title: Mn porphyrin in combination with ascorbate acts as a pro-oxidant and mediates caspase-independent cancer cell death.
abstract: Resistance to therapy-mediated apoptosis in inflammatory breast cancer, an aggressive and distinct subtype of breast cancer, was recently attributed to increased superoxide dismutase (SOD) expression, glutathione (GSH) content, and decreased accumulation of reactive species. In this study, we demonstrate the unique ability of two Mn(III) N-substituted pyridylporphyrin (MnP)-based SOD mimics (MnTE-2-PyP(5+) and MnTnBuOE-2-PyP(5+)) to catalyze oxidation of ascorbate, leading to the production of excessive levels of peroxide, and in turn cell death. The accumulation of peroxide, as a consequence of MnP+ascorbate treatment, was fully reversed by the administration of exogenous catalase, showing that hydrogen peroxide is essential for cell death. Cell death as a consequence of the action of MnP+ascorbate corresponded to decreases in GSH levels, prosurvival signaling (p-NF-κB, p-ERK1/2), and in expression of X-linked inhibitor of apoptosis protein, the most potent caspase inhibitor. Although markers of classical apoptosis were observed, including PARP cleavage and annexin V staining, administration of a pan-caspase inhibitor, Q-VD-OPh, did not reverse the observed cytotoxicity. MnP+ascorbate-treated cells showed nuclear translocation of apoptosis-inducing factor, suggesting the possibility of a mechanism of caspase-independent cell death. Pharmacological ascorbate has already shown promise in recently completed phase I clinical trials, in which its oxidation and subsequent peroxide formation was catalyzed by endogenous metalloproteins. The catalysis of ascorbate oxidation by an optimized metal-based catalyst (such as MnP) carries a large therapeutic potential as an anticancer agent by itself or in combination with other modalities such as radio- and chemotherapy.
authors: Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA; Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA.
authors: Myron K
authors: MK
authors: Evans
authors: Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA.
authors: Artak
authors: A
authors: Tovmasyan
authors: Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA; Duke Cancer Institute, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: ibatinic@duke.edu.
authors: Ines
authors: I
authors: Batinic-Haberle
authors: Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA; Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA; Duke Cancer Institute, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: gayathri.devi@duke.edu.
authors: Gayathri R
authors: GR
authors: Devi
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001205:Ascorbic Acid / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D020169:Caspases / Q000235:genetics; D005260:Female; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D008665:Metalloporphyrins / Q000008:administration & dosage*; D016328:NF-kappa B / Q000378:metabolism; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000378:metabolism* / Q000633:toxicity; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D008665:Metalloporphyrins; D016328:NF-kappa B; D010545:Peroxides; D017382:Reactive Oxygen Species; C431023:manganese (III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D020169:Caspases; D001205:Ascorbic Acid
keywords: Apoptosis; Ascorbate; H(2)O(2); Inflammatory breast cancer; Manganese porphyrins; MnTE-2-PyP(5+); MnTnBuOE-2-PyP(5+); ROS; SOD; SUM149; SUM190; XIAP