HDAC6 and HDAC8 orchestrate sphingolipid metabolic reprogramming to regulate glioma cell fate

Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor in adults, characterized by rapid growth and poor clinical outcome. In fact, standard treatments, including surgical resection, radiotherapy, and chemotherapy with Temozolomide, provide only modest survival benefits, highlighting the urgent need for new therapeutic strategies. Histone deacetylases (HDACs), particularly HDAC6 and HDAC8, are frequently overexpressed in GBM and represent promising therapeutic targets due to their dual roles in nuclear and cytoplasmic processes. GBM also shows alterations in sphingolipid metabolism, which are recognized as a hallmark of tumor progression. Within this network, the balance between the pro-death mediator ceramide and the pro-survival lipid sphingosine-1-phosphate (S1P) – the so-called sphingolipid rheostat – is typically shifted towards tumor survival. Conversely, ceramide levels increase in response to chemotherapy or radiotherapy, correlating with reduced tumor progression and improved outcomes. Based on these considerations, we investigated the effects of selective HDAC6 and HDAC8 inhibition with Tubastatin A and PCI-34051, respectively, on cell viability and sphingolipid metabolism in U87-MG glioma cells. Both inhibitors reduced cell viability in a time-dependent manner, with the strongest cytotoxicity observed upon combined treatment. Lipidomic profiling revealed that both inhibitors induced accumulation of complex sphingolipids and disruption of sphingomyelin metabolism. Mechanistically, HDAC6 inhibition blocked sphingolipid recycling, causing passive ceramide buildup, whereas HDAC8 inhibition enhanced acidic sphingomyelinase activity, actively producing ceramide from sphingomyelin. Together, these studies identify HDAC6 and HDAC8 as key regulators of sphingolipid turnover and lysosomal dynamics in GBM. Their pharmacological targeting creates a ceramide-driven pro-death environment, offering a promising therapeutic avenue against glioblastoma.