Abstract 2616: A novel iron-chelating agent reduces MYC transcription via E2F gene family regulation

Childhood neuroblastoma, a disease of the sympathetic nervous system, is the most common solid tumour of infancy. Amplification of the MYCN oncogene, which occurs in approximately 25% of patients with neuroblastoma, is one of the most powerful independent prognostic markers for this disease. MYCN belongs to the Myc gene family that codes for transcription factors often aberrantly expressed in both solid and liquid malignancies. However, despite their importance in adult and childhood malignancies, Myc oncoproteins have to date proven to be ‘undruggable’. Using a chemical library of 34,000 compounds we aimed to identify novel MYCN inhibitors, and among a number of molecules identified, M606 was found to markedly reduce MYCN protein levels as well as its downstream targets in MYCN-amplified SK-N-BE(2)-C neuroblastoma cells. Bioinformatic analysis of signalling pathways affected by M606 using FACTORIAL™ technology (Attagene Inc) demonstrated that this compound inhibits Myc-mediated transcription and simultaneously activates the HIF1α pathway. MYCN/MYC protein and mRNA stability were unaltered whereas their mRNA levels were significantly decreased. Metabolomics analysis suggested that the mechanism by which M606 inhibits MYCN transcription involves its capacity to chelate iron and, in this regard, M606-mediated inhibition of MYCN was reversed by the addition of iron. Progressive deletions of the MYCN promoter in luciferase reporter assays identified a minimal promoter region responsive to M606 that contains two E2F sites. Microarray assays performed on SK-N-BE(2)-C cells after M606 treatment showed significant changes in the expression level of the E2F gene family. Chromatin immune precipitation (ChIP) and gel shift (EMSA) assays revealed a reduction in E2F binding at the MYCN promoter region after M606 treatment. Moreover, western blot analysis showed that the RB protein, which is involved in E2F binding and transcriptional activation, becomes inactive due to hypophosphorylation following M606 treatment. On the other hand, M606 lost its inhibitory activity on a pRB-deficient osteosarcoma cell line SAOS-2, underlying the importance of the RB/E2F axis for M606 function. In conclusion, M606 is a novel Myc inhibitor and iron chelator that directly downregulates MYCN/MYC transcription via the E2F signalling pathway, providing a potentially valuable therapeutic approach in the treatment of cancers overexpressing Myc oncoproteins. Citation Format: Emanuele Valli, Chengyuan Xue, Leanna Cheung, Laura Gamble, Ruby Pandher, Simone Di Giacomo, Catherine Burkhart, Natalia Fedtsova, Francesca Ferrucci, Sergei Makarov, Thomas Telfer, Rachel Codd, David Scott, Giovanni Perini, Andrei Osterman, Andrei Gudkov, Murray Norris, Michelle Haber. A novel iron-chelating agent reduces MYC transcription via E2F gene family regulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2616.