Inhibition of BCRP-mediated drug efflux by fumitremorgin-type indolyl diketopiperazines.

A library of 42 diastereoisomeric mixtures of fumitremorgin-type indolyl diketopiperazines, prepared by parallel solid-phase synthesis, was screened for Breast Cancer Resistance Protein inhibitory activity and compared with GF120918. Demethoxy-fumitremorgin C was synthesized by solid-phase techniques and tested as well. Structure-activity relationship studies have identified several potent analogues, both in assays using the T6400 mouse and the T8 human cell line, whereas low cytotoxicity was seen at effective concentrations.