The anti-tumor agent, ingenol-3-angelate (PEP005), promotes the recruitment of cytotoxic neutrophils by activation of vascular endothelial cells in a PKC-delta dependent manner

The modes of action of the novel anti-skin tumor agent ingenol-3-angelate (PEP005) are incompletely understood. Crucially, the cytotoxic functions of neutrophils recruited to the tumor in response to topical application of PEP005 are necessary for effective ablation of the treated lesion. Here, we investigated the hypothesis that the phorbol ester-like properties of PEP005 and its ability to activate PKC could directly activate endothelial cells (EC) so that they support the recruitment of neutrophils. Exposure of EC to PEP005 induced mRNA and/or protein for E-selectin, ICAM-1 and IL-8 in a dose dependent manner, while in a flow based adhesion assay, PEP005 treated EC supported the recruitment of neutrophils at levels comparable to EC stimulated with TNF-alpha. Neutrophil adhesion was inhibited by antibody against E-selectin but not P-selectin. Activation of EC was inhibited by the PKC inhibitor bisindolylmaleimide-1 and confocal immuno-fluorescent studies demonstrated translocation of PKC-delta from the cytosol to the peri-nuclear membrane in response to PEP005. Importantly, the knock down of PKC-delta using siRNA completely abolished neutrophil recruitment to EC subsequently treated with PEP005. Thus, we describe a novel route by which the anti-tumor agent PEP005 regulates the recruitment of cytotoxic leukocytes by directly activating EC in a PKC-delta dependent manner.