A comparison of the sensitivity to photodynamic treatment of endothelial and tumour cells in different proliferative states.

Bovine aorta endothelial and human colon adenocarcinoma (WiDr) cells were exposed to haematoporphyrin derivative plus light. Cell survival was determined using a [3H]thymidine incorporation and a clonogenic assay for both cell types. The endothelial cells were more sensitive to photodynamic treatment. This could be explained in terms of increased drug uptake into the endothelial cells despite there being no difference in cell volume between the cells. For both tumour and endothelial cells, exponentially growing cells were more sensitive to photodynamic treatment than plateau-phase cells. This was associated with a reduction in drug uptake into plateau-phase endothelial cells. However, there was no difference in uptake into exponentially growing and plateau-phase WiDr cells.