Research ArticlePharmacology

Inhibition of the oncogenic fusion protein EWS-FLI1 causes G2-M cell cycle arrest and enhanced vincristine sensitivity in Ewing’s sarcoma

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Sci. Signal.  03 Oct 2017:
Vol. 10, Issue 499, eaam8429
DOI: 10.1126/scisignal.aam8429

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A multipronged attack on Ewing’s sarcoma

Chemotherapy is a standard treatment for Ewing’s sarcoma (ES), but toxicity limits dosing and hence its efficacy. Some ES tumors are driven by the oncogenic fusion protein EWS-FLI1, a transcription factor and mRNA splicing protein that can be inhibited by the drug YK-4-279. Zöllner et al. found that YK-4-279 sensitized ES cells to the chemotherapeutic drug vincristine in ways that converged on mitotic catastrophe. The drug decreased the EWS-FLI1–dependent expression of microtubule stability proteins and of a ubiquitin ligase, which increased the amount of the cell cycle arrest protein cyclin B1, thus promoting mitotic arrest. The drug also decreased the amount of alternatively spliced, antiapoptotic BCL2 family proteins, altogether poising cells for apoptosis upon exposure to vincristine. The combination blocked tumor growth and induced tumor regression in mice at doses of each drug that had no effects alone. Thus, this drug combination might be effective and might have less toxicity in ES patients.

Abstract

Ewing’s sarcoma (ES) is a rare and highly malignant cancer that grows in the bones or surrounding tissues mostly affecting adolescents and young adults. A chimeric fusion between the RNA binding protein EWS and the ETS family transcription factor FLI1 (EWS-FLI1), which is generated from a chromosomal translocation, is implicated in driving most ES cases by modulation of transcription and alternative splicing. The small-molecule YK-4-279 inhibits EWS-FLI1 function and induces apoptosis in ES cells. We aimed to identify both the underlying mechanism of the drug and potential combination therapies that might enhance its antitumor activity. We tested 69 anticancer drugs in combination with YK-4-279 and found that vinca alkaloids exhibited synergy with YK-4-279 in five ES cell lines. The combination of YK-4-279 and vincristine reduced tumor burden and increased survival in mice bearing ES xenografts. We determined that independent drug-induced events converged to cause this synergistic therapeutic effect. YK-4-279 rapidly induced G2-M arrest, increased the abundance of cyclin B1, and decreased EWS-FLI1–mediated generation of microtubule-associated proteins, which rendered cells more susceptible to microtubule depolymerization by vincristine. YK-4-279 reduced the expression of the EWS-FLI1 target gene encoding the ubiquitin ligase UBE2C, which, in part, contributed to the increase in cyclin B1. YK-4-279 also increased the abundance of proapoptotic isoforms of MCL1 and BCL2, presumably through inhibition of alternative splicing by EWS-FLI1, thus promoting cell death in response to vincristine. Thus, a combination of vincristine and YK-4-279 might be therapeutically effective in ES patients.

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