Methylene blue reverts multidrug resistance: sensitivity of multidrug resistant cells to this dye and its photodynamic action

Photodynamic action has been advocated as an alternative treatment of tumor s but the most common used dyes, hematoporphyrin derivatives, are substrate for P-glycoprotein. This study investigated the MDR-reverting properties o f methylene blue (MB) and compared the sensitivity to its photodynamic acti on (PDA) in five cell lines that either express or do not express the MDR p henotype. MB was able to revert the MDR phenotype and there was no differen ce in sensitivity to MB-PDA between MDR and non-MDR cells, suggesting that MB has the advantage of being used simultaneously as a MDR reverser and a p hotodynamic agent. (C) 2000 Elsevier Science Ireland Ltd. All rights reserv ed.