Abstract 2078: Treatment with auranofin induces oxidative and lethal endoplasmic reticulum (ER) stress exerting single agent activity against mantle cell lymphoma cells
Authors: Manepalli Rekha Rao , Chauhan Lata , Fiskus Warren , Balusu Ramesh , Nalabothula Narasimha , Venkannagari Sreedhar , Ganguly Siddhartha , Bhalla Kapil 
Published: August 2012

Abstract
Auranofin (AF) (Ridaura®) is an oral, FDA-approved, lipophilic, gold-containing compound used for the treatment of rheumatoid arthritis. In the present studies, we determined for the first time the lethal activity of AF (100 to 1000 nM) and its underlying mechanism(s) in cultured and primary Mantle Cell Lymphoma (MCL) cells. We demonstrate that treatment with AF in JeKo-1 and Z138C cells induced 2 to 3.5 fold increase in reactive oxygen species (ROS) levels (assessed by flow cytometry), decrease in thioredoxin reductase (TRR) activity (mean reduction of 35-40%) without alteration in the expression of TRR. These findings were associated with induction of nuclear factor erythroid 2-related factor 2 (NRF2) activity marked by substantial increase in heme oxygenase-1 (HMOX1) expression. Microarray analysis revealed that AF treatment significantly upregulated ER stress and oxidative stress inducible genes including that of the ER-stress induced pro-apoptotic transcription factor CHOP (CAAT/enhancer binding protein homologous protein), ATF3 (Activated Transcription Factor 3) and Glutamate-cysteine ligase (GCL), modifier subunit (GCLM), the rate-limiting enzyme in the glutathione (GSH) biosynthesis. Exposure to AF induced significantly more apoptosis in primary MCL cells, as compared to CD19+ normal B cells, CD34+ human cord blood and bone marrow progenitor cells (&lt; 15% apoptosis) (p &lt; 0.01). Based on the observations that AF treatment induced oxidative and ER stress, we determined whether exposure to AF increased the intracellular levels of misfolded and polyubiquitylated proteins, which would disrupt the cytosolic complex consisting of the heat shock protein (hsp) 90, heat shock factor (hsf) 1, histone deacetylase 6 (HDAC6) and p97/VCP, resulting in hyperacetylation and inhibition of the chaperone function of hsp90. Indeed, treatment with AF disrupted the association between hsp90 and HDAC6, HSF1 and p97, resulting in hyperacetylation of hsp90 and depletion of the levels of hsp90 client proteins including HDAC6, AKT and Cyclin D1 in MCL cells. Co-treatment of MCL cells with AF and the proteasome inhibitor carfilzomib (CZ) resulted in synergistic apoptosis in cultured MCL cells and significantly more apoptosis in primary MCL cells, than treatment with each agent alone. Based on the induction of GCLM and anti-oxidant response genes following AF treatment, we tested the anti-MCL activity of the combination of AF and the GCL inhibitor Buthionine sulphoximine (BSO), against MCL cells. Co-treatment with BSO and AF resulted in significantly more apoptosis of MCL cells than treatment with each agent alone. Collectively, our data creates a strong rationale for determining the in vivo activity of AF in patients with MCL as a single agent and in combination with other ER and oxidative stress-inducing agents, especially GCL inhibitors.
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 2078. doi:1538-7445.AM2012-2078