In this application note, we demonstrate a MALDI MS cellular drug uptake and inhibition assay [1]. It was conducted in HEK293 cells overexpressing the transport protein OATP2B1.

Estrone-3-Sulfate (E3S) is a substrate for this transporter and its uptake was investigated in a pilot screen with 294 drugs with potential OATP2B1 uptake inhibiting properties. The use of the rapifleX mass spectrometer combined with MPP software led to a measurement time of ~5 min per 384 well target plate enabling MALDI MS-based screening and determination of precise IC50 values in concentration-response experiments.