The combined administration of PPP and IFN-γ blocks malignant T-cell growth. (A-B) ST4 (○, •), PF382 (⋄, ♦) and Jurkat (□, ▪) T cells were cultured in complete medium with scalar doses of PPP in the absence (white symbols) or presence (black symbols) of IFN-γ. After 48 hours, cells were harvested and (A) stained with trypan blue and counted or (B) stained with PE-conjugated annexin-V and analyzed by flow cytometry. (C) To verify that the doses of PPP used were effective in inhibiting IGF-1 signaling, ST4 (○, •), PF382 (⋄, ♦) and Jurkat (□, ▪) cells were cultured for 48 hours with PPP (from 0 to 5 μM) in serum-free medium with (black symbols) or without (white symbols) IGF-1 (100 ng/mL), then cells were harvested and counted. All the experiments were performed independently at least 3 times. (D) ST4, Jurkat, and PF382 T cells were preincubated with or without PPP (1 μM) for 6 hours before stimulation with or without IGF-1 for 15 minutes. Akt activation was evaluated by Western blot analysis of protein cell extracts with anti–phospho-Ser (473)-Akt Ab. Membranes were subsequently probed with an anti-Akt Ab. Phospho-Akt fold induction in cells treated with IGF-1 (▪) or IGF-1 + PPP (□), shown as means of fold induction ± SEM from 3 independent experiments, was quantified after normalization to Akt. (E) ST4, Jurkat, and PF382 T cells were treated with or without PPP (1 μM) for 6 hours and then stimulated with or without IFN-γ for 15 minutes. STAT1 activation was evaluated by Western blot analysis with anti–phospho-Tyr (701)-STAT1 Ab. Phospho-STAT1 fold induction in cells treated with IFN-γ (▪) or IFN-γ + PPP (□), shown as means of fold induction ± SEM from 3 experiments, was measured after normalization to total STAT1.