Figure 2. Effects of gliptins on DPPIV activity and growth/survival in CML cells.

(A) DPPIV activity was measured in lysates of KU812 GFP⁺ cells, KU812 CD26⁺ cells, highly purified CD34⁺/CD38⁻/CD26⁺ CML SCs, and CD34⁺/CD38⁻/CD26⁻ (normal) BM SCs (left subpanel). DPPIV activity was expressed as relative luminescence units (RLUs) per 25 × 10³ cells. Results represent the mean ± SD of triplicates. In the middle and right subpanels of (A), the effects of sitagliptin and vildagliptin on DPPIV enzyme activity in CML-T1 cells were tested. Cell lysates of CML-T1 were preincubated with various concentrations of sitagliptin or vildagliptin (1–1,000 nmol/L) at 37°C for 30 minutes and then DPPIV/CD26 activity was measured. Results (in RLUs) represent the mean ± SD of three experiments. (B) KU812 GFP⁺ cells (negative control; left panel), KU812 CD26⁺ cells (middle panel), and CML-T1 cells (right panel) were incubated in control medium (Co) or in various concentrations of vildagliptin (10–10,000 nmol/L) at 37°C for 48 hours and then ³H-thymidine uptake was measured. Results are expressed as a percentage of control and represent the mean ± SD from three experiments. (C) KU812 GFP⁺ cells (left panel), KU812 CD26⁺ cells (middle panel), and CML-T1 cells (right panel) were incubated in control medium (Co) or in various concentrations of vildagliptin (10–10,000 nmol/L) at 37°C for 48 hours. After incubation, apoptosis was determined by flow cytometry using an antibody against active caspase-3. Results are expressed as the percentage of active caspase-3-positive cells and represent the mean ± SD from three independent experiments. The dimethyl sulfoxide (DMSO) control is also shown. (D) KU812 GFP⁺ (left panels), KU812 CD26⁺ (middle panels), and CML-T1 cells (right panels) were incubated in control medium (0) or in various concentrations of nilotinib (2–12 nmol/L, upper panels) or imatinib (50–225 nmol/L, lower panels) alone or in combination with vildagliptin (10 μmol/L) at 37°C for 48 hours and then ³H-thymidine uptake was measured. Results are expressed as a percentage of control and represent the mean ± SD from three independent experiments (*p < 0.05).