Using this unique reagent, we demonstrate that I3C triggers an elastase-dependent anti-proliferative response in the 10AT-Her2 breast cancer cell population by promoting nucleostemin to interact with and sequester the murine double mutant 2 (MDM2) protein into the nucleolus, thereby allowing the p53 tumor suppressor protein to escape from the MDM2 inhibition of apoptotic activity. The gene discussed is ERBB2; the disease is breast cancer.