A highly selective peptide agonist of the endothelin-B receptor. Endothelin B receptor agonist SPI-1620 binds to endothelin-B receptors on endothelial cells in tumor blood vessels, which, unlike the angioarchitecture of normal blood vessels, are relatively devoid of smooth muscle. This agent may induce a transient, selective increase in blood flow to a tumor, which may result in an increase in the delivery of anticancer agents to the tumor and, so, an increase in anticancer agent efficacy. Check for active clinical trials using this agent. (NCI Thesaurus)