Inhibition of thioredoxin-dependent HO removal sensitizes malignant B-cells to pharmacological ascorbate.
Graczyk-Jarzynka Agnieszka,Goral Agnieszka,Muchowicz Angelika,Zagozdzon Radoslaw,Winiarska Magdalena,Bajor Malgorzata,Trzeciecka Anna,Fidyt Klaudyna,Krupka Joanna Alicja,Cyran Julia,Szczygiel Kacper,Efremov Dimitar G,Gobessi Stefania,Jagielski Adam,Siudakowska Karolina,Bobrowicz Malgorzata,Klopotowska Marta,Barankiewicz Joanna,Malenda Agata,Lech-Maranda Ewa,Miazek-Zapala Nina,Skarzynski Piotr Henryk,Domagala Antoni,Golab Jakub,Firczuk Malgorzata
L-ascorbate (L-ASC) is a widely-known dietary nutrient which holds promising potential in cancer therapy when given parenterally at high doses. The anticancer effects of L-ASC involve its autoxidation and generation of HO, which is selectively toxic to malignant cells. Here we present that thioredoxin antioxidant system plays a key role in the scavenging of extracellularly-generated HO in malignant B-cells. We show that inhibition of peroxiredoxin 1, the enzyme that removes HO in a thioredoxin system-dependent manner, increases the sensitivity of malignant B-cells to L-ASC. Moreover, we demonstrate that auranofin (AUR), the inhibitor of the thioredoxin system that is used as an antirheumatic drug, diminishes the HO-scavenging capacity of malignant B-cells and potentiates pharmacological ascorbate anticancer activity in vitro and in vivo. The addition of AUR to L-ASC-treated cells triggers the accumulation of HO in the cells, which results in iron-dependent cytotoxicity. Importantly, the synergistic effects are observed at as low as 200 µM L-ASC concentrations. In conclusion, we observed strong, synergistic, cancer-selective interaction between L-ASC and auranofin. Since both of these agents are available in clinical practice, our findings support further investigations of the efficacy of pharmacological ascorbate in combination with auranofin in preclinical and clinical settings.
Investigation of the role of extracellular H2O2 and transition metal ions in the genotoxic action of ascorbic acid in cell culture models.
Duarte Tiago L,Almeida Gabriela M,Jones George D D
In the presence of oxygen, ascorbic acid (AA) is unstable in aqueous media and oxidises to dehydroascorbate (DHA), generating reactive intermediates such as ascorbate free radical and H2O2. It is proposed that the cytotoxicity of AA is due to the extracellular production of H2O2 and that this is mediated by transition metal ions present in cell media. Here we investigate the role of extracellular H2O2 and metal ions in the genotoxicity of AA in cell culture models. Our preliminary results confirmed that physiological concentrations of AA were not toxic to confluent human fibroblasts, although they inhibited the proliferation of cells at low density. No inhibition was observed with ascorbic acid 2-phosphate (AA2P), a vitamin C derivative that remains stable in culture media. Furthermore, high concentrations of AA induced DNA strand breakage in a dose-dependent manner, whereas DHA and AA2P were not genotoxic. The genotoxic effect of AA was transient, required the formation of extracellular H2O2 and the presence of intracellular iron, but not of extracellular transition metal ions. These observations further clarify the pro-oxidant effect of AA solutions in cell culture models. The possibility that intravenous administration of high-dose AA may cause a similar genotoxic effect in vivo is discussed.
Sodium ascorbate (vitamin C) induces apoptosis in melanoma cells via the down-regulation of transferrin receptor dependent iron uptake.
Kang Jae Seung,Cho Daeho,Kim Young-In,Hahm Eunsil,Kim Yeong Seok,Jin Shun Nu,Kim Ha Na,Kim Daejin,Hur Daeyoung,Park Hyunjeong,Hwang Young Il,Lee Wang Jae
Journal of cellular physiology
Sodium ascorbate (vitamin C) has a reputation for inconsistent effects upon malignant tumor cells, which vary from growth stimulation to apoptosis induction. Melanoma cells were found to be more susceptible to vitamin C toxicity than any other tumor cells. The present study has shown that sodium ascorbate decreases cellular iron uptake by melanoma cells in a dose- and time-dependent fashion, indicating that intracellular iron levels may be a critical factor in sodium ascorbate-induced apoptosis. Indeed, sodium ascorbate-induced apoptosis is enhanced by the iron chelator, desferrioxamine (DFO) while it is inhibited by the iron donor, ferric ammonium citrate (FAC). Moreover, the inhibitory effects of sodium ascorbate on intracellular iron levels are blocked by addition of transferrin, suggesting that transferrin receptor (TfR) dependent pathway of iron uptake may be regulated by sodium ascorbate. Cells exposed to sodium ascorbate demonstrated down-regulation of TfR expression and this precedes sodium ascorbate-induced apoptosis. Taken together, sodium ascorbate-mediated apoptosis appears to be initiated by a reduction of TfR expression, resulting in a down-regulation of iron uptake followed by an induction of apoptosis. This study demonstrates the specific mechanism of sodium ascorbate-induced apoptosis and these findings support future clinical trial of sodium ascorbate in the prevention of human melanoma relapse.