Targeted inhibition of p38α MAPK suppresses tumor-associated endothelial cell migration in response to hypericin-based photodynamic therapy

Photodynamic therapy (PDT) is an established anticancer modality and hypericin is a promising photosensitizer for the treatment of bladder tumors. We show that exposure of bladder cancer cells to hypericin PDT leads to a rapid rise in the cytosolic calcium concentration which is followed by the generation of arachidonic acid by phospholipase A(2) (PLA(2)). PLA(2) inhibition significantly protects cells from the PDT-induced intrinsic apoptosis and attenuates the activation of p38 MAPK, a survival signal mediating the up-regulation of cyclooxygenase-2 that converts arachiclonic acid into prostanoids. Importantly, inhibition of p38 alpha MAPK blocks the release of vascular endothelial growth factor and suppresses tumor-promoted endothelial cell migration, a key step in angiogenesis. Hence, targeted inhibition of p38a MAPK could be therapeutically beneficial to PDT, since it would prevent COX-2 expression, the inducible release of growth and angiogenic factors by the cancer cells, and cause an increase in the levels of free arachidonic acid, which promotes apoptosis. (c) 2005 Elsevier Inc. All rights reserved.