The vascular targeting agent combretastatin A-4-phosphate induces neutrophil recruitment to endothelial cells in vitro

BACKGROUND: Combretastatin A-4-phosphate (CA-4-P) is a microtubule depolymerising agent currently in clinical trial as a tumour vascular-targeting agent. In vivo, CA-4-P causes rapid shutdown of tumour blood flow (within minutes) and a significant neutrophil infiltration at later times. MATERIALS AND METHODS: Using an in vitro flow-cell assay, we investigated neutrophil-endothelial cell interactions and associated mechanisms, following endothelial cell exposure to CA-4-P. Cellular adhesion molecule (CAM) expression was examined using immunoblotting and immunofluorescence, and the role of CAM in neutrophil recruitment was investigated using specific blocking antibodies. RESULTS: Exposure of HUVEC to CA-4-P, resulted in significant neutrophil recruitment, and increased expression of endothelial CAM. Results of antibody studies demonstrated that endothelial CAM expression induced by CA-4-P is responsible for the observed neutrophil recruitment. DISCUSSION: This study demonstrated that the tumour vascular targeting agent, CA-4-P, directly induces endothelial CAM expression and subsequent neutrophil recruitment. In vivo, neutrophil infiltration probably contributes to CA-4-P-induced tumour cell kill. Therefore, increasing neutrophil recruitment into tumours may have potential for optimising vascular-targeted strategies for cancer therapy.