Identification of Mithramycin Analogues with Improved Targeting of the EWS-FLI1 Transcription Factor

Abstract

Purpose The goal of this study was to identify second-generation mithramycin analogs that better target the EWS-FLI1 transcription factor for Ewing sarcoma. We previously established mithramycin as an EWS-FLI1 inhibitor, but the compound’s toxicity prevented its use at effective concentrations in patients. Experimental Design We screened a panel of mithralogs to establish their ability to inhibit EWS-FLI1 in Ewing sarcoma. We compared the IC50 to the maximum tolerated dose established in mice to determine the relationship between efficacy and toxicity. We confirmed the suppression of EWS-FLI1 at the promoter, mRNA, gene signature, and protein levels. We established an improved therapeutic window by using time-lapse microscopy to model the effects on cellular proliferation in Ewing sarcoma cells relative to HepG2 control cells. Finally, we established an improved therapeutic window using a xenograft model of Ewing sarcoma. Results EC-8105 was found to be the most potent analog and was able to suppress EWS-FLI1 activity at concentrations nontoxic to other cell types. EC-8042 was substantially less toxic than mithramycin in multiple species but maintained suppression of EWS-FLI1 at similar concentrations. Both compounds markedly suppressed Ewing sarcoma xenograft growth and inhibited EWS-FLI1 in vivo. Conclusions These results provide a basis for the continued development of EC-8042 and EC-8105 as EWS-FLI1 inhibitors for the clinic.

Oncogenes Activate an Autonomous Transcriptional Regulatory Circuit That Drives Glioblastoma

“…These findings provide a proof-of-concept for the targeting of the SOX2 transcriptional circuit in GBM. The recent development of mithramycin analogs with an improved toxicity profile (Osgood et al, 2016; Vizcaino et al, 2012) may provide the basis for testing this therapeutic strategy in clinical trials. Since we observed an upregulation of expression of genes that have pro-apoptotic functions or are implicated in antigen presentation, there is a strong rationale for future studies of the combination of mithramycin treatment with radiation therapy, chemotherapy (temozolomide) and/or immunotherapy in preclinical GBM models.…”

A phase I/II trial and pharmacokinetic study of mithramycin in children and adults with refractory Ewing sarcoma and EWS–FLI1 fusion transcript

“…Overall, mithramycin was well tolerated with the exception of the significant hepatic toxicity. Interestingly, the same effect was seen with trabectedin another compound linked to the suppression of EWS–FLI1 [18]. As is the case with mithramycin, the transaminitis associated with trabectedin is mitigated by pretreatment with dexamethasone [31].…”

“…However, a definitive answer to this question would aid in future development efforts for this class of compounds. Indeed, these data would help guide the selection of second-generation mithramycin analogs that offer the hope of therapeutic suppression of EWS–FLI1 based on an improved toxicity profile [18]. …”

Direct therapeutic targeting of SWI/SNF induces epigenetic reprogramming and durable tumor regression in rhabdoid tumor

“…In this report, we sought to determine if SWI/SNF dysregulation was a molecular feature contributing to the heightened sensitivity of tumors to mithramycin. We analyzed two independently generated datasets and found that cell lines with mutated or dysregulated SWI/SNF were indeed particularly sensitive to mithramycin and EC8042 (15). Using rhabdoid tumor as a model of dysregulated SWI/SNF, we show that mithramycin directly targets SWI/SNF by evicting the complex from chromatin.…”