IL-6 mediates platinum-induced enrichment of ovarian cancer stem cells
Yinu Wang, Xingyue Zong, Sumegha Mitra, Anirban Kumar Mitra, Daniela Matei, Kenneth P. Nephew
Yinu Wang, Xingyue Zong, Sumegha Mitra, Anirban Kumar Mitra, Daniela Matei, Kenneth P. Nephew
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Research Article Inflammation Stem cells

IL-6 mediates platinum-induced enrichment of ovarian cancer stem cells

Abstract

In high-grade serous ovarian cancer (OC), chemotherapy eliminates the majority of tumor cells, leaving behind residual tumors enriched in OC stem cells (OCSC). OCSC, defined as aldehyde dehydrogenase–positive (ALDH+), persist and contribute to tumor relapse. Inflammatory cytokine IL-6 is elevated in residual tumors after platinum treatment, and we hypothesized that IL-6 plays a critical role in platinum-induced OCSC enrichment. We demonstrate that IL-6 regulates stemness features of OCSC driven by ALDH1A1 expression and activity. We show that platinum induces IL-6 secretion by cancer-associated fibroblasts in the tumor microenvironment, promoting OCSC enrichment in residual tumors after chemotherapy. By activating STAT3 and upregulating ALDH1A1 expression, IL-6 treatment converted non-OCSC to OCSC. Having previously shown altered DNA methylation in OCSC, we show here that IL-6 induces DNA methyltransferase 1 (DNMT1) expression and the hypomethylating agent (HMA) guadecitabine induced differentiation of OCSC and reduced — but did not completely eradicate — OCSC. IL-6 neutralizing antibody (IL-6-Nab) combined with HMA fully eradicated OCSC, and the combination blocked IL-6/IL6-R/pSTAT3–mediated ALDH1A1 expression and eliminated OCSC in residual tumors that persisted in vivo after chemotherapy. We conclude that IL-6 signaling blockade combined with an HMA can eliminate OCSC after platinum treatment, supporting this strategy to prevent tumor recurrence after standard chemotherapy.

Authors

Yinu Wang, Xingyue Zong, Sumegha Mitra, Anirban Kumar Mitra, Daniela Matei, Kenneth P. Nephew

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Figure 2

Platinum-induced IL-6 secretion contributes to enrichment of OCSC in residual tumors.

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Platinum-induced IL-6 secretion contributes to enrichment of OCSC in res...
(A) Basal expression of IL-6 and (B) IL-6 receptor mRNA expression in human OC cells (ng/ml) were measured by qPCR. Bars represent average measurements of 3 independent experiments ± SD (n = 3). (C) COV318, OVCAR4, Kuramochi, EFO-27, HeyA8, A2780_CR5, SKOV3, and A2780 OC cells were cultured under starving condition for 24 hours. ELISA was used to measure IL-6 levels in the conditioned media. IL-6 secretion (pg/ml/1 × 105 cells) was determined and normalized to the cell number (n = 3). (D) Kuramochi, OVCAR4, and A2780 OC cells were cultured under starving conditions for 24 hours and then treated with CDDP (IC50 or half of IC50). ELISA was used to measure IL-6 levels in the CM. IL-6 secretion (pg/ml/ 1 × 105 cells) was determined and normalized to the cell number. Average fold change of IL-6 secretion (± SD) of CDDP-treated cells compared with control-treated is shown (2-tailed Student’s t test, *P < 0.05, **P < 0.01, and ***P < 0.001) (n = 3). (E) Nude mice were bearing A2780 i.p.-derived xenograft tumors were treated with carboplatin (50 mg/kg, weekly for 3 weeks). Blood samples and xenograft tumors were collected after CDDP treatment. Average relative IL-6 expression level (± SEM) in the plasma compared baseline plasma IL-6 level was measured by IL-6 ELISA and shown (n = 6). (F) IL-6 and IL-6R expression in the tumor residuals treated with control and carboplatin were measured by using qPCR. Mean fold change of IL-6 and IL-6R expression of 6 independent experiments is reported. Two-tailed Student’s t test was used to analyze statistical significance (*P < 0.05, **P < 0.01, and ***P < 0.001).