Background: Serum selenium (Se) concentration at presentation is prognostic of outcome in patients with aggressive B-cell lymphoma (Last et al., JCO, 2003). In vitro studies in human lymphoma cell lines have shown that the Se compound methylseleninic acid (MSA) can enhance the efficacy of chemotherapeutic agents at non-cytotoxic concentrations, potentially via a decrease in NF-\#954;B activity (Juliger et al., Can Res, 2007). MSA activity is different in non-malignant cells. In a xenograft solid tumour model the administration of Se to a plasma concentration of >20µmol/l enhanced the anti-tumour activity of cytotoxic agents but reduced toxicity to normal tissue (Cao et al., Clin Can Res, 2004). This study has investigated whether different endoplasmic reticulum (ER) stress responses underlie these differential activities. In addition we have studied whether there are differences in uptake and metabolism of MSA between malignant and non-malignant cells. Methods: Lymphoma cell lines (CRL-2261 and DHL4) and peripheral blood mononuclear cells (PBMCs) were exposed to MSA in concentration and time-course experiments. Changes in mRNA and protein expression were determined by real-time PCR and western blotting respectively and in NF-\#954;B activity by ELISA. Intracellular Se and volatile species generated after MSA exposure were determined using mass spectrometry. Results: MSA induced the expression of protein disulfide isomerase, indicating protein mis-folding, but induced different ER stress responses in lymphoma cells and PBMCs. A clear induction in GRP78, an ER chaperone that mediates cell survival, was seen at 1\#956;M MSA in PBMCs, but the same response required 3-5 fold higher concentrations in lymphoma cell lines. Moreover there was marked induction of GADD153, which mediates cell death, in lymphoma cells, but in PBMCs GADD153 induction was less at comparable concentrations. Studies have reported that ER stress can activate NF-\#954;B which acts to inhibit GADD153 expression. We found that MSA-induced cellular stress increased NF-\#954;B activity by a mean of 2.5 fold (p=0.02) in 6/8 PBMC samples. However, in lymphoma cell lines MSA decreased NF-\#954;B activity and expression of its downstream target survivin. In the DHL4 cell line induction of ER stress at chemosensitising concentrations of MSA resulted in the conversion of microtubule associated protein light chain (LC3)-I to LC3-II, indicating the induction of autophagy. The uptake of MSA by lymphoma cells and PBMCs does not appear to differ significantly and the volatile species, dimethyldiselenide and dimethylselenide, are rapidly generated. Conclusions: MSA induces protein mis-folding and ER stress in lymphoma cell lines and PBMCs but the survival response is more effective in PBMCs as seen by a larger increase in GRP78 expression and an increase in NF-\#954;B activity. In addition, MSA decreases survivin expression in lymphoma cell lines. This data supports the clinical use of Se in lymphoma therapy.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5585.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO