Angiogenesis is a primary disease target in ocular retinopathy and a secondary target in numerous other angiogenic diseases such as cancer, rheumatoid arthritis and psoriasis. Clinical trials using antiangiogenic antisense oligonucleotides (aso's) for the treatment of ocular disorders or cancer are well advanced. Clusterin aso's are currently under investigation for the treatment of prostate cancer. We have investigated the antiangiogenic properties of clusterin aso's using a capillary cell (HUVEC) viability assay. In this study we included aso's to known apoptosis modulators (bcl-2, bcl-xl and survivin) which were previously identified in HUVEC's. We have also studied the effect of clusterin aso's on angiogenesis using an in vitro, matrigel assay and on HUVEC apoptosis using an ELISA DNA fragmentation assay. Clusterin, bcl-2, bcl-xl and survivin aso's were all found to inhibit HUVEC growth. The apoptosis-inducing drugs paclitaxel, camptothecin and doxorubicin were also found to inhibit HUVEC proliferation. Combinations of aso's with these drugs demonstrated a minor additive but not synergistic inhibitory effect on HUVEC proliferation. Clusterin aso's were found to strongly inhibit angiogenesis and induce high levels of apoptosis in HUVECs. In cancer cells the prosurvival protein clusterin may protect the cells from apoptosis-inducing agents so that the clusterin aso's may act as chemosensitization agents. These data demonstrate a strong antiangiogenic action of clusterin aso's, that is not necessarily related to any chemosensitization effect of this agent.