P-Glycoprotein (Pgp)-mediated drug efflux can yield a multidrug-resistance phenotype that is associated with poor response to cancer chemotherapy. Pervilleines B and C (PB and PC), two new tropane alkaloid aromatic esters obtained from a chloroform extract of the roots of Erythroxylum pervillei as the result of bioactivity-guided fractionation, were found to restore the vinblastine (VLB) sensitivity of cultured multidrug-resistant KB-V1 cells, with 50% inhibitory concentration values of 0.17 muM in each case. To explore the potential relevance of this response, KB-V1 cells were placed in hollow fibers and implanted into NCr nu/nu mice. Cell growth was not significantly inhibited when VLB or PB or PC were administered as single agents, but when used in combination with vinblastine inhibition of up to 77.7% was observed. Equimolar doses of verapamil were less effective. These data suggest that PB and PC are effective inhibitors of Pgp and should be further evaluated for clinical utility. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.