Compositions and methods are disclosed for improving the effectiveness of a chemotherapeutic regimen to eradicate multidrug-resistant transformed cells from the body of a mammal, preferably from the body of a human. The present disclosure capitalizes on the discovery of a novel multidrug-resistance associated protein (MRP), herein designated MRP-β. The disclosed compositions include MRP-β nucleic acids, including probes and antisense oligonucleotides, MRP-β polypeptides and antibodies, MRP-β expressing host cells, and non-human mammals transgenic or nullizygous for MRP-β. The disclosed methods include methods for attenuating aberrant MRP-β gene expression, protein production and/or protein function. In addition, methods are disclosed for identifying and using a modulator, such as an inhibitor, of MRP-β. Preferably, the modulator is a small molecule.
