JAK/STAT inhibition in macrophages promotes therapeutic resistance by inducing expression of protumorigenic factors

Tumor-associated macrophages contribute to tumor progression and therapeutic resistance in breast cancer. Within the tumor microenvironment, tumor-derived factors activate pathways that modulate macrophage function. Using in vitro and in vivo models, we find that tumor-derived factors induce activation of the Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) pathway in macrophages. We also demonstrate that loss of STAT3 in myeloid cells leads to enhanced mammary tumorigenesis. Further studies show that macrophages contribute to resistance of mammary tumors to the JAK/STAT inhibitor ruxolitinib in vivo and that ruxolitinib-treated macrophages produce soluble factors that promote resistance of tumor cells to JAK inhibition in vitro. Finally, we demonstrate that STAT3 deletion and JAK/STAT inhibition in macrophages increases expression of the pro-tumorigenic factor cyclooxygenase-2 (COX-2) and that COX-2 inhibition enhances responsiveness of tumors to ruxolitinib. These findings define a novel mechanism through which macrophages promote therapeutic resistance and highlight the importance of understanding the impact of targeted therapies on the tumor microenvironment. Primary human macrophages were treated with breast tumor cell (MCF7, MDA-MB-231, or control) conditioned medium, in combination with ruxolitinib (or control), and processed for gene expression analysis in triplicate. Bone marrow derived macrophages from STAT3 wild type or STAT3 conditional knockout mice were extracted and were processed for gene expression analysis in triplicate.

肿瘤相关巨噬细胞（tumor-associated macrophages, TAMs）在乳腺癌中可促进肿瘤进展与治疗抵抗。在肿瘤微环境（tumor microenvironment, TME）中，肿瘤来源因子可激活调控巨噬细胞功能的信号通路。本研究通过体外（in vitro）与体内（in vivo）模型发现，肿瘤来源因子可诱导巨噬细胞内贾纳斯激酶（Janus kinase, JAK）/信号转导与转录激活因子3（signal transducer and activator of transcription 3, STAT3）通路的激活。本研究同时证实，髓系细胞中STAT3的缺失会加剧乳腺肿瘤发生。进一步研究显示，巨噬细胞可在体内介导乳腺肿瘤对JAK/STAT抑制剂芦可替尼（ruxolitinib）的耐药性，且经芦可替尼处理的巨噬细胞会分泌可溶性因子，在体外促进肿瘤细胞对JAK抑制治疗的抵抗。最后，本研究证实，巨噬细胞中STAT3的敲除以及JAK/STAT通路的抑制，会促进促肿瘤因子环氧合酶-2（cyclooxygenase-2, COX-2）的表达；而环氧合酶-2的抑制则可增强肿瘤对芦可替尼的响应性。上述研究结果明确了巨噬细胞介导治疗抵抗的全新机制，并凸显了阐明靶向治疗对肿瘤微环境影响的重要性。原代人巨噬细胞分别接受乳腺癌细胞（MCF7、MDA-MB-231或对照细胞）的条件培养基处理，并联合芦可替尼（或对照溶剂）处理，随后进行三次重复的基因表达分析。提取STAT3野生型或STAT3条件性敲除小鼠的骨髓来源巨噬细胞，随后进行三次重复的基因表达分析。