Effects of combretastatin A4 phosphate on endothelial cell morphology in vitro and relationship to tumour vascular targeting activity in vivo.

BACKGROUND: Combretastatin A4 Phosphate (CA4P) is a tubulin binding agent which causes rapid tumour vascular shutdown. It has anti-proliferative and apoptotic effects on dividing endothelial cells after prolonged exposure, but these effects occur on a much longer time scale than the reduction in tumour blood flow. This study compared the time course of CA4P effects on endothelial cell shape and reduction in red cell velocity.
METHODS: Endothelial cell area and form factor (1-4 pi x area x perimeter-2) were measured for proliferating and confluent HUVECs after CA4P treatment. Recovery of shape after CA4P and colchicine was compared. Window chamber studies of tumours were used to measure red cell velocity. Results 70% reduction in red cell velocity and 44% reduction in HUVEC form factor occurred by 10 minutes. Proliferating HUVECs underwent greater cell shape change after CA4P, which occurred at lower doses than for confluent cells. Cell shape recovered 24 hours after 30 minutes exposure to CA4P, but not after colchicine.
CONCLUSIONS: The similar time course of cell shape change and red cell velocity reduction suggests endothelial cell shape change may be involved early in the in vivo events leading to vascular shutdown. Differences in the recovery from the shape changes induced by CA4P and colchicine could underlie the different toxicity profiles of these drugs.