Contrasting features of MDR phenotype in leukemias by using two fluorochromes: implications for clinical practice.

The expression and activity of P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP1) were analyzed in 178 leukemia samples. Rhodamine-123 (Rho-123) and DiOC(2) were used as substrate to evaluate efflux pump activity. Chronic myeloid leukemia (CML) exhibited a higher percentage of positivity using Rho-123 than DiOC(2) (p=0.000) as compared to other types of leukemia. Moreover, Rho-123 was able to detected Pgp positive cells in a higher proportion of samples than DiOC(2) samples (p=0.004). Similarly, MRP1 positive cells were best detected by Rho-123 as opposed to DiOC(2) (p=0.003). The co-functionality of Rho-123 and DiOC(2) was observed in 26 out of 105 (24.8%) leukemic samples. Co-expression between Pgp and MRP1 was detected in 30 out of 56 (53.6%) samples. As a whole, when the same samples were analyzed, Rho-123 was able to detect Pgp positive cells in a higher proportion of samples than DiOC(2) (p=0.000). Similarly, MRP1 positive cells were best detected by Rho-123 as opposed to DiOC(2) (p=0.007). Our results support the idea that Rho-123 is the substrate of choice for leukemic cells.