Development and validation of an antibody-drug conjugate bioassay

Antibody-drug conjugates (ADCs) are a class of drugs used in the treatment of different cancers. Unlike chemotherapy, ADCs are designed to only target and kill tumour cells. Several tests are requested by the regulatory authorities in order to prove the quality, safety and efficacy of ADCs. Among these tests, a bioassay must be developed to demonstrate the cytotoxic effect of ADCs on target cells (specific cytotoxicity) as well as on cells that do not express the antigen (non-specific cytotoxicity).

In this context, Quality Assistance has developed a cytotoxicity assay using trastuzumab emtansine (T-DM1) as a model compound. T-DM1 is an ADC that combines the humanised trastuzumab antibody (anti-HER-2) and the potent anti-microtubule agent DM1 (derivative of maytansine) using a highly stable linker. This ADC is used as a treatment for patients diagnosed with a HER-2 positive breast cancer.

This study demonstrates the successful development and validation of a cytotoxicity bioassay using trastuzumab emtansine as a model antibody-drug conjugate. It also highlights the importance of the revelator agent choice. Agents measuring the metabolic activity of the cells are not always the best choice depending of the cell culture conditions. It is therefore more appropriate to use agents that directly measure the cytotoxicity based on exclusion dyes, DNA intercalant agents or change of the mitochondria membrane potential.

The method was finally validated according to USP <1033> guideline in terms of specificity, linearity, precision (repeatability and intermediate precision) and relative accuracy. Moreover, the method was demonstrated to be stability-indicating and therefore allows for the detection of degraded samples