The use of a stably expressed FRET biosensor for determining the potency of cancer drugs.

Many cancer drugs are intended to kill cancer cells by inducing apoptosis. However, the potency assays used for measuring the bioactivity of these products are generally cell viability assays which do not distinguish between cell death and growth inhibition. Here we describe a cell-based fluorescence resonance energy transfer (FRET) biosensor designed to measure the bioactivity of apoptosis inducing cancer drugs. The biosensor contains cyan fluorescent protein (CFP) linked via caspase 3 and caspase 8 specific cleavage recognition sequences to yellow fluorescent protein (YFP). Upon caspase activation, as in the case of apoptosis induction, the linker is cleaved abolishing the cellular FRET signal. This assay closely reflects the mechanism of action of cancer drugs, in killing cancer cells and therefore can function as a potency test for different cancer drugs. We rigorously demonstrate this through characterization of a class of proteins targeting the death receptors. The one-step assay appears to be superior to other apoptosis-based assays because of its simplicity, convenience, and robustness.