Efficient inhibitor of P-glycoprotein (Pgp, MDR-1) function through direct interactions. By inhibiting MDR-1, active compounds remain in the cytoplasm longer and allowing them to be more effective within the cell. Reversing agent for the treatment of multidrug resistance (MDR) in Pgp-overexpressing tumors. Potentiates the cytotoxicity of established P-gp substrates such as colchicine, vinblastine and paclitaxel. Antiproliferative and cytotoxic compound. Potent antifouling compound.