Cell migration in paediatric glioma; characterisation and potential therapeutic targeting.

Paediatric high grade glioma (pHGG) and diffuse intrinsic pontine glioma (DIPG) are highly aggressive tumours associated with dismal prognosis. Paediatric high grade gliomas account for 8–12% of all primary paediatric CNS tumours (Jones et al, 2012). Current treatment regimens involve maximal surgical resection, radiation therapy and chemotherapy. However, despite this intensive treatment approach, 5-year survival remains between 15 and 35% (Broniscer and Gajjar, 2004). Diffuse intrinsic pontine gliomas are the most common brainstem tumours of childhood and represent one of the most challenging paediatric tumours to treat. Surgery is not an option, chemotherapeutics have failed to improve outcomes, and radiotherapy can only temporarily slow disease progression, which is associated with median survival of less than 1 year (Warren, 2012). Both pHGG and DIPG are known to have diffuse infiltrative growth patterns, and this invasive phenotype contributes to their limited therapeutic response (Demuth and Berens, 2004; Louis, 2006). As a result, there is a pressing clinical need to develop novel therapeutic approaches that effectively reduce such paediatric brain tumour migration and invasion. Adult HGG cells are known to migrate in specific patterns, following the orientation of white matter tracts, capillaries and unmyelinated axons (Louis, 2006; Agudelo-Garcia et al, 2011). Recent studies have suggested that glycogen synthase kinase-3 (GSK-3), a serine/threonine protein kinase, plays a key role in orchestrating cell migration, through regulating cellular structure, motility and dynamics of the cytoskeleton (Grimes and Jope, 2001; Wakefield et al, 2003; Sun et al, 2009). The effects of small molecule GSK-3 inhibitors on blocking adult glioma migration and invasion have been demonstrated both in vitro and in vivo (Nowicki et al, 2008; Williams et al, 2011) and offer a potential novel anti-invasive approach for glioma. The effects of GSK-3 inhibitors on pHGG and DIPG migration and invasion are unknown, and given the distinct biological and clinical phenotype of the adult and paediatric diseases (Jones et al, 2012), warrant separate investigation. Very few studies have focused on identifying existing or novel therapeutic agents that are capable of impairing migration and invasion in pHGG and DIPG owing to limited patient tissue availability. We have conducted a comprehensive analysis of cell migration in two pHGG cell lines and one rare patient-derived DIPG cell line using a range of 2D and 3D assays. In addition, we also demonstrate for the first time that treatment with the small molecule GSK-3 inhibitors, lithium chloride (LiCl) and the indirubin derivative 6-bromoindirubin-oxime (BIO), which have previously been shown to block migration of adult glioma cells (Nowicki et al, 2008; Williams et al, 2011), also inhibit the migration of pHGG and DIPG cells in vitro. These agents represent novel anti-invasive candidates that may improve the clinical management of these challenging diseases in children.