Biricodar (VX-710) is a modulator of P-glycoprotein and MRP-1; shows effective chemosensitizing activity in multidrug resistant cells. In Vitro: Biricodar shows activity against both P-glycoprotein (Pgp) and MRP-1 and also has activity in increasing drug uptake and retention and reversing drug resistance mediated by wild-type BCRP (BCRPR⁴⁸²). In 8226/Dox6 cells (Pgp), biricodar increases mitoxantrone and daunorubicin uptake by 55 and 100%, respectively, increases their retention by 100 and 60%, respectively, and increases their cytotoxicity 3.1- and 6.9-fold, respectively. Biricodar also increases the uptake, retention and cytotoxicity in HL60/Adr (MRP-1) and 8226/MR20 cells (BCRP(R482)), but has little effect in MCF7 AdVP3000 cells (BCRP(R482T))^[1]. VX-710 is a non-macrocyclic pipecolinate derivative which binds the FK506 receptor protein. VX-710 has been shown to restore sensitivity in a range of multidrug-resistant cells, including myeloma, melanoma, carcinoma and leukaemia^[2]. Biricodar effectively inhibits photoaffinity labeling of P-glycoprotein by [³H]azidopine or [¹²⁵I]iodoaryl azido-prazosin with EC₅₀ values of 0.75 and 0.55 μM^[3].