Fluorescent probes for rapid screening of potential drug-drug interactions at the CYP3A4 level.

Steroid derivatives bearing fluorescent groups such as anthracene, dansyl, deazaflavin, and pyrene attached to C6 were synthesized. These compounds are unique inhibitors of cytochrome P450 3A4 (CYP3A4) and display similar IC(50) values in the microM range for the CYP3A4 substrates midazolam, testosterone, and nifedipine. On binding to CYP3A4, the fluorescence of the dansyl, deazaflavin, and pyrene probes is quenched by photophysical interaction of the fluorophore with the heme. The addition of drug candidates with binding constants in the nM-microM range causes displacement of the probes from the active site, and hence leads to restoration of fluorescence. Accordingly, relative affinities of drug candidates to CYP3A4 can be easily and accurately determined by fluorescence measurements.