Inhibitors of hydroperoxide metabolism enhance ascorbate-induced cytotoxicity

Abstract

Pharmacological ascorbate, via its oxidation, has been proposed as a pro-drug for the delivery of H2O2 to tumors. Pharmacological ascorbate decreases clonogenic survival of pancreatic cancer cells, which can be reversed by treatment with scavengers of H2O2. The goal of this study was to determine if inhibitors of intracellular hydroperoxide detoxification could enhance the cytotoxic effects of ascorbate. Human pancreatic cancer cells were treated with ascorbate alone or in combination with inhibitors of hydroperoxide removal including the glutathione disulfide reductase inhibitor 1,3 bis (2-chloroethyl)-1-nitrosurea (BCNU), siRNA targeted to glutathione disulfide reductase (siGR), and 2-deoxy-D-glucose (2DG), which inhibits glucose metabolism. Changes in the intracellular concentration of H2O2 were determined by analysis of the rate of aminotriazole-mediated inactivation of endogenous catalase activity. Pharmacological ascorbate increased intracellular H2O2 and depleted intracellular glutathione. When inhibitors of H2O2 metabolism were combined with pharmacological ascorbate the increase in intracellular H2O2 was amplified and cytotoxicity was enhanced. We conclude that inclusion of agents that inhibit cellular peroxide removal produced by pharmacological ascorbate leads to changes in the intracellular redox state resulting in enhanced cytotoxicity.

The unpaved journey of vitamin C in cancer treatment

“…Gilloteaux et al 2014;Gilloteaux et al 2005;Herst et al 2012;Ma et al 2014;Martinotti et al 2011;Monti et al 2012;Ohtani et al 2007;Philips et al 2009;Verrax et al 2011;Welsh et al 2013). Some other studies took the strategy to facilitate peroxide formation by combing ascorbate with metal-based catalyst (Evans et al 2014;Kelley et al 1997;Rawal et al 2013), or inhibitors of peroxide metabolism (Olney et al 2013).…”

“…2). In contrast to oral ascorbate, IV administration of ascorbate, at large doses, was similar to drug administration, producing concentrations that could be 100 fold or higher than maximally tolerated oral doses, and the peak could last for hours in millimolar range (Padayatty and Levine 2000;Padayatty et al 2004). …”

“…Following these papers, a similar study in Japan repeated Pauling and Cameron's results (Murata et al 1982). Pauling and Cameron's research was embraced by many, but criticized by many others for not properly randomized and lacking of blinding inherent to a retrospective case-series design; the underlying susceptibility of the rural Scottish patient population to endogenous scurvy; lacking of independent pathologic confirmation of diagnosis; and the possibility of placebo effect (Creagan et al 1979;Moertel et al 1985;Padayatty and Levine 2000).…”

“…Pharmacokinetics had been overlooked in the earlier cancer studies (Padayatty and Levine 2000). While the same dose of 10 g/day vitamin C was used in both the Mayo Clinic trials and Cameron and Pauling's studies, the route of administration was different.…”

Two Grams BID Is an Oral Dosage of Vitamin C to Reduce the Risk of Recurrence of Superficial Bladder Carcinoma

“…"Observational reports described ascorbate, given in pharmacologic doses of 10 g daily, as effective in treating some cancers and in improving patient well-being" [2] (Figure 1 [3] [4]). Ongoing research continues to improve the effectiveness of AA in killing cancer cells [5]. Subsequently, the same dose had no effect on patient well-being and survival in two double-blind placebo-controlled trials, and AA was discarded as a treatment modality [6] [7].…”