Rolipram potentiates bevacizumab-induced cell death in human glioblastoma stem-like cells.

AIMS

Glioblastoma cancer stem-like cells (GCSCs) promote themselves proliferation by secreting the vascular endothelial growth factor A (VEGF) in an autocrine manner, positively regulated by phosphodiesterase IV (PDE4). In the current study, we investigated the putative cytotoxic effect of bevacizumab, a VEGF blocker, alone and in combination with a specific inhibitor of PDE4 called rolipram on GCSCs isolated from human surgical tumor specimen with a focus on PI3K/AKT pathway.

MAIN METHODS

CD133+/CD15+ GCSCs were characterized by flow cytometry and expanded in a serum-free primary culture system. The cell survival, apoptosis, and protein expression values were measured using MTT assay, TUNEL staining and western blot, successively. Intracellular cAMP and free secreted VEGF levels were assessed by cAMP enzyme immunoassay and ELISA, respectively.

KEY FINDINGS

Bevacizumab suppressed GCSCs survival with IC~6.5μg/ml and enhanced the levels of apoptosis, p53 and cleaved-caspase3 along with a decrease in free VEGF levels and ERKs activation. However, there was no significant modulation of AKT phosphorylation on serine 473, the intracellular PDE4A, VEGF and cAMP levels. More cytotoxicity in co-treated cells coupled with a more substantial decline in the free VEGF levels and a greater increase in the quantities of p53 and cleaved-caspase3 compared to those treated with bevacizumab alone. Co-treatment reduced phospho-AKT, endogenous VEGF and PDE4A values but elevated cAMP levels.

SIGNIFICANCE

This study highlighted a booster cytotoxic effect of combined rolipram and bevacizumab treatment on the GCSCs primary culture, suggesting that this approach is warranted in treatment of GBMs overexpressing VEGF and PDE4A.