Proton pump inhibitors induce apoptosis of human B-cell tumors through a caspase-independent mechanism involving reactive oxygen species.
Proton pumps like the vacuolar-type H+ ATPase (V-ATPase) are involved in the control of cellular pH in normal and tumor cells. Treatment with proton pump inhibitors (PPI) induces sensitization of cancer cells to chemotherapeutics via modifications of cellular pH gradients. It is also known that low pH is the most suitable condition for a full PPI activation. Here, we tested whether PPI treatment in unbuffered culture conditions could affect survival and proliferation of human B-cell tumors. First, we showed that PPI treatment increased the sensitivity to vinblastine of a pre-B acute lymphoblastic leukemia (ALL) cell line. PPI, per se, induced a dose-dependent inhibition of proliferation of tumor B cells, which was associated with a dose- and time-dependent apoptotic-like cytotoxicity in B-cell lines and leukemic cells from patients with pre-B ALL. The effect of PPI was mediated by a very early production of reactive oxygen species (ROS), that preceded alkalinization of lysosomal pH, lysosomal membrane permeabilization, and cytosol acidification, suggesting an early destabilization of the acidic vesicular compartment. Lysosomal alterations were followed by mitochondrial membrane depolarization, release of cytochrome c, chromatin condensation, and caspase activation. However, inhibition of caspase activity did not affect PPI-induced cell death, whereas specific inhibition of ROS by an antioxidant (N-acetylcysteine) significantly delayed cell death and protected both lysosomal and mitochondrial membranes. The proapoptotic activity of PPI was consistent with a clear inhibition of tumor growth following PPI treatment of B-cell lymphoma in severe combined immunodeficient mice. This study further supports the importance of acidity and pH gradients in tumor cell homeostasis and suggests new therapeutic approaches for human B-cell tumors based on PPI.
De Milito
Angelo
A
Department of Drug Research and Evaluation, Pharmacogenetic, Drug Resistance, and Experimental Therapeutic Section, Istituto Superiore di Sanità, Rome, Italy. Angelo.demilito@iss.it
Iessi
Elisabetta
E
Logozzi
Mariantonia
M
Lozupone
Francesco
F
Spada
Massimo
M
Marino
Maria Lucia
ML
Federici
Cristina
C
Perdicchio
Maurizio
M
Matarrese
Paola
P
Lugini
Luana
L
Nilsson
Anna
A
Fais
Stefano
S
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019169:Jurkat Cells; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D009853:Omeprazole / Q000494:pharmacology; D015452:Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D054328:Proton Pump Inhibitors; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014747:Vinblastine / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays
D000972:Antineoplastic Agents, Phytogenic; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D054328:Proton Pump Inhibitors; D017382:Reactive Oxygen Species; D014747:Vinblastine; D020169:Caspases; D009853:Omeprazole