Metronomic chemotherapy: an antiangiogenic scheduling.

Conventional cytotoxic anticancer chemotherapeutic drugs were developed with the intent of treating cancer by direct killing or inhibition of growth of cycling tumour cells. Recently, however, there has been considerable interest in the notion of exploiting such drugs as angiogenesis inhibitors. The rationale is based on the fact that virtually all classes of cancer chemotherapeutic drugs are designed to damage DNA or disrupt microtubules of dividing cells, and endothelial cell division takes place during new blood vessel formation, including tumour angiogenesis. The results of recent experimental studies have suggested that frequent administration of certain cytotoxic agents at low doses, known as "metronomic chemotherapy", increases the putative antiangiogenic activity of certain drugs. Metronomic chemotherapy refers to the chronic administration of comparatively low doses of cytotoxic drugs at close, regular intervals, with no prolonged drug-free interruptions. The advantage of this strategy is lower toxicity and risk of emergence of drug-resistant tumour cells than conventional administration. This review describes the possible antiangiogenesis basis of this therapeutic strategy, the experimental studies published and the recent clinical studies that explore this less toxic schedule.