Tools and Technologies A c-Myc Activation Sensor-Based High-Throughput Drug Screening Identifies an Antineoplastic Effect of Nitazoxanide

Deregulation of c-Myc plays a central role in the tumorigenesis of many human cancers. Yet, the development of drugs regulating c-Myc activity has been challenging. To facilitate the identification of c-Myc inhibitors, we developed a molecular imaging sensor–based high-throughput screening (HTS) system. This systemuses a cell-basedassay todetect c-Myc activation in aHTS format,which is established fromapure clone of a stable breast cancer cell line that constitutively expresses a c-Myc activation sensor. Optimization of the assay performance in theHTS format resulted in uniform and robust signals at the baseline. Using this system, we conducted a quantitative HTS against approximately 5,000 existing bioactive compounds from five different libraries. Thirty-nine potential hits were identified, including currently known c-Myc inhibitors. There are a few among the top potent hits that are not known for anti–c-Myc activity. One of these hits is nitazoxanide, a thiazolide for treating human protozoal infections. Validation of nitazoxanide in different cancer cell lines revealed a high potency for c-Myc inhibition with IC50 ranging between 10 and 500 nmol/L. Oral administration of nitazoxanide in breast cancer xenograft mouse models significantly suppressed tumor growth by inhibition of c-Myc and induction of apoptosis. These findings suggest a potential of nitazoxanide to be repurposed as a new antitumor agent for inhibition of c-Myc–associated neoplasia. Our work also demonstrated the unique advantage of molecular imaging in accelerating discovery of drugs for c-Myc– targeted cancer therapy. Mol Cancer Ther; 12(9); 1–10. 2013 AACR.