Background Trastuzumab (TRZ) (Herceptin) is a humanised monoclonal antibody IgG1 that acts against human epidermal growth factor receptor 2 (HER2). It is indicated in the treatment of early and metastatic breast cancer and metastatic gastric cancer.

Purpose To evaluate the biological activity (BA) that remains in Herceptin after single-use vials have been opened in a long-term study. We also evaluated the remaining activity when TRZ was exposed to different stress conditions.

Material and methods An indirect non-competitive ELISA was developed for this purpose and validated to test the stability of BA of TRZ. ELISA plates were sensitised with recombinant human HER2. Calibration function was between 100.0 and 500.0 ng/mL; detection and quantification limits were 31.8 and 100.0 ng/mL; precision – as intraday and interday reproducibility (%RSD – was <10% and accuracy (% recovery) >95%. Stress study at 100 ng/mL included basic (NaOH 0.1M), acidic (HCl 0.1M), oxidative (H₂O₂ 10%) and ionic-strength (NaCl 1M) conditions (33% v/v); temperature 50°C and 70°C and light exposure. Surplus samples of Herceptin were stored at 4°C, −20°C and −80°C in the dark. The BA was tested up to 15 days.

Results The BA of Herceptin decreased by 25%, 30% and 47% the initial activity 24 h after opening when vials were stored at 4°C, −20°C and −80°C respectively. The decrease was 50–60% after 2 days for the three storage conditions and it was maintained along the study (up to 15 days). Residual BA remained in all samples submitted to the stress except in samples heated at 70°C. There was no cross reaction with similar IgG1.

Conclusion Herceptin lost a significant percentage of the BA when tested by ELISA after 24 h of storage both refrigerated (4°C) and frozen (−20°C and −80°C). Nevertheless, these results will be further investigated by flow cytometry.

References and/or acknowledgements Financial support: PI10/00201 (MICINN, Government of Spain).

No conflict of interest.