In vitro activity: KS176 is a novel potent and highly selective/specific inhibitor of the breast cancer resistance protein (BCRP) multidrug transporter with IC50 values of 0.59 and 1.39 μM in Pheo A and Hoechst 33342 assays respectively. It displays no inhibitory activity against P-gp or MRP1. KS176 and its analogs share a noncompetitive-type interaction with pheophorbide A. Experiments with imatinib and pheophorbide A revealed a mixed-type interaction. This class of specific breast cancer resistance protein (BCRP) inhibitors showed no inhibition of the ATP binding cassette (ABC) transporters P-gp and MRP1. Some of these modulators inhibit BCRP with high potency; they are only slightly less potent than Ko143 and could serve as promising lead structures for the design of novel effective BCRP inhibitors. These inhibitors are structurally related to tariquidar (XR9576) and belong to a library of multidrug-resistance modulators

Kinase Assay: KS176 is a novel potent and highly selective/specific inhibitor of the breast cancer resistance protein (BCRP) multidrug transporter with IC50 values of 0.59 and 1.39 μM in Pheo A and Hoechst 33342 assays respectively.

Cell Assay: