Metronomic chemotherapy dosing-schedules with estramustine and temozolomide act synergistically with anti-VEGFR-2 antibody to cause inhibition of human umbilical venous endothelial cell growth

The effects of ‘metronomic'or extended chemotherapy dosing schedules (ECS) are mediated through poorly understood anti-angiogenic mechanisms. ECS combined with biological anti-angiogenic agents have produced promising pre-clinical results. Materials and Methods. We have expanded the list of agents with an in vitro ECS profile to include the methylating agent temozolomide (Temodal®) and the anti-mitotic agent estramustine (Estracyt®). These agents were also combined with a specific anti-angiogenic inhibitor IMC-1C11 and a non-specific agent with anti-angiogenic properties, Compound 5h. The in vitro HUVEC ECS model system was optimised and cell proliferation assays undertaken. Results. As a single agent, estramustine inhibited endothelial cell proliferation with an IC50 of 4.5 µM and was active at 10–33% of the maximum tolerated dose (MTD) from clinical schedules, whilst temozolomide had IC50 of 6.6 µM and was active at 1–6% of MTD. In combination, significant synergy was seen with IMC-1C11 in combination with either drug, whilst modest additive effects were observed with Compound 5h. None of the combinations resulted in significant cytotoxicity or apoptosis. Discussion. The results show that ECS of temozolomide and estramustine can be significantly enhanced when combined with specific anti-angiogenic inhibitors in an in vitro HUVEC system.