Flow cytometric analysis of low-grade multidrug resistance using fluo-e : a comparison with rhodamine-123

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Six cell lines including drug-sensitive K562/parent cells, multidrug-resistant(MDR) K562/VCR, K562/ADR and K562/tetrahydropyranyl(THP)-ADR cells, methotrexate-resistant K562/MTX and revertant K562/ADR-R cell lines were used in this study : Although P-glycoprotein(P-gp)was overexpressed only in K562/VCR and K562/ADR cells, the RT-PCR method revealed distinct expression of MDR1mRNA even in the K562/parent cells. Intracellular accumulation of Fluo-3 and rhodamine-123 (Rh-123) was measured by incubation of cells with 4 muM Fluo-3 or 1muM Rh-123 for 20 min. by using a flow cytometer. Verapamil(Ver, 20 muM) or cepharanthine (biscoclaurine alkaloid, CP, 10muM) was added just before the addition of the fluorescent agents, Efflux patterns were also studied 30 and 60 min. after incubation with or without Ver ad CP.Increased intracellular accumulation and delayd efflux pattern of Fluo-3 by Ver and CP were shown in MDR K562/VCR and K562/ADR cells, and most interestingly, similar increase of uptake and delayd efflux pattern of Fluo-3 by Ver and CP butin a lower grade, were also demonstrated in P-gp-non-expressed K562/parent, K562/MTX and K562/THP cells. Accumulation of Rh-123 waas not influenced by Ver and CP.Thirteen of 31 clinical leukemic cell samples expressing MDR1mRNA, but not P-gp demonstrated enhancement of intracellular accumulation of Fluo-3 by Ver and Cp, indicating that flow cytometric functional analysis using Fluo-3 with Ver and CP may be usefl for more sensitive functional assay of low-grade multidrug resistance.