Figure 6.

The co-culture with MSC induces changes in ABC transporters’ activity in B-ALL cells, and PKC inhibition with HKPS increases this effect. (A) Influence of the mesenchymal support on MDR1, MRP, and BCRP activity in leukemic cells. Co-cultures were treated with 250 nM of DEXA for 72 h, then both MSC and adherent B-ALL cells were incubated with specific inhibitors for each transporter. Comparatively, leukemic cells in suspension were treated with the chemotherapeutic agent in similar time and concentration conditions. The transporter’s activity was evaluated by flow cytometry, it is expressed as MAF (multidrug resistance activity factor), based on the MFI values in the presence of the respective inhibitor and the basal activity without inhibitor. Red histograms correspond to unstained cells, blue to the vehicle (1.25% DMSO) (basal activity), and green, violet, and orange to cells treated with the inhibitors (MK-571, Verapamil, and Novobiocin, respectively). (B) Effect of PKC inhibition on drug efflux by ABC transporters. MSC were pre-treated with HKPS (40 µM) or ENZA (20 µM) for 2 h, and co-cultures were established for additional 72 h in the presence of DEXA (250 nM). The transporter’s activity was determined by flow cytometry as indicated before. (C) Quantification of the ABC transporters activity in B-ALL cells after PKC inhibition in MSC. As control, the PS peptide (40 µM) was used since the hydrophobic HK sequence could interfere with the transporters activity. Data are expressed as mean ± SEM (p values: two-way ANOVA. * p < 0.05. ** p < 0.01) from two independent experiments; NT: non- treated.