Abstract 2494: Identification of mithramycin analogues with increased potency and more selective inhibition of EWS-FLI1 for the treatment of Ewing sarcoma

Abstract

Abstract Background: Ewing Sarcoma Family Tumors (ESFT) is characterized by a chromosomal translocation, most commonly, between chromosomes 11 and 22, resulting in the fusion of the EWS and FLI1 genes. The fusion protein EWS-FLI1 is known to function as a constitutively activated transcription factor responsible for the oncogenic phenotype of ESFT. The identification of potent and specific inhibitors of EWS-FLI1 offers the hope of improved outcomes for ESFT patients. We have recently identified mithramycin, an antineoplastic antibiotic produced by Streptomyces plicatus, as a potent inhibitor of EWS-FLI1. In this report, we have investigated a series of mithramycin structural analogs in an effort to find compounds with better pharmacological properties. Methods: We evaluated the relative effects of the mithramycin analogs on ESFT viability using MTS, XTT and IncuCyte® real time cell confluence assays. The compounds were screened against a panel of pediatric cell lines within the Pediatric Preclinical Testing Program (PPTP) to evaluate selectivity. Western blot analysis and luciferase assays were used to determine the effects on EWS-FLI1 downstream target expression. Results: The mithramycin analogs 6 and 16 exhibit better potency and improved selectivity relative to mithramycin for both cell viability and downstream target inhibition. Furthermore, compound 6 is known to have a higher 200mg/kg maximum tolerated dose (MTD) relative to the 5 mg/kg MTD of mithramycin in xenograft models. Conclusions: In comparison to the drug mithramycin, we have shown that some of its structural analogs display better pharmacological properties such as increased potency and more specificity for ESFT cells. These results indicate that studies of analogs of DNA binding drugs are an important aspect of transcription factor drug development. We are working to further characterize the mechanism of these analogs and evaluate them in an in vivo model. The ultimate goal would be to translate these compounds to the clinic and improve therapeutic outcomes in patients with ESFT. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2494. doi:1538-7445.AM2012-2494