Ovarian carcinoma-associated mesenchymal stem cells (CA-MSC) produce not only high levels of interleukin-6 (IL6) but also the related cytokine leukemia inhibitory factor (LIF). IL6-mediated activation of STAT3 is implicated as a critical therapeutic target for cancer therapy. Less is known about the role of LIF, which can similarly activate STAT3, in ovarian cancer. We therefore sought to evaluate the tumorigenic effects of CA-MSC paracrine LIF signaling and the redundancy of IL6 and LIF in activating ovarian cancer STAT3 mediated cancer growth. As expected, we found that both IL6 and LIF induce STAT3 phosphorylation in tumor cells. In addition, both IL6 and LIF increased the percentage of ALDH+ ovarian cancer stem-like cells (CSC). Supporting redundancy of function by the two cytokines, CA-MSC induced STAT3 phosphorylation and increased cancer cell "stemness". This effect was not inhibited by LIF or IL6 blocking antibodies alone, but was prevented by dual IL6/LIF blockade or JAK2 inhibition. Similarly, small hairpin RNA (shRNA)-mediated reduction of IL6 or LIF in CA-MSC partially decreased but could not completely abrograte the ability of CA-MSC to induce STAT3 phosphorylation and stemness. Importantly, the in vivo pro-tumorigenic effect of CA-MSC is abrogated by dual blockade with the JAK2 inhibitor ruxolitinib to a much greater extent than treatment with anti-IL6 or anti-LIF antibody alone. Ruxolitinib treatment also improves survival in the immunocompetent ovarian cancer mouse model system with ID8 tumor cells plus MSC. Ruxolitinib-treated tumors in both the immunocompromised and immunocompetent animal models demonstrate decreased phospho-STAT3, indicating on-target activity. In conclusion, CA-MSC activate ovarian cancer cell STAT3 signaling via IL6 and LIF and increase tumor cell stemness. This functional redundancy suggests that therapeutic targeting of a single cytokine may be less effective than strategies such as dual inhibitor therapy or targeting shared downstream factors of the JAK/STAT pathway.

中文翻译：

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白血病抑制因子与白细胞介素 6 共同作用，促进卵巢癌的生长。

卵巢癌相关间充质干细胞 (CA-MSC) 不仅产生高水平的白细胞介素 6 (IL6)，还产生相关的细胞因子白血病抑制因子 (LIF)。IL6 介导的 STAT3 激活被认为是癌症治疗的关键治疗靶点。关于 LIF 在卵巢癌中的作用知之甚少，LIF 可以类似地激活 STAT3。因此，我们试图评估 CA-MSC 旁分泌 LIF 信号传导的致瘤作用以及 IL6 和 LIF 在激活卵巢癌 STAT3 介导的癌症生长中的冗余。正如预期的那样，我们发现 IL6 和 LIF 都诱导肿瘤细胞中的 STAT3 磷酸化。此外，IL6 和 LIF 都增加了 ALDH+ 卵巢癌干细胞样细胞 (CSC) 的百分比。支持两种细胞因子的功能冗余，CA-MSC 诱导 STAT3 磷酸化并增加癌细胞“干性”。这种作用不会被单独的 LIF 或 IL6 阻断抗体抑制，但会被双重 IL6/LIF 阻断或 JAK2 抑制阻止。类似地，小发夹 RNA (shRNA) 介导的 CA-MSC 中 IL6 或 LIF 的减少部分降低，但不能完全消除 CA-MSC 诱导 STAT3 磷酸化和干细胞的能力。重要的是，与单独使用抗 IL6 或抗 LIF 抗体相比，JAK2 抑制剂鲁索替尼的双重阻断在更大程度上消除了 CA-MSC 的体内促肿瘤发生作用。Ruxolitinib 治疗还提高了具有 ID8 肿瘤细胞和 MSC 的免疫活性卵巢癌小鼠模型系统的存活率。Ruxolitinib 治疗的肿瘤在免疫功能低下和免疫活性动物模型中均显示磷酸化 STAT3 降低，表明靶向活性。总之，CA-MSC 通过 IL6 和 LIF 激活卵巢癌细胞 STAT3 信号并增加肿瘤细胞干性。这种功能冗余表明，单一细胞因子的治疗靶向可能不如双重抑制剂疗法或靶向 JAK/STAT 通路的共享下游因子等策略有效。