We have designed MI-219 as a potent, highly selective and orally active small-molecule inhibitor of the MDM2–p53 interaction. MI-219 binds to human MDM2 with a K _i value of 5 nM and is 10,000-fold selective for MDM2 over MDMX. It disrupts the MDM2–p53 interaction and activates the p53 pathway in cells with wild-type p53, which leads to induction of cell cycle arrest in all cells and selective apoptosis in tumor cells. MI-219 stimulates rapid but transient p53 activation in established tumor xenograft tissues, resulting in inhibition of cell proliferation, induction of apoptosis, and complete tumor growth inhibition. MI-219 activates p53 in normal tissues with minimal p53 accumulation and is not toxic to animals. MI-219 warrants clinical investigation as a new agent for cancer treatment.

NF-κB may be a potential therapeutic target for acute myelogenous leukemia (AML) because NF-κB activation is found in primitive human AML blast cells. In this report, we initially discovered that the potent antineoplastic effect of niclosamide, a Food and Drug Administration–approved antihelminthic agent, was through inhibition of the NF-κB pathway in AML cells. Niclosamide inhibited the transcription and DNA binding of NF-κB. It blocked tumor necrosis factor–induced IκBα phosphorylation, translocation of p65, and expression of NF-κB–regulated genes. Niclosamide inhibited the steps TAK1→IκB kinase (IKK) and IKK→IκBα. Niclosamide also increased the levels of reactive oxygen species (ROS) in AML cells. Quenching ROS by the glutathione precursor N-acetylcysteine attenuated niclosamide-induced apoptosis. Our results together suggest that niclosamide inhibited the NF-κB pathway and increased ROS levels to induce apoptosis in AML cells. On translational study of the efficacy of niclosamide against AML, niclosamide killed progenitor/stem cells from AML patients but spared those from normal bone marrow. Niclosamide was synergistic with the frontline chemotherapeutic agents cytarabine, etoposide, and daunorubicin. It potently inhibited the growth of AML cells in vitro and in nude mice. Our results support further investigation of niclosamide in clinical trials of AML patients. Cancer Res; 70(6); 2516–27