[Mechanisms of cytotoxic drug-induced emesis and its prevention]

In this review, I have attempted to provide an overview of the pathways by which cytotoxic drugs induce emesis. The mechanisms of serotonin 5-HT3 antagonists and new antiemetics are also discussed. Old data especially from the experiments employing area postrema ablation must be re-evaluated because it is likely that the operation has damaged other important nucleus in the brain stem. Therefore, the concept of the chemoreceptor trigger zone and "vomiting center" proposed by Borison et al. in 1950s is questionable. Nausea and vomiting caused by cytotoxic drugs have been a serious problem in anti-cancer therapy and prompted lots of scientists to find the mechanism and to develop antiemetics. Effectiveness of 5-HT3 antagonists were shown in late 1980s, and now they are clinically available. I have investigated their mechanisms using Suncus murinus and proposed that the pathways by which cisplatin, one of most emetogenic drugs, induces emesis are as follows: 1) cisplatin is converted to an active metabolite(s), 2) the metabolite(s) somehow produces oxygen free radicals in the enterochromaffin cells, 3) the free radicals release serotonin, 4) the released serotonin stimulates 5-HT3 receptors located on the vagus afferents, 5) impulses are transmitted to the brain stem, or emetic pattern generator and initiate emetic reflex. Therefore, scavengers of free radicals and antioxidants can be a new type of antiemetic drug.