The present invention provides compounds for the regulation of P-
glycoprotein and
cytochrome P450 (e.g., CYP3A4 and CYP3A5 isoforms) enzymes, which a) significantly improve the
bioavailability of substrates of these enzymes, including anticancer drugs, b) overcome multidrug resistance in tumors, and c) reduce serious side effects while improving the delivery of P-
glycoprotein substrates to the brain. [Solution] Compounds of formula (I), as well as their prodrugs and pharmaceutically acceptable salts, are provided. Further disclosure relates to pharmaceutical compositions containing the compounds, methods of use, and methods for preparing them. TIFF2026086798000135.tif39128