MB-81: THE GD3 ACETYLATION PATHWAY AS A POTENTIAL THERAPEUTIC TARGET FOR PAEDIATRIC MEDULLOBLASTOMA

Medulloblastoma survivors frequently suffer from low quality of life as a result of aggressive treatment. New treatments are urgently needed to reduce down-stream sequelae. GD3, an oncofoetal ganglioside is re-expressed in medulloblastoma and when accumulated causes mitochondrially-mediated apoptosis. 9-O-acetyl GD3 (GD3^A), its acetylated form, has been shown to protect cells from GD3-mediated apoptosis. In three medulloblastoma cell lines RES256, UW402 and CHLA-01-Med expression of GD3 (56.7%, 61.3% and 45.1%) and GD3^A (84.5%, 74.4% and 79.4%) was confirmed. Sialate-O-acetylesterase (SIAE), the human endogenous deacetylation enzyme of GD3^A is significantly down-regulated in medulloblastoma tissue (p < 0.001), shown by genome-wide transcriptional analysis. In order to evaluate this pathway as a potential therapeutic target we used an inducible SIAE over-expression approach in RES256 cells. Upon over-expression of SIAE we show a significant increase in GD3 expression (p < 0.05), and a significant increase in depolarisation of the mitochondrial membrane potential (p < 0.05). These changes were not seen on induction of expression of a catalytic mutant SIAE-S127A or vector controls. Induction of SIAE over-expression in combination with etoposide treatment resulted in a significant reduction in IC₅₀ (5.2 mM to 3.3 mM; p < 0.0001, n = 2). In SIAE-S127A expressing cells there was also a significant reduction in IC₅₀, (3.5 mM to 2.4 mM; p < 0.01 n = 2). IC₅₀ values for empty vector control could not be determined. Our preliminary results suggest that SIAE over-expression leads to a collapse of the mitochondrial membrane potential in RES256 cells. Additionally, these results suggest that SIAE over-expression may sensitise cells to chemotherapeutics, potentially reducing side-effects.