Polycationic peptide R(7)-G-Aβ(25-35) selectively induces cell death in leukemia Jurkat T cells through speedy mitochondrial depolarization, and CASPASE-3 -independent mechanism

BACKGROUND: Acute lymphoblastic leukemia (ALL) is still incurable hematologic neoplasia in an important percentage of patients. Therefore, new therapeutic approaches need to be developed. METHODS: To evaluate the cellular effect of cell-penetrating peptides (C-PP) on leukemia cells, Jurkat cells -a model of ALL were exposed to increasing concentration (50–500 μM) Aβ(25–35), R(7)-G-Aβ(25-35) and Aβ(25–35)-G-R(7) peptide for 24 h. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry (FC), and fluorescent microscopy (FM) analysis were used to assess metabolic viability, cell cycle and proliferation, mitochondria functionality, oxidative stress, and cell death markers. RESULTS: We report for the first time that the R(7)-G-Aβ(25-35), but not Aβ(25–35) peptide, induced selective cell death in Jurkat cells more efficiently than the Aβ(25–35)-G-R(7) peptide. Indeed, R(7)-G-Aβ(25-35) (200 μM) altered the metabolic activity (−25%), arrested the cell cycle in the G2/M-phase (15%), and induced a significant reduction of cellular proliferation (i.e., −74% reduction of Ki-67 nuclei reactivity). Moreover, R(7)-G-Aβ(25-35) induced the dissipation of mitochondrial membrane potential (ΔΨ(m,) 51%) and produced an important amount of reactive oxygen species (ROS, 75% at 8 h) in Jurkat cells. The exposure of cells to antioxidant/cytoprotectant N-acetylcysteine (NAC) did not prevent R(7)-G-Aβ(25-35) from a loss of ΔΨ(m) in Jurkat cells. The peptide was also unable to activate the executer CASPASE-3, thereby preserving the integrity of the cellular DNA corroborated by the fact that the caspase-3 inhibitor NSCI was unable to protect cells from R(7)-G-Aβ(25-35) -induced cell damage. Further analysis showed that the R(7)-G-Aβ(25-35) peptide is specifically localized at the outer mitochondria membrane (OMM) according to colocalization with the protein translocase TOMM20. Additionally, the cytotoxic effect of the poly-R(7) peptide resembles the toxic action of the uncoupler FCCP, mitocan oligomycin, and rotenone in Jurkat cells. Importantly, the R(7)-G-Aβ(25-35) peptide was innocuous to menstrual mesenchymal stromal cells (MenSC) –normal non-leukemia proliferative cells. CONCLUSION: Our findings demonstrated that the cationic Aβ peptide possesses specific anti-leukemia activity against Jurkat cells through oxidative stress (OS)- and CASPASE-3-independent mechanism but fast mitochondria depolarization.