Research ArticleCancer

Targeting the XPO1-dependent nuclear export of E2F7 reverses anthracycline resistance in head and neck squamous cell carcinomas

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Science Translational Medicine  27 Jun 2018:
Vol. 10, Issue 447, eaar7223
DOI: 10.1126/scitranslmed.aar7223

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Restoring balance in the nucleus

Despite recent advances in cancer treatment, resistance to cancer therapy and resulting mortality remain common in head and neck squamous cell carcinoma. In their search for the causes of treatment resistance, Saenz-Ponce et al. identified a mechanism dependent on the balance of two proteins that regulate transcription and these proteins’ localization within cancer cells. Specifically, the authors discovered that a transcriptional inhibitor called E2F7 is frequently mislocalized to the cytoplasm in these tumors, whereas its transcription-activating counterpart, E2F1, remains in the nucleus and drives transcription of treatment resistance genes. The authors also identified an approved drug that can prevent the export of E2F7 from the nucleus and thereby restore the efficacy of anthracycline chemotherapy in head and neck cancer.

Abstract

Patient mortality rates have remained stubbornly high (40%) for the past 35 years in head and neck squamous cell carcinoma (HNSCC) due to inherent or acquired drug resistance. Thus, a critical issue in advanced SCC is to identify and target the mechanisms that contribute to therapy resistance. We report that the transcriptional inhibitor, E2F7, is mislocalized to the cytoplasm in >80% of human HNSCCs, whereas the transcriptional activator, E2F1, retains localization to the nucleus in SCC. This results in an imbalance in the control of E2F-dependent targets such as SPHK1, which is derepressed and drives resistance to anthracyclines in HNSCC. Specifically, we show that (i) E2F7 is subject to exportin 1 (XPO1)–dependent nuclear export, (ii) E2F7 is selectively mislocalized in most of SCC and multiple other tumor types, (iii) mislocalization of E2F7 in HNSCC causes derepression of Sphk1 and drives anthracycline resistance, and (iv) anthracycline resistance can be reversed with a clinically available inhibitor of XPO1, selinexor, in xenotransplant models of HNSCC. Thus, we have identified a strategy to repurpose anthracyclines for use in SCC. More generally, we provide a strategy to restore the balance of E2F1 (activator) and E2F7 (inhibitor) activity in cancer.

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