Abstract 1837: Cellular glutathione is an essential mediator of the enhancing effect of plant polyphenolic antioxidants on vitamin D-induced differentiation of acute myeloid leukemia cells
Authors: Novik Victoria , Pesakhov Stella , Sharoni Yoav , Studzinski George P. , Danilenko Michael 
Published: August 2012

Abstract
Acute myeloid leukemia (AML) is an aggressive malignancy with poor prognosis. Differentiation therapy may provide an alternative AML treatment, based on the induction of leukemic blasts to mature. The hormonal form of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25D), is a powerful inducer of monocytic differentiation of AML cells in vitro; however, it causes severe hypercalcemia in vivo at pharmacologically effective doses. We have previously shown that various plant polyphenolic antioxidants (PAOx), such as carnosic acid (CA), curcumin (CUR), and silibinin (SIL), strongly potentiate the differentiation of AML cells induced by a low, near physiologic dose of 1,25D (1 nM). Further, we have demonstrated that a functionally active transcription factor Nrf2 is required for the differentiation-enhancing effect of CA; however, the mechanism whereby Nrf2 contributes to this effect was unclear. Here we show that similar to CA, CUR and SIL transactivated the Nrf2 response element (antioxidant response element; ARE), induced Nrf2/ARE-responsive gene products, such as NADP(H)-quinone oxidoreductase, thioredoxin reductase-1 and the α-glutamylcysteine synthetase heavy subunit (≥GCSh), and elevated the total glutathione content in human AML cells (HL60 and U937). Interestingly, 1,25D markedly potentiated these effects of PAOx. Stable expression of dominant negative Nrf2 (dnNrf2) abolished the differentiation-enhancing effects of all the PAOx tested. Importantly, such inhibitory action of dnNrf2 was mimicked by treatment of untransfected cells with non-cytotoxic concentrations of L-buthionine-sulfoximine (BSO), the specific inhibitor of αGCS. Glutathione depletion in BSO-treated cells was associated with attenuation of both the transactivation of the transcription factor activating protein-1 (AP-1) and elevation of protein levels of the vitamin D receptor (VDR) and retinoid X receptor alpha (RXRα) induced by 1,25D/PAOx combinations. This may account for the reduction in the extent of 1,25D/PAOx-induced differentiation observed following BSO treatment. Collectively, our data suggest that cooperative elevation of glutathione levels by PAOx and 1,25D, as a result of Nrf2/ARE-dependent induction of αGCS, may mediate the enhancing effects of PAOx on 1,25D-induced differentiation of AML cells. These findings may provide a mechanistic basis for the therapy and/or prevention of AML using combinations of vitamin Dand plant antioxidants. (This research was supported by the Israel Science Foundation grant 635/11 to both M.D. and Y.S., and by the NIH-NCI grant RO1-CA117942-04 to both G.P.S. and M.D.).
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1837. doi:1538-7445.AM2012-1837