131 I-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 131 I-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 131 I-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 131 I-trastuzumab was 98 ± 0.4% with retention time of 17 minutes by high-performance liquid chromatography. In vitro stability studies exhibited RCP of more than 90% in serum at 37°C after 120 hours of radioiodination. In vitro cell binding with 131 I-trastuzumab in HER2+ cells showed binding of 28% to 35% which was inhibited significantly, with unlabeled trastuzumab confirming its specificity. Kd value of 131 I-trastuzumab was 0.5 nM, while its immunoreactivity was more than 80%. Uptake of more than 12% and retention were observed in the tumors up to 120 hours p.i. 131 I-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.