IRL-1620, an endothelin-B receptor agonist, enhanced radiation induced reduction in tumor volume in Dalton's Lymphoma Ascites tumor model.

ETB receptor agonist, IRL-1620 (or SPI-1620) presently in US Phase 1 clinical trial, has been demonstrated to selectively and transiently increase tumor blood flow. The present study was conducted to determine the effect of IRL-1620 on radiation therapy in tumor bearing mice inoculated with Dalton's Lymphoma Ascites cells. Tumors were allowed to grow for 30 days to a size of 1.10-1.29 cm3 before starting the treatment. The animals with or without IRL-1620 treatment were exposed to radiation (4 Gy/dose) on every alternate day for a total of 5 doses. Tumor volume was determined twice every week till the end of study. Radiation alone did not affect the tumor volume; however, animals treated with IRL-1620 followed by radiation produced a significant (64%) reduction in tumor volume. Survival of mice improved from 0/10 at 56 days after tumor inoculation in vehicle plus radiation group to 6/10 at 70 days in IRL-1620 (9 nmol/kg) plus radiation group. It is concluded that IRL-1620 improves the efficacy of radiation treatment in tumor bearing mice. (These findings have been earlier presented as an abstract ).