5-Aminolaevulinic acid-mediated photodynamic therapy in multidrug resistant leukemia cells

To verify if photodynamic therapy (PDT) could overcome multidrug resistance (MDR) when it it applied to eradicate minimal residual disease in patients with leukemia, we investigated the fluorescence kinetics of 5-aminolavulin ic acid (ALA)-induced protoporphyrin IX (PpIX) and the effect of subsequent photodynamic therapy on MDR leukemia cells, which express P-glycoprotein ( P-gp), as well as on their parent cells. Evaluation of PpIX accumulation by flow cytometry showed that PpIX accumulated at higher levels in mdr-1 gene -transduced MDR cells (NB4/MDR) and at lower levels in doxorubicin-induced MDR cells (NOMO-1/ADR) than in their parent cells. A P-gp inhibitor could n ot increase PpIX accumulation. Measurement of extracellular PpIX concentrat ion by fluorescence spectrometry showed that P-gp did not mediate the fluor escence kinetics of ALA-induced PpIX production. Assessment of ferrochelata se activity using high-performance liquid chromatography indicated that PpI X accumulation in drug-induced MDR cells was probably regulated by this enz yme. Assessment of phototoxicity of PDT using the 3-(4,5-dimethylthiazol-2- yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that PDT was effecti ve in NB4, NB4/MDR, NOMO-1 and NOMO-1/ADR cells, which accumulated high lev els of PpIX, but not effective in K562 and K562/ADR cell lines, which accum ulated relatively low levels of PpIX. These findings demonstrate that P-gp does not mediate the ALA-fluorescence kinetics. and multidrug resistant leu kemia cells do not have cross-resistance to ALA-PDT. (C) 2001 Elsevier Scie nce BV All rights reserved.