Abstract 3651: Methylseleninic acid (MSA) is an HDAC inhibitor and suppresses VEGF production in lymphoma cell lines

Abstract

Abstract Background: Serum selenium (Se) concentration at presentation is prognostic of outcome in patients with aggressive B-cell lymphoma (Last et al., JCO, 2003). We have shown that the Se compound MSA enhanced the efficacy of chemotherapeutic agents at non-cytotoxic concentrations in lymphoma cell lines (Juliger et al., Can Res, 2007). Others have reported that Se enhanced the anti-tumour activity of cytotoxic agents, but reduced toxicity to normal tissue in a xenograft model (Cao et al., Clin Can Res, 2004). In addition, Se has been reported to have antiangiogenic properties including the reduction of tumour microvessel density (Wang et al., Int J Can, 2008). We have therefore investigated the effect of MSA on histone deacetylases (HDACs) and HIF1α, the latter being in part regulated by HDAC activity. Methods: Lymphoma cell lines (RL, SUD4, DHL4) and peripheral blood mononuclear cells (PBMCs) were exposed to MSA in concentration and time-course experiments in normoxic and hypoxic conditions (1% O2). Changes in protein expression were determined by western blotting, HDAC activity measured using an HDAC fluorimetric assay (Biomol), and VEGF levels in cellular supernatants determined using an electrochemiluminescence assay (Meso Scale Discovery). Results: In lymphoma cell lines, exposure to MSA concentrations ≥5μM for 24 hours resulted in acetylation of histone H3 and induction of p21 protein. Acetylation of α-tubulin (mediated by HDAC6, a class II HDAC) occurred to a lesser extent. MSA did not inhibit HDAC activity in an isolated enzyme assay using HeLa cell nuclear extract. However, in whole cells pre-incubated with MSA HDAC activity was inhibited in a concentration-dependent manner. In DHL4 cells, exposure to 10μM and 30μM MSA for 2 hours inhibited HDAC activity by 34% (p=0.01 cf control) and 50% (p=0.02) respectively. 24 hour exposure to MSA concentrations ≥5μM markedly increased histone H3 acetylation in PBMCs. These results suggest that a cellular metabolite of MSA inhibits HDAC activity in intact cells. The effect of MSA on HIF1α expression and VEGF secretion was then investigated. In DHL4 cells, exposure to hypoxia for 24 hours induced HIF1α expression (1.8 fold), an effect not seen in the presence of 20µM MSA. In addition, hypoxia increased VEGF levels to 157% of basal levels, but this was reduced to 43% by 20μM MSA (p=0.007). Conclusions: At clinically relevant concentrations, a cellular metabolite of MSA inhibits HDAC activity and suppresses HIFα induction and VEGF secretion. This effect may account for some of the observed pre-clinical activity with Se species, particularly in animal models. The mechanism of HDAC inhibition is now being investigated. In addition, histone H3 acetylation in PBMCs may serve as a biomarker of Se activity in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3651.