ALTERED DRUG MEMBRANE-PERMEABILITY IN A MULTIDRUG-RESISTANT LEISHMANIA-TROPICA LINE

We selected a Leishmania tropica cell line resistant re, daunomycin (D NM) that presents a multidrug-resistant (MDR) phenotype characterized by overexpression of a P-glycoprotein of 150 kDa. The resistant line o verexpressed an MDR-like gene, called ltrmdr1, located in an extrachro mosomal circular DNA. DNM uptake experiments using laser flow cytometr y showed a significant reduction in drug accumulation in the resistant parasites. The initial stages of the interaction of DNM with membrane s from wild-type and DNM-resistant. parasites were defined by a rapid kinetic stopped-flow procedure which can be described by two kinetic c omponents. On the basis of a previous similar kinetic study with tumor cells, we ascribed the fast component to rapid interaction of DNM wit h membrane surface components and the slow component to passive diffus ion of the drug across the membranes. The results reported here indica te that entrance of DNM into wild-type parasites was facilitated in re spect to the resistant ones. We propose that resistance to DNM in L. t ropica is a multifactorial event involving at least two complementary mechanisms: an altered drug membrane permeability and the overexpressi on of a protein related to P-glycoprotein that regulates drug efflux. (C) 1998 Elsevier Science Inc.