Eribulin Mesylate Targets Human Telomerase Reverse Transcriptase in Ovarian Cancer Cells

<div><p>Treatment of advanced ovarian cancer involves platinum-based chemotherapy. However, chemoresistance is a major obstacle. Cancer stem cells (CSCs) are thought to be one of the causes of chemoresistance, but the underlying mechanism remains elusive. Recently, human telomerase reverse transcriptase (hTERT) has been reported to promote CSC-like traits. In this study, we found that a mitotic inhibitor, eribulin mesylate (eribulin), effectively inhibited growth of platinum-resistant ovarian cancer cell lines. Eribulin-sensitive cells showed a higher efficiency for sphere formation, suggesting that these cells possess an enhanced CSC-like phenotype. Moreover, these cells expressed a higher level of hTERT, and suppression of hTERT expression by siRNA resulted in decreased sensitivity to eribulin, suggesting that hTERT may be a target for eribulin. Indeed, we found that eribulin directly inhibited RNA-dependent RNA polymerase (RdRP) activity, but not telomerase activity of hTERT <i>in</i><i>vitro</i>. We propose that eribulin targets the RdRP activity of hTERT and may be an effective therapeutic option for CSCs. Furthermore, hTERT may be a useful biomarker to predict clinical responses to eribulin.</p></div

Eribulin inhibits growth of cisplatin-resistant ovarian cancer cells.

<p>Cells were treated with cisplatin or eribulin for 72 h, and then cell viability was determined by MTT assays. (A) Mean IC₅₀ values for cisplatin (µM). (B) Mean IC₅₀ values for eribulin (nM). Eribulin-sensitive (Eribulin S) cell lines are shown as open bars, and eribulin-resistant (Eribulin R) cell lines are shown as closed bars. Error bars represent the SD of at least three independent experiments.</p

Eribulin inhibits RdRP activity but not telomerase activity of hTERT.

<p>(A) RdRP activity of hTERT immune complexes prepared from HeLa cells arrested in the mitotic phase was assayed without or with 10 and 50 µM eribulin. (B) Telomerase activity in HeLa cell extracts was assayed without or with 10 and 50 µM eribulin. (C) RdRP activity of hTERT immune complexes was assayed without or with 10 and 100 µM paclitaxel (PTX).</p

Suppression of hTERT expression by siRNA results in decreased sensitivity to eribulin.

<p>(A) A2780 cells expressing control siRNA (open bars), TERT siRNA1 (closed bars), or TERT siRNA2 (shaded bars) were treated with eribulin for 72 h, and then cell viability was determined by MTT assays. *p<0.05 vs. cells expressing control siRNA. (B) The level of hTERT protein expression in A2780 cells expressing control siRNA (open bars), TERT siRNA1 (closed bars), or TERT siRNA2 (shaded bars) was determined by ELISA (indicated as ng/ml). (C and D) The experiments described in (A and B) were performed in the same manner using ES-2 cells expressing control siRNA (open bars), TERT siRNA1 (closed bars), or TERT siRNA2 (shaded bars). *p<0.05 vs. cells expressing control siRNA.</p

Eribulin-sensitive ovarian cancer cells express higher levels of hTERT protein.

<p>(A) The level of hTERT protein expression was determined by ELISA (indicated as ng/ml). Eribulin S cell lines are shown as open bars, and Eribulin R cells are shown as closed bars. Each experiment was performed at least three times, and mean values ± SD are indicated. (B) The mean hTERT level of Eribulin S cell lines (n = 8) and Eribulin R cell lines (n = 6) shown in (A). Error bars indicate SD.</p