Label-free assessment of complement-dependent cytotoxicity of therapeutic antibodies via a whole-cell MALDI mass spectrometry bioassay.

Potency assessment of monoclonal antibodies or corresponding biosimilars in cell-based assays is an essential prerequisite in biopharmaceutical research and development. However, cellular bioassays are still subject to limitations in sample throughput, speed, and often need costly reagents or labels as they are based on an indirect readout by luminescence or fluorescence. In contrast, whole-cell Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry (MS) has emerged as a direct, fast and label-free technology for functional drug screening being able to unravel the molecular complexity of cellular response to pharmaceutical reagents.

Glucuronidation of the soyabean isoflavones genistein and daidzein by human liver is related to levels of UGT1A1 and UGT1A9 activity and alters isoflavone response in the MCF-7 human breast cancer cell line.

The soyabean isoflavones genistein and daidzein, which may protect against some cancers, cardiovascular disease and bone mineral loss, undergo substantial Phase 2 metabolism, predominantly glucuronidation. We observed a correlation between rates of metabolism of marker substrates of specific UGTs and rates of glucuronidation of genistein and daidzein in vitro by a panel of human liver microsomes, demonstrating that UGT1A1 and UGT1A9, but not UGT1A4, make a major contribution to the metabolism of these isoflavones by human liver. These findings were substantiated by observations that recombinant human UGT1A1 and UGT1A9, but not UGT1A4, catalysed the production of the major glucuronides of both genistein and daidzein in vitro.