Direct Binding of Arsenic Trioxide to AMPK and Generation of Inhibitory Effects on Acute Myeloid Leukemia Precursors

Abstract

Arsenic trioxide (As2O3) exhibits potent antineoplastic effects and is used extensively in clinical oncology for the treatment of a subset of patients with acute myeloid leukemia (AML). Although As2O3 is known to regulate activation of several signaling cascades, the key events, accounting for its anti-leukemic properties, remain to be defined. We provide evidence that arsenic can directly bind to cysteine 299 in AMPKα and inhibit its activity. This inhibition of AMPK by arsenic is required in part for its cytotoxic effects on primitive leukemic progenitors from patients with AML, while concomitant treatment with an AMPK activator antagonizes in vivo the arsenic-induced antileukemic effects in a xenograft AML mouse model. A consequence of AMPK inhibition is activation of the mTOR pathway as a negative regulatory feedback loop. However, when AMPK expression is lost, arsenic-dependent activation of the kinase RSK downstream of MAPK activity compensates the generation of regulatory feedback signals through phosphorylation of downstream mTOR targets. Thus, therapeutic regimens with arsenic trioxide will need to include inhibitors of both the mTOR and RSK pathways in combination to prevent engagement of negative feedback loops and maximize antineoplastic responses.

Arsenic Triglutathione [As(GS)3] Transport by Multidrug Resistance Protein 1 (MRP1/ABCC1) Is Selectively Modified by Phosphorylation of Tyr920/Ser921 and Glycosylation of Asn19/Asn23

“…Interestingly, multiple studies have shown that arsenic can influence both kinase and phosphatase signaling pathways. For example, arsenic can activate mitogen-activated protein kinase, c-Jun N-terminal kinase, and PI3K/Akt/mTOR pathways (Verma et al, 2002;Giafis et al, 2006;Platanias, 2009;Goussetis and Platanias, 2010;Beauchamp et al, 2015). Phosphoproteomic studies comparing untreated and arsenictreated cell lines have also shown a general increase in protein phosphorylation through these pathways (Alp et al, 2010;Wen et al, 2010).…”

“…In vitro results are promising, but clinical success has been limited by the higher doses of As 2 O 3 required for induction of non-acute promyelocytic leukemia tumor cell death (Platanias, 2009). Considerable effort has been made to target kinase pathways that are activated by As 2 O 3 to increase the efficacy of this agent (Verma et al, 2002;Giafis et al, 2006;Dolniak et al, 2008;McNeer et al, 2010;Galvin et al, 2013;Beauchamp et al, 2015;Lozano-Santos et al, 2015). It may be that the kinase pathways responsible for phosphorylation of Tyr920 and Ser921 of MRP1 overlap with the kinase pathways activated by As 2 O 3 .…”

Differential Response of Glioma Stem Cells to Arsenic Trioxide Therapy Is Regulated by MNK1 and mRNA Translation

“…As arsenic compounds can directly bind to proteins or enzymes, altering their activity (24, 35), we set out to determine whether arsenic could bind MNK1. Arsenic compounds form covalent bonds with cysteine residues, and in some cases, histidine residues, leading to conformational changes that alter kinase activity or promote degradation (25, 36).…”

“…36). ATO can directly bind to cysteine residues in protein kinases like hexokinase 2 (HK2) and AMP-activated protein kinase (AMPK), which results in inhibition of kinase activity (24, 35). Among the most interesting findings of our study, was the evidence for direct activation of MNK by arsenic.…”

“…Arsenic binding was assessed using a previously described streptavidin pull-down assay (24, 25). Briefly, LN229 cells or recombinant MNK1 protein were treated with the arsenic-biotin (As-Biotin) conjugate for 2 hours.…”