PP2A–mediated cell cycle arrest in response to OSU-2S. Representative plots (n = 7) (A) and quantification (B) of mass cytometric analysis of primary AML cells treated with Veh or OSU-2S (3 µM, 48 hours) showing a decrease in cell cycle and proliferation markers of phosphoretinoblastoma (pRb), cyclin B1, IdU, and Ki67 with OSU-2S treatment. (C) Mass cytometric analysis of primary AML cells (n = 5; AML 2, 8, 14, 15, and 21) treated with Veh or OSU-2S (3 μM, 48 hours) showed a significant increase in G0/G1 (P = .0265) and a significant decrease in S phase (P = .0339) with OSU-2S. No significant changes in G2/M were observed. pRb, IdU, and cyclin B1 were used to gate the cell cycle phases.41 (D) OSU-2S (5 μM, 48 hours) decreased cyclin B1, pRb, and Ki67 levels in HL-60 cells, as detected by mass cytometry. (E) Percentage of cells in the G0/G1, S, and G2M phases of the cell cycle in HL-60 cells (n = 3) treated with Veh or OSU-2S (5 μM, 16 hours), with or without pretreatment (2 hours) with 5 nM okadaic acid (OA), as detected by propidium iodide staining and flow cytometry. OSU-2S significantly accumulated cells in the G0-G1 phase (P = .0017) and decreased the proportion of cells in the S phase (P = .0003), which was rescued with OA (P = .0347). (F) Analysis of proliferation vs differentiation markers (Ki67 vs CD14 and CD15) show that cells induced to differentiate by OSU-2S are negative for Ki67. (G) OSU-2S–mediated induction of maturation markers in cells in the G0/G1 phase but not in the S phase. *P < .05; **P < .01; ***P < .001.