title: Vitamin C inactivates the proteasome inhibitor PS-341 in human cancer cells.
abstract: OBJECTIVE
  PS-341 (bortezomib, Velcade), the first proteasome inhibitor approved by the Food and Drug Administration for the treatment of patients with relapsed multiple myeloma, induces apoptosis in human cancer cell lines. Vitamin C (ascorbic acid) is an essential water-soluble vitamin required for many normal physiologic functions and has to be obtained through diet or supplemental tablets in humans. Here we studied the potential effect of vitamin C on the anticancer activity of PS-341 in human cancer cell lines.
  
  
  METHODS
  The effects of vitamin C on apoptosis induction by PS-341 alone and by PS-341 combined with tumor necrosis factor-related apoptosis-inducing ligand were studied. In addition, the effects of vitamin C and other antioxidants on PS-341-mediated proteasome inhibition were also examined. Finally, the direct chemical interaction between vitamin C and PS-341 was determined.
  
  
  RESULTS
  Vitamin C abrogated the ability of PS-341 to induce apoptosis in various human cancer cell lines, to induce G(2)-M arrest, and to augment apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand. Moreover, vitamin C suppressed PS-341-mediated inhibition of proteasome activity. PS-341 itself did not induce generation of intracellular reactive oxygen species whereas other antioxidants failed to abrogate its biological activity. Importantly, we detected a direct chemical interaction between vitamin C and PS-341.
  
  
  CONCLUSIONS
  Vitamin C directly binds to PS-431, thus inactivating PS-341 independent of its antioxidant activity. Our findings suggest that vitamin C may have a negative effect on PS-341-mediated anticancer activity.
authors.affiliation: Department of Hematology and Oncology, Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Zou
authors.forename: Ping
authors.initials: P
authors.lastname: Yue
authors.forename: Na
authors.initials: N
authors.lastname: Lin
authors.forename: Min
authors.initials: M
authors.lastname: He
authors.forename: Zhongmei
authors.initials: Z
authors.lastname: Zhou
authors.forename: Sagal
authors.initials: S
authors.lastname: Lonial
authors.forename: Fadlo R
authors.initials: FR
authors.lastname: Khuri
authors.forename: Binghe
authors.initials: B
authors.lastname: Wang
authors.forename: Shi-Yong
authors.initials: SY
authors.lastname: Sun
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001205:Ascorbic Acid / Q000737:chemistry / Q000494:pharmacology*; D015153:Blotting, Western; D001897:Boronic Acids / Q000737:chemistry / Q000494:pharmacology*; D000069286:Bortezomib; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004347:Drug Interactions; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects; D011719:Pyrazines / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; D001897:Boronic Acids; D011719:Pyrazines; D000069286:Bortezomib; D046988:Proteasome Endopeptidase Complex; D001205:Ascorbic Acid