Abstract 5431: Polysialyltransferase ST8SiaII: A novel target for the treatment of neuroblastoma
Authors: Elkashef Sara M. , Viprey Virginie , Saeed Rida F. , Springett Bradley R. , Sutherland Mark , Loadman Paul M. , Patterson Laurence H. , Shnyder Steven D. , Falconer Robert A. 
Published: August 2015

Polysialic acid (polySia) is a carbohydrate polymer expressed on the surface of NCAM (neuronal cell adhesion molecule) in many cancer cells where it modulates cell-cell and cell-matrix adhesion, migration, invasion and metastasis. PolySia expression is strongly associated with poor clinical prognosis and correlates with aggressive/invasive disease in neuroblastoma and many other tumours principally of neuroendocrine origin [1]. SiRNA knockdown of polysialyltransferase ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumours, has been shown to abolish tumour cell migration [2]. Besides brain regions with persistent neuronal plasticity, polySia is essentially absent from the body post-embryogenesis. ST8SiaII inhibition thus presents a novel, selective and largely unexplored therapeutic opportunity to reduce neuroblastoma dissemination [1].

Progress towards development of ST8SiaII inhibitors has been limited by lack of an efficient technique for quantitative assessment of enzyme activity. We have validated a highly sensitive HPLC-based inhibition assay, amenable to high-throughput screening [3]. Having demonstrated that inhibition of ST8SiaII by small molecules leads to a reduction in tumour cell migration and invasion, we have designed and synthesised ST8SiaII inhibitors. Using isogenic cell lines (C6-STX: polySia+/ST8SiaII+ and C6-WT: polySia-/ST8SiaII-) and naturally polySia expressing human neuroblastoma cells (SH-SY5Y, IMR-32) these compounds were evaluated for their ability to reduce polySia expression and to modulate cell migration in vitro. We have identified CMP-sialic acid precursors, including ICT-3176, which reduced polySia expression (as determined by flow cytometry and HPLC analysis) and tumour cell migration by up to 70%. These effects were only found in cell lines expressing ST8SiaII and polySia. Specificity of agents for polySTs over other sialyltransferases (α-2,3 and α-2,6) was subsequently investigated using lectin differential labelling probes. Agents did not inhibit sialyltransferase activity, as evidenced by lack of effect on α-2,3 and α-2,6-sialic acid expression.

Furthermore, we have investigated effects of polyST inhibition by ICT3176 on key intracellular signalling pathways. ICT3176 has been shown to disturb the dynamics of focal adhesion kinase and modulate ERK1/2 and AKT signalling. We have also investigated the effects of ICT3176 on chemosensitivity of neuroblastoma cells to various molecularly targeted chemotherapeutics.

In summary, we have identified ST8SiaII inhibitors which dramatically decrease cell migration and invasion in vitro through modulation of polySia assembly. This work paves the way for development of a novel therapeutic for the treatment of neuroblastoma.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939; [2] Schreiber et al., Gastroenterology, 2008, 134, 1555-1566; [3] Al-Saraireh YMJ et al., PLoS ONE, 2013, 8:e73366.

Citation Format: Sara M. Elkashef, Virginie Viprey, Rida F. Saeed, Bradley R. Springett, Mark Sutherland, Paul M. Loadman, Laurence H. Patterson, Steven D. Shnyder, Robert A. Falconer. Polysialyltransferase ST8SiaII: A novel target for the treatment of neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5431. doi:10.1158/1538-7445.AM2015-5431