Brevianamide F , also known as cyclo-(L-Trp-L-Pro), belongs to a class of naturally occurring 2,5-diketopiperazines.

Ko 143 is a potent and selective breast cancer resistance protein multidrug transporter (BCRP) inhibitor (EC90 = 26 nM), Ko 143 displays > 200-fold selectivity over P-gp and MRP-1 transporters.

KS176 is a potent and selective inhibitor of the breast cancer resistance protein (BCRP) multidrug transporter (IC50 values are 0.59 and 1.39 μM in Pheo A and Hoechst 33342 assays respectively). Displays no inhibitory activity against P-gp or MRP1.

YHO-13177 is a potent and specific inhibitor of BCRP; potentiated the cytotoxicity of SN-38 in cancer cells and no effect on P-glycoprotein–mediated paclitaxel resistance in MDR1-transduced human leukemia K562 cells.