AHR and breast cancer: AFP464 exhibits differential in vitro cytotoxicity in breast cancer cell lines with inhibitory 50% (IC50) concentrations ranging from 0.01 to 30 μM. AFP464 plasma levels that can safely be reached in patients are ∼1 μM. In sensitive cells, AFP464 induces AhR-mediated cytochrome P450- (CYP-) dependent xenobiotic response and cell death.